ch3-4

F.B types
There are four basic types of feedback amplifier:
1- The voltage shunt
2- The current series
3- the current shunt
4- the voltage series
1- In its circuit, the output voltage, is sampled by feedback network composed of the resistances and The sampled voltage is fed back in such a way that the closed-loop input voltage, is the sum of (the voltage across the input port of the amplifier) and (developed across in the feedback subcircuit). Since the output port of the feedback configuration can be viewed as connected in series with the amplifier input port. On the other hand, output voltage sampling constraints the net load current, to the algebraic sum of the amplifier output port current, and the feedback network input current, Accordingly, the output topology is indicative of a shunt connection of the feedback subcircuit to the amplifier output port. The fact that the voltage is fed back to a voltage-driven input port renders the driving point input resistance, of the closed-loop amplifier large, whereas the output resistance is small.
2- Here the feedback circuit well behaves as a voltage amplifier, the shunt-series configuration, In its circuit, the current on equal to the output signal current, (approximately equal for BJT’s), is sampled by the feedback network formed by resistors and The sampled current is fed back to a current-driven input port. Thus, the resultant driving point output resistance is large, and the driving point input resistance is small. These characteristics allow for a closed loop current gain, that is relatively independent of source and load resistances as well as insensitive to transistor parameters.