I am working with the 'View -> FFT' function of LTspice, it says ' Fourier components are normalized to correspond to the time domain RMS amplitude', which I don't quite understand the math behind this statement and the magnitude of the FFT result is 'dB' by default.
I am doing some conducted EMI simulation, which should have unit of 'dBuV' ( dB micro volt), so I am wandering how can I convert the default 'dB' into 'dBuV'. (I am doing this with MATLAB, I exported the FFT result in 'Real, Imaginary' form, I need equation to do the conversion).
Could anyone help me on this problem? Thank you!
You can plot formulas.
Just plot V(abc)/1u instead of V(abc). Now all numbers are multiplied by 1e6.
You can also right click on the y-axis of the FFT plot and change to Linear (Volts) which should be the RMS value of the FFT components. For example, a 1Vp sine wave would show as 0.707V.
This is good. Actually, I tried this, but it still doesn't solve my problem. Because I cannot export this data with the linear range as you showed. I tried in LTspice to show with different range options, but the exported data (to .txt) are always the one with default 'dB' unit.
Since I need to do some comparison in MATLAB, I wonder if there is any way to get the data with linear range so I can convert it to 'dBuV' myself.
Thanks for your reply. Is this what you mean ? (yellow curve: V(v1)/1e-6?)
Are you saying now the yellow curve means 'dBuV' ?
I tried some points on the curves, it looks like
VdB = 20*log(Vlinear)
I think I can do the conversion with this information.