[SI-LIST] Re: Measure ESD induced noise

Jinhua,

There are reference measurements you can take: whether
it is active probe or coax, solder both pins (signal and
ground) to the ground point only.  With active probes,
make sure the position and orientation of probe head is
the same that you have in subsequent measurements. 

You will find that active probes, passive probes and
direct coax connections alike pick up noise from the
nearby noise sources to varying degree.  You have to
use the connection, which gives a background reading
comfortably lower than your measured data trace with
your real connections.

Regards

Istvan Novak
SUN MIcrosystems

chen, jinhua wrote:

>Hi, All
>
>I want to measure the ESD induced noise on the power and ground planes.
>First thing I need to make sure is that the probe itself did not cause any
>inaccuracy.
>
>Two different type of probes were used:
>1.) high impedance single ended FET probe. Signal pin solder to power side
>of decoupling cap, and ground pin soldered to ground side of cap.
>2.) high impedance differential FET probe. '+' pin solder to cap power, and
>'-' side solder to cap ground.
>
>I calibrated method 1 with a same size cap soldered on probe pins, but the
>cap was not mounted on the board. Probe was placed on the same point as real
>measurement. 
>
>Are those two methods are valid way to measure the ESD noise?
>
>The results from two methods had some differences. Method 1 measured bigger
>noise. The noise switching with 1 - 2 ns period and ~ 10 V swing in the
>beginning, then decay to zero in about 100 ns. Method 2 had similar period
>and 6 - 7 V swing, then decay to zero. But it had a wide pulse (50 + ns)
>after the high frequency switching noise. I don't know how to interpret the
>data.
>
>Thanks!
>
>Jinhua Chen
>EMC Corp.
>  
>

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