Abstract
A class AD audio amplifier system ( 10 ) with DC output detection logic ( 26 ) is disclosed. The amplifier system ( 10 ) includes multiple audio channels ( 20 ), each of which includes a pulse-width-modulator (PWM) ( 24 ). The DC detection logic ( 26 ) includes a sigma-delta modulator ( 60 ) and a digital low-pass filter ( 62 ) that monitors the PWM output signals from the PWM modulators ( 24 ). The sigma-delta modulator ( 60 ) operates at a first clock frequency, while the low-pass filter ( 62 ) operates at a much lower clock frequency, so that AC audio components, PWM harmonics, and sigma-delta quantization error is suppressed from the DC detection. The modulated filtered signal is compared against a threshold level (THRSH) to determine whether the amplitude of a DC component at the PWM output is sufficiently high to constitute a fault. If so, a fault detection signal (DC_DET) is issued, and the PWM modulators ( 24 ) are disabled to prevent unsafe conditions in the system ( 10 ).
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