this is used to explain the basic concept of feedback and types of feedback.

1. By,
Dr. D. Veera Vanitha,
AP/ECE,
School of Engineering,
Avinashilingam Institute for Home Science and Higher
Education for Women, Coimbatore

2. Definition:
• The process of returning the fraction of the output of a
circuit or system to the input in order to minimise the
error.
• Types:
 Positive feedback
 Negative feedback

3.  Positive feedback:
The feedback signal is in phase with the input. So,
the amplifier gain is increased and often the output is
distorted and oscillates.
Af=A/(1-Aβ)
 Negative feedback:
The feedback signal is out of phase with the input.
So the amplifier gain is reduced and the output is
improved. Stabilization in gain is obtained.
Af=A/(1+Aβ)

4. Characteristics of negative feedback
 Higher input impedance
 Lower output impedance
 Stabilization in voltage gain
 Improved frequency response
 More linear operation
 Reduced noise
 Reduced distortion

5. Connection types
 4 ways to connect feedback signal in negative feedback
 They are,
Voltage series feedback
Voltage shunt feedback
Current series feedback
Current shunt feedback
 Voltage means, connecting output voltage as input to the
feedback network
 Current means, tapping some output current through the
feedback network
 Series refers to connecting feedback signal in series with
input signal voltage
 Shunt refers to connecting feedback signal in series with
input current source

6.  Voltage series feedback
 Fraction of the output signal voltage is fed
back in series with input signal voltage. This is
also called voltage amplifier.
A= Vo/Vs
 Voltage shunt feedback
 Fraction of the output signal voltage is fed
back in shunt with input current source. This is
also called trans resistance amplifier.
A= Vo/Is

7.  Current series feedback
 Fraction of the output current is sampled
and given as the input to the feedback circuit, that
is, the fraction of current is converted into a
proportional voltage and then given as input
signal. This is also called trans conductance
amplifier.
A= Io/Vs
 Current shunt feedback
 The Fraction of the output current is fed
back in parallel with the input current. This is
also called current amplifier.
A= Io/Is

8. THANK YOU