Equivalent Waveform Model for Static Timing Analysis
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Solution Overview
Problem
Conventional static timing analysis tools struggle to accurately capture waveform shape variations and non-idealities such as overshoots and ringing in modern integrated circuits, especially in deep sub-micron technologies, due to limitations in pre-characterization models and approximations, leading to inaccuracies in delay calculations.
Innovation Solution
The method involves generating an equivalent waveform model using an analog model of an inner component to simulate complex waveforms, producing multiple analog simulation output characterization waveforms and an equivalent waveform model that can accurately represent complex input waveforms, thereby improving delay calculations in static timing analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional pre-characterization models and approximations are used in static timing analysis, then analysis speed is maintained, but accuracy in capturing waveform shape variations and non-idealities deteriorates
Solution Approach 1:
The complex waveform modeling problem is segmented into multiple discrete waveform templates (e.g., 9 templates representing different waveform shapes). Instead of attempting to model all possible waveform variations continuously, the patent divides the waveform space into discrete categories, each represented by a template. This segmentation allows STA tools to select appropriate templates based on input conditions while maintaining computational efficiency.
Solution Approach 2:
The patent introduces waveform shape as an additional parameter beyond the traditional slew and delay parameters. By changing the parameter set to include waveform shape characteristics (through template selection), the model can accurately represent non-ideal waveform behaviors such as overshoots, ringing, and non-monotonic transitions without requiring complex continuous modeling approaches.
2Measurement precision
If analog simulation is used to characterize cells, then waveform accuracy is improved, but computation time increases significantly
Solution Approach 1:
The patent performs waveform template generation and characterization in advance, before actual static timing analysis. Analog simulations are run offline to create a library of waveform templates and their associated delay characteristics. During production STA, the pre-computed templates are simply selected and applied based on input slew and waveform shape matching, eliminating the need for real-time analog simulation and achieving both accuracy and speed.
Solution Approach 2:
Instead of performing full analog simulations during STA, the patent creates simplified copy representations of complex waveforms in the form of templates. These templates capture the essential characteristics of analog-simulated waveforms (shape, slew, delay) in a compressed format that can be rapidly processed during timing analysis without requiring the computational resources of full analog simulation.
3Productivity
If predetermined characterization parameters are used, then STA computational efficiency is maintained, but ability to describe deep sub-micron waveform variations deteriorates
Solution Approach 1:
The patent makes the waveform characterization dynamic by introducing template selection based on input conditions. Rather than using fixed predetermined parameters, the system dynamically selects appropriate waveform templates based on the input slew rate and observed waveform characteristics. This dynamic adaptation allows the STA tool to handle diverse waveform shapes encountered in deep sub-micron technologies while maintaining computational efficiency through template-based matching.
Data Source
AI summary
A method is provided for use during static timing analysis of an integrated circuit design to produce an equivalent waveform model, the method comprising: using an analog model of the inner component, to simulate an inner component to produce multiple analog simulation output characterization waveforms as a function of multiple input waveforms used to characterize the design cell; using the analog model of the inner component to simulate the inner component to produce an analog simulation output waveform as a function of the complex waveform; and producing the equivalent waveform model as a function of the multiple analog simulation output characterization waveforms and the analog simulation output waveform.