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Signal Integrity

IBIS Day in Boston

Wondering what IBIS Open Forum actually does? Mike LaBonte lifts the curtain and invites you to learn more about IBIS models.

August 22, 2017

If you have ever simulated a digital system for signal integrity, you have almost certainly used IBIS models. While there are many means to extract channel models for system interconnect, the I/O Buffer Information Specification (IBIS) defines the must have models that we download to accurately represent the behavior of digital chips in simulation circuits, when the time comes to verify signal/power integrity and timing. The IBIS specification is developed by the IBIS Open Forum, a coalition of IC companies, EDA software companies, and end user system designers all cooperating to make portable models and compatible tools a reality. That’s not easy, but it’s working.

The IBIS model technology generating the most excitement today is IBIS-AMI, used to model the behavior of high speed SerDes buffers. The IBIS-AMI executable models enable reasonable simulation times for multi-million bit time domain test patterns. They also support statistical analysis to handle the very low bit error rates (BER) required by technologies such as PCIe, without the need to simulate billions or trillions of bits in time domain. And of course, you can simulate PAM4 and DDR5 with IBIS-AMI models as well.

Image 1
PAM4 eye diagram produced using IBIS-AMI models.

September 13 at EDICON USA in Boston, Massachusetts this year is shaping up to look like IBIS Day. On that Wednesday, EDICON USA conference attendees can join sessions that are based on, or at least touch on, IBIS-AMI, all morning and all afternoon.

The morning will begin with Signal Integrity Methodology for Double-Digit Multi-Gigabit Interfaces, presented by Ken Willis, Product Engineering Architect – Signal Integrity at Cadence Design Systems. IBIS-AMI models are part of the PCI Express Gen 4 design methodology, and the presentation will become extra practical where the question of how to create IBIS-AMI models if they are not available when you need them is addressed. According to Willis, “IBIS-AMI models seem to now be expected as standard deliverables from suppliers of multi-gigabit IP. As ever, there are new challenges such as complex adaptive equalization, back-channel modeling, PAM4, and even DDR components now. So it appears IBIS-AMI modeling and usage will continue to grow for the foreseeable future.”

Next up on IBIS Day will be Addressing DDR5 Design Challenges with IBIS-AMI Models, presented by Todd Westerhoff, VP of Semiconductor relations at SiSoft. This session will examine SerDes IBIS-AMI analysis techniques that can be used to evaluate DDR5 equalization tradeoffs. Analysis of single-ended and multi-drop configurations is possible with IBIS-AMI, but it presents new challenges. “It’s been great to see the adoption and growth of IBIS-AMI over 

the years. We originally crafted IBIS-AMI to allow us to model equalizers for 6 Gb/s links, and we’ve seen IBIS-AMI expand to include repeaters, fiber optic links, 50+ Gb/s signaling, PAM4 modulation and now DDR5/single ended signaling. The ongoing efforts of the IBIS consortium have been critical in allowing IBIS-AMI to keep up with the industry’s rapidly changing needs,” said Westerhoff.

Syed Bokhari, Technical Manager of Signal Integrity & EMC at Fidus Systems Inc., will continue IBIS Day with Debugging High Speed SERDES Links in Multi-Board Interconnect Systems, which will examine nearly every aspect of SerDes operation through various channels. Eye diagram simulation using IBIS-AMI models is part of the process to confirm error free SerDes link operation. “IBIS-AMI models will provide simulation results that are the closest to actual measurements in a reasonable simulation time,” said Bokhari, adding “They are not only indispensable in design, but will provide the ultimate verification of link operation.”

After lunch, IBIS Day will continue with the IBIS Summit at EDICON USA, hosted by EDICON and conducted by the IBIS Open Forum. The meeting will be open to anyone holding at least an EDICON USA exhibition hall pass. This will involve a few more technical presentations about IBIS, and some discussion about what will go into the next specification release, IBIS 7.0. SPOILER ALERT: there may be some disagreement! For registered attendees, there will be free food and beverage to keep the action going.

Anyone who has or will be using IBIS models might enjoy IBIS Day in Boston. The core “insiders” of the IBIS Open Forum meet several times every week to hash out what the next generation of IBIS models will allow us to do. IBIS Day is a chance for all of us to get together for a peek into that process, to learn what others are doing, and to weigh in.