Analog Electronics – Page 41
Voltage Shunt Feedback Amplifier – Complete Derivation
Voltage shunt feedback is a feedback configuration in which:
- Output voltage is sampled
- Feedback signal is applied in parallel (shunt) with the input
This configuration is commonly used in transresistance amplifiers.
Closed Loop Gain Derivation
Let
- A = Open loop gain
- β = Feedback factor
- Af = Closed loop gain
Feedback voltage:
Vf = βVo
Input signal current becomes:
Ii = Is − If
Output voltage:
Vo = A Ii
Substituting feedback:
Vo = A(Is − βVo)
Rearranging:
Vo + AβVo = AIs
Vo(1 + Aβ) = AIs
Closed loop gain:
Af = A / (1 + Aβ)
Input Resistance with Feedback
Shunt mixing reduces input resistance.
Rif = Ri / (1 + Aβ)
Output Resistance with Feedback
Voltage sampling reduces output resistance.
Rof = Ro / (1 + Aβ)
Key Characteristics
- Input resistance decreases
- Output resistance decreases
- Gain becomes stable
- Bandwidth increases
Important GATE Points
- Voltage shunt feedback → Transresistance amplifier
- Closed loop gain = A / (1 + Aβ)
- Input resistance decreases
- Output resistance decreases
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