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Cannonball Stack for Conductor Roughness Modeling

June 24, 2015 | Bert Simonovich, Lamsim Enterprises

In the GB/s regime, accurate modeling of conductor losses is a precursor to successful high-speed serial link designs. Failure to model roughness effects can ruin your day. The cannonball stack is an example of a cubic close-packing of equal spheres, and is the basis of modeling the surface roughness of a conductor in this article. So, what do cannonballs have to do with modeling copper roughness anyway? Bert Simonovich explains.



LATEST COLUMNS
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Beyond Design: Stackup Planning, Part 1

Beyond Design by Barry Olney
IThe PCB substrate that physically supports the components, links them together via high-speed interconnects and also distributes high-current power to the ICs is the most critical component of the electronics assembly. The PCB is so fundamental that we often forget that it is a component and, like all components, it must be selected based on specifications in order to achieve the best possible performance of the product. Stackup planning involves careful selection of materials and transmission line parameters to avoid impedance discontinuities, unintentional signal coupling and excessive electromagnetic emissions. Barry Olney explains.
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Impedance Control, Revisited

The Pulse by Martyn Gaudion
The positives for new fabricators and designers lie in the fact that, even though impedance control may be new to them, there is a wealth of information available. Some of this information is common sense and some is a little counterintuitive. So, this month I’d like to go back to the fundamentals, and even if you are an experienced hand at the subject, it can be worth revisiting the basics from time to time.
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The Do’s and Don’ts of Signal Routing for Controlled Impedance

The Bare (Board) Truth by Mark Thompson
In this column, we will once again be focusing on controlled impedance structures, both from the layout side and the simulation side. I will break them down into the sub-categories of the models they represent and the important points to remember when using the various models. I will also be asking questions such as, “Why would a fabricator ask for a larger impedance tolerance?” and “Where does the fabricator draw the line for controlling various structures?”
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