RE: [SI-LIST] : Decoupling capacitors (again!)

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From: Larry Miller (ldmiller@nortelnetworks.com)
Date: Thu Aug 17 2000 - 20:10:32 PDT


Well, I have an HP 8752C-- that reads out in vector format (real,
imaginary), but it has 50 ohm inputs and outputs. With a 50-ohm source
generator you are looking at signals that are 68 dB down at best. That tends
to be pretty close to the noise floor to get any accuracy. I don't say you
don't get the numbers (15 pH). I just probably don't believe them.

Larry Miller

> -----Original Message-----
> From: Istvan Novak - Board Design Technology
> [SMTP:inovak@pompom.East.Sun.COM]
> Sent: Thursday, August 17, 2000 4:09 PM
> To: Miller, Larry [SC7:322:EXCH]
> Cc: Martin.J.Thompson@trw.com; si-list@silab.eng.sun.com;
> istvan.novak@east.sun.com
> Subject: RE: [SI-LIST] : Decoupling capacitors (again!)
>
> Larry,
>
> If my math is correct, 0.02 ohms at 200MHz represents about 15pH of
> inductance. Not
> easy, but today we can measure such low values with vector network
> analyzers. With
> two-port measurements, the limit is really due to the probe configuration
> and
> connection. With nothing fancy, you can go down to a few picohenrys with
> the residual
> inductance.
>
> Regards
>
> Istvan Novak
> SUN Microsystems
>
> X-Unix-From: ldmiller@nortelnetworks.com Thu Aug 17 17:34:42 2000
> From: "Larry Miller" <ldmiller@nortelnetworks.com>
> To: Martin J Thompson <Martin.J.Thompson@trw.com>, si-list
> <si-list@silab.eng.sun.com>
> Subject: RE: [SI-LIST] : Decoupling capacitors (again!)
> Date: Thu, 17 Aug 2000 13:51:49 -0700
> MIME-Version: 1.0
>
> Twenty milli-ohms. 0.02 ohm. At 100 MHz. How does one measure such a
> curiosity?
>
> Thanks,
>
> Larry Miller
> (Not the other Larry)
>
> > -----Original Message-----
> > From: Martin J Thompson [SMTP:Martin.J.Thompson@trw.com]
> > Sent: Wednesday, August 16, 2000 11:58 PM
> > To: si-list
> > Subject: RE: [SI-LIST] : Decoupling capacitors (again!)
> >
> > Larry, another question on buried capacitance...
> > What is it about Hadco's material that allows you to get 2mils
> separation?
> > Can this not be achieved with straight FR-4?
> >
> > Thanks,
> > Martin
> >
> > <snipped for context>
> > >>> Larry Smith <Larry.Smith@Eng.Sun.COM> 16 August 2000 23:55:52
> >>>
> > It turns out that the spreading inductance of power planes
> > spaced 4 mils apart will give you roughly 20 mOhms at 100 MHz. We
> are
> > using Hadco 'buried capacitance' planes that are 2 mils apart in
> many
> > of our products to get lower impedance.
> >
> >
> >
> >
> > TRW Automotive Advanced Product Development,
> > Stratford Road, Solihull, B90 4GW. UK
> > Tel: +44 (0)121-627-3569
> > mailto:martin.j.thompson@trw.com
> >
> >
> >
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>
> Istvan Novak Sun Microsystems, Inc.
> Istvan.Novak@Sun.Com Workgroup Servers, BDT Group,
> One Network Drive, Burlington, MA 01803
> Phone: (781) 442 0340
>
>
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