Hi Zhangkun, Sorry for the late reply. All formulae are based on approx to one degree or another. What I think is more important is to consider the effects in your particular application. If you consider it for power connections where there are high current and low impedance you would concentarte on the inductance and resistance parameters. However, for transmission you should not neglect the effects of capacitance and stub length. If of interest i have a presentation of some these effects and "approximations". -- Regards, __________ James G Roberts /___ ____ | jrobert@xxxxxxxxxxxxxxxxxxxxx Jim __ / /___/ / jgroberts@xxxxxxxxxx / /_/ /---| | Room: BE436, Hilversum \____/ /_/ Tel: +31 35 687 4308 Fax: 5976 Could anyone tell me how to calculate the resistance and inductance of vias. The frequancy range is from DC to 50MHz. I have seen two formulars to calculate the inductance of vias. They are very differenct. One is from High Speed Digital Design written by Howard Johnson: L=5.08*h*(ln(4h/d)+1) L:inductance of via, nH h:length of via, inch d:diameter of via, inch The other is from one paper written by Mark Alexander: L=5.08*h*(ln(4h/d)-0.75) L:inductance of via, nH h:length of via, inch d:diameter of via, inch These two formular are different. ------------------------------------------------------------------ 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