Demonstration of use of Octave scripting for post-processing
This demo is based on the example in section 6.7.4 of the Qucs-S help web site at https://qucs-help.readthedocs.io/en/spice4qucs/PostSim.html.
A two-stage BJT amplifier is driven by a sinusoidal source. Both a transient and HB simulation are performed. The results are plotted by an Octave script.
This is done by creating a ".m" file with the same base name as the schematic, in this case "testTwoStageBJT.m". Then, in the File->Document Settings... dialog, check the "run script after simulation" box. (You will see that testTwoStatgeBJT.m will already be there in the "Octave Script" box --- qucs-s will put it there automatically.)
Select "View->Octave Window" in the menu bar, and run the schematic through Xyce. Octave will open 4 graph windows.
Prerequisites:
To make it work, you must have Octave installed on your system, and Qucs-s must be able to find it. In File->Application Settings..., choose the "Locations" tab and make sure that the "Octave Path" is the directory name where the Octave executable is installed.
If you start qucs-s in a directory other than the one where this schematic and its octave scripts reside, then open the schematic using the "Open" menu option, octave will be started with the current working directory in the directory where you start qucs-s, and will therefore be unable to find the scripts. This always happens if you are launching qucs-s from a Mac OS X application icon.
To fix the path issue for octave, either start qucs-s in the same directory where the schematic is stored, launch qucs-s with the "-i" command line option to load the schematic rather than the "Open" command, or change octave's working directory before starting the simulation. Only the last one is possible when launching qucs-s from the OS X application icon. To do this, open the "Octave Window" under the "View" menu, then "cd" to the directory where scripts live before starting the simulation.
Graphs displayed
Time domain data for the V(nin) and V(nout) signals are plotted in figure 1.
Time domain data for the values of the Pr1 current probe and Pr2 voltage probe are plotted in figure 2.
Frequency domain (HB) data for V(nin) and V(nout) are plotted in figure 3.
Frequency domain data for the values of the Pr1 current probe and Pr2 voltage probe are plotted in figure 4.
Differences from Qucs-S help
The example in Qucs-S Help was clearly written a long time ago, and the script displayed there does not actually work. It references functions that do not exist, and even when one substitutes function names that really are included in the qucs-s install (in $prefix/share/qucs/octave), the "plotFFT2V" function turns out not to be written in a way that is correct for the example. (It takes time-domain signals and FFTs them before plotting, whereas in the example on Qucs-S Help, it is being used to plot frequency-domain HB results).
Further, the "plotCartesian2D2V.m" file provided with Qucs-S defines the function "PlotCartesian2D2V", not "plotCartesian2D2V". Octave complains that the function name does not match the file name. It was may have been created on a Mac, where filename case is ignored.
To fix these two issues, I have provided .m files for a copy of plotCartesian2D2V with the case issue fixed, and a "plotFD2V.m" function that is a simple modification of plotFFT2V, but which uses an input vector of frequencies, and plots the data directly without FFTing it. They are found by Octave because they are in the same directory as the testTwoStageBJT.m script.
Exported schematic image
