REV. A

Information furnished by Analog Devices is believed to be accurate and

reliable. However, no responsibility is assumed by Analog Devices for its

use, nor for any infringements of patents or other rights of third parties that

may result from its use. No license is granted by implication or otherwise

under any patent or patent rights of Analog Devices.

a

SSM2167

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700

www.analog.com

Fax: 781/326-8703

© Analog Devices, Inc., 2002

Low Voltage Microphone

Preamplifier with Variable

Compression and Noise Gating

FEATURES

Complete Microphone Conditioner in a 10-Lead Package

Single 3 V Operation

Low Shutdown Current < 2

A

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 communi-

cations 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 characteristic. 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 amplifica-

tion of background noise or hum. This results in optimized signal

levels prior to digitization, thereby eliminating the need for addi-

tional 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 SSM2167 is available in two versions, with different amounts

of fixed gain. The SSM2167-1 has 18 dB of fixed gain, while

the SSM2167-2 features only 8 dB of fixed gain.

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

for operation over the extended industrial temperature range of

–40

°C to +85°C.

PIN CONFIGURATION

10-Lead MSOP

(RM Suffix)

INPUT – dB

LIMITING

REGION

LIMITING

THRESHOLD

(ROTATION POINT)

COMPRESSION

REGION

1

r

1

1

DOWNWARD

EXPANSION

THRESHOLD

(NOISE GATE)

DOWNWARD

EXPANSION

REGION

VCA GAIN

Figure 1. General Input/Output Characteristics

SSM2167

GND

SHUTDOWN

BUF OUT

INPUT

OUTPUT

COMPRESSION RATIO

GATE THRS

AVG CAP

1

2

3

4

5

10

9

8

7

6