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High fidelity hearing aid amplifier

  • US 5,131,046 A
  • Filed: 11/03/1989
  • Issued: 07/14/1992
  • Est. Priority Date: 11/03/1989
  • Status: Expired due to Term
First Claim
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1. A hearing aid including microphone means for developing an input electrical signal in response to an applied audio signal, receiver means for developing an audio output signal in response to an applied electrical signal, a battery, and amplifier means arranged for energization from said battery and for receiving said input electrical signal from said microphone means and applying a corresponding output signal to said receiver means, said amplifier means comprising:

  • an integrated circuit chip, a variable gain amplifier system including transistors on said integrated circuit chip and having an input responsive to said input electrical signal, a signal output and a gain control input, and a gain control circuitry including transistors on said integrated circuit chip, said gain control circuitry having logarithmic response characteristics and being arranged to apply a control signal to said gain control input of said variable gain amplifier system to control gain as a logarithmic function of signal level, said transistors of said gain control circuitry on said integrated circuit chip including an input transistor having a base electrode, feedback diode means for applying a feedback signal to said base electrode, and bias current reduction means on said integrated circuit chip and separate from said feedback diode means, said bias current reduction means including a transistor connected to said base electrode of said input transistor for applying to said base electrode a biasing current which corresponds closely to current flow into said base electrode of said input transistor in order to reduce biasing current required from said feedback diode means.

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