Compression circuit for hearing aid - has opto-electronic coupler as nonlinear impedance in negative feedback path of amplifier

摘要

The negative feedback path may extend over one or more stages of the amplifier. A full wave rectifier bridge (30) is connected to the input LED side of the optoelectronic coupler. A variable resistor (32) connects the bridge's output to the LED and is used to adjust the slope of the control signal. A changeover switch (26) at the input of the feedback path may connect either the output of the non-controlled amplifier stages or their input to the input of the feedback path. Distortion at low frequencies is small.