Electronic Circuit Analysis

Multistage Amplifiers 43
Example : 2.4
An amplifier has ~ = O.SKQ and Ro = O.OSKQ. The amplifier gives an output voltage of 1 V peak for
an input voltage of 1m V peak. Find Av, Ai' Ap in db.
Solution:
V 0 (peak) = I V.
Vo (rms) =
VO(peak)
.fi
IV
Yo (rms)= .fi
Pv ~ 20 log [~~ )
= 2~ log (.~Y) = 60 db
~i (peak) = Yi (Peak) / Ri
= ImY/SOO
= 2 x 10- 6 A.
10 (peak) = YO (Peak) / RO
= 1ISO
10 (Peak) = 0.02 A.
0.02 )
.. Current Gain (Ai) = 20 log ( 2xlO- 6 = 80 dl'
y2
p. = _I = 10-9 W.
I R
j
,
Y02
Po = R = 1O- 2 W.
o
Power gain,
Ap ~ 10 log [:~ ) ~ 70 db
2.2 n - Stage Cascaded Amplifier
2.2.1 Overall Voltage Gain
The resultant voltage gain is given by the product of the individual voltage gains of each stage.
Y 2
AVI = V =A 1 L. 9 1
I