Class-D Amplifier circuits

• Main Authors: Toru Ido, John Paul Lesso
• Format: Patent
• Language: English
• Published: 13.06.2018
• Subjects: AMPLIFIERS; BASIC ELECTRONIC CIRCUITRY; ELECTRICITY

A class-D amplifier circuit includes an output stage 101 having at least first and second switches, a modulator 104 and a frequency controller 301. The modulator has a switching cycle frequency based on a received first clock signal FIN, and controls the duty cycles of the first and second switches within the switching cycle based on a received input signal, e.g. audio. In response to an indication of the amplitude of the input signal, which may be from the input signal SIN, volume control VOL, envelope value, or modulator output (Fig.16), the frequency controller controls the first clock signal to provide first and second switching frequencies fSW, where a lower switching frequency is provided at the second, lower, input signal amplitude. The controller implements the transition between switching frequencies over a period of time (Fig. 9a), applying a gradual rate of change of switching frequency at the beginning and end of a transition and an increased rate in the middle, e.g. sinusoidal (Fig. 9b). Switching losses in a class-D audio amplifier are reduced by reducing the switching frequency at low signal amplitudes, and output signal transients caused by a switching frequency transition are reduced using a gradual or smoothed rate of change.