Power gain and bandwidth of tuned transistor amplifier stages

Relationships between operating power gain and bandwidth of an active four-pole network are developed, with particular reference to single-stage tuned transistor amplifiers. The power gain is first investigated in terms of Stern´s stability factor, k, the maximum gain for a given value of k being derived by analytical-numerical means without recourse to graphical procedures. It is then shown that the power gain is more fundamentally expressed in terms of a new performance factor, n, and in particular that for large values of n (corresponding to k ¿ 1) the product of maximum power gain and n approaches an invariant, independent of the set of four-pole parameters selected for design purposes. The power gains of amplifier stages with and without unilateralizing feedback are expressed and related in terms of the performance factor, and the conditions under which the latter possibility gives higher gain are indicated. Analytical procedures and expressions for the evaluation of the bandwidth of tuned amplifier stages are presented and the conditions for maximum power gain at a given bandwidth are investigated for amplifiers with and without unilateralizing feedback. Computed results for the performance of a particular high-frequency transistor in the common-base and common-emitter configurations verify the main conclusions of the analysis and indicate the relative merits of the two configurations in regard to power gain with and without feedback applied. It is seen that for bandwidths up to a certain value a simple mismatched stage without feedback is advantageous.