[SI-LIST] Re: Calculating the Z0 of a trace
- From: "Cosentino, Tony" <Tony.Cosentino@xxxxxxxxxxx>
- To: <farid_syed77@xxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Thu, 26 May 2005 08:12:34 -0500
Fareed,=20
=09
As Giancarlo said you can use a field solver to calculate the impedance
and you will get pretty accurate results. I personally like to use the
tools from Applied Simulation Technology but I do know that Ansoft and
Polar also make fine tools. If you do not have access to a field solver
then your bare board manufacture should be able to help you out with
these calculations. However, if you just need some basic formulas and
basic knowledge related to different transmission line stackups then you
should start with the IPC specifications. Try IPC-2221 "Generic Standard
on Printed Circuit Design" and go to the section titled Impedance
Controls. The stackup you are referring to is called Dual (Asymmetric)
Stripline. This is similar to the Stripline stackup except that one or
more conductor layers are asymmetrically located between the two
reference planes. Asymmetric Stripline is when a layer of circuitry is
placed between two ground (or power) layers, but is not centered between
them. In this case the stripline equations must be modified to account
for the increased coupling between the circuit and the nearest plane,
since this is more significant than the weakened coupling to the distant
plane. Dual-Strip transmission line (which probably resembles your
example the most) closely approximates a stripline except that there are
two signal layers between the ground (or power) planes. The circuits on
one layer are generally orthogonal to those on the other to keep
crosstalk between layers to a minimum. You should check out the specific
formulas in the IPC-2221 Specification that pertain to the Dual
Stripline impedance. I think this is a good starting place. If you do
not have access to a copy of this IPC Specification then you can go
online and purchase a copy (www.ipc.org).
Thanks
Tony Cosentino
PCB Design Engineer
Tekelec - USA
919-460-3656 office
919-466-3031 fax
tony.cosentino@xxxxxxxxxxx
www.tekelec.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of farid syed
Sent: Thursday, May 26, 2005 6:23 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Calculating the Z0 of a trace=20
Dear all,
I am new to PCB design and i have a few doubts as listed
below
=20
1. I have a board with the stack up S G S S P G S S P S if i want to
find the Z0 of a trace on the 4th layer then how do i do it?=20
2. is that type called a stripline, i have read that stipline is a trace
bounded by ground planes on either side. and microstrip is the one with
ground on one side and air on the other. what is the type of trace on
the 4th layer of my board?=20
3. I have been through Dr. howard jhonson's handbook where crosstalk is
calculated as =3D k/1+(d/h)^2 what is K and when we get a number as a
result of the calculation how to use that number in determining the
crosstalk or use it for our purpose. =20
=20
can anybody please help/guide me
thanks in advance
warm regards
Fareed=20
Yahoo! India Matrimony: Find your life partneronline.
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