Patent ID: 7151404

Claim:
A class-D amplifier for generating an audio output signal from an audio input signal, comprising: a pulse width modulation (PWM) circuit for generating a PWM output signal by a current from a voltage difference between the audio input signal and a gain-amplified signal; negative channel metal oxide semiconductor (NMOS) and positive channel metal oxide semiconductor (PMOS) transistors for responding to the PWM output signal; a loop filter for demodulating a signal driven by the PMOS and NMOS transistors; and a gain amplifier for generating the gain-amplified signal by amplifying an output of the loop filter, wherein the PWM circuit comprises: an input circuit receiving a PWM output sianal; a first controller for generating an output of a first voltage level by a first current in response to an input signal and an output of the input circuit; a first Schmidt trigger for generating an output of a first logic level when the output of the first controller reaches the first voltage level; a second controller for generating an output of a second voltage level by a second current in response to the input signal and the output of the first Schmidt trigger; and a second Schmidt trigger for generating the PWM output signal whose frequency is variable in accordance with the first and second currents.