Design007 Magazine

PCBD-July2016

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50 The PCB Design Magazine • July 2016 In my journey to learn everything I could about impedance, I had the joyful experience of working with some of the best and bright- est software engineers around. In the process, we've come up with the coolest impedance calculator I've found yet, available as an app for the Droid and the iPhone. Yes, you can download this fabulous gem and impress all your industry colleagues with your knowl- edge of microstrip and stripline impedance calculations. Some of you already have a solid under- standing of impedance calculators. But even if you're far from an expert in this arena, an im- pedance calculator can help you take this: And turn it into this: Just look at it. Don't you want to use it right now? Our impedance calculator allows you to determine your wire widths based on your di- electric heights, or the other way around. Build- ing the stack-up and the design rules have sud- denly become fun. I am as much in love with my TI calculator as the next electronics geek, but having an app that can calculate both back- ward and forward gives you the ability to really focus on the end-goal instead of checking and rechecking your work. It's a fantastic productiv- ity booster. But what I became acutely aware of during this project, first and foremost, is that designers must always exhibit great patience. The process of beginning a brand new circuit design never has a defined point A and point B, and no real start and finish. It is just as circuitous as the fin- ished design displays; while one engineer is off calculating impedances, another one may be calculating signal integrity or EMI. The board designer may or may not be aware of what these engineers are doing, all the while being right in the middle of placement and routing processes. This is often the source of that familiar frus- tration with the "us" and "them." So when you're putting the finishing touches on your beautiful hand routes and the engineer comes back and asks you to switch out the resistors for a different value, and space out your wires by .005" instead of .004", take a deep breath and try to recognize why! These design changes can be caused by nu- merous drivers, such as heat dissipation, electri- cal interference, or too much "noise." These is- sues can be controlled in a variety of ways, such as using different valued resistors to dampen the speed of the signal, shielding areas of cir- cuitry from the rest of the design, or carefully distributing properly sized heat sinks through- out the design. Sometimes the solution to the problem feels like an artistic swipe of a brush in a very square and confined space, in a perfect marriage of the logical and the creative. While patience is an important value for us as designers, I must also highlight that humility is key. Just when you believe you have become the expert on a topic, you will come to find that there is so much more to learn. Five years from now, we'll still be learning new methods for de- HAVING FUN WITH IMPEDANCE

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