Multi-Height Cell IR/EM Analysis via Sink Current Distribution
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Solution Overview
Problem
Existing methods for IR/EM analysis face complications, especially when dealing with cells having a height that is a multiple of the standard cell height, as they assume evenly distributed sink currents across power/ground rail sets, leading to significant errors in analysis accuracy, particularly for multi-height cells.
Innovation Solution
The method involves determining precise sink current distribution information for each power/ground rail set, using a slew-load table to estimate current proportions, and employing this information in IR/EM analysis to generate accurate results, especially for cells with heights that correspond to multiple rail sets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sink current is assumed to be evenly distributed across power/ground rail sets, then the analysis process is simplified, but the analysis accuracy deteriorates significantly for multi-height cells
Solution Approach 1:
The patent applies local quality by determining sink current distribution specific to each power/ground rail set based on the cell's vertical position. Instead of uniformly distributing current across all rail sets, the method calculates distinct current proportions for each rail set according to its location within the multi-height cell, thereby achieving accurate local current characterization that resolves the accuracy-complexity contradiction.
Solution Approach 2:
The patent changes the parameter distribution model from uniform to non-uniform based on cell height characteristics. By introducing height-based current distribution ratios as varying parameters rather than fixed equal values, the method accurately captures the physical reality of current flow in multi-height cells while maintaining computational tractability through systematic parameterization.
2Ease of manufacture
If standardized cell height constraints are enforced (single height or multiple of standard height), then cell placement and routing become easier, but power/ground rail planning complexity increases for electro migration and voltage drop analysis
Solution Approach 1:
The patent introduces dynamic current distribution parameters based on cell height multiples. By parameterizing the current split ratios according to the number of standard cell heights and the position of power/ground rails, the method systematically handles varying cell heights while maintaining ease of placement and routing. This parameterized approach transforms the complexity into a manageable calculation rather than a planning burden.
3Area of stationary object
If multi-height cells are used to reduce cell row density, then area utilization improves, but sink current distribution becomes non-uniform requiring more complex analysis
Solution Approach 1:
The patent applies local quality by assigning specific current distribution characteristics to each power/ground rail set based on its vertical position within the multi-height cell. This local differentiation accurately captures the non-uniform current distribution that naturally occurs in multi-height cells, enabling precise IR/EM analysis that respects the area utilization benefits while correctly modeling the resulting current variations.
Data Source
AI summary
An integrated circuit (IC) design method is disclosed. The method includes: using a computer to perform synthesis upon a register transfer level (RTL) IC design to generate a gate level netlist; performing place and route (P&R) upon the gate level netlist to generate a layout; determining a sink current distribution information of the layout; and generating a voltage (IR) drop/electro-migration (EM) analysis result of the layout according to the sink current distribution information; wherein the layout includes a cell having a cell height that is N times higher than a single cell height, where N is an integer and greater than 1, and the cell corresponds to N power/ground (P/G) rail sets; wherein the sink current distribution information includes a proportion of a sink current flowing through each of the N power/ground (P/G) rail sets with respect to the cell when operated. Associated non-transitory computer-readable medium is also disclosed.