VLSI Multiple Choice Questions on “nMOS Inverter”.
1. Inverters are essential for ________
A. NAND gates
B. NOR gates
C. sequential circuits
D. all of the mentioned
Answer: D
Clarification: Inverters are needed for restoring logic levels for NAND and NOR gates, sequential and memory circuits.
2. In basic inverter circuit _____________ is connected to ground.
A. source
B. gates
C. drain
D. resistance
Answer: A
Clarification: A basic inverter circuit consists of transistor with a source connected to ground and a load resistor connected from drain to positive supply rail Vdd.
3. In inverter circuit ________ transistors is used as load
A. enhancement mode
B. depletion mode
C. all of the mentioned
D. none of the mentioned
Answer: B
Clarification: Depletion mode transistors are preferred to be used as load in inverter circuits as it occupies a lesser area and are produced on silicon substrate unlike resistors.
4. For depletion mode transistor, gate should be connected to ________
A. source
B. drain
C. ground
D. positive voltage rail
Answer: A
Clarification: For the depletion mode transistor, gate is connected to source so it is always on and only the characteristic curve Vgs=0 is relevant.
5. In nMOS inverter configuration depletion mode device is called as ________
A. pull up
B. pull down
C. all of the mentioned
D. none of the mentioned
Answer: A
Clarification: In nMOS inverter configuration, depletion mode devices are called as pull up and enhancement mode devices are called as pull down transistor.
6. How is nMOS inverter represented?
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Answer: B
Clarification: nMOS inverter can be represented using two transistors, depletion mode pMOS transistor followed by nMOS transistor. Input is given to the nMOS.
7. What is the ratio of Zp.u/Zp.d?
A. 1/4
B. 4/1
C. 1/2
D. 2/1
Answer: B
Clarification: The ratio of Zp.u/Zp.d, where Z is determined by the length to width ratio of the transistor, is given by 4/1.
8. Pass transistors are transistors used as ________
A. switches connected in series
B. switches connected in parallel
C. inverters used in series
D. inverter used in parallel
Answer: A
Clarification: Pass transistors are transistor used as switches in series with lines carrying logic levels due to its isolated nature of the gate.
9. An inverter driven through one or more pass transistors has Zp.u/Zp.d ratio of ________
A. 1/4
B. 4/1
C. 1/8
D. 8/1
Answer: D
Clarification: An inverter driven directly from output of another has the ratio of 4/1 and if driven through one or more pass transistors has the ratio of 8/1.
10. In depletion mode pull-up, dissipation is high since current flows when?
A. Vin = 1
B. Vin = 0
C. Vout = 1
D. Vout = 0
Answer: A
Clarification: In nMOS depletion mode pull-up, dissipation is high since current flows Vin = logical 1.
11. In complementary transistor pull-up, current flows when?
A. Vin = 1
B. Vin = 0
C. current doesn’t flow
D. Vout = Vin
Answer: C
Clarification: In complementary transistor pull-up no current flows either for logical 1 or 0, full logical 1 and 0 levels are presented at the output.