Class D hearing aid amplifier
First Claim
1. In a hearing aid having a microphone, a power amplifier, and an output receiver transducer, said power amplifier having positive and negative supply terminals adapted to be connected to a source of direct voltage, said amplifier being coupled to receive audio frequency input signals produced by said microphone for driving said transducer from amplifier output terminals in response to the input to said microphone, the improvement comprising:
- a power amplifier of the pulse-width modulation type, so that in response to the absence of an input signal from said microphone said power amplifier provides to said output terminals an alternating electrical signal pulse train of positive and negative electrical pulses of substantially zero average value at an ultrasonic frequency, said amplifier including means for providing at said output terminals an audio frequency facsimile of said input signal by controlling the time duration of said positive and negative electrical pulses responsively to the received audio frequency input signal, said power amplifier including output polarity switching means for producing a peak-to-peak voltage provided at said output terminals which is greater than the magnitude of said direct voltage by connecting said supply terminals to said output terminals at a given polarity to produce said positive pulses and at an opposite polarity to produce said negative pulses.
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Accused Products
Abstract
A sub-miniature power amplifier for hearing aids configured to be completely self-contained and to fit within the user'"'"'s ear features a Class D amplifier stage providing a peak-to-peak output voltage greater than the power supply voltage. By configuring all signal elements as digital units, circuit balance is readily maintained. A substantial economy of battery drain is achieved while preserving a low value of distortion at low signal levels. Oscillator frequency is governed by a single resistance element. The amplifier and an optional efficiency-improving inductor can be accommodated entirely within the residual volume of the motor chamber of a state-of-the-art earphone housing. Pulse feedback networks are provided to achieve positive stable latching of each output pulse throughout its duration without producing significant pulse duration distortions.
183 Citations
21 Claims
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1. In a hearing aid having a microphone, a power amplifier, and an output receiver transducer, said power amplifier having positive and negative supply terminals adapted to be connected to a source of direct voltage, said amplifier being coupled to receive audio frequency input signals produced by said microphone for driving said transducer from amplifier output terminals in response to the input to said microphone, the improvement comprising:
- a power amplifier of the pulse-width modulation type, so that in response to the absence of an input signal from said microphone said power amplifier provides to said output terminals an alternating electrical signal pulse train of positive and negative electrical pulses of substantially zero average value at an ultrasonic frequency, said amplifier including means for providing at said output terminals an audio frequency facsimile of said input signal by controlling the time duration of said positive and negative electrical pulses responsively to the received audio frequency input signal, said power amplifier including output polarity switching means for producing a peak-to-peak voltage provided at said output terminals which is greater than the magnitude of said direct voltage by connecting said supply terminals to said output terminals at a given polarity to produce said positive pulses and at an opposite polarity to produce said negative pulses.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
Specification