Top 15 VLSI Interview Questions and Answers

There are thousands of openings for VLSI developers. For the students to have the finest employment chances in the future, they need to have an in-depth understanding of the subject. As a successful VLSI engineer, you can earn around ₹670,631 per year. 

This comprehensive list of the top VLSI design engineer interview questions will guide you through topics like

• Introduction to VLSI
• VLSI Designing
• VLSI Designing Architecture
• Digital Design.

List of 15 Ideal VLSI Interview Questions for Your Upcoming Interviews

For newcomers and experienced applicants looking to land their dream job, the most often asked basic to advanced VLSI interview questions are below.

 

• Explain Verilog in simple terms.

 

The HDL (Hardware Description Language) used to describe electronic circuits and systems is called Verilog. Circuit parts are constructed inside a Module in Verilog. Both behavioural and structural statements are present. 

Structural statements serve as a representation for circuitry components such as logic gates, counters, and microprocessors. Behavioural statements represent programming constructs like loops, if-then statements, and stimulus vectors.

 

• What do you mean by the depletion region?

 

The substrate region beneath the Gate is pushed back or repelled by the free holes (positive charge) when a positive voltage is applied across the Gate. When driven down the substrate, these holes leave a carrier depletion region behind.

 

• What does it indicate when "the channel is pinch off"?

 

When the power between the gate and source (VGS) surpasses the threshold voltage, a MOSFET's channel is induced (Vt). The channel depth at the drain end reduces practically to zero as the VGS - VDS voltage between the gate and channel at the drain end equals Vt. 

As we increase, VDS current begins to flow from Drain to Source. The canal is believed to be "pinched off" at this point. At this point, the canal is thought to have been "pinched off." In these conditions, the MOSFET enters the saturation region.

 

• How can a binary number generate or transform into a digital signal?

 

Binary numbers (either 0 or 1) convey two instructions, where 1 denotes the ON state and 0 is the OFF state. By conducting mathematical calculations and sorting activities, these binary numbers can operate billions of machines by combining them into a single circuit or machine.

 

• What exactly is Slack?

 

The time gap between the anticipated and actual delays in a particular path is referred to as slack. Slack may be harmful or beneficial depending on a specific situation.

 

• What are the various skews implemented in VLSI?

 

The different skews include

Local skew: The difference between the launching flip-flop and the destination flip-flop is typically included in the local skew. This distinction aids in defining a timeline connecting the two.

Global skew: The discrepancy between the earliest components reaching the flip flop within the same clock domain is known as the global skew. The clock is the same for both. Therefore, the delays are not measured.

Useful skew: The useful skew is used to specify the delay in capturing flip-flop paths, which subsequently aids in creating a setting with precise criteria for the launch and capture of the timing path. For design considerations to satisfy the hold requirements, it must be mentioned.

 

• What mechanism does Boolean logic used to control logical gates?

 

The true state in Boolean algebra is represented by the number one, often known as logic one or logic high. While logic zero, also known as a logic low, or the number zero, stands in for the false condition. Additionally, in digital electronics, the presence of a voltage potential designates a logic high.

 

• What does the term "threshold voltage" mean to you?

 

The threshold voltage is often denoted by the symbol V??. It can be described as a voltage, or VGS, between the Gate and Source. 

When enough mobile electrons are in the channel region, they build up and form a conducting channel. The lowest gate-to-source voltage is necessary to establish a route for current to flow between the source and drain terminals. The threshold voltage is a crucial scaling factor for preserving power efficiency.

 

• What are tie-high and tie-low cells used for?

 

The transistors of the gate are connected, utilising either the power or the ground by the tie-high and tie-low cells. Because power bounces off the ground, the gates are connected to the power or ground to switch them on and off.

The cells ease the current from one cell to another and stop the bouncing. These cells need Vdd, which connects to the tie-high cell when the power supply is high, and the tie-low cell links to Vss when the power supply is low. Transistors work properly after the connection; no cell experiences a ground bounce.

 

• Describe Moore's law.

 

Moor's law is one of the most important laws that characterise the emergence of large-scale integration technologies. The co-founder of Intel, Gordon Moor, anticipated that an integrated circuit's transistor count would double every 1.5 years.

 

• Mention the two categories of Verilog procedural blocks.

 

In Verilog, there are two kinds of procedural blocks: 

Initial: Initial blocks only execute once at a time. 

Always: As suggested by its name, this block loop will run continuously.

 

• Describe why CMOS gates typically only have four gate inputs.

 

The slower the gate, the more stacks there are. The number of gates included in the stack of NOR and NAND gates is typically equal to the number of inputs plus one. Input is therefore limited to four.

 

• What is an SCR (Silicon Controlled Rectifier) in the context of VLSI?

 

A four-layered solid-state device called an SCR regulates the current flow. It is a particular class of rectifiers managed by a gate signal. It has four layers and three terminals.

 

• Describe the purpose of defparam.

 

Any module instance in the design can have its parameter values set by using the keyword defparam. A design file that is several levels underneath the current design file can receive parameters via a Defparam Statement. For instance, top.v can pass parameter values straight to middle.v and bottom.v in the case when top.v instantiates middle.v, which then instantiates bottom.v.

 

• How many transistors are required for static RAM?

 

In a static RAM, six transistors are frequently deployed. In the static RAM, read and write procedures share the same port.

Conclusion

Keep in mind that during the interview, the examiner frequently tests your foundational understanding of the subject. If your foundation is solid, you can land the job of your dreams. Industry professionals are aware that it is simple for a corporation to train an employee toward advanced capabilities if the student's foundation is already established.

One of the top online course providers for VLSI course, Skill-Lync offers advanced training in the subject. With our team of highly skilled professional tutors from VLSI engineers, we guarantee the engineers a top-notch education. Along with that, we also provide placement training by conducting mock interviews and resume-building sessions.