Series-shunt Feedback Amplifier Explained: Computing Voltage Gain & Impedances

How to find closed-loop Gain and impedances of (Voltage-Voltage) Series-Shunt Feedback Amplifier Circuit are discussed in this series-parallel Feedback Amplifier Tutorial using a cascade of BJT transistor example. This feedback voltage amplifier is implemented with two stages of NPN Bipolar junction transistors that are biased in the active region. For more examples see the analog circuits and feedback amplifier videos playlist Electrical Engineering, Analog, Digit... . This Series-Shunt Feedback Amplifier Tutorial starts with evaluating the Negative Feedback throughout the circuit and identifying the open loop amplifier and feedback circuit network. Then the DC bias analysis is presented to find the quiescent points or the steady-state DC voltages and currents of the BJT transistors to find the value of AC parameters of the BJT transistor hybrid model (including hie or base ac impedance which is thermal voltage VT divided by the Base current of the BJT transistor).  These parameters are then used to find the overall open-loop AC gain and feedback factor Beta of the circuit to find the loop gain of the amplifier and then the closed-loop gain of the feedback network. Both input impedance and output impedance with and without feedback are computed as well.

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