Patent ID: 7953234

Claim:
An audio signal output circuit, comprising: a volume setting circuit arranged to receive a digital input audio signal including an AC component superposed on a given reference voltage, said volume setting circuit adapted to amplify said AC component with an amplification rate that varies from a predetermined level to zero, or from zero to the predetermined level, in accordance with a received mute/release mute signal, with said given reference voltage kept constant; a modulator arranged to perform pulse density modulation on the audio signal received from the volume setting circuit; a transition signal generation circuit arranged to generate a pulse-density-modulated transition signal in response to a reset signal associated with said mute/release mute signal, said transition signal varying in level from said reference voltage to zero volt or from zero volt to said reference voltage; a switching circuit connected to said modulator and said transition signal generation circuit and arranged to receive an audio signal and a transition signal, respectively, from said modulator, said switch circuit adapted to selectively output one of said audio signal and said transition signal according to a switching signal received to an electro-acoustic transducing apparatus; and a control circuit arranged to generate a control signal that includes said mute/release mute signal, said reset signal, and said switching signal, wherein in switching said audio signal output circuit from a sound reproducing mode to a power-off mode or a mute mode, said switching circuit is switched to said transition signal having said reference voltage after said output level of said audio signal of said modulator is varied to said reference voltage, and then the level of said transition signal is varied from said reference voltage towards zero volt; while in switching said audio signal output circuit from the power-off mode or the mute mode to the sound reproducing mode, the output level of said transition signal is varied from zero volt to said reference voltage, and then said switching circuit is switched from said transition signal received from said transition signal generation circuit to said audio signal including said reference voltage.