Classification (or) topologies of feedback Amplifiers

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.

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 .