TCD (Test-key Critical Dimension) Cell
FAB工厂定位检测用，防止工艺偏差。
A TCD cell is placed at every 2mmX2mm square。
The TCD structure is required to be placed at regular intervals throughout the chip.It could be a significant size, which may need to be allocated on the die early on.
This may impact a floorplan of a block at a later stage if this fact is not considered early on, such as in a block packed with memories.
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来源：CSDN
作者：每天一个小脚印
链接：https://blog.csdn.net/hepiaopiao_wemedia/article/details/104753775