Gain control circuit for suppressing Larsen effect in a loudspea

Details Gain control circuit for suppressing Larsen effect in a loudspea Gain control circuit for suppressing Larsen effect in a loudspea

1988-02-18

1989-05-30

Mullins, James B.

Amplifiers

With control of power supply or bias voltage

With control of input electrode or gain control electrode bias

330141, 379390, 379420, H03G 320

Patent

active

048354848

ABSTRACT:
A gain control circuit (10) of an amplifier (3) for listening via a loudspeaker (4) in an apparatus, more specifically a telephone set, which includes a microphone (1), in order to suppress the Larsen effect. The gain control circuit comprises first control means (100) which control a first gain reduction of the amplifier (3) when the amplitude of the microphone signal (S) exceeds a first predetermined threshold determined by a first reference voltage VR1, in dependence on a first time constant (RD1+RD2.C). The gain control circuit also includes second control means (200) which start operating only after the said first time constant, and provide a supplementary reduction of the gain depending on a second time constant (RD2.C) which is shorter than the first time constant, as long as the amplitude of the microphone signal (S) exceeds a second threshold, which is lower than the first threshold, determined by a second reference voltage VR2.

REFERENCES:
patent: 4488007 (1984-12-01), Chataignon et al.

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