SUM/-: ClRCl IT A.Sl'KCTS Oi Till'. TR.WSISTDK 



5H5i 



dilations; but one can normally count on stable gains of 15 to 20 db per 

 stage, the transformers being perhaps somewhat mismatched. 



Interesting possibilities for a good cascade amplifier with more gain than 

 the grounded base cascade are offered by the grounded emitter connection, 

 incidentally, this gain advantage is also enjoyed by the grounded cathode 

 or conventional tube connection, so that one would exi>ect it to apply here 

 from the electron tube analogy; but in transistors the feature that a may be 

 greater than 1 brings in complications having no simple analogy for tubes. 



Without feed back (<-j^i2 = 0) : 

 Iterative impedance Rg = fJvsi . -^l = fivu 

 Circuit determinant A = (^u + 9^22)^ 



R21 \^ 



Insertion Power Gain Gj = 





Nominal Tj'pe A Gain = S""* 



Fig. 17 — Synojisis of grounded laase cascade. 



The iterated grounded emitter cascade without feedback (that is, emitter 

 resistance Vo = 0) is unstable for the nominal Type A transistor, but can be 

 stabilized in many ways of which we shall mention only one. The equivalent 

 circuit of Fig. 19 shows an added resistor which may be thought of as ad- 

 justing the value of the collector resistance, and tends to make the unit 

 more stable. When this resistor is adjusted to make the total collector 

 resistance Re about equal to the net mutual resistance fm, thus reducing 

 the effective value of a to the neighborhood of unity, then the cascade am- 

 {)lifier becomes stable, its gain being sensitive to the e.xact value chosen for 

 the adjusting resistor. A numerical calculation for the grounded emitter 



