Patent ID: 6563376
Filing Date: 2003-05-13
Classification: H03F,H03G

Abstract:
A mute circuit for a digital audio amplifier circuit, which includes a PWM drive circuit receiving analog audio signals and generating PWM modulated drive pulses depending on the amplitude of the received analog audio signals, and an output circuit performing a push-pull operation driven by the drive pulses and applying its output to a speaker via an output capacitor, and which causes to produce in the output circuit an output signal corresponding to an amplitude reference level of the analog audio signal by driving the output circuit with drive pulses even under a condition where the amplitude level of the analog audio signal is substantially zero, wherein the output circuit comprises a first transistor performing a push operation and a second transistor performing a pull operation of which output sides are connected in series between a power source line and a reference potential line, the PWM drive circuit generates the drive pulses depending on the positive and negative polarities of the analog audio signals with respect to the amplitude reference level, and further the mute circuit comprises a switch circuit including a third transistor inserted either between the first transistor and the power source line or between the second transistor and the reference potential line, and a time constant circuit which drives the third transistor from OFF to ON depending on the ON state of a power source.