Common Feedback Topologies

Depending on the type of sampling and mixing networks, the feedbacks are classified into four categories. These are also known as feedback topology.

1. Voltage series feedback 
2. Voltage shunt feedback or Parallel voltage feedback 
3. Current series feedback 
4. Current shunt feedback or Parallel current feedback 

FeedBack Topology

1. Voltage Series Feedback: Input resistance of the amplifier and feedback network are in series and Output resistance of the amplifier and feedback circuit are in parallel, hence effective input resistance will increase and effective output resistance of the feedback amplifier will reduce. A block diagram of Voltage series feedback is drawn in figure (a).
2. Voltage shunt feedback: Output resistance of the amplifier and output resistance of the feedback circuit are in parallel and similarly overall input resistance of the feedback amplifier will reduce due to parallel connection of amplifier.  A block diagram of voltage shunt feedback or Parallel voltage feedback  is drawn in figure (b).
3. Current series feedback: Output resistance of the amplifier and feedback circuit are in series and input resistance of the amplifier and feedback network are in series hence effective output resistance of the feedback amplifier will increase and input resistance will increase too. Thus Current series feedback circuit behaves like a voltage controlled current source.  A block diagram of current series feedback is drawn in figure (c).
4. Current shunt feedback: Effective output resistance of the feedback amplifier will increase. Effective input resistance will decrease. Thus current shunt feedback circuit behave like a current controlled current source.  A block diagram of Current shunt feedback or Parallel current feedback is drawn in figure (d).