Linearization of class D amplifiers

Signal dependent propagation delay and supply modulation are among the major sources of performance deterioration in class D amplifiers. More so in the case where the control of the common-mode EMI of a Class D amplifier utilizes DSP-based signal spreading techniques and requires the switching amplifier to be "linear" to avoid folding the high frequency spectrum into the audio band. This paper reviews the sources of nonlinearity and describes two original solutions based on analog feedback techniques for a 3W audio amplifier that were implemented in a 110 nm CMOS process.