Analog Electronics – Page 43
Current Shunt Feedback Amplifier – Complete Derivation
In a Current Shunt Feedback Amplifier:
- The output current is sampled.
- The feedback signal is applied in parallel (shunt) with input.
This configuration is commonly used in Current Amplifiers.
Closed Loop Gain Derivation
Let:
- A = Open loop current gain
- β = Feedback factor
- Af = Closed loop gain
Feedback current:
If = βIo
Input current becomes:
Ii = Is − If
Output current:
Io = A Ii
Substitute:
Io = A(Is − βIo)
Rearranging:
Io(1 + Aβ) = AIs
Closed loop gain:
Af = Io / Is = A / (1 + Aβ)
Input Resistance with Feedback
Since feedback is applied in parallel, input resistance decreases.
Rif = Ri / (1 + Aβ)
Output Resistance with Feedback
Current sampling increases output resistance.
Rof = Ro (1 + Aβ)
Key Characteristics
- Input resistance decreases
- Output resistance increases
- Gain stabilizes
- Bandwidth improves
Important GATE Points
- Current Shunt Feedback → Current Amplifier
- Closed loop gain = A / (1 + Aβ)
- Input resistance decreases
- Output resistance increases
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