There are 4 different combinations possible with negative feedback in Amplifiers as given below
 VoltageSeries.
 CurrentSeries.
 VoltageShunt.
 CurrentShunt.
The first part represents the type of sampling at the output .
 i.e , Voltage Shunt connection.
 CurrentSeries connection.
and the second part represents the type of Mixing at the input
 Series Voltage is applied at the input.
 ShuntCurrent 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.
VoltageSeries 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 .
CurrentSeries feedback Connection:
Series connection increases i/p impedance and Current at the o/p indicates an increase in o/p impedance.
i.e, and .
VoltageShunt feedback Connection:
In this connection, both i/p and o/p impedance decreases .
i.e, and .
CurrentShunt 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 
VoltageSeries  decreases  increases  increases  decreases 
CurrentSeries  decreases  increases  increases  increases 
VoltageShunt  decreases  increases  decreases  decreases 
CurrentShunt  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 .