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
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