Abstract: A programmable low voltage compressor circuit suitable for use with hearing aids is described. The compressor has a continuously variable compression ratio wherein the gain of the compressor may be programmably controlled over a wide range and the compressor may be powered from a power source as low as 1.1 volt. The compressor employs a variolosser wherein the gain is controlled by the ratio of the currents flowing out of first and second control terminals. A control circuit coupled to the variolosser controls the magnitude of the currents flowing out of the two control terminals. The control circuit includes a peak detector which generates a signal related to the peak positive envelope of the signal input to the compressor. A voltage to current converter is coupled to the peak detector for increasing the magnitude of the current flowing out of one of the control terminals of the variolosser as the voltage output of the peak detector increases.

Abstract: A programmable low voltage multi-band compression system suitable for use with hearing aids is described. Received audio signals are processed by a band split filter which separates the received audio signal into a plurality of frequency bands. A plurality of compressors coupled to the band split filter compresses each of the respective frequency bands. The output of the compressor are then summed to generate a composite audio signal. The compression ratio of each of the compressors is set, in response to a set of control signals, to a preselected independent value. The average gain of each of the compressors is set to a preselected level independently of the other compressors. In addition, the compression ratio of each compressor may vary with input signal level. Another set of control signals is employed for setting the gain of the compressor to provide a volume control function.

Abstract: An improved variable gain circuit is described having an input for an audio signal and an output for an audio signal. An operational amplifier having inverting and non-inverting inputs and an output has its input connected to the audio input. The first differential cell having inverting and non-inverting inputs, output, and a first control current terminal, has one input connected to the output of the operational amplifier and the other input connected to a reference potential. The output of the first differential cell is connected to one of the inputs of the operational amplifier in negative feedback relation and a source of controlling current is connected to the control current terminal. The second differential cell is also provided having inverting and non-inverting inputs, an output, and a second control current terminal. One input of the second differential cell is connected to the output of the operational amplifier and the other of the inputs is connected to the source of reference potential.

Abstract: An improved variable gain circuit is described having an input for an audio signal and an output for an audio signal. An operational amplifier having inverting and non-inverting inputs and an output has its input connected to the audio input. The first differential cell having inverting and non-inverting inputs, output, and a first control current terminal, has one input connected to the output of the operational amplifier and the other input connected to a reference potential. The output of the first differential cell is connected to one of the inputs of the operational amplifier in negative feedback relation and a source of controlling current is connected to the control current terminal. The second differential cell is also provided having inverting and non-inverting inputs, an output, and a second control current terminal. One input of the second differential cell is connected to the output of the operational amplifier and the other of the inputs is connected to the source of reference potential.