Question

Assertion (A) : The drain induced barrier lowering and channel length modulation are some of the short channel effects in MOSFET

Reason (R): The cut-off frequency of a MOSFET is independent of gate to source and gate to drain capacitance. 

1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2.

Both (A) and (R) are true, but (R) is not the correct explanation of (A)

3. (A) is true, but (R) is false
4. (A) false, but (R) is true

Answer 1

Correct Answer - Option 3 : (A) is true, but (R) is false

Short-channel effect in MOSFET: 

If the channel length of MOSFET becomes comparatively equal to the depletion layer widths of source and drain junction then it is called that MOSFET suffers from the short-channel effect.

Due to this effect, the following parameters are affected

1. Mobility of charge carrier in the channel

2. The threshold voltage changed due to a shorter length of the channel.

3. Drain current also changed as threshold voltage changed

4. Channel length modulation takes place.

The cut-off frequency of a MOSFET is given as:

\(f_H=\frac{1}{2\pi(R_{Sig}||R_G)(C_{gs}+C_M)}\)

Where, 

C_gs = gate to source capacitance

C_gd = gate to drain capacitance

C_M = Miller capacitance and it is given as:

CM = Cgd(1 + gmRL')

∴The cut-off frequency of a MOSFET is dependent on the gate to source and gate to drain capacitance

Hence, (A) is true, but (R) is false.