DIGICOMM Semiconductor Interview Questions and Answers

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.

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

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.

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

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

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

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

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