Class D amplifiers challenge "golden ears": audiophiles will find that delta-sigma modulation with closed-loop feedback makes a difference.(Putting New Technology In Perspective)

Electronic Design, February, 2005 by Tuite, Don

Conventional wisdom has it that class D amplifiers occupy an applications niche in which efficiency is paramount, and that several factors compromise sound quality. The latter includes difficulty in implementing feedback, mediocre power-supply rejection ratio (PSRR), and the drawbacks of constant switching-frequency pulse-width modulators (PWMs).

Countering the conventional wisdom, Analog Devices (ADI) integrated a delta-sigma modulator with its AD1991 class D driver. It also incorporated a feedback loop to deliver a family of class D amplifiers with "audiophile performance" for the high-end automotive and flat-panel TV markets (Fig. 1).

[FIGURE 1 OMITTED]

First, ADI replaced the usual class D constant-frequency PWM with a...

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