A PWM DAC for digital audio power conversion: from theory to performance

Digital pulse width modulation (PWM) is combined with simple noise shaping to convert 8 times Nyquist sampled digital audio signals directly to analogue audio. A digital interpolating filter is used to provide such over-sampled test signals from a compact disc (CD). A low noise crystal based oscillator is used to synchronise the required digital elements via fast asynchronous counters based on 1.3 mu CMOS. Output is suitable for power-efficient control of MOSFET switching devices and can be used directly, giving >100 dB dynamic range and >120 dB peak signal to noise floor ratio. Comparison between a pulse amplitude modulation (PAM) digital to analogue converter (DAC) and the PWM converter is shown using spectral plots. The PWM unit is shown to follow theoretical analysis very closely.<
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