Ignitarium Technology Solutions Vlsi Design Engineer Interview Questions and Answers

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Q1. Hr will call for interview
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Q2. Tell me about you
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Q1. Describe the PD flow
Ans. 
The PD flow is the process of designing the physical layout of integrated circuits.
• Initial floorplanning to determine the placement of blocks and macros

• Placement and optimization of standard cells

• Routing of interconnects to connect the various components

• Physical verification to ensure design rules are met

• Timing closure to meet performance targets
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Q2. How to fix setup and hold violation
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Setup and hold violations can be fixed by adjusting timing constraints, optimizing clock tree, and redesigning critical paths.
• Adjust timing constraints to allow more time for signals to propagate

• Optimize clock tree to reduce clock skew and improve timing

• Redesign critical paths by adding buffers or restructuring logic

• Use ECO (Engineering Change Order) to make necessary changes without redoing the entire design
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Q3. What is you domain experties
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My domain expertise is in physical design engineering, specifically in the areas of floorplanning, placement, routing, and timing closure.
• Floorplanning

• Placement

• Routing

• Timing closure
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Q4. Why are you looking for job switch
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Q5. Why does setup and hold ail on same path
Ans. 
Setup and hold time violations can occur on the same path due to different reasons.
• Timing violations can occur due to variations in process, voltage, and temperature (PVT)

• Clock skew between different paths can lead to setup and hold violations on the same path

• Issues with clock tree synthesis or routing can also contribute to setup and hold time violations

• Improper constraints or incorrect timing analysis setup can resul
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Q1. 1st test we have 65 questions focusing on only Opamps
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Q1. We have mixed questions 40 in this test
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Q2. 20 from technical
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Q3. 20 from aptitude
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Q1. Asked few questions on network theory based circuits
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Q1. About the college experience
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Q2. About family and basic HR questions
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Q1. Write code randc behaviour
Ans. 
randc behavior generates random complex numbers with specified distribution
• Use randc to generate random complex numbers

• Specify distribution using arguments like mean, variance, etc.

• Example: randc(10, 1, 2) generates 10 random complex numbers with mean 1 and variance 2
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Q2. Functinal coverage
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Q3. Code coverage related questions
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Q4. Monitor and scoreboard connections
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Q5. Project related questions
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Q1. What are the PD inputs and outputs
Ans. 
PD inputs are design specifications and constraints, while outputs are physical layout of the design.
• Inputs include design specifications, constraints, technology libraries, and floorplan.

• Outputs include physical layout, placement of components, routing of wires, and design verification.

• Example: Input - RTL design, clock frequency, power constraints. Output - GDSII layout, timing analysis report.
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Q2. Describe each stage of PNR flow
Ans. 
PNR flow consists of synthesis, floorplanning, placement, clock tree synthesis, routing, and signoff stages.
• Synthesis: Convert RTL code to gate-level netlist

• Floorplanning: Define chip area, core, and I/O locations

• Placement: Place gates in specific locations to meet timing constraints

• Clock tree synthesis: Create clock distribution network

• Routing: Connect gates with wires while considering timing and congestion

• Signoff: V...read more
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Q3. What are the different techniques to minimize congestion?
Ans. 
Techniques to minimize congestion include buffer insertion, wire spreading, and layer assignment.
• Buffer insertion: Adding buffers to critical paths to improve timing and reduce congestion.

• Wire spreading: Distributing wires evenly to reduce congestion in specific areas.

• Layer assignment: Properly assigning different signal layers to reduce congestion on a single layer.
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Q4. What is the setup and hold time and different techniques to fix the setup and hold time violations?
Ans. 
Setup and hold time are timing constraints in digital circuits. Techniques to fix violations include adjusting clock skew, buffering signals, and optimizing routing.
• Setup time is the minimum amount of time a data input must be stable before the clock edge for proper operation.

• Hold time is the minimum amount of time a data input must be stable after the clock edge for proper operation.

• Techniques to fix setup and hold ti...read more
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Q5. What is signal integrity?
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Signal integrity refers to the quality of an electrical signal as it travels through a circuit or system.
• It involves ensuring that the signal remains clear and undistorted from the transmitter to the receiver.

• Factors affecting signal integrity include impedance matching, noise, crosstalk, and reflections.

• Signal integrity analysis is crucial in high-speed digital design to prevent data errors and ensure reliable communi...read more
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Q6. What is crosstalk and noise and how to fix it?
Ans. 
Crosstalk is unwanted interference between signals on adjacent lines, while noise is random unwanted signals that can degrade performance.
• Crosstalk occurs when signals on adjacent lines interfere with each other due to coupling effects.

• Noise is random unwanted signals that can be caused by various sources such as electromagnetic interference or power supply fluctuations.

• To fix crosstalk, techniques like spacing out lin...read more
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Q7. What is clock latency, skew and jitter?
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Clock latency is the delay between the clock signal being generated and reaching the destination, skew is the variation in arrival times of the clock signal at different destinations, and jitter is the variation in the period of the clock signal.
• Clock latency is the delay between the clock signal being generated and reaching the destination.

• Skew is the variation in arrival times of the clock signal at different destina...read more
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Q8. What is useful skew, negative skew and positive skew?
Ans. 
Useful skew, negative skew, and positive skew are terms used in physical design to describe timing constraints.
• Useful skew refers to intentional delay added to certain paths to meet timing requirements.

• Negative skew occurs when data arrives later than expected, leading to potential timing violations.

• Positive skew occurs when data arrives earlier than expected, potentially causing setup time violations.

• Skew can be adjus...read more
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