560 THE BELL SYSTEM TECHNICAL JOURNAL, JXJLY 1951 



sponds to a gain-bandwidth product of 1.2(10)^ cps and shows that useful 

 gain could be obtained at frequencies well above a megacycle, provided 

 alpha and emitter cutoffs did not interfere. 



Collector Cutoff in the Grounded-Emitter Stage 

 The procedure described in the last section leads, in this case, to 



"'^"'~'r.+ {n + R,){l-rJr.) ^^^^ 



+ IreRL/rc + in + R,){re + i^JAcld + JTcCcCc) 



For the transistor of our numerical example, the imaginary term in the 

 numerator is completely neghgible at frequencies below (10)^ cps. Neglecting 

 it leads to 



r ^ J_ 1 + Rl/tc + [{n -f- Ra)/re][l - {rm - re - RL)/re\ ,^2) 

 •^'^'^ 2irCe Rl + [{n + Ra)/re](re + Rl) 



In this case the values of Rg and 7^^ (619 ohms and 671,000 ohms respec- 

 tively) which correspond to maximum available gain give 



fee = 3740 cps and 

 M.A.G. = 53 db. 

 Reducing R^ to 100,000 and increasing Rg to 1000 ohms gives 



fee = 11,120 cps 

 G = 50 db. 

 For Rg = 1000 ind Rl = 10,000, 



fee = 97,900 cps 

 G = 41.3 db. 

 and for Rg = R^ = 1000 ohms, 



fee = 943,000 cps 

 G = 31.4 db. 



The gain-bandwidth product for this stage is 1.3(10)^ cps as compared to 

 1.2(10)* cps for the same transistor connected as a grounded base amplifier. 

 It should be pointed out, however, that this stage is particularly sensitive 

 to change in a and on this account alpha cutoff may influence the response 

 at fairly low frequencies. For example, when the terminating resistances are 

 both 1000 ohms, reducing a from 0.9785 to 0.900 reduces the gain from 

 31.4 db to 0.2 db. 



