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What is the behaviour of a FET, for large value of |VDS|?

What is the behaviour of a FET, for large value of |VDS|? Correct Answer Voltage controlled current source

Case 1: When VDS is smaller

VDS ≤ VGS - Vt

The characteristic of Id vs VDS curve is linear indicating that it behaves as a Resistor. Therefore, for a small value of VDS. MOSFET behaves as a voltage-controlled resistor.

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As we increase the value of VDS the channel becomes tapered at drain end and its resistance increases therefore curve does not continue to he linear but bends.

Where

VGS = Gate to source voltage

VOV = overdrive voltage

Vt = threshold voltage

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Case (ii): When VDS is large

As we further increase VDS, the channel pinch off and for the increase in VDs does not affect the channel anymore and therefore drain current saturates. In this region, MOSFET behaves as a voltage-controlled current source.

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Initially, the curve is almost a straight line with a slope proportional to VOV.

At current VDS ≥ VOV, current saturates because the channel is pinched off at the drain end and VDS no longer affects the channel. VOV = VGS - Vt

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