Signal Integrity

On High Speed Digital Chip-to-Chip Links

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What About the *.ibs File?

Posted December 15th, 2011 · Please leave a comment · Survey

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As you may know we have W1714 SystemVue AMI Modeling Kit to generate the AMI portion of an IBIS model (the *.ami file plus either *.dll on Windows or *.so on Linux) for Channel Simulation. But I often get questions on how to generate the analog part: *.ibs file itself. Or sometimes the question is about how to generate the analog part with no AMI for the traditional IBIS flow, based on SPICE-like transient. At present, Agilent doesn’t offer a solution in this space, but my customers tell me they do one of several things:

  1. Follow the IBIS Cookbook http://www.vhdl.org/pub/ibis/cookbook/cookbook-v4.pdf or
  2. Engage a consultant like Teraspeed http://www.teraspeed.com/ for a measurement-based model
  3. Use a free tool s2ibis (SPICE to IBIS) http://iometh.com/Product/s2ibis3/index.html
  4. Paid tool like SharkSim Developer http://sharksim.com/developer_features.html which is also uses a SPICE to IBIS appraoch

Hope this helps! Please leave a comment if you’d like share your method of generating *.ibs files.

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Interview and Webcast Series

Posted December 8th, 2011 · Please leave a comment · Webcast

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If you can’t get enough of me here on my blog, then surf on over to EE Web. They interviewed me for their “Featured Engineer” series. The interview is posted here:

Featured Engineer: Colin Warwick

Let me know what you think?

Also, I’m presenting the first of a series of three webcasts. The second and third will be presented by my colleagues Sanjay Sethi and Hany Fahmy. You can sign up for all three here:

Overcome High Speed Digital Design Challenges Webcast Series

Series Abstract

When digital signals reach gigabit/s speeds, the unpredictable becomes the norm. The process of getting your project back on track starts with the best tools for the job. You’ll need techniques taken from communication science (like adaptive equalization) and tools taken from microwave engineering (like field solvers) to overcome the three main design challenges: signal integrity, power integrity, and EMI/EMC. In this series of webcasts we’ll show you how to improve time-to-market by proactive application of these modern techniques.

Webcast 1: Overcome Signal Integrity Challenges in the Multigigabit/s Era

December 15, 2011

First Session: 7AM PT/10AM ET/3PM GMT/16:00 CET

Second Session: 10AM PT/1PM ET/6PM GMT/19:00 CET

To mitigate channel impairments in the multigigabit/s regime, modern SERDES employ signal processing techniques such as receive equalization. The equalizer taps and other parameters can be tuned to the optimum values in the field via register settings available to the user. However, to find these optimum values, it is necessary to explore the design space. The design space multiplies combinatorially when one considers transmitter parameters and channel design parameters. In addition, the logic block that implements the signal processing function can be quite large — tens of thousands of transistors — making conventional SPICE-like transient simulations with netlist-based IC models impractical. New simulation techniques are needed as well as new types of IC models. In this webcast we’ll explain how channel simulation and IC models based on the emerging IBIS 5.0 AMI flow can solve these challenges.

Webcast 2: Overcome PI Challenges on Perforated Power/Ground Planes

January 19, 2012

First Session: 7AM PT/10AM ET/3PM GMT/16:00 CET

Second Session: 10AM PT/1PM ET/6PM GMT/19:00 CET

Traditional power integrity tools fail when applied to PCBs and packages with heavily perforated power/ground planes because they were built for high layer count boards that can afford the luxury of solid power/ground planes. Thus, they sacrifice generality to gain speed and capacity. In this webcast, we’ll explain a different approach that’s applicable to PI analysis on cost reduced consumer boards whose power/ground planes are perforated with signal traces.

Webcast 3: Introduction to EMI/EMC Challenges and Their Solution

February, 16 2012

First Session: 7AM PT/10AM ET/3PM GMT/16:00 CET

Second Session: 10AM PT/1PM ET/6PM GMT/19:00 CET

In the multigigabit era, passing EMI/EMC specs is increasingly challenging. Discovery of an EMI/EMC failure late in the project can force a recourse to makeshift solutions that add unit cost and delay time to market.

In this webcast, we explain the causes of EMI/EMC and propose a proactive methodology that we dub “Virtual EMI lab.” This methods uses EM simulation to identify and mitigate issues early in the design when many more design options are available. The “Virtual EMI lab” discipline includes both pre-manufacture EM simulations and methodology refinement via post-manufacture co-relation against measured data from EM chambers and EM scans. Our examples include: trace emission from MA/CMD memory, return-current emission on data nets on packages, SSO emission due to Icc(t), and HDMI cable emission due to grounding issues between the connector and the PCB.

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Conductor Surface Roughness

Posted November 20th, 2011 · Please leave a comment · Application Note

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multi-level conductor surface roughness model reflects actual topography

We introduced a multi-level conductor surface roughness model in ADS 2011. Multi-level means you model little hemispheres on bigger hemispheres like the scanning electron micrograph (SEM) shown here. You can use it for transmission lines such as our Multi-layer Models library or in our laminar 3DEM solver Momentum. There’s a joint Agilent-Cisco MTT MicroApps presentation about it titled A Multi-level Conductor Surface Roughness Model by Yunhui Chu, Amolak Badesha, Jing-Jiang Yu of Agilent Technologies, and Sammy Hindi of Cisco Systems.

The topic has an interesting history dating back to the era when computer meant a human computer, in this case Miss J. G. Asbury who solved Maxwell’s equations by hand to 1% precision for the case of a periodic roughness. She was working for Samuel P. Morgan Jr. in his work leading the publication of Effect of Surface Roughness on Eddy Current Losses at Microwave Frequencies in the Journal of Applied Physics, Vol. 20, p. 352-362, April, 1949.

Our model is an excellent compromise between accuracy and computation efficiency. Of course, to model the frequency response of transmission lines on FR4 PCB materials you need to model not just skin effect and conductor surface roughness but also dielectric effects. Our version of the Svensson/Djordjevic model is a good approximation for the last one but it doesn’t account for resonant absorption peaks in the dielectric. (You can see two such peaks at ~18.2 and ~18.9 GHz on slide 10 of the MTT presentation cited above.) If you need a model that accounts for these, Prof. Paul Huray discusses an approach in his book The Foundations of Signal Integrity pp. 198-215. Maybe that’s a topic for another day and another posting.

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