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BELL SYSTEM TECHNICAL JOURNAL 



to cathode, base to grid, and collector to plate; the conventional or grounded 

 cathode tube connection is therefore analogous to the grounded emitter 

 connection of a transistor, shown on Fig. 10. It is found that when a = \ 

 the analogy is fairly close, in that the transistor has comparatively high- 



TUBE ANALOGY- GROUNDED CATHODE 



EQUIVALENT CIRCUIT 



Equations: 



Circuil determinant: 



Input impedance 



Output impedance 



Operating Gain 



hiRc + rh + /-,) + h}\ = I'G ■ 



h{r, - Ym) + HRl + /-. + ;-c - r,n) = 



A = (/?G + rt + }\){Rl + i\ + Tc - /-„,) + r,{r,„ - r.) 

 > for stability 



Ru = n + r,+ 



re + r, — Ym + 



Rl + r^ + re - r„ 

 r,(rm — r,) 



Gf = 4 



"•'<^') 

 '•(*} 



Ra + Tb-^r, 



Backward Operating Gain Gr = 4 R 



Typical values: For Ra = 500'^, R, = 20000"'. Then Rn = 21 00-, R-^-i = -6900-, Gy = 

 ' 24'"', Gh= - 19'"' 



Kig. 10 — Synoi)sis of grounded emitter amplifier. 



input impedance, high-output imjK'dance, and changes signal polarity in 

 transmission. When a > 1, as is usual, the analogy becomes less close, and 

 feedback effects tend to become large and obnoxious; the open-circuit 

 output impedance is usually negative. This behavior is readily under- 



