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.