High fidelity hearing aid amplifier
First Claim
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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Accused Products
Abstract
A high fidelity hearing aid amplifier is operable at a very low battery voltage and includes a single integrated circuit chip which provides a variable gain amplifier and gain control circuitry operative at low signal levels to enhance gain at higher frequencies relative to gain at lower frequencies, such circuitry including a logarithmic rectifier arrangement and a peak detector in a compression ratio control circuit. Operation at a low battery voltage is enhanced through a compression ratio control circuit which provides a level shift between an AC output of the logarithmic rectifier arrangement and the peak detector. Current mirrors are provided to obtained balanced and stable operation, and an arrangement is provided for manual control by a user to obtain an optimum response characteristic.
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Citations
27 Claims
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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.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. An amplifier comprising:
- an integrated circuit chip, a variable gain amplifier system including transistors on said integrated circuit chip and having a signal input, 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.
- View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
- 25. 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, 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, a variable attenuator circuit associated with said amplifier means for attenuation of signals developed by said microphone means, a rectifier circuit for receiving signals from said amplifier means and developing a DC control signal proportional to signal amplitudes above a certain threshold level and for applying said control signal to said variable attenuator circuit, and an integrated circuit chip including transistors and other components associated with said amplifier means and variable attenuator and rectifier circuit, wherein said rectifier circuit is a variable threshold full-wave rectifier circuit which comprises reference potential means for developing two different reference potentials at first and second circuit points, a pair of semi-conductor junctions connected between said first and second circuit points and a third circuit point, means including a capacitor for coupling said third circuit point to said amplifier means, the charge of said capacitor being changed in one direction through current flow through one of said pair of semi-conductor junctions during half cycles of an applied signal of one polarity and being changed in an opposite direction through current flow through the other of said pair of semi-conductor junctions during half cycles of an applied signal of an opposite polarity, means for developing an output signal in response to current flow through one of said pair of semi-conductor junctions above a certain level, and means for controlling said reference potential means to control said reference potentials and control the signal level above which said output signal is developed.
Specification