Principles of Analog Electronics

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 Figure11.56, 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 ...