Patent ID: 7872522

Claim:
A noise reduction system for a switching amplifier system including a differential output stage and demodulator filter responsive to complementary PWM signals, said noise reduction system comprising: a charging circuit for generating in-phase PWM signals and gradually adjusting their duty cycle between a low duty cycle and the full duty cycle of said complementary PWM signals; an out-phasing circuit for generating full duty cycle PWM signals and gradually shifting their relative phase between in-phase and out-of-phase; and a control circuit responsive to a turn-on signal to enable said charging circuit to adjust the in-phase PWM signals from low to full duty cycle and enable said out-phasing circuit to shift the relative phase from in-phase to out-of-phase, and responsive to a turn-off signal to enable said out-phasing circuit to shift the relative phase from out-of-phase to in-phase and enable said charging circuit to adjust the in-phase PWM signals from full to low duty cycle for maintaining balanced charge on the demodulation filter to reduce audible noise.