A class D amplifier with a guard band quantizer to prevent output of narrow pulses

摘要

A PWM circuit comprises a quantiser arranged to block low level signal inputs to the modulator stage, thereby preventing the output of very narrow pulses. For low level signals between threshold TL and TU the quantiser outputs either a zero output or a code representing a minimum desired pulse width. This ensures that either no pulse is output from the PWM or else a pulse having at least a minimum width is produced. The H-bridge may be controlled by relatively long non-overlapping pulses, thereby reducing predriver power consumption (figures 11 and 12). Double-sided PWM using shuffling of the leading edge is disclosed. The use of a noise shaping loop around the shuffler quantizer (figures 9 and 10) allows odd pulse lengths to be output without distortion or noise.