Re[2]: GND Plane Bounce Question

Text item:

     Frank,
     
     Thank you very much for taking the time to address this problem. In
     fact I would like to know more about this tool, if you can send me
     some info on it. My address is with Quad, and also at the bottom. The
     numbers you give me are a big help. With a formula provided by someone
     else, I will have a good idea of what to expect.
     
     
     I would like to comment on this whole issue a bit, and address what
     prompted my question in the first place:-
     
      Some of the colleagues who answered my inquiry, correctly indicated
     that I should designate the source of the current and not just its
     sink. So I answered one of them by saying the following: Assume that I
     can magically inject the current into the GND plane thru the
     via...etc. The reason I say that is because I was really interested in
     local bounce, with the closest discontinuity to the GND plane being a
     few inches away. Such a case arises when you are dealing with, say,
     open collector buffers, where the collector is tied to a signal trace
     on the top layer of my hypothetical board, while the emitter pumps the
     GND plane thru the via. The source of the current has to tie back to
     the plane at some distant point, but that is not very relevant (in my
     opinion) during the first few 100 ps's of the transient around the
     via.
     
      The real reason I asked the above question has not been stated by me
     yet. Well, here it goes: If one is trying to measure Clk-out delay
     (Tco) of a buffer using a scope, and places the scope ground near my
     via, while placing the scope's active lead at the bit of interest,
     then, I believe, that if many bits are switching, that the waveform
     seen by the scope would be distorted by the GND plane bounce. Say you
     have a falling edge (while many bits toggle down), then since the GND
     bounces up, the scope would read a smaller voltage (its gnd lead is
     moving up too), and show the edge to be just as fast as when a single
     bit switches (or nearly so) even though the edge has --in reality--
     slowed down due to SSO. So one has to be more clever as to where to
     measure Tco is such situations.
     
     Do others agree with my assesment ??
     
     Sincerely,
     
     Samie Samaan
     Intel
     2111 NE 25th Ave
     Hillsboro, OR 97124.

______________________________ Reply Separator _________________________________
Subject: Re: GND Plane Bounce Question
Author: fyuan%qdt.com%uunet@uunet.uu.net at SMTPGATE
Date: 8/21/95 6:31 PM

   Hi, Samie,

   I did some quick and simple simulations for your GND plane bounce problem
   using the power/ground plane simulation tool we have at Quad Design.
   The PCB is same as yours, and the size is 10x10 inch. Assume the current
   is 10 mA (instead of 10 Amps in your message), and there are no de-caps or
   other loads between the power/ground plane, the local ground bound is about
   8 ~ 10 mV, assuming the current source has a 50 ohm internal resistance.
   The ground noise propagates all over the plane, so the bounce away from the
   via is lower but not too much than that at the vis. Depending on location,
   the bounce is 2 ~ 6 mV. The location of the via also have some effects on
   bounce, but is usually small.

   Note that if you really have a 10 Amps current, the bounce would be 8 ~ 10
   volts. That will be a truly unusual or extrame situation.

   The above results assuming the power/ground planes are open (or no other
   terminations), This usually gives higher estimate of GND bounce because of
   the resonance of the plane. From my experice, the things affect the ground
   bounce mostly are your loads, especially decoupling capacitors. Proper
   placement of de-caps of 10~100 nf can significantly reduce the GND bounce
   in the above situation, by 5 ~ 10 times. Resistive loads have little
   effects on the GND bounce unless it is really small ( about 0.1 ohm for
   the above example).

   Our tool can do a much better job in extimating GND bounce if you have
   more information about the geometry, the ternimation or load conditions,
   and the source or device characteristics. Hope this is useful for you.

   Regards

   Frank Yuan
   Quad Design Technology
   (805) 988-8250

> From uunet!ccm2.jf.intel.com!Samie_Samaan Mon Aug 21 13:11:20 1995
> Date: Mon, 21 Aug 95 11:22:00 PDT
> From: Samie Samaan <uunet!ccm2.jf.intel.com!Samie_Samaan>
> To: uunet!vhdl.org!ibis
> Subject: GND Plane Bounce Question
> Content-Length: 1709
>
>
> Text item: Text_1
>
>
> All IBISians (SI experts by Default !!)
>
> I would like to pose the following SI question, and solicit help from
> those who actually know the answer or have a very good idea of how to
> estimate it by scaling from previous experience:
>
>
> Assume one GND and one power plane in a PCB separated by say 10 mil,
> with a dielectric constant of say 4. assume that the power plane has a
> via opening where current is injected thru the via down to the GND
> plane. Let's say that the current is 10 Amps. with a riserime of 1 ns.
> Assume nominal via diameter. The drawing below shows the structure:
>
>
> | Vcc
> ---------------- | ------------------
> | GND 10 mil, Er=4
> -----------------|-------------------
>
>
> What I would like to hear from anybody who actually has experienced
> GND plane bounce, is:
>
> *howmuch do you expect the GND plane (not the via stem) to bounce up
> (locally) given the above assumptions, and
>
> *howfar away from the via (radially) do you expect the bounce to drop
> to 10% of the peak which occurs right where the via meets the plane ?
>
> I would apprciate a good guess (and Why: perhaps from previous
> experience), or direction as to "who ?" you think could answer such a
> question. I know that I might need to do a 3-D or radial transmission
> line analysis of the system, but I'm really just looking for a quick
> answer.
>
>
> Thanks for taking the time to read or answer this question.
>
> Samie Samaan
> Intel Corp.
>

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Cc: uunet!qdt.com!jonp@uunet.uu.net, uunet!qdt.com!fyuan@uunet.uu.net
Subject: Re: GND Plane Bounce Question
To: uunet!uunet!ccm2.jf.intel.com!Samie_Samaan@uunet.uu.net
Message-Id: <9508220131.AA09604@hal.qdt.com>
From: uunet!qdt.com!fyuan@uunet.uu.net (Frank Yuan)
Date: Mon, 21 Aug 95 18:31:04 PDT
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