There is an old joke about the guy who dropped a diamond ring on the ground one night. He’s down on his knees looking for it and another fellow comes along and asks to help. They’re both down on their knees for a few minutes with no luck. The stranger then says, “I can’t find it anywhere. Where did you drop it?”
The other guy says, “I dropped it over there,” pointing ten feet away. The stranger replies, “If you dropped it over there, why are you looking over here?” He replies, “Because the lights better over here.”
I think this story illustrates one of the limitations of traditional power integrity analysis. We tend to do what is easy, where the light is, rather than tackle the real questions, because they are hard.
Doing a simple SPICE simulation of the impedance profile of a collection of capacitors is easy, and every engineer should be doing this. But, taking the next step to explore the interaction of the capacitors and the planes, or how the mounting geometry influences the ESL and the resulting impedance profile, is hard. The only tool that will take into account the arbitrary, odd shaped power and ground planes, a fact of life in real world product design, is a 3D field solver.
While many of these tools have jewels of insight hidden within them, they are positioned ten feet away from most engineers, in the darkness. They are hard to understand, hard to use, hard to evaluate if the answer is correct or not, and take a while to spin through a lot of what ifs.
I think the recent announcement by Mentor Graphics at DesignCon 2009, of the release of HyperLynx 8.0, which includes power integrity analysis, now expands the circle of light into the power integrity world. Since its first release more than 15 years ago, HyperLynx has been an incredibly easy to use circuit simulator. With the inclusion of lossy line models and eye diagrams, it enables high speed serial link simulation to greater than 10 Gbps.
This easy to use interface and fast computation speed has been extended to power integrity analysis. Now it is easy to evaluate questions like, does position really matter? What is the impact of a Swiss cheese clearance hole field on the impedance of the decoupling capacitor? What is the impedance profile of the capacitors and the planes? Up to what frequency or rise time are decoupling capacitors really effective? For an odd, irregular shaped power plane, what is the DC resistance and are there any hot spots?
I’ve had the opportunity to take the beta version for a test drive and I think it will dramatically reduce the fear, uncertainty and doubt of designing the power distribution network in your design.
Also I have a chance to use Beta HL 8.0. I agree with Eric's comment. This is an easy to use and easy to understand PI Tool, will bring productivity to board designer. One of the weakness I saw in Beta HL 8.0 is the poor performance of scratching pre-layout planes