Re: [SI-LIST] : Measuring Ground Noise

Chris Rokusek (crokusek@viewlogic.com)
Thu, 25 Jun 1998 09:02:08 -0700

Andrew Ingraham wrote:
>
> > Agreed on all points. What follows, however, is that you can measure
> > localized noise on your ground plane - you just need to figure out
> what
> > your reference point will be.
>
> But, to measure noise _across_ your ground plane, requires attaching
> probe wires some distance apart ... which requires wires of some length.

If you don't mind measuring in the frequency domain, a tunable LC "wire"
can be used to act as an effective short enabling extension of a
specific ground point some distance away (at the resonant frequency
only!). I can't remember who manufacturers this. Has anyone used this
technique?

> How to do that effectively and believe the results? (And in the first
> place, what is the significance of noise across the ground plane?)

One consequence of noise across ground plane is it can effectively drive
common-mode current on attached cables (Imagine two cables on
opposite sides of the board--hey those look like rabbit ears!) or drive
the cable against the ground plane of the board.

Regards,

Chris Rokusek
Viewlogic Systems
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