Re: [SI-LIST] : Cross hatched planes

Syed Huq (shuq@cisco.com)
Fri, 18 Jun 1999 14:08:51 -0700 (PDT)

Hello,

If you are using XFX(2-D from Quad), you can model the cross hatch using
MESHED_GROUND. For example:

MESHED_GROUND HORIZ_PLANE y: 27.80 29.20 P_X: 15.0 A_X: 10.0 P_Z: 15.0 A_Z:
10.0
MESHED_GROUND HORIZ_PLANE y: 0.000 1.400 P_X: 15.0 A_X: 10.0 P_Z: 15.0 A_Z:
10.0

Impedance becomes a function of your cross hatch geometry plus more..

We have done this sort of study.
Regards,
Syed.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Syed B. Huq shuq@cisco.com ~
Signal Integrity Engineer(ELB) ~
Cisco Systems, Inc. ~
Ph:(408)525-3399 Fax:(408)526-5504 ~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

>
> I have a question regarding high frequency (over 500MHz) signals running
> over ground planes that are cross hatched, which is commonly done on flex
> circuits. The issue is how to accurately model the characteristic and
> differential impedance for the flex circuit traces. If, for example, I use
> a 2D field solver (where I assume an ideal ground plane) and am designing
> for 100 ohms differential impedance, what percent increase in impedance
> should I expect if the ground plane will actually be cross hatched?

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