Fundamental study on drain efficiency of EPWM transmitter
using class-EM Power amplifier <Abstract> Drain efficiency of EPWM (envelope pulse width modulation) transmitter composed of a class-E_M amplifier is evaluated by circuit simulation, and the pulse modulation method to the constant envelope RF signal by PWM pulses is studied. The E_M amplifier, which is composed of a class-E amplifier and a auxiliary circuit reducing its switching loss during turn-off, is designed normally for continuous wave. Each transistor is modeled with an ideal switch and an on-resistor, where the drain-source capacitance is modeled as a linear one together with the shunt capacitor. Simulation results show that the conventional PWM switching method gating the input RF signal produces unnecessary transient responses making the drain voltage rise and the output signal distorted: the efficiency is degraded. Another method that gates the DC supply voltage by the PWM pulses works as expected and intended, and the result shows the drain efficiency as high as that of an E_M amplifier in case of CW signal. |