Static Timing Analysis Derate Adjustment for IC Design
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Solution Overview
Problem
Existing static timing analysis tools determine timing derates for integrated circuit designs based on a single default condition, which can lead to either optimistic or pessimistic results due to variations in delay caused by capacitive load, slew rate, and voltage changes, resulting in potential timing errors and unnecessary buffer insertion.
Innovation Solution
A method that adjusts timing derates based on the expected design condition surrounding each logic cell, using a derate adjustment factor to accurately track actual delay variations, reducing both optimism and pessimism, and thereby improving the accuracy of timing analysis without unnecessary buffer insertion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single default timing derate is used for all cells, then the STA tool operates simply and quickly, but the timing analysis becomes either optimistic or pessimistic and inaccurate
Solution Approach 1:
The patent applies local quality by determining different timing derates for different logic cells based on their specific design conditions. Each cell's timing derate is adjusted according to its local characteristics such as capacitive load, slew rate, and voltage changes, rather than using a uniform derate for all cells. This localized approach improves timing analysis accuracy while maintaining manageable complexity through automated derivation of adjustment factors.
Solution Approach 2:
The patent implements dynamics by making timing derates adaptive to actual design conditions. The timing derate for each cell is dynamically adjusted based on its specific operating conditions (capacitive load, slew rate, voltage), allowing the STA tool to adapt to varying cell characteristics rather than using static default values. This dynamic adjustment resolves the contradiction by improving accuracy without requiring manual intervention for each cell.
2Measurement precision
If timing derate is adjusted for each cell's design condition, then timing analysis accuracy improves, but computational complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-deriving timing derate adjustment factors for different design conditions before performing the actual timing analysis. The adjustment factors are determined in advance based on cell characteristics such as capacitive load, slew rate, and voltage, so that during timing analysis, the tool can efficiently apply these pre-computed factors without performing complex calculations for each cell. This approach improves timing derate accuracy while maintaining STA tool efficiency.
3Loss of energy
If optimistic timing derate is used, then fewer buffers are inserted and power consumption is reduced, but timing errors may occur in practice
Solution Approach 1:
The patent replaces the mechanical approach of inserting buffers to ensure timing compliance with a computational approach using adjusted timing derates. Instead of adding physical buffers to compensate for pessimistic timing estimates, the system uses accurately derived timing derates that reflect actual cell operating conditions. This substitution eliminates the need for unnecessary buffers, reducing power consumption while maintaining circuit reliability through accurate timing prediction.
4Reliability
If pessimistic timing derate is used, then timing violations are detected conservatively, but unnecessary buffers are inserted increasing power consumption and area
Solution Approach 1:
The patent replaces the mechanical solution of inserting buffers to ensure timing compliance with an accurate computational model using design-condition-specific timing derates. By deriving timing derates that accurately reflect each cell's operating conditions (capacitive load, slew rate, voltage), the system can reliably detect actual timing violations without the pessimism that triggers unnecessary buffer insertion. This eliminates wasted circuit area while maintaining timing requirement compliance through accurate prediction.
Data Source
AI summary
A static timing analysis method and apparatus that determine an expected design condition surrounding a target cell in an integrated circuit design. A derate adjustment is determined based on the expected design condition for a target cell and a timing derate, representing variation in propagation delay for a default design condition, is then adjusted based on the derate adjustment. An expected timing of a signal path including the target cell is determined based on the adjusted timing derate. The derate adjustment may be determined based on simulated variance of the propagation delay through the target cell for the expected design condition. This approach avoids unnecessary optimism or pessimism in the timing derate, which reduces the number of false positive or false negative detections of timing violations in the static timing analysis.