Sigma-delta modulation (SDM) and pulse-width modulation (PWM) are compared as a means of structuring power digital-to-analogue converters (PDAC) designed specifically for wide-band audio, low power loss and direct loudspeaker dive. Recent innovations in SDM coding and output-stage topologies using pulse shaping techniques are discussed with emphasis on achieving stable and low distortion operation especially under high-level signal excitation having a modulation index circa 0.7 necessary to process peak transients. A simplified variant of predictive SDM with step back is introduced that offers both low latency and probability of instability and structures for both analogue and digital input data reviewed.
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