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

  • From: "Muranyi, Arpad" <arpad.muranyi@xxxxxxxxx>
  • To: <ibis-macro@xxxxxxxxxxxxx>
  • Date: Tue, 1 Nov 2005 11:34:40 -0800

Correction, HE would give 0.0 at t=0 in the first
paragraph below the table (not 0.1)...

Arpad
=================================================

-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] 
On Behalf Of Muranyi, Arpad
Sent: Tuesday, November 01, 2005 11:29 AM
To: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Question on PWL building block implementations

Mike,

I am talking about a table like this: 

   X : real_vector := (0.50e-9,  1.00e-9,  2.00e-9,  2.50e-9);
   Y : real_vector := (0.00,     0.10,     0.90,     1.00));

Note that the time doesn't start a t=0, and that the last
slopes are not horizontal.  In this case the results may
differ at the trigger event t=0.  HE would give you 0.1,
SE would give you -0.1.  Similarly at the end, if time
goes on, HE would give you 1.0, SE would give you 1.1 at 3ns
and so on.

This concept would also apply to non triggered PWL sources.

The question is whether I should be compatible with existing
tools, or do it the most useful and flexible way.  If "maximum
flexibility" is our goal, I would actually add a parameter that
allows the user to select between HE, or SE, but then the
question becomes whether SPICE only people will be able to
substitute with their own native elements.

Regarding the triggered PWL source question, there is more
than just the format (or syntax) I am talking about.  But
I would rather explain that verbally in the meeting...
(Don't want to write a book in this).

Arpad
=============================================================

-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] 
On Behalf Of Mike LaBonte (milabont)
Sent: Tuesday, November 01, 2005 11:09 AM
To: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Question on PWL building block implementations

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.

Mike

________________________________

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...
 
Thanks,
 
Arpad
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