This video is taken from the INT 100 course on Ansys Innovation Courses.
Transcript
S-parameter elements are used for a wide range of applications and play a variety of roles
in circuits.
The optical digital filter properties depend on the s-parameter element's role in the circuit.
In determining the optimal settings, we must ask ourselves, what is most critical?
Is it most critical that the group delay be accurate?
Is it most critical that the frequency dependent transmission amplitude be accurate?
Or is this a frequency independent element with zero group delay?
In the following we'll walk through these three cases and recommend digital filter settings.
In cases where the group delay is most critical, like resonant structures, feedback loops and
interferometers, the following settings are recommended: Set the digital filter type to
FIR (which stands for finite impulse response), set the number of taps estimation to group
delay and set the fractional delay to true.
This requires that the group delay data is provided in the S-parameter file.
The performance of the s-parameter element with these settings is the same as that for
the waveguide presented in the last unit.
The complex transmission is accurate at the center frequency of the simulation.
The accuracy of the group delay at the center frequency and the frequency dependent transmission
depend on the delay compensation and sample rate.
In cases where the transmission amplitude is most critical, like grating couplers and
optical filters, the following digital filter settings are recommended: Set the digital
filter type to FIR, the number of taps estimation to fit tolerance.
When the S-parameter element is implemented with these settings, the accuracy of the group
delay and frequency dependent transmission depend on the fit tolerance, which is a digital
filter property highlighted here, and the sample rate.
The lower the fit tolerance, and the higher the sample rate, the more accurate your results
will be.
Finally, in some cases, it is desired that the S-parameter element introduces no time
delay, and that the transmission amplitude be also constant over the frequency range
of interest.
One example is a point directional coupler.
We recommend the following settings: Set the digital filter type to FIR, the number of
taps estimation to disabled and the number of FIR taps to 1.
This element has a constant frequency independent response with zero group delay.
The complex transmission is accurate at the center frequency of the simulation.