| 摘要 |
An integrator (40), when active, generates an analog voltage (SIG14) such that the duty ratio of an output signal (Vsw) of a D-class amplifier (10) gets close to a duty ratio specified by an analog audio signal (SIG12). A first muting circuit (20), when active, forcefully turns off the D-class amplifier (10). A voltage fixing circuit (50), when active, fixes an output terminal (104) of the D-class amplifier (10) to a predetermined fixed potential (Vdd/2). A second muting circuit (16), which is disposed between an output terminal of a filter (14) and a ground point, when active, grounds the output terminal of the filter (14). A muting control part (60) controls each of the integrator (40), first muting circuit (20), voltage fixing circuit (50) and second muting circuit (16). As a result, the noise can be appropriately reduced at the time of activation and at the time of halt.
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