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Old 13th December 2005, 11:54 AM   #1
hacknet is offline hacknet  Singapore
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Join Date: Nov 2002
Location: sg
Default simulation software

hey guys!

is there a downloadable simulation software i can use to get distortion figures. i've recently been working on SwCAD and I don't seem to be able to churn out distortion figures.

Thanks a million guys!
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Old 13th December 2005, 03:03 PM   #2
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Join Date: May 2005
Location: Stittsville, Ontario, Canada
I use Switcher CAD, aka LTSpice, for distortion all the time. An example of the standard SPICE op code to use is

.FOUR 1000 5 V(Out)

where 1000 is the fundamental frequency, 5 is the number of harmonics (including the fundamental) to report, and V(Out) is the name of the node. Change these to suit your own requirements, place the statement anywhere on your schematic, and after you execute a transient run view the results by clicking on View | SPICE Error Log.

Make sure your signal source frequency is the same as the fundamental specified, and also make sure your time step is small enough to give accurate results.
Robert McLean
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Old 13th December 2005, 07:29 PM   #3
andrei is offline andrei  Canada
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Well, you could try mine ...
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Old 14th December 2005, 01:33 PM   #4
hacknet is offline hacknet  Singapore
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Join Date: Nov 2002
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andrei, i'll try out your proggie.

thanks for the help guys!!!
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Old 14th December 2005, 05:20 PM   #5
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For low level distortion analysis you should use the following settings:

In transient analysis set the time for 11 cycles, start saving data after 1 cycle, maximum timestep of saved data time/FFT no of data point samples in time. For instance for 1kHz, with 8192 FFT samples, maximum timestep is 10ms/8192 or 1.2us.

Tools/Control Panel/Compression, clear check boxes. The waveform compression introduces spurious distortion products, clearing the check boxes removes compression.

If this isn't good enough try Tools/Control Panel/Spice, reduce Reltol, default is 0.001, try 0.0005 or 0.0001, but convergence may be more difficult.

When using FFT Blackman window seems to give the lowest FFT noise floor.

Using these settings should give FFT dynamic range of at least 100dB or so with good frequency resolution, of course your actual circuit probably won't perform the same.
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Old 15th December 2005, 02:06 PM   #6
hacknet is offline hacknet  Singapore
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Join Date: Nov 2002
Location: sg
whoa...! i just tried out the FFT functions and i realise that the voltage source is distortion ridden.

i'll try it out and report back!

thanks a million!!!
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Old 15th December 2005, 02:11 PM   #7
hacknet is offline hacknet  Singapore
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Join Date: Nov 2002
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thanks man! it works like a charm now!
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