Class-D GaN 15MHz-bandwidth amplitude modulator with a direct CMOS interface

Switching supply modulators are key in achieving reasonable energy efficiency in a polar amplitude modulating RF power amplifier. However, achieving good conversion efficiency, high tracking bandwidth and low switching harmonic feedthrough at high power are challenging to meet at the same time. GaN technology is a viable candidate for this task, but signal interfacing and level shifting at high switching rates can be difficult and power hungry. Here we present a 100MHz GaN switching, multi-stage, highly integrated class-D amplifier that can be driven with a single ended CMOS level PWM signal. It provides up to 3.5W of power with 83% efficiency and 15MHz Fourier-flat bandwidth with less than 20mVpp ripple.