LTspice FFT Phase

[George]

I admit I'm not a seasoned LTspice user, but after looking at FFT,
available in the plot window, I have concluded that it only provides
magnitude data, not phase data. At least I couldn't find phase data.
Can anyone confirm this? If this is true, is there anyway to get both
magnituide and phase in LTspice? I'm using wav data as input in
transient analysis, so ac analysis won't be helpful. Matlab allows input
of stereo wav data and can calculate mag and phase with FFT. Just
wondering if I could get LTspice to do the same <smile>.

Thanks,

George

 

[ldg]

On Fri, 21 May 2004 08:42:32 -0500, George <steber@execpc.com> wrote:

I admit I'm not a seasoned LTspice user, but after looking at FFT,
available in the plot window, I have concluded that it only provides
magnitude data, not phase data. At least I couldn't find phase data.
Can anyone confirm this? If this is true, is there anyway to get both
magnituide and phase in LTspice? I'm using wav data as input in
transient analysis, so ac analysis won't be helpful. Matlab allows input
of stereo wav data and can calculate mag and phase with FFT. Just
wondering if I could get LTspice to do the same <smile>.

Thanks,

George

Phase data can be seen in the Ltspice fft when you do a measurement.
Both magnitude and phase are shown in the little box. So it's there.

Perhaps others can tell you if phase can actually be plotted with the
software.

Regards,
Larry

 

[Helmut Sennewald]

"George" <steber@execpc.com> schrieb im Newsbeitrag
news:40AE0748.49FEB520@execpc.com...

I admit I'm not a seasoned LTspice user, but after looking at FFT,
available in the plot window, I have concluded that it only provides
magnitude data, not phase data. At least I couldn't find phase data.
Can anyone confirm this? If this is true, is there anyway to get both
magnituide and phase in LTspice? I'm using wav data as input in
transient analysis, so ac analysis won't be helpful. Matlab allows input
of stereo wav data and can calculate mag and phase with FFT. Just
wondering if I could get LTspice to do the same <smile>.

Hello George,
indeed I was surprised too, that I couldn't see the phase in my FFT-plot,
but then I found the way to make it visible.

I assume your FFT-window is the active window.
Move the cursor onto the right side of the graph where you probably
don't see a scale. Normally this is the phase axis in a .AC simulation.
Now your cursor will look like a ruler.
Then press the left mouse button. You will get the box to show the phase.
Just press OK. That's it.

Best Regards,
Helmut

 

[George]

Thanks for the help, here in this group and in private e-mails. Yes the
phase info is there and can be plotted too. It appears to be wrapped but I
think suitable waveform manipulation can unwrap it. Click on right side of
FFT plot to access it as others have said.

I'm wondering now if the FFT data can be saved and manipulated. For example
it would be nice to take ratio FFT(output) / FFT(input) to find transfer
function from stereo wav data. But that may be too much to ask <grin>.

George

ldg wrote:

On Fri, 21 May 2004 08:42:32 -0500, George <steber@execpc.com> wrote:

I admit I'm not a seasoned LTspice user, but after looking at FFT,
available in the plot window, I have concluded that it only provides
magnitude data, not phase data. At least I couldn't find phase data.
Can anyone confirm this? If this is true, is there anyway to get both
magnituide and phase in LTspice? I'm using wav data as input in
transient analysis, so ac analysis won't be helpful. Matlab allows input
of stereo wav data and can calculate mag and phase with FFT. Just
wondering if I could get LTspice to do the same <smile>.

Thanks,

George

Phase data can be seen in the Ltspice fft when you do a measurement.
Both magnitude and phase are shown in the little box. So it's there.

Perhaps others can tell you if phase can actually be plotted with the
software.

Regards,
Larry

 

[analog]

George wrote:

Thanks for the help, here in this group and in private e-mails.
Yes the phase info is there and can be plotted too. It appears to
be wrapped but I think suitable waveform manipulation can unwrap it.
Click on right side of FFT plot to access it as others have said.

I'm wondering now if the FFT data can be saved and manipulated.
For example it would be nice to take ratio FFT(output) / FFT(input)
to find transfer function from stereo wav data. But that may be
too much to ask <grin>.

When the FFT window is open and active, use the Export option from
the File drop down menu to save the entire data set in ascii tabular
format. Then use Excel or some other suitable program to calculate
and plot the ratio.

If both input and output data sets are available in LTspice, don't
bother with the above and just use LTspice's built in waveform math
to do the calculations all from within LTspice. -- analog

 

[George]

Thanks, I tried it and it works well.

analog wrote:

George wrote:

Thanks for the help, here in this group and in private e-mails.
Yes the phase info is there and can be plotted too. It appears to
be wrapped but I think suitable waveform manipulation can unwrap it.
Click on right side of FFT plot to access it as others have said.

I'm wondering now if the FFT data can be saved and manipulated.
For example it would be nice to take ratio FFT(output) / FFT(input)
to find transfer function from stereo wav data. But that may be
too much to ask <grin>.

When the FFT window is open and active, use the Export option from
the File drop down menu to save the entire data set in ascii tabular
format. Then use Excel or some other suitable program to calculate
and plot the ratio.

If both input and output data sets are available in LTspice, don't
bother with the above and just use LTspice's built in waveform math
to do the calculations all from within LTspice. -- analog