PULSE-CODE TO PULSE WIDTH MODULATION SIGNAL CONVERSION WITH CONTINUOUSLY VARIABLE RATIO BETWEEN CLOCK AND SAMPLING FREQUENCIES AND APPLICATIONS HEREOF

摘要

Digital audio circuitry including modulation circuitry (35) for generating a pulse- width modulated (PWM) signal from processed pulse-code modulated (PCM) audio signals. The modulation circuitry includes a duration quantizer function (32) that generates a sequence of duration values d(k) from received PCM samples, quantized to integer multiples of periods of a master PWM clock (CLKpwm). The duration quantizer function also produces a feedback PCM value x(k) from each quantized duration value d(k) that is applied to a loop filter (36), the output of which modifies the received PCM sample stream to suppress quantization noise. Transient effects caused by modulation or abrupt changes in the desired PWM period are suppressed by digitally filtering (34) the PWM period sample stream.