
Principles of Analog Electronics
436
11.10 BIAS STABILITY
It is necessary that the quiescent Q-point, determined in DC conditions by the bias
network, be as stable as possible to guarantee that the BJT is always working in
the active region, regardless of the boundary conditions (for example, variations of
the parameters of the components caused by changes in temperature). If not, that
point could “move” from Q
1
to Q
2
for instance, as represented in Figure11.56, and
the output signal could be clipped.
The bias stability can be represented by the request to maintain a xed DC col-
lector current I
CQ
. However, this current can change quite rapidly ...