Low Voltage Microphone Preamplifier with Variable Compression & Noise Gating

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 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 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.

Applications

* Desktop, portable, or palmtop computers

* Telephone conferencing

* Communication headsets

* Two-way communications

* Surveillance systems

* Karaoke and DJ mixers

* Complete microphone conditioner in a 10-lead package * Single 3 V operation * Low shutdown current < 2 μA * Adjustable noise gate threshold