[SI-LIST] Re: Decoupling capacitors
- From: Ross Jatou <RJatou@xxxxxxxxxx>
- To: "'raymond.anderson@xxxxxxx'" <raymond.anderson@xxxxxxx>,si-list <si-list@xxxxxxxxxxxxx>
- Date: Thu, 23 May 2002 11:54:49 -0700
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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