Philips
Semiconductors
SA572
Programmable analog compandor
Product specification
1998 Nov 03
INTEGRATED CIRCUITS
IC17 Data Handbook
Philips Semiconductors
Product specification
SA572
Programmable analog compandor
2
1998 Nov 03
853-0813 20294
DESCRIPTION
The SA572 is a dual-channel, high-performance gain control circuit
in which either channel may be used for dynamic range
compression or expansion. Each channel has a full-wave rectifier to
detect the average value of input signal, a linearized,
temperature-compensated variable gain cell (
G) and a dynamic
time constant buffer. The buffer permits independent control of
dynamic attack and recovery time with minimum external
components and improved low frequency gain control ripple
distortion over previous compandors.
The SA572 is intended for noise reduction in high-performance
audio systems. It can also be used in a wide range of
communication systems and video recording applications.
FEATURES
Independent control of attack and recovery time
Improved low frequency gain control ripple
Complementary gain compression and expansion with
external op amp
Wide dynamic range--greater than 110dB
Temperature-compensated gain control
Low distortion gain cell
Low noise--6
V typical
Wide supply voltage range--6V-22V
System level adjustable with external components
PIN CONFIGURATION
1
2
3
4
5
6
7
8
9
10
11
12
13
14
16
15
D
1
, N, Packages
TRACK TRIM A
RECOV. CAP A
RECT. IN A
ATTACK CAP A
THD TRIM A
GND
G OUT A
G IN A
TRACK TRIM B
RECOV. CAP B
RECT. IN B
ATTACK CAP B
THD TRIM B
G OUT B
G IN B
VCC
NOTE:
1. D package released in large SO (SOL) package only.
SR00694
Figure 1. Pin Configuration
APPLICATIONS
Dynamic noise reduction system
Voltage control amplifier
Stereo expandor
Automatic level control
High-level limiter
Low-level noise gate
State variable filter
ORDERING INFORMATION
DESCRIPTION
TEMPERATURE RANGE
ORDER CODE
DWG #
16-Pin Plastic Small Outline (SOL)
40 to +85
C
SA572D
SOT162-1
16-Pin Plastic Dual In-Line Package (DIP)
40 to +85
C
SA572N
SOT38-4
ABSOLUTE MAXIMUM RATINGS
SYMBOL
PARAMETER
RATING
UNIT
V
CC
Supply voltage
22
V
DC
T
A
Operating temperature range
T
A
SA572
40 to +85
C
P
D
Power dissipation
500
mW
Philips Semiconductors
Product specification
SA572
Programmable analog compandor
1998 Nov 03
3
BLOCK DIAGRAM
(7,9)
(6,10)
(3,13)
(16)
(8)
(4,12)
(2,14)
(1,15)
(5,11)
GAIN CELL
RECTIFIER
P.S.
6.8k
10k
BUFFER
10k
270
500
R1
G
+
+
SR00695
Figure 2. Block Diagram
DC ELECTRICAL CHARACTERISTICS
Standard test conditions (unless otherwise noted) V
CC
=15V, T
A
=25
C;
Expandor mode (see Test Circuit).
Input signals at unity gain level (0dB) = 100mV
RMS
at 1kHz; V
1
= V
2
; R
2
= 3.3k
; R
3
= 17.3k
.
SYMBOL
PARAMETER
TEST CONDITIONS
SA572
UNIT
SYMBOL
PARAMETER
TEST CONDITIONS
Min
Typ
Max
UNIT
V
CC
Supply voltage
6
22
V
DC
I
CC
Supply current
No signal
6.3
mA
V
R
Internal voltage reference
2.3
2.5
2.7
V
DC
THD
Total harmonic distortion (untrimmed)
1kHz C
A
=1.0
F
0.2
1.0
%
THD
Total harmonic distortion (trimmed)
1kHz C
R
=10
F
0.05
%
THD
Total harmonic distortion (trimmed)
100Hz
0.25
%
No signal output noise
Input to V
1
and V
2
grounded (2020kHz)
6
25
V
DC level shift (untrimmed)
Input change from no signal to 100mV
RMS
20
50
mV
Unity gain level
1.5
0
+1.5
dB
Large-signal distortion
V
1
=V
2
=400mV
0.7
3
%
Tracking error
Rectifier input
(measured relative to value at unity
i ) [V
V (
it
i )]dB V dB
V
2
=+6dB V
1
=0dB
0.2
dB
gain)= [V
O
V
O
(unity gain)]dB V
2
dB
V
2
=30dB V
1
=0dB
0.5
2.5, +1.6
dB
Channel crosstalk
200mV
RMS
into channel A,
measured output on channel B
60
dB
PSRR
Power supply rejection ratio
120Hz
70
dB
Philips Semiconductors
Product specification
SA572
Programmable analog compandor
1998 Nov 03
4
TEST CIRCUIT
BUFFER
RECTIFIER
NE5234
+15V
15V
(7,9)
(2,14)
(4,12)
6.8k
(5,11)
(6,10)
(8)
(1,15)
(16)
3.3k
(3,13)
G
V1
V2
V0
270pF
82k
2.2k
17.3k
1%
2.2
F
22
F
2.2
F
22
F
.1
F
1
F
2.2
F
5
= 10
F
R3
1%
R2
100
1k
+
+
+
+
SR00696
Figure 3. Test Circuit
AUDIO SIGNAL PROCESSING IC COMBINES VCA
AND FAST ATTACK/SLOW RECOVERY LEVEL
SENSOR
In high-performance audio gain control applications, it is desirable to
independently control the attack and recovery time of the gain
control signal. This is true, for example, in compandor applications
for noise reduction. In high end systems the input signal is usually
split into two or more frequency bands to optimize the dynamic
behavior for each band. This reduces low frequency distortion due
to control signal ripple, phase distortion, high frequency channel
overload and noise modulation. Because of the expense in
hardware, multiple band signal processing up to now was limited to
professional audio applications.
With the introduction of the Signetics SA572 this high-performance
noise reduction concept becomes feasible for consumer hi fi
applications. The SA572 is a dual channel gain control IC. Each
channel has a linearized, temperature-compensated gain cell and an
improved level sensor. In conjunction with an external low noise op
amp for current-to-voltage conversion, the VCA features low
distortion, low noise and wide dynamic range.
The novel level sensor which provides gain control current for the
VCA gives lower gain control ripple and independent control of fast
attack, slow recovery dynamic response. An attack capacitor C
A
with an internal 10k resistor R
A
defines the attack time t
A
. The
recovery time t
R
of a tone burst is defined by a recovery capacitor
C
R
and an internal 10k resistor R
R
. Typical attack time of 4ms for
the high-frequency spectrum and 40ms for the low frequency band
can be obtained with 0.1
F and 1.0
F attack capacitors,
respectively. Recovery time of 200ms can be obtained with a 4.7
F
recovery capacitor for a 100Hz signal, the third harmonic distortion
is improved by more than 10dB over the simple RC ripple filter with
a single 1.0
F attack and recovery capacitor, while the attack time
remains the same.
The SA572 is assembled in a standard 16-pin dual in-line plastic
package and in oversized SOL package. It operates over a wide
supply range from 6V to 22V. Supply current is less than 6mA. The
SA572 is designed for applications from 40
C to +85
C.
Philips Semiconductors
Product specification
SA572
Programmable analog compandor
1998 Nov 03
5
SA572 BASIC APPLICATIONS
Description
The SA572 consists of two linearized, temperature-compensated
gain cells (
G), each with a full-wave rectifier and a buffer amplifier
as shown in the block diagram. The two channels share a 2.5V
common bias reference derived from the power supply but otherwise
operate independently. Because of inherent low distortion, low noise
and the capability to linearize large signals, a wide dynamic range
can be obtained. The buffer amplifiers are provided to permit control
of attack time and recovery time independent of each other.
Partitioned as shown in the block diagram, the IC allows flexibility in
the design of system levels that optimize DC shift, ripple distortion,
tracking accuracy and noise floor for a wide range of application
requirements.
Gain Cell
Figure 4 shows the circuit configuration of the gain cell. Bases of the
differential pairs Q
1
-Q
2
and Q
3
-Q
4
are both tied to the output and
inputs of OPA A
1
. The negative feedback through Q
1
holds the V
BE
of Q
1
-Q
2
and the V
BE
of Q
3
-Q
4
equal. The following relationship can
be derived from the transistor model equation in the forward active
region.
D
V
BE
Q3Q4
+ D
BE
Q1Q2
(V
BE
= V
T
I
IN
IC/IS)
V
T
I
n
1
2
I
G
)
1
2
I
O
I
S
*
V
T
I
n
1
2
I
G
*
1
2
I
O
I
S
where I
IN
+
V
IN
R
1
R
1
= 6.8k
I
1
= 140
A
I
2
= 280
A
V
T
I
n
I
1
)
I
IN
I
S
*
V
T
I
n
I
2
*
I
1
*
I
IN
I
S
(2)
where I
IN
+
V
IN
R
1
R
1
= 6.8k
I
1
= 140
A
I
2
= 280
A
I
O
is the differential output current of the gain cell and I
G
is the gain
control current of the gain cell.
If all transistors Q
1
through Q
4
are of the same size, equation (2)
can be simplified to:
I
O
+
2
I
2
@
I
IN
@
I
G
*
1
I
2
I
2
*
2I
1
@
I
G
(3)
The first term of Equation 3 shows the multiplier relationship of a
linearized two quadrant transconductance amplifier. The second
term is the gain control feedthrough due to the mismatch of devices.
In the design, this has been minimized by large matched devices
and careful layout. Offset voltage is caused by the device mismatch
and it leads to even harmonic distortion. The offset voltage can be
trimmed out by feeding a current source within
25
A into the THD
trim pin.
The residual distortion is third harmonic distortion and is caused by
gain control ripple. In a compandor system, available control of fast
attack and slow recovery improve ripple distortion significantly. At
the unity gain level of 100mV, the gain cell gives THD (total harmonic
distortion) of 0.17% typ. Output noise with no input signals is only
6
V in the audio spectrum (10Hz-20kHz). The output current I
O
must feed the virtual ground input of an operational amplifier with a
resistor from output to inverting input. The non-inverting input of the
operational amplifier has to be biased at V
REF
if the output current
I
O
is DC coupled.
VREF
THD
TRIM
V+
R1
6.8k
1
2
I
G
)
1
2
I
O
I1
140
A
280
A
I2
IG
IO
Q4
Q3
Q1
Q2
VIN
+
A1
SR00697
Figure 4. Basic Gain Cell Schematic
Philips Semiconductors
Product specification
SA572
Programmable analog compandor
1998 Nov 03
6
Rectifier
The rectifier is a full-wave design as shown in Figure 5. The input
voltage is converted to current through the input resistor R
2
and
turns on either Q
5
or Q
6
depending on the signal polarity. Deadband
of the voltage to current converter is reduced by the loop gain of the
gain block A
2
. If AC coupling is used, the rectifier error comes only
from input bias current of gain block A
2
. The input bias current is
typically about 70nA. Frequency response of the gain block A
2
also
causes second-order error at high frequency. The collector current
of Q
6
is mirrored and summed at the collector of Q
5
to form the full
wave rectified output current I
R
. The rectifier transfer function is
I
R
+
V
IN
*
V
REF
R
2
(4)
If V
IN
is AC-coupled, then the equation will be reduced to:
I
RAC
+
V
IN
(AVG)
R
2
The internal bias scheme limits the maximum output current I
R
to be
around 300
A. Within a
1dB error band the input range of the rectifier
is about 52dB.
VIN
VREF
V+
A2
+
R2
Q6
Q5
D7
I
R
+
V
IN
*
V
REF
R
2
SR00698
Figure 5. Simplified Rectifier Schematic
Buffer Amplifier
In audio systems, it is desirable to have fast attack time and slow
recovery time for a tone burst input. The fast attack time reduces
transient channel overload but also causes low-frequency ripple
distortion. The low-frequency ripple distortion can be improved with
the slow recovery time. If different attack times are implemented in
corresponding frequency spectrums in a split band audio system,
high quality performance can be achieved. The buffer amplifier is
designed to make this feature available with minimum external
components. Referring to Figure 6, the rectifier output current is
mirrored into the input and output of the unipolar buffer amplifier A
3
through Q
8
, Q
9
and Q
10
. Diodes D
11
and D
12
improve tracking
accuracy and provide common-mode bias for A
3
. For a
positive-going input signal, the buffer amplifier acts like a
voltage-follower. Therefore, the output impedance of A
3
makes the
contribution of capacitor CR to attack time insignificant. Neglecting
diode impedance, the gain Ga(t) for
G can be expressed as
follows:
Ga(t)
+
(Ga
INT
*
Ga
FNL
e
*
t
t
A
)
Ga
FNL
Ga
INT
=Initial Gain
Ga
FNL
=Final Gain
A
=R
A
CA=10k
CA
where
A
is the attack time constant and R
A
is a 10k internal
resistor. Diode D
15
opens the feedback loop of A
3
for a
negative-going signal if the value of capacitor CR is larger than
capacitor CA. The recovery time depends only on CR
R
R
. If the
diode impedance is assumed negligible, the dynamic gain G
R
(t) for
G is expressed as follows.
G
R
(t)
+
(G
RINT
*
G
RFNL
e
*
t
t
R
)
G
RFNL
G
R
(t)=(G
R INT
G
R FNL
) e +G
R FNL
R=R
R
CR=10k
CR
where
R is the recovery time constant and R
R
is a 10k internal
resistor. The gain control current is mirrored to the gain cell through
Q
14
. The low level gain errors due to input bias current of A
2
and A
3
can be trimmed through the tracking trim pin into A
3
with a current
source of
3
A.
Philips Semiconductors
Product specification
SA572
Programmable analog compandor
1998 Nov 03
7
Q8
Q9
Q10
Q17
X2
Q16
X2
Q18
10k
D13
Q14
CR
D15
A3
10k
D11
D12
CA
TRACKING
TRIM
IR1
IR2
IQ
=
2IR2
V+
I
R
+
V
IN
R
+
SR00699
Figure 6. Buffer Amplifier Schematic
Basic Expandor
Figure 7 shows an application of the circuit as a simple expandor.
The gain expression of the system is given by
V
OUT
V
IN
+
2
I
1
@
R
3
@
V
IN(AVG)
R
2
@
R
1
(5)
(I
1
=140
A)
Both the resistors R
1
and R
2
are tied to internal summing nodes. R
1
is a 6.8k internal resistor. The maximum input current into the gain
cell can be as large as 140
A. This corresponds to a voltage level of
140
A
6.8k=952mV peak. The input peak current into the rectifier
is limited to 300
A by the internal bias system. Note that the value
of R
1
can be increased to accommodate higher input level. R
2
and
R
3
are external resistors. It is easy to adjust the ratio of R
3
/R
2
for
desirable system voltage and current levels. A small R
2
results in
higher gain control current and smaller static and dynamic tracking
error. However, an impedance buffer A
1
may be necessary if the
input is voltage drive with large source impedance.
The gain cell output current feeds the summing node of the external
OPA A
2
. R
3
and A
2
convert the gain cell output current to the output
voltage. In high-performance applications, A
2
has to be low-noise,
high-speed and wide band so that the high-performance output of
the gain cell will not be degraded. The non-inverting input of A
2
can
be biased at the low noise internal reference Pin 6 or 10. Resistor
R
4
is used to bias up the output DC level of A
2
for maximum swing.
The output DC level of A
2
is given by
V
ODC
+
V
REF
1
)
R
3
R
4
*
V
B
R
3
R
4
(6)
V
B
can be tied to a regulated power supply for a dual supply system
and be grounded for a single supply system. CA sets the attack time
constant and CR sets the recovery time constant. *5COL
Philips Semiconductors
Product specification
SA572
Programmable analog compandor
1998 Nov 03
8
+
A1
(7,9)
R5
100k
R2
3.3k
(3,13)
(8)
(16)
CA
CR
(4,12)
(2,14)
1k
(6,10) R6
17.3k
(5,11)
BUFFER
A2
R4
R3
VOUT
VIN
CIN1
CIN2
CIN3
VREF
R1
6.8k
+VB
+VCC
G
10
F
1
F
2.2
F
C1
2.2
F
2.2
F
SR00700
Figure 7. Basic Expandor Schematic
Basic Compressor
Figure 8 shows the hook-up of the circuit as a compressor. The IC is
put in the feedback loop of the OPA A
1
. The system gain expression
is as follows:
V
OUT
V
IN
+
I
1
2
@
R
2
@
R
1
R
3
@
V
IN(AVG)
1
2
(7)
R
DC1
, R
DC2
, and CDC form a DC feedback for A
1
. The output DC
level of A
1
is given by
V
ODC
+
V
REF
1
)
R
DC1
)
R
DC2
R
4
(8)
*
V
B
@
R
DC1
)
R
DC2
R
4
The zener diodes D
1
and D
2
are used for channel overload
protection.
(7,9)
BUFFER
VREF
R1
6.8k
G
R4
RDC1
RDC2
9.1k
CDC
9.1k
D1
D2
A1
R3
17.3k
C1
1k
R5
(6,10)
(5,11)
(2,14)
(4,12)
CR
CA
(8)
(3,13)
3.3k
R2
(16)
CIN3
VCC
10
F
.1
F
C2
2.2
F
CIN1
VIN
10
F
1
F
2.2
F
CIN2
2.2
F
VOUT
+
SR00701
Figure 8. Basic Compressor Schematic
Philips Semiconductors
Product specification
SA572
Programmable analog compandor
1998 Nov 03
9
Basic Compandor System
The above basic compressor and expandor can be applied to
systems such as tape/disc noise reduction, digital audio, bucket
brigade delay lines. Additional system design techniques such as
bandlimiting, band splitting, pre-emphasis, de-emphasis and
equalization are easy to incorporate. The IC is a versatile functional
block to achieve a high performance audio system. Figure 9 shows
the system level diagram for reference.
COMPRESSION
IN
EXPANDOR
OUT
REL LEVEL
ABS LEVEL
dB
dBM
3.0V
547.6MV
400MV
100MV
10MV
1MV
+29.54
+14.77
+12.0
0.0
20
40
60
80
+11.76
3.00
5.78
17.78
37.78
57.78
77.78
97.78
VRMS
100
V
10
V
INPUT TO
G
AND RECT
2
1
2
SR00702
Figure 9. SA572 System Level
Philips Semiconductors
Product specification
SA572
Programmable analog compandor
1998 Nov 03
10
SO16:
plastic small outline package; 16 leads; body width 7.5 mm
SOT162-1
Philips Semiconductors
Product specification
SA572
Programmable analog compandor
1998 Nov 03
11
DIP16:
plastic dual in-line package; 16 leads (300 mil)
SOT38-4
Philips Semiconductors
Product specification
SA572
Programmable analog compandor
1998 Nov 03
12
Definitions
Short-form specification -- The data in a short-form specification is extracted from a full data sheet with the same type number and title. For
detailed information see the relevant data sheet or data handbook.
Limiting values definition -- Limiting values given are in accordance with the Absolute Maximum Rating System (IEC 134). Stress above one
or more of the limiting values may cause permanent damage to the device. These are stress ratings only and operation of the device at these or
at any other conditions above those given in the Characteristics sections of the specification is not implied. Exposure to limiting values for extended
periods may affect device reliability.
Application information -- Applications that are described herein for any of these products are for illustrative purposes only. Philips
Semiconductors make no representation or warranty that such applications will be suitable for the specified use without further testing or
modification.
Disclaimers
Life support -- These products are not designed for use in life support appliances, devices or systems where malfunction of these products can
reasonably be expected to result in personal injury. Philips Semiconductors customers using or selling these products for use in such applications
do so at their own risk and agree to fully indemnify Philips Semiconductors for any damages resulting from such application.
Right to make changes -- Philips Semiconductors reserves the right to make changes, without notice, in the products, including circuits, standard
cells, and/or software, described or contained herein in order to improve design and/or performance. Philips Semiconductors assumes no
responsibility or liability for the use of any of these products, conveys no license or title under any patent, copyright, or mask work right to these
products, and makes no representations or warranties that these products are free from patent, copyright, or mask work right infringement, unless
otherwise specified.
Philips Semiconductors
811 East Arques Avenue
P.O. Box 3409
Sunnyvale, California 940883409
Telephone 800-234-7381
Copyright Philips Electronics North America Corporation 1998
All rights reserved. Printed in U.S.A.
Date of release: 11-98
Document order number:
9397 750 04749
Philips
Semiconductors
Data sheet
status
Objective
specification
Preliminary
specification
Product
specification
Product
status
Development
Qualification
Production
Definition
[1]
This data sheet contains the design target or goal specifications for product development.
Specification may change in any manner without notice.
This data sheet contains preliminary data, and supplementary data will be published at a later date.
Philips Semiconductors reserves the right to make chages at any time without notice in order to
improve design and supply the best possible product.
This data sheet contains final specifications. Philips Semiconductors reserves the right to make
changes at any time without notice in order to improve design and supply the best possible product.
Data sheet status
[1]
Please consult the most recently issued datasheet before initiating or completing a design.
PDF 
ZIP