A 2x40W integrated stereo sigma-delta class D amplifier with 100 dB SNR is realized in 0.6um BCDMOS technology. Feedback from power stage outputs gives 0.001% THD and 65dB PSRR. Modulator clock rate is 6 MHz, but dynamically adjusted quantizer hysteresis reduces output data rate to 450 kHz, helping achieve 88% efficiency. At AM radio frequencies, the modulator output spectrum contains a single peak related to the hysteresis, but is otherwise tone-free, unlike PWM modulators which contain many harmonics of the PWM clock frequency.
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