A Class E Power Amplifier with Low Voltage Stress

A new output structure for class E power amplifier (PA) is proposed in this paper. A series LC resonator circuit, tuned near the second harmonic of the operating frequency is added to the output circuit. This resonator causes low impedance at the second harmonic. The output circuit is designed to shape the switch voltage of the class E amplifier and lower the voltage stress of the transistor. The maximum switch voltage of the conventional class E PA is 3.56Vdc. However, higher switch voltage of about 4.5VDC may be occurred, by considering nonlinear drain-to-source capacitance in class E PA. The obtained peak switch voltage of the designed class E PA is approximately 75% of the conventional one with the same conditions, which shows a significant reduction in peak switch voltage. MOSFET parasitic nonlinear gate-to-drain and nonlinear drain-to-source capacitances of the MOSFET body junction diode also affect the switch voltage in class E PA, which are considered in this paper. The actual MOSFETs have these parasitic capacitances; therefore, it is necessary to consider these elements in the design procedure. Reduced switch voltage in class E PA relaxes the breakdown voltage constraints of the active device. In the switch voltage of the designed circuit, the zero voltage and zero derivative switching (ZVS and ZVDS) conditions are satisfied. Simulation of the presented circuit is performed using PSpice and LTspice softwares. For verification of the designed circuit, the presented PA is fabricated and measured.