Analysis and Study of the Duty Ratio Effects on the Class-EM Power Amplifier Including MOSFET Nonlinear Gate-to-Drain and Drain-to-Source Capacitances

Abstract

In this paper, the effects of the duty ratio variation on the class-EM power amplifier are studied and analyzed, including nonlinear gate-to-drain and drain-to-source parasitic capacitances. The duty ratio is one of the important parameters in class-EM power amplifiers, which has high effects on the switch voltage and current waveforms, output power, efficiency, power loss, and output phase shift. To achieve a better agreement between theoretical and experimental results, the nonlinear gate-to-drain and drain-to-source parasitic capacitances are included in theoretical analysis. To demonstrate the validity of the presented analysis, five class-EM power amplifiers are designed, simulated, fabricated, and tested using IRF510 mosfet with the duty ratio equal to 0.5, 0.6, and 0.7 and IRFZ24N mosfet with the duty ratio equal to 0.5 with and without considering mosfet nonlinear capacitances. It is shown that the amplifier with IRFZ24N mosfet has higher efficiency than that with IRF510 mosfet . This is because of the lower drain-to-source on-state resistance of the IRFZ24N mosfet . The obtained efficiency with IRFZ24N mosfet considering nonlinear capacitances at the operating frequency of 3.5 MHz was 95.7%. The obtained output power for IRF510 and IRFZ24N mosfet s at the duty ratio equal to 0.5 was 14.41 and 17.82 W, respectively. Simulation and theoretical results are performed using PSpice and MATLAB, respectively. The theoretical results and PSpice simulations agreed with experimental results.