VLSI Interview Questions, VLSI Interview Questions and Answers

VLSI Interview Questions and Answers, VLSI Interview Questions and Answers Freshers, VLSI Interview Questions and Answers, VLSI Interview Questions

Before getting on to the VLSI interview questions, the student must know that the VLSI is a continuously varying field which needs the students as well as professionals to upgrade their skills with the new features and knowledge, to get fit for the jobs associated with VLSI. This post related to VLSI Interview Questions and Answers, VLSI Interview Questions and Answers Freshers, VLSI Interview Questions and Answers, VLSI Interview Questions will help you let out find all the solutions that are frequently asked in you upcoming VLSI interview.

Over thousands of vacancies available for the VLSI developers, experts must be acquaintance with all the component of VLSI technologies. This is necessary for the students in order to have in-depth knowledge of the subject so that they can have best employment opportunities in the future. Knowing every little detail about VLSI is the best approach to solve the problems linked with problem.

APTRON has spent hours and hours in researching about the VLSI Interview Questions and Answers, VLSI Interview Questions and Answers Freshers, VLSI Interview Questions and Answers, VLSI Interview Questions that you might encounter in your upcoming interview.  All these questions will alone help you to crack the interview and make you the best among all your competitors.

First of all, let us tell you about how the VLSI technology is evolving in today’s world and how demanding it is in the upcoming years. In fact, according to one study, most of the companies and businesses have moved to the VLSI. Now, you cannot predict how huge the future is going to be for the people experienced in the related technologies.

Hence, if you are looking for boosting up your profile and securing your future, VLSI will help you in reaching the zenith of your career. Apart from this, you would also have a lot of opportunities as a fresher.

These questions alone are omnipotent. Read and re-read the questions and their solutions to get accustomed to what you will be asked in the interview. These VLSI interview questions and answers will also help you on your way to mastering the skills and will take you to the giant world where worldwide and local businesses, huge or medium, are picking up the best and quality VLSI professionals.

This ultimate list of best VLSI interview questions will ride you through the quick knowledge of the subject and topics like VLSI Designing, VLSI Designing Architecture, Introduction to VLSI, Digital Design. This VLSI interview questions and answers can be your next gateway to your next job as a VLSI expert.

These are very Basic VLSI Interview Questions and Answers for freshers and experienced both.

Q1: Explain how logical gates are controlled by Boolean logic?
A1: 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.

Q2: Mention what are the different gates where Boolean logic are applicable?
A2:

• NOT Gate: It has one out input and one output. For example, if the value of A= 0 then the Value of B=1 and vice versa
• AND Gate: It has one output due to the combination of two output. For example, if the value of A and B= 1 then value of Q should be 1
• OR Gate: Either of the value will show the same output. For example, if the value of A is 1 or B is 0 then value of Q is 1

These are the basic three types of gates where Boolean logic work, apart from these, other gates that are functional works with the combination of these three basic gates, they are XNOR gate, NAND gate, Nor gate and XOR gate.

Q3: Explain how binary number can give a signal or convert into a digital signal?
A3: Binary number consists of either 0 or 1, in simple words number 1 represents the ON state and number 0 represents OFF state. These binary numbers can combine billion of machines into one machines or circuit and operate those machines by performing arithmetic calculations and sorting operations.

Q4: Mention what is the difference between the TTL chips and CMOS chips?
A4:

Q5: Explain what is a sequential circuit?
A5: A sequential circuit is a circuit which is created by logic gates such that the required logic at the output depends not only on the current input logic conditions, but also on the sequences past inputs and outputs.

Q6: Explain how Verilog is different to normal programming language?
A6: Verilog can be different to normal programming language in following aspects

• Simulation time concept
• Multiple threads
• Basic circuit concepts like primitive gates and network connections

Q7: Explain what is Verilog?
A7: Verilog is an HDL (Hardware Description Language) for describing electronic circuits and systems. In Verilog, circuit components are prepared inside a Module. It contains both behavioral and structural statements. Structural statements signify circuit components like logic gates, counters and micro-processors. Behavioral statements represent programming aspects like loops, if-then statements and stimulus vectors.

Q8: In Verilog code what does “timescale 1 ns/ 1 ps” signifies?
A8: In Verilog code, the unit of time is 1 ns and the accuracy/precision will be upto 1ps.

Q9: Explain what is the depletion region?
A9: When positive voltage is transmitted across Gate, it causes the free holes (positive charge) to be pushed back or repelled from the region of the substrate under the Gate. When these holes are pushed down the substrate, they leave behind a carrier depletion region.

Q10: Explain why is the number of gate inputs to CMOS gates usually limited to four?
A10: Higher the number of stacks, slower the gate will be. In NOR and NAND gates the number of gates present in the stack is usually alike as the number of inputs plus one. So input are restricted to four.

Q11: Explain what is multiplexer?
A11: A multiplexer is a combination circuit which selects one of the many input signals and direct to the only output.

Q12: Explain what is SCR (Silicon Controlled Rectifier)?
A12: SCR is a 4 layered solid state device which controls current flow. It is a type of rectifier that is controlled by a logical gate signal. It is a 4 layered, 3-terminal device.

Q13: Explain what is Slack?
A13: Slack is referred as a time delay difference from the expected delay to the actual delay in a particular path. Slack can be negative or positive.

Q14: Explain what is the use of defpararm?
A14: With the keyword defparam, parameter values can be configured in any module instance in the design.

Q15: Explain What Is The Depletion Region?
A15: When positive voltage is transmitted across Gate, it causes the free holes (positive charge) to be pushed back or repelled from the region of the substrate under the Gate. When these holes are pushed down the substrate, they leave behind a carrier depletion region.

Q16: Explain Why Is The Number Of Gate Inputs To Cmos Gates Usually Limited To Four?
A16: Higher the number of stacks, slower the gate will be. In NOR and NAND gates the number of gates present in the stack is usually alike as the number of inputs plus one. So input are restricted to four.

Q17: Explain What Is Multiplexer?
A17: A multiplexer is a combination circuit which selects one of the many input signals and direct to the only output.

Q18: Explain What Is Scr (silicon Controlled Rectifier)?
A18: SCR is a 4 layered solid state device which controls current flow. It is a type of rectifier that is controlled by a logical gate signal. It is a 4 layered, 3-terminal device.

Q19: Explain What Is Slack?
A19: Slack is referred as a time delay difference from the expected delay to the actual delay in a particular path. Slack can be negative or positive.

Q20: Explain What Is The Use Of Defpararm?
A20: With the keyword defparam, parameter values can be configured in any module instance in the design.

Q21: Why Does The Present Vlsi Circuits Use Mosfets Instead Of Bjts?
A21: Compared to BJTs, MOSFETs can be made very small as they occupy very small silicon area on IC chip and are relatively simple in terms of manufacturing. Moreover digital and memory ICs can be implemented with circuits that use only MOSFETs i.e. no resistors, diodes, etc.

Q22: What Are The Various Regions Of Operation Of Mosfet? How Are Those Regions Used?
A22: MOSFET has three regions of operation: the cut-off region, the triode region, and the saturation region.

The cut-off region and the triode region are used to operate as switch. The saturation region is used to operate as amplifier.

Q23: What are the steps required to solve setup and Hold violations in VLSI?
A23: 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.

Q24: What are the different ways in which antenna violation can be prevented?
A24: 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 atleast 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.

Q25: What is the function of tie-high and tie-low cells?
A25: Tie-high and tie-low are used to connect the transistors of the gate by using either the power or the ground. The gates are connected using the power or ground then it can be turned off and on due to the power bounce from the ground. The cells are used to stop the bouncing and easy from of the current from one cell to another. These cells are required Vdd that connects to the tie-high cell as there is a power supply that is high and tie-low gets connected to Vss. This connection gets established and the transistors function properly without the need of any ground bounce occurring in any cell.

Q27: What is the main function of metastability in VSDL?
A27: Metastability is an unknown state that is given as neither one or zero. It is used in designing the system that violates the setup or hole time requirements. The setup time requirement need the data to be stable before the clock-edge and the hold time requires the data to be stable after the clock edge has passed. There are potential violation that can lead to setup and hold violations as well. The data that is produced in this is totally asynchronous and clocked synchronous. This provide a way to setup the state through which it can be known that the violations that are occuring in the system and a proper design can be provided by the use of several other functions.

Q28: What are the steps involved in preventing the metastability?
A28: Metastability is the unknown state and it prevents the violations using the following steps:

1. Proper synchronizers are used that can be two stage or three stage whenever the data comes from the asynchronous domain. This helps in recovering the metastable state event.
2. The synchronizers are used in between cross-clocking domains. This reduces the metastability by removing the delay that is caused by the data element that are coming and taking time to get removed from the surface of metal.
3. Use of faster flip-flops that allow the transaction to be more faster and it removes the delay time between the one component to another component. It uses a narrower metastable window that makes the delay happen but faster flip-flops help in making the process faster and reduce the time delay as well.

Q29: What are the different design constraints occur in the Synthesis phase?
A29: The steps that are involved in which the design constraint occurs are:

1. first the creation of the clock with the frequency and the duty cycle gets created. This clock helps in maintaining the flow and synchronizing various devices that are used.
2. Define the transition time according the requirement on the input ports.
3. The load values are specified for the output ports that are mapped with the input ports.
4. Setting of the delay values for both the input and output ports. The delay includes the input and output delay.
5. Specify the case-settings to report the correct time that are matched with the specific paths.
6. The clock uncertainty values are setup and hold to show the violations that are occurring.

Q30: What are the different types of skews used in VLSI?
A30: There are three types of skew that are used in VLSI. The skew are used in clock to reduce the delay or to understand the process accordingly. The skew are as follows:

Local skew:
This contain the difference between the launching flip-flop and the destination flip-flop. This defines a time path between the two.

Global skew:
Defines the difference between the earliest component reaching the flip flow and the the latest arriving at the flip flow with the same clock domain. In this delays are not measured and the clock is provided the same.

Useful skew:
Defines the delay in capturing a flip flop paths that helps in setting up the environment with specific requirement for the launch and capture of the timing path. The hold requirement in this case has to be met for the design purpose.

Q31: What are the changes that are provided to meet design power targets?
A31: To meet the design power target there should be a process to design with Multi-VDD designs, this area requires high performance, and also the high VDD that requires low-performance. This is used to create the voltage group that allow the appropriate level-shifter to shift and placed in cross-voltage domains. There is a design with the multiple threshold voltages that require high performance when the Vt becomes low. This have lots of current leakage that makes the Vt cell to lower the performance. The reduction can be performed in the leakage power as the clock in this consume more power, so placing of an optimal clock controls the module and allow it to be given more power. Clock tree allow the switching to take place when the clock buffers are used by the clock gating cells and reduce the switching by the power reduction.

VLSI Conclusion Interview FAQs

We know the list of VLSI Interview Questions and Answers, VLSI Interview Questions and Answers Freshers, VLSI Interview Questions and Answers, VLSI Interview Questions is overwhelming but the advantages of reading all the questions will maximize your potential and help you crack the interview. The surprising fact is that this VLSI interview questions and answers post covers all the basic of the VLSI technology and you have to check out the FAQs of different components of VLSI too.

However, you will be asked with the questions in the interview related to the above mentioned questions. Preparing and understanding all the concept of VLSI technology will help you strengthen the other little information around the topic.

After preparing these interview questions, we recommend you to go for a mock interview before facing the real one. You can take the help of your friend or a VLSI expert to find the loop holes in your skills and knowledge. Moreover, this will also allow you in practicing and improving the communication skill which plays a vital role in getting placed and grabbing high salaries.

Remember, in the interview, the company or the business or you can say the examiner often checks your basic knowledge of the subject. If your basics is covered and strengthened, you can have the job of your dream. The industry experts understand that if the foundation of the student is already made up, it is easy for the company to educate the employ towards advance skills. If there are no basics, there is no meaning of having learnt the subject.

Therefore, it’s never too late to edge all the basics of any technology. If you think that you’ve not acquired the enough skills, you can join our upcoming batch of VLSI Training in Noida. We are one of the best institute for VLSI in noida which provide advance learning in the field of VLSI Course. We’ve highly qualified professionals working with us and promise top quality education to the students.

We hope that you enjoyed reading VLSI Interview Questions and Answers, VLSI Interview Questions and Answers Freshers, VLSI Interview Questions and Answers, VLSI Interview Questions and all the FAQs associated with the interview. Do not forget to revise all the VLSI interview questions and answers before going for the VLSI interview. In addition to this, if you’ve any doubt or query associated with VLSI, you can contact us anytime. We will be happy to help you out at our earliest convenience. At last, we wish you all the best for your upcoming interview on VLSI Technology.