Charge-driven HF transistor-tuned power amplifier

A new approach to the design of HF transistor-tuned power amplifiers is proposed that uses the concepts of charge control. A circuit arrangement and design technique is described that allows the performance of tuned power amplifiers operating at high frequencies to be specified and predicted accurately. The collector current of a transistor is, within limits, proportional to the charge stored in the base. A technique is described that defines this stored charge by a sinusoidal drive voltage across a capacitor in series with the base. Sinusoidally varying charge in phase with the drive voltage is injected into the base and approximately forms a truncated sinusoid of collector current with a predictable and controlled conduction angle and height. Dynamic collector characteristics are described that relate the stored base charge to the collector voltage and current. From these, or by direct measurement, are obtained dynamic constant current curves that are plotted on the graph of base charge versus collector voltage. This graph enables the collector current pulse shape to be predicted, and thus the difficult design problem where the collector current pulse shape is unknown is overcome. An amplifier is designed using this technique, and design and experimental results are in good agreement.