[ibis-macro] Re: Question on PWL building block implementations

  • From: "Mike LaBonte (milabont)" <milabont@xxxxxxxxx>
  • To: <ibis-macro@xxxxxxxxxxxxx>
  • Date: Tue, 1 Nov 2005 14:08:41 -0500

I prefer to extend the final slope. That gives maximum flexibility,
since it can be used to mimic HE too.
About triggered sources, is this the Cadence "DATAPOINTS timecoeff ..."
format we are talking about? We would need to have the description in
front of us, and it's up to Cadence whether or not that's OK.



From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad
Sent: Tuesday, November 01, 2005 1:17 PM
To: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Question on PWL building block implementations
Importance: High

Hello everyone,
I need to ask a few questions regarding the PWL sources
in our library, so I thought I would write this message
before the meeting so people could get ready for the
discussion on this topic in the meeting.
One question is general.  What should the PWL sources do
when the input is outside the range of the table definition?
The two options I can think of are:
1) Repeat the first or last points, which amounts to a
horizontal extrapolation (HE), or
2) use the first or last slope and extrapolate with that,
which I call slope extrapolation (SE).
The easier way of doing it is the second way, because the
$table_model keyword in Verilog-A(MS) which is used for
this in our library can only do it that way.  This is how
the library has it now.  However, with a few IF statements
I found a relatively easy way to implement HE, and I am
leaning towards implementing this in our library.
The reason I am asking, though, is because I would like to
be compatible with existing SPICE implementations while
also serving the needs of the macro modeling engineers.
My understanding of HSPICE is that the PWL tables in it
use HE.  How about other SPICE tools?  How about the
practical usage of these PWL building blocks?
The second question is regarding the event triggered PWL
sources.  So far the only tool that I know has these
PWL sources is Cadence's K-SPICE.  Is it OK if I
implemented it the same way they do it?  My current
implementation is somewhat different from it in the
library, but I think using their implementation would
make a lot of sense.  I can explain the details verbally
in the meeting, but first I wanted to find out whether
there are any other SPICE tools which have such an animal,
and if so who's implementation we should pick...
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