Townsend & Townsend
Hearing aid amplifier
 A general purpose hearing aid amplifier is programmably adaptable to the prescription requirements of the hearing impaired. The hearing aid amplifier comprises a bank of bandpass-restricted channels, each channel having a voltage-controlled input amplifier, a voltage-controlled compressor, and a voltage-controlled output amplifier for shaping the gain, attack and delay characteristics of the selected channel. The bank is fed through a fixed high-pass filter from a microphone input, and a mixed output drives a power amplifier for an output transducer such as a hearing aid speaker. The amplifier is programmably adaptable through the use of a monolithic programmable switch array using, for example, semiconductor fuseable link technology to preset digital-to-analog converters voltage controllable levels of the amplifiers and compressors of each channel according to a digital control input. The monolithic switch array is coupled to the programmable amplifiers through digital to analog converters which establish the programming voltages for the amplifiers and compressors. The monolithic switch array digital to analog converters may be constructed on the same monolithic semiconductor chip. 
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Jared A.
Anderson