The present invention relates to an audio amplifier using a pulse width modulation,
and more particularly, to a pulse width modulation type audio amplifier which an
average switching frequency or a cutoff frequency of a low pass filter is variable
in accordance with frequency of input signal. The present invention has a method
for using average switching frequency of an output pulse by lowering the average
switching frequency in accordance with the bandwidth of the input audio signal
for relative narrow bandwidth than that of an input audio signal having a usual
bandwidth of 20 kHz like as a pulse width modulation type radio signal and a low
bandwidth signal for a subwoofer, a method for lowering a cutoff frequency of a
low pass filter for restoring an output pulse to a continuous time signal together
an average switching frequency of the output pulse, and a method for using respective
average switching frequencies different to each other for each channel having respective
different bandwidths in a multi-channel amplifier. By using the average switching
frequency as lower as possible in accordance with the bandwidth of the input audio
signal, the power efficiency is enhanced and the electromagnetic interference affecting
peripheral devices can be minimized.
