Push-Pull Class $\Phi_2$ RF Power Amplifier

The Class $\Phi_2/\text{EF}_2$ amplifier is an attractive topology for high-voltage and high-frequency power conversion because of the high efficiency, reduced device voltage stress, simplicity of gate driving, and load-independent ZVS operation. Due to many degrees of freedom for tuning, previous studies can only solve the single-ended $\Phi_2$ circuit using numerical methods. This work focuses on improving the design and operating characteristics of a push-pull $\Phi_2$ amplifier with a $T$ network connected between the switch nodes, or a PPT $\Phi_2$ amplifier. The PPT $\Phi_2$ amplifier has less circulating energy and achieves higher cut-off frequency $\mathcal{f}_T$ than other $\Phi_2/\text{EF}_2$ circuits. We then present a series-stacked input configuration to reduce the switch voltage stress and improve the efficiency and power density. A compact 6.78 MHz, 100 V, 300 W prototype converter is demonstrated that uses low-cost Si devices and achieves 96% peak total efficiency and maintains above 94.5% drain efficiency across a wide range of voltage and power. Together with the advances in wide-bandgap semiconductors and magnetic materials, the PPT $\Phi_2$ circuit opens more possibilities for the state-of-the-art performance of solid-state RF amplifiers in high-frequency, high-power applications, including wireless charging for electric vehicles, plasma RF drives, and nuclear magnetic resonance (NMR) spectroscopy.