US 5,165,017 A · Automatic gain control circuit in a feed forward configuration

Abstract

An input signal representing speech is preamplified, filtered, and fed foward in parallel to Automatic Gain Control (AGC) circuitry and to a gain controllable amplifier. The AGC detects the peak absolute value of the input signal, charing a capacitor in accordance with such detections. The capacitor is discharged at a faster rate (variable down to 1 msec) when a greater charge value is stored but at a slower rate (variable up to 4 seconds) when a lower charge value is stored. The gain controllable amplifier is controlled for gain inversely to the charge value stored on the capacitor. The AGC captures greater than 60 dB of allowable input signal range, compressing such input signal into a (controllable) limited amplitude dynamic range. The AGC provides that 1) environmental background sound is clearly heard in the absence of speech, 2) during speech the gain level is controlled so as not to allow background sounds to come in during normal speech pauses, simultaneous that 3) recovery to desired gain is quick folloiwng plossive sounds present in normal speech. In a preferred embodiment, the AGC circuitry and associated amplification circuitry is implemented as a monolithic semicustom integrated circuit.

Claims30

Dependent claims

In a hearing device including an input transducer for converting sounds of differing loudness into an electrical input signal having a dynamic range, an output device selected from a group consisting of:

(i) transducers for converting electrical signals into vibrations and (ii) audio electrodes;
and coupling means for electrically coupling the input transducer to the output transducer, said coupling means containing the improvement comprising:
a means for compressing the dynamic range of the input signals coupled to the input and output transducers, wherein the compression means has a controllable gain that may be altered at variable rates;
and
a control means coupled to the compressing means for rapidly increasing the gain following loud sounds and for more slowly increasing the gain following quieter sounds.

2 more elements

Dependencies are inferred from the claim text.

Automatic gain control circuit in a feed forward configuration

Life of this patent

Automatic gain control circuit in a feed forward configuration

Life of this patent

Abstract

Claims30