eldo_user

Working with S, Y, Z Parameters
Instantiating a Block Defined by S, Y, Z Parameters
• NO_DELAY=val
Used to enable or prevent delay extraction in the CPF or DSP methods. NO_DELAY=0
enables delay extraction, NO_DELAY=1 disables it. The default value is 0.
• GROUPFIT=val
Used in CPF to force group fitting instead of individual for every matrix component. As a
rule, with this option, fitting requires less effort but this might compromise accuracy. The
default value is 0, corresponding to individual fitting.
• SYMMETRY=val
The default assumption (SYMMETRY=1) made in CPF on the fitting stage is that the
original S (or Y or Z) matrix is symmetric. Matrix symmetry is a valid assumption as long as
the S-model describes a reciprocal subcircuit. We cannot simply rely on symmetry of the
matrices in the input data. Very often, the input matrices generated by field-solvers or
measured from reciprocal systems, are not strictly symmetric, however they should be
handled as symmetric. Set to 0 to disable the default assumption.
• FORCE_PASSIVITY=val
Enables or disables each of the two different types of passivity enforcement available in the
CPF method. These types are (1) pre-fit passivity enforcement, in which the original
sampled data is worked with to make it “passive,” and (2) post-fit enforcement, in which
poles/residues are corrected in such a way as to make the approximation strictly passive.
FORCE_PASSIVITY=0 means there is no passivity enforcement.
FORCE_PASSIVITY=1 activates pre-fit passivity enforcement.
FORCE_PASSIVITY=2 activates post-fit enforcement.
FORCE_PASSIVITY=3 (default) activates them both.
Pre-fit passivity enforcement is recommended for all passive devices. It removes occasional
passivity violations from the input data (which may result from measurement errors).
However, even for the passive data created by pre-fit passivity enforcement, fitting may still
result in a non-passive model if this data is defined within a limited frequency range (typical
case). With two different methods of passivity enforcement, you can determine the true
reason for non-passivity: poor accuracy of the input data or fitting errors. The reason for
both could be incomplete frequency range, non-causality, or insufficient resolution of the
input data. For causal, accurate, and smooth input data, fitting accuracy is quite high.
By default, Eldo performs a passivity check on the Touchstone file S parameter data. When
non-passivity is detected, data passivity will be enforced and a corresponding information
message will be issued. After the fitting of the S parameter data a new passivity check is
performed on the fitting results. If passivity violation is detected then passivity of the fitting
is enforced and a message is again issued.
Warning message examples:
o non-passive data found:
700
Eldo® User's Manual, 15.3