Assertion A: When MOSFET is in conductive state, the saturation current flow after the channel is pinchedoff. Reason R: The substrate bias affects the threshold voltage of a MOSFET.
86) Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: When MOSFET is in conductive state, the saturation current flow after the channel is pinchedoff.
Reason R: The substrate bias affects the threshold voltage of a MOSFET.
In light of the above statements, choose the most appropriate answer from the options given below
1. Both A and R are correct and R is the correct explanation of A [Option ID = 3173]
2. Both A and R are correct but R is NOT the correct explanation of A [Option ID = 3174]
3. A is correct but R is not correct [Option ID = 3175]
4. A is not correct but R is correct [Option ID = 3176]
Answer: 2
Explanation:
Analysis of Assertion A:This statement is Correct. In a MOSFET, when the drain-to-source voltage (VDS) reaches the overdrive voltage (VGS - Vth), the inversion layer at the drain end disappears; this is called "pinch-off." Despite the channel being pinched off, current continues to flow because electrons are swept across the depletion region by the high electric field. This is the definition of the Saturation Region.
Analysis of Reason R:This statement is also Correct. This phenomenon is known as the Body Effect. When a voltage is applied to the substrate (body) relative to the source, it changes the amount of charge in the depletion layer, which directly modifies the threshold voltage (Vth) required to create a conducting channel.
Relationship:While both statements are scientifically true, the fact that substrate bias affects the threshold voltage (Reason R) does not explain why current flows after pinch-off (Assertion A). The pinch-off current flow is a result of carrier transport physics in the saturation region, whereas Reason R describes the control of the channel's turn-on point.