There are 4 different combinations possible with negative feedback in Amplifiers as given below
- Voltage-Series.
- Current-Series.
- Voltage-Shunt.
- Current-Shunt.
The first part represents the type of sampling at the output .
- i.e , Voltage- Shunt connection.
- Current-Series connection.
and the second part represents the type of Mixing at the input
- Series- Voltage is applied at the input.
- Shunt-Current is applied at the input.
For any Amplifier circuit we require
- High Gain
- High Band Width
- High Input Impedance
- and Low Output Impedance.
Classification of feedback Amplifiers is also known as feedback Topologies.
Voltage-Series feedback Connection:-
at i/p side connection is Series and at o/p side connection used is Shunt since o/p is collected is voltage.
Series connection increases i/p impedance and Voltage at the o/p indicates a decrease in o/p impedance.
i.e, and
.
Current-Series feedback Connection:-
Series connection increases i/p impedance and Current at the o/p indicates an increase in o/p impedance.
i.e, and
.
Voltage-Shunt feedback Connection:-
In this connection, both i/p and o/p impedance decreases .
i.e, and
.
Current-Shunt feedback Connection:-
Shunt connection decreases i/p impedance and Current at the o/p indicates an increase in o/p impedance.
i.e, and
.
Effect of negative feedback on different topologies:-
| Type of f/b |
Voltage gain
|
Band Width with f/b | i/p impedance |
o/p impedance |
| Voltage-Series | decreases | increases | increases | decreases |
| Current-Series | decreases | increases | increases | increases |
| Voltage-Shunt | decreases | increases | decreases | decreases |
| Current-Shunt | decreases | increases | decreases | increases |
Similarly negative feedback decreases noise and harmonic distortion for all the four topologies.
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p style=”text-align: justify;”>Note:- for any of the characteristics in the above table, increase ‘s shown by multiplying the original value with and decrease ‘s shown by dividing with
.
