PROPERTIES AND APPLICATIONS OF n-p-tl TRANSISTORS 



547 



The Grounded Emitter Stage 



For many applications the grounded emitter connection is more desirable 

 than either of the other two. The power gains which can be obtained are 

 high — of the order of 50 db — and the interstage coupling problem is sim- 

 plified by the fact that the input impedance is somewhat higher than that 

 of the grounded base stage while the output impedance is very much lower. 

 The input impedance may be of the order of a few hundred ohms and the 

 output impedance of the order of a few hundred thousand ohms. Both volt- 

 age and current amplification are produced (with a phase reversal) and 

 gains of the order of 30 db or more per stage can be obtained without the 



i^mLe 



Fig, 16 — The grounded emitter connection of a transistor and the equivalent circuit 



use of interstage coupling transformers. The input and output impedance- 

 depend very critically on a and may vary appreciably from unit to unit 

 For this connection, which is indicated schematically in Fig. 16, 



-^11 = Te -\- Tb = 266 ohms 



^12 = Te = 25.9 ohms 



i?2i = Te- rm= -13.1 (10)« ohms 



R22 = re-\- Tc- rm = 0.288 (10)« ohms 



(31) 



Putting these values into equation (8) shows v^ is always opposite in sign 

 compared with Vg , that is, that the grounded emitter stage produces a 

 phase reversal as does the grounded cathode vacuum tube. 



If Rl is infinite and Rn = 



V2 = r, 



Te — r„ 



= -4.93 (10)' V, 



