[SI-LIST] Re: Transmission line impedance is related to signal switching frequency ?
- From: Martyn Gaudion <martyn.gaudion@xxxxxxxxxxxxxxxxxxxx>
- To: peter_pang@xxxxxxxxxxxxxxxx
- Date: Wed, 26 Jan 2005 22:32:42 +0000
Hello Peter,
For a lossless line impedance is broadly independent
of frequency.
Er does have an effect but the impedance varies as 1/ Sq root Er
so the variation from Er is typically not the key driver of impedance.
On surface traces the soldermask fill between the traces and any
line width variation on narrow traces can have more of an effect than
simply the Er of the base material.
In general the finer the line width the harder it gets to achieve
a given tolerance, and yields will fall as you push to smaller
line thicknesses.
Innerlayers go through less processes and it is easier to
achieve a given tolerance on an innerlayer.
If you need more information, please feel free to contact
me.
Kind regards
Martyn Gaudion
www.polarinstruments.com
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