Bausch-lomb Incorporated

Telex Communications, Inc.

Starkey Laboratories, Inc.

Thomas A Scheller

Ivo Merks

John Ellison

Timothy V Statz

Peter T Salmi

A hearing aid circuit using an averaging detector and a plurality of time constants to produce a compression control signal to control the gain of a compression amplifier which compresses an input signal when the averaging detector signal exceeds a predetermined threshold. The compression control signal has an attack and release time. The release time of the compression control signal is proportional to the duration of time during which the averaging signal's amplitude exceeds the predetermined threshold level. The release has a variable recovery rate. The recovery rate is relatively fast during an initial portion of the release time and relatively slower during the remaining portion of the release time. The hearing aid circuit may also use a volume control to adjust the gain of the signal produced by the compression amplifier without adjusting the gain of the signal produced by a linear amplifier to provide volume control for soft sounds independent of loud sounds.

Compression systems for hearing aids

An electroacoustic device such as a hearing aid having a battery, microphone, speaker, a preamplifier, a voltage regulator and power amplifier. The power amplifier includes identically configured output and bridge stages connected to opposite sides of the speaker, the output signals from the output stage being connected through a blocking capacitor to the input of the bridge stage. The output/bridge stage circuit includes an interface stage and two current gain stages. The interface stage converts voltage signals to current signals with a pair of outputs respectively connected to the two like-configured current gain stages. Each current gain stage includes two successive sections, each having a pair of transistors, one of which is configured as a diode connected in series with a resistor to shunt current from the base of the other transistor. The current output of the current gain stages is thus responsive to the input current level, permitting low quiescent current with efficient delivery of current to the receiver, and providing high peak currents with minimum distortion. Also, quiescent current is essentially insensitive to variations in battery voltage and temperature.

Hearing aid amplifier circuitry

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Fridley, MN, United States of America

Thomas A Scheller