Feedback concept

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

1. CONCEPT OF FEEDBACK 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. A f =A/(1-A β ) 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. A f =A/( 1+A β )

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= V o /V s 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= V o /I s

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 = I o /V s 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= I o /I s

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