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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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.

AD9801

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700

World Wide Web Site: http://www.analog.com

Fax: 617/326-8703

© Analog Devices, Inc., 1997

CCD Signal Processor

For Electronic Cameras

FUNCTIONAL BLOCK DIAGRAM

SHP

AD9801

PGA

PGACONT1 PGACONT2

CLAMP

CLPDM

CDS

PBLK

PIN

DIN

SHD ADCCLK

TIMING

GENERATOR

CMLEVEL VRT VRB STBY

REFERENCE

S/H

CLPOB

CLAMP

A/D

DOUT

ACVDD

ADVDD

DVDD

DRVDD

FEATURES
10-Bit, 18 MSPS A/D Converter
18 MSPS Full-Speed CDS
Low Noise, Wideband PGA
Internal Voltage Reference
No Missing Codes Guaranteed
+3 V Single Supply Operation
Low Power CMOS: 185 mW
48-Pin TQFP Package

PRODUCT DESCRIPTION

The AD9801 is a complete CCD signal processor developed for
electronic cameras. It is well suited for both video conferencing
and consumer level still camera applications.

The signal processing chain is comprised of a high speed CDS,
variable gain PGA and 10-bit ADC. Required clamping
circuitry and an onboard voltage reference are also provided.
The AD9801 operates from a single +3 V supply with a typical
power consumption of 185 mW.

The AD9801 is packaged in a space saving 48-pin thin-quad
flatpack (TQFP) and is specified over an operating temperature
range of 0

C to +70

PRODUCT HIGHLIGHTS

1. On-Chip Input Clamp and CDS

Clamp circuitry and high speed correlated double sampler
allow for simple ac coupling to interface a CCD sensor at full
18 MSPS conversion rate.

2. On-Chip PGA

The AD9801 includes a low noise, wideband amplifier with
analog variable gain from 0 dB to 31.5 dB (linear in dB).

3. 10-Bit, High Speed A/D Converter

A linear 10-bit ADC is capable of digitizing CCD signals at
the full 18 MSPS conversion rate. (Typical DNL is

0.5 LSB

and no missing code performance is guaranteed.)

4. Low Power

At 185 mW, the AD9801 consumes a fraction of the power of
presently available multichip solutions. The part's power-
down mode (15 mW) further enhances its desirability in low
power, battery operated applications.

5. Digital I/O Functionality

The AD9801 offers three-state digital output control.

6. Small Package

Packaged in a 48-pin, surface-mount thin-quad flatpack, the
AD9801 is well suited to very tight, low headroom designs.

REV. 0

AD9801SPECIFICATIONS

MIN

to T

MAX

with ACVDD = 3.15 V, ADVDD = 3.15 V, DVDD = 3.15 V, DRVDD = 3.15 V unless

otherwise noted)

Parameter

Min

Typ

Max

Units

TEMPERATURE RANGE

Operating

Storage

150

POWER SUPPLY VOLTAGE

(For Functional Operation)

ACVDD

3.00

3.15

3.50

ADVDD

3.00

3.15

3.50

DVDD

3.00

3.15

3.50

DRVDD

3.00

3.15

3.50

POWER SUPPLY CURRENT

ACVDD

39.5

ADVDD

14.6

DVDD

4.7

DRVDD

0.07

POWER CONSUMPTION

Normal Operation

185

Power-Down Mode

MAXIMUM SHP, SHD, ADCCLK RATE

MHz

ADC

Resolution

Bits

Differential Nonlinearity

0.5

LSB

No Missing Codes

GUARANTEED

ADCCLK Rate

MHz

Reference Top Voltage

1.75

Reference Bottom Voltage

1.25

Input Range

1.0

V p-p

CDS

Maximum Input Signal

500

mV p-p

Pixel Rate

MHz

PGA

Maximum Gain

31.5

High Gain

Medium Gain

0.5

3.5

6.5

Minimum Gain

CLAMP

Average Black Level (During CLPOB. Only
Stable Over PGA Range 0.3 V to 2.7 V)

LSB

PGA test conditions: max gain PGACONT1 = 2.7 V, PGACONT2 = 1.5 V; high gain PGACONT1 = 2.0 V, PGACONT2 = 1.5 V; medium gain

PGACONT1 =

0.5 V, PGACONT2 = 1.5 V; minimum gain PGACONT1 = 0.3 V, PGACONT2 = 1.5 V.

Specifications subject to change without notice.

DIGITAL SPECIFICATIONS

Parameter

Symbol

Min

Typ

Max

Units

LOGIC INPUTS

High Level Input Voltage

2.4

Low Level Input Voltage

0.6

High Level Input Current

Low Level Input Current

Input Capacitance

LOGIC OUTPUTS

High Level Output Voltage

2.4

Low Level Output Voltage

0.6

Specifications subject to change without notice.

MIN

to T

MAX

with ACVDD = 3.15 V, ADVDD = 3.15 V, DVDD = 3.15 V, DRVDD = 3.15 V unless otherwise noted)

AD9801

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TIMING SPECIFICATIONS

Parameter

Min

Typ

Max

Units

ADCCLK CLOCK PERIOD

55.6

ADCCLK High Level Period

24.8

27.8

ADCCLK Low Level Period

24.8

27.8

SHP, SHD Clock Period

55.6

Digital Output Delay

Digital Output Data Control

Mode1

Mode2

Digital Output Data (D9D0)

Normal Operation

1 0 1 0 1 0 1 0 1 0

0 1 0 1 0 1 0 1 0 1

High Impedance

MIN

to T

MAX

with ACVDD = 3.15 V, ADVDD = 3.15 V, DVDD = 3.15 V, DRVDD = 3.15 V unless otherwise noted)

ABSOLUTE MAXIMUM RATINGS*

Parameter

With Respect To

Min

Max

Units

ADVDD

ADVSS, SUBST

0.3

6.5

ACVDD

ACVSS, SUBST

0.3

6.5

DVDD

DVSS, DSUBST

0.3

6.5

DRVDD

DRVSS, DSUBST

0.3

6.5

SHP, SHD

DSUBST

0.3

DVDD + 2.0

ADCCLK, CLOB, CLPDM

DSUBST

0.3

DVDD + 0.3

PGACONT1, PGACONT2

SUBST

0.3

ACVDD + 0.3

PIN, DIN

SUBST

0.3

ACVDD + 0.3

DOUT

DSUBST

0.3

DRVDD + 0.3

VRT, VRB

SUBST

0.3

ADVDD + 0.3

CLAMP_BIAS

SUBST

0.3

ACVDD + 0.3

CCDBYP1, CCDBYP2

SUBST

0.3

ACVDD + 0.3

STBY

DSUBST

0.3

DVDD + 0.3

MODE1, MODE2

SUBST

0.3

ADVDD + 0.3

DRVSS, DVSS, ACVSS, ADVSS

SUBST, DSUBST

0.3

+0.3

Junction Temperature

+150

Storage Temperature

+150

Lead Temperature (10 sec)

+300

* 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 other conditions above those indicated in the operational sections of this
specification is not implied. Exposure to absolute maximum ratings for extended periods may affect device reliability.

WARNING!

ESD SENSITIVE DEVICE

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 the AD9801 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.

ORDERING GUIDE

Model

Temperature

Package Description

Package Option*

AD9801

C to +70

48-Pin TQFP

ST-48

*ST = Thin Quad Flatpack Package.

AD9801

REV. 0

Pin No.

Pin Name

Type

Description

ADVSS

Analog Ground

211

D0D9

Digital Data Outputs

DRVDD

+3 V Digital Driver Supply

DRVSS

Digital Driver Ground

DSUBST

Digital Substrate

DVSS

Digital Ground

ADCCLK

ADC Sample Clock Input

DVDD

+3 V Digital Supply

STBY

Power down (Active HIGH)

PBLK

Pixel Blanking (Active LOW)

CLPOB

Black Level Restore Clamp (Active LOW)

SHP

Reference Sample Clock Input

SHD

Data Sample Clock Input

CLPDM

Input Clamp (Active Low)

DVSS

Digital Ground

CCDBYP2

CCD Bypass (Decouple to Analog Ground Through 0.1

DIN

CDS Input (Tie to Pin 27 and AC-Couple to CCD Output Through 0.1

CDS Input (See Above)

CCDBYP1

CCD Bypass (Decouple to Analog Ground Through 0.1

PGACONT1

Coarse PGA Gain Control (0.3 V2.7 V Decoupled to Analog Ground Through 0.1

PGACONT2

Fine PGA Gain Control (0.3 V2.7 V Decoupled to Analog Ground Through 0.1

ACVSS

Analog Ground

CLAMP_BIAS

Clamp Bias Level (Decouple to Analog Ground Through 0.1

ACVDD

+3 V Analog Supply

ACVDD

+3 V Analog Supply

ACVDD

+3 V Analog Supply

INT_BIAS1

Internal Bias Level (Decouple to Analog Ground Through 0.1

CMLEVEL

Common-Mode Level (Decouple to Analog Ground Through 0.1

INT_BIAS2

Internal Bias Level (Decouple to Analog Ground Through 0.1

MODE2

ADC Test Mode Control (See Digital Output Data Control)

MODE1

ADC Test Mode Control (See Digital Output Data Control)

ADVSS

Analog Ground

ADVDD

+3 V Analog Supply

ADVDD

+3 V Analog Supply

ADVSS

Analog Ground

ADVSS

Analog Ground

SUBST

Substrate (Connect to Analog Ground)

VRB

Bottom Reference Bypass (Decouple to Analog Ground Through 0.1

VRT

Top Reference Bypass (Decouple to Analog Ground Through 0.1

PIN CONFIGURATION

10 11 12

36 35 34 33 32

27 26 25

31 30 29 28

PIN 1
IDENTIFIER

TOP VIEW

(Not to Scale)

AD9801

VRT

VRB

SUBST

ADVSS

ADVDD

ADVSS

MODE1

MODE2

INT_BIAS2

CMLEVEL

DRVSS

DSUBST

DVSS

ADCCLK

INT_BIAS1

DVDD

STBY

PBLK

CLPOB

SHP

SHD

CLPDM

DVSS

ACVDD

CLAMP_BIAS

ACVSS

PGACONT2

PGACONT1

CCDBYP1

PIN

DIN

CCDBYP2

ADVSS

(LSB) D0

(MSB) D9

DRVDD

AD9801

REV. 0

THEORY OF OPERATION
Introduction

The AD9801 is a 10-bit analog-to-digital interface for CCD
cameras. The block level diagram of the system is shown in
Figure 13. The device includes a correlated double sampler
(CDS), 0 dB31 dB variable gain amplifier (PGA), black level
correction loop, input clamp and voltage reference. The only
external analog circuitry required at the system level is an emitter
follower buffer between the CCD output and AD9801 inputs.

CLAMP

CDS

BLACK

LEVEL

PGA

10b

ADC

REF

OUT

GAIN

Figure 13.

Correlated Double Sampling (CDS)

CDS is important in high performance CCD systems as a
method for removing several types of noise. Basically, two
samples of the CCD output are taken: one with the signal
present ("data") and one without ("reference"). Subtracting
these two samples removes any noise that is common--or
correlated--to both.

Figure 14 shows the block diagram of the AD9801's CDS. The
S/H blocks are directly driven by the input and the sampling
function is performed passively, without the use of amplifiers.

10pF

S/H

OUT

FROM

CCD

Figure 14.

This implementation relies on the off-chip emitter follower
buffer to drive the two 10 pF sampling capacitors. Only one
capacitor at a time is seen at the input pin.

The AD9801 actually uses two CDS circuits in a "ping pong"
fashion to allow the system more acquisition time. In this way,
the output from one of the two CDS blocks will be valid for an
entire clock cycle. Thus, the bandwidth requirement of the
subsequent gain stage is reduced as compared to that for a single
CDS channel system. This lower bandwidth translates to lower
power and noise.

Programmable Gain Amplifier (PGA)

The on-chip PGA provides a (linear in dB) gain range of
0 dB31.5 dB. A typical gain characteristic plot is shown in
Figure 15. Only the range from 0.3 V to 2.7 V is intended for
actual use.

GAIN dB

PGACONT1 Volts

15

0.5

1.5

2.5

10

Figure 15.

As shown in Figure 16, PGA control is provided through the
PGACONT1 and PGACONT2 inputs. PGACONT1 provides
coarse and PGACONT2 fine (1/16) gain control.

PGACONT1

PGACONT2

PGACONT1 = COURSE CONTROL
PGACONT2 = FINE CONTROL (1/16)

Figure 16.

Black Level Clamping

For correct processing, the CCD signal must be referenced to a
well established "black level" by the AD9801. At the edge of the
CCD, there is a collection of pixels that are covered with metal
to prevent any light penetration. As the CCD is read out, these
"black pixels" provide a calibration signal that is used to
establish the black level.

The feedback loop shown in Figure 17 is closed around the
PGA during the calibration interval (CLPOB = LOW) to set the
black level. As the black pixels are being processed, an integrator
block measures the difference between the input level and the
desired reference level. This difference, or error, signal is
amplified and passed to the CDS block where it is added to the
incoming pixel data. As a result of this process, the black pixels
are digitized at one end of the ADC range, taking maximum
advantage of the available linear range of the system.

PGA

ADC

CLPOB

NEG REF

INTEGRATOR

CDS

Figure 17.

AD9801

REV. 0

The actual implementation of this loop is slightly more compli-
cated as shown in Figure 18. Because there are two separate
CDS blocks, two black level feedback loops are required and
two offset voltages are developed. Figure 18 also shows an
additional PGA block in the feedback loop labeled "RPGA."

PGA

ADC

CLPOB

NEG REF

CONTROL

CDS1

RPGA2

INT2

CDS1

RPGA1

INT1

Figure 18.

The RPGA uses the same control inputs as the PGA, but has
the inverse gain. The RPGA functions to attenuate by the same
factor as the PGA amplifies, keeping the gain and bandwidth of
the loop constant.

Input Bias Level Clamping

The buffered CCD output is connected to the AD9801 through
an external coupling capacitor. The dc bias point for this coupling
capacitor is established during the clamping (CLPDM = LOW)
period using the "dummy clamp" loop shown in Figure 19.
When closed around the CDS, this loop establishes the desired
DC bias point on the coupling capacitor.

BLACK

LEVEL CLP

CCD

INPUT

CLAMP

CDS

CLPDM

TO ADC

PGA

Figure 19.

Input Blanking

In some applications, the AD9801's input may be exposed to
large signals from the CCD. These signals can be very large,
relative to the AD9801's input range, and could thus saturate
on-chip circuit blocks. Recovery time from such saturation
conditions could be substantial.

To avoid problems associated with processing these transients,
the AD9801 includes an input blanking function. When active
(PBLK = LOW), this function stops the CDS operation and
allows the user to disconnect the CDS inputs from the CCD
buffer.

If the input voltage exceeds the supply rail by more than
0.3 V, protection diodes will be turned on, increasing current
flow into the AD9801 (see Equivalent Input Circuits). Such
voltage levels should be externally clamped to prevent device
damage or reliability degradation.

10-Bit Analog-to-Digital Converter (ADC)

The ADC employs a multibit pipelined architecture, which is
well-suited for high throughput rates while being both area and
power efficient. The multistep pipeline presents a low input
capacitance resulting in lower on-chip drive requirements. A
fully differential implementation was used to overcome head-
room constraints of the single +3 V power supply.

Differential Reference

The AD9801 includes a 0.5 V reference based on a differential,
continuous-time bandgap cell. Use of an external bypass
capacitor reduces the reference drive requirements, thus
lowering the power dissipation. The differential architecture was
chosen for its ability to reject supply and substrate noise.
Recommended decoupling shown in Figure 20.

VRT

REF

VRB

1µF

0.1µF

Figure 20.

Internal Timing

The AD9801's on-chip timing circuitry generates all clocks
necessary for operation of the CDS and ADC blocks. The user
needs only to synchronize the SHP and SHD clocks with the
CCD waveform, as all other timing is handled internally. The
ADCCLK signal is used to strobe the output data, and can be
adjusted to accommodate desired timing.

AD9801

REV. 0

APPLICATION INFORMATION
Generating Clock Signals

For best performance, the AD9801 should be driven by 3 V
logic levels. As shown in the Equivalent Input Circuits, the use
of 5 V logic for ADCCLK will turn on the protection diode to
DVDD, increasing the current flow into this pin. As a result,
noise and power dissipation will increase. The CDS clock inputs,
SHP and SHD, have additional protection and can withstand
direct 5 V levels.

External clamping diodes or resistor dividers can be used to
translate 5 V levels to 3 V levels, but the lowest power dissipa-
tion is achieved with a logic transceiver chip. National Semi-
conductor's 74LVX4245 provides a 5 V to 3 V level shift for up
to eight clock signals, and features a three-state option and low
power consumption. Philips Semiconductor and Quality also
manufacture similar devices.

Digitally Programmable Gain Control

The AD9801's PGA is controlled by an analog input voltage of
0.3 V to 2.7 V. In some applications, digital gain control is
preferable. Figure 21 shows a circuit using Analog Devices'
AD8402 Digital Potentiometer to generate the PGA control
voltage. The AD8402 functions as two individual potentiom-
eters, with a serial digital interface to program the position of
each wiper over 256 positions. The device will operate with 3 V
or 5 V supplies, and features a power-down mode and a reset
function.

To keep external components to a minimum, the ends of the
"potentiometers" can be tied to ground and +3 V. One pot is
used for the coarse gain adjust, PGACONT1, with steps of
about 0.2 dB/LSB. The other pot is used for fine gain control,
PGACONT2, and is capable of around 0.01 dB steps if all
eight bits are used. The two outputs should be filtered with 1

or larger capacitors to minimize noise into the PGACONT pins
of the AD9801.

The disadvantage of this circuit is that the control voltage
will be supply dependent. If additional precision is required,
an external op amp can be used to amplify the VREFT (1.75 V)
or VREFB (1.25 V) pins on the AD9801 to the desired voltage
level. These reference voltages are stable over the operating
supply range of the AD9801. Low power, low cost, rail-to-rail
output amplifiers such as the AD820, OP150 and OP196 are
specified for 3 V operation. Alternatively, a precision voltage

AD8402-10

+3V

SDI CLK

SHDN

1µF

PGACONT2

1µF

0.1µF

+3V

PGACONT1

Figure 21. Digital Control of PGA

reference may be used. The REF193 from Analog Devices
features low power, low dropout performance, maintaining a
3 V output with a minimum 3.1 V supply when lightly loaded.

Power and Grounding Recommendations

The AD9801 should be treated as an analog component when
used in a system. The same power supply and ground plane
should be used for all of the pins. In a two-ground system, this
requires that the digital supply pins be decoupled to the analog
ground plane and the digital ground pins be connected to
analog ground for best noise performance. If any pins on the
AD9801 are connected to the system digital ground, noise can
capacitively couple inside the AD9801 (through package and die
parasitics) from the digital circuitry to the analog circuitry.
Separate digital supplies can be used, particularly if slightly
different driver supplies are needed, but the digital power pins
should still be decoupled to the same point as the digital ground
pins (analog ground plane). If the AD9801 digital outputs need
to drive a bus or substantial load, a buffer should be used at the
AD9801's outputs, with the buffer referenced to system digital
ground. In some cases, when system digital noise is not
substantial, it is acceptable to split the ground pins on the
AD9801 to separate analog and digital ground planes. If this is
done, be sure to connect the ground pins together at the
AD9801.

To further improve performance, isolating the driver supply
DRVDD from DVDD with a ferrite bead can help reduce
kickback effects during major code transitions. Alternatively,
the use of damping resistors on the digital outputs will reduce
the output risetimes, reducing the kickback effect.

AD9801

REV. 0

AVSS

AD707

C50
0.1µF

C55
0.01µF

C56
0.1µF

C49
0.01µF

R14
68

C37
0.1µF

AVCC

10k

TP25

C70
10µF
16V

PGACONT1

AVCC

36 35 34 33 32

27 26 25

31 30 29 28

10 11 12

AD9801

ADVSS

DRVDD

D0 (LSB)

D9 (MSB)

DRVSS

DVSS

CLPDM

SHD

SHP

CLPOB

PBLK

STBY

DVDD

ADCCLK

DVSS

DSUBST

VRT

VRB

SUBST

ADVSS

ADVDD

ADVSS

CLAMP_BIAS

MODE1

MODE2

INT_BIAS2

CMLEVEL

ADVSS

ACVDD

ACVSS

PGACONT2

PGACONT1

CCDBYP1

PIN

DIN

CCDBYP2

C14

0.1µF

C28

0.01µF

VDD

0.1µF

C1
1µF

0.1µF

C4
0.1µF

VDD

C8
0.1µF

C23

0.1µF

PIN

C10
2µF

C9
2µF

C12

0.1µF

C61

0.1µF

PGACONT1

PGACONT2

VDD

TP5

PBLK

CLPOB

STBY

SHP

SHD

CLPDM

ADCCLK

C13
0.1µF

C29
0.01µF

VDD

DIN

0.1µF

VDD

JP3

JP2

JP1

JP4

FB4

C11
0.1µF

C46
0.1µF

C47
22µF

FB1

TP28

C66
0.1µF

VDD

+3V

JP1

C45
0.1µF

C44
22µF

FB2

TP27

C67
0.1µF

+5V

JP2

AVCC

INT_BIAS1

C40
0.1µF

C41
22µF

FB3

TP26

C68
0.1µF

AVSS

5V

JP3

TP29

GND

JP5

AVCC

AVSS

AD707

C51
0.1µF

C57
0.01µF

C52
0.1µF

C54
0.01µF

R15
68

C36
0.1µF

AVCC

10k

TP24

C71
10µF
16V

PGACONT2

2
4
6
8

10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40

1
3
5
7
9

11
13
15
17
19
21
23
25
27
29

31
33
35
37
39

40 PIN HEADER

D9 (MSB)
D8
D7
D6
D5
D4
D3
D2
D1
D0 (LSB)

ADCCLK

Figure 22. AD9801EB Schematic

EVALUATION BOARD

Figure 22 shows the schematic for the AD9801 evaluation
board. Notice the use of a common ground and supply for the
AD9801, and the extensive supply and reference decoupling.

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ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: AD9801