1-23
Figure 1-20A.—Decoupling (bypass) capacitor in a transistor amplifier.
Figure 1-20B.—Decoupling (bypass) capacitor in a transistor amplifier.
Regardless of the method used to provide positive feedback in a circuit, the purpose is to increase the
output signal amplitude.
Negative Feedback
Negative feedback is accomplished by adding part of the output signal out of phase with the input
signal. You have seen that an emitter resistor in a common-emitter transistor amplifier will develop a
negative feedback signal. Other methods of providing negative feedback are similar to those methods
used to provide positive feedback. The phase relationship of the feedback signal and the input signal is the
only difference.
Figure 1-21 shows negative feedback in a common-emitter transistor amplifier. The feedback
network of C2 and R2 couples part of the output signal of Q1 back to the input. Since the output signal is
180º out of phase with the input signal, this causes negative feedback.
