When some part of output signal is again fed back to input then that signal is called as feedback signal.If the feedback signal and input signal are in phase means they have same polarities the feedback is said to be positive. If the feedback and input signal are out of phase then the feedback is said to be negative.

• There are four basic ways of connecting the feedback signal. Its also known as feedback topologies. Both voltage and current can be fed back to the input either in series or parallel.Specifically there can be following types of feedback present.

1. Voltage Series Feedback : In this type a part of output voltage fed back in series with the input signal,resulting in overall gain reduction.It reduces the output impedance and increase the input resistance.

2. Voltage Shunt feedback: In this type a part of output voltage fed back in shunt (parallel) with an input signal.The voltage-shunt feedback provides a stabilized overall gain and decrease both input and output resistance.

3. Current Series Feedback: In current series feedback a voltage is develop which is proportional to the output current. This is called current feedback even though it is a voltage that subtracted from the input voltage.Because of the series connection at the input and output,the input and output resistance get increased.This type of amplifier is called trans conductance amplifier.

4. Current Shunt Feedback: It is called a series derived shunt-fed feedback.The connection at the input reduces the input resistance.and the series connection at the output increases the output resistance.This is the true current amplifier

all above four feedback topologies and their advantages and disadvantages summarized by below table:

following Fig shows different feedback topologies