A STUDY OF CLASS C APPLICATIONS OF POWER TRANSISTORS AT HIGH AND VERY HIGH FREQUENCIES
STANFORD UNIV CA STANFORD ELECTRONICS LABS
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The operation of power transistors in Class C amplifiers at high and very high frequencies is considered. At the lower end of this frequency range, static characteristics are an appropriate basis for the analysis. Two analytic methods and one graphical method of analysis are developed for the nonsaturating case. These methods present the output power, efficiency, and power gain as functions of the operating conditions. By plotting these quantities as contours on peak collector current - flow angle coordinates it is possible to optimize the design. Operation into saturation is examined and equations developed for this case. It is shown that significantly better results can be obtained for this mode of operation. Very high frequency operation is next examined. The various factors affecting such operation are explained and an approximate analysis developed based on an analogy to an RC transmission line. A new method of simulation of a transistor is presented based on the excess charge-density two-lump model. It is shown how this method can be applied to simulate operation in saturation and to account for the major nonlinearities and two-dimensional effects present in a transistor. Test results are presented for a single two-lump approximation for a vhf power transistor operating as a Class C amplifier.
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