Amplification circuit e.g. for analogue or digital hearing aid

摘要

Output from the microphone (1) or coil (2) is selected (3) for application by a preamplifier (4) followed by a three-stage AGC circuit (5-7) in which each stage has a different threshold and compression ratio. A tone filter is divided into two parts (8.1, 8.2) preceding and following the AGC. The output power amplifier (9) drives a loudspeaker (16) in the earpiece (17). Adjustments are programmed into a memory (10). The amplification characteristic resulting from the time-varying AGC gives a compression ratio falling as the input level rises, either continuously or within defined time intervals.