Class-D amplifier circuits

摘要

Methods and apparatus for Class-D amplifier circuits with improved power efficiency. The circuit has an output stage with at least first and second switches and a modulator that receives an input signal to be amplified, SIN, and a first clock signal fSW. The modulator controls the duty cycles of the first and second switches, within a switching cycle based on the input signal, wherein the switching cycle has a switching frequency based on the first clock signal. A frequency controller controls the frequency of the first clock signal in response to an indication of the amplitude of the input signal so as to provide a first switching frequency at a first input signal amplitude and a second, lower, switching frequency at a second, lower, input signal amplitude. A lower switching frequency can be tolerated at low signal amplitudes and varying the switching frequency in this way thus maintains stability whilst reducing switching power losses.

主权项

1. A Class-D amplifier circuit for amplifying an input signal comprising: an output stage comprising at least first and second switches;
a modulator comprising a signal input for receiving said input signal and a clock input for receiving a first clock signal, the modulator being configured to control the duty cycles of said first and second switches within a switching cycle based on said input signal, wherein said switching cycle has a switching frequency based on said first clock signal; and a frequency controller for controlling the frequency of said first clock signal in response to an indication of the amplitude of the input signal so as to provide a first switching frequency at a first input signal amplitude and a second, lower, switching frequency at a second, lower, input signal amplitude; wherein said modulator comprises a reference waveform generator for generating a reference waveform at a frequency based on said first clock signal; wherein said reference waveform generator is configured such that the amplitude of the reference waveform is substantially the same at said first and second switching frequencies; and wherein said frequency controller is configured to generate a gain control signal indicating any changes in said switching frequency and the reference waveform generator is configured to receive the gain control signal and adjust a slope of the reference waveform based on said gain control signal to compensate for any change in switching frequency.