LP502 Datasheet, PDF (1/4 Pages) Gennum Corporation – Low Distortion AGC Compression Amplifier

Low Distortion AGC
Compression Amplifier
LP502 CUSTOM DATA SHEET
FEATURES
• 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 µV
• <1 % distortion at 10 mVRMS output
• operates from 1.05 to 3 VDC
STANDARD PACKAGING
• 8 pin MICROpac
• 8 pin PLID ^®
• Chip (64 x 62 mils)
Au Bump
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.
V_B
7
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
of supply voltages, 1.05 to 3 VDC for LP502 without any
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
4
2
V_REG
VOLTAGE
REGULATOR
1
A IN
AMPLIFIER
A OUT
3
FULL WAVE
RECTIFIER
AGC IN
6
8
5
GND
AGC FILTER
BLOCK DIAGRAM
Patented 1985
Canada 1183580
Patent Pending Europe 83.300836.0
USA 4506169
Japan 58-06886
Document No. HP2802-1
GENNUM CORPORATION P.O. Box 489, Stn A, Burlington, Ontario, Canada L7R 3Y3 tel. [phone] fax: [phone]
Gennum Japan Corporation:C-101 Mi yamae Vill age, 2–10–42 Mi yamae, Suginami–ku, Tokyo 168-0081, Japan tel. [phone] fax [phone]