AC analysis of op-amp loop gain and phase

[kymatica]

@kymatica

How does KiCad access the vectors for plotting? Could it be made to ask ngspice about available vectors? I’m thinking that it would be awesome if one could just add control statements like

  let AB=V("/m2")/V("/m1")
  let dbAB=db(AB) 
  let phAB= 180/pi*ph(AB)

to a textbox and have those vectors show up in the internal ngspice viewer.

I found a trick to do this with internal ngspice!

By adding a global netlabel with the same name as a custom calculated vector, this vector shows up in the signals list so it can be viewed by the internal plot viewer. The netlabel must be connected to a dummy resistor.

The plot won’t update when schematic is changed, so one must close and re-open the plot window, however. Not sure why or how it could be fixed.

Looking at the code, I see eeschema/dialogs/dialog_signal_list.cpp : TransferDataToWindow() calls m_exporter->GetNetIndexMap() to get the available voltages. It would be cool if we could append any vectors found in the ngspice instance that’s not already listed. Alternatively, adding a way to manually add a vector by name.