Configurable Clock Grid H-Tree Pruning for Skew Reduction
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Solution Overview
Problem
Existing clock tree routing methods struggle to effectively manage clock skew, particularly unknown skew caused by PVT variations, leading to performance losses due to the need for margins that reduce circuit performance.
Innovation Solution
A configurable clock grid structure with uncommitted wire segments allows for the construction of arbitrary-shaped clock trees, enabling the reduction of clock skew by aligning and pruning H-trees to optimize clock signal routing based on performance, and selectively routing clock signals to minimize clock loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If margins are included to compensate for unknown skew, then hold and setup time constraints are met, but circuit performance is reduced
Solution Approach 1:
The patent replaces traditional mechanical timing margin compensation with a statistical modeling approach. Instead of adding fixed time margins to account for unknown skew, the system uses analytical models to predict delay distributions and calculates precise timing constraints based on statistical parameters, eliminating the need for conservative margin additions.
Solution Approach 2:
The patent changes the approach from fixed margin values to dynamic statistical parameters. By modeling delay variations as statistical distributions and using parameters like mean and standard deviation, the system adapts timing constraints to actual process variations rather than using worst-case fixed margins, thereby improving circuit performance while maintaining reliability.
2Reliability
If clock tree routing compensates for known skew, then clock skew is reduced, but unknown skew from PVT variations remains difficult to evaluate and compensate
Solution Approach 1:
The patent performs preliminary statistical modeling and delay distribution analysis during the design phase. By pre-characterizing the clock tree structure and wire segments, the system establishes analytical models that predict delay variations under PVT conditions before actual fabrication, enabling evaluation of unknown skew without requiring post-fabrication measurement.
Solution Approach 2:
The patent introduces analytical models and statistical parameters as intermediaries between the physical clock tree structure and the timing analysis process. These models act as mediators that translate physical wire characteristics and process variations into predictable delay distributions, making unknown skew evaluable through computation rather than direct measurement.
3Reliability
If timing analysis tools build in margin for unknown skew, then hold and setup time constraints are met, but clock loss increases
Solution Approach 1:
The patent replaces the mechanical approach of adding fixed time margins with a statistical timing analysis system. By using analytical models to predict actual delay distributions, the system calculates precise setup and hold time constraints without requiring additional margin time, thereby reducing clock loss while maintaining timing constraint satisfaction.
Solution Approach 2:
The patent changes timing analysis from using fixed margin parameters to dynamic statistical parameters derived from delay distributions. By modeling delays as statistical variables and computing constraints based on distribution characteristics rather than worst-case margins, the system minimizes clock loss while ensuring timing constraints are met with high probability.
Data Source
AI summary
A clock-tree construction method for a configurable clock grid structure having a plurality of sectors and a plurality of wire segments includes defining a clock region within the clock grid structure and constructing an H-tree that has a smallest size to cover the clock region. The method further includes aligning the clock region within the H-tree, pruning the H-tree and removing an unused segment from the H-tree. The method further includes performing a tree height reduction procedure to the pruned H-tree, and generating a clock tree with a reduced size or a reduced height from the tree height reduction procedure.