Correlation up to 50GHz

Last week I attended DesignCon, and as usual correlation between simulation and measurement was a hot topic, especially for the newer “bleeding edge” bus speeds.  In fact, I recently wrote an article on the topic that can be found here.  As we start approaching 50Gb/s speeds, proper materials characterization is crucial to achieving good correlation.  In other words, putting the right material properties into your simulation becomes essential to getting an accurate answer.  Even at slower speeds, basic material properties are essential to getting accurate results, and can often be difficult to obtain.  Fortunately, material suppliers and board manufacturers are more aware of these issues than they were before, so you can rely a little bit more on their expertise.  But, it is still your responsibility to get that information from the material supplier, and to push them to make sure the info they are supplying is correct.  Even something as basic as the dielectric constant of the dielectric materials, which will vary based on thickness, and will also vary closer to the traces (which I have written about in previous blogs), is crucial to getting accurate timing numbers and impedances.  As frequencies get higher, more advanced factors like properly characterizing the surface roughness of the traces and using a wideband dielectric model become increasingly important.