Cell Characterization Using Input Waveforms with Different Tail Characteristics
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Solution Overview
Problem
In static timing analysis for integrated circuit (IC) chip design, the accuracy of delay calculation is compromised due to distortion in the propagated input waveform caused by increased interconnect lengths and Miller capacitance in miniaturized transistors, which is not accounted for when using a predetermined input waveform.
Innovation Solution
Characterizing cells with respect to different circuit topologies to generate input waveforms that better resemble the distorted propagated waveforms, and applying sensitivity corrections to improve the accuracy of delay calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a predetermined input waveform is used for cell characterization, then the characterization process is simple, but the accuracy of delay calculation deteriorates due to waveform distortion from interconnects and Miller capacitance
Solution Approach 1:
The patent segments the input waveform characterization into multiple distinct waveform types (e.g., fast-rise/slow-fall, slow-rise/fast-fall, symmetric) with different tail characteristics. Each waveform type is characterized separately and stored in lookup tables, allowing the timing analysis tool to select the appropriate waveform based on the actual propagated waveform characteristics, thereby improving accuracy without requiring a single overly complex characterization model
Solution Approach 2:
The patent introduces dynamic selection of input waveforms based on the actual propagated waveform characteristics (rise time, fall time, tail characteristics). Instead of using a fixed predetermined waveform, the system dynamically chooses the most appropriate waveform from multiple options by comparing waveform parameters, enabling adaptive accuracy that matches the actual circuit behavior while maintaining manageable complexity through parameter-based selection
2Measurement precision
If circuit topology effects are considered in waveform generation, then the resemblance to propagated waveforms improves, but the waveform generation process becomes more complex
Solution Approach 1:
The patent changes key parameters of the input waveform (rise time, fall time, tail duration, tail amplitude) to match the characteristics of propagated waveforms from different circuit topologies. By adjusting these parameters systematically and storing them in lookup tables, the method captures topology effects without requiring complex real-time simulation, balancing waveform accuracy with generation simplicity
Solution Approach 2:
The patent creates simplified copies of actual propagated waveforms by generating representative input waveforms that capture the essential characteristics (rise/fall times, tail behavior) of waveforms from different circuit topologies. These copied waveform models are stored in lookup tables and can be quickly selected during timing analysis, avoiding the need for complex real-time waveform generation while maintaining high resemblance to actual propagated waveforms
Data Source
AI summary
In some embodiments, a plurality of first input waveforms having a same first input transition characteristic and different first tail characteristics are obtained. A first cell is characterized using the plurality of first input waveforms to create a plurality of corresponding first entries associated with the first input transition characteristic in a library. A design layout is generated based on performing circuit simulation using at least one entry of the plurality of first entries. An integrated circuit (IC) chip is manufactured using the design layout.