FFT plots for currents [SOLVED]

Schematic Simulation (Ngspice)
1

Hi everybody,

I been working a lot with SPICE simulations and it is very good to see that ngspice integration has been greatly improved these last releases.

I could make useful transient simulations but I got some problems when trying to get Fourier analysis. It turns out that you need to run them from global labels for no apparent reason, but this only works for voltages. I guess that is a feature that has not yet developed because even after selecting the currents to plot in the New Simulation Tab window they will just disappear in the simulation tab configuration window.

Has anybody been able to run a FFT from currents? If so, can you describe the procedure?

Thank you!

2

FFT with net lables on voltage nodes is possible for me (8.99 nightly on MS Windows).

FFT on device currents seems to be not supported. A buggy netlist is sent to ngspice.

This will require a bug report at Issues · KiCad / KiCad Source Code / kicad · GitLab .

3

In the meantime you may do something like this:

circuit
circuit1434×743 23.8 KB

and make an fft of v(/vmeas)

4

Hi @holger,

Thank you very much for your reply. Nice workaround, I use to solve this complications like you showed in your schematic. However It does not work out of the box by putting the source and changing the gain. I had to configure the SPICE model of the source with the following lines:

.subckt ammeter in+ in- out+ out- params: gain=1Meg
Emeas out+ out- in+ in- {gain}
.ends