816 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1956 



frequency? What impedance should it be supplied from? What impedance 

 should it feed? What gain will be obtained using a pair of impedances 

 different from the optimimi ones? The answering of these and related 

 (juestions amounts to establishing a convenient means of translating 

 the parameter values into the ciuantities of interest applying to the 

 amplifier. Such a convenient translating means for solving these problems 

 is described in this section. 



Earlier explicit solutions to special cases of the problem are well known. 

 Wallace and PietenpoP have given simple expressions in terms of the 

 transistor parameters for matching input and output impedances and 

 the maximum available gain when the transistor has purely real parame- 

 ters. An implicit solution for optimum source and load impedances for 

 maximum gain in the complex case has been known for a long time. It 

 is simply that the transistor be terminated at the input and output by 

 conjugate matching impedances. The implicit nature of this solution 

 arises from the fact that the input impedance is a function of the load 

 impedance, and the output impedance is a function of the source impe- 

 dance for transistors wdth internal feedback. The solution for optimum 

 source and load impedance from this approach amounts to the solution 

 of simultaneous quadratic equations with complex unknoA\nis and be- 

 comes involved. 



Fig. 2 — Two terminal impedance measurements for determination of two-port 

 parameters. 



^ R. L. Wallace and W. J. Pietenpol, Some Circuit Properties of n-p-n Transis- 

 tors, Proc. I.R.E., 39, pp. 753-67, July, 1951. 



