Hi Michael,
I wasn't even aware that S-parameters were supported in W elements in the
flavor of SPICE I work with, but sure enough there it is! That's a very useful
feature creating a length-adjustable S-parameter. This was definitely not an
option when we created IBIS-ISS from the donated syntax of HSPICE. We'd need
to update IBIS-ISS to support such a feature. If we ever update IBIS-ISS, this
would be an excellent feature to add. It would be interesting to know how many
EDA tools could support such a function if added to IBIS-ISS.
Randy
From: ibis-interconn-bounce@xxxxxxxxxxxxx <ibis-interconn-bounce@xxxxxxxxxxxxx>
On Behalf Of Radek Biernacki
Sent: Thursday, January 27, 2022 11:19 AM
To: Mirmak, Michael <michael.mirmak@xxxxxxxxx>; IBIS-Interconnect
<ibis-interconn@xxxxxxxxxxxxx>
Subject: [EXT] [ibis-interconn] Re: IBIS-ISS question
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Hi Michael,
Yes, for such applications a "cascading multiplicity" would be a convenient
feature.
Radek
From: Mirmak, Michael
<michael.mirmak@xxxxxxxxx<mailto:michael.mirmak@xxxxxxxxx>>
Sent: Thursday, January 27, 2022 10:02 AM
To: Radek Biernacki
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IBIS-Interconnect
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Subject: RE: IBIS-ISS question
Radek,
Thanks! This is certainly true, in theory, but becomes impractical when
S-parameters are unitary. For example, to be maximally useful, I might create
an S-parameter model of a single centimeter of cable. If I need to simulate a
3-meter cable assembly, the creation of the necessary subcircuit would be very
tedious.
In addition, I would need a new subcircuit for even the smallest change in
length, making convenient length sweeps in simulation effectively impossible.
A cascaded S-parameter within the W-element allows me to control the final
length with a single parameter.
* MM
From: Radek Biernacki
<radek_biernacki@xxxxxxxxxxxx<mailto:radek_biernacki@xxxxxxxxxxxx>>
Sent: Thursday, January 27, 2022 9:57 AM
To: Mirmak, Michael
<michael.mirmak@xxxxxxxxx<mailto:michael.mirmak@xxxxxxxxx>>; IBIS-Interconnect
<ibis-interconn@xxxxxxxxxxxxx<mailto:ibis-interconn@xxxxxxxxxxxxx>>
Subject: RE: IBIS-ISS question
Hi Michael,
In IBIS_ISS you can create a subcircuit with as many S-elements as you wish and
connected as desired. Then you can use that subcircuit in the interconnect
model.
Radek
From:
ibis-interconn-bounce@xxxxxxxxxxxxx<mailto:ibis-interconn-bounce@xxxxxxxxxxxxx>
<ibis-interconn-bounce@xxxxxxxxxxxxx<mailto:ibis-interconn-bounce@xxxxxxxxxxxxx>>
On Behalf Of Mirmak, Michael
Sent: Thursday, January 27, 2022 9:52 AM
To: IBIS-Interconnect
<ibis-interconn@xxxxxxxxxxxxx<mailto:ibis-interconn@xxxxxxxxxxxxx>>
Subject: [ibis-interconn] IBIS-ISS question
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The current IBIS-ISS format definition supports W-elements for RLGC structures
and S-elements for Touchstone S-parameters. However, in some commercial
flavors of SPICE today, the two can be combined (i.e., W-elements can "wrap
around" S-parameters).
1. Is there a reason why this particular feature was *not* included in
IBIS-ISS? Was this an oversight or a deliberate omission?
2. In the absence of this feature, IBIS-ISS has a significant limitation,
which the new IBIS Interconnect Model does not alleviate: cascading instances
of S-parameters is not supported.
S-parameters can and are used to represent unitary circuit elements (for
example, a solder pad), but are also used to represent scalable structures (for
example, a portion of PCB trace modeled as a transmission line). The "M"
structure for subcircuits supports easy *parallel* connection of elements, but
without a W-element wrapper, I don't see a way to easily cascade multiple
S-parameter elements in series. Is there any known way using existing IBIS-ISS
structures to do this? If not, would a change to IBIS-ISS to support this be
feasible (without a parser, this seems not very burdensome).
Thanks in advance...
* MM
