2-Channel 500 MSPS DDS

with 10-Bit DACs

AD9958

Rev. 0

Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700

www.analog.com

Fax: 781.461.3113

FEATURES

2 synchronized DDS channels @ 500 MSPS
Independent frequency/phase/amplitude control between

channels

Matched latencies for frequency/phase/amplitude changes
Excellent channel-to-channel isolation (>72 dB)
Linear frequency/phase/amplitude sweeping capability
Up to 16 levels of frequency/phase/amplitude modulation

(pin-selectable)

2 integrated 10-bit D/A converters (DACs)
Individually programmable DAC full-scale currents
32-bit frequency tuning resolution
14-bit phase offset resolution
10-bit output amplitude scaling resolution
Serial I/O Port (SPI) with 800Mbps data throughput
Software-/hardware-controlled power-down
Dual supply operation (1.8 V DDS core/3.3 V serial I/O)
Multiple device synchronization
Selectable 4Ч to 20Ч REF_CLK multiplier (PLL)
Selectable REF_CLK crystal oscillator
56-Lead LFCSP

APPLICATIONS

Agile local oscillator
Phased array radar/sonar
Instrumentation
Synchronized clocking
RF source for AOTF
Single-side band suppressed carrier
Quadrature communications

FUNCTIONAL BLOCK DIAGRAM

AD9958

IOUT

DAC

COS(X)

DDS CORE

IOUT

FTW

SYNC_CLK

CLK_MODE_SEL

BUFFER/

XTAL

OSCILLATOR

SYSTEM

CLK

1.8V

AVDD

DVDD

SYNC_IN

SYNC_OUT

I/O_UPDATE

PHASE/

PHASE

AMP/

AMP

IOUT

DAC

IOUT

DAC_RSET

REF_CLK

PWR_DWN_CTL

MASTER_RESET

SCLK

SDIO_0

SDIO_1

SDIO_2

SDIO_3

TIMING AND CONTROL LOGIC

SCALABLE

DAC REF

CURRENT

MUX

I/O

PORT

BUFFER

CONTROL

REGISTERS

CHANNEL

REGISTERS

PROFILE

REGISTERS

REF CLOCK

MULTIPLIER

TO 20

1.8V

PS0 PS1 PS2 PS3

DVDD_I/O

COS(X)

DDS CORE

05252-001

Figure 1.

AD9958

Rev. 0 | Page 2 of 40

TABLE OF CONTENTS

Features .............................................................................................. 1

Applications....................................................................................... 1

Functional Block Diagram .............................................................. 1

General Description ......................................................................... 3

Specifications..................................................................................... 4

Absolute Maximum Ratings............................................................ 8

ESD Caution.................................................................................. 8

Equivalent Input and Output Circuits....................................... 8

Pin Configuration and Function Descriptions............................. 9

Typical Performance Characteristics ........................................... 11

Application Circuits ....................................................................... 14

Theory of Operation ...................................................................... 17

DDS Core..................................................................................... 17

D/A Converter ............................................................................ 17

Modes of Operation ....................................................................... 18

Channel Constraint Guidelines ................................................ 18

Power Supplies ............................................................................ 18

Single-Tone Mode ...................................................................... 18

Reference Clock Modes ............................................................. 19

Scalable DAC Reference Current Control Mode ................... 20

Power-Down Functions............................................................. 20

Modulation Mode....................................................................... 20

Modulation Using SDIO Pins for RU/RD............................... 22

Linear Sweep (Shaped) Modulation Mode ............................. 22

Linear Sweep--No-Dwell Mode............................................... 24

Sweep and Phase Accumulator Clearing Functions .............. 25

Output Amplitude Control Mode............................................ 26

Synchronizing Multiple AD9958 Devices ................................... 27

Automatic Mode Synchronization ........................................... 27

Manual Software Mode Synchronization................................ 27

Manual Hardware Mode Synchronization.............................. 27

I/O_Update, SYNC_CLK, and System Clock Relationships 28

Serial I/O Port ................................................................................. 29

Overview ..................................................................................... 29

Instruction Byte Description .................................................... 30

Serial I/O Port Pin Description ................................................ 30

Serial I/O Port Function Description ...................................... 30

MSB/LSB Transfer Description ................................................ 30

Serial I/O Modes of Operation................................................. 31

Control Register Map ................................................................ 34

Channel Register Map ............................................................... 35

Profile Register Map................................................................... 35

Control Register Descriptions ...................................................... 36

Channel Select Register (CSR) ................................................. 36

Channel Function Register (CFR) Description...................... 37

Outline Dimensions ....................................................................... 39

Ordering Guide .......................................................................... 39

REVISION HISTORY

9/05--Revision 0: Initial Version

AD9958

Rev. 0 | Page 3 of 40

GENERAL DESCRIPTION

The AD9958 consists of two DDS cores that provide indepen-
dent frequency, phase, and amplitude control on each channel.
This flexibility can be used to correct imbalances between
signals due to analog processing such as filtering, amplification,
or PCB layout related mismatches. Since both channels share a
common system clock, they are inherently synchronized.
Synchronization of multiple devices is supported.

The AD9958 can perform up to a 16-level modulation of
frequency, phase, or amplitude (FSK, PSK, ASK). Modulation is
performed by applying data to the profile pins. In addition, the
AD9958 also supports linear sweep of frequency, phase, or
amplitude for applications such as radar and instrumentation.

The AD9958 serial I/O port offers multiple configurations to
provide significant flexibility. The serial I/O port offers an SPI-
compatible mode of operation that is virtually identical to the
SPI operation found in earlier Analog Devices DDS products.
Flexibility is provided by four data pins (SDIO_0:3) that allow
four programmable modes of serial I/O operation.

The AD9958 uses advanced DDS technology that provides low
power dissipation with high performance. The device
incorporates two integrated, high speed 10-bit DACs with
excellent wideband and narrowband SFDR. Each channel has a
dedicated 32-bit frequency tuning word, 14 bits of phase offset,
and a 10-bit output scale multiplier.

The DAC outputs are supply referenced and must be termin-
ated into AVDD by a resistor or an AVDD center-tapped
transformer. Each DAC has its own programmable reference to
enable different full-scale currents for each channel.

The DDS acts as a high resolution frequency divider with the
REF_CLK as the input and the DAC providing the output. The
REF_CLK input source is common to both channels and can be
driven directly or used in combination with an integrated
REF_CLK multiplier (PLL) up to a maximum of 500 MSPS. The
PLL multiplication factor is programmable from 4 to 20, in
integer steps. The REF_CLK input also features an oscillator
circuit to support an external crystal as the REF_CLK source.
The crystal must be between 20 MHz and 30 MHz. The crystal
can be used in combination with the REF_CLK multiplier.

The AD9958 comes in a space-saving 56-lead LFCSP package.
The DDS core (AVDD and DVDD pins) is powered by a 1.8 V
supply. The digital I/O interface (SPI) operates at 3.3 V and
requires the pin labeled DVDD_I/O (Pin 49) be connected
to 3.3 V.

The AD9958 operates over the industrial temperature range of
-40°C to +85°C.

AD9958

Rev. 0 | Page 4 of 40

SPECIFICATIONS

AVDD and DVDD = 1.8 V ± 5%; DVDD_I/O = 3.3 V ± 5%; R

SET

= 1.91 k; external reference clock frequency = 500 MSPS (REF_CLK

multiplier bypassed), unless otherwise noted.

Table 1.

Parameter

Min

Typ

Max

Unit

Test Conditions/Comments

REF CLOCK INPUT CHARACTERISTICS

See

Figure 33

and

Figure 34

Frequency

Range

REF_CLK Multiplier Bypassed

500

MHz

REF_CLK Multiplier Enabled

125

MHz

Internal VCO Output Frequency Range

VCO Gain Bit Set High

255

500

MHz

Internal VCO Output Frequency Range

VCO Gain Bit Set Low

100

160

MHz

Crystal REF_CLK Source Range

MHz

Input Power Sensitivity

-5

dBm

Measured at the pin (single-ended)

Input Voltage Bias Level

1.15

Input Capacitance

Input Impedance

1500

Duty Cycle w/REF_CLK Multiplier Bypassed

Duty Cycle w/REF_CLK Multiplier Enabled

CLK Mode Select (Pin 24) Logic 1 Voltage

1.25

1.8

1.8V digital input logic

CLK Mode Select (Pin 24) Logic 0 Voltage

0.5

1.8 V digital input logic

DAC OUTPUT CHARACTERISTICS

Must be referenced to AVDD

Resolution

Bits

Full-Scale Output Current

1.25

Gain Error

-10

%FS

Channel-to-Channel Output Amplitude Matching Error

2.5

Output Current Offset

µA

Differential Nonlinearity

±0.5

LSB

Integral Nonlinearity

±1.0

LSB

Output

Capacitance

Voltage Compliance Range

AVDD 0.50

AVDD + 0.50

Channel-to-Channel Isolation

DAC supplies tied together
(see

Figure 21

)

WIDEBAND SFDR

The frequency range for wideband SFDR
is defined as dc to Nyquist

1 to 20 MHz Analog Out

-65

dBc

20 to 60 MHz Analog Out

-62

dBc

60 to 100 MHz Analog Out

-59

dBc

100 to 150 MHz Analog Out

-56

dBc

150 to 200 MHz Analog Out

-53

dBc

NARROWBAND SFDR

1.1 MHz Analog Out (

10 kHz)

-90

dBc

1.1 MHz Analog Out (

50 kHz)

-88

dBc

1.1 MHz Analog Out (

250 kHz)

-86

dBc

1.1 MHz Analog Out (

1 MHz)

-85

dBc

15.1 MHz Analog Out (

10 kHz)

-90

dBc

15.1 MHz Analog Out (

50 kHz)

-87

dBc

15.1 MHz Analog Out (

250 kHz)

-85

dBc

15.1 MHz Analog Out (

1 MHz)

-83

dBc

40.1 MHz Analog Out (

10 kHz)

-90

dBc

40.1 MHz Analog Out (

50 kHz)

-87

dBc

40.1 MHz Analog Out (

250 kHz)

-84

dBc

40.1 MHz Analog Out (

1 MHz)

-82

dBc

75.1 MHz Analog Out (

10 kHz)

-87

dBc

AD9958

Rev. 0 | Page 5 of 40

Parameter

Min

Typ

Max

Unit

Test Conditions/Comments

75.1 MHz Analog Out (

50 kHz)

-85

dBc

75.1 MHz Analog Out (

250 kHz)

-83

dBc

75.1 MHz Analog Out (

1 MHz)

-82

dBc

100.3 MHz Analog Out (

10 kHz)

-87

dBc

100.3 MHz Analog Out (

50 kHz)

-85

dBc

100.3 MHz Analog Out (

250 kHz)

-83

dBc

100.3 MHz Analog Out (

1 MHz)

-81

dBc

200.3 MHz Analog Out (

10 kHz)

-87

dBc

200.3 MHz Analog Out (

50 kHz)

-85

dBc

200.3 MHz Analog Out (

250 kHz)

-83

dBc

200.3 MHz Analog Out (

1 MHz)

-81

dBc

PHASE NOISE CHARACTERISTICS

Residual Phase Noise @15.1 MHz (f

OUT

)

@ 1 kHz Offset

150

dBc/Hz

@ 10 kHz Offset

159

dBc/Hz

@ 100 kHz Offset

165

dBc/Hz

@ 1 MHz Offset

165

dBc/Hz

Residual Phase Noise @40.1 MHz (f

OUT

)

@ 1 kHz Offset

142

dBc/Hz

@ 10 kHz Offset

151

dBc/Hz

@ 100 kHz Offset

160

dBc/Hz

@ 1 MHz Offset

162

dBc/Hz

Residual Phase Noise @ 75.1 MHz (f

OUT

)

@ 1 kHz Offset

135

dBc/Hz

@ 10 kHz Offset

146

dBc/Hz

@ 100 kHz Offset

154

dBc/Hz

@ 1 MHz Offset

157

dBc/Hz

Residual Phase Noise @ 100.3 MHz (f

OUT

)

@ 1 kHz Offset

134

dBc/Hz

@ 10 kHz Offset

144

dBc/Hz

@ 100 kHz Offset

152

dBc/Hz

@ 1 MHz Offset

154

dBc/Hz

Residual Phase Noise @ 15.1 MHz (f

OUT

)

w/REF_CLK Multiplier Enabled 5Ч

@ 1 kHz Offset

139

dBc/Hz

@ 10 kHz Offset

149

dBc/Hz

@ 100 kHz Offset

153

dBc/Hz

@ 1 MHz Offset

148

dBc/Hz

Residual Phase Noise @ 40.1 MHz (f

OUT

)

w/REF_CLK Multiplier Enabled 5Ч

@ 1 kHz Offset

130

dBc/Hz

@ 10 kHz Offset

140

dBc/Hz

@ 100 kHz Offset

145

dBc/Hz

@ 1 MHz Offset

139

dBc/Hz

Residual Phase Noise @ 75.1 MHz (f

OUT

) w/REF_CLK

Multiplier Enabled 5Ч

@ 1 kHz Offset

123

dBc/Hz

@ 10 kHz Offset

134

dBc/Hz

@ 100 kHz Offset

138

dBc/Hz

@ 1 MHz Offset

132

dBc/Hz

Residual Phase Noise @ 100.3 MHz (f

OUT

) w/REF_CLK

Multiplier Enabled 5Ч

@ 1 kHz Offset

120

dBc/Hz

@ 10 kHz Offset

130

dBc/Hz

@ 100 kHz Offset

135

dBc/Hz

@ 1 MHz Offset

129

dBc/Hz

AD9958

Rev. 0 | Page 6 of 40

Parameter

Min

Typ

Max

Unit

Test Conditions/Comments

Residual Phase Noise @ 15.1 MHz (f

OUT

)

w/REF_CLK Multiplier Enabled 20Ч

@ 1 kHz Offset

127

dBc/Hz

@ 10 kHz Offset

136

dBc/Hz

@ 100 kHz Offset

139

dBc/Hz

@ 1 MHz Offset

138

dBc/Hz

Residual Phase Noise @ 40.1 MHz (f

OUT

)

w/REF_CLK Multiplier Enabled 20Ч

@ 1 kHz Offset

117

dBc/Hz

@ 10 kHz Offset

128

dBc/Hz

@ 100 kHz Offset

132

dBc/Hz

@ 1 MHz Offset

130

dBc/Hz

Residual Phase Noise @ 75.1 MHz (f

OUT

) w/REF_CLK

Multiplier Enabled 20Ч

@ 1 kHz Offset

110

dBc/Hz

@ 10 kHz Offset

121

dBc/Hz

@ 100 kHz Offset

125

dBc/Hz

@ 1 MHz Offset

123

dBc/Hz

Residual Phase Noise @ 100.3 MHz (f

OUT

) w/REF_CLK

Multiplier Enabled 20Ч

@ 1 kHz Offset

107

dBc/Hz

@ 10 kHz Offset

119

dBc/Hz

@ 100 kHz Offset

121

dBc/Hz

@ 1 MHz Offset

119

dBc/Hz

SERIAL PORT TIMING CHARACTERISTICS

Maximum Frequency Serial Clock (SCLK)

200

MHz

Minimum SCLK Pulse Width Low (t

PWL

)

1.6

Minimum SCLK Pulse Width High (t

PWH

)

2.2

Minimum Data Set-Up Time (t

)

2.2

Minimum Data Hold Time

Minimum CSB Set-Up Time (t

PRE

)

1.0

Minimum Data Valid Time for Read Operation

MISCELLANEOUS TIMING CHARACTERISTICS

Master_Reset Minimum Pulse Width

Min pulse width = 1 sync clock period

I/O_Update Minimum Pulse Width

Min pulse width = 1 sync clock period

Minimum Set-Up Time (I/O_Update to SYNC_CLK)

4.8

Rising edge to rising edge

Minimum Hold Time (I/O_Update to SYNC_CLK)

Rising edge to rising edge

Minimum Set-Up Time (Profile Inputs to SYNC_CLK)

5.4

Minimum Hold Time (Profile Inputs to SYNC_CLK)

Minimum Set-Up Time (SDIO Inputs to SYNC_CLK)

2.5

Minimum Hold Time (SDIO Inputs to SYNC_CLK)

Propagation Time Between REF_CLK and SYNC_CLK

2.25

3.5

5.5

CMOS LOGIC INPUTS

2.0

0.8

Logic 1 Current

µA

Logic 0 Current

-12

µA

Input Capacitance

CMOS LOGIC OUTPUTS (1 mA Load)

2.7

0.4

POWER SUPPLY

Total Power Dissipation

Both Channels On, Single-

Tone Mode

315

380

Dominated by supply variation

Total Power Dissipation

Both Channels On, with

Sweep Accumulator

350

420

Dominated by supply variation

Total Power Dissipation

Full Power Down

IAVDD

Both Channels On, Single Tone Mode

105

AD9958

Rev. 0 | Page 7 of 40

Parameter

Min

Typ

Max

Unit

Test Conditions/Comments

IAVDD

Both Channels On, Sweep Accumulator,

REF_CLK Multiplier and 10-Bit Output Scalar Enabled

110

IDVDD

Both Channels On, Single Tone Mode

IDVDD

Both Channels On, Sweep Accumulator,

REF_CLK Multiplier and 10-Bit Output Scalar Enabled

IDVDD_I/O

IDVDD = read

IDVDD_I/O

IDVDD = write

IAVDD Power-Down Mode

2.5 mA

IDVDD Power-Down Mode

2.5 mA

DATA LATENCY (PIPELINE DELAY) SINGLE TONE MODE

2, 3

Frequency, Phase, and Amplitude Words to DAC Output

w/Matched Latency Enabled

Sys

Clk

Frequency Word to DAC Output w/Matched Latency

Disabled

Sys

Clk

Phase Offset Word to DAC Output w/Matched Latency

Disabled

Sys Clk

Amplitude Word to DAC Output w/Matched Latency

Disabled

Sys

Clk

DATA LATENCY (PIPELINE DELAY) MODULATION MODE

, 4

Frequency Word to DAC Output

Sys Clk

Phase Offset Word to DAC Output

Sys Clk

Amplitude Word to DAC Output

Sys Clk

DATA LATENCY (PIPELINE DELAY) LINEAR SWEEP MODE

Frequency Rising/Falling Delta Tuning Word to DAC

Output

Sys Clk

Phase Offset Rising/Falling Delta Tuning Word to DAC

Output

Sys Clk

Amplitude Rising/Falling Delta Tuning Word to DAC

Output

Sys Clk

For the VCO frequency range of 160 MHz to 255 MHz there is no guarantee of operation.

Data latency is reference to the I/O_UPDATE>

Data latency is fixed.

Data latency is referenced to a profile change.

AD9958

Rev. 0 | Page 8 of 40

ABSOLUTE MAXIMUM RATINGS

Table 2.

Parameter

Rating

Maximum Junction Temperature

150°C

DVDD_I/O (Pin 49)

4 V

AVDD, DVDD

2 V

Digital Input Voltage (DVDD_I/O = 3.3 V)

-0.7 V to +4 V

Digital Output Current

5 mA

Storage Temperature

65°C to +150°C

Operating Temperature

40°C to +85°C

Lead Temperature (10 sec Soldering)

300°C

21°C/W

2°C/W

Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.

ESD CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.

EQUIVALENT INPUT AND OUTPUT CIRCUITS

CMOS

DIGITAL

INPUTS

AVOID OVERDRIVING

DIGITAL INPUTS.

FORWARD BIASING

DIODES MAY COUPLE

DIGITAL NOISE ON

POWER PINS.

DVDD_I/O = 3.3V

INPUT

OUTPUT

05252-002

DAC OUTPUTS

TERMINATE OUTPUTS

INTO AVDD. DO NOT

EXCEED OUTPUTS'

VOLTAGE COMPLIANCE.

IOUT

05252-003

REF_CLK INPUTS

REF_CLK INPUTS ARE

INTERNALLY BIASED AND

NEED TO BE AC-COUPLED.

OSC INPUTS ARE DC-

COUPLED.

AMP

REF_CLK

OSC

AVDD

1.5k

AVDD

1.5k

AVDD

05252-004

Figure 2.

Figure 3.

Figure 4.

AD9958

Rev. 0 | Page 9 of 40

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

PIN 1
INDICATOR

NC = NO CONNECT

SYNC_IN

SYNC_OUT

MASTER_RESET

PWR_DWN_CTL

AVDD

AGND

AVDD

CH0_IOUT

AGND

AVDD

AGND

CH1_IOUT

AVDD

_
R

1
9

2
0

2
2

2
3

2
4

_
M

2
5

2
6

2
7

_
F

I
L

2
8

1
8

4
5

4
6

I
/
O

4
7

4
8

4
9

I
/
O

5
0

I
O

5
1

I
O

4
3

TOP VIEW

(Not to Scale)

AD9958

NOTES
1. THE EXPOSED EPAD ON BOTTOM SIDE OF PACKAGE IS

AN ELECTRICAL CONNECTION AND MUST BE
SOLDERED TO GROUND.

2. PIN 49 IS DVDD_IO AND IS TIED TO 3.3V.

05252-005

Figure 5. Pin Configuration

Table 3. Pin Function Descriptions

Pin No.

Mnemonic

I/O

Description

SYNC_IN

Used to Synchronize Multiple AD9958s. Connects to the SYNC_OUT pin of the
master AD9958 device.

SYNC_OUT

Used to Synchronize Multiple AD9958s. Connects to the SYNC_IN pin of the slave
AD9958 devices.

MASTER_RESET

Active High Reset Pin. Asserting the MASTER_RESET pin forces the AD9958's
internal registers to their default state, as described in the Register Map.

PWR_DWN_CTL

External Power-Down Control.

5, 7, 11, 15, 19, 21,
26, 29, 30, 31, 33,
35, 36, 37, 39

AVDD

Analog Power Supply Pins (1.8 V).

6, 10, 12, 16, 18, 20,
25

AGND

Analog Ground Pins.

45, 55

DVDD

Digital Power Supply Pins (1.8 V).

44, 56

DGND

Digital Power Ground Pins.

CH0_IOUT

True DAC Output. Terminates into AVDD.

CH0_IOUT

Complementary DAC Output. Terminates into AVDD.

CH1_IOUT

True DAC Output. Terminates into AVDD.

CH1_IOUT

Complementary DAC Output. Terminates into AVDD.

DAC_RSET

Establishes the Reference Current for all DACs. A 1.91 k resistor (nominal) is
connected from Pin 17 to AGND.

REF_CLK

Complementary Reference Clock/Oscillator Input. When the REF_CLK is operated
in single-ended mode, this pin should be decoupled to AVDD or AGND with a
0.1 µF capacitor.

23 REF_CLK

Reference Clock/Oscillator Input. When the REF_CLK is operated in single-ended
mode, this is the input. See Modes of Operation section for the reference clock
configuration.

AD9958

Rev. 0 | Page 10 of 40

Pin No.

Mnemonic

I/O

Description

CLK_MODE_SEL

Control Pin for the Oscillator Section. CAUTION: Do not drive this pin beyond 1.8 V.
When high (1.8 V), the oscillator section is enabled to accept a crystal as the
REF_CLK source. When low, the oscillator section is bypassed.

LOOP_FILTER

Connects to the external zero compensation network of the PLL loop filter.
Typically the network consists of a 0 resistor in series with a 680 pF capacitor tied
to AVDD.

28, 32, 34, 38

No Connection.

40, 41,42,43

P0, P1, P2, P3

Data pins used for modulation (FSK, PSK, ASK), start/stop for the sweep
accumulators or are used to ramp up/down the output amplitude. Note the
SYNC_CLK must be enabled in these modes. Any toggle of these data inputs is
equivalent to an I/O_UPDATE. The data is synchronous to the SYNC_CLK (Pin 54).
The data inputs must meet the set-up and hold time requirements to the
SYNC_CLK. This guarantees a fixed pipeline delay of data to the DAC output;
otherwise, a ±1 SYNC_CLK period of uncertainty exists. The functionality of these
pins is controlled by profile pin configuration (PPC) bits in Register FR1 <12:14>.

I/O_UPDATE

A rising edge transfers data from the serial I/O port buffer to active registers.
I/O_UPDATE is synchronous to the SYNC_CLK (Pin 54). I/O_UPDATE must meet the
set-up and hold time requirements to the. SYNC_CLK to guarantee a fixed pipeline
delay of data to DAC output. If not, a ±1 SYNC_CLK period of uncertainty exists.
The minimum pulse width is one SYNC_CLK period.

Active low chip select allowing multiple devices to share a common I/O bus (SPI).

SCLK

Serial Data Clock for I/O Operations. Data bits are written on the rising edge of
SCLK and read on the falling edge of SCLK.

DVDD_I/O

3.3 V Digital Power Supply for SPI Port and Digital I/O.

SDIO_0,

I/O

Data Pin SDIO_0 is dedicated to the Serial Port I/O only.

51 52, 53

SDIO_1 SDIO_2,
SDIO_3

I/O

Data Pins SDIO_1:3 can be used for the serial port I/O port or used to initiate a
ramp up/down (RU/RD) of the DAC output amplitude.

SYNC_CLK

The SYNC_CLK runs at one fourth the system clock rate. It can be disabled.
I/O_UPDATE or data (Pins 40 to 43) is synchronous to the SYNC_CLK. To guarantee
a fixed pipeline delay of data to DAC output, I/O_UPDATE or data (Pins 40 to 43)
must meet the set-up and hold time requirements to the rising edge of SYNC_CLK.
If not, a ±1 SYNC_CLK period of uncertainty exists.

AD9958

Rev. 0 | Page 11 of 40

TYPICAL PERFORMANCE CHARACTERISTICS

100

(dB)

10

20

30

40

50

60

70

80

90

05252-006

START 0Hz

STOP 250MHz

25MHz/DIV

DELTA 1 (T1)
71.73dB
4.50901804MHz

RBW

20kHz

RF ATT

20dB

VBW

20kHz

SWT

1.6s

UNIT

REF LVL
0dBm

1AP

Figure 6. f

OUT

= 1.1 MHz, f

CLK

= 500 MSPS, Wideband SFDR

100

(dB)

10

20

30

40

50

60

70

80

90

05252-007

START 0Hz

STOP 250Hz

25MHz/DIV

DELTA 1 (T1)
62.84dB
40.08016032MHz

RBW

20kHz

RF ATT

20dB

VBW

20kHz

SWT

1.6s

UNIT

REF LVL
0dBm

1AP

Figure 7. f

OUT

= 40.1 MHz, f

CLK

= 500 MSPS, Wideband SFDR

100

(dB)

10

20

30

40

50

60

70

80

90

05252-008

START 0Hz

STOP 250MHz

25MHz/DIV

DELTA 1 (T1)
59.04dB
100.70140281MHz

RBW

20kHz

RF ATT

20dB

VBW

20kHz

SWT

1.6s

UNIT

REF LVL
0dBm

1AP

Figure 8. f

OUT

= 100.3 MHz, f

CLK

= 500 MSPS, Wideband SFDR

100

(dB)

10

20

30

40

50

60

70

80

90

05252-009

START 0Hz

STOP 250MHz

25MHz/DIV

DELTA 1 (T1)
69.47dB
30.06012024MHz

RBW

20kHz

RF ATT

20dB

VBW

20kHz

SWT

1.6s

UNIT

REF LVL
0dBm

1AP

Figure 9. f

OUT

= 15.1 MHz, f

CLK

= 500 MSPS, Wideband SFDR

100

(dB)

10

20

30

40

50

60

70

80

90

05252-010

START 0Hz

STOP 250MHz

25MHz/DIV

DELTA 1 (T1)
60.13dB
75.15030060MHz

RBW

20kHz

RF ATT

20dB

VBW

20kHz

SWT

1.6s

UNIT

REF Lv]
0dBm

1AP

Figure 10. f

OUT

= 75.1 MHz, f

CLK

= 500 MSPS, Wideband SFDR

100

(dB)

10

20

30

40

50

60

70

80

90

05252-011

START 0Hz

STOP 250MHz

25MHz/DIV

DELTA 1 (T1)
53.84dB
101.20240481MHz

RBW

20kHz

RF ATT

20dB

VBW

20kHz

SWT

1.6s

UNIT

REF LVL
0dBm

1AP

Figure 11. f

OUT

= 200.3 MHz, f

CLK

= 500 MSPS, Wideband SFDR

AD9958

Rev. 0 | Page 12 of 40

100

(dB)

10

20

30

40

50

60

70

80

90

05252-012

CENTER 1.1MHz

SPAN 1MHz

100kHz/DIV

DELTA 1 (T1)
84.73dB
254.50901604kHz

RBW

500Hz

RF ATT

20dB

VBW

500Hz

SWT

20s

UNIT

REF LVL
0dBm

1AP

Figure 12. f

OUT

= 1.1 MHz, f

CLK

= 500 MSPS, NBSFDR, ±1 MHz

100

(dB)

10

20

30

40

50

60

70

80

90

05252-013

CENTER 40.1MHz

SPAN 1MHz

100kHz/DIV

DELTA 1 (T1)
84.10dB
120.24048096kHz

RBW

500Hz

RF ATT

20dB

VBW

500Hz

SWT

20s

UNIT

REF LVL
0dBm

1AP

Figure 13. f

OUT

= 40.1 MHz, f

CLK

= 500 MSPS, NBSFDR, ±1 MHz

100

(dB)

10

20

30

40

50

60

70

80

90

05252-014

CENTER 100.3MHz

SPAN 1MHz

100kHz/DIV

DELTA 1 (T1)

82.63dB

400.80160321kHz

RBW

500Hz

RF ATT

20dB

VBW

500Hz

SWT

20s

UNIT

REF LVL
0dBm

1AP

Figure 14. f

OUT

= 100.3 MHz, f

CLK

= 500 MSPS, NBSFDR, ±1 MHz

100

(dB)

10

20

30

40

50

60

70

80

90

05252-015

CENTER 15.1MHz

SPAN 1MHz

100kHz/DIV

DELTA 1 (T1)
84.86dB
200.40080160kHz

RBW

500Hz

RF ATT

20dB

VBW

500Hz

SWT

20s

UNIT

REF LVL
0dBm

1AP

Figure 15. f

OUT

= 15.1 MHz, f

CLK

= 500 MSPS, NBSFDR, ±1 MHz

100

(dB)

10

20

30

40

50

60

70

80

90

05252-016

CENTER 75.1MHz

SPAN 1MHz

100kHz/DIV

DELTA 1 (T1)
86.03dB
262.56513026kHz

RBW

500Hz

RF ATT

20dB

VBW

500Hz

SWT

20s

UNIT

REF LVL
0dBm

1AP

Figure 16. f

OUT

= 75.1 MHz, f

CLK

= 500 MSPS, NBSFDR, ±1 MHz

100

(dB)

10

20

30

40

50

60

70

80

90

CENTER 200.3MHz

SPAN 1MHz

05252-017

100kHz/DIV

DELTA 1 (T1)
83.72dB
400.80160321kHz

RBW

500Hz

RF ATT

20dB

VBW

500Hz

SWT

20s

UNIT

REF LVL
0dBm

1AP

Figure 17. f

OUT

= 200. 3MHz, f

CLK

= 500 MSPS, NBSFDR, ±1 MHz

AD9958

Rev. 0 | Page 13 of 40

170

160

150

140

130

120

110

100

10k

100k

10M

FREQUENCY OFFSET (Hz)

SE N

OISE (

05252-018

75.1MHz

100.3MHz

40.1MHz

15.1MHz

Figure 18. Residual Phase Noise (SSB) with f

OUT

= 15.1 MHz, 40.1MHz,

75.1 MHz, 100.3 MHz, f

CLK

= 500 MHz with REF_CLK Multiplier Bypassed

70

170

10M

05252-019

FREQUENCY OFFSET (Hz)

HAS

NOIS

(dBc

/Hz)

80

90

100

110

120

130

140

150

160

100

10k

100k

100.3MHz

75.1MHz

15.1MHz

40.1MHz

Figure 19. Residual Phase Noise (SSB) with f

OUT

= 15.1 MHz, 40.1MHz,

75.1 MHz, 100.3 MHz, f

CLK

= 500 MHz with REF_CLK Multiplier = 5x

70

170

10M

05252-020

FREQUENCY OFFSET (Hz)

HAS

NOIS

(dBc

/Hz)

80

90

100

110

120

130

140

150

160

100

10k

100k

100.3MHz

75.1MHz

15.1MHz

40.1MHz

Figure 20. Residual Phase Noise(SSB) with f

OUT

= 15.1 MHz, 40.1MHz,

75.1 MHz,100.3 MHz, f

CLK

= 500 MHz with REF_CLK Multiplier = 20Ч

60

85

25.3

200.3

FREQUENCY OF COUPLING SPUR (MHz)

HANNE

I
O

(
d

Bc)

65

70

75

80

50.3

75.3

100.3

125.3

150.3

175.3

SEPARATED DAC POWER PLANES

SINGLE DAC POWER PLANE

Figure 21. Channel Isolation at 500 MSPS Operation. Conditions are Channel

of Interest Fixed at 110.3 MHz, the Other Channels Are Frequency Swept.

600

500

REFERENCE CLOCK FREQUENCY (MHz)

TOTAL POWER DISSIPATION (mW)

500

400

300

200

100

450

400

350

300

250

200

150

100

2 CHANNELS ON

1 CHANNEL ON

05252-022

Figure 22. Reference Clock Frequency vs. Power Dissipation vs. Channel(s)

Power On/Off

45

75

1.1

OUT

(MHz)

DR (dBc

)

50

55

60

65

70

15.1

40.1

75.1

100.3

200.3

SFDR AVERAGED

05252-023

Figure 23. Averaged Channel SFDR vs. f

OUT

AD9958

Rev. 0 | Page 15 of 40

AD9958

(SLAVE 1)

AD9958

(MASTER)

CLOCK

SOURCE

AD9958

(SLAVE 2)

AD9958

(SLAVE 3)

REF_CLK

FPGA

DATA

SYNC_CLK

FPGA

DATA

SYNC_CLK

FPGA

DATA

SYNC_CLK

FPGA

DATA

SYNC_CLK

A_END

CENTRAL

CONTROL

AD9510

CLOCK DISTRIBUTOR

WITH

DELAY EQUALIZATION

SYNC_IN

SYNC_OUT

AD9510

SYNCHRONIZATION

DELAY EQUALIZATION

05252-027

Figure 27. Synchronizing Multiple Devices to Increase Channel Capacity Using the AD9510 as a Clock Distributor for the Reference and SYNC Clock

ACOUSTIC OPTICAL

TUNABLE FILTER

OPTICAL FIBER CHANNEL

W/MULITIPLE DISCRETE

WAVELENGTHS

OUTPUTS

INPUTS

SELECTABLE WAVELENGTH FROM EACH

CHANNEL VIA DDS TUNING AOTF

SPLITTER

WDM

SOURCE

WDM SIGNAL

CH 0

CH 1

CH 0 CH 1

CH 0

CH 1

AD9958

REF CLK

AMP

05252-028

Figure 28. DDS Providing Stimulus for Acoustic Optical Tunable Filter

AD9958

Rev. 0 | Page 17 of 40

THEORY OF OPERATION

DDS CORE

The AD9958 has two DDS cores each consisting of a 32-bit
phase accumulator and phase-to-amplitude converter. Together
these digital blocks generate a digital sine wave when the phase
accumulator is clocked and the phase increment value
(frequency tuning word) is greater than 0. The phase-to-
amplitude converter simultaneously translates phase
information to amplitude information by a COS () operation.

The output frequency (f

) of each DDS channel is a function of

the rollover rate of each phase accumulator. The exact
relationship is given in the following equation:

)

)(

(

FTW

with

FTW

where:
f

= the system clock rate.

FTW = the frequency tuning word.
2

represents the phase accumulator's capacity.

Since both channels share a common system clock, they are
inherently synchronized.

The DDS core architecture also supports the capability to phase
offset the output signal. This is performed by the channel phase
offset word (CPOW). The CPOW is a 14-bit register that stores
a phase offset value. This value is added to the output of the
phase accumulator to offset the current phase of the output
signal. Each channel has its own phase offset word register. This
feature can be used for placing both channels in a known phase
relationship relative to one another. The exact value of phase
offset is given by the following equation:

360

POW

D/A CONVERTER

The AD9958 incorporates two 10-bit current output DACs. The
DAC converts a digital code (amplitude) into a discrete analog
quantity. The DAC's current outputs can be modeled as a
current source with high output impedance (typically 100 k).
Unlike many DACs, these current outputs require termination
into AVDD via a resistor or a center-tapped transformer for
expected current flow.

Each DAC has complementary outputs that provide a combined
full-scale output current (I

OUT

+ I

OUTB

). The outputs always sink

current and their sum equals the full-scale current at any point
in time. The full-scale current is controlled by means of an
external resistor (R

SET

) and the scalable DAC current control

bits discussed in the Modes of Operation section. The resistor
R

SET

is connected between the DAC_RSET pin and analog

ground (AGND). The full-scale current is inversely
proportional to the resistor value as follows:

OUT

SET

The maximum full-scale output current of the combined DAC
outputs is 15 mA, but limiting the output to 10 mA provides
optimal spurious-free dynamic range (SFDR) performance. The
DAC output voltage compliance range is AVDD + 0.5 V to
AVDD - 0.5 V. Voltages developed beyond this range can cause
excessive harmonic distortion. Proper attention should be paid
to the load termination to keep the output voltage within its
compliance range. Exceeding this range could potentially
damage the DAC output circuitry.

DAC

LPF

IOUT

AVDD

1:1

IOUT

05252-031

Figure 31. Typical DAC Output Termination Configuration

AD9958

Rev. 0 | Page 18 of 40

MODES OF OPERATION

There are many combinations of modes (for example, single-
tone, modulation, linear sweep) that the AD9958 can perform
simultaneously. However, some modes require multiple data
pins, which can impose limitations. The following guidelines
can help determine if a specific combination of modes can be
performed simultaneously by the AD9958.

Note the SYNC_CLK must be enabled in all modes except
single-tone mode.

CHANNEL CONSTRAINT GUIDELINES

Single tone generation, 2-level modulation, and linear
sweep modes can be enabled on either channel and in any
combination simultaneously.

Both channels can perform 4-level modulation
simultaneously.

Either channel can perform 8-level or 16-level modulation.
The other channel can only be in single-tone mode.

The RU/RD function can be used on both channels in
single-tone generation mode. See the Output Amplitude
Control Mode section for the RU/RD function.

When Profile Pins P2 and P3 are used for RU/RD, either
channel can perform 2-level modulation with RU/RD or
both channels can perform linear frequency or phase
sweep with RU/RD.

When Profile Pin P3 is used for RU/RD, either channel can
be used in 8-level modulation with RU/RD. The other
channel can only be in single-tone generation mode.

When SDIO_1:3 pins are used for RU/RD, either or both
channels can perform 2-level modulation with RU/RD. If
one channel is not in 2-level modulation it can only be in
single-tone generation mode.

When the SDIO_1:3 pins are used for RU/RD, either or
both channels can perform 4-level modulation with
RU/RD. If one channel is not in 4-level modulation it can
only be in single-tone generation mode.

When the SDIO_1:3 pins are used for RU/RD, either
channel can perform 8-level modulation with RU/RD. The
other channel can only be in single-tone generation mode.

10.

When the SDIO_1:3 pins are used for RU/RD, either
channel can perform 16-level modulation with RU/RD.
The other channel can only be in single-tone generation
mode.

11.

Amplitude modulation, linear amplitude sweep modes,
and the RU/RD function cannot operate simultaneously,
but frequency and phase modulation can operate
simultaneously with the RU/RD function.

POWER SUPPLIES

The AVDD and DVDD supply pins provide power to the DDS
core and supporting analog circuitry. These pins connect to a
1.8 V nominal power supply.

The DVDD_I/O pin connects to a 3.3 V nominal power
supply. All digital inputs are 3.3 V logic except for the
CLK_MODE_SEL input. The CLK_MODE_SEL (Pin 24) is
an analog input and should be operated by 1.8 V logic.

SINGLE-TONE MODE

Single-tone mode is the default mode of operation after a
master reset signal. In this mode, both DDS channels share a
common address location for the frequency tuning word
(Register 0x04) and phase offset word address location
(Register 0x05). Channel enable bits are provided in combi-
nation with these shared addresses. As a result, the frequency
tuning word and/or phase offset word can be independently
programmed between channels (see the following Step 1
through Step 5). The channel enable bits do not require an I/O
update to enable or disable a channel.

See the Register Map section for a description of the channel
enable bits in the channel select register or CSR (Register 0x00).
The channel enable bits are enabled or disabled immediately
after the CSR's data byte is written.

Address sharing enables channels to be written simultaneously,
if desired. The default state enables all channel enable bits.
Therefore, the frequency tuning word and/or phase offset word
is common to both channels, but written only once through the
serial I/O port.

The following steps present a basic protocol to program a
different frequency tuning word and/or phase offset word for
each channel using the channel enable bits.

Power up DUT and issue a master reset. A master reset
places the part in single-tone mode and single-bit mode for
serial programming operations (refer to the Serial I/O
Modes of Operation section). Frequency tuning words and
phase offset words default to 0 at this point.

Enable only one channel enable bit (Register 0x00), disable
the other channel enable bit.

Using the serial I/O port, program the desired frequency
tuning word (Register 0x04) and/or the phase offset word
(Register 0x05) for the enabled channel.

Repeat Step 2 and Step 3 for each channel.

Send an I/O update signal. After an I/O update, both
channels should output their programmed frequency
and/or phase offset value.

AD9958

Rev. 0 | Page 19 of 40

Single-Tone Mode--Matched Pipeline Delay

In single-tone mode, the AD9958 offers matched pipeline delay
to the DAC input for all frequency, phase, and amplitude
changes. This avoids having to deal with different pipeline
delays between the three input ports for such applications. The
feature is enabled by asserting the match pipeline delay bit
found in the channel function register (CSR) (Register 0x03).
This feature is available in single-tone mode only.

REFERENCE CLOCK MODES

The AD9958 supports multiple reference clock configurations
to generate the internal system clock. As an alterative to
clocking the part directly with a high frequency clock source,
the system clock may be generated using the internal, PLL-
based reference clock multiplier. An on-chip oscillator circuit is
also available for providing a low frequency reference signal by
connecting a crystal to the clock input pins. Enabling these
features allows the part to operate with a low frequency clock
source and still provide a high update rate for the DDS and
DAC. However, using the clock multiplier changes the output
phase noise characteristics. For best phase noise performance, a
clean, stable clock with a high slew is required. Refer to
Figure 19 and Figure 20.

Enabling the PLL allows multiplication of the reference clock
frequency from 4Ч to 20Ч, in integer steps. The PLL
multiplication value is represented by a 5-bit multiplier value.
These bits are located in the Function Register 1 (FR1),
bits <22:18>. Refer to the Register Map.

When FR1 <22:18> is programmed with values ranging from 4
to 20 (decimal) the clock multiplier is enabled. The integer
value in the register represents the multiplication factor. The
system clock rate with the clock multiplier enabled is equal to
the reference clock rate times the multiplication factor. If FR1
<22:18> is programmed with a value less than 4 or greater than
20 the clock multiplier is disabled and the multiplication factor
is effectively 1.

Whenever the PLL clock multiplier is enabled or the
multiplication value is changed, time should be allowed to lock
the PLL (typically 1 ms).

Note that the output frequency of the PLL is restricted to a
frequency range of 100 MHz to 500 MHz. However, there is a
VCO gain bit that must be used appropriately. The VCO gain
bit defines two ranges (low/high) of frequency output. The
VCO gain bit defaults to low (see Specifications for details).

The charge pump current in the PLL defaults to 75

µA.

This

setting typically produces the best phase noise characteristics.
Increasing charge pump current may degrade phase noise, but
decreases the lock time and changes the loop bandwidth.

Enabling the on-chip oscillator for crystal operation is per-
formed by driving the CLK_MODE_SEL (Pin 24) to logic high
(1.8 V logic). With the on-chip oscillator enabled, connection of
an external crystal to the REF_CLK and REF_CLKB inputs is
made producing a low frequency reference clock. The crystal's
frequency must be in the range of 20 MHz to 30 MHz.

Table 4 summarizes the clock modes of operation. See the
Specifications section for more details.

Table 4.

CLK_MODE_SEL
Pin (24)

FR1<22:18>
PLL, Bits = M

Oscillator
Enabled

System
Clock
(f

SYS CLK

)

Min/Max
Freq. Range
(MHz)

High = 1.8 V
logic

4 M 20

Yes

SYS CLK

OSC

Ч M

100 < f

SYSCLK

< 500

High = 1.8 V
logic

M < 4 or
M > 20

Yes

SYS CLK

OSC

20 < f

SYSCLK

< 30

Low

4 M 20

SYS CLK

REF CLK

100 < f

SYSCLK

< 500

Low

M < 4 or
M > 20

SYS CLK

REF CLK

0 < f

SYS CLK

500

Reference Clock Input Circuitry

The reference clock input circuitry has two modes of operation
controlled by the logic state of Pin 24 (clock mode select). The
first mode (logic low) configures as an input buffer. In this
mode, the reference clock must be ac-coupled to the input due
to internal dc biasing. This mode supports either differential
or single-ended configurations. If single-ended mode is
chosen, the complementary reference clock input (Pin 23)
should be decoupled to AVDD or AGND via a 0.1 µF capacitor.
Figure 32 and Figure 34 exemplify typical reference clock
configurations for the AD9958.

1:1

BALUN

REF_CLK

PIN 23

REFERENCE

CLOCK

SOURCE

REF_CLK

PIN 22

0.1

05252-032

Figure 32.

The reference clock inputs can also support an LVPECL or
PECL driver as the reference clock source.

REF_CLK

PIN 23

REF_CLK

PIN 22

0.1

LVPECL/

PECL

DRIVER

TERMINATION

05252-033

Figure 33.

The second mode of operation (Pin 24 = logic high = 1.8 V)
provides an internal oscillator for crystal operation. In this
mode, both clock inputs are dc-coupled via the crystal leads and
bypassed. The range of crystal frequencies supported is from
20 MHz to 30 MHz. Figure 34 shows the configuration for
using a crystal.

AD9958

Rev. 0 | Page 20 of 40

REF_CLK

PIN 23

25MHz

XTAL

REF_CLK

PIN 22

22pF

05252-034

Figure 34.

SCALABLE DAC REFERENCE CURRENT CONTROL
MODE

The R

SET

is common to both DACs. As a result, the full-scale

currents are equal as a default. The scalable DAC reference can
be used to set each DAC's full-scale current independently from
one another. This is accomplished by using the CFR register bits
<9:8>. Table 5 shows how each DAC can be individually scaled
for independent channel control. This provides for binary
attenuation.

Table 5.

CFR <9:8>

LSB Current State

Full scale

0 1 Half

scale

1 0 Quarter

scale

Eighth scale

POWER-DOWN FUNCTIONS

The AD9958 supports an externally controlled power-down
feature and the more common software programmable power-
down bits found in previous Analog Devices DDS products.

The software control power down allows the input clock
circuitry, DAC, and the digital logic (for each separate channel)
to be individually powered down via unique control bits
(CFR <7:6>). These bits are not active when the externally
controlled power-down pin (PWR_DWN_CTL) is high. When
the PWR_DWN_CTL input pin is high, the AD9958 enters a
power-down mode based on the FR1 <6> bit. When the
PWR_DWN_CTL input pin is low, the external power-down
control is inactive.

When the FR1 <6> bit is zero, and the PWR_DWN_CTL input
pin is high, the AD9958 is put into a fast recovery power-down
mode. In this mode, the digital logic and the DACs digital logic
are powered down. The DACs bias circuitry, oscillator, and
clock input circuitry is not powered down.

When the FR1 <6> bit is high and the PWR_DWN_CTL pin is
high, the AD9958 is put into the full power-down mode. In this
mode, all functions are powered down. This includes the DACs
and PLL, which take a significant amount of time to power up.
When the PLL is bypassed, the PLL is shut down to conserve
power.

When the PWR_DWN_CTL input pin is high, the individual
power down bits (CFR <7:6>) and FR1 <7>) are invalid (don't
care) and are unused. When the PWR_DWN_CTL input pin is
low, the individual power-down bits control the power-down
modes of operation.

Note that the power-down signals are all designed such that a
Logic 1 indicates the low power mode and Logic 0 indicates the
powered-up mode.

MODULATION MODE

The AD9958 can perform 2-/4-/8- or 16-level modulation of
frequency, phase, or amplitude (FSK, PSK, ASK). Modulation is
achieved by applying data to the profile pins. Each channel can
be programmed separately, but the ability to modulate both
channels simultaneously is constrained by the limited number
of profile pins. For instance, 16-level modulation uses all four
profile pins, which inhibits modulation for the remaining
channel.

In addition, the AD9958 has the ability to ramp up or ramp
down the output amplitude before, during, or after a
modulation (FSK, PSK only) sequence. This is performed by
using the 10-bit output scalar. If the RU/RD feature is desired,
unused profile pins or unused SDIO_1:3 pins can be configured
to initiate the operation. See the Output Amplitude Control
Mode section for more details of the RU/RD feature.

In modulation mode, each channel has its own set of control
bits to determine the type (frequency, phase, or amplitude) of
modulation. Each channel has 16 profile registers for flexibility.
Register Addresses 0x0A through 0x18 are profile registers for
modulation of frequency, phase, or amplitude. Registers 0x04,
0x05, and 0x06 are dedicated registers for frequency, phase, and
amplitude, respectively. These registers contain the first
frequency, phase offset, and amplitude word.

Frequency modulation has a 32-bit resolution, phase modula-
tion is 14 bits, and amplitude is 10 bits. When modulating phase
or amplitude, the word value must be MSB-aligned in the
profile registers and the unused bits are don't care bits.

In modulation mode, AFP bits (CFR <23:22>) and level bits
(FR1 <9:8>) are programmed to configure the modulation type
and level. See Table 6 and Table 7 settings. Note that the linear
sweep enable bit must be set to Logic 0 in direct modulation
mode.

Table 6.

AFP CFR
<23:22>

Linear Sweep
Enable CFR <14>

Description

Modulation disabled

Amplitude modulation

Frequency modulation

Phase modulation

AD9958

Rev. 0 | Page 21 of 40

Table 7.

Modulation Level Bits FR1 <9:8>

Description

2-level modulation

4-level modulation

8-level modulation

16-level modulation

When modulating, the RU/RD function can be limited based
on pins available for controlling the feature. SDIO pins are for
RU/RD only, not modulation.

Table 8.

RU/RD Bits
FR1 <11:10>

Description

RU/RD disabled.

Only profile Pin 2 and Pin 3 available for RU/RD
operation.

Only profile Pin 3 available for RU/RD
operation.

Only SDIO Pins 1, 2, and 3 available for RU/RD
operation. Forces the serial I/O to only be used
in 1-bit mode.

If profile pins are used for RU/RD, Logic 0 is for ramp-up and
Logic 1 is for ramp-down.

Because of the two channels and limited data pins, it is
necessary to assign the profile pins and/or SDIO_1:3 pins to a
dedicated channel. This is controlled by the profile pin
configuration or PPC bits (FR1 <14:12>). Each modulation
description to follow incorporates data pin assignments.

2-Level Modulation--No RU/RD

Modulation level bits are set to 00 (2-level). AFP bits are set to
the desired modulation type. RU/RD bits and the linear sweep
bit are disabled. Table 9 displays how the profile pins and
channels are assigned.

Table 9.

Profile Pin
Configuration(PPC)
Bits FR1<14:12>

Description

N/A

N/A CH0 CH1 2-level

mode both
channels,
no RU/RD

As shown in Table 9, only Profile Pin P2 can be used to
modulate Channel 0. If the P2 pin is Logic 0, Register 0
(Register 0x04) is chosen; if the P2 pin is Logic 1, Register 1
(Register 0x0A) is chosen.

4-Level Modulation--No RU/RD

Modulation level bits are set to 01 (4-level). AFP bits are set to
the desired modulation type. RU/RD bits and the linear sweep
bit are disabled. Table 10 displays how the profile pins and
channels are assigned to each other.

Table 10.

Profile Pin
Config. (PPC)
Bits FR1
<14:12>

P0 P1 P2 P3 Description

1 CH0 CH0 CH1 CH1 4-level

modulation

on CH0 and CH1,
no RU/RD

For this condition, the profile register chosen is based on the
two bit value presented to profile pins <P0:P1> or <P2:P3>.

For example, if PPC = 101, <P0:P1>= 11, and <P2:P3>= 01,
then the contents of Profile Register 3 of Channel 0 are
presented to Channel 0's output and the contents of Profile
Register 1 of Channel 1 are presented to Channel 1's output.

8-Level Modulation--No RU/RD

Modulation level bits are set to 10 (8-level). AFP bits are set to a
nonzero value. RU/RD bits and the linear sweep bit are
disabled. Note that the AFP bits of the three channels not being
used must be set to 00. Table 11 shows the assignment of profile
pins and channels.

Table 11.

Profile Pin
Config. Bits
FR1

<14:12>

P0 P1 P2 P3

Description

CH0

8-level modulation
on CH0, no RU/RD

CH1

8-level modulation
on CH1, no RU/RD

For this condition, the profile register (1 of 16) chosen is based
on the 3-bit value presented to the profile <P0-P2> pins. For
example, if PPC = X10 and <P0-P2> = 111, the contents of
Profile Register 7 of Channel 0 are presented to Channel 0.

16-Level Modulation--No RU/RD

Modulation level bits are set to 11 (16-level). AFP bits are set to
the desired modulation type. RU/RD bits and the linear sweep
bit are disabled. The AFP bits of the three channels not being
used must be set to 00. Table 12 displays how the profile pins
and channels are assigned.

Table 12.

Profile Pin
Config. (PPC) Bits
FR1 <14:12>

P0 P1 P2 P3 Description

CH0

16-level
modulation on
CH0, no RU/RD

CH1

16-level
modulation on
CH1, no RU/RD

For these conditions, the profile register chosen is based on
the 4-bit value presented to profile <P0-P3> pins. For example
if PPC = X11 and <P0-P3> = 1110, the contents of Profile
Register 14 of Channel 1 is presented to Channel 1.

AD9958

Rev. 0 | Page 22 of 40

2-Level Modulation Using Profile Pins for RU/RD

When the RU/RD bit = 01, Profile Pins P2 and P3 are available
for RU/RD. Note that only a modulation level of two is available
in this mode. See Table 13 for available pin assignments.

Table 13.

Profile Pin
Config. Bits
FR1 <14:12>

P0 P1 P2

Description

CH0

CH1

CH0

CH1

2-level
modulation

RU/RD

With RU/RD, CH0,
CH1

8-Level Modulation Using a Profile Pin for RU/RD

When the RU/RD bit = 10, Profile Pin P3 is available for
RU/RD. Note that only a modulation level of eight is available.
See Table 14 for available pin assignments.

Table 14.

Profile Pin Config. Bits
FR1 <14:12>

P0 P1 P2 P3

Description

CH0 CH0 CH0 CH0

RU/RD

8-level modulation
with RU/RD,
CH0

CH1 CH1 CH1 CH1

RU/RD

8-level modulation
with RU/RD,
CH1

MODULATION USING SDIO PINS FOR RU/RD

For RU/RD bits = 11, SDIO Pins 1, 2, and 3 are available for
RU/RD. In this mode, modulation levels of 2/4/16 are available.
Note that the serial I/O port can only be used in 1-bit serial
mode.

2-Level Modulation Using SDIO Pins for RU/RD

Table 15.

Profile Pin Config. Bits
FR1 <14:12>

P0 P1 P2 P3

N/A

N/A CH0

CH1

For this configuration, each profile pin is dedicated to a specific
channel. In this case, the SDIO pins can be used for the RU/RD
function, as described in Table 16.

Table 16.

SDIO Pins

1 2 3

Description

Triggers the ramp-up function for CH0

Triggers the ramp-down function for CH0

Triggers the ramp-up function for CH1

Triggers the ramp-down function for CH1

4-Level Modulation Using SDIO Pins for RU/RD

For RU/RD = 11 (SDIO Pins 1 and 2 are available for RU/RD),
the modulation level is set to four. See Table 17 for pin
assignments, including SDIO pin assignments.

Table 17.

Profile Pin Config.
Bits FR1 <14:12>

SDIO 1 SDIO 2 SDIO 3

1 CH0 CH0 CH1 CH1 CH0

CH1

N/A

RU/RD

For the configuration shown in Table 17, the profile register is
chosen based on the two bit value presented to <P1:P2> or
<P3:P4>.

For example, if PPC = 101, <P0:P1> = 11, and <P2:P3> = 01,
then the contents of Profile Register 3 of Channel 0 are
presented to Channel 0's output and the contents of Profile
Register 1 of Channel 1 are presented to Channel 1's output.
SDIO Pins 1 and 2 provide the RU/RD function.

16-Level Modulation Using SDIO Pins for RU/RD

RU/RD = 11 (SDIO Pin 1 available for RU/RD) and the level is
set to 16. See the pin assignment shown in the Table 18.

Table 18.

Profile Pin
Configuration
FR1<14:12> P0 P1 P2 P3

SDIO
1

SDIO
2

SDIO
3

CH0

RU/RD

CH1

RU/RD

For the configuration shown in Table 18, the profile register is
chosen based on the 4-bit value presented to <P0:P3>. For
example, if PPC = X11 and <P0-P3> = 1101, then the contents
of Profile Register 13 of Channel 1 is presented to Channel 1.
The SDIO_1 pin provides the RU/RD function.

LINEAR SWEEP (SHAPED) MODULATION MODE

Linear sweep enables the user to sweep frequency, phase, or
amplitude from a starting point (S0) to an endpoint (E0). The
purpose of linear sweep modes is to provide better bandwidth
containment compared to direct modulation by replacing
greater instantaneous changes with more gradual, user-defined
changes between S0 and E0.

In linear sweep mode, S0 is loaded into Profile Register 0
(Profile 0 is represented by one of the three Registers 0x04,
0x05, or 0x06 depending on the type of sweep) and E0 is always
loaded into Profile Register 1 (Register 0x0A). If E0 is
configured for frequency sweep, the resolution is 32 bits, phase
sweep is 14 bits, and amplitude sweep is 10 bits. When sweeping
phase or amplitude, the word value must be MSB-aligned in
Profile 1 register. The unused bits are don't care bits.

The profile pins are used to trigger and control the direction of
the linear sweep for frequency, phase, and amplitude. Both
channels can be programmed separately for a linear sweep. In
linear sweep mode, Profile Pin 2 is dedicated to Channel 0.
Profile Pin 3 is dedicated to Channel 1, and so on.

AD9958

Rev. 0 | Page 23 of 40

The AD9958 has the ability to ramp up or ramp down (RU/RD)
the output amplitude (using the 10-bit output scalar) before and
after a linear sweep. If the RU/RD feature is desired, unused
profile pins or unused SDIO_1:3 pins can be configured for the
RU/RD operation.

To enable linear sweep mode for a particular channel, AFP bits
(CFR <23:22>), modulation level bits (FR1 <9:8>), and the
linear sweep enable bit (CFR <14>) are programmed. The AFP
bits determine the type of linear sweep to be performed. The
modulation level bits must be set to 00 (2-level) for that specific
channel (see Table 19 and Table 20).

Table 19.

AFP
CFR <23:22>

Linear Sweep Enable
CFR <14>

Description

N/A

Amplitude sweep

Frequency sweep

Phase sweep

Table 20.

Modulation Level Bits FR1 <9:8>

Description

2-level modulation

4-level modulation

8-level modulation

16-level modulation

Setting the Slope of the Linear Sweep

The slope of the linear sweep is set by the intermediate step size
(delta-tuning word) between S0 and E0 and the time spent
(sweep ramp rate word) at each step. The resolution of the
delta-tuning word is 32 bits for frequency, 14 bits for phase, and
10 bits for amplitude. The resolution for the delta ramp rate
word is 8 bits.

In linear sweep, each channel is assigned a rising delta word
(RDW, Register 0x08) and a rising sweep ramp rate word
(RSRR, Register 0x07). These settings apply when sweeping up
towards E0. The falling delta word (FDW, Register 0x09) and
falling sweep ramp rate (FSRR, Register 0x07) apply when
sweeping down towards S0.

Note the sweep accumulator overflows if the rising or falling
delta word is too large. To prevent this from happening, the
magnitude of the rising or falling delta word should not be
greater than the difference between full scale and the E0 value
(full scale - E0). For a frequency sweep, full scale is 2

-1. For

a phase sweep, full scale is 2

-1. For an amplitude sweep, full

scale is 2

-1.

The following graph displays a linear sweep up and then down
using a profile pin. Note that the no-dwell bit is disabled; other-
wise, the sweep accumulator returns to 0 upon reaching EO.

(FREQUENCY/

HASE/

PLI

UDE)

NEAR SWEEP

RDW

RSRR

FSRR

f,p,a

FDW

TIME

PROFILE PIN

f,p,a

05252-035

Figure 35.

For a piecemeal or a nonlinear transition between S0 and E0,
the delta-tuning words and ramp rate words can be repro-
grammed during the transition to produce the desired response.

The formulae for calculating the step size of RDW or FDW for
delta frequency, delta phase, or delta amplitude are as follows:

CLK

SYNC

RDW

(Hz)

360

RDW

1024

RDW

(DAC full-scale current)

The formula for calculating delta time from RSRR or FSRR is

CLK

SYNC

RSRR

At 500 MSPS operation (SYNC_CLK =125 MHz), the maxi-
mum time interval between steps is 1/125 MHz Ч 256 = 2.048 µs.
The minimum time interval is (1/125 MHz) Ч 1 = 8.0 ns.

The sweep ramp rate block (timer) consists of a loadable 8-bit
down counter that continuously counts down from the loaded
value to 1. When the ramp rate timer equals 1, the proper ramp
rate value is loaded and the counter begins counting down to 1
again. This load and count down operation continues for as
long as the timer is enabled. However the count can be reloaded
before reaching 1 by either of the following two methods.

Method one is by changing the profile pin. When the profile pin
changes from Logic 0 to Logic 1, the rising sweep ramp rate
register (RSRR) value is loaded into the ramp rate timer, which
then proceeds to count down as normal. When the profile pin
changes from Logic 1 to Logic 0, the falling sweep ramp rate
register (FSRR) value is loaded into the ramp rate timer, which
then proceeds to count down as normal.

AD9958

Rev. 0 | Page 24 of 40

Method two is by setting the CFR <14> bit and issuing an I/O
update. If sweep is enabled and CFR <14> is set, the ramp rate
timer loads the value determined by the profile pin: If the
profile pin is high the ramp rate timer loads the RSRR, if the
profile pin is low the ramp rate timer loads the FSRR.

Frequency Linear Sweep Example: AFP Bits = 10

Modulation level bits = 00, sweep enable = 1, no-dwell bit = 0.

In linear sweep mode, when the profile pin transitions from low
to high, the RDW is applied to the input of the sweep
accumulator and the RSRR register is loaded into the sweep rate
timer.

The RDW accumulates at the rate given by the ramp rate
(RSRR) until the output is equal to the CTW1 register value.
The sweep is then complete and the output is held constant in
frequency.

When the profile pin transitions from high to low, the FDW is
applied to the input of the sweep accumulator and the FSRR
register is loaded into the sweep rate timer.

The FDW accumulates at the rate given by the ramp rate
(FSRR) until the output is equal to the CTW0 register value.

The sweep is then complete and the output is held constant in
frequency.

See Figure 36 for the linear sweep block diagram. Figure 38
depicts a frequency sweep with no-dwell mode disabled. In this
mode, the output follows the state of the profile pin. A phase or
amplitude sweep works in the same manner.

LINEAR SWEEP--NO-DWELL MODE

If the linear sweep no-dwell bit is set (CFR <15>), the rising
sweep is started in an identical manner to the dwell linear
sweep mode. That is, upon detecting Logic 1 on the profile
input pin, the rising sweep action is initiated. The word
continues to sweep up at the rate set by the rising sweep ramp
rate at the resolution set by the rising delta tuning word until it
reaches the terminal value. Upon reaching the terminal value,
the output immediately reverts back to the starting point and
remains until Logic 1 is detected on the profile pin. Figure 37
shows an example of the no-dwell mode. The points labeled "A"
indicate where a rising edge is detected on the profile pin and
the points labeled "B" indicate where the AD9958 has
determined that the output has reached E0 and reverts to S0.

The falling ramp rate register and the falling delta word are
unused in this mode.

RATE TIME

LOAD CONTROL

LOGIC

LIMIT LOGIC TO

KEEP SWEEP BETWEEN

S0 AND E0

RAMP RATE TIMER:

8-BIT LOADABLE DOWN COUNTER

ACCUMULATOR RESET

LOGIC

MUX

PROFILE PIN

MUX

FDW

RDW

FSRR

RSRR

PROFILE PIN

CTW1

SWEEP ACCUMULATOR

SWEEP ADDER

CTW0

05252-036

Figure 36. Linear Sweep Block Diagram

AD9958

Rev. 0 | Page 25 of 40

FTW0

SINGLETONE

MODE

LINEAR SWEEP MODE ENABLE, NO-DWELL BIT SET

FTW1

OUT

TIME

PS<2> = 1 PS<2> = 0

PS<2> = 0

PS<2> = 1

PS<2> = 0

05252-037

Figure 37.

FTW0

SINGLETONE

MODE

LINEAR SWEEP MODE

AT POINT A: LOAD RISING RAMP RATE REGISTER, APPLY RISING DFTW.
AT POINT B: LOAD FALLING RAMP RATE REGISTER, APPLY FALLING DFTW.

PS<2> = 1

PS<2> = 0

TIME

FTW1

OUT

05252-038

Figure 38. Linear Sweep with the No-Dwell Feature Disabled

SWEEP AND PHASE ACCUMULATOR CLEARING
FUNCTIONS

The AD9958 allows two different clearing functions. The first
is a continuous zeroing of the sweep logic and phase accumu-
lator (clear and hold). The second is a clear and release or
automatic zeroing function. CFR <4> is the automatic clear
sweep accumulator bit and CFR <2> is the automatic clear
phase accumulator bit. The continuous clear bits are located in
CFR, where CFR <3> clears the sweep accumulator and
CFR <1> clears the phase accumulator.

Continuous Clear Bits

The continuous clear bits are static control signals that, when
active high, hold the respective accumulator at 0 while the bit is
active. When the bit goes low, the respective accumulator is
allowed to operate.

Clear and Release Bits

The auto clear sweep accumulator bit, when set, clears and
releases the sweep accumulator upon an I/O update or a change
in the profile input pins. The auto clear phase accumulator,
when set, clears and releases the phase accumulator upon an
I/O update or a change in the profile pins. The automatic clear-
ing function is repeated for every subsequent I/O update or
change in profile pins until the clear and release bits are reset
via the serial port.

AD9958

Rev. 0 | Page 26 of 40

OUTPUT AMPLITUDE CONTROL MODE

The 10-bit scale factor (multiplier) controls the ramp-up and
ramp-down (RU/RD) time of an on/off emission from the
DAC. In burst transmissions of digital data, it reduces the
adverse spectral impact of abrupt bursts of data. It can be
bypassed by clearing the multiplier enable bit (ACR <12> = 0).

Automatic and manual RU/RD modes are supported. The
automatic mode generates a zero-scale up to a full-scale
(10 bits) linear ramp at a rate determined by the amplitude
ramp rate control register. The start and direction of the ramp
can be controlled by either the profile pins or the SDIO1:3 pins.

Manual mode allows the user to directly control the output
amplitude by manually writing to the amplitude scale factor
value in the amplitude control register (Register 0x06).
Manual mode is enabled by setting the ACR <12> = 1 and
ACR <11> = 0 bits.

Automatic RU/RD Mode Operation

The automatic RU/RD mode is active when both the ACR <12>
and ACR <11> bits are set. When automatic RU/RD is enabled,
the scale factor is internally generated and applied to the multi-
plier input port for scaling the output. The scale factor is the
output of a 10-bit counter that increments/decrements at a
rate set by the 8-bit output ramp rate register. The scale factor
increments if the external pin is high and decrements if the
pin is low. The internally generated scale factor step size is
controlled by the <15:14> bits in the ACR register. Table 21
describes the increment/decrement step size of the internally
generated scale factor per the ACR <15:14> bits.

Table 21.

Autoscale Factor Step Size
ASF <15:14> (Binary)

Increment/Decrement
Size

A special feature of this mode is that the maximum output
amplitude allowed is limited by the contents of the amplitude
scale factor register (ASFR). This allows the user to ramp to a
value less than full scale.

Ramp Rate Timer

The ramp rate timer is a loadable down counter, which
generates the clock signal to the 10-bit counter that generates
the internal scale factor. The ramp rate timer is loaded with the
value of the ASFR every time the counter reaches 1 (decimal).
This load and count down operation continues for as long as
the timer is enabled unless the timer is forced to load before
reaching a count of 1.

If the load ARR timer bit ACR <10> is set, the ramp rate timer
is loaded at an I/O update, a change in profile input, or on
reaching a value of 1. The ramp timer can be loaded before
reaching a count of 1 by three methods.

In the first method the profile pin(s) or SDIO_1:3 pins are
changed. When the control signal changes state, the ACR
value is loaded into the ramp rate timer, which then
proceeds to count down as normal.

In the second method, the load ARR timer bit (ACR <10>)
is set and an I/O update is issued.

The last method is by changing from inactive auto RU/RD
mode to active auto RU/RD mode.

RU/RD Pin-to-Channel Assignment

When both channels are in single-tone mode, the profile
pins are used for RU/RD operation.

When both linear sweep and RU/RD modes are activated,
SDIO_1:3 are used for RU/RD operation.

In modulation mode, please refer to the modulation mode
section for pin assignments.

Table 22.

Profile Pin

RU/RD Operation

Ch 0

Ch 1

Table 23.

SDIO

LS and RU/RD Modes
Enable
Simultaneously

1 2

Ramp-Up/Ramp-
Down Control
Signal Assignment

Enable for CH0

Ramp-up function
for CH0

Enable for CH0

Ramp-down
function for CH0

Enable for CH1

Ramp-up function
for CH1

Enable for CH1

Ramp-down
function for CH1

AD9958

Rev. 0 | Page 27 of 40

SYNCHRONIZING MULTIPLE AD9958 DEVICES

The AD9958 allows easy synchronization of multiple AD9958
devices. At power-up the phase of SYNC_CLK can be offset
between multiple devices. To correct for the offset and align the
SYNC_CLK edges, there are three methods (one automatic
mode and two manual modes) of synchronizing SYNC_CLKs.
These modes force the internal state machines of multiple
devices to a known state, which aligns SYNC_CLKs.

Any mismatch in REF_CLK phase between devices results in a
corresponding phase mismatch on the SYNC_CLKs.

AUTOMATIC MODE SYNCHRONIZATION

In automatic mode, multiple part synchronization is achieved
by connecting the SYNC_OUT pin on the master device to the
SYNC_IN pin of the slave device(s). Devices are configured as
master or slave through programming bits, accessible via the
serial port.

A configuration for synchronizing multiple AD9958/59 devices
in automatic mode is shown in the Application Circuits section.
In this configuration, the AD9510 provides coincident
REF_CLKs and SYNC_OUTs to all devices.

Operation

The first step is to program the master and slave devices for
their respective roles. Enabling the master device is performed
by writing its master enable bit (FR2 <6>) true. This causes the
SYNC_OUT of the master device to output a pulse that has a
pulse width equal to one system clock period and a frequency
equal to one fourth of the system clock frequency. Enabling
device(s) as slaves is performed by writing the slave enable bit
(FR2 <7>) true.

In automatic synchronizing mode, the slave device(s) sample
SYNC_OUT pulses from the master device and a comparison of
all state machines is made by the autosynchronization circuitry.
If the slave device(s) state machines are not identical to the
master, the slave device(s) state machines are stalled for one
system clock cycle. This procedure synchronizes the slave
device(s) within three SYNC_CLK periods.

Delay Time Between SYNC_OUT and SYNC_IN

When the delay between SYNC_OUT and SYNC_IN exceeds
one system clock period, phase offset bits (FR2 <1:0>) are used
to compensate. The default state of these bits is 00, which
implies that the SYNC_OUT of the master and the SYNC_IN of
the slave have a propagation delay of less than one system clock
period. If the propagation time is greater than one system clock
period, the time should be measured and the appropriate offset
programmed. Table 24 describes the delays required per system
clock offset value.

Table 24.

System Clock
Offset Value

SYNC_OUT/SYNC_IN
Propagation Delay

0 delay 1

1 delay 2

2 delay 3

3 delay 4

Automatic Synchronization Status Bits

If a slave device falls out of sync, the sync status bit is set high.
This bit can be read through the serial port bit (FR2 <5>). It is
automatically cleared when read.

The synchronization routine continues to operate regardless of
the state of the status bit. The status bit can be masked by
writing Logic 1 to the synchronization status mask bit
(FR2 <4>). If the status bit is masked, it is held low.

MANUAL SOFTWARE MODE SYNCHRONIZATION

The manual software mode is enabled by setting the manual
synchronization bit (FR1 <0>) to Logic 1 in a device. In this
mode, the I/O update that writes the Manual SW synchro-
nization bit to Logic 0 stalls the state machine of the clock
generator for one system clock cycle. Stalling the clock
generation state machine by one cycle changes the phase
relationship of SYNC_CLK between devices by one system
clock period (90°).

Note that the user may have to repeat this process until the
devices have their SYNC_CLK signals in phase. The SYNC_IN
input may be left floating since it has an internal pull-up. The
SYNC_OUT is not used.

The synchronization is complete when the master and slave(s)
devices have their SYNC_CLK signals in phase.

MANUAL HARDWARE MODE SYNCHRONIZATION

Manual hardware mode is enabled by setting the manual SW
synchronization bit (FR1 <1>) to Logic 1 in a device. In manual
HW synchronization mode, the SYNC_CLK stalls by one
system clock cycle each time a rising edge is detected on the
SYNC_IN input. Stalling SYNC_CLK's state machine by one
cycle changes the phase relationship of SYNC_CLK between
devices by one system clock period (90°).

Note that the user may have to repeat the process until the
devices have their SYNC_CLK signals in phase. The SYNC_IN
input might be left floating since it has an internal pull-up. The
SYNC_OUT is not used.

The synchronization is complete when the master and slave(s)
devices have their SYNC_CLK signals in phase.

AD9958

Rev. 0 | Page 28 of 40

I/O_UPDATE, SYNC_CLK, AND SYSTEM CLOCK
RELATIONSHIPS

The I/O UPDATE is essentially over sampled by the
SYNC_CLK. Therefore, I/O_UPDATE must have a
minimum pulse width greater than one SYNC_CLK period.

I/O_UPDATE and SYNC_CLK are used together to transfer
data from the serial I/O buffer to the active registers in the
device. Data in the buffer is inactive.

The timing diagram shown in Figure 39 depicts when data in
the buffer is transferred to the active registers.

SYNC_CLK is a rising edge active signal. It is derived from
the system clock and a divide-by-4 frequency divider. The
SYNC_CLK is externally provided, which can be used to
synchronize external hardware to the AD9958's internal clocks.

I/O_UPDATE initiates the start of a buffer transfer. It can be
sent synchronously or asynchronous relative to the SYNC_CLK.
If the set-up time between these signals is met, then constant
latency (pipeline) to the DAC output exists. For example, if
repetitive changes to phase offset via the SPI port are desired,
the latency of those changes to the DAC output is constant,
otherwise a time uncertainty of 1 SYNC_CLK period is present.

SYNC_CLK

SYSCLK

DATA 2

DATA 3

DATA 1

DATA IN

REGISTERS

DATA IN

I/O BUFFERS

DATA 1

DATA 2

DATA 3

I/O UPDATE

THE DEVICE REGISTERS AN I/O UPDATE AT POINT A. THE DATA IS TRANSFERRED FROM THE ASYNCHRONOUSLY LOADED I/O BUFFERS AT POINT B.

05252-039

Figure 39.

AD9958

Rev. 0 | Page 29 of 40

SERIAL I/O PORT

OVERVIEW

The AD9958 serial I/O port offers multiple configurations to
provide significant flexibility. The serial I/O port offers an SPI-
compatible mode of operation that is virtually identical to the
SPI operation found in earlier Analog Devices DDS products.
The flexibility is provided by four data (SDIO_0:3) pins that
allow four programmable modes of serial I/O operation.

Three of the four data pins (SDIO_1:3) can be used for other
functions than serial I/O port operation. These pins can also be
used to initiate a ramp-up or ramp-down (RU/RD) of the 10-bit
amplitude output scalar. In addition, one of these pins
(SDIO_3) can also be used to provide the SYNC_I/O function
that resynchronizes the serial I/O port controller if it is out of
proper sequence.

The maximum speed of the serial I/O port SCLK is 200 MHz,
but the four data (SDIO_0:3) pins can be used to further
increase data throughput. The maximum data throughput using
all SDIO_0:3 pins is 800 Mbps.

Note that both channels share Registers 0x03 to 0x18, which are
shown in the Register Map section. This address sharing
enables both DDS channels to be written to simultaneously. For
example, if a common frequency tuning word is desired for
both channels, it can be written once through the serial I/O port
to both channels. This is the default mode of operation (both
channels enabled). To enable each channel to be independent,
the two channel enable bits found in the channel select register
(CSR) must be used.

There are effectively two sets or copies of addresses (0x03 to
0x18) that channel enable bits can access to provide channel
independence. See the Control Register Descriptions section for
further discussion of programming channels that are common
or independent from each other.

Serial operation of the AD9958 occurs at the register level, not
the byte level. That is, the controller expects that all byte(s)
contained in the register address are accessed. The SYNC_I/O
function can be used to abort an I/O operation, thereby
allowing fewer than all bytes to be accessed. This feature can be
used to program only a part of the addressed register. Note that
only completed bytes are affected.

There are two phases to a serial communications cycle. Phase 1
is the instruction cycle, which writes the instruction byte into
the AD9958. Each bit of the instruction byte is registered on
each corresponding rising edge of SCLK. The instruction byte
defines whether the upcoming data transfer is either a write or
read operation and contains the serial address of the address
register.

Phase 2 of the I/O cycle consists of the actual data transfer
(write/read) between the serial port controller and the serial
port buffer. The number of bytes transferred during this phase
of the communication cycle is a function of the register being
accessed. The actual number of additional SCLK rising edges
required for the data transfer and instruction byte depends on
the number of byte(s) in the register and the serial I/O mode of
operation.

For example, when accessing Function Register 1, (FR1) which
is three bytes wide, Phase 2 of the I/O cycle requires that three
bytes be transferred. After transferring all data bytes per the
instruction byte, the communication cycle is completed for that
register.

At the completion of a communication cycle, the AD9958 serial
port controller expects the next set of rising SCLK edges to be
the instruction byte for the next communication cycle. All data
written to the AD9958 is registered on the rising edge of SCLK.
Data is read on the falling edge of SCLK. See Figure 36 and
Figure 37.

Each set of communication cycles does not require an
I/O_UPDATE to be issued. The I/O_UPDATE transfers data
from the I/O port buffer to active registers. The I/O_UPDATE
can be sent for each communication cycle or can be sent when
all serial operations are complete. However, data is not active
until an I/O_UPDATE is sent, with the exception of the channel
enable bits in the Channel Select Register (CSR). These bits do
not require an I/O_UPDATE to be enabled.

PRE

DSU

SCLK

SCLKPWL

SCLKPWH

DHLD

SCLK

SDIO

SYMBOL

DEFINITION

PRE

CS SETUP TIME

SCK

PERIOD OF SERIAL DATACLOCK

SCLKPWH

SERIAL DATA SETUP TIME

SCLKPWL

SERIAL DATA CLOCK PULSE WIDTH HIGH

DHLD

SERIAL DATA CLOCK PULSE WIDTH LOW

DSU

SERIAL DATA HOLD TIME

MIN

1.0ns

2.2ns

5.0ns

2.2ns
1.6ns
0ns

05252-040

Figure 40. Setup and Hold Timing for the Serial I/O Port

AD9958

Rev. 0 | Page 30 of 40

SCLK

SDIO

SDO (SDIO_2)

SYMBOL

DEFINITION

MIN

DATA VALID TIME

12ns

05252-041

Figure 41. Timing Diagram for Data Read for Serial I/O Port

INSTRUCTION BYTE DESCRIPTION

The instruction byte contains the following information.

Table 25.

MSB

LSB

R/Wb

x = don't care bit.

Bit 7 of the instruction byte (R/Wb) determines whether a read
or write data transfer occurs after the instruction byte write. A
logic high indicates a read operation. Logic 0 indicates a write
operation.

Bits 4 to 0 of the instruction byte determine which register is
accessed during the data transfer portion of the
communications cycle. The internal byte addresses are
generated by the AD9958.

SERIAL I/O PORT PIN DESCRIPTION

Serial Data Clock (SCLK). The serial clock pin is used to
synchronize data to and from the internal state machines of the
AD9958. The maximum SCLK toggle frequency is 200 MHz.

Chip Select (CS). The chip select pin allows more than one
AD9958 device to be on the same set of serial communications
lines. The chip select is an active low enable pin. Defined SDIO
inputs go to a high impedance state when CS is high. If CS is
driven high during any communications cycle, that cycle is
suspended until CS is reactivated low. The CS pin can be tied
low in systems that maintain control of SCLK.

Serial Data I/O (SDIO_0:3). Of the four SDIO pins, only the
SDIO_0 pin is a dedicated SDIO pin. SDIO_1:3 can also be used
to RU/RD the output amplitude. Bits <2:1> in the channel select
register (CSR Register 0x00) control the configuration of these
pins. See the Serial I/O Modes of Operation section for more
information.

SERIAL I/O PORT FUNCTION DESCRIPTION

Serial Data Out (SDO). The SDO function is available in single-
bit (3-wire) mode only. In SDO mode, data is read from the
SDIO_2 pin for protocols that use separate lines for trans-
mitting and receiving data (see Table 26 for pin configuration
options). Bits <2:1> in the CSR register (Register 0x00) control
the configuration of this pin. The SDO function is not available
in 2-bit or 4-bit serial I/O modes.

SYNC_I/O. The SYNC_I/O function is available in 1-bit and
2-bit modes. SDIO_3 serves as the SYNC_I/O pin when this
function is active. Bits <2:1> in the CSR register (Register 0x00)
control the configuration of this pin. Otherwise the SYNC_I/O
function is used to synchronize the I/O port state machines
without affecting the addressable register contents. An active
high input on the SYNC_I/O (SDIO_3) pin causes the current
communication cycle to abort. After SDIO_3 returns low
(Logic 0), another communication cycle can begin, starting
with the instruction byte write. The SYNC_I/O function is not
available in 4-bit serial I/O mode.

MSB/LSB TRANSFER DESCRIPTION

The AD9958 serial port can support both MSB-first or LSB-first
data formats. This functionality is controlled by CSR <0> in the
channel select register (CSR). MSB-first is the default mode.
When CSR <0> is set high, the serial port is in LSB-first format.
The instruction byte must be written in the format indicated by
CSR <0>. That is, if the AD9958 is in LSB-first mode, the
instruction byte must be written from LSB to MSB. If the
AD9958 is in MSB-first mode (default), the instruction byte
must be written from MSB to LSB.

Example Operation

To write the Function Register 1 (FR1) in MSB-first format,
apply an instruction byte of MSB > 00000001 < LSB, starting
with the MSB. From this instruction, the internal controller
recognizes a write transfer of three bytes starting with the MSB,
Bit <23>, in the FR1 address (Register 0x01). Bytes are written
on each consecutive rising SCLK edge until Bit<0> is
transferred. Once the last data bit is written, the I/O
communication cycle is complete and the next byte is
considered an instruction byte.

To write the Function Register 1 (FR1) in LSB-first format,
apply an instruction byte of MSB > 00000001 < LSB, starting
with the LSB. From this instruction, the internal controller
recognizes a write transfer of three bytes, starting with the
LSB <0> in the FR1 address (0x01). Bytes are written on each
consecutive rising SCLK edge until Bit <23> is transferred.
Once the last data bit is written, the I/O communication cycle is
complete and the next byte is considered an instruction byte.

AD9958

Rev. 0 | Page 31 of 40

SERIAL I/O MODES OF OPERATION

The following are the four programmable modes of the serial
I/O port operation:

Single bit serial 2-wire mode (default mode).

Single bit serial 3-wire mode.

2-bit serial mode.

4-bit serial mode (SYNC_I/O not available).

Table 6 displays the function of all six serial I/O interface pins,
depending on the mode of serial I/O operation programmed.

Table 26. Serial I/O Port Pin Function vs. Serial I/O Mode

Pin
Name

Single Bit
Serial 2-Wire
Mode

Single Bit
Serial 3-Wire
Mode

2-Bit
Serial
Mode

4-Bit
Serial
Mode

SCLK

Serial

Clock

CSB

Chip Select

Chip
Select

SDIO_0

Serial Data
I/O

Serial Data In

Serial
Data I/O

Serial
Data
I/O

SDIO_1

Not used for
SDIO

Serial
Data I/O

Serial
Data
I/O

SDIO_2

Not used for
SDIO

Serial Data
Out (SDO)

Not used
for SDIO

Serial
Data
I/O

SDIO_3

SYNC_I/O

Serial
Data
I/O

In serial mode, these pins can be used for RU/RD operation

The two bits CSR <2:1> in the channel select register set the
serial I/O mode of operation are defined as follows:

CSR <2:1> = 00. Single bit serial mode (2-wire mode).

CSR <2:1> = 01. Single bit serial mode (3-wire mode).

CSR <2:1> = 10. 2-bit serial mode.

CSR <2:1> = 11. 4-bit serial mode.

Single Bit Serial (2- and 3-Wire) Modes

The single bit serial mode interface allows read/write access to
all registers that configure the AD9958. MSB-first or LSB-first
transfer formats are supported. In addition, the single bit serial
mode interface port can be configured as either a single pin I/O,
which allows a two-wire interface or two unidirectional pins for
in/out, which enable a 3-wire interface. Single bit mode allows
the use of the SYNC_I/O function.

In single-bit serial mode, 2-wire interface operation, the
SDIO_0 pin is the single serial data I/O pin. In single-bit serial
mode 3-wire interface operation, the SDIO_0 pin is the serial
data input pin and the SDIO_2 pin is the output data pin.
Regardless of the number of wires used in the interface, the
SDIO_3 pin is configured as an input and operates as the
SYNC_I/O pin in the single-bit serial mode and 2-bit serial
mode. The SDIO_1 pin is unused in this mode. See Table 26.

2-Bit Serial Mode

The SPI port operation in 2-bit serial mode is identical to the
SPI port operation in single bit serial mode, except that two bits
of data are registered on each rising edge of SCLK. Therefore, it
only takes four clock cycles to transfer eight bits of information.
The SDIO_0 pin contains the even numbered data bits using
the notation D <7:0> and the SDIO_1 pin contains the odd
numbered data bits. This even and odd numbered pin/data
alignment is valid in both MSB- and LSB-first formats (see
Figure 39).

4-Bit Serial Mode

The SPI port in 4-bit serial mode is identical to the SPI port in
single bit serial mode, except that four bits of data are registered
on each rising edge of SCLK. Therefore, it only takes two clock
cycles to transfer eight bits of information. The SDIO_0 and
SDIO_2 pins contain even numbered data bits using the
notation D <7:0> and the SDIO_0 pin contains the LSB of the
nibble. The SDIO_1 and SDIO_3 pins contain the odd
numbered data bits and the SDIO_1 pin contains the LSB of the
nibble to be accessed.

Note that when programming the device for 4-bit serial mode,
it is important to keep the SDIO_3 pin at Logic 0 until the
device is programmed out of the single bit serial mode. Failure
to do so can result in the serial I/O port controller being out of
sequence.

Figure 42 through Figure 44 represent write timing diagrams
for each serial I/O modes available. Both MSB and LSB-first
modes are shown. LSB-first bits are shown in parenthesis. The
clock stall low/high feature shown is not required. It is used to
show that data (SDIO) must have the proper setup time relative
to the rising edge of SCLK.

AD9958

Rev. 0 | Page 32 of 40

SCLK

SDIO_0

INSTRUCTION CYCLE

DATA TRANSFER CYCLE

(I0)

(I1)

(I2)

(I3)

(I4)

(I5)

(I6)

(I7)

(D0)

(D1)

(D2)

(D3)

(D4)

(D5)

(D6)

(D7)

05252-042

Figure 42. Single-Bit Serial Mode Write Timing--Clock Stall Low

INSTRUCTION CYCLE

DATA TRANSFER CYCLE

SCLK

SDIO_1

SDIO_0

(D1)

(D3)

(D5)

(D7)

(D0)

(D2)

(D4)

(D6)

(I0)

(I2)

(I4)

(I6)

(I1)

(I3)

(I5)

(I7)

05252-043

Figure 43. 2-Bit Serial Mode Write Timing--Clock Stall Low

INSTRUCTION CYCLE

DATA TRANSFER CYCLE

SCLK

SDIO_1

SDIO_0

SDIO_2

SDIO_3

(I3)

(I5)

(I1)

(I7)

(I2)

(I4)

(I0)

(I6)

(D3)

(D5)

(D1)

(D7)

(D2)

(D4)

(D0)

(D6)

05252-044

Figure 44. 4-Bit Serial Mode Write Timing--Clock Stall Low

Figure 45 through Figure 48 represent read timing diagrams for each serial I/O modes available. Both MSB and LSB-first modes are
shown. LSB-first bits are shown in parenthesis. The clock stall low/high feature shown is not required. It is used to show that data (SDIO)
must have the proper set-up time relative to the rising edge of SCLK for the instruction byte and the read data that follows the falling edge
of SCLK.

AD9958

Rev. 0 | Page 33 of 40

INSTRUCTION CYCLE

DATA TRANSFER CYCLE

(I0)

SDIO_0

SCLK

(I1)

(I2)

(I3)

(I4)

(I5)

(I6)

(I7)

(D0)

(D1)

(D2)

(D3)

(D4)

(D5)

(D6)

(D7)

05252-045

Figure 45. Single-Bit Serial Mode (2-Wire) Read Timing--Clock Stall High

INSTRUCTION CYCLE

DATA TRANSFER CYCLE

SDIO_0

SCLK

DON'T CARE

SDO

(SDIO_2 PIN)

(I0)

(I1)

(I2)

(I3)

(I4)

(I5)

(I6)

(I7)

(D0)

(D1)

(D2)

(D3)

(D4)

(D5)

(D6)

(D7)

05252-046

Figure 46. Single-Bit Serial Mode (3-Wire) Read Timing--Clock Stall Low

INSTRUCTION CYCLE

DATA TRANSFER CYCLE

SCLK

SDIO_1

SDIO_0

(D1)

(D3)

(D5)

(D7)

(D0)

(D2)

(D4)

(D6)

(I0)

(I2)

(I4)

(I6)

(I1)

(I3)

(I5)

(I7)

05252-047

Figure 47. 2-Bit Serial Mode Read Timing--Clock Stall High

INSTRUCTION CYCLE

DATA TRANSFER CYCLE

(I3)

(I5)

(I1)

(I7)

(I2)

(I4)

(I0)

(I6)

SCLK

SDIO_0

SDIO_1

SDIO_2

SDIO_3

(D3)

(D5)

(D1)

(D7)

(D2)

(D4)

(D0)

(I6)

05252-048

Figure 48. 4-Bit Serial Mode Read Timing--Clock Stall High

AD9958

Rev. 0 | Page 34 of 40

CONTROL REGISTER MAP

Table 27.

Bit
Range

Bit 7 (MSB)

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0 (LSB)

Default
Value

Channel
Select
Register
(CSR)
(0x00)

<7:0>

Channel 1
enable

Channel 0
enable

Open Open Must

Serial I/0 mode select <2:1>

LSB first

0xF0

Function
Register 1
(FR1)
(0x01)

<7:0>

Reference clock
input power
down

External power
down mode

Sync clock
disable

DAC reference
power down

Open

Manual
hardware
synchronization

Manual
software
synchronization

0x00

<15:8>

Open

Profile pin configuration <14:12>

Ramp up/ramp

down <11:10>

Modulation Level <9:8>

0x00

<23:16>

VCO gain
control

PLL divider ratio <22:18>

Charge pump control <17:16>

0x00

Function
Register
Two (FR2)
(0x02)

<7:0>

Multi-device
synchronization
slave enable

Multi-device
synchronization
master enable

Multi-device
synchronization
status

Multi-device
synchronization
mask

Open <3:2>

System clock offset <1:0>

0x00

<15:8>

Both channels
auto clear
sweep
accumulator

Both channels
clear sweep
accumulator

Both channels
auto clear
phase
accumulator

Both channels
clear phase
accumulator

Open <11:10>

Open <9:8>

0x00

Channel enable bits do not require an I/O update to be activated. These bits are active immediately after the byte containing the bits is written. All other bits need an

I/O update to become active. The two channel enable bits shown in the register map are used to enable/disable any combination of the four channels. Both channels'
default are enabled.

In the CSR register, if the user wants different frequencies for both DDS channels, the following protocol suffices.

Enable (Logic 1) the CH0 bit, which is located in the channel select register and disable the CH1 enable bit (Logic 0).

Write the desired frequency tuning word for CH0, as described in Step 1.

Disable CH0 enable bit (Logic 0) and enable the CH1 bit in the channel select register.

Write the desired frequency tuning word for CH1.

AD9958

Rev. 0 | Page 35 of 40

CHANNEL REGISTER MAP

Table 28.

Bit
Range

Bit 7 (MSB)

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

(LSB)
Bit 0

Defaul
t Value

Channel
Function

(CFR)

(0x03)

<7:0>

Digital power-
down

DAC
power
down

Matched
pipe delays
active

Auto clear
sweep
accumulator

Clear sweep
accumulator

Auto clear
phase
accumulator

Clear phase
accumulator

Sine
wave
output
enable

0x02

<15:8>

Linear sweep
no-dwell

Linear
sweep
enable

Load SRR
at I/O
Update

Open

Must be 0

DAC full-scale current

control <9:8>

0x03

<23:16>

Amplitude freq. phase

select <23:22>

Open <21:16>

0x00

<7:0>

Frequency Tuning Word 0 <7:0>

0x00

<15:8>

Frequency Tuning Word 0 <15:8>

<23:16> Frequency

Tuning Word 0 <23:16>

Channel
Frequency Tuning
Word 0

(CTW0)

(0x04)

<31:24> Frequency

Tuning Word 0 <31:24>

<7:0>

Phase Offset Word 0

0x00

Channel Phase

Offset Word 0
(CPW0) (0x05)

<15:8> Open

<15:14>

Phase Offset Word 0 <13:8>

0x00

<7:0> Amplitude

scale

factor

0x00

<15:8>

Increment/decrement
step size <15:14>

Open

Amplitude
multiplier
enable

Ramp-up/
ramp-down
enable

Load ARR at I/O
update

Amplitude scale
factor <9:8>

0x00

Amplitude
Control (ACR)
(0x06)

<23:16> Amplitude

ramp rate <23:16>

<7:0>

Linear sweep rising ramp rate (RSRR) <7:0>

Linear Sweep
Ramp Rate

(LSR)

(0x07)

<15:8>

Linear sweep falling ramp rate (FSRR) <15:8>

LSR Rising Delta

(RDW) (0x08)

<7:0>

Rising delta word <7:0>

<15:8>

Rising delta word <15:8>

<23:16>

Rising delta word <23:16>

<31:24>

Rising delta word <31:24>

LSR Falling Delta

(FDW) (0x09)

<7:0>

Falling delta word <7:0>

<15:8>

Falling delta word <15:8>

<23:16>

Falling delta word <23:16>

<31:24>

Falling delta word <31:24>

There are two sets of channel registers and profile registers, one per channel. This is not shown in the channel or profile register maps because the addresses of all

channel registers and profile registers are the same for each channel. Therefore, the channel enable bits determine if the channel's channel registers and/or profile
registers are written to or not.

The clear accumulator bit is set to Logic 1 after a master reset. It self clears or is set to Logic 0 when an I/O update is asserted.

PROFILE REGISTER MAP

Table 29.

Register Name (address)

Bit Range

(MSB)
Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

(LSB)
Bit 0

Default
Value

Channel Word 1 (CTW1) (0x0A)

<31:0>

Freq. tuning word <31:0> or phase word <31:18> or amplitude word <31:22>

Channel Word 2 (CTW2) (0x0B)

<31:0>

Freq. tuning word <31:0> or phase word <31:18> or amplitude word <31:22>

Channel Word 3 (CTW3) (0x0C)

<31:0>

Freq. tuning word <31:0> or phase word <31:18> or amplitude word <31:22>

Channel Word 3 (CTW4) (0x0D)

<31:0>

Freq. tuning word <31:0> or phase word <31:18> or amplitude word <31:22>

Channel Word 5 (CTW5) (0x0E)

<31:0>

Freq. tuning word <31:0> or phase word <31:18> or amplitude word <31:22>

Channel Word 6 (CTW6) (0x0F)

<31:0>

Freq. tuning word <31:0> or phase word <31:18> or amplitude word <31:22>

Channel Word 7 (CTW7) (0x10)

<31:0>

Freq. tuning word <31:0> or phase word <31:18> or amplitude word <31:22>

Channel Word 8 (CTW8) (0x11)

<31:0>

Freq. tuning word <31:0> or phase word <31:18> or amplitude word <31:22>

Channel Word 9 (CTW9) (0x12)

<31:0>

Freq. tuning word <31:0> or phase word <31:18> or amplitude word <31:22>

Channel Word 10 (CTW10) (0x13)

<31:0>

Freq. tuning word <31:0> or phase word <31:18> or amplitude word <31:22>

Channel Word 11 (CTW11) (0x14)

<31:0>

Freq. Tuning Word <31:0> or phase word <31:18> or amplitude word <31:22>

Channel Word 12 (CTW12) (0x15)

<31:0>

Freq. Tuning Word <31:0> or phase word <31:18> or amplitude word <31:22>

Channel Word 13 (CTW13) (0x16)

<31:0>

Freq. tuning word <31:0> or phase word <31:18> or amplitude word <31:22>

Channel Word 14 (CTW14) (0917)

<31:0>

Freq. tuning word <31:0> or phase word <31:18> or amplitude word <31:22>

Channel Word 15 (CTW15) (0x18)

<31:0>

Freq. tuning word <31:0> or phase word <31:18> or amplitude word <31:22>

AD9958

Rev. 0 | Page 36 of 40

CONTROL REGISTER DESCRIPTIONS

CHANNEL SELECT REGISTER (CSR)

The CSR register determines if channels are enabled or disabled
by the status of the two channel enable bits. Both channels are
enabled by default. The CSR register also determines which
serial mode of operation is selected. In addition, the CSR
register offers a choice of MSB-first or LSB-first format. The
functionality of each bit is detailed as follows:

The CSR is comprised of one byte located in Register 0x00.

CSR <0> LSB-first.

CSR <0> = 0 (default), the serial interface accepts serial data in
MSB-first format. CSR <0> = 1, the serial interface accepts
serial data in LSB-first format.

CSR <2:1> Serial I/O mode select.

CSR <2:1> 00 = Single bit serial (2-wire mode).

01 = Single bit serial (3-wire mode).

10 = 2-bit serial mode.

11 = 4-bit serial mode.

See the Serial I/O Modes of Operation section for more details.

CSR <3> = must be set to 0.

CSR <7:6> channel enable bits.

CSR <7:4> bits are active immediately after being written. They
do not require an I/O update to take effect.

There are two sets of channel registers and profile registers, one
per channel. This is not shown in the channel or profile register
map. The addresses of both channel registers and profile
registers are the same for each channel. Therefore, the channel
enable bits distinguish each channel's channel registers and
profile registers values.

For example,

CSR <7:6> = 10, only Channel 1 receives commands from the
channel registers and profile registers.

CSR <7:6> = 01, only Channel 0 receives commands from the
channel registers and profile registers.

CSR <7:6> = 11, both Channel 0 and Channel 1 receive
commands from the channel registers and profile registers.

Function Register 1 (FR1) Description

FR1 is comprised of three bytes located in Register 0x01. The
FR1 is used to control the mode of operation of the chip. The
functionality of each bit is detailed as follows:

FR1 <0> manual software synchronization bit.

FR1 <0> = 0 (default), the software manual synchronization
feature of multiple devices is inactive. FR1 <0> = 1. The manual
software synchronization feature of multiple devices is active.
See the Synchronizing Multiple AD9958 Devices section for
details.

FR1 <1> manual hardware synchronization bit.

FR1<1> = 0 (default), the manual hardware synchronization
feature of multiple devices is inactive.FR1 <1> = 1, the manual
hardware synchronization feature of multiple devices is active.

FR1 <2:3>. See the Synchronizing Multiple AD9958 Devices
section for details.

FR1 <4> DACs reference power-down.

FR1 <4> = 0 (default). DACs reference is enabled. FR1 <4> = 1.
DAC reference is powered down.

FR1 <5> SYNC_CLK disable.

FR1 <5> = 0 (default), the SYNC_CLK pin is active.
FR1 <5> = 1. The SYNC_CLK pin assumes a static Logic 0
state (disabled). In this state, the pin drive logic is shut down.
However, the synchronization circuitry remains active
internally to maintain normal device operation.

FR1 <6> external power-down mode.

FR1 <6> = 0 (default). The external power-down mode is in the
fast recovery power-down mode. In this mode, when the
PWR_DWN_CTL input pin is high, the digital logic and the
DACs digital logic are powered down. The DACs bias circuitry,
PLL, oscillator, and clock input circuitry are not powered down.

FR1 <6> = 1. The external power down mode is in the full
power-down mode. In this mode, when the PWR_DWN_CTL
input pin is high, all functions are powered down. This includes
the DACs and PLL, which take a significant amount of time to
power up.

FR1 <7> clock input power-down.

FR1 <7> = 0 (default). The clock input circuitry is enabled for
operation. FR1 <7> = 1. The clock input circuitry is disabled
and is in a low power dissipation state.

FR1 <9:8> modulation level bits.

The modulation (FSK, PSK, and ASK) level bits control the level
(2/4/8/16) of modulation to be performed for a channel. See the
Modulation Mode section for more details.

FR1<10:11> RU/RD bit.

AD9958

Rev. 0 | Page 37 of 40

The RU/RD bits control the amplitude RU/RD time of a
channel (see the Output Amplitude Control Mode section).

FR1 <12:14> profile pin configuration bits.

The profile pin configuration bits control the configuration of
the data and SDIO pins for the different modulation modes. See
the Modulation Mode section for details.

FR1 <15> open.

FR1 <17:16> charge pump current control.

FR1 <17:16> = 00 (default), the charge pump current is 75 µA.

= 01 charge pump current is 100 µA.

= 10 charge pump current is 125 µA.

= 11 charge pump current is 150 µA.

FR1 <22:18> PLL divider values.

FR1 <22:18>, if the value is > 3 and < 21, the PLL is enabled and
the value sets the multiplication factor. If the value is < 4 or >20
the PLL is disabled.

FR1 <23> PLL VCO gain.

FR1 <23> = 0 (default), the low range (system clock below
160 MHz). FR1 <23> = 1, the high range (system clock above
255 MHz).

Function Register 2 (FR2) Description

The FR2 is comprised of two bytes located in Address 0x02.

The FR2 is used to control the various functions, features, and
modes of the AD9958. The functionality of each bit is detailed
as follows:

FR2<1:0> system clock offset.

See the Synchronizing Multiple AD9958 Devices section for
more details.

FR2 <3:2> open.

FR2 <4> multi-device synchronization mask bit.

FR2 <5> multi-device synchronization status bit.

FR2 <6> multi-device synchronization master enable bit.

FR2<7> multi-device synchronization slave enable bit.

FR2 <4:7>. see the Synchronizing Multiple AD9958 Devices
section for more details.

FR2 <11:8> open.

FR2 <12> both channels clear phase accumulator.

FR2 <12> = 0 (default), the phase accumulator functions as
normal. FR2 <12> = 1, the phase accumulator memory
elements for both channels are asynchronously cleared.

FR2 <13> both channels auto clear phase accumulator.

FR2 <13> = 0 (default). A new frequency tuning word is applied
to the inputs of the phase accumulator, but not loaded into the
accumulator.

FR2 <13> = 1. This bit automatically synchronously clears
(loads zeros into) the phase accumulator for one cycle upon
reception of the I/O update sequence indicator on both
channels.

FR2 <14> both channels clear sweep accumulator.

FR2 <14> = 0 (default), the sweep accumulator functions as
normal.FR2 <14> = 1, the sweep accumulator memory
elements for both channels are asynchronously cleared.

FR2 <15> both channels auto clear sweep accumulator.

FR2 <15> = 0 (default). A new delta word is applied to the
input, as in normal operation, but not loaded into the accumu-
lator. FR2 <15> = 1. This bit automatically synchronously clears
(loads 0s) the sweep accumulator for one cycle upon reception
of the I/O_UPDATE sequence indicator on both channels.

CHANNEL FUNCTION REGISTER (CFR)
DESCRIPTION

CFR <0> enable sine output.

CFR <0> = 0 (default). The angle-to-amplitude conversion logic
employs a cosine function. CFR <0> = 1. The angle-to-
amplitude conversion logic employs a sine function.

CFR <1> clear phase accumulator.

CFR <1> = 0 (default). The phase accumulator functions as
normal. CFR <1> = 1. The phase accumulator memory
elements are asynchronously cleared.

CFR <2> clear phase accumulator.

CFR <2> = 0 (default). A new frequency tuning word is applied
to the inputs of the phase accumulator, but not loaded into the
accumulator. CFR <2> = 1. This bit automatically synchro-
nously clears (loads 0s) the phase accumulator for one cycle
upon reception of the I/O_UPDATE sequence indicator.

CFR <3> clear frequency accumulator.

CFR <3> = 0 (default). The sweep accumulator functions as
normal .CFR <3> = 1. The sweep accumulator memory
elements are asynchronously cleared.

CFR <4> auto clear sweep accumulator.

AD9958

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CFR <4> = 0 (default). A new delta word is applied to the input,
as in normal operation, but not loaded into the accumulator.
CFR <4> = 1. This bit automatically synchronously clears (loads
0s) the sweep accumulator for one cycle upon reception of the
I/O_UPDATE sequence indicator.

CFR <5> match pipe delays active.

CFR <5> = 0 (default), match pipe delay mode is inactive.
CFR <5> = 1, match pipe delay mode is active. See the Single-
Tone Mode--Matched Pipeline Delay section for details.

CFR <6> DAC power-down.

CFR <6> = 0 (default). The DAC is enabled for operation.
CFR <6> = 1. The DAC is disabled and is in its lowest power
dissipation state.

CFR <7>. digital power-down.

CFR <7> = 0 (default). The digital core is enabled for operation.

CFR <7> = 1. The digital core is disabled and is in its lowest
power dissipation state.

CFR <8:9>. DAC LSB control.

CFR <8:9> = 00 (default). The DAC is at the largest LSB value.

CFR <10> must be set to 0.

CFR <13>.linear sweep ramp rate load at I/O_UPDATE.

CFR <13> = 0 (default). The linear sweep ramp rate timer is
loaded only upon timeout (timer =1) and is not loaded because
of an I/O_UPDATE input signal.

CFR <13> = 1. The linear sweep ramp rate timer is loaded upon
timeout (timer =1) or at the time of an I/O_UPDATE input
signal.

CFR <14> linear sweep enable.

CFR <14> = 0 (default). The linear sweep capability of the
AD9958 is inactive. CFR <14> = 1. The linear sweep capability
of the AD9958 is enabled. When enabled, the delta frequency
tuning word is applied to the frequency accumulator at the
programmed ramp rate.

CFR <15> linear sweep no-dwell.

CFR <15> = 0 (default). The linear sweep no-dwell function is
inactive. CFR <15> = 1. The linear sweep no-dwell function is
active. If CFR <15> is active, the linear sweep no-dwell function
is activated. See the Linear Sweep (Shaped) Modulation Mode
section for details. If CFR <14> is clear, this bit is don't care.

CFR <18:16> open.

CFR <23:22> amplitude frequency phase select controls what
type of modulation is to be performed for that channel. See the
Modulation Mode section for details.

Channel Frequency Tuning Word (CFTWO) Description

CFTW0 <32:0> Frequency Tuning Word 0 for each channel.

Channel Phase Offset Word (CPOW) Description

CPO0 <13:0> Phase Offset Word 0 for each channel.

CPO0 <15:14> open.

Amplitude Control Register (ACR) Description

ACR <9:0> amplitude scale factor for each channel.

ACR <10> amplitude ramp rate load control bit.

ACR <10> = 0 (default). The amplitude ramp rate timer is
loaded only upon timeout (timer = 1) and is not loaded due to a
I/O_UPDATE input signal (or change in the profile bits).

ACR <10> = 1. The amplitude ramp rate timer is loaded upon
timeout (timer =1) or at the time of an I/O_UPDATE input
signal (or change in PS bits).

ACR <11> auto RU/RD enable (only valid when ACR <12> is
active high).

ACR <11> = 0 (default). When ACR <12> is active, Logic 0 on
ACR <11> enables the manual RU/RD operation. ACR <11> = 1.
If ACR <12> is active, a Logic 1 on ACR <11> enables the
AUTO RU/RD operation. See the Output Amplitude Control
Mode section of this document for details.

ACR <12> amplitude multiplier enable.

ACR <12> = 0 (default). Amplitude multiplier is disabled. The
clocks to this scaling function (auto RU/RD) are stopped for
power saving and the data from the DDS core is routed around
the multipliers.

ACR <12> = 1, amplitude multiplier is enabled.

ACR <13> open.

ACR <15:14> amplitude increment/decrement step size.

ACR <23:16> amplitude ramp rate value.

Channel Linear Sweep Register (LSR) Description

LSR <15:0> linear sweep rising ramp rate.

Channel Linear Sweep Rising Delta Word Register (RDW)
Description

RDW <31:0> 32-bit rising delta tuning word.

Channel Linear Sweep Falling Delta Word Register
(FDW) Description

FDW <31:0> 32-bit falling delta tuning word.

РР»РµРєС‚СЂРѕРЅРЅС‹Р№ РєРѕРјРїРѕРЅРµРЅС‚: AD9958

Document Outline

Р­Р»РµРєС‚СЂРѕРЅРЅС‹Р№ РєРѕРјРїРѕРЅРµРЅС‚: AD9958

Document Outline

РР»РµРєС‚СЂРѕРЅРЅС‹Р№ РєРѕРјРїРѕРЅРµРЅС‚: AD9958