# VLSI Questions and Answers – Drivers

This set of VLSI Multiple Choice Questions & Answers (MCQs) focuses on “Drivers”.

1. For shorter delays ______ resistance should be used.
a) smaller
b) larger
c) does not depend on resistance
d) very large

Explanation: For shorter delays low resistance should be used as delay is directly proportional or related to resistance.

2. To reduce resistance value of inverters, channels must be made __________
a) wider
b) narrower
c) lenghthier
d) shorter

Explanation: Channels must be made wider to reduce the resistance value that is low resistance values for Zp.u. ad Zp.d. imply low L:W ratios and thus consequently an inverter to meet this need occupies a larger area.

3. As width increases, capacitive load __________
a) increases
b) decreases
c) does not change
d) exponentially increases

Explanation: As width of the channel increases, capacitive load also increases and with this the area occupied also increases. The rate at which the width increases affects the stages N and load capacitance.

4. Delay per stage for logic 0 to 1 transition can be given as __________
a) fƮ
b) 2fƮ
c) 3fƮ
d) 4fƮ

Explanation: Delay per stage for logic 0 to 1 transition can be given as fƮ. With large f, N decreases but delay per stage increases.

5. Delay per stage for logic 1 to 0 transition can be given as __________
a) fƮ
b) 2fƮ
c) 3fƮ
d) 4fƮ

Explanation: Delay per stage for logic 1 to 0 transition can be given as 4fƮ. Using the delay for transition from 1 to 0 and 0 to 1 total nMOS delay can be obtained.
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6. What is the total delay of an nMOS pair?
a) fƮ
b) 2fƮ
c) 5fƮ
d) 4fƮ

Explanation: Total delay of an nMOS pair is equal to 5fƮ. This can be calculated by knowing delay per stage, that is for two different transitions from 0 to 1 and vice versa.

7. What is the total delay of a CMOS pair?
a) 5fƮ
b) 7fƮ
c) 8fƮ
d) 4fƮ

Explanation: Total delay of an CMOS pair is equal to 7fƮ. This can be calculated by knowing thee delay per stage of CMOS.

8. The number of stages N can be given as ___________
a) ln(y)*ln(f)
b) ln(y)/ln(f)
c) ln(f)/ln(y)
d) ln(f)/ln(2y)

Explanation: The number of stages N can be given as ln(y)/ln(f). By knowing whether the number of stages N is even or odd we can calculate the total delay for nMOS, CMOS etc.

9. When number of stages N is even, the total delay for nMOS can be?
a) 1.5NfƮ
b) 2.5NfƮ
c) 3.5NfƮ
d) 4.5NfƮ

Explanation: When number of stages N is even, the total delay for nMOS can be given as 2.5NfƮ. This is calculated by using the formula (N/2)*5fƮ.

10. When number of stages N is even, the total delay for CMOS can be?
a) 1.5NfƮ
b) 2.5NfƮ
c) 3.5NfƮ
d) 4.5NfƮ

Explanation: When the number of stages N is even, the total delay for CMOS can be given as 3.5NfƮ. This is calculated by using the formula (N/2)*7fƮ.

11. In BiCMOS drivers, the input voltage Vbe is _______ on base width.
a) directly proportional
b) inversely proportional
c) logarithmically proportional
d) exponentially proportional

Explanation: In BiCMOS driver, the input voltage Vbe is logarithmically proportional to the base width Wb and on electron mobility.

12. Which has a larger value?
a) Tin
b) TL
c) Rc
d) None of the mentioned

Explanation: In BiCMOS drivers, the initial time Tin necessary to charge base emitter junction is larger than the time TL requires to charge the output load capacitance.

13. In BiCMOS driver, a good bipolar transistor should have ___________
a) low Rc
b) high hfe
c) high gm
d) all of the mentioned

Explanation: In BiCMOS drivers, a good bipolar transistor should have low Rc, high hfe, high gm, etc.

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