Philips SA5750D, SA5750N, SA5751D, SA5751N, SA575AD Datasheet

Philips Semiconductors

SA575

Low voltage compandor

Product specification
Replaces data of 1997 June 28

1997 Nov 07

RF COMMUNICATIONS PRODUCTS

IC17

Philips Semiconductors Product specification

SA575Low voltage compandor

2

1997 Nov 07 853-1665 18666

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

APPLICA TIONS

•Portable communications

•Cellular radio

•Cordless telephone

•Consumer audio

PIN CONFIGURATION

+V

IN1

-V

IN1

V

OUT

1

RECT. IN1

C

RECT1

COMP. IN1

V

REF

GND

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

SUM OUT 1

D1 and DK Packages

NOTE:

1. Available in large SOL package only.

GAIN CELL IN1

1
2
3
4
5
6
7
8

9

10

SR00703

Figure 1. Pin Configuration

•Portable broadcast mixers

•Wireless microphones

•Modems

•Electric organs

•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

SA575

UNITS

V

CC

Single supply voltage –0.3 to 8 V

V

IN

Voltage applied to any other pin –0.3 to (VCC+0.3) V

T

A

Operating ambient temperature range -40 to +85 °C

T

STG

Storage temperature range -65 to +150 °C

θ

JA

Thermal impedance SOL 112 °C/W

SSOP 117 °C/W

Philips Semiconductors Product specification

SA575Low voltage compandor

1997 Nov 07

3

BLOCK DIAGRAM and TEST CIRCUIT

1

2

3

4

5

6

7

8

9

10

20

19

18

17

16

15

14

13

12

11

Σ

∆G

∆G

V

REF

Σ

+

–

+

–

OP AMP

OP AMP

V

CC

575

4.7µF

10µF

0.1µF

V

CC

+5V

10µF

2.2µF

10µF

C

RECT

1µF

V

IN

V

REF

V

OUT

C

RECT

2.2µF

10µF

V

IN

+

+

+

+

+

+

+

+

+

V

OUT

C3

GND

C6

GND

GND

GND

3.8k

3.8k

10k

10k

10k

10k

GND

R8

30k

R7

30k

C8

GND

C11

C10

R13

10k

C14

C15

V

REF

10µF

SR00704

Figure 2. Block Diagram and Test Circuit

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

CC

= 5V , unless otherwise stated. Both channels are tested in the Expandor mode (see Test Circuit)

LIMITS

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

V

REF

Reference voltage

2

VCC = 5V 2.4 2.5 2.6 V

R

L

Summing amp output load 10 kΩ
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

Gain cell input = 0dB, 1kHz
Rectifier input = 6dB, 1kHz

-1.0 1.0 dB

Tracking error relative to 0dB

Gain cell input = 0dB, 1kHz
Rectifier input = -30dB, 1kHz

-1.0 1.0 dB

Philips Semiconductors Product specification

SA575Low voltage compandor

1997 Nov 07

4

DC ELECTRICAL CHARACTERISTICS (cont.)

LIMITS

SYMBOL PARAMETER TEST CONDITIONS SA575 UNITS

MIN TYP MAX

Crosstalk 1kHz, 0dB, C

REF

= 220µF -80 -65 dB

For operational amplifier

V

O

Output swing RL = 10kΩ VCC-0.4 V

CC

V

R

L

Output load 1kHz 600 Ω

CMR Input common-mode range 0 V

CC

V

CMRR Common-mode rejection ratio 60 80 dB

I

B

Input bias current VIN = 0.5V to 4.5V -1 1 µA

V

OS

Input offset voltage 3 mV

A

VOL

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

CC

= 2V is possible, but performance is reduced. See curves in Figure 7a and 7b.

2. Reference voltage, V

REF

, is typically at 1/2VCC.

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.

DEMONSTRA TED 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 +

18dB 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 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

REF

is always 1/2 VCC 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

Philips Semiconductors Product specification

SA575Low voltage compandor

1997 Nov 07

5

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.

4V

IN

(avg)

3.8k x 100µA

where VIN(avg) = 0.95V

IN(RMS)

τR = τA = 10k x C

RECT

= 10k x C4

Expandor gain =

Equation 2.

Equation 1.

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.

4V

IN

(avg)

3.8k x 100µA

where VIN(avg) = 0.95V

IN(RMS)

τR = τA = 10k x C

RECT

= 10k x C4

1/2

Compressor gain =

Equation 3.

Equation 4.

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.

4V

IN

(avg)

3.8k x 100µA

τR = τA = 10k x C

RECT

= 10k x C9

Equation 5.

Equation 6.

ALC gain =

2.2µF

10µF

10µF

V

REF

∆G

Σ

EXP IN

EXP OUT

10k

C5

9

4

3.8k

5

C4

C3

10k

7

6

8

SR00705

Figure 3. Typical Expandor Configuration