# [SI-LIST] How to calculate the resistance and inductance of vias

*From*: Eric Bogatin <eric@xxxxxxxxxxxx>*To*: SI list <si-list@xxxxxxxxxxxxx>*Date*: Tue, 07 Jan 2003 11:20:54 -0600

Andy, and others- Inductance is one of the most confusing topics in signal integrity because we more often than not use the term with out a preface qualifier. One person says "inductance" and really means loop self inductance, while another person says "inductance" and really means partial mutual inductance. We must get in the habit of using the correct qualifier and there will be no ambiguity or confusion. Here is my list of the various types of inductance, each of which is precisely defined with no ambiguity. The various "flavors" of inductance: loop self inductance loop mutual inductance partial self inductance partial mutual inductance total, or net or effective inductance To save space, I refer interested folks to read the various papers I've written on inductance or attend our Fundamental Principles Course (#122) where all the details are spelled out. If you'd like to download one of our papers, please go to the www.gigatest.com web site, sign into the publications section (it's all free) and download the following papers: 9, 29, 32, 33, 72, 80, 81, 83, 88, 94 --eric ************************************************************ ******** next training classes in Sunnyvale, CA: Fundamental Principles: Feb 20-21 High Speed Board Design: Feb 24-25 Hi Bandwidth Models from Measurements: Feb 26-27 ------------------------------------------------------------ ------------------------- Dr. Eric Bogatin CTO, GigaTest Labs 26235 w 110th Terr Olathe, KS 66061 v: 913-393-1305, f: 913-393-1306 e: eric@xxxxxxxxxxxx www.GigaTest.com ************************************************************ ******** Msg: #4 in digest Subject: [SI-LIST] Re: How to calculate the resistance and inductance of vias Date: Mon, 6 Jan 2003 10:41:11 -0500 From: "Ingraham, Andrew" <Andrew.Ingraham@xxxxxx> Greg Edlund and Rich Peyton are 100% correct ... you must look at the whole current path as a loop ... include return paths in the inductance calculation. These formulas are for the partial inductance. The total loop inductance could be much greater or much less. As to where these formulas come from ... I believe there are no closed form solutions to all but the simplest of inductance problems. Thus, almost all inductance formulas you see, are approximations, derived decades ago. Any approximation has some region over which it fits the actual data reasonably well, and regions where it doesn't. Sometimes pairs of formulas like this one, are meant to apply over two different ranges of values. Sometimes one formula was an improvement over the other. And occasionally a formula is just plain wrong, but it continues to be quoted in publications decades later. Off-hand, I know nothing about the origins of these two formulas. They might be perfectly good approximations, given their limitations. They are no good without knowing their limitations. Regards, Andy ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu

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