At 09:51 31/07/97 -0700, you wrote:
>I am a lowly board designer, and I have been asked to
>replace our standard via types (0.18 hole diameter) with
>vias that are twice as large (.036 holes) to reduce the
>inductance. I haven't seen any data to warrant a change 
>like this, so I was hoping:
>
>Can anyone steer me towards finding out the inductance of
>vias at 1.9GHz based on their diameter?
>
>Is anyone brave enough to hazard an opinion as to the REAL
>effect of vias on a 1.9GHz circuit? I should mention that 
>all signals are on one layer, the vias are ONLY for power 
>and ground access. 
>
>confused but want to learn,                         Jack
>
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Jack,

Bigger via holes on multilayer backplane PCBs transmission lines often
increase the via hole capacitance.  Broadly speaking (and ignoring skin effect)
if there is more cross-sectional area (& a larger hole diameter will do this)
then there is less resistance to current flow.  In layman's terms series
inductance opposes the flow of AC current.  So reducing the inductance of
the POWER/GND via holes should allow the device to handle transient effects
more easily, ie better decoupling.

No time to write a full response, but hope this helps somewhat.

Best regards

Andy Burkhardt <[log in to unmask]>
Tel: + 44 1481 53081
Fax: + 44 1481 52476
http://www.polar.co.uk
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