Patent ID: 7170339

Claim:
A digital amplifier comprising: a switching means for outputting a driving signal by switching an operation voltage constituted by a DC voltage based on a pulse width modulation input signal; an operation voltage control means for controlling the value of the operation voltage; wherein the switching means includes an input signal conversion means and a first and a second field effect transistors of mutually identical polarity; the drain of the first field effect transistor is connected to the operation voltage; the source of the first field effect transistor and the drain of the second field effect transistor are connected in common to an output terminal of the switching means; the source of the second field effect transistor is connected to a reference voltage; the input signal conversion means generates a first input signal in phase with the input signal and a second input signal of an inverted phase with respect to the input signal; the first input signal is supplied to the gate of the first field effect transistor while the second input signal is supplied to the gate of the second field effect transistor; and wherein the digital amplifier further comprises: a first input signal controlling means for controlling an amplitude of the first input signal according to a change in the operation voltage in order to make a gate-source voltage of the first field effect transistor approximately constant.