The single most important thing I miss in LTspice is the ability to plot things of multiple runs on top of each other. Cadence Virtuoso calls that "Append Plot".

What I mean: I want to plot one node of my circuit, hit "Run" and plot. Then change the topology and run again and plot the result on top of the first one. This makes it easy to see the impact of multiple blocks/parsitics/changes directly in the waveform.

I know I can export the plot after each run and plot them on top in MATLAB for example. I also know I can use .step. But this does not (easily) allow for topology changes. None of these two are solutions.

  • \$\begingroup\$ I'm afraid you're out of luck then, because .step would have been the solution, without external intervention. Cadence must have a behind-the-scenes merge utility that appends the results of the simulation, or, at the very least, involve some sort of temporary save. Alas. Otherwise, if you do intend to go the .step way, maybe this can be of a help. \$\endgroup\$ Commented Jul 22, 2020 at 19:59
  • \$\begingroup\$ My crude work-around is just to open a Google Docs document and copy and paste each graph into it as I go. If I'm not lazy I put notes about what changed for each plot. Disadvantage is you don't actually get the plots on top of each other. The advantage is you don't lose all the memory if you restart LTSpice. \$\endgroup\$
    – The Photon
    Commented Jul 22, 2020 at 21:06
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    \$\begingroup\$ From LTspice HELP: "There is an export utility(Waveform Menu: File=>Export) that allows data to be exported to an ASCII file. There is also a 3rd party free utility written by Helmut Sennewald. It is available from the independent users' group groups.io/g/LTspice(formerly hosted on Yahoo). This utility allows various forms of manipulation of the data including the ability to merge waveforms from different simulation runs." \$\endgroup\$
    – jonk
    Commented Jul 23, 2020 at 4:20
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    \$\begingroup\$ You could also copy circuits with the different architectures and literally run all in parallel at once naming each node of interest differently(vout1,vout2,...) . Then plot them all for comparison. I've done that. Saves from processing outside LTspice. \$\endgroup\$
    – pat
    Commented Sep 11, 2021 at 17:51

1 Answer 1


There is not an easy way to do this in LT spice. A very unorthodox way (that I have used in the past) is export the file and then use a PWL source to read a file (that you have exported). I can't remember if I had to write a script to translate the PWL.

A better way would be to run the Lt spice file, export, and then plot both signals in excel, matlab or python matplotlib.

The best way is to figure out how to use .step to run both of the circuits in the same simulation. With b-sources there are many clever ways to use a voltage source to switch other b-sources to change compoent values with if statements ect.


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