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Changed the title because it's now apparent that LTSPICE itself is really part of the question.

edited Apr 30, 2018 at 14:38

watkipet

What's the junk at the end of my FFT in LTSPICE?

Why do FFTs have junk on the high frequency end? Suppose I go to simulate this circuit in LTSPICE:

schematic

^{simulate this circuit – Schematic created using CircuitLab}

Where the LTSPICE sine and simulation parameters are:

SINE(0 1 1K 0 0 0 1000)
.tran 1 startup

Then I ask LTSPICE to give me an FFT with no window and 1,000,000 points:

What's all the junk at the end for? I would expect only one spike at 1KHz, not an additional one at 3KHz, etc. Does this happen to all FFTs? What controls the spikes that you get after your fundamental?

ltspice fft

asked Apr 26, 2018 at 23:57

watkipet