# What is Static Timing Analysis in VLSI?

## What is Static Timing Analysis in VLSI?

Static timing analysis (STA) is a way of evaluating a design’s timing performance by testing for timing violations along all conceivable paths. Dynamic simulation, which determines the whole behaviour of the circuit for a given set of input stimulus vectors, is another technique to do timing analysis. One of the tools for verifying design in terms of time is static timing analysis (STA). This type of analysis is independent of any data or logic inputs at the input ports. The routed netlist, clock definitions (or clock frequency), and external environment specifications are all inputs to an STA tool in the VLSI course

## What is Static Timing Analysis and how does it work?

STA breaks down the design into time pathways before doing timing analysis. The following factors make up each time path:

Startpoint: The beginning of a timing route in which data is launched by a clock edge or must be ready at a certain moment. Every startpoint must be a register clock pin or an input port.

Combinational logic network: It includes elements with no internal state or memory. AND, OR, XOR, and inverter elements are allowed in combinational logic, but flip-flops, latches, registers, and RAM are not.

Endpoint: When data is caught by a clock edge or when it needs to be provided at a specified moment, this is the end of a timing path. A register data input pin or an output port must be present at each endpoint.

Static timing analysis calculates a maximum delay using the longest way and a minimum delay using the shortest path.

## For time analysis, STA additionally examines the following sorts of paths:

The journey of the clock: A path from a clock input port or cell pin to the clock pin of a sequential element, via one or more buffers or inverters, for data setup and hold checks.

Clock-gating path: A path from an input port to a clock-gating element is required for clock-gating setup and hold checks.

Asynchronous path: A path from an input port to a sequential element’s asynchronous set or clear pin for recovery and removal checks.

An STA tool estimates the delay along each path after breaking down a design into a series of timing pathways. The sum of all cell and net delays in a path is the path’s total delay.

The delay between the input and output of a logic gate in a path is known as cell delay. The tool estimates the cell delay from delay tables given in the logic library for the cell in the absence of back-annotated delay information from an SDF file. A delay table, for example, lists the amount of delay as a function of one or more factors like input transition time and output load capacitance. The tool estimates each cell delay based on these table entries. The amount of time it takes for a cell’s output to reach the input of the following cell in a timing path is known as net delay.

## Static timing analysis then looks for time restrictions, such as setup and hold limitations, to see whether they have been broken:

• A setup restriction specifies how much time data must be available at the sequential device’s input before the clock edge that records the data. This restriction sets a maximum data path delay in relation to the clock edge.
• After the clock edge that captures the data in the device, a hold restriction indicates how much time is required for data to be stable at the input of a sequential device. This requirement ensures that the data flow is kept as close to the clock edge as possible in the VLSI design course.

## Is there a Synopsys STA solution?

Synopsys’ PrimeTime static timing analysis tool delivers a single, golden, trusted signoff solution for timing, signal integrity, power, and variation-aware analysis. Synopsys PrimeTime package includes PrimeTime, PrimeTime SI, PrimeTime ADV, and PrimeTime PX. It provides HSPICE with accurate signoff analysis, which aids in the identification of issues prior to tape out, decreasing schedule risk, ensuring design integrity, and saving design costs.

This industry-standard solution boosts your team’s productivity by offering rapid development timelines for big and small designs, as well as assuring first-pass silicon success with improved predictability and accuracy.

## Conclusion:

Static timing analysis is substantially faster than dynamic simulation since it does not need to simulate the circuit’s logical process. STA is also more comprehensive since it examines all time routes rather than simply the logical circumstances affected by a set of test vectors. STA, on the other hand, can only examine the timing of a circuit design, not its functioning.

Chipedge being one of the best VLSI training institutes in India offers a static analysis course in which you will study the fundamentals of static timing analysis and how to apply them to limit a design. You use these principles to define limits, compute slack values for various path types, identify timing issues, and examine static timing analysis tool results.

## Subscribe to our Blog

Get the latest VLSI news, updates, technical and interview resources