D.C. Analysis of Differential
Amplifier
The d.c.
analysis means to obtain the operating point values i.e. I Cq and V CEQ
for the transistors used. The supply voltages are d.c. while the input signals
are a.c., so d.c equivalent circuit can be obtained simply by reducing the
input a.c. signals to zero. The d.c. equivalent circuit thus obtained is shown
in the Fig.. Assuming Rs1 = R S2, the source resistance
is simply denoted by Rs ,
The
transistors Q1 and Q 2 are matched transistors and hence for such a
matched pair we can assume :
i) Both the
transistors have the same characteristics.
ii) R E1
= R E2 hence R E= R E1ll R E2.
iii) R C1
= R c 2 hence denoted as R C.
iv)lVCCI
= lVEE I and both are measured with respect to ground.
As the
two transistors are matched and circuit is symmetrical, it is enough to find
out
operating
point I CQ and V CEQ, for any one of the two transistors.
The same is applicable for the other transistor.
Apply-g
KVL to base-emitter loop of the transistor Q1
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