Latch-up in CMOS MCQ Quiz – Objective Question with Answer for Latch-up in CMOS MCQ

1. In latch-up condition, parasitic component gives rise to __________ conducting path.

A. low resistance
B. high resistance
C. low capacitance
D. high capacitance

Answer: A

In latch-up conditions, the parasitic component gives rise to low resistance conducting path between Vdd and Vss with disastrous results. Careful control during fabrication is necessary to avoid this problem.

 

2. Latch-up can be induced by __________

A. incident radiation
B. reflected radiation
C. etching
D. diffracted radiation

Answer: A

Latch-up can be induced by glitches on the supply rail or by incident radiation.

 

3. How many transistors might bring up a latch-up effect in the p-well structure?

A. two
B. three
C. one
D. four

Answer: A

Two transistors and two resistances might bring up the latch-up effect in the p-well structure. These are associated with p-well and with regions of the substrate.

 

4. Substrate doping level should be decreased to avoid the latch-up effect.

A. true
B. false

Answer: B

An increase in substrate doping level with a consequent drop in the value of Rs can be used as a remedy for the latch-up problem.

 

5. What can be introduced to reduce the latch-up effect?

A. latch-up rings
B. guard rings
C. latch guard rings
D. substrate rings

Answer: B

The introduction of guard rings can reduce the effect of the latch-up problem. Guard rings are diffusions that decouple the parasitic bipolar transistors.

 

6. Which process produces a circuit that is less prone to the latch-up effect?

A. CMOS
B. nMOS
C. pMOS
D. BiCMOS

Answer: D

BiCMOS process produces circuits that are less likely to suffer from latch-up problems whereas CMOS circuits are very highly prone to latch-up problems.

 

7. Which one of the following is the main factor for reducing the latch-up effect?

A. reduced p-well resistance
B. reduced n-well resistance
C. increased n-well resistance
D. increased p-well resistance

Answer: B

One of the main factors in reducing the latch-up effect is reduced n-well resistance Rw. Reduction in Rw means that a larger lateral current is necessary to invite latch-up and a higher value of holding current is also required.

 

8. The parasitic PNP transistor has the effect of _______ carrier lifetime.

A. increasing
B. decreasing
C. exponentially decreasing
D. exponentially increasing

Answer: B

The parasitic PNP transistor has the effect of reducing carrier lifetime in the n-base region.

 

9. The reduction in carrier lifetime brings about __________

A. reduction in alpha
B. reduction in beta
C. reduction in current
D. reduction in voltage

Answer: B

The parasitic PNP transistor has the effect of reducing carrier lifetime in the n-base region which results in radiation in beta.

 

10. To reduce the latch-up effect substrate resistance should be high.

A. true
B. false

Answer: B

To reduce the latch-up effect, substrate resistance Rs should be low. The reduction of Rs and Rw means that a larger lateral current is necessary to invite a latch-up.

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