I need to run USB signals around a board using differential traces. I = found the following equations for Diff Zo from the ultracad paper by = Doug Brooks: Zdiff =3D 2*Zo[1- 0.48*e^(0.96*(S/H)] Zo =3D 60*Ln(5.98*H/(0.8W + T)](Er +1.41)^0.5 My trace to ground spacing (H) =3D 0.5mm (If possible).=20 Problem USB 1.1 calls for 90 ohm diff Zo (+/- 15%). Using the equations above I = can get 90 ohm diff Zo with a number of trace spacings and thickness = combinations. Of course the Zo for the isolated trace also changes, I am = not sure what this really wants to or should be. Its not defined in the = USB1.1 SPEC. So do I put the two traces really close together or space = them ? Any suggestions on this would be helpful. I have a feeling that = the Zo equation above may not be good enough as it doesnt account for = the presence of another trace ? HELP Thanks in advance=20 Steve Rogers B.Eng (Hons) C.Eng IEE RF Design Engineer Micromill Electronics Limited Leydene House Waterberry Drive=20 Waterlooville Hampshire PO7 7XX Tel: +44 (0) 23 9236 6600 Fax: +44 (0) 23 9236 6673 Registered No. 1456922 (England). =20 Registered Office Brook Road Wimborne, Dorset BH21 2BJ *********************************************************************** "This email and any attached files are confidential and may be legally = privileged.If you are not the addressee, any disclosure, = reproduction,copying, distribution,, or other dissemination or use of = this communication is strictly prohibited. If you have received this = transmission in error please notify the sender immediately and then = delete this email. It is the policy of Micromill Electronics Limited that no legally = binding statements, representations or commitments (collectively = 'statements') may be made by email. Any such statements must be = confirmed either by facsimilie or by post before they will have legal = effect. The sender of this email is not authorised to commit the company = in any way and the addressee is hereby formally notified of that fact." *********************************************************************** ------------------------------------------------------------------ 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 technical documents are available at: http://www.si-list.org 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