[SI-LIST] Re: How to measure voltage drop on plane
- From: zhangkun 29902 <zhang_kun@xxxxxxxxxx>
- To: reanderson@xxxxxxxxxxxxx, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 20 Jul 2004 07:22:59 +0800
Dear Ray
In Paul's paper "Modeling Electromagnetic Interference Properties of Printed
Circuit Boards", he proposed how to measure the voltage drop on the ground net.
I think this method is not suitable for the complex PCB.
At one time, we are check one PCB with Intel. The engineer said that "the noise
on the ground" was too large. I ask them how to measure "the noise on the
ground". There is no answer.
Is the voltage drop on the ground plane useful?
Best Regards
Zhangkun
2004.7.20
----- Original Message -----
From: Ray Anderson <reanderson@xxxxxxxxxxxxx>
Date: Monday, July 19, 2004 11:54 pm
Subject: [SI-LIST] Re: How to measure voltage drop on plane
> Zhangkun-
>
> The measurement of power/ground noise is a differential
> measurement
> (even if you use a single-ended probe) of the power voltage (Vdd)
> with
> respect to the associated ground voltage (Gnd).
>
> When making these sort of measurements you need to measure Vdd
> with
> respect Gnd at the same XY spatial location for the measurement to
> make
> sense. (i.e. vertically coincident). If you measure Vdd with
> respect to
> Gnd where the Gnd node is physically offset some significant
> distance
> (wrt lambda) then the measurement just doesn't make sense.
>
> If the Gnd measurement point is offset from the Vdd measurement
> point by
> only a small fraction of an inch instead exactly coincident with
> the
> measured Vdd location that is probably an acceptably small error,
> however if the offset is on the order of inches or more then the
> measured voltage doesn't make sense. Why? Because you are
> measuring
> voltages 'across time' where the time is the time-of-flight from
> the Gnd
> node coincident with the Vdd node (which you should be using as a
> reference) to the Gnd node which is distant (which you should NOT
> be
> using as a reference). Measurements of voltage across time are
> undefined, at least with respect to the measurement of
> power/ground
> noise which you propose.
>
> -Ray Anderson
>
>
>
> Zhangkun wrote:
>
> >Dear all
> >The power ground noise at one location is easy to measure. How to
> measure voltage drop on plane at different location? Is it
> impossible? There is one method proposed by C. R. Paul. However,
> the structure of Paul's is too simple.
> >
> >Best Regards
> >
> >Zhangkun
> >2004.7.19
> >
> >
> >
> .
>
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