This set of Microelectronics Multiple Choice Questions & Answers (MCQs) focuses on “Models of a MOSFET”.
1. What can we infer from this model of a MOSFET?
a) It is a VCVS
b) It is a ICIS
c) It is a VCIS
d) It is a ICVS
View Answer
Explanation: The MOSFET is a voltage controlled current source since the drain current is dependent on the gate voltage. This cannot be a current controlled device because the input resistance of the device is infinite.
2. In which region of operation, the model of MOSFET shown below is valid?
a) Active
b) Saturation
c) Triode
d) Deep triode
View Answer
Explanation: This model is used to represent the MOSFET in saturation. r0 is the output impedance offered due to the early effect.
3. For which type of MOSFET is the following model suitable?
a) NMOS
b) PMOS
c) This model doesn’t represent a MOSFET
d) Cannot be determined
View Answer
Explanation: The above model doesn’t really reveal whether the drain potential is higher than the source potential or is it lower than the source potential. Since the MOSFET is a symmetrical device, we cannot conclude which kind of MOSFET is being represented by the above model.
4. Which region of operation, of a MOSFET, is represented by the above model?
a) Triode region
b) Saturation region
c) Forward-Active region
d) Depletion region
View Answer
Explanation: The MOSFET behaves as a voltage-controlled resistor in the triode region. The drain current follows an almost linear relationship with the drain voltage where the resistance between the source and the drain region is varied by the overdrive voltage.
5. How many capacitances are supposed to arise within the MOSFET during it’s fabrication?
a) 3
b) 4
c) 6
d) 5
View Answer
Explanation: There are 6 capacitances that arise during the fabrication of a MOSFET. The source, gate and drain gives rise to 3 capacitances with the substrate. The gate and the drain give rise to two capacitances with the source. The source and the drain gives rise to a capacitance which is almost insignificant.
6. A current source is used to represent the body effect. Where in the model of a MOSFET does it fit?
a) Between source and drain
b) Between source and bulk
c) Between drain and bulk
d) Between gate and bulk
View Answer
Explanation: The body effect is modelled by a current source between source and drain. The body effect leads to an increase in the drain current since the width of the channel increases.
7. Which type of capacitance is formed between the source and substrate?
a) Junction
b) Depletion
c) Inversion
d) Modal
View Answer
Explanation: The source and the substrate are doped with different carriers and the behave like a pn junction along the interface separating them. Hence the capacitance arising between them is junction capacitance.
8. Which type of capacitance is formed between the drain and substrate?
a) Inversion
b) Depletion
c) Junction
d) Modal
View Answer
Explanation: The drain and the substrate are doped with different carriers and the behave like a pn junction along the interface separating them. Hence the capacitance arising between them is junction capacitance.
9. Which capacitance is neglected during modelling the MOSFET?
a) Gate-drain
b) Source-drain
c) Source-bulk
d) Gate-bulk
View Answer
Explanation: The source and drain are situated far apart from each other. They don’t share a junction and the capacitance between them is the mostly neglected.
10. Why is CGS almost equal to CGD?
a) CGS is negligible
b) They are not equal
c) No such capacitances exist
d) The gate is equidistance from the source and the drain
View Answer
Explanation: The source and the drain are equidistant from the gate. The capacitance rising between them is the depletion capacitance and is almost same.
Sanfoundry Global Education & Learning Series – Microelectronics.
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