VLSI interview questions and answers for both freshmen and veterans. You can also discover online practice tests on VLSI to help you prepare for written tests and certification exams.
We’ve covered practically every VLSI question, like intel interview questions, designed interview questions that might be posed during an interview in this area.
List of 10 VLSI Interview Questions and Answers
1. What steps do you go through to resolve VLSI setup and hold violations?
To fix the setup and hold violations in VLSI, a few procedures must be taken. The process is as follows:
- The logic between the flops is optimized and restructured in this way. Therefore, the reason is connected in this manner, which aids in the solution of the problem.
- There is a technique to tweak the flip-flops such that they have a shorter setup time and give a faster device setup.
- For example, modifying the launch-flop to have a better hold on the clock pin, resulting in CK->Q, which speeds up the launch-flop and aids in the correction of setup violations.
- The clock’s network can be changed to lessen the delay or slowness of the watch that catches the flip-movement.
- A delay/buffer can be applied to the function being utilized, allowing for a minor delay.
2. What are the different approaches to avoiding antenna violations?
During the plasma etching process, the charges generated from one metal strip to the next accumulate in a specific location, causing antenna violation. In addition, the more time the strip is used, the more charges accrue. To avoid this, use the following method:
- Forming a jogging metal line that extends over the protected layer by at least one metal.
- The metal that is above the metal receiving the etching effect must be jogged. If one metal is etched, the other metal will be detached if no precautions are made.
- It can be avoided by using reverse diodes at the gates in the circuits.
3. What are the roles of tie-high and tie-low cells in the body?
Tie-high and tie-low are used to connect the transistors of the gate using either the power or the ground. The gates are related to the management or environment, and the power bounce from the bottom allows them to be turned off and on.
The cells prevent the electricity from bouncing and flowing freely from one cell to the next. There is a high-power supply and tie-low links to Vss; these cells require Vdd that connects to the tie-high cell. This connection is made, and the transistors typically perform without any ground bounce in any cells.
4. In VSDL, what is the primary function of metastability?
Metastability is a state that can’t be classified as either one or zero. It’s used to create a system that doesn’t meet the setup or hold time requirements.
The setup time necessitates data stability before the clock edge, and the hold time necessitates data stability after the clock edge has passed. Other potential violations could result in setup and hold violations. The data generated in this process is entirely asynchronous and clocked synchronously.
This provides a technique to build up the state in which the system’s violations may be identified, and the right design can be provided by using various additional functions.
5. What measures are involved in preventing metastability?
Metastability is an unknown state that prevents violations by following the methods below:
- When data comes from the asynchronous domain, suitable synchronizers are used, which can be two-stage or three-stage. This aids in the recovery of the metastable condition.
- Between cross-clocking domains, synchronizers are utilized. This minimizes metastability by eliminating the delay caused by data elements arriving and removing time from the metal surface.
- Quick flip-flops allow for speedier transactions and eliminate the time delay between one component and the next. However, it employs a narrower metastable window, which causes the delay, although faster flip-flops aid in speeding up the process and reducing the time delay.
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6. In the Synthesis phase, what are the various design constraints?
The design restriction occurs as a result of the following steps:
- First, a clock with a frequency and duty cycle is established. This clock aids in the flow of information and the synchronization of numerous devices.
- Based on the input port requirements, allows the time for transition..
- The load values are given for the output ports which are connected to the input ports.
- Delay values for both the input and output ports are set. The input and output delays are included in the hold.
- Define the case settings that will be used to report the proper time for the relevant pathways.
- The clock uncertainty values are set and maintained to display any violations that occur.
7. What changes are being made to fulfil design power targets?
There should be a procedure for designing with multi-VDD designs to reach the design power objective, as this region requires high performance and the high VDD that requires a low version.
This is used to make a voltage group that allows the level-shifter to shift and be placed in cross-voltage domains.
When Vt goes down, there is a design with several threshold voltages that necessitates excellent performance. Unfortunately, this has a lot of current leakages, which causes the Vt cell to function poorly.
The leakage power can be reduced since the clock consumes more power in this module; thus, inserting an ideal clock regulates the module and allows it to be provided more ability. Furthermore, when the clock gating cells use the clock buffers, the clock tree allows switching and reduces switching by lowering the intensity.
8. What are the various design strategies needed to develop a Digital Circuits Layout?
The following are the several design methodologies for creating the layout for digital circuits:
- Digital design is made up of standard cells that represent the layout’s required height. The arrangement is determined by the transistor’s size. It also includes the standard for Vdd and GND metal routes, which must be kept consistent.
- Only use metal in one direction when applying it directly. Any direction can be used and exhibited with the metal.
- Placing the substrate at the location where it will reveal all of the vacant places in the layout where resistances exist.
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9. What are the various procedures that must be taken to achieve the design for increased yield?
Manufacturability faults should be reduced to get an improved yield. Because the circuit performance must be excellent, the parametric result must be reduced. Variations in the manufacturing process are to blame for this decline. The following are few steps that can be taken: – Create powerful sunset files that include spacing and shorting rules. This consists of all of the rights that must be granted to the user.
- Examine the regions of the design that have lithographic concerns, such as sharp cuts.
- The use of redundant vias to reduce current and barrier breakdown.
- Optimal placement of the de-coupling capacitances can be achieved to reduce power surges.
10. What is an enhancement-mode transistor, and what does it do?
Because they rely on the electric field to change the shape and conductivity of the channel, enhancement mode transistors are also known as field-effect transistors. In a semiconductor material environment, this consists of one sort of charge carrier.
The unipolar transistors are also used to distinguish themselves from the single-carrier type operation transistors, which are bipolar junction transistors. When compared to bipolar transistors, field-effect transistors are used for the practical implementation of semiconductor materials.
Conclusion on VLSI Interview Questions
These are some of the most common VLSI interview questions. Make sure you look over our responses again and try to come up with some new ones.
To improve your chances of landing the job, practice your posture, voice, and response skills, as well as basic interview skills.
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