Analysis of high-Q Class-E power amplifier, rectifier and amplitude modulator

The effects of component variations on a high-Q Class-E amplifier are analyzed, simulated and measured. Design equations are provided for the case of a 50% duty-cycle signal driving the switch, with the shunt capacitance at its optimum value for a given output resistance. Several distinct operating points are analyzed for the output network. The problem of tuning a high-Q Class-E amplifier is addressed. Normally, it cannot be tuned for maximum output power without degrading efficiency. A circuit modification is made to the design so that it can be tuned for maximum output power in order to achieve optimum efficiency. Measured data is obtained at low frequencies for an amplifier with a loaded Q of 340.; The analysis is then used to design and build a 30 MHz Class-E DC-DC converter with a loaded Q of 12.5 for use as a high-level amplitude modulator. An analysis is performed for the case of output network tuning and for the case of variable frequency tuning. Theoretical results are presented showing the trade-offs involved between efficiency, loaded Q, voltage stress to the components, and the output network tuning range. The dynamic response of the DC-DC converter is measured by applying a unit-step change to the value of the output network tuning capacitor. This confirms that the control-to-output transfer function contains a RHP zero. For the first time, a theoretical equation is derived that predicts the amount of frequency-shift tuning required versus the loaded Q to vary the output power by a specific amount. The amplitude modulator is operated at a switching frequency of 30 MHz and a power level of up to 16 W. The effect of the REP zero on dynamic performance is experimentally tested using modulation frequencies from 20 kHz up to 500 kHz.