Very Large Scale Integration (VLSI) is when you create a circuit by adding millions of metal-oxide transistors (MOS) to a single chip, such as a microchip. Understanding this process is essential if you want to apply for a computer engineering job. To prepare for an interview on this topic, you can research and practice common interview questions. In this article, we’ll explore 11 VLSI interview questions and sample answers, including 25 more questions you can use to prepare for your upcoming interview.
VLSI Interview Questions and Model Answers
Here are 11 frequently asked VLSI interview questions and sample answers that you can refer to for inspiration:
How would you define VLSI or large scale integration?
This question sets the context for the rest of the interview, so it may be the first question they ask that they expect you to know. Make sure you read the general definition of VLSI to answer with confidence.
Example: “VLSI is basically just a process that you use to create integrated circuits by incorporating millions of MOS transistors into a single chip. These integrated circuits are necessary to build integrated circuit microchips. You can then use the microchips for a wide variety of tools, such as telecommunications technology and semiconductors.”
What is Boolean logic and how do you operate it?
Boolean logic is a core element of VLSI and microchip development, so you can expect this question. Since this is related to Boolean algebra, you may also mention it in your answer to further demonstrate your knowledge.
Example: “Boolean logic is the basis of Boolean algebra, which states that all values are either true or false. You can use Boolean logic in programs that perform basic comparisons. It can benefit you to make more well-versed decisions based on whether a value is true or false.”
What is Verilog and how does it vary from other regular programming languages?
This question requires you to understand other programming languages, so make sure you familiarize yourself with some of them to make a clear distinction.
Example: “Verilog is a type of hardware description language that describes electronic systems and circuits. You basically prepare circuit components inside a module that contains structural and behavioral statements. There are several reasons why it differs from other common programming languages. For example, triggers have multiple threads and use the concept of simulation time, which the others don’t. It also has basic circuit concepts like primitive gates.”
What is the depletion region in VLSI?
Make sure you familiarize yourself with the concept so you can answer with confidence and minimal delay, and try to elaborate on the exhaustion area as much as possible.
Example: “The depletion region is the invention of a positive voltage across the gates, which then originates positive charge to be repelled from the region of the substrate below the channel region. Pushing the holes down in the substrate creates this depletion region. In this region or zone, all mobile charge carriers are gone and only accept impurities and ionized donors.”
What is a procedural block and what are the two forms in Verilog?
For this question, you can go to further explanation to elaborate on the two types. If you don’t remember both, try to name at least one of them.
Example: “A procedural block is an infinite loop in Verilog that automatically repeats the process of executing statements inside the loop. You use procedural blocks to perform repetitive maintenance activities without affecting the design. The two kinds are original and always.”
What is skew and what types can you use in VLSI?
Research and remember what a contortion is so you can give a complete but concise answer. To further illustrate your knowledge, provide a brief definition of each type.
Example: “In VLSI, bias is an element that decreases the amount of interruption and makes the route easier to know. There are several types of bias, but the three most important are local bias, global bias, and useful bias.”
What are setup violations and suspensions?
Explain what setup violations and suspensions are, detailing why they are important. You can also briefly explain some of the violations that occur.
Example: “Set-and-suspend violations describe circumstances where design work processes do not transfer in time. Each set-and-suspend timing must occur in the correct order to ensure that data is executed from one flop to the next according to the state machine design. When these settings and holding paths fail, the design is inconsistent.”
What steps will you take to resolve setup and hold violations in VLSI?
It is important that you research and memorize the steps so that you can answer this question confidently and tactfully. There are four basic steps you need to learn. If you don’t remember all the steps, try to describe at least two or three of them.
Example: “There are many steps to help you solve the setup and contain the violation. In my experience, you can optimize and then restructure the logic between each flop. This will cause the logic to converge, solving the problem. You can also adjust the clock network so that it reduces the slowdown or lag when capturing flip actions.”
What is an antenna violation and how do you avoid it?
Answer this question directly and clearly. There are several ways to prevent this violation, so try to list at least two prevention methods to demonstrate your current knowledge.
Example: “During plasma etching, antenna distortion can occur when charges from one metal strip to another metal strip accumulate in one area. This happens because charges accumulate based on the length of the strip, so a longer strip can collect more charges” You can solve the problem by moving the metal. You can also prevent this violation by adding reverse diodes to the gates of the circuit.”
What are some differences between a CMOS chip and a TTL chip?
There are a few differences that you can mention. Try to describe at least two basic differences.
Example: “The primary difference is in their function. You mostly use CMOS chips for cell phones, while TTL chips for computers. CMOS chips also use FETs, while TTL chips use BJTs. Another difference is that TTL chips use a significant amount of power and energy, even when it’s in sleep mode. A CMOS chip consumes a significantly lower amount of power.”
What are integrated circuits and what are their four generations?
If you are familiar with the concept and have the time, you can elaborate on each of the four generations to make the differences between them more apparent. If you describe each, provide brief definitions.
Example: “An integrated circuit is a group of electronic circuits placed on a minor flat silicon semiconductor. The four generations of integrated circuits include small, medium, large, and very large.”
25 More VLSI Questions
Explore this list of 25 more VLSI interview questions an employer may ask you during an interview.
- What method do you use to stop metastability in VLSI?
- Define a multiplexer?
- What gates use boolean logic?
- What advantages does a CMOS chip have over a TTL chip?
- Give some reasons why VLSI circuits use MOSFETs instead of BJTs.
- What are the three main areas of MOSFET operation?
- Define what is a silicon rectifier.
- What does channel length modulation mean?
- Describe the phrase “channel is disconnected”.
- What are DCMs and how do you use them?
- What is defparam and what is its use?
- List the different types of Cmos processes.
- What is Moore’s Law?
- What is channel length modulation?
- Describe the function of tie-high and tie-low cells.
- What are some of the various design constraints in the synthesis phase?
- How many transistors does static RAM use?
- What are PLA and PAL and what are their differences?
- Describe the design rules for VLSI-based technology.
- Where is the difference between a pass transistor and CMOS domino logic?
- What are ROBDD and OBDD and how are they different?
- What is a soft bug and give an example of how you could fix it.
- Describe some problems with DSM
- What is MTBF in VLSI?
- What are the main differences between the Mealy machine model and the Moore machine model?
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