Wild River ISI-56 Platform Accelerates SerDes Testing

Estimated reading time: 13 minutes

I recently spoke with Al Neves, founder and CTO of Wild River Technology, about the release of their new ISI-56 loss modeling platform. Al explains why it was so critical that this tool meets the stringent requirements of the IEEE P370 specification (which he helped develop), and why he believes this is currently the best tool for SerDes testing and characterization. 

Andy Shaughnessy: How’s it going, Al? Why don’t you tell us about this new ISI-56 modeling platform?

Al Neves: It’s going really well, Andy. We started making test fixtures for SerDes characterization for both compliant and characterization testing about 11 years ago. The focus was from 10 to 32G NRZ (non-return to zero). It’s either high or low, and that business went pretty well for us. Then PAM4, which is four levels and not two, came out, and in the last two or three years we’ve seen a big rush to 56G PAM4, and we have scores of existing customers asking us about 112G, even a few at 224G, PAM-6!  Now, the issue is that there is a 9.0406 dB penalty versus NRZ because of the multiple levels. When you have multiple levels, your test fixtures need to be better by almost 10dB. When that happened, that business went through the roof. We couldn’t keep those products in stock. So, we focused on that and we slightly improved the ISI-32, which was for 32 G NRZ, and we’ve just released the ISI-56. It’s extremely good signal integrity; the product looks simple, but it isn’t.

Our company ran for a pretty good period without having any competitors. We have some competitors now, and as I was doing some analysis this morning, I see we’re exactly twice as good as our closest competitor, Keysight Technologies. Having said that, our product meets the highest signal integrity metrics for the new specification IEEE P370, and the Keysight test fixture does not. My comment is not to denigrate Keysight, they make very good equipment, just not so good test fixtures.  

Shaughnessy: Why don’t you talk about the significance of IEEE P370?

Neves: One of the problems that plagued test fixtures and products was the lack of standardization and compliance agreement for signal integrity. There are two key indicators of good signal integrity: return loss and TDR impedance. Return loss is measured with a VNA; TDR impedance is measured with a TDR and then you do an impedance calculation. Having said that, there really was no standardization, and IEEE P370 changed that recently with a compliance specification. There are three tiers of signal integrity quality. Our test fixtures meet the highest tier, and they’ve met that tier for about nine years now, before the spec was even out. So, we’re pretty fanatical about our signal integrity, almost to a fault!

Having said that, the new requirements for these high-speed multiple-level PAM4 are pretty extreme. You’re trying to mimic a backplane and establish how long the SerDes can run a TX to RX at a certain bit error rate. If your signal integrity is not good, you’re not testing SerDes electrical length reach; you’re testing your test fixture signal integrity. Think about it in terms of the Hubble telescope. As long as the telescope was earthbound, you had to deal with the atmosphere and the atmosphere obscured the measurement. Poor signal integrity does the same thing. It disperses the signals you want and adds stuff that you don’t want, and you can’t accurately characterize SerDes if you have poor signal integrity.

I’ll give you an example of this, and this is published so I’m not violating any confidentiality agreement. We wrote a paper with Xilinx several years ago on the ISI-32, which we still sell. The signal integrity isn’t as good as the ISI-56, but we were able to run the  32G SerDes to 47dB of loss. They had never seen that before. So, their VP runs into the lab and says, “Gee, is that actually 47dB? We haven’t seen it before!” And I said, “Because the test fixtures you’ve been using are junk.” They laughed that nervous laughter. I said, “No, it really wasn’t a joke. Your test fixtures are junk. Now you have a good test fixture and now you’re seeing the true performance of your SerDes because you don’t have reflections and resonance and all the nasty stuff from junk test fixtures.” That was eye opening.   

What’s happened is the IEEE P370 is a specification for 50 gigahertz. We’re working on 70 gigahertz right now. We almost have that done, and we’re going to have a plethora of products coming out in the 70-gigahertz space. So, we’re going to be achieving 70-gigahertz signal integrity performance. Most test fixtures have issues up around 26 gigahertz. If you’re interested, I have some graphs and we have some comparisons. It was a seminal paper on doing systematic SerDes characterization based upon design of experiments.

Shaughnessy: I’m curious. You’re a small company; how did you guys get to this point where you’ve got a tool that’s better than the big guys? How are you all able to do that?

Neves: Actually, it’s based on a stubborn and uncompromising mindset: What’s your objective? Is your objective to build something that you think is marketable, or is it your objective to create the best signal integrity you possibly can and not care what the market wants at that time?

John Trudel is a good friend of mine and he once told me something very interesting. He’s a retired, brilliant guy who started Tektronix Labs and the whole TDR idea. John said, “Don’t listen to your customers.” I said, “No? Tell me why. You’re always supposed to listen to your customers.” John said, “Your customers will tell you what they’re struggling with today. You don’t want to design what they’re struggling with today. You want to guess at what they’re going to be struggling with three, five, or 10 years from now and build something for that market.”

So, once you start listening to your customers and you give them something, by the time you give it to them, it’s an obsolete product and it’s a different problem. You have to predict where the market’s going, and you maybe want to just do something that the market’s not ready to embrace it. When we first came out with these ISI platforms and our other test fixtures, the market wasn’t ready for it. They didn’t need it. Most people were doing 10G, maybe 20G, and we didn’t sell that many fixtures; We were ready to do 32G. We now have had requests this past year for 224 gigabits per second, over 100 gigahertz!  We’re tied into the connector companies, using their products at beta level to design it in. We’re working with teams of people. For example, Samtec introduced a new 2.4-mm connector this last year. Now, the 2.4-mm connector has been in the market a long time, but Samtec made a better one. I looked at it and I said, “It’s better than what I’ve seen in the market, let’s transition to that solution.”    

We used it and that’s the trick about how we’ve improved our signal integrity over other folks. They just grab what’s been available in the marketplace and what their purchasing people say is available for them to use. I’m not constrained by that. Then we used very extreme simulation methodology using HFSS and hundreds of hours of simulation time. There were some other proprietary tricks we used. The test fixtures look rather simple, but they are not. If we could all hit a 90-mile-an-hour fastball, baseball players wouldn’t make $15 million a year. It’s not easy doing that. Having said that, the test fixtures are of uncompromising quality and this ISI-56 is an example of that.

Shaughnessy: Right, it’s transparent.

Neves: Exactly, transparency versus opacity.

Shaughnessy: I remember Dr. Bruce Archambeault saying, “All of the connector companies will say, ‘These connectors are totally transparent.’” But he said, “There’s never been a connector ever made that was completely transparent.”

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