Hello Steve! it is possible to design the impedance of a coplanar differential pair without ground reference. Brian Wadells "Transmission Line Design Handbook", ISBN 0-89006-436-9 covers this. The impedance calculator of Polar Instruments www.polarinstruments.com may be helpful too. Another valuable source of information is the si-list (Signal Integrity) on Yahoo. Regards Thomas > -----Original Message----- > From: Steve Kelly [mailto:[log in to unmask]] > Sent: Wednesday, March 03, 2004 8:53 PM > Subject: Impedance design question > > > Good day to all, > > I have been asked by a customer to design a single layer 100 ohm > differential pair circuit. I realize the impedance may be > highly variable > but I do not know how to do the calculation when there is > only one layer of > copper. If I assume there is a ground line next to the > differential pair do > I use this as the reference? Any advice or help would be > appreciated. Thanks > in advance. Steve Kelly > > > > PFC Flexible Circuits Limited > > Ph: (416) 750-8433 > > Fax: (416) 750-0016 > > Cell: (416) 577-8433 > > E-Mail: [log in to unmask] > > > > > --------------------------------------------------- > Technet Mail List provided as a service by IPC using LISTSERV 1.8e > To unsubscribe, send a message to [log in to unmask] with > following text in > the BODY (NOT the subject field): SIGNOFF Technet > To temporarily halt or (re-start) delivery of Technet send > e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) > To receive ONE mailing per day of all the posts: send e-mail > to [log in to unmask]: SET Technet Digest > Search the archives of previous posts at: > http://listserv.ipc.org/archives > Please visit IPC web site > http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for > additional information, or contact Keach Sasamori at > [log in to unmask] or 847-509-9700 ext.5315 > ----------------------------------------------------- > --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------