各位大神，能否帮我总结下保护环的作用是什么？谢谢

就是在芯片外面加一环狀填充 METAL + VIA 的保护, 不会使芯片受到切割刀破坏芯片内容也可使芯片 Size 更为精准。

cmos combination combine NMOS and PMOSstructure . In some cases the N and P structure use in each process can createa parasitic path between the supply and the ground. By using a guard ring thedesigner can reduce these parasitic effects (NPN-PNP parasitic transistors created).

The parasitic effect in this case is called:latch up. The latch up is basically a SCR circuit. If it turns on, it runs fastto an increasing current due to positive feedback causing malfunctioning or evendestruction. Recommend you to read the book of ‘the art of analog layout’