A D-class signal amplification circuit of the invention intends to repress the
influence by a fluctuations of the power supply voltage with a simplified circuit
construction and inexpensive components. The D-class signal amplification circuit
includes: a multiplier that multiplies an input signal by a correction coefficient,
a first modulator that executes a delta-sigma modulation to an output signal from
the multiplier, a D-class amplifier supplied with a power supply voltage VDD, which
amplifies an output signal from the first modulator, a voltage conversion circuit
that generates a power supply voltage VDD/2 from the power supply voltage VDD,
a first low pass filter that inputs a signal converted into a level of VDD/2 on
the basis of the output signal outputted from the D-class amplifier, a reference
signal generation circuit supplied with VDD/2, which generates a reference signal
on the basis of the input signal, a second low pass filter that inputs the reference
signal, a first comparator that compares levels of the signals outputted from the
first with the second low pass filters, and a coefficient control circuit that
increases or decreases the correction coefficient by a predetermined modifying
breadth, on the basis of the comparison result.