Low Voltage Microphone Preamplifier with

Variable Compression and Noise Gating

Data Sheet

SSM2167

Rev. G

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FEATURES

Complete microphone conditioner in a 10-lead package

Single 3 V operation

Low shutdown current < 2 µA

Adjustable noise gate threshold

Adjustable compression ratio

Automatic limiting feature prevents ADC overload

Low noise and distortion: 0.2% THD + N

20 kHz bandwidth

APPLICATIONS

Desktop, portable, or palmtop computers

Telephone conferencing

Communication headsets

Two-way communications

Surveillance systems

Karaoke and DJ mixers

GENERAL DESCRIPTION

The SSM2167 is a complete and flexible solution for conditioning

microphone inputs in personal electronics and computer audio

systems. It is also excellent for improving vocal clarity in com-

munications and public address systems. A low noise voltage

controlled amplifier (VCA) provides a gain that is dynamically

adjusted by a control loop to maintain a set compression charac-

teristic. The compression ratio is set by a single resistor and can

be varied from 1:1 to over 10:1 relative to the fixed rotation

point. Signals above the rotation point are limited to prevent

overload and to eliminate popping. A downward expander (noise

gate) prevents amplification of background noise or hum. This

results in optimized signal levels prior to digitization, thereby

eliminating the need for additional gain or attenuation in the

digital domain. The flexibility of setting the compression ratio

and the time constant of the level detector, coupled with two

values of rotation point, make the SSM2167 easy to integrate in

a wide variety of microphone conditioning applications.

The device is available in a 10-lead MSOP package, and is

guaranteed for operation over the extended industrial

temperature range of −40°C to +85°C.

PIN CONFIGURATION

GND

1

SHUTDOWN

3

INPUT

5

10

OUTPUT

9

COMPRESSION RATIO

8

GATE THRS

7

AVG CAP

6

SSM2167

TOP VIEW

(Not to Scale)

Figure 1. 10-Lead MSOP (RM Suffix)

LIMITING

REGION

LIMITING

THRESHOLD

(ROTATION POINT)

COMPRESSION

REGION

1

r

1

1

DOWNWARD

EXPANSION

THRESHOLD

(NOISE GATE)

DOWNWARD

EXPANSION

REGION

VCA GAIN

INPUT (dB)

Figure 2. General Input/Output Characteristics