AUDIO PROCESSING CIRCUIT, STARTING METHOD THEREOF AND ELECTRONIC APPARATUS USING THESE

PROBLEM TO BE SOLVED: To solve the problem that pop-up noise occurs because there is a lower limit in pulsewidth of an output pulse of a ΔΣ modulator. SOLUTION: In a digital audio processing circuit 100, a transition signal generating part 22 generates a transition signal upon starting the circuit. The ΔΣ modulator 40 performs ΔΣ modulation of the transition signal S7. A duty ratio adjusting part 60 adjusts a duty ratio of a bit stream S6 output from the ΔΣ modulator 40 and outputs the duty ratio to a class D amplifier 50 of a post stage. The duty ratio adjusting part 60 changes the pulsewidth of the bit stream S6 to thereby adjust the duty ratio. The duty ratio adjusting part 60 gradually increases the pulsewidth of the bit stream S6 from a predetermined minimum value to the pulsewidth of an input bit stream with the elapse of time upon starting the circuit. COPYRIGHT: (C)2008,JPO&INPIT