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

µF

22

µF

2.2

µF

22

µF

.1

µF

1

µF

2.2

µF

5

Ω

= 10

µF

R3

1%

R2

100

Ω

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

the high-frequency spectrum and 40ms for the low frequency band

can be obtained with 0.1

µF and 1.0µF attack capacitors,

respectively. Recovery time of 200ms can be obtained with a 4.7

µF

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

µF 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.