Re: [SI-LIST] : PCB Pwr Planes

jzhao@ee1-gw.ee.binghamton.edu
Fri, 20 Mar 1998 22:45:12 -0500 (EST)

Hi Jim,

Since I posted a reply to your question on the SI-list, Ed Miller at
Hewlett Packard made some comments on my reply. I don't think I was
very clear on the question you asked when I posted the reply. For your
reference, here I enclosed portions of e-mail conversations between Ed
Miller and Jiayuan Fang on the subject you raised. Hope that will help
to answer your question.

Regards,

Jin Zhao

Dept. of Electrical Engineering
State University of New York at Binghamton
Binghamton, NY 13902-6000
Tel: (607) 777-4684
Fax: (607) 777-4464
Email: jzhao@emlab1.ee.binghamton.edu
jzhao@binghamton.edu

On Fri, 20 Mar 1998 fangj@binghamton.edu wrote:
>
>
> Hi Ed,
>
> (Irrelevant paragraph deleted)
>
> On the question posted on the SI-list, "Is a Vcc power plane really the
> same as a Gnd power plane at high freq's (assuming good bypass cap's)?"
> I am not absolutely sure what the person really asks.
>
> If his question is whether the Vcc power plane can be considered
> short-circuited to the Gnd power plane at high freq's (assuming good
> bypass caps), then the answer could be:
>
> A Vcc power plane can be considered short-circuited to the Gnd
> power plane at high frequencies assuming IDEAL bypass capacitors are
> placed EVERYWHERE between the Vcc and the Gnd planes. In reality,
> bypass capacitors are not ideal and can not be placed everywhere between
> the Vcc and the Gnd planes. Therefore, impedance between the power and
> ground planes may not be small at certain frequencies. If there are
> resonances between planes, the impedance between planes can be
> significantly large at resonant frequencies. So one has to design the
> power and ground supply system carefully to ensure low impedance (and no
> resonance) in the entire frequency range of interest. This is exactly
> where SPEED97 can be applied for.
>
> Best regards,
>
> Jiayuan Fang
>
>
>
>
> On Fri, 20 Mar 1998, Edward Miller wrote:
>
> > Hello Jiayuan,
> >
> > I just happened to read this SI posting and it was of interest because the
> > responder was located at SUNY Binghamton.
> >
> > I would not feel comfortable making a statement that the power and ground
> > planes could be considered equivalent even if you assumed that the by-pass
> > capacitance was "good". High frequency equivalency for these planes, given
> > a real world shot as providing optimized bypassing, would still be optimized
> > on discrete bandwidth sections of the frequency spectrum and the application
> > would be the key as to whether ac equivalency could be inferred. In other
> > words, I believe there will be portions of the frequency spectrum where "good"
> > bypassing will still show reasonably high impedance between the planes.
> >
> > What is your feeling about this? It seems that the response below could be
> > interpreted improperly by the asking party.
> >
> > (Irrelevant paragraph deleted)
> >
> > Best regards,
> >
> > Ed Miller
> >
> >
> > >
> > > Hi, Jim
> > >
> > > In my opinion, or from the view of microwave tech., I think that they are
> > > same.
> > >
> > > Jin Zhao
> > >
> > > Dept. of Electrical Engineering
> > > State University of New York at Binghamton
> > > Binghamton, NY 13902-6000
> > > Tel: (607) 777-4684
> > > Fax: (607) 777-4464
> > > Email: jzhao@emlab1.ee.binghamton.edu
> > > jzhao@binghamton.edu
> > >
> > >
> > > On Thu, 19 Mar 1998, Peterson, James F (FL51) wrote:
> > >
> > > >
> > > > I'd like to verify an assumption of mine:
> > > > Is a Vcc power plane really the same as a Gnd power plane at high freq's
> > > > (assuming good bypass cap's)?
> > > > Thanks for your input,
> > > > Jim
> > > > Jim Peterson
> > > > jfpeterson@space.honeywell.com
> > > > Honeywell, Space Systems Division, M/S 934-5
> > > > 13350 US 19 N., Clearwater, FL, 34624
> > > > 813-539-2719
> > > >