[SI-LIST] Re: Decoupling capacitors

Ross, Larry, Ray

I couldn't agree with Larry more on the need to include the effects of
chip-capacitance, package-inductance and on-package capacitors along with
those of the PCB in doing an analysis of the power distribution system. In
general terms, what is needed is the ability to electromagnetically analyze
the package and the board together; such structures are often of multiple
plane layers and are segmented as well.  In addition, it should be possible
to add circuit components of any kind wherever necessary in the combined
structure. This is actually the approach used in Sigrity software tools.


Best Regards,


Raj Raghuram
Sigrity, Inc.
"Achieve what others can't"
raghu@xxxxxxxxxxx
http://www.sigrity.com
4675 Stevens Creek Blvd. , Ste 130
Santa Clara, CA-95051
PH: 408-260-9344 x116
CELL: 408-390-7614
FAX: 408-260-9342


> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Larry Smith
> Sent: Thursday, May 23, 2002 12:54 PM
> To: raymond.anderson@xxxxxxx; si-list@xxxxxxxxxxxxx; RJatou@xxxxxxxxxx
> Subject: [SI-LIST] Re: Decoupling capacitors
>
>
>
> Ross - You are quite correct in identifying the need for chip
> capacitance to be accounted for when doing a power distribution
> analysis.  Not only is the chip capacitance important, but the package
> inductance is also extremely important.  These reactances form a
> resonant tank circuit that often dominates the power impedance seen by
> the chip circuits in the 50MHz to 200MHz band.  We call this
> chip/package resonance.  Many packaged chips also include discrete
> decoupling capacitors somewhere between the chip and the PCB.  The
> chip-capacitance, package-inductance and on-package capacitors are
> extremely important components that must be accounted for when doing
> power distribution system analysis.
>
> The Cadence SQPI tool is excellent for designing a broad band low
> impedance at the PCB level.  But to make the tool really useful, we
> must include the effects of chip/package resonance.  I know that
> Cadence has this enhancement on their roadmap.  Perhaps a little more
> pressure from SI-list will help motivate them to put the resource on
> it.  :)  I have seen some scripts from Intel that essentially embed the
> SQPI noise source inside a package.  It would be nice to get a fully
> supported version from Cadence.
>
> regards,
> Larry Smith
> Sun Microsystems
>
> > Delivered-To: si-list@xxxxxxxxxxxxx
> > From: Ross Jatou <RJatou@xxxxxxxxxx>
> > To: "'raymond.anderson@xxxxxxx'" <raymond.anderson@xxxxxxx>, si-list
> <si-list@xxxxxxxxxxxxx>
> > Subject: [SI-LIST] Re: Decoupling capacitors
> > Date: Thu, 23 May 2002 11:54:49 -0700
> > MIME-Version: 1.0
> > Content-Transfer-Encoding: 8bit
> > X-archive-position: 2948
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> > X-original-sender: RJatou@xxxxxxxxxx
> > X-list: si-list
> >
> >
> > Ray,
> >
> > We have SQPI as well and have been trying to correlate it to
> measurements.
> > My question is: how do you incorporate chip capacitance ?
> > The capacitance is in two forms:
> > 1) package and die capacitance between power and ground
> > 2) integrated caps that are placed in the package.
> >
> >
> >
> > Ross
> >
> > -----Original Message-----
> > From: Ray Anderson [mailto:raymond.anderson@xxxxxxx]
> > Sent: Thursday, May 23, 2002 11:08 AM
> > To: si-list
> > Subject: [SI-LIST] Re: Decoupling capacitors
> >
> >
> >
> >
> >
> >
> > > Specctraquest has a power integrity option which allows the
> simulation of
> > > parallel resonaces of capacitor decoupling, which also accounts for
> > > propagation delay between the capacitors.  It uses a multinode mesh of
> > > transmission lines to model the decoupling capacitor system.
> I haven't
> > had
> > > a chance to use it, but it sounds like a good strategy for modelling
> > > decoupling capacitors as a complete system, taking into
> account capacitor
> > > locations as well as capacitor values.  Has anybody in this
> group had a
> > > chance to use this?
> > >
> > > Wayne Cooke
> > > Signal Integrity Engineer, Innovance Networks
> > > 19 Fairmont Ave., Ottawa, Ont.  K1Y 1X4
> > > email: wcooke@xxxxxxxxxxxxx
> >
> >
> > Disclaimer: I am one of the original developers of the power integrity
> > analysis tool that was licensed to Cadence and is now integrated into
> > Specctraquest, so my views may be biased....
> >
> >
> > As mentioned by Wayne, the SpecctraQuest Power Integrity tool (SQPI)
> > is based on a plane model comprised of an orthoganal mesh of
> transmission
> > lines where various decoupling capacitors can be placed at any of the
> > mesh nodes of the plane model for performing a frequency domain
> analysis.
> >
> > There are actually two modes of analysis in the tool: single-node and
> > multi-node.
> >
> > The single-node analysis places all the decoupling caps in
> > parallel, connected to just a single pair of nodes, (the hot side and
> > ground),
> > with no plane circuit in the model. This mode of analysis can
> be utilized
> > as an initial step in the selection of a set of decaps that provides a
> > broadband low Z response. It is quick but not particularly accurate as
> > it doesn't account for the spatial placement on the planes.
> >
> > The multi-node analysis adds the plane model into the mix. In this
> > scenario, the decaps as well as a noise source(s) and a VRM are
> spatially
> > placed on the plane. Then a frequency domain simulation is run and the
> > resultant impedance profile is generated. Note that the inductance
> > associated
> > with the mounting structures (pads, escapes, and planes) can be
> specified
> > in addition to the 'intrinsic' inductance of the capacitor
> which is included
> > in the decap model.
> >
> > When you place decaps on the plane and perform the frequency domain
> > simulation,
> > there are three types of resonances which you will observe and must be
> > managed to produce a properly decoupled power distribution
> system. These are
> > the a) plane resonances (actually cavity resonances), b) series RLC
> > resonances
> > where each decap resonates, and c) anti-resonances caused by
> the inductance
> > of the decap resonating with the interplane capacitance of the planes.
> >
> > For more details on the methodology, go to
> > http://groups.yahoo.com/group/si-list/files/
> > and follow the links to a number of published conference papers
> dealing with
> > the subject of power distribution system design and simulation
> authored by
> > our group here at Sun.
> >
> > -Ray Anderson
> > Sun Microsystems
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