[SI-LIST] Re: Why is capacitor with high ESR
- From: steve weir <weirsp@xxxxxxxxxx>
- To: sguzek@xxxxxxxxx, "Si-List" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 06 Dec 2004 15:08:23 -0800
Slawek, not at all. If you want to know more about DET you can read any of
Istvan's papers on the subject.
The idea for DET as it pertains to decoupling is simple- satisfy |Z| <=
di/dt at near zero phase. All noise energy is absorbed while remaining
within the noise budget. Since the network appears to be resistive, it
cannot and does not resonate.
DET is not without its practical problems. But, it is physically very
reasonable, even if it is economically challenged. If you find a way to
make your via fence resistive, then you will have reinvented DET.
Regards,
Steve
At 11:34 PM 12/6/2004 +0100, Slawek Guzek wrote:
>Steve,
>
>I think you whish to eat a cake and have a cake. Two demands are in confilct
>about DET: from one side you requires strong decoupling facilities, from
>other
>high resistance to disipate EM energy picked from propagating EM waves
>trough vias.
>
>What is decoupling ? Maximum possibility to act as short term current source
>to supply device consuming short but strong peak currents, to not to allow
>peak current to propagate farther ? So - lower resistance - better. Am I
>wrong ?
>
>On the other hand - to not to reflect EM energy you'lll have to have some
>resistance build into cap, to match impedance of propagating wave.
>
>So does DET works ? I think it should be a question "So does DET should
>better do EMI suppression or better do decoupling ?"
>
>I would think the fences at the edges are good because they eliminate electric
>dipole formed by edges of planes. But they reflect energy back into PCB ?
>So ?.
>Why then don't make fence dissipative too ? Or why don't make some additional
>EM energy absorbers build from vias and connected resistors ? Even if we
>reflect
>all energy from edges back to the PCB we don't have to rely only on
>dissipation
>characteristics of substrate material to dissipate it.
>
>I think It would be much easier to controll impedance of structure
>ground-Resistor-via-ground build for absorbing EM energ than control,
>or find DET with impedance matched for particular PCB stackup.
>Dielectric thickness, Er, and layer configuration will change
>wave impedance from project to project, if even not between PCBs from
>different manufacturing series, unless you'll use substrate with stabilized
>Er parameter, which I think is not very common for non-RF substrates.
>
>Regards,
>Slawek
>
>
>
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of steve weir
> > Sent: Monday, December 06, 2004 9:41 PM
> > To: Chris Cheng; Chris Cheng; Chris Cheng; Chris Cheng;
> '''sguzek@xxxxxxxxx ' ' '; '''Si-List ' ' '
> > Subject: [SI-LIST] Re: Why is capacitor with high ESR
> >
> >
> > Chris, I see two separate threads:
> >
> > 1. Does DET work?
> > 2. Is DET technically and economically practical.
> >
> > I have a hard time seeing DET becoming practical due to human
> > nature. Istvan disagrees with me, but the problem that I see is that DET
> > caps are very specialized so it will be really hard to convince a mfg to
> > make them unless there is both strong customer demand, and customer demand
> > at a premium over ordinary caps. At the same time, OEMs will be very
> > hesitant to do something new especially if it involves risk in the supply
> > chain and "expensive" commodity items. I would like Istvan's vision to
> > work-out, but I don't see it happening. That might change if some really
> > big OEMs decide that they want to demand high ESR caps from their
> suppliers.
> >
> > As to DET working? Istvan is probably the most prominent individual
> > carrying the banner for DET with a number of papers and a whole lot of
> > invested effort, but he is not alone. Patents by Hitachi back in the mid
> > 1990s address damping planes for among other reasons EMI reduction.
> >
> > Now, let's look at the thought problem that you propose: TIG welding shut
> > one side of a cavity, versus placing a lossy load across the
> > aperture. Although it may not be intuitively obvious, in the perfect case
> > for each, no energy escapes. The difference between the two is that with
> > the DET case, the energy has been dissipated. In the TIG welded case, the
> > energy has simply been reflected and is still available to escape
> somewhere
> > else, and that from an EMI perspective is the problem that DET sets out to
> > address.
> >
> > Personally, I like TIG welds. If I could find a TIG weld that supports DC
> > I would have a really good decoupling capacitor.
> >
> > Regards,
> >
> >
> > Steve.
> > At 12:10 PM 12/6/2004 -0800, Chris Cheng wrote:
> > >I have a hard time getting through the thought experiment.
> > >I you have a computer chassis with solid ground and you cut it in half and
> > >isolate one half and tie it to power. You then connect the to halfs by
> your
> > >DET caps, do you think the EMI performance will be better than spot
> > >soldering the two halfs together and maintaining both at ground ?
> Remember,
> > >spot soldering is almost free and I can always put more solder joints than
> > >DET caps.
> > >
> > >-----Original Message-----
> > >From: steve weir [mailto:weirsp@xxxxxxxxxx]
> > >Sent: Monday, December 06, 2004 11:18 AM
> > >To: Chris Cheng; Chris Cheng; Chris Cheng; '''sguzek@xxxxxxxxx ' ' ';
> > >'''Si-List ' ' '
> > >Subject: RE: [SI-LIST] Re: Why is capacitor with high ESR
> > >
> > >
> > >Chrsi no problem, we'll take care of that noise with single points and
> > >splits! Seriously, if you would like to do a test vehicle out of academic
> > >interest, I think you will find that DET does a better job suppressing EMI
> > >than a highly reflective fence.
> > >
> > >Regards,
> > >
> > >
> > >Steve
>[...]
>
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