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VLSI Interview Questions and Answers

1
What are the steps required to solve setup and Hold violations in VLSI?

There are few steps that has to be performed to solved the setup and hold violations in VLSI. The steps are as follows:
the optimization and restructuring of the logic between the flops are carried way. This way the logics are combined and it helps in solving this problem.
There is way to modify the flip-flops that offer lesser setup delay and provide faster services to setup a device.
Modifying the launch-flop to have a better hold on the clock pin, which provides CK->Q that makes the launch-flop to be fast and helps in fixing the setup violations.
The network of the clock can be modified to reduce the delay or slowing down of the clock that captures the action of the flip-flop.
There can be added delay/buffer that allows less delay to the function that is used.

2
Explain how logical gates are controlled by Boolean logic?

In Boolean algebra, the true state is denoted by the number one, referred as logic one or logic high. While, the false state is represented by the number zero, called logic zero or logic low. And in the digital electronic, the logic high is denoted by the presence of a voltage potential.

3
What is the difference between CMOS and Bipolar technologies?

CMOS technology allows the power dissipation to be low and it gives more power output, whereas bipolar takes lots of power to run the system and the ciricutary require lots of power to get activated.
CMOS technology provides high input impedance that is low drive current that allow more current to be flown in the cirucit and keep the circuit in a good position, whereas it provides high drive current means more input impedance.
CMOS technology provides scalable threshold voltage more in comparison to the Bipolar technology that provides low threshold voltage.
CMOS technology provides high noise margin, packing density whereas Bipolory technology allows to have low noise margin so that to reduce the high volues and give low packing density of the components.

4
Explain what is the use of defpararm?

With the keyword defparam, parameter values can be configured in any module instance in the design.

5
What are the different ways in which antenna violation can be prevented?

Antenna violation occurs during the process of plasma etching in which the charges generating from one metal strip to another gets accumlated at a single place. The longer the strip the more the charges gets accumulated. The prevention can be done by following method:
Creating a jogging the metal line, that consists of atleas one metal above the protected layer.
There is a requirement to jog the metal that is above the metal getting the etching effect. This is due to the fact that if a metal gets the etching then the other metal gets disconnected if the prevention measures are not taken.
There is a way to prevent it by adding the reverse Diodes at the gates that are used in the circuits.

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