Transistor design for predictable power gain at maximum frequency |
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Authors: | McGregor JM Roulston DJ |
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Affiliation: | Dept. of Electr. & Comput. Eng., Waterloo Univ., Ont.; |
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Abstract: | Equations which define the neutral base width, collector doping, and epitaxial collector thickness of a bipolar transistor giving a specified unilateral power gain at the highest frequency, possible are derived. Emitter-base capacitance, emitter delay, emitter stripe width, base doping, and the operating base-collector voltage are assumed to be known and fixed. The hybrid-π equivalent circuit is assumed valid up to the transition frequency ft. Peak fmax (maximum oscillation frequency) is examined as a function of the collector doping. Maximizing fmax at all costs leads to a design with an ft which approaches zero. In designing a transistor, the two figures of merit must be traded off against each other. A simple expression giving maximum fmax/ft is derived and used to define the transistor design which gives some specified power gain at the highest possible frequency |
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