I am using LTspice on the circuit EMI spectrum study. Let's say I have two waveforms for V1 and V2. I wonder if in LTspice, I can plot the FFT results for :
(2) FFT(V1) and FFT(V2) on the same figure
I tried but it does not seem LTspice support these functions. Could anyone help me with LTspice? Thanks for help!
I'm sure there's more than one way to approach this, but I had success using an arbitrary behavioral voltage source (bv) to add the voltage of two nodes. I also didn't have any trouble adding more than one node to an FFT plot. By default, they were all overlaid on top of each other, but I was able to split the up by adding plot planes and dragging the curves to individual plot planes:
You can do math equations like V(a)+V(b) even with the FFT results in the FFT-waveform view.Just enter V(a)+V(b) instead of V(a) in the FFT waveform viewer.
The FFT is a linear process. Thus FFT( V(V(a)+V(b) ) is equal to FFT(V(a)) + FFT(V(b)).
Oh yes, I like this better. The only way I could figure out how to do it was to plot one node, and then right-click on the node name to edit it to include the addition of a second node:
Thanks Helmuts and AnneM, I tried this, but I still have problem. Every time I 'View -> FFT'， I am asked to select one node that's in the schematic, and when I select one, a NEW Window pops up and for a second signal, another window pops up, they are not showing in the same plot for me to do the summations. Please see the screen shot. But thanks for the information, I may have changed some configurations for the environment. Please let me know if you know what might have I done to my FFT window. Thanks.
are you able to select more than one in each window?