Introduction

Signoff is the process of verifying the design at final stage before going to the tape out. Clean signoff reports are the green signal to the fabrication because clean signoff reports ensure the design satisfies all the required specifications and constraints at the final stage.

Signoff tools are the analysis tools only, but PnR tools are implementation tools. So, all the changes noticed in the signoff stage have to implement only in PnR tools.Some of the major checks are discussed in below:

• STA
• EM
• IR
• Physical Verification

STA

STA means Static Timing Analysis. STA main agenda is to make sure that signals propagate through the design within specified time constraints. During STA tool divides entire design circuit into 4 sets of timing paths, which are in2reg, reg2reg, reg2out and in2out.Then analyzes the delay of signal paths in the circuit. By considering these delays, the analysis determines the worst-case and best-case timings for various paths. This information is important to make sure that the design functions properly and meets all performance requirements (like clock frequency and setup/hold timings).The famous tools for STA are PrimeTime and Tempus.

EM Analysis

      EM means Electromigration. It refers to the phenomenon where the movement of metal atoms within a conductor is induced by the flow of high current densities. This causes the metal atoms to break the metal or short with near by metal.  This will create issues like increased resistance, altered signal propagation, and eventually, circuit malfunction or complete failure. So, designers take care of this issue and they follow some strategies to fix this effect. The famous tools for EM analysis are Redhawk and Voltus.

IR Drop Analysis

IR Drop also known as Voltage Drop. Due to the internal resistance of the metal of power delivery network there could a drop-in voltage.This is becoming more critical as design complexity increases. An IR drop can lead to variations in supply voltage levels in the design, which causes performance degradation, functionality errors and even complete failures. Excessive IR drop can result in slower circuit operation, reduced noise margins and timing violations. The tools to analyze IR Drop are Redhawk and Voltus.

Physical verification

      Physical verification ensures the correctness of the layout before manufacturing. During this stage, tool analyzes the design layout data against a set of predefined design rules, which can cover various aspects such as minimum feature sizes, metal spacing, metal density, LVS, and more. By performing this stage, designers can identify the critical issues early in the design, reducing the risk of costly manufacturing errors and post-fabrication failures. The most famous tool for physical verification is caliber.