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BELL SYSTEM TECHNICAL JOURNAL 



emitter if the latter is arranged to emit anomalous charge carriers, that 

 is, carriers of the sign not normally present in the interior of the material. 



Equivai.kntt Circuits 



As has been explained by liardecn, Bratlain, and Shockley, many features 

 of the transistor are nicely explained by this picture of its action; but, for 

 present purposes of circuit analysis, we shall now take the purely empirical 



EQUIVALENT CIRCUIT 



Equations 



/■l'g21 + t2Cg22 + Z^) = 



Circuit determinant A = C^u + Zg)(^i2 + Zl) — %-^-ii 



Input impedance Zu = '%u — 



Output impedance Z22 = ^22 — 



Operating power gain Go = ^RgRl 



?22 + Zl 



?ii + Zg 



A 1 



(Zg + Zl)% 



Insertion power gain G\ = 



Fig. 3 — Synopsis of general four-pole — imjiedancc analysis. 



view and regard the transistor as a black box whose performance is to be 

 determined by electrical measurements on its terminals. 



A picture of a black box is shown in Fig. 3 along with the equations de- 

 scribing it. The performance is completely characterized if one knows the 

 voltage and current at each of the two pairs of terminals. Now, of these 

 four variables, only two are independent since, if any two are fixed, the other 

 two are determined. One can therefore describe the network in terms of 

 any two variables and, since there are six possible ways to choose a pair of 

 variables from a set of four, there are sk ways of describing the network. 



To recall what is done for electron tubes is helpful. In the case of a triode 



