[ibis-interconn] Re: Sparse Touchstone Proposal, with some more thought pu into it
- From: "Walter Katz" <wkatz@xxxxxxxxxx>
- To: "'IBIS-Interconnect'" <ibis-interconn@xxxxxxxxxxxxx>
- Date: Mon, 20 Jul 2009 19:35:35 -0400
Mike,
A "Function" is a method of returning a value for any given set of
independent variable. In this case the value is an imaginary number
representing the phase and amplitude of a signal measured at some "node" of
a circuit when a sine wave of amplitude one and frequency f is inserted at
another node. This is a "Transfer Function". Touchstone is a mathematical
way of expressing this function to a software tool by stating what the value
of this function is at some specified sampled frequencies. A Spice PWL is
another, similar, way of describing a function. A polynomial expansion (e.g.
Taylor series) is another representation of a function. A Taylor series
expansion is only an approximation (unless one can support an infinite
number of coefficients). Unfortunately, Touchstone does not force any
standards on how many frequencies need to be sampled, or how the function is
to be interpolated between the sampled points. A Pole Zero representation of
a Transfer Function can only be correct at N frequencies if there are N
Poles and Zeros. A Pole Zero representation has the advantage of telling the
EDA tool how to interpolate between these accurately sampled points.
Walter
-----Original Message-----
From: ibis-interconn-bounce@xxxxxxxxxxxxx
[mailto:ibis-interconn-bounce@xxxxxxxxxxxxx] On Behalf Of Mirmak, Michael
Sent: Monday, July 20, 2009 6:26 PM
To: Walter Katz; IBIS-Interconnect
Subject: [ibis-interconn] Re: Sparse Touchstone Proposal, with some more
thought pu into it
In as much as "Framis" is a neologism it may save a lot of argument. :-)
Perhaps I am a bit obtuse, but fundamentally, my objection has been to the
word "function" in this context. To my math-avoiding mind, a function is
any expression containing an equals sign and one or more variables.
Touchstone files contain no expressions or equations but only values or
coefficients. Therefore, no functions are involved.
Awaiting a deluge of corrections.
- MM
From: ibis-interconn-bounce@xxxxxxxxxxxxx
[mailto:ibis-interconn-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Saturday, July 18, 2009 6:32 PM
To: IBIS-Interconnect
Subject: [ibis-interconn] Sparse Touchstone Proposal, with some more thought
pu into it
All,
I think we can all agree that an Sij (imaginary number as a list of sampled
frequencies) is a numerical approximation of a Transfer Function. I would
like to name this a "Framis".
Here is a BNF an enhancements to Touchstone to handle Sparse Matrix data
that should satisfy all of the issues raise in the past several meetings.
[Number of Unique Framis's] <number of unique framis's>
{Framis Names]
1 <framis name>
2 <framis name>
.
<number of unique framis's> <frames name>
{End Framis Names]
[Sparse Framis Data]
<frames name> : (<row,column>) (<row,column>) (<row,column>) (<row,column>)
.
<frames name> : (<row,column>) (<row,column>) (<row,column>) (<row,column>)
.
(<row,column>) (<row,column>) (<row,column>)
(<row,column>) .
< frames name> : (<row,column>) (<row,column>) (<row,column>) (<row,column>)
.
[End Sparse Framis Data]
The actual network data will have at each frequency <number of unique
framis's> imaginary numbers.
[Framis Names] section is optional, the default <framis name> of any Framis
is its' <framis number>. A <framis name> can consists of any legal IBIS
character, except ":" is not allowed as a Framis name.
Walter
Walter Katz
Chief Scientist
Signal Integrity Software, Inc.
wkatz@xxxxxxxxxx
303.449-2308
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