Find the input capacitance for a common source(CS) MOSFET amplifier, when Cgs = 5pF, Cgd = 3pF, and Av = 3.

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SSC JE Electrical 10 Oct 2023 Shift 2 Official Paper-I
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  1. 17 pF
  2. 15 pF
  3. 10 pF
  4. 12 pF

Answer (Detailed Solution Below)

Option 1 : 17 pF
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Detailed Solution

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Concept

The small signal model of a common source MOSFET amplifier is:

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The input capacitance for a common source(CS) MOSFET amplifier is given by:

\(C_{in}=C_{gs}+(1+A_V)C_{gd}\)

where, Cgs = Gate to source capacitance

Cgd = Gate to drain capacitance

AV = Voltage gain

Calculation

Given, Cgs = 5 pF

Cgd = 3 pF

AV = 3

\(C_{in}=5+(1+3)3\)

Cin = 17 pF

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