The Class D amplifier, with reference to its use as an oscillator

This thesis examines the Class D tuned amplifier, emphasizing the factors which govern its use as a Class D power oscillator. The relative merits of the voltage-switched and current-switched modes for use in an oscillator are discussed. The most desirable properties are exhibited by the current-switched mode, therefore the current-switched amplifier is examined as a basis for the oscillator circuit. A comparison of sinusoidal drive and quasi-voltage drive for the current-switched amplifier illustrates the improved collector current rise time capability of the quasi-voltage drive. Factors such as saturation voltage, base storage time, current rise time, and passive collector circuit components are investigated to determine their effect on the overall efficiency of the quasi-voltage driven amplifier. It is shown the effect of long storage time may be neutralized by delay time and that rise and fall times are short and relatively unimportant. Saturation voltage and tuned circuit losses are shown to present the major efficiency limitation both at higher powers and higher frequencies. It is demonstrated that the phase lag caused by storage time and rise time must be compensated if the Class D oscillator is to be efficient.