Re: [SI-LIST] : Crosshatched ground planes

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From: Mike Jenkins (jenkins@lsil.com)
Date: Thu Jun 22 2000 - 13:46:46 PDT


Martyn,

Just one more caveat on crosshatched planes. If the return
currents are forced to take a non-straight-line path under
the trace, the effective velocity of propagation will be
slower. (This actually happened a number of years ago to
some folks trying to make their signals faster by lowering
capacitance. They used a 45 degree crosshatch and got
slower signals instead.)

Mike

Martyn Gaudion wrote:
>
> Dear all...
>
> Can anyone help me with regard to crosshatching of ground
> planes.
>
> There does seem to be a practice of crosshatching to
> increase trace impedance whilst keeping impedance controlled
> lines at a manufacturable width, I would guess though that at
> higher frequencies the crosshatching looks like a large
> number of impedance discontinuities.
>
> Does anyone have any guidelines on this?
>
> Kind regards
>
> Martyn Gaudion
> Marketing Manager
> Polar Instruments
> Tel: + 44 1481 253081
> Fax: + 44 1481 252476
>
> www.polar.co.uk
> email: <martyn.gaudion@polar.co.uk>
> ----------------------------------------------------------
> Download your FREE evaluation
> PCB controlled impedance calculator
> "CITS25" from www.polar.co.uk
> ----------------------------------------------------------

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