Posted by Hélène Thibiéroz on February 24, 2012
“Chose promise, chose due” – In other words, I owed you a full report on our S-parameters tutorial 🙂
As mentioned in one of my previous posts, we received a lot of interest for the AMS tutorial we created for DesignCon 2012. We managed to hold 120 persons in average for three hours talking about S-parameter modeling for SI without even locking doors 🙂 . Our three Speakers (Brad Brim, Sigrity; Amir H. Motamedi, Aruba Networks; Donald Telian, SiGuys) explored this topic from an intermediate to a more advanced level. Because each speaker is an expert in a different area, we were able to cover this topic from different angles and with a lot of depth. In this interview, Amir, Brad and Donald talk about their presentations and share their overall impressions (I have also listed each presentation below). We will further explore and refine this topic at next year tutorial so you’d better be there !
Q> I will be including each of your presentations at the end of this post. Would each of you give a few lines summary of your presentation?
[Brad] My presentation can be described as: An introduction to S-parameters with a focus on issues relevant to designers of chips/packages/boards and systems with high-speed signals. A few basic definitions are covered with the major focus being on practical issues SI engineers tend to learn and re-learn all too often.
[Amir] My presentation is titled “SPICE Simulation with Frequency Domain Models” and covers the following topics: What to learn about the channel just by observing its S-parameter and impulse response and group delay; Correlation/Calibration the models with measurements to increase accuracy; S-parameter data interpolation/extrapolation; What to do about missing DC data, how to “interpolate”, simulate or estimate it; Requirements for transient simulation; passivity, causality; Convolution and maximizing simulator performance; Best practices at getting good S-parameters from EM solvers; Efficient EM solver data formats for SPICE simulation; Handling reference planes for S-parameter Ports; Defining high-speed link simulations in SPICE; Special cases: Power delivery systems and needed modifications to S-parameters; Nonlinear I/O modeling with IBIS and encrypted HSPICE buffers; and Adding DJ and RJ effects with SPICE Thermal noise.
[Donald] My presentation explains how to combine S-Parameters with active models to simulate high-speed serial links and assess performance using eye diagrams. Now that S-Parameter and AMI models are flowing more freely throughout the industry it has become possible to examine and validate link behavior, pre-hardware. I offer a full-day Seminar on this topic that shows how to use these techniques to validate a design and its compliance with the major serial standards, even though the standards still have a post-hardware bias. There’s huge value in figuring out how to do this before you fabricate or assemble anything.
Q> It appears that this topic was really well received among DesignCon community. Which feedback did you receive from the attendees?
[Brad] I received positive feedback from attendees concerning the breadth of what was covered. Not from a technical or theoretical perspective but from basic concepts to detailed application for high-speed serial link systems. My choice not to focus on regurgitating basic concepts and definitions that may be found elsewhere on the web, in college texts or in commercially available training classes seemed to resonate with attendees; especially the lessons I covered for which I work with EDA tool users on a daily basis to learn and re-learn. Amir’s intuitive description of the relevance of S-parameter behaviors was also noted as a big positive by attendees. They liked the practical knowledge Amir was able to share based on his experience applying S-parameters in his designs. Donald’s presentation addressed a hot topic for DesignCon for the past few years – high speed serial links. Since a large portion of the attendees are focused on board design, his system-centric focus of bits-to-bits serial link communications through each chip/package/board was highly relevant. For all three presentations I received feedback they were received well in the tutorial nature intended; not as too detailed or too factual, but rather fun and informative.
[Donald] One attendee claimed it was the most useful session he attended. I think the combination of the talks – all the way from matrices to Bit Error Rates – scratched where people itched.
Q> I noticed DesignCon had an increasing content of AMS/RF related papers and subjects. Have you noticed a change in DesignCon traditional venue?
[Brad] I have observed the number of RF-related topics peak and valley over the years at DesignCon. Each year the TPC (technical program committee) does a good job of maintaining the traditional focus of DesignCon with its paper selections. In fact, notice the title of the RF-centric track is “RF/Microwave Techniques for Signal Integrity”. This is true also for the “Test and Measurement Methodology” track. Other conferences such as IEEE MTT Symposium are intended for more pure RF/microwave topics. RF/microwave measurement conferences also exist; as I am suspect Analog IC conferences are plentiful. I believe the “mixed-signal” portion of AMS and analog-specific designs required to support high-speed signaling is very relevant to DesignCon attendees. As bandwidths increase for high-speed signals, we can expect to see a continued increase in the analog content present in topics of interest to DesignCon. For example, the coupling of analog to digital signal and power noise seems a relevant topic for DesignCon, though the design of a purely analog circuit not relevant to high speed signaling may not be.
[Donald] Higher frequencies have forced SI Engineers to increasingly borrow from RF tools and techniques. In addition, the abundance of silicon gates has pushed things we used to solve on the PCB inside silicon causing convergence of SI, AMS, and DSP design techniques. So yes, things are changing – they always do.
Q> which subjects would you add for our next year tutorial? Are there emerging trends/hot topics we should cover?
[Brad] We should ask ourselves what questions we ask ourselves or what questions our colleagues and customers ask us repeatedly. As authors or “faculty” as DesignCon called us this year, we sometimes forget the presentation is for the benefit of the attendee (not to hear ourselves talk). This is especially true for a tutorial forum. Even if we personally believe the issue to be trivial or covered well in other readily available media we should consider the frequency with which the issue comes up as an indicator of need for further discussion. A tutorial forum is ideal for this type of discussion, since the authors are likely accustomed to addressing the topic daily and have the skill and readily available materials to share with DesignCon attendees.
I was surprised at the high percentage of package and board designers who attended this AMS-sponsored tutorial. Seems the topic was not as well understood even by these attendees, as I had suspected it would be unfamiliar for AMS IC-centric designers.
[Donald] Emerging equalization techniques and associated IC/PCB design capabilities are the next big thing that will push interfaces faster than 10 Gbps into the mainstream. Engineers are calling for Tutorials that help them bring these things together at the system level.