# VLSI Questions and Answers – Simulators

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

1. Simulator converts circuit information to
a) design plan
b) does verification
c) set of equations
d) floor plan

Explanation: The circuit description contains information about circuit components and interconnections. This is transformed using a simulator to a set of equations from which predictions of behaviour are made.

2. The electrical behaviour of a circuit is given using
a) design rules
b) floor plan
c) structures and layouts
d) mathematical modelling

Explanation: The electrical behaviour is defined by mathematical modelling and its accuracy is measured using the accuracy of simulation and computing power and time for simulation.

3. Which gives the main electrical behaviour of various parts of the circuit?
a) circuit simulator
b) timing simulator
c) logic level simulator
d) functional simulator

Explanation: Circuit simulators are concerned with the electrical behaviour of the various parts of the circuit to be implemented in silicon.

4. Which takes lots of simulating time?
a) circuit simulator
b) timing simulator
c) logic level simulator
d) functional simulator

Explanation: Circuit simulators takes lot of computing time to simulate even small section of system and are completely impractical for circuits of any real magnitude.

5. Timing simulator concentrates on
a) quiescent nodes
b) active nodes
c) passive nodes
d) electrical nodes

Explanation: Timing simulator concentrates on active nodes and ignores the quiescent nodes in simulation and improves the design accordingly.
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6. The accuracy of simulation depends on accuracy of
a) fabrication house parameters
b) electrical parameters
c) active parameters
d) functional parameters

Explanation: The accuracy of simulation depends on accuracy of fabrication house parameters which must be fed into the simulator which is in the range of 20% or better.

7. Which is important during the design phase?
a) circuit simulator
b) timing simulator
c) logic level simulator
d) functional simulator

Explanation: Timing simulators are increasingly important during the design phase because of their speed and consequent interactive qualities.

8. Run times are _______ to number of devices and nodes.
a) linearly related
b) inversely related
c) exponentially equal
d) does not relate

Explanation: Run time is linearly related to the number of devices and nodes being simulated. The structure of timing simulator tools ensure this relationship.

9. Improvement of transistor modelling includes
a) body effect
b) channel length modulation
c) carrier velocity saturation
d) all of the mentioned

Explanation: To improve the transistor modelling it is possible to include body effect, channel length modulation and carrier velocity saturation.

10. Channel length modulation is for voltages
a) exceeding threshold
b) exceeding onset of saturation
c) exceeding power supply
d) exceeding onset of non saturation

Explanation: Channel length modulation is for voltages exceeding the onset of saturation there is an effective decrease in channel lengthof a short channel transistor.

11. The charge carriers reach _________ scattering limited velocity before pinch off.
a) maximum
b) minimum
c) less
d) equal

Explanation: Velocity saturation occurs when the drain to source voltage of a short channel transistor exceeds a critical value, the charge reach their maximum scattering limited velocity before pinch off.

12. Less current is available from
a) short channel transistor
b) large channel transistor
c) very large channel transistor
d) does not depend on channel transistor

Explanation: Less current is available from a short channel transistor than from a long channel transistor with similar width to length ratio and processing.

13. Which can cope up with large sections of layout?
a) circuit simulator
b) timing simulator
c) logic level simulator
d) functional simulator

Explanation: Logic level simulator can cope with large section of the layout at one time but the performance is assumed in terms of logic levels with no or little timing information.

14. Logic simulators can be replaced by simulators which operate at transistor level.
a) true
b) false

Explanation: Logic simulators may be replaced by simulators which operate at the register transfer level.

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