Corner Analysis

Definition: Corner analysis is a technique used in static timing analysis (STA) to assess the timing performance of a digital circuit under various operating conditions, known as corners. A corner represents a combination of process, voltage, and temperature (PVT) variations that can affect the speed and functionality of the circuit.

Key Points:

  • Evaluates the circuit’s performance under best-case and worst-case scenarios
  • Considers variations in process parameters, supply voltage, and operating temperature
  • Helps ensure the circuit functions correctly across all specified operating conditions
  • Performed during the STA phase of the VLSI design flow

Common Corners:

  • Slow-Slow (SS): Worst-case process, lowest voltage, highest temperature
  • Fast-Fast (FF): Best-case process, highest voltage, lowest temperature
  • Typical-Typical (TT): Nominal process, nominal voltage, nominal temperature
  • Slow-Fast (SF) and Fast-Slow (FS): Skewed corners for setup and hold analysis

Importance:

  • Ensures the circuit meets timing requirements under all operating conditions
  • Identifies potential timing violations and performance bottlenecks
  • Helps optimize the design for robustness and reliability
  • Ensures the manufactured chips will function correctly in the specified environment

Corner Analysis Flow:

  1. Characterize the standard cell library for each corner
  2. Create corner-specific timing models (e.g., .lib files)
  3. Run STA for each corner using the corresponding timing models
  4. Analyze timing reports and identify violations
  5. Optimize the design to meet timing at all corners

Challenges:

  • Increased runtime due to multiple STA runs
  • Managing and maintaining multiple corner-specific libraries and constraints
  • Balancing performance and robustness across corners
  • Dealing with corner-specific timing violations and optimizations

Advanced Techniques:

  • Multi-corner optimization (MCO) to simultaneously optimize for multiple corners
  • On-chip variation (OCV) analysis to account for local variations within a die
  • Statistical static timing analysis (SSTA) to consider statistical distributions of process parameters

Corner analysis is a critical step in the VLSI design flow, ensuring that the circuit functions correctly and meets performance targets under various operating conditions. By analyzing the design at different corners, designers can create robust and reliable circuits that can withstand PVT variations.