GATE EC 2015 Set 1 — Question 49
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Electronic Devices → MOS Capacitor & MOSFET → I-V & Transconductance
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Question
For the NMOSFET in the circuit shown, the threshold voltage is , where . The source voltage is varied from to . Neglecting the channel length modulation, the drain current as a function of is represented by
Correct answer
(A) [figure]
Solution
In the given circuit, the gate and drain are both connected to . Thus, and . The source is at .
and .
Since , the condition for saturation () is always satisfied as long as the device is ON ().
The device is ON when .
In saturation, the drain current is given by:This is a parabolic relationship where decreases as increases, reaching zero at . For , the device is in cutoff and . Graph (A) correctly represents this behavior.
and .
Since , the condition for saturation () is always satisfied as long as the device is ON ().
The device is ON when .
In saturation, the drain current is given by:This is a parabolic relationship where decreases as increases, reaching zero at . For , the device is in cutoff and . Graph (A) correctly represents this behavior.
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