Amplitude modulator utilizing a high-Q Class-E DC-DC converter

Abstract

A high-level amplitude modulator is designed and tested utilizing a high-Q Class-E DC-DC converter operating at a nominal switching frequency of 30 MHz. The output power is a maximum of 16.1 W and the efficiency is as high as 77.9%. The switching frequency is varied to control the output amplitude of the modulator. It is shown theoretically that the maximum useful dynamic range is 12.0 dB. An equation is derived that predicts the amount of frequency variation necessary to vary the output amplitude by a specific amount, based on the loaded Q of the circuit design. A RHP zero in the control-to-output transfer function is shown to have a detrimental effect on the modulation frequency to switching frequency ratio. The modulator is used to generate a DC-offset triangle-wave at frequencies as high as 500 kHz.