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BELL SYSTEM TECHNICAL JOURNAL 



Fe = 250 ohms, rb = 250 ohms, To = 20,000 ohms, rn, = 40,000 ohms, so 

 that a = 2 and both base and emitter resistances r,, and rb are negUgible. 



tube analogy - grounded plate 

 (cathode follower) 



EQUIVALENT CIRCUIT 



Equations: 



Circuit determinant 



Input impedance 



Output impedance 



Operating Gain 



ii{Ra + rb + re) + h{rc — fm) = iig 

 i\ re + «2(i?L -]rri + rc — r„^ = vl 



^ = {Ro+ n+ Tc){Ri. + r, + r, - ;-.„) + ;>(;•„, - ;v) 

 > for stability 



Rn == rb + re + 



rdrm — re) 



/?22 = I't + re — rm + 



Rl + re + re - r, 



Teirm — re) 



Ro + rb + re 



Backward Operating Gain Gr = ^ R 

 Typical values: 





= (1 - o)^G^ 



For Rg = 20000", Rl = 10000" 

 Then Rn = -41000" 



i^j, = -7600" 



Gp = IS-** 



Gh = \i'"' 



Fig. 11 — Synopsis of grounded collector amplifier 



Working l)et\veen 20,000-ohm terminations, such an umplilier should have 

 6 db power gain in both directions and should still be stable even if one of 

 its terminations changes 50% in the unfavorable direction. 



