Zhangkun, As far as I know: Andy quote -"I believe there are no closed form solutions to all but the simplest of inductance problems.", is the correct answer. The same goes for via capacitance, and more importantly, via impedance. If anyone else on the list comes up with an analytical solution, I'd love to hear about it. Ken -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Ingraham, Andrew Sent: Monday, January 06, 2003 8:41 AM To: si-list Subject: [SI-LIST] Re: How to calculate the resistance and inductance of vias 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: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //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 ------------------------------------------------------------------ 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: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //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