wyyll wrote on Dec 3rd, 2007, 6:21am:From what I have seen and read, I agree with Jerry that guard rings are not the be-all and end-all for getting
rid of pesky noise problems. They do however increase the distance between aggressor and victim, without appearing
as white space. Thanks for the link.
The ED article, even as a 2 part series, had to be watered down a lot to get it published. Key thing here is a comprehensive and distributed approach to noise, not just slapping a few guard rings down and keeping your fingers crossed.
With all the discussion and black magic opinions on guard rings swirling around, we did a foundry based study and got a bunch of empirical data in the lab. It made a lot of people stop thinking of rings as the universal noise fix.
Key thing to remeber - rings are only 1-2 microns deep, noise goes underneath these, so you havent built a perfect wall. I do a PPT on the topic as part of industry training, and rings are only a small part of a methodology that includes -- grounding, shielding, differential systems, path balancing, reducing generation sources, physical seperation, time and frequency division, impedance of power and ground, distributed filtering, selective bandwidth limiting, and a multitiude of others.
The talker/listener, (aggressor/victim, or whatever name you like) is a good approach, but is only the starting point.
Interference noise has been a big part of my technical design efforts, but the interesting thing is that I generally get dragged into the issue after somebody has a DOA chip due to noise. Beter to train the team prior to design. Its a training seminar that pays for itself multiple time over.