PROBLEM TO BE SOLVED: To operate a class D amplifier normally and output a driving signal even when an ON duty ratio of a modulated signal remains near an upper limit.SOLUTION: A modulated signal generated from a driving waveform signal is power-amplified and then smoothed to generate a driving signal. A digital power amplifier for power-amplifying the modulated signal has a push-pull connection of two N channel (hereinafter abbreviated to ch) MOSFETs between a power supply and a ground, and a parallel connection of a Pch MOSFET to the power supply side Nch MOSFET. Even when a charge stored in a bootstrap capacitor for turning on the power supply side Nch MOSFET is insufficient to turn on the Nch MOSFET, the Pch MOSFET can be turned on to perform power amplification and enable the driving signal to be output.
