Clock Path Delay Determination Using Proximity Factors
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Solution Overview
Problem
Static timing analysis (STA) tools often produce overly optimistic or pessimistic results for clock path delays in circuit designs, leading to potential timing violations or suboptimal clock speeds due to assumptions about topologically similar clock paths having identical delays, which neglect proximity effects and random variations.
Innovation Solution
The method involves determining clock path delays by considering proximity factors, metal layer variations, and statistical factors for random variations, allowing for more accurate clock skew prediction and optimization by selecting wire segments based on their proximity to physical structures and metal layers, and adjusting programmable delays to equalize delays in clock trees.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If STA tools assume worst-case delay for topologically similar clock paths, then timing constraints are satisfied, but the implemented circuit operates at a slower frequency than potentially achievable
Solution Approach 1:
The patent applies local quality by assigning unique delay values to individual wire segments based on their specific physical characteristics (proximity to logic blocks, metal layer, length) rather than assuming uniform delay for topologically similar paths. This localized delay characterization allows accurate identification of actual critical paths while providing slack for non-critical paths, enabling higher clock frequencies without violating timing constraints.
2Device complexity
If STA tools use uniform delay values for topologically similar clock paths, then analysis is simplified, but proximity effects and random variations are neglected leading to inaccurate delay prediction
Solution Approach 1:
The patent segments the clock distribution network into individual wire segments, each characterized by unique delay values based on physical attributes such as proximity to logic blocks, metal layer, and segment length. This segmentation enables precise delay prediction for each segment while maintaining systematic tractability through automated characterization and propagation of delay values through the clock tree.
Solution Approach 2:
The patent changes the delay parameter from a uniform value applied to topologically similar paths to variable values specific to each wire segment. By introducing parameters such as proximity factors, metal layer variations, and statistical factors for random variations, the system achieves accurate delay prediction that accounts for physical effects and manufacturing variations.
3Productivity
If STA produces optimistic delay results, then faster clock speeds are predicted, but the physical circuit may violate timing constraints
Solution Approach 1:
The patent applies local quality by characterizing each wire segment with unique delay values based on its specific physical environment (proximity to logic blocks, metal layer, length) rather than using uniform optimistic estimates. This localized characterization ensures that actual critical paths are accurately identified and timing constraints are reliably satisfied while still achieving the highest possible clock frequency.
Data Source
AI summary
The disclosed approaches process a circuit design that specifies a clock signal. A plurality of wire segments of an integrated circuit (IC) are selected for a clock path to carry the clock signal. A delay of the clock path is determined based on delay values associated with identifiers of the wire segments and variation factors. Configuration data is generated from the circuit design once the delay of the clock path satisfies a timing constraint, and a circuit is generated from the configuration data to implement a circuit according to the circuit design.