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
