Patented 1985

Patent Pending Europe 83.300836.0

Canada 1183580

USA 4506169

Japan 58-06886

BLOCK DIAGRAM

Low Distortion AGC

Compression Amplifier

LP502 CUSTOM DATA SHEET

• adjustable gain from 0 to 60 dB

• 0.94 V DC voltage regulator on-chip

• attack time fixed at less than 1 ms

• release time adjustable from 40 to 500 ms

• low input referred noise 1.2

STANDARD PACKAGING

• 8 pin MICROpac

• 8 pin PLID

®

• Chip (64 x 62 mils)

Au Bump

FEATURES

GENNUM CORPORATION P.O. Box 489, Stn A, Burlington, Ontario, Canada L7R 3Y3

tel. (905) 632-2996 fax: (905) 632-5946

Document No. HP2802-1

DESCRIPTION

The LP502 is a compression (AGC) preamplifier that consists

of a single-ended input inverting amplifier, with an internal

current controlled resistance connected between input and

output.

By using R

GT

(see test circuit) to vary the value of this current

controlled resistance, the amplifier gain and compression

threshold can be controlled over a range of 60 dB.

The AGC current is derived from a full wave rectifier driven by

a differential amplifier. The attack time of the AGC circuit is

fixed at less than 1 ms. The release time is adjustable from

40 to 500 ms by selecting the value of an external capacitor

(C3).

Internally, a series shunt voltage regulator produces a 0.94 V

DC regulated output voltage. This provides a bias for electret

microphones and permits circuit operations over a wide range

degradation of electrical performances.

As compared to the LD502, the LP502 incorporates an

additional diode between the amplifier output and the AGC

filter point. This “attack diode” is responsible for precharging

the AGC filter point, which enables quicker attack time and

helps to reduce the gain overshoot (during transients) that is

observed in the LD502 with certain combinations of AGC input

coupling and filter capacitors. However, with this diode

connected, some level of AGC is always present with higher

output levels even when the AGC input is disconnected.

Therefore the LP502 cannot be used as a “pure” linear

amplifier.

GAIN SET

A OUT

AGC IN

AGC FILTER

GND

A IN

VOLTAGE

REGULATOR

AMPLIFIER

FULL WAVE

RECTIFIER

85

6

3

4

7

2

1