In a MOSFET operating in the saturation region, the channel length modulation
effect causes
a)
an increase in the gate-source capacitance
b)
a decrease in the Transconductance
c)
a decrease in the unity-gain cutoff frequency
d)
a decrease in the output resistance
Correct answer is option 'D'. Can you explain this answer?

Question

In a MOSFET operating in the saturation region, the channel length modulation
effect causes

a)
an increase in the gate-source capacitance
b)
a decrease in the Transconductance
c)
a decrease in the unity-gain cutoff frequency
d)
a decrease in the output resistance

Correct answer is option 'D'. Can you explain this answer?

Answer

Introduction:
In a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), the channel length modulation effect refers to the change in the effective channel length as a result of the variation in the voltage between the drain and source terminals. This effect occurs when the MOSFET is operating in the saturation region, where the drain current is relatively constant with respect to the drain-source voltage.

Explanation:
The channel length modulation effect primarily arises due to the depletion region at the drain end of the channel. As the drain voltage increases, the depletion region expands, effectively shortening the channel length. This reduction in channel length leads to several consequences:

Decrease in Output Resistance:
When the channel length is modulated, the effective channel length decreases. This decrease in channel length results in a decrease in the effective channel resistance. As a result, the output resistance of the MOSFET decreases. Therefore, option 'D' is the correct answer.

Increase in Gate-Source Capacitance:
The channel length modulation effect does not have a direct impact on the gate-source capacitance. The gate-source capacitance is primarily determined by the overlap between the gate and source electrodes. Therefore, option 'A' is incorrect.

Decrease in Transconductance:
Transconductance is a measure of how the output current of a device changes in response to a change in the input voltage. The channel length modulation effect does not directly affect the transconductance of a MOSFET. Therefore, option 'B' is incorrect.

Decrease in Unity-Gain Cutoff Frequency:
The unity-gain cutoff frequency is a measure of the frequency at which the device's gain drops to 1. The channel length modulation effect does not directly affect the unity-gain cutoff frequency of a MOSFET. Therefore, option 'C' is incorrect.

Conclusion:
In summary, the channel length modulation effect in a MOSFET operating in the saturation region leads to a decrease in the output resistance. This effect does not significantly impact the gate-source capacitance, transconductance, or unity-gain cutoff frequency.

Similar GATE Doubts

A MOSFET in saturation has a drain current of 1mA for VDS = 0.5V. If the channel lengthmodulation coefficient is 0.05 V-1 , the output resistance (in k?)of the MOSFET is Correct answer is '20'. Can you explain this answer?

For an ideal p-channel MOSFET, μp = 300cm2/v-s, W = 15μm, L = 1.5μm, tox = 300A, Vt = -0.7V. If the transistor is non-saturation region at VSD = 0.5V, then what is the Transconductance gm?

A good transconductance amplifier should have

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