Method and apparatus for filter-less class D audio amplifier EMI reduction

An integrated circuit (IC) chip, comprising:

• one or more input pins for receiving one or more input signals;
• a first signal processing circuit coupled to the one or more input signals and configured for providing a first and a second output signals;
• a first and a second output pins coupled to the first and the second output signals, respectively, wherein a common-mode signal is related to a sum of the first and the second output signals;
• a second signal processing circuit, coupled to first and second output signals for providing an inverse common-mode signal which is related to sum of inverses of the first and the second output signals;
• and
• a third output pin for providing the inverse common mode signal.

An audio system, comprising:

• a class D amplifier, comprising:
• a class-D PWM (pulse width modulation) modulator configured for generating first and second PWM signals, the first and the second PWM signals forming a differential signal with three differential output levels;
• a differential output driver, configured for driving a first and a second output signals onto a first and a second output terminals in response to the first and the second PWM signals wherein the first and the second output signals form a differential output signal having three differential output levels;
• an inverse common-mode signal generator, coupled to first and second output signals for providing an inverse common-mode signal;
• and
• one or more inverse output terminals for providing the inverse common mode signal;
• a speaker having first and second input connectors coupled to the first and the second output terminals, respectively;
• and
• a wire or a trace on a PCB (printed circuit board) coupled to the inverse common mode signal.