[SI-LIST] Re: power planes (4-layer-board)
- From: "Todd Hubing" <HUBING@xxxxxxxxxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Mon, 16 Feb 2009 18:35:52 -0500
Daniel,
I can answer your question about the stripline calculation. The web
calculator you mentioned in your message was written by a student of
mine several years ago. It was modeled after a similar PC calculator
written by Doug Brooks. Not long after we put the web page up, we began
hearing about people getting inaccurate results because they were typing
in data that exceeded the valid range of the closed-form equations. I
modified the calculator so that it would only accept input in the range
specified by the IPC document. I also had a student use a 2D simulator
to test the accuracy of the closed form expression for data within, or
slightly exceeding, this range. (That is the information at the bottom
of the page.)
Why "W/(H-T) < 0.35; T/H <0.25"? Because if you exceed these input
limits, the closed form expression rapidly becomes inaccurate. The
closed form expression is a convenient, easy-to-use tool; however if you
are doing designs that require controlled impedance traces, I recommend
you use a 2D transmission line simulator.
Best regards,
Todd Hubing
P.S. I haven't had an opportunity to update this calculator since I
moved to Clemson 2.5 years ago. However, this same calculator and
several others are on my website at http://www.cvel.clemson.edu/emc. My
students and I continue to revise them as we find bugs or get updated
information.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Daniel Bauer
Sent: Monday, February 16, 2009 4:39 PM
To: davidjp@xxxxxxx; steve weir
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: power planes (4-layer-board)
Hi,
do you know any rule of thumb for the maximal size of such an power
island versus the signal frequency / signal rise (fall) time? Only a
default example: power island with one dimension in x direction of 12cm
has a bare-board resonance of approximately 244MHz; which max rise time
/ signal frequency should the signal have?
David, could you please tell me the reasons for the restrictions for the
stripline calculation (http://emclab.mst.edu/pcbtlc2/stripline.html)?
W/(H-T) < 0.35; T/H <0.25;
best regards
Daniel
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