Does Noise Analysis Accuracy Really Matter?

There have been a lot of new faces springing up in the signoff analysis market over the past few years and the trend seems to be pointing toward products that deliver quick and reasonably good timing signoff with some signal integrity analysis tacked on as an afterthought. This prompted me to ask the question: Just how important is noise analysis accuracy and quality?

To answer this question, I first looked back at the history of noise analysis and how it evolved from being a nice-to-have security blanket to an integral part of design closure. To make a long story short: Signal Integrity (SI) analysis began to catch on in 2000 as 180nm - 130nm design starts increased. 90nm design starts began to ramp up in 2002 and by 2004, signal integrity analysis hit the mainstream and was seen as a must-have to ensure reliability while maintaining design margins. Now enter present day where SI fixing is a regular part of the design closure loop and a standard offering of all signoff timing solutions.

Throughout the rise of SI analysis, it has proven its worth many times over by saving numerous designs from failing in silicon. This is no small feat and is accomplished by finding and then fixing functional and timing failures induced by crosstalk noise during design implementation. In today's world of cutting-edge low-power design, this means that SI analysis must be able to take into account the complex signal integrity problems that can come from mixing Multi-Vt cells, domains with different supply voltages, and new low power cells such as level-shifters and power gates.

So will any SI solution do?

Digging deeper, I found that SI analysis accuracy and quality matters in a big way.  I've recently come across 4 instances in customer evaluations where the very accurate CeltIC technology in Encounter Timing System found major noise-induced problems that the others could not catch. When all of these issues were checked against the golden SPICE simulation, they proved to be issues that, if left unresolved, would very likely have caused failures in silicon. Issues such as "Double Clocking", unpredictable accuracy, and delay pushout optimism were the most common. While some solutions offer impressive turnaround time at the expense of accuracy, these customers decided that they weren't ready to take the risk of a re-spin which could cost over $1M at smaller process nodes.

If that isn't reason enough to consider SI accuracy, you can also consider that better accuracy means less pessimism which in-turn results in fewer violations to resolve in the final stages of design closure. So, based on this, I think it's reasonable to say that noise analysis accuracy matters in really big way and that any shortcuts just aren't worth the risk of failing silicon.

So what do you think? How important is noise analysis accuracy to you?