Hi I am trying to generate an I/V curve for an nfet in xschem using ngspice. I am able to plot the current with ngspice in interactive mode using the following script: .lib /usr/local/share/pdk/sky130B/libs.tech/ngspice/sky130.lib.spice tt .DC V2 0 1.95 0.05 .probe I(XM1,3) .save all then from the terminal I do plot m1:s#branch. I was wondering if there is a way to do this using a control commands in the netlist instead. Follow up, what is the proper way to add control code to netlists generated with xschem; should you just edit the netlist using your text editor of choice?

to add arbitrary spice code in a xschem schematic just use a

code.sym

or

code_shown.sym

. All xschem_sky130 example circuits do this.

Thank you so much, this is extremely helpful!

Yes, you can add arbitrary spice code, including plot commands. In this case you get the plots drawn by ngspice. In the example above the plots are not drawn by ngspice, but directly by xschem. Xschem is now also a (rather complete) spice waveform viewer. To use xschem own wave rendering the flow is: • Write the spice commands to run the simulation, run the simulation (Typically press Simulate button). • Write the command to create the binary raw file (

write circuit.raw

if schematic name is circuit.sch) • Place a graph in xschem (

Simulation->Graphs -> Add waveform graph

) • Load the raw file (

Waves->tran

or

Waves->dc

, ...., depending on the simulation you have created). • Display signals in the graph. See this tutorial.