High Fidelity Switching Audio Amplifiers Using TMOS Power MOSFETs

Almost all switching amplifiers operate by generating a high frequency square wave of variable duty cycle. This square wave can be generated much more efficiently than an analog waveform. By varying the duty cycle from 0 to 100%, a net dc component is created that ranges between the negative and positive supply voltages. A low pass filter delivers this dc component to the speaker. The square wave must be generated at a frequency well above the range of hearing in order to be able to cover the full audio spectrum from dc to 20 kHz. Figure 1 shows a square wave generating a sine wave of one–ninth its frequency as its duty cycle is varied.