What is the next layer? Signal? or is it a layer covered only by dielectric.
I would guess it is next to another signal layer that is of alternate direction.
Something like a coupled stripline?
If you don't plan on going that route then your working on something I wondered about.
Can you treat a trace as an embedded microstrip....? I wonder.
Sorry that is now out of my league, but I'm very interested in hearing what you find.
Chris Robertson
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----- Original Message -----
From: John Parsons
To: [log in to unmask]
Sent: Wednesday, November 19, 2003 2:07 PM
Subject: Re: [TN] Co-planar Impedance Calculations
Chris,
I hear what you are saying, and yes, I used the word "ground" out of habit.
My confusion though lies in the fact that there will be no reference plane
below the signal trace (hence coplanar) and that the designer seems to think
that they (end user) only want the reference line on one side of the signal
line.
When I try and use the Polar calculator with the parameters given below, and
I deselect the "plane" radio buttons it tells me that I need a reference
line width of at least 10x the dielectric thickness, which is 62mil) or 10x
the coplanar separation.
Again, to clarify, my confusion is in the fact that I do not have reference
"plane" surrounding the signal trace. I need to understand how the proposed
design will work, and how to reconcile the calculations before
manufacturing.
Thanks
John
-----Original Message-----
From: Chris Robertson [mailto:[log in to unmask]]
Sent: November 19, 2003 11:48 AM
To: TechNet E-Mail Forum.; John Parsons
Subject: Re: [TN] Co-planar Impedance Calculations
It doesn't have to be ground. That is why they are always called reference
planes.
I personally use + and - voltages with no problems. I also have used split
planes
above and below, but I also recommend not to use split plane reference
planes in
the areas where controlled impedance traces are or on very high
frequencies.
This is just my personal findings.
I like the polar calculator and actually compared my calculator on their
findings.
Go to www.pcbdr.com and get the spread sheet calculator. or directly to
http://home.hiwaay.net/~robdne/files/Beta%20ResourceV4.xls to use the
calculator online. (click on the "stack" tab at the bottom)
The updated version is much better. These calculate the entire board and
adds the thickness on the fly.
Chris Robertson
Author "PCB Designer's Reference"
[log in to unmask]
ISBN: 0130674818
Search for it at www.Amazon.com
----- Original Message -----
From: John Parsons
To: [log in to unmask]
Sent: Wednesday, November 19, 2003 1:14 PM
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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