Impedance Control, Revisited


Reading time ( words)

Surprising me on a regular basis is the way that demand for impedance control continues to extend into a broader range of product. After some 20 years of involvement in this field, I would have expected that everyone who needed to consider impedance control would have the capability nailed. Fortunately, that’s not the case, and a steady stream of “how to” questions keep coming my way.

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.

Standards

It’s worth remembering that traceable reference impedance standards are available and all impedance measurement systems should be able to be compared to a traceable standard. The reference air line is the de facto standard for impedance—a precision manufactured coaxial standard “air” referring to the fact that air is employed as the dielectric in this type of precision reference line. 

To read this entire article, which appeared in the May 2015 issue of The PCB Design Magazine, click here.

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