This paper presents a pure digital real-time power supply compensation scheme for both single-ended and bridgetied-load configured noise-shaped class D amplifiers. Using the appropriate power supply measurement circuitry, the scaled AC and DC components of the power supply voltage rail(s) are fed back into the PWM controller to modify the feedback path and the direct path of the noise shaper. All delays through the feedback loop have been minimized such that the ripple cancellation of the output stage is accomplished in real time. A two-chip ADC/PWM controller with this compensation scheme achieves 40dB power supply rejection of a 60Hz ripple and 100dB system dynamic range.
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