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sa575
DATASHEETS
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Philips sa575 DATASHEETS

RF COMMUNICATIONS PRODUCTS
SA575
Low voltage compandor
Product specification Replaces data of 1997 June 28
IC17
Philips Semiconductors
1997 Nov 07
SYMBOL
PARAMETER
UNITS
SA575Low voltage compandor

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.

FEA TURES

•Operating voltage range from 3V to 7V
•Reference voltage of 100mV
RMS
= 0dB
•One dedicated summing op amp per channel and two extra
uncommitted op amps
•600Ω drive capability
•Single or split supply operation
•Wide input/output swing capability
•3000V ESD protection

APPLICATIONS

•Portable communications
•Cellular radio
•Cordless telephone
•Consumer audio

PIN CONFIGURATION

D1 and DK Packages
1
+V
IN1
2
-V
IN1
3
V
OUT
1
RECT1
V
REF
GND
4 5 6 7 8
9
10
RECT. IN1
C
SUM OUT 1
COMP. IN1
GAIN CELL IN1
NOTE:
1. Available in large SOL package only.
Figure 1. Pin Configuration
•Portable broadcast mixers
•Wireless microphones
•Modems
•Electric organs
•Hearing aids
20 V
CC
19 +V
IN2
18 -V
IN2
17 V
OUT2
16 RECT.IN2 15 C
RECT2
14 SUM OUT2
13 COMP.IN2 12 SUM NODE 2
11 GAIN CELL IN2
SR00703

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
SA575
T
V
V
θ
CC
IN
T
A
STG
JA
Single supply voltage –0.3 to 8 V Voltage applied to any other pin –0.3 to (VCC+0.3) V Operating ambient temperature range -40 to +85 °C Storage temperature range -65 to +150 °C Thermal impedance SOL 112 °C/W
SSOP 117 °C/W
1997 Nov 07 853-1665 18666
2
SA575Low voltage compandor

BLOCK DIAGRAM and TEST CIRCUIT

0.1µF
+5V
V
CC
V
REF
V
OUT
GND
V
+
IN
GND
+
C3
10µF
C
RECT
2.2µF
10µF
+
C6
10µF
+
GND
+
1
2
–
OP AMP
3
4
3.8k
575
OP AMP
V
CC
5
10k
10k
V
Σ
Σ
REF
∆G
∆G
GND
6
7
8
9
10
Figure 2. Block Diagram and Test Circuit
+
–
3.8k
10k
10k
20
19
18
17
16
15
14
13
12
11
C
RECT
C11
+
2.2µF
+
4.7µF
R7
30k
R13
10k
C15
C8
10µF
+
C14
+
R8
30k
GND
1µF
V
+
IN
C10
10µF
GND
V
REF
V
OUT
SR00704

DC ELECTRICAL CHARACTERISTICS

Typical values are at TA = 25°C. Minimum and Maximum values are for the full operating temperature range: -40 to +85°C for SA575, except SSOP package is tested at +25°C only. V
SYMBOL PARAMETER TEST CONDITIONS SA575 UNITS
For compandor, including summing amplifier
V
CC
I
CC
V
REF
R
Supply voltage Supply current No signal 3 4.2 5.5 mA Reference voltage Summing amp output load 10 kΩ
L
1
2
THD Total harmonic distortion 1kHz, 0dB BW = 3.5kHz 0.12 1.5 %
E
NO
Output voltage noise BW = 20kHz, RS = 0Ω 6 30 µV 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
Tracking error relative to 0dB
= 5V, unless otherwise stated. Both channels are tested in the Expandor mode (see Test Circuit)
CC
LIMITS
MIN TYP MAX
3 5 7 V
VCC = 5V 2.4 2.5 2.6 V
Gain cell input = 0dB, 1kHz Rectifier input = 6dB, 1kHz
Gain cell input = 0dB, 1kHz Rectifier input = -30dB, 1kHz
-1.0 1.0 dB
-1.0 1.0 dB
1997 Nov 07
3
SA575Low voltage compandor
DC ELECTRICAL CHARACTERISTICS (cont.)
LIMITS
SYMBOL PARAMETER TEST CONDITIONS SA575 UNITS
MIN TYP MAX
Crosstalk 1kHz, 0dB, C
For operational amplifier
V
O
R
Output swing RL = 10kΩ VCC-0.4 V
Output load 1kHz 600 Ω
L
CMR Input common-mode range 0 V
CMRR Common-mode rejection ratio 60 80 dB
A
V
VOL
I
B
OS
Input bias current VIN = 0.5V to 4.5V -1 1 µA
Input offset voltage 3 mV
Open-loop gain RL = 10kΩ 80 dB
SR Slew rate Unity gain 1 V/µs
GBW Bandwidth Unity gain 3 MHz
E
NI
Input voltage noise BW = 20kHz 2.5 µV
PSRR Power supply rejection ratio 1kHz, 250mV 60 dB
NOTES:
1. Operation down to V
2. Reference voltage, V
= 2V is possible, but performance is reduced. See curves in Figure 7a and 7b.
CC
, is typically at 1/2VCC.
REF

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 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
cell. In addition, the SA575 has two
REF
= 220µF -80 -65 dB
REF
CC
CC
V
V
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
= 5V. In the expandor mode, the typical input
CC
dynamic range was from -34dB to +12dB where 0dB is equal to 100mV input was +
. The typical unity gain level measured at 0dB @ 1kHz
RMS
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 + gain level was +
18dB with a tracking error +0.1dB and the typical unity
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 20kΩ 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 without clipping. The 0dB ref is 100mV 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
is always 1/2 VCC to provide the maximum headroom
REF
. The input is AC
RMS
1997 Nov 07
4
SA575Low voltage compandor
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 1.
4V
(avg)
Expandor gain =
where VIN(avg) = 0.95V
IN
3.8k x 100µA
IN(RMS)
Equation 2.
τR = τA = 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 3.
1/2
IN(RMS)
Compressor gain =
where VIN(avg) = 0.95V
3.8k x 100µA 4V
(avg)
IN
Equation 4.
τR = τA = 10k x C
RECT
= 10k x C4

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 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.
Equation 5.
ALC gain =
τR = τA = 10k x C
3.8k x 100µA 4V
(avg)
IN
= 10k x C9
RECT
Equation 6.
COMP
is necessary
EXP IN
C5
10µF
7
9
10k
4
3.8k
∆G
5
2.2µF
C4
10k
Σ
8
V
REF
6
C3
EXP OUT
10µF
SR00705
Figure 3. Typical Expandor Configuration
1997 Nov 07
5
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