The feedback resistor Rf is used to prevent the DC gain from becoming infinite, given that the capacitor is an open at DC. From: Embedded System Interfacing, 2019.

Positive or regenerate feedback: • In positive feedback, the feedback energy (voltage or currents), is in. phase with the input signal and thus aids it. Positive feedback increases gain of the amplifier also increases distortion, noise and instability.

A circuit method that is very important for linear amplifiers is called feedback. Feedback means taking a fraction of the output wave of an amplifier and connecting it to the input. This fed-back signal can be connected so that it either adds to the normal input or subtracts from it (Figure 4.11).

If the feedback signal (A_V × B × V_out) has the same phase as the V_IN signal, the amplifier circuit has positive feedback. If the feedback signal has the opposite phase to the V_IN signal, the amplifier circuit has negative feedback.