Combined Tie Cell Layout for Routing Congestion
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Solution Overview
Problem
In circuit layout, after chip tap out, engineering changes often lead to routing congestion due to replaced standard cells being distant from their corresponding tie cells, causing inefficiencies in connecting spare cells to provide the required voltages.
Innovation Solution
The introduction of combined tie cells, comprising both tie-high and tie-low circuits, which are strategically placed near spare and standard cells to provide the necessary voltages, reducing routing congestion by allowing easy connection and voltage tying.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate tie-high cells and tie-low cells are used for each spare cell, then voltage tying is achieved, but routing congestion increases due to multiple distant connections
Solution Approach 1:
The patent combines multiple tie cells (tie-high and tie-low) into a single integrated structure called a combined tie cell. This merged structure provides both high voltage and low voltage tying functions in one location, reducing the number of separate tie cells needed and minimizing routing congestion while maintaining proper voltage connections for spare cells.
Solution Approach 2:
The combined tie cell serves multiple functions simultaneously: it provides both tie-high and tie-low connections, and can serve multiple spare cells from a single location. This multi-functional design eliminates the need for separate dedicated tie cells for each spare cell, reducing overall routing complexity while ensuring proper voltage tying.
2Adaptability or versatility
If spare cells are placed distant from tie cells, then layout flexibility is improved, but routing distance increases causing congestion
Solution Approach 1:
The combined tie cells are pre-positioned at strategic locations in the layout before final cell placement. This preliminary positioning allows subsequent spare cells to be placed flexibly while knowing that tie connections are already available at predetermined locations, reducing the need for long routing distances while maintaining layout adaptability.
Solution Approach 2:
The combined tie cell acts as an intermediary structure that mediates between the power network and multiple spare cells. By providing a centralized intermediate connection point, it reduces the total routing distance required compared to connecting each spare cell individually to separate tie cells, while still allowing flexible placement of spare cells throughout the layout.
Data Source
AI summary
A layout circuit is provided, comprising standard cells, a spare cell, combined tie cells and normal filler cells. The standard cells are disposed and routed on a layout area. The spare cell is added on the layout area and provided for replacing one of the standard cells while adding or changing functions later. The combined tie cells are added on the layout area. The normal filler cells are added on the rest of the layout area. The combined tie cell comprises a tie-high circuit, a tie-low circuit and a capacitance circuit. Some standard cells are disposed near at least one combined tie cell for avoiding routing congestion between the combined tie cells and the replaced standard cell. A circuit layout method is also provided.