Exporting LTspice waveforms to txt or csv

Question

I have used the file _>export facility to generate txt /csv file for subsequent analysis in Matlab. The problem is that the exported waveform time steps are not uniform and the waveform is quantized. Is there a way to avoid this happening to get uniform time steps? As it is I can't use the exported txt waveform.

Answer 1

LTspice, by default, uses a variable step size which has large values when nothing critical happens (e.g. steady-state) and it tightens them for transients and such. For a specific time-step you can use the builtin maximum simulation step, for example:

.TRAN 0 {final_time} {start_saving_data_optional} {time_step}

Adding an options card such as: .OPT plotwinsize=0 will force the compression to be turned off, as well. There are more options to play around, see the help file or, if you have more intimate questions, ask in the Yahoo's LTspice group (I hope this doesn't count as advertising)

Answer 2

use the .wave ltspice command to produce a .wav file.

wav files can be read using matlab's Audioread command

http://ltwiki.org/LTspiceHelp/LTspiceHelp/_WAVE_Write_selected_nodes_to_a_wav_file_.htm

.WAVE -- Write Selected Nodes to a .Wav File.

LTspice can write .wav audio files. These files can then be listened to or be used as the input of another simulation.

Syntax: .wave <filename.wav> <Nbits> <SampleRate> V(out) [V(out2) ...]

example: .wave C:\output.wav 16 44.1K V(left) V(right)

<filename.wav> is either a complete absolute path for the .wav file you wish to create or a relative path computed from the directory containing the simulation schematic or netlist. Double quotes may be used to specify a path containing spaces. <Nbits> is the number of sampling bits. The valid range is from 1 to 32 bits. <SampleRate> is the number of samples to write per simulated second. The valid range is 1 to 4294967295 samples be second. The remainder of the syntax lists the nodes that you wish to save. Each node will be an independent channel in the .wav file. The number of channels may be as few as one or as many as 65535. It is possible to write a device current, e.g., Ib(Q1) as well as node voltage. The .wav analog to digital converter has a full scale range of -1 to +1 Volt or Amp.

Note that it is possible to write .wav files that cannot be played on your PC sound system because of the number of channels, sample rate or number of bits due to limitations of your PC's codec. But these .wav files may still be used in LTspice as input for another simulation. See the sections LTspice=>Circuit Elements=>V. Voltage Source and I. Current source for information on playing a .wav file into an LTspice simulation. If you want to play the .wav file on your PC sound card, keep in mind that the more popularly supported .wav file formats have 1 or 2 channels; 8 or 16 bits/channel; and a sample rate of 11025, 22050, or 44100 Hz.

insert this into your scematic using the edit->spice directive menu option

Answer 3

.param T=100n
.meas tran result find V(Out) at = T
.step param T 0 1500n 12.5n

This will sample the signal V(Out) with 12.5ns. Open Error Log to view the result. This will look like this:

...
Measurement: result
step    v(out)  at
1  0.000333577  0
2    -0.191173  1.25e-008
3    -0.180665  2.5e-008
4    -0.169657  3.75e-008
...

Keep in mind, that the parametric sweep (.param T=100n) leads to repeation of the transient simulations. Depending on the circuit this can take much time. A workaround is to specify the sampled timesstamps by separate measure-commands. This commands can be generated easily by e.g. sublimetext with text pastry plugin (automatic numer increment at multiple cursors).

.meas tran result0 find V(Out) at = 0u
.meas tran result1 find V(Out) at = 1u
...
.meas tran result10 find V(Out) at = 10u

Answer 4

The best way to get uniformly sampled data points out of LTSPice is to take the FFT of the data, then take the FFT again of the FFT´d data. This returns the time domain data quantized in uniform steps. This leverages the fact that LTSpice interpolates the data when performing the FFT.