Pulse width modulation method

A pulse width modulation (PWM) method, which is configured to convert an input signal into a corresponding output PWM signal, the PWM method comprising:

• generating a first linear periodic wave and a second linear periodic wave, wherein an amplitude of the first linear periodic wave is greater than an amplitude of the second linear periodic wave, wherein each of the first linear periodic wave and the second linear periodic wave is a triangular wave or a sawtooth wave;
• determining whether a level of the input signal is less than a light load threshold,
• when the level of the input signal is less than the light load threshold, generating the output PWM signal according to a comparison between the input signal and the second linear periodic wave;
• and
• when the level of the input signal is greater than the light load threshold, generating the output PWM signal according to a comparison between the input signal and the first linear periodic wave;
• wherein there is a common mode non-zero offset between a common mode level of the second linear periodic wave and a common mode level of the input signal, so that a root mean square (RMS) power of the output PWM signal when the level of the input signal is less than the light load threshold is less than a RMS power of the output PWM signal when the common mode offset is zero.