SA575.PDF
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RF COMMUNICATIONS PRODUCTS
SA575
Low voltage compandor
Product specification
Replaces data of 1997 June 28
1997 Nov 07
IC17
Philips Semiconductors
Philips Semiconductors
Product specification
Low voltage compandor
SA575
DESCRIPTION
The SA575 is a precision dual gain control circuit designed for low
voltage applications. The SA575’s channel 1 is an expandor, while
channel 2 can be configured either for expandor, compressor, or
automatic level controller (ALC) application.
PIN CONFIGURATION
D
1
and DK Packages
+V
IN1
-V
IN1
V
OUT
1
RECT. IN1
1
20 V
CC
19 +V
IN2
18 -V
IN2
17 V
OUT2
16 RECT.IN2
15 C
RECT2
14 SUM OUT2
2
3
FEATURES
•
4
Operating voltage range from 3V to 7V
5
C
RECT1
•
Reference voltage of 100mV
RMS
= 0dB
SUM OUT 1
6
•
One dedicated summing op amp per channel and two extra
uncommitted op amps
COMP. IN1
7
8
V
REF
13 COMP.IN2
12 SUM NODE 2
•
600
W
drive capability
GAIN CELL IN1
9
10
•
Single or split supply operation
GND
11 GAIN CELL IN2
•
Wide input/output swing capability
NOTE:
1. Available in large SOL package only.
•
3000V ESD protection
SR00703
Figure 1. Pin Configuration
APPLICATIONS
•
•
Portable broadcast mixers
Portable communications
•
•
Wireless microphones
Cellular radio
•
•
Modems
Cordless telephone
•
•
Electric organs
Consumer audio
•
Hearing aids
ORDERING INFORMATION
DESCRIPTION
TEMPERATURE RANGE
ORDER CODE
DWG
20-Pin Plastic Small Outline Large
-40 to +85
°
C
SA575D
SOT163-1
20-Pin Plastic Shrink Small Outline Package (SSOP)
-40 to +85
°
C
SA575DK
SOT266-1
ABSOLUTE MAXIMUM RATINGS
RATING
SYMBOL
PARAMETER
UNITS
SYMBOL
PARAMETER
UNITS
SA575
V
CC
Single supply voltage
–0.3 to 8
V
V
IN
Voltage applied to any other pin
–0.3 to (V
CC
+0.3)
V
T
A
Operating ambient temperature range
-40 to +85
°
C
T
STG
Storage temperature range
-65 to +150
°
C
q
JA
Thermal impedance
SOL
112
°
C/W
SSOP
117
C/W
°
2
1997 Nov 07
853-1665 18666
Philips Semiconductors
Product specification
Low voltage compandor
SA575
BLOCK DIAGRAM and TEST CIRCUIT
0.1
F
m
V
CC
+5V
C15
+
GND
1
20
10
m
F
575
V
CC
V
IN
+
+
–
2
19
C14
R13
10k
OP AMP
V
REF
C3
–
3
18
V
OUT
+
OP AMP
10
m
F
4
17
3.8k
C11
+
5
16
+
4.7
m
F
3.8k
C
RECT
2.2
m
F
C10
C
RECT
S
+
6
15
+
V
OUT
2.2
m
F
GND
10
m
F
S
C6
7
14
10k
V
IN
+
10
m
F
8
13
R8
30k
V
REF
V
REF
10k
+
R7
30k
9
12
D
G
+
10
F
m
10k
1
m
F
C8
10
D
G
11
10k
GND
GND
GND
GND
SR00704
Figure 2. Block Diagram and Test Circuit
DC ELECTRICAL CHARACTERISTICS
Typical values are at T
A
= 25
°
°
C for SA575, except
SSOP package is tested at +25
°
C only. V
CC
= 5V, unless otherwise stated. Both channels are tested in the Expandor mode (see Test Circuit)
LIMITS
C. Minimum and Maximum values are for the full operating temperature range: -40 to +85
SYMBOL
PARAMETER
TEST CONDITIONS
SA575
UNITS
MIN
TYP
MAX
For compandor, including summing amplifier
V
CC
Supply voltage
1
3
5
7
V
I
CC
Supply current
No signal
3
4.2
5.5
mA
Reference voltage
2
V
REF
V
CC
= 5V
2.4
2.5
2.6
V
R
L
Summing amp output load
10
k
W
THD
Total harmonic distortion
1kHz, 0dB BW = 3.5kHz
0.12
1.5
%
E
NO
Output voltage noise
BW = 20kHz, R
S
= 0
W
6
30
m
V
0dB
Unity gain level
1kHz
-1.5
1.5
dB
V
OS
Output voltage offset
No signal
-150
150
mV
Output DC shift
No signal to 0dB
-100
100
mV
Gain cell input = 0dB, 1kHz
Rectifier input = 6dB, 1kHz
-1.0
1.0
dB
Gain cell input = 0dB, 1kHz
Rectifier input = -30dB, 1kHz
Tracking error relative to 0dB
-1.0
1.0
dB
3
1997 Nov 07
Philips Semiconductors
Product specification
Low voltage compandor
SA575
DC ELECTRICAL CHARACTERISTICS
(cont.)
LIMITS
SYMBOL
PARAMETER
TEST CONDITIONS
SA575
UNITS
MIN
TYP
MAX
Crosstalk
1kHz, 0dB, C
REF
= 220
m
F
-80
-65
dB
For operational amplifier
V
O
Output swing
R
L
= 10k
W
V
CC
-0.4
V
CC
V
R
L
Output load
1kHz
600
W
CMR
Input common-mode range
0
V
CC
V
CMRR
Common-mode rejection ratio
60
80
dB
I
B
Input bias current
V
IN
= 0.5V to 4.5V
-1
1
m
A
V
OS
Input offset voltage
3
mV
A
VOL
Open-loop gain
R
L
= 10k
W
80
dB
SR
Slew rate
Unity gain
1
V/
m
s
GBW
Bandwidth
Unity gain
3
MHz
E
NI
Input voltage noise
BW = 20kHz
2.5
m
V
PSRR
Power supply rejection ratio
1kHz, 250mV
60
dB
NOTES:
1. Operation down to V
CC
= 2V is possible, but performance is reduced. See curves in Figure 7a and 7b.
2. Reference voltage, V
REF
, is typically at 1/2V
CC
.
FUNCTIONAL DESCRIPTION
This section describes the basic subsystems and applications of the
SA575 Compandor. More theory of operation on compandors can
be found in AN174 and AN176. The typical applications of the
SA575 low voltage compandor in an Expandor (1:2), Compressor
(2:1) and Automatic Level Control (ALC) function are explained.
These three circuit configurations are shown in Figures 3, 4, 5
respectively.
The SA575 has two channels for a complete companding system.
The left channel, A, can be configured as a 1:2 Expandor while the
right channel, B, can be configured as either a 2:1 Compressor, a
1:2 Expandor or an ALC. Each channel consists of the basic
companding building blocks of rectifier cell, variable gain cell,
summing amplifier and V
REF
cell. In addition, the SA575 has two
additional high performance uncommitted op amps which can be
utilized for application such as filtering, pre-emphasis/de-emphasis
or buffering.
Figure 6 shows the complete schematic for the applications demo
board. Channel A is configured as an expandor while channel B is
configured so that it can be used either as a compressor or as an
ALC circuit. The switch, S1, toggles the circuit between compressor
and ALC mode. Jumpers J1 and J2 can be used to either include
the additional op amps for signal conditioning or exclude them from
the signal path. Bread boarding space is provided for R1, R2, C1,
C2, R10, R11, C10 and C11 so that the response can be tailored for
each individual need. The components as specified are suitable for
the complete audio spectrum from 20Hz to 20kHz.
The most common configuration is as a unity gain non-inverting
buffer where R1, C1, C2, R10, C10 and C11 are eliminated and R2
and R11 are shorted. Capacitors C3, C5, C8, and C12 are for DC
blocking. In systems where the inputs and outputs are AC coupled,
these capacitors and resistors can be eliminated. Capacitors C4
and C9 are for setting the attack and release time constant.
C6 is for decoupling and stabilizing the voltage reference circuit.
The value of C6 should be such that it will offer a very low
impedance to the lowest frequencies of interest. Too small a
capacitor will allow supply ripple to modulate the audio path. The
better filtered the power supply, the smaller this capacitor can be.
R12 provides DC reference voltage to the amplifier of channel B.
R6 and R7 provide a DC feedback path for the summing amp of
channel B, while C7 is a short-circuit to ground for signals. C14 and
C15 are for power supply decoupling. C14 can also be eliminated if
the power supply is well regulated with very low noise and ripple.
DEMONSTRATED PERFORMANCE
The applications demo board was built and tested for a frequency
range of 20Hz to 20kHz with the component values as shown in
Figure 6 and V
CC
= 5V. In the expandor mode, the typical input
dynamic range was from -34dB to +12dB where 0dB is equal to
100mV
RMS
. The typical unity gain level measured at 0dB @ 1kHz
input was
+
0.5dB and the typical tracking error was
+
0.1dB for input
range of -30 to +10dB.
In the compressor mode, the typical input dynamic range was from
-42dB to
+1
8dB with a tracking error +0.1dB and the typical unity
gain level was
+0
.5dB.
In the ALC mode, the typical input dynamic range was from -42dB to
+8dB with typical output deviation of
+
0.2dB about the nominal
output of 0dB. For input greater than +9dB in ALC configuration, the
summing amplifier sometimes exhibits high frequency oscillations.
There are several solutions to this problem. The first is to lower the
values of R6 and R7 to 20k
W
each. The second is to add a current
limiting resistor in series with C12 at Pin 13. The third is to add a
compensating capacitor of about 22 to 30pF between the input and
output of summing amplifier (Pins 12 and 14). With any one of the
above recommendations, the typical ALC mode input range
increased to +18dB yielding a dynamic range of over 60dB.
EXPANDOR
The typical expandor configuration is shown in Figure 3. The
variable gain cell and the rectifier cell are in the signal input path.
The V
REF
is always 1/2 V
CC
to provide the maximum headroom
without clipping. The 0dB ref is 100mV
RMS
. The input is AC
coupled through C5, and the output is AC coupled through C3. If in
a system the inputs and outputs are AC coupled, then C3 and C5
can be eliminated, thus requiring only one external component, C4.
The variable gain cell and rectifier cell are DC coupled so any offset
4
1997 Nov 07
Philips Semiconductors
Product specification
Low voltage compandor
SA575
voltage between Pins 4 and 9 will cause small offset error current in
the rectifier cell. This will affect the accuracy of the gain cell. This
can be improved by using an extra capacitor from the input to Pin 4
and eliminating the DC connection between Pins 4 and 9.
The expandor gain expression and the attack and release time
constant is given by Equation 1 and Equation 2, respectively.
Equation 3.
1/2
3.8k x 100
m
A
Compressor gain =
4V
IN
(avg)
where V
IN
(avg) = 0.95V
IN(RMS)
Equation 1.
Equation 4.
4V
IN
(avg)
3.8k x 100
m
A
t
R
=
t
A
= 10k x C
RECT
= 10k x C4
Expandor gain =
AUTOMATIC LEVEL CONTROL
The typical Automatic Level Control circuit configuration is shown in
Figure 5. It can be seen that it is quite similar to the compressor
schematic except that the input to the rectifier cell is from the input
path and not from the feedback path. The input is AC coupled
through C12 and C13 and the output is AC coupled through C8.
Once again, as in the previous cases, if the system input and output
signals are already AC coupled, then C12, C13 and C8 could be
eliminated. Concerning the compressor, removing R6, R7 and C7
will cause motor-boating in absence of signals. C
COMP
is necessary
to stabilize the summing amplifier at higher input levels. This circuit
provides an input dynamic range greater than 60dB with the output
within
+
0.5dB typical. The necessary design expressions are given
by Equation 5 and Equation 6, respectively.
where V
IN
(avg) = 0.95V
IN(RMS)
Equation 2.
t
R
=
t
A
= 10k x C
RECT
= 10k x C4
COMPRESSOR
The typical compressor configuration is shown in Figure 4. In this
mode, the rectifier cell and variable gain cell are in the feedback
path. R6 and R7 provide the DC feedback to the summing amplifier.
The input is AC coupled through C12 and output is AC coupled
through C8. In a system with inputs and outputs AC coupled, C8
and C12 could be eliminated and only R6, R7, C7, and C13 would
be required. If the external components R6, R7 and C7 are
eliminated, then the output of the summing amplifier will motor-boat
in absence of signals or at extremely low signals. This is because
there is no DC feedback path from the output to input. In the
presence of an AC signal this phenomenon is not observed and the
circuit will appear to function properly.
The compressor gain expression and the attack and release time
constant is given by Equation 3 and Equation 4, respectively.
Equation 5.
3.8k x 100
m
A
ALC gain =
4V
IN
(avg)
Equation 6.
t
R
=
t
A
= 10k x C
RECT
= 10k x C9
7
10k
C5
9
EXP IN
C3
G
D
S
6
10
m
F
10k
EXP OUT
10
m
F
4
3.8k
5
8
2.2
m
F
C4
V
REF
SR00705
Figure 3. Typical Expandor Configuration
5
1997 Nov 07
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NE577.PDF
(50 KB)
SA571.PDF
(143 KB)
SA572.PDF
(136 KB)
SA575.PDF
(102 KB)
SAA572.PDF
(102 KB)
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