546 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



From equations (12) and (13), the matched input and output impedances 

 are approximately 



Rim = (re + n) \/l — an/ (re + n) 

 = 91 ohms 



(27) 

 (28) 



Rom = (fc + fb) Vl — arb/(re + ri) 

 = 4.58(10)« ohms. 

 With matched impedances, the maximum available gain is 



M.A.G. = ^^'"^ + ''^ [1 + Vl - an/ire + n)]-' , , 



^e + n (29) 



= 2.7 (10)' or 44.3 db. 



The matched output impedance of this stage is inconveniently high but 

 a useful amount of gain can be maintained if Rl is reduced to a more rea- 



\fr- 





Fig. 15 — One practical arrangement of a grounded base amplifier stage. 



sonable value. For example, if Rl = 200,000 and Ry = 25, equation (9) 

 gives 



G = 5.3 (10)3 or 37.2 db. 



If stages of this sort are to be cascaded, a step-down transformer must 

 be used to couple each collector to the following emitter. Otherwise, since 

 the current amplification factor of the transistor is slightly less than unity, 

 the gain per stage will also be slightly less than unity. 



One practical arrangement of a grounded base stage would be as shown 

 in Fig. 15. The required value of R will be approximately 



li = ^' (30) 



where h is the desired collector current and Ebi is the voltage of the emitter- 

 bias battery. For operating at /c = 1 ma, for example, £«i = 1.5 v and 

 R = 1500 ohms would be suitable. 



