David, I had considered this as well but a differential pair still needs a reference plane, does it not, and from the information I got from the designer there will not be a plane on the opposing side of the board. I will call the designer again this morning to verify that I have all the facts clear. Thanks John > -----Original Message----- > From: TechNet [mailto:[log in to unmask]]On Behalf Of David Ricketts > Sent: November 19, 2003 10:25 PM > To: [log in to unmask] > Subject: Re: [TN] Co-planar Impedance Calculations > > > First, I have to say I'm astonished Intel would let someone without > impedance experience do an impedance design for them. Lowest bidder? But > that's not your fault, as you said, they're your customer, so we do what > we can. > > At first, I thought you might be describing a coplanar waveguide, a > trace embedded in a plane on the same layer, which might also reference > another plane layer. These are common in microwave design, and are > becoming more common as RF devices proliferate. > > But your description of a "pair of traces" sounds just like a > differential pair, if both traces are the same width. You probably have > the calculator for that. > > Finally, if you have specific guidelines from Intel regarding line > width, spacing and material, follow them. Don't worry about the > calculator. > > David Ricketts > PCB Design Services > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of John Parsons > Sent: Wednesday, November 19, 2003 11:14 AM > To: [log in to unmask] > Subject: [TN] Co-planar Impedance Calculations > > > Greetings all, > > I have a customer who is doing an impedance design for Intel and he has > no previous impedance experience. This is the information I have. > > - double sided board > - target impedance 50ohm > - signal line 5mil wide, spaced 5mil from "ground" trace and this pair > of traces should be spaced a minimum of 20mil from adjacent traces. > > This is what he was given from Intel. I am using an older Polar model > (CITS25 calculator) which does have models for co-planar designs but > from what I can tell they assume that the signal trace is sandwiched > between ground (return lines) on both sides. Is this a correct > interpretation? Is it possible to model the design as described above? > > While we have some experience with controlled impedance I have no > experience with the aforementioned design and could use some assistance. > > Best Regards > John Parsons --------------------------------------------------- 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 -----------------------------------------------------