THE EARTHED EMITTER TRANSISTOR 



ri2 = 



22 



L'54ut. 

 L ^^ut J 



(5/in = 



<5/i„ = 



77((? hybrid parameter system — Describes the transistor in terms of a 

 resistance, a conductance, and two ratios, as follows : 



^Kout^O 



dLr 







5F„„. = 



Hybrid parameters are sometimes used with a different set of subscripts, i.e. 



hi = /Jii 



hf = /»2i 



/'r = ^12 



77?e MuUard parameter system — By giving 5 parameters in all, so that 

 one is theoretically redundant, this system is in the author's opinion the 

 most useful of the 'black box' descriptions. The maximum current gain 

 and the limits of output and input resistance are at once evident. The 

 parameters are: 



a = 



dL 



in J 



dv. 



out 







11 



. <5/iii J (3/out 







in 



L^/inJ 



(3K„,„ = 



r^i — 



^out — 



_^/outJ<3/ir 







dV, 



out 



L^A)utJ 



dV„ 







Thus, in the earthed emitter mode, the Mullard parameter a' is the quantity 

 we have called |5. r^ is the input resistance when the load is infinite, and 

 is our R^ + 7?ft. r^^ is the input resistance when the load is zero, and is our 

 Rf, + y^R^ where y^ — /5. Similarly, r22 is the output resistance when the 



46— (12 pp.) 



693 



