RF Power Amplifier, 2nd Edition

4.9 Class D RF Power Amplifier with Amplitude Modulation

A circuit of the Class D power amplifier with AM is shown in Fig. 4.18. The modulating voltage source is connected in series with the dc supply voltage . AM can be accomplished in the Class D amplifier because the amplitude of the output voltage is directly proportional to the dc supply voltage . Voltage waveforms that explain the AM process are depicted in Fig. 4.19. The modulating voltage waveform is given by

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The AM voltage waveform across the bottom switch is

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Since

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the AM voltage waveform across the bottom switch is

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It can be seen that the fundamental component and the odd harmonics of the voltage across the bottom MOSFET (i.e., at the input of the resonant circuit) are modulated in amplitude. The amplitudes ...