These are positive or regenerative feedback and negative or degenerative feedback (Ellinger, 2008). The different between the two types of feedback entails whether the feedback signal is out of phase or in phase with an input signal.
Positive or Regenerative feedback is said to occur whenever the feedback signal happens to be in phase with an input signal (Maas 53). The block diagram below shows an amplifier having a positive feedback. It can be deduced from the diagram that the input signal and the feedback signal are in phase implying that the feedback signal regenerates or adds the input signal. Following this, there occurs somewhat larger amplitude in the output signal that it could occur without there being the feedback.
Considering a positive feedback in the transistor amplifier, it is noted that it is somewhat simple providing a positive feedback in the common-base transistor amplifier. Given that the output and the input signals are both in phase, what one requires to do is to couple a section of the input signal back to an input. The block diagram below shows these phenomena. Basing on this diagram, it is clear that the feedback network is constituted by C2 and R2, with the value of C2 being larger in order for the capacitive reactance labelled XC to become low and to enable the capacitor to be able to couple the signal quite easily. Moreover, the value of the resistive R2 must be larger in order for it to limit the amount of feedback signal, as well as in ensuring that the majority of an output signal is connects to the next stage via C3.
As widely cited, the common-emitter configuration is one of the most common configurations for the transistor amplifiers (Maas 34). However, a positive feedback seems to be somehow more difficult with the common emitter configuration since in most cases, the output and input signals are often 180º out of phase (Maas 46).
Negative feedback, on the other hand, is often achieved through adding part of