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80 DESIGN007 MAGAZINE I OCTOBER 2021 In the science of high-speed signalling, the signals obey the laws of physics, so when a design won't work or meet a specification, no amount of psychological persuasion will smooth the signal's path from source to load. Wouldn't life be different if speaking nicely (or shouting) at an underperforming circuit would spring it to life? (ough the application of warm air to drive out moisture can help, as long as it's dry, hot air.) Feedback Facts I'm not referring to electrical feedback, but process feedback. PCB fabricators will look at process measurements and adjust process parameters to optimise yields; this saves cost and time, and produces a better product for lower material cost over time. Trace width Fake Fudged Facts— Using Software Tools to Get the Right High-speed Answer dielectric separation, glass-to-resin ratios, datasheet values, and measurements can all go into the mix when feeding back production measurement values to tailor transmission line characteristics to get better yields on the next build. Fudge Why the mention of this sugary sweet yet addictive substance? Sometimes the feed- back from measurement doesn't correlate as expected; there is always a good reason for this, but until you know the root cause it can be tempting to "what if ?" a hard-to-measure parameter from the datasheet that wasn't cor- rect. en the temptation is to "fudge" the results of the correlation by adjusting said tricky-to-measure parameter. Perhaps a more The Pulse by Martyn Gaudion, POLAR INSTRUMENTS

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