--- In LTspice@..., "vincenzovaroli" <varoli@...> wrote:
I need to export group delay data from several circuit simulation
for comparison purposes.
From plot window i can only export trace data in polar or cartesian
format, even if I plot only group delay.
I exported the trace data in cartesian format and then I got the
group delay data with excel, but this procedure is not simple.
Is there a better solution or can Mike add a suitable export option?
Regards
Varoli
Hello Varoli,
There is no way to directly export group delay in LTspice.
You could plot and export the phase ph(V(out). This will require a
little bit less work in the external post processing to get the
group delay.
You still hav to calculate the group delay fom the phase.
Tg = dph/df
The best approximation is achieved at the freqencies half between
the exported data poins with the following formula.
Tg = (phi(fn+1)-ph(fn))/(fn+1 - fn)
I asked yesterday Mike about his opinion. He doesn't like to add
export of group delay for several reasons. See his answer below.
Maybe I should add this function to the utility program ltsputil.exe.
Best regards,
Helmut
Mike's answer
-------------
Helmut,
The group delay data points do not lie on the
same discrete frequency data points as the magnitude
and phase. That is, where the data format can be
freq1 Mag1 Phase1
freq2 Mag2 Phase2
freq3 Mag3 Phase3
.
.
.
or
freq1 Re1 Im1
freq2 Re2 Im2
freq3 Re3 Im3
.
.
.
The group delay data would look like this:
freq1 Mag1
.5*(freq1+freq2) Delay1
freq2 Mag2 Phase2 Mag2
.5*(freq2+freq3) Delay2
freq3 Mag3 Phase3 Mag3
.5*(freq3+freq4) Delay3
.
.
.
You can verify this by turning on
Plot Settings=>Mark Data Points and seeing
that the group delay is plotted between the
magnitude/phase/real/imag data points. The
group delay is computed by finite differences
of the simulation data.
So I don't anticipate adding the ability to export
group delay for the following reasons:
i) There has not been a single request for this
feature to the address on the help=>About dialog
box.
ii) The whole idea of this export utility was
to convert LTspice's binary data file to
clear text so that people don't feel
restricted to some proprietary data format.
Group delay is more of a plotting mode than
data. It would be a bit like wanted different
data exported when plotting in Bode vs Nyquist
modes.
iii) It would complicate the file format without
making more simulation data available.
iv) Anyone who manipulates the data themselves
should have no trouble computing the group
delay themselves, too.
Feel free to post this.
--Mike
