[ibis-macro] Control inputs for building blocks

  • From: "Muranyi, Arpad" <arpad.muranyi@xxxxxxxxx>
  • To: <ibis-macro@xxxxxxxxxxxxx>
  • Date: Tue, 23 Aug 2005 14:30:07 -0700

To all,

This subject came up again in today's macro modeling meeting.
Here is a short summary to recap the issue.

Parameters in both *-AMS languages are handled as constants,
which means that they can only be changed at the beginning of
a simulation.  If there is a need for a "dynamic" parameter
which can change during a simulation, such as a voltage controlled
resistor (VCR), then we need to add another terminal or port
to the model which contains the control input.  This can be done
very easily in the *-AMS languages, no problems there.

The question revolves around the original goal of the "standard
macro modeling library" idea.  The purpose with this was to make
macro models possible using the *-AMS netlisting syntax using the
building block in the standard library, and then SPICE vendors
who don't have *-AMS capabilities could substitute their own
native elements for the building blocks found in the library.

With this goal the question becomes, can a resistor, capacitor
etc... *-AMS model be substituted by a corresponding SPICE
element if it has more than just two terminals?  It was
suggested that this could be done by writing a wrapper
around a "normal" element.  For example, in HSPICE we could
write the following code to substitute such a controlled

.SUBCIRCUIT  myVCRmodel  n1  n2  ctrl  ctrl_ref
R1  n1  n2  R='V(ctrl, ctrl_ref)'

where the voltage between terminals "ctrl and ctrl_ref"
contains the value for the resistor, represented as a

The follow-on question is whether this could also be done 
when the control terminal in the *-AMS model is not a voltage
or current (electrical type), but simply just a "real" number?
I.e., the conversion from voltage or current to a real number
would take place outside the building block, and the building
block would only have three terminals.

This option is less SPICE like, so from the macro model writer's
perspective it may be a less familiar syntax.

I am now in the process of writing the building blocks for
the library.  I would like to solicit responses to the following

1)  Should we include this capability in the building block
    library, or is it enough to have a set of constant valued
    R, L, C elements?
2)  If we had this capability, should we have two additional
    terminals for a controlling voltage or current, or should
    we make the control input a single terminal where a real
    number is supplied to the building block?

Please speak up now, or forever hold your piece...



-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] 
On Behalf Of Todd Westerhoff (twesterh)
Sent: Wednesday, August 17, 2005 1:18 PM
To: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Charge conserving capacitor model

My vote:

Keep it simple for now, and come up with a solution for a charge
conserving model when we're developing a model template that needs one.


Todd Westerhoff
High Speed Design Group Manager
Cisco Systems
1414 Massachusetts Ave - Boxboro, MA - 01719 email:twesterh@xxxxxxxxx
ph: 978-936-2149

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