Why are designers scared of high speed designs?

 

We all have talked, learnt, studied about high speed designs and it is no more a grey area. We also know how to classify the high signals based on their frequency. There are enough resources over the internet which talk about the high speed designs. Still, talk to designers working on hardware and let us tell you more than 50% of the people express their concern working on high speed designs. Yes, there is indeed lot of "black magic" around these which scares the electronics engineers. Let us explain a scenario, to just give you a glimpse of high speed designs, if you haven't already jumped into it. There was a scenario long back while we were working on high speed designs and there was issue with Ethernet signals between MAC and PHY. The challenge we faced was that interface was not working and we couldn't probe those signals properly. While we probed we were seeing lot of jitter and unable to conclude whether it was actually noise on the board or it was improper probing technique. While scopes and probes have improved now, still that uncertainty exists. Any slight loading due to the probe capacitance on those signals is a concern. Active probes, probing guidelines by various oscilloscope vendors are all there to help us but still any mistakes in probing puts engineer in a tough situation.

While there are lot of rules of thumb, best guidelines available, I shall treat below points as the major points to keep in mind:

• PCB Layout is the engineer is the god for high speed designs. Well, electrical engineer would have looked at datasheets, application notes, performed simulation, it is ultimately in the hands of PCB layout engineer. Let me tell you, you might think, well! I have post layout simulation and I am always in a safe situation. Simulation gives us an indication but not a true reflection of the PCB
• Now, you might have passed the PCB engineer test, you cannot cross the manufacturing test. If material is not selected properly or if manufacturer by mistake ignores your material requirements, the PCB might go useless. While PCB layout is atleast under the designer control but the manufacturing is not. Only a close follow up can help here
• You might have crossed above two steps but if unfortunately there is an issue and if a particular interface is not working, you are going to face the music of probing. While the modern day engineers handle them easily with support from various equipment vendors, the stress that they pass through this phase is only known to guys who experienced it
• This is not the end of it. You might tick all the above points but you might still need a strong firmware guy with hardware skills to vary various drive parameters and other settings of the processor

There are designers who worked smoothly without all the hassles above and came with first time right board. They set an example for us. Throughout the high speed design cycle you must become a good mathematician, good thinker, good analytical skills and what not. I don't mean to say all these are required for every design. Follow the guidelines and review thoroughly and keep a tab on every step to avoid issues later in the design. While you might be laughing off this post thinking that this too exaggerated, you ask designers who spend sleepless nights debugging an issue. 

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