Unless otherwise indicated, the foregoing is not admitted to be prior art to the claims recited herein and should not be construed as such.
Switching amplifiers, such as Class-D audio amplifiers, offer high efficiency operation due to the use of switching output stages. Accordingly class-D amplifiers are commonly used for audio presentation in portable device applications such as MP3 players, smartphones, computer tablets, and other battery operated devices, where power efficiency is an important consideration. DC offsets inherent in the amplifier circuits comprising class-D amplifier designs, however, impact their effectiveness in portable devices. DC offsets manifest themselves audibly as clicks and pops in the audio output, which can negatively impact the user experience; and DC offsets tend to increase quiescent power consumption, which can negatively impact power performance.
Typical class-D amplifier designs use a 3-state pulse width modulation (PWM) modulator. The 3-state PWM modulator allows for filter-less designs, thus avoiding the cost of reconstruction filters in terms of silicon area on the chip. 3-state PWM modulators, however, can suffer from cross-talk between the plus and minus PWM channels. The cross-talk can arise from coupling with comparators in the PWM modulator design or between the comparators and the output stages of the PWM modulator. Cross-talk can degrade the total harmonic distortion (THD) characteristics of the class-D amplifier caused by PWM misfiring due to the cross-talk.