[SI-LIST] Re: Measure ESD induced noise

Doug

I did more test with a 50 ohm coax cable as probe. Does coax has common mode
issue?

I did the 'null experiments' with coax, SE FET probe and diff FET probe.
Diff FET probe 
gave the wrong response. Coax and SE FET probe gave the similar results.
Coax is slightly
Better (3v vs. 4v).

In the real noise measurements, coax result is similar to SE FET probe (10+
V). Again, diff FET probe
Output is different. Do you think both results were not reliable?

I spent a few hours in your web. I definitely need more ESD fundamentals.

Talking about Fischer BCP-2 passive balanced probe, what scope it can work
with? Any eval item?

Thanks!

Jinhua

-----Original Message-----
From: Doug Smith [mailto:doug@xxxxxxxxxx] 
Sent: Friday, August 26, 2005 10:03 AM
To: chen_jinhua@xxxxxxx
Cc: 'Istvan Novak'; si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: Measure ESD induced noise

Hi Jinhua,

You cannot use most, if not all, active (FET) probes around ESD. The 
latest generation of such probes cannot tolerate ESD even in the same 
room as they are easily saturated in common mode. Most of these probes 
have a common mode range of only a few volts, easily exceeded by an 
ESD event in the same room. If you want to make a differential 
measurement with high bandwidth there is only one probe I know of, the 
Fischer BCP-2 passive balanced probe which is flat (including 
connection hardware, to about 2 GHz and has a higher input impedance 
than many active probes in that frequency range. It can take common 
mode signals MUCH higher than active probes and has better common mode 
rejection than many.

Most measurement arrangements for noise voltage do not work with ESD 
nearby. You have to check the scope and the probe. The gold standard 
is the "null experiment" which involves shorting the probe to check 
its response. There are many articles on my website, http://dsmith.org 
, about this. Take an hour or so to read the relevant articles.

You also have to pay attention to how the probe shield is connected to 
the board and/or chassis. It can act as an antenna and conduct more 
noist into the system and even introduce problems that are not really 
there.

The BCP-2 data sheet is at: http://dsmith.org/instrmts.htm

Doug

chen, jinhua wrote:

> Istvan
> 
> I did those reference measurements. I also did the reference measurements
> with a cap, which has the same size and value as the on board decoupling
> caps. I expected the reference noise with cap should be bigger than the
> reference noise with short. Because cap impedance is always higher than
> short. But the result is opposite. Reference noise is bigger with short.
In
> general, both reference noises (background readings) are much smaller than
> the real noise.
> 
> Thanks!
> 
> Jinhua
> 
> -----Original Message-----
> From: Istvan Novak [mailto:istvan.novak@xxxxxxx] 
> Sent: Friday, August 26, 2005 8:48 AM
> To: chen_jinhua@xxxxxxx
> Cc: si-list@xxxxxxxxxxxxx
> Subject: Re: [SI-LIST] 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.
>> 
>>
> 
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> 
> or to administer your membership from a web page, go to:
> http://www.freelists.org/webpage/si-list
> 
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> 
> List FAQ wiki page is located at:
>                 http://si-list.org/wiki/wiki.pl?Si-List_FAQ
> 
> List technical documents are available at:
>                 http://www.si-list.org
> 
> List archives are viewable at:     
>               http://www.freelists.org/archives/si-list
> or at our remote archives:
>               http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
>               http://www.qsl.net/wb6tpu
>   
> 
> 
> 

-- 
------------------------------------------------------------
     ___          _            Doug Smith
      \          / )           P.O. Box 1457
       =========               Los Gatos, CA 95031-1457
    _ / \     / \ _            TEL/FAX: 408-356-4186/358-3799
  /  /\  \ ] /  /\  \          Mobile:  408-858-4528
|  q-----( )  |  o  |         Email:   doug@xxxxxxxxxx
  \ _ /    ]    \ _ /          Web:     http://www.dsmith.org
------------------------------------------------------------
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
                http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: