Page 325 - Build Your Own Transistor Radios a Hobbyists Guide to High-Performance and Low-Powered Radio Circuits

+V IF Tlransformer

с
~ : IF Signal

0 .1 uf ,J А

Т2

СсЬ

+ Vbias
С Ьур

Q1 м

2 го

(e.g "12N3904)
IF Transformer ~
V E
5_ _1

6 L С

8 4
Т1 m RE

Note: IF Tгansfoгmeг Тl Secondaгy has inductance L
and IF Tгansfoгmeг Т2 has ап inteгnal capacitoг.

FIGURE 17-38 Common-baseamplifier that was used in General Electric
transi$tor radio$ in the 1960$.
In а common-emitter amplifier, as seen in Figure 17-28, the feedback capacitance
СсЬ along with inveгting voltage gain -А = -gmRL at the collectoг foгms а M il leг
capacitance fгom the base of Ql to gгound. This Milleг capacitance is equal to

СсЬ(l + А) = Cin
from the base to ground. Thus the Mi lleг capacitance is а result of capacitance
multiplication. Note that there will befuгther dеsсгiрtiоп of the Miller capacitance in
Chapter 19. However, in а common-base amplifier, as shown in Figure 17-3В, there

is по Miller capacitance because the base is grounded, and the input terminal is at
the emitter. Note: The gain, А, is the magnitude of the inverting gain and А is
positive.
In Figure 17-3А, the common-base amplifier isdriven Ьу the secondary winding of
а parallel-tuned ciгcuit. То preseгve а геаsопаЫе amount of Q > ЗО, the step-down