Signal Integrity, In Practice

Managing Loss and Discontinuities

The practice of Signal Integrity increasingly focuses on managing loss and discontinuities. Each system struggles with one or the other, making it imperative to determine which issue is dominant and respond appropriately. If your interconnect is long, you’ll likely grapple with loss. If it is short and/or modular, minimizing discontinuities becomes imperative. While long and short are simplifications that track with loss and discontinuities respectively, the challenge of managing their imp...

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Donald Telian, SiGuys - Guest Blogger 7/1/2020 Comments(0)

Signal Integrity, Then and Now

When I compare "Signal Integrity" now to what we practiced in the 1980s, it is unrecognizable. Integration has consumed the old task giving way to the new, and so the next generation will not practice the Signal Integrity of the previous. Not surprisingly, SI methodology has adapted to keep pace with a 10,000x increase in data rate and a 100,000x increase in integration. Indeed, I've seen major shifts in the practice of SI about every 10 years. Amidst that much change it's important to understan...

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Donald Telian, SiGuys - Guest Blogger 6/15/2020 Comments(0)

Why Serial Links?

Author: Donald Telian , SI Guys - Guest Blogger Over the past couple decades every style of high-speed interface switched to serial transmission. I/O, Graphics, Disk, Backplanes, CPU, Long-Reach, Short-Reach, you name it - everything except memory . Serial technology is reliable, extensible, and will be with us for many years to come. In practice, Serial Links are now the primary focus of Signal Integrity. Yet serial links brought significant disruption to the industry. New signaling, new ...

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Donald Telian, SiGuys - Guest Blogger 5/13/2020 Comments(0)

Simulators, Models, and the Next Great Thing

Author: Donald Telian, SiGuys - Guest Blogger Day one at my first engineering job and my manager is explaining the problem I need to solve. Signals need to transmit in a new configuration at a faster data rate than before, and it wasn't clear if it would work. Little did I know how many times I'd get handed that same problem in the decades to come. But this time was different. Fresh out of college, my mind was full of circuit theory, network nodal analysis and differential equations, so I prop...

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Donald Telian, SiGuys - Guest Blogger 4/9/2020 Comments(0)

Simulating Serial Link Compliance

Author: Donald Telian, SI Guys - Guest Blogger Simulating a serial link typically involves confirming compliance with one of the many Serial Link Standards. PCIe, SATA, XFI, CEI, SFP+, USB, KR4, and so on. With over a dozen common standards - each with their own compliance nuances - this feels like it could be a vast and complex topic. Indeed, it takes a full-day class to address only the most popular standards. While serial links is the clear winner in signaling methods, there is no clear winne...

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Donald Telian, SiGuys - Guest Blogger 3/9/2020 Comments(0)

Serial Link Equalization Primer

Author: Donald Telian , SI Guys - Guest Blogger Equalization is powerful. SerDes Serializer-Deserializer Equalization has enabled data rates we would not have thought possible, and it continues to be the secret sauce of serial links. While good performance depends on doing basic things in hardware Steps 1 to 6 , it is arguably the configuration of SerDes Equalization Settings SES, Step 7 that determines eye margins - as illustrated in Fixing Signal Integrity Issues in Software . As such, SI an...

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Donald Telian, SiGuys - Guest Blogger 1/14/2020 Comments(0)

Understanding Connector and Package Impedance

Author: Donald Telian , SI Guys - Guest Blogger I've grown accustomed to viewing passive interconnect as the road signals drive on. Impedance discontinuities appear as the speed bumps or potholes that make the ride bumpy and unpleasant, if not slower. Perhaps I've looked at too many TDR plots ? For many years our industry has been well-tooled to understand and manage PCB trace impedance , which continues to define the majority of the "road" signals travel on. Over time higher data rates have c...

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Donald Telian, SiGuys - Guest Blogger 12/9/2019 Comments(0)

On Exercising Engineering Judgment

Author: Donald Telian , SI Guys - Guest Blogger Signal Integrity Engineering requires Engineering Judgment. The same thing that makes SI require Creativity causes it to also require above average Judgment; namely that you will consistently be asked to craft clear answers from insufficient data based on ill-defined measures of success. There’s no way around it, Engineering Judgment Required. So we’ll address this topic here in our mini-series on the soft skills required for Signal I...

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Donald Telian, SiGuys - Guest Blogger 11/8/2019 Comments(0)

On Working WITH Your Layout Engineer

Author: Donald Telian , SI Guys - Guest Blogger I have a distant cousin who spent his career doing high-speed PCB layout. At a family gathering we were learning what each other did for a living, and when he learned I’m in Signal Integrity he looked at me warily. I was one of those guys. He then shared how we was going crazy routing, re-routing, and re-routing a high-speed PCB because an SI Engineer was giving him constraints that were impossible to meet. Lots of time wasted, and he was c...

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Donald Telian, SiGuys - Guest Blogger 10/8/2019 Comments(0)

What is Signal Integrity?

Author: Donald Telian , SI Guys - Guest Blogger Great question. Now that I’ve devoted well over 30 years to the field, I’ll venture an answer. My simplistic definition has always been the analog side of digital. I still like that description, because in practice the binary world of ones and zeroes only exists in theory. And, hopefully, in system memory - assuming the interface’s Signal Integrity SI was done correctly. My answer to the question will describe Signal Integri...

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Donald Telian, SiGuys - Guest Blogger 8/5/2019 Comments(0)

The History of IBIS

Author: Donald Telian , SI Guys - Guest Blogger Every time I sit down to simulate a PCB, quickly download IBIS models and produce meaningful results in minutes, I am still amazed. I can’t help but think about how things used to be, back when all this wasn’t possible. Not only were simulators slow and cumbersome, component-level device models simply did not exist. True, there were a few transistor-level models around, but using them made simulation even more slow and cumbersome. There...

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Donald Telian, SiGuys - Guest Blogger 7/11/2019 Comments(0)

DDRx Memory Interfacing

Author: Donald Telian , SI Guys - Guest Blogger Memory. Every system has it. Short-term, long-term, 2 nd level, static, dynamic, EPROM, graphic, internal, cache – but, by far, from an SI perspective the most common memory interface is DDRx. Double-Data Rate DDR memory arrived in the late 1990s, and has remained the dominant interface for decades. It has proven to be extensible and, now in its 5 th generation, DDRx has achieved a 20x increase in bandwidth. DDR memory occupies an impo...

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Donald Telian, SiGuys - Guest Blogger 6/4/2019 Comments(0)

Measurement Correlation

Author: Donald Telian , SI Guys - Guest Blogger I believe what simulators tell me. It’s funny because, throughout my career, I’ve met many who don’t. How is it that I somehow learned to trust them? Measurement Correlation.Over the years, taking the time to build, measure, and compare what I simulated taught me what’s good – and what’s not so good – about simulation. I developed confidence in my results and intuition that tells me when they’re suspe...

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Donald Telian, SiGuys - Guest Blogger 5/8/2019 Comments(0)

Simulating a Serial Link

Author: Donald Telian , SI Guys - Guest Blogger And now one of my favorite topics: simulating a serial link. Good technology, good models, good margins, endless options. Yet how do I construct an accurate simulation? And what do I measure? Part of what makes this topic interesting is the variety of answers out there. And the almost infinite number of dials makes the task an engineer’s dream. In a world like that, how do I get started? …and how do I know when I’m done? How good ...

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Donald Telian, SiGuys - Guest Blogger 4/15/2019 Comments(0)

Thinking About Power Integrity

Author: Donald Telian , SI Guys - Guest Blogger Early February, over a foot of snow outside my office and the power is out. Good day to think about Power Integrity. Power matters. But why here in a series on Signal Integrity ? Good question. Power Integrity PI and Signal Integrity SI are intimately intertwined. Here are a few reasons why: PI and SI problems cause similar intermittent issues in systems PI problems can cause SI problems, and vice versa Because of 1 and 2 above, the problems are of...

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Donald Telian, SiGuys - Guest Blogger 3/22/2019 Comments(0)

Understanding Trace Impedance

Author: Donald Telian , SI Guys - Guest Blogger The way high-speed signals interact with trace impedance has changed a bit over time, making the subject worthy of our attention. Thankfully, the importance - and even mechanics - of proper trace impedance is widely understood and agreed upon. So much so, the concept almost seems mundane – particularly against the rising importance of proper via impedance . However, I have found that engineers can benefit by improving their trace impedance in...

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Donald Telian, SiGuys - Guest Blogger 2/7/2019 Comments(0)

Managing PCB Crosstalk

Author: Donald Telian , SI Guys - Guest Blogger Crosstalk occurs when energy in one signal often called an aggressor couples onto another signal the victim adversely affecting the victim signal’s performance. The aggressor/victim language associated with crosstalk indicates danger is lurking, provoking a hardware engineer to consistent vigilance. How can we tame this foe? Or, more specifically, what causes crosstalk? …when does it become problematic? …and what can you do to ens...

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Donald Telian, SiGuys - Guest Blogger 1/16/2019 Comments(0)

7 Steps to Successful Serial Link Layout - Part 3

Author: Donald Telian , SI Guys - Guest Blogger This is the final installment in our 7 Steps series. If you’re just now tuning in, Part 1 detailed the primary problems we need to solve when implementing serial links: loss and discontinuities. In Part 2 we examined the pragmatic side of how those problems are handled during the layout process. Now in Part 3 we focus on issues that arise in manufacturing as well as opportunities related to software configuration – both important topics...

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Donald Telian, SiGuys - Guest Blogger 11/30/2018 Comments(0)

7 Steps to Successful Serial Link Layout, Part 2

Author: Donald Telian , SI Guys - Guest Blogger This is a continuation of my previous post detailing the 7 Steps required to successfully implement a serial link. While all 7 steps aim at controlling discontinuities and loss concepts introduced in Steps 1 and 2 , this post ventures into the pragmatic aspects of managing loss and discontinuities during the routing process. Ever wonder how a tiny via stub can destroy your signal? Read on. Step 3: Route Using Best Practices While it would seem self...

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Donald Telian - Guest Blogger, SiGuys 11/5/2018 Comments(1)

7 Steps to Successful Serial Link Layout, Part 1

Author: Donald Telian , SI Guys - Guest Blogger Over the past 15+ years I’ve been accumulating a checklist of items required for successful serial link layout. I refer to the list when a customer requests a design review of their implementation, without simulation. The swelling list also regularly appears as an Appendix in reports I write for other customers. So when we began developing our Pragmatic Signal Integrity course often co-taught by SiSoft and SiGuys at DesignCon , I thought Woul...

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Donald Telian - Guest Blogger, SiGuys 10/4/2018 Comments(0)

When Should I Simulate?

Author: Donald Telian , SI Guys - Guest Blogger This question is not asked as much as it should be. Companies that simulate routinely or never at all can both benefit by asking it. As a Consultant, asking and answering this question for my customer is part of my value add; defining effort and expense commensurate with the task at hand – no more, no less. Learning how to answer this question is one of engineering’s soft skills and the subject of this post. To be sure, inventors an...

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Donald Telian - Guest Blogger, SiGuys 9/5/2018 Comments(0)

Fixing Signal Integrity Issues in Software?

Author: Donald Telian , SI Guys - Guest Blogger Yes, you read that right. Unheard of? Read on. The history of electronics is checkered with many things that should have caught on, and others – like the internet – that surprised us with their ubiquity. This post is about something I expected to become one of the greatest boons for Signal Integrity SI : SerDes Equalization Settings SES, only accessible through software . I was wrong. You’d be surprised to learn how many of my cus...

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Donald Telian, SiGuys - Guest Blogger 8/9/2018 Comments(0)

Which Discontinuities are Small Enough to Ignore?

Author: Donald Telian , SI Guys - Guest Blogger A 60 mil via is too small to worry about, right? And that 20 mil solder pad - the signal certainly won’t see that, correct? If you work with high-speed signals, no doubt you’ve asked these questions and someone told you it depends. You might have your own rule-of-thumb RoT that helps you decide which discontinuities – or features – might impact signal quality. In this post I’m going to share my favorite rule-of-thumb r...

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Donald Telian, SiGuys - Guest Blogger 7/9/2018 Comments(1)

Understanding Via Impedance

Author: Donald Telian , SI Guys - Guest Blogger If you routinely give attention to trace impedance but are not accustomed to thinking about via impedance, this post is for you. Or, if you are paying attention to via impedance yet are unsure what dimensions will yield the right impedance, this help with that too. So, when should I use an 8 mil drill? Why should I care? Serial links can fail because of impedance miss-matches discontinuities . In practice, discontinuities are likely causing more pr...

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Donald Telian, SiGuys - Guest Blogger 5/23/2018 Comments(0)