Class-D Power Amplifier with RF Pulse-Width Modulation

Single-ended (monopolar) and push-pull (bipolar) power amplifiers (PAs) are based upon complementary class-D PAs. The radio-frequency pulse-width modulation (RFPWM) waveform is produced in software and downloaded to a programmable-waveform generator. The PAs operate at 500 kHz and produce peak outputs of 100 W (monopolar) and 187 W (bipolar) with 85-percent efficiency. These amplifiers exhibit excellent linearity; IM products for single-tone AM and two-tone signals are about 40 dB below the desired sidebands. High efficiency is maintained over a dynamic range of 13 to 15 dB. This results in average efficiencies of 84 percent for signals with peak-to-average ratios up to 6 dB and 80 percent for a peak-to-average ratio of 10 dB. RFPWM also produces a clean output spectrum in which the spurious products are well removed from the desired signal.