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Old 14th June 2004, 02:45 AM   #1
SkyChu is offline SkyChu  Taiwan
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Question distortion of SW CAD III

I'm trying to simulate circuit by LTC SWCAD III . But the 3rd (Odd)distortion of input voltage source is too high when I use FFT simluation (V1, see attached files). the transient is ".tran 0 15m 1m 0.1u".
How can I reduce the distortion ?
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Old 14th June 2004, 02:48 AM   #2
SkyChu is offline SkyChu  Taiwan
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The FFT:
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File Type: gif vas2_error_fft.gif (17.1 KB, 87 views)
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Old 14th June 2004, 04:51 PM   #3
jcx is online now jcx  United States
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have you turned off compression? expecting long sims of switching power regulator circuits LtSpice compresses the sim output data files by default - Tools>Control Panel>Compression - clik off all the boxes every time you open LtSpice

more recent versions accept a spice directive:

.options plotwinsize=0


in the fft menu i increase length to 131072 and use the Blackman window, keep averaging low or off(=1) since it is a digital low pass filter appiled to your data - i think mine defaults to 5
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Old 14th June 2004, 05:15 PM   #4
DarkOne is offline DarkOne  Slovakia
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You have feedback attached only to "negative" half of the circuit
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Old 14th June 2004, 07:17 PM   #5
SkyChu is offline SkyChu  Taiwan
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Thanks Jcx ! It can work !
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Old 14th June 2004, 07:30 PM   #6
SkyChu is offline SkyChu  Taiwan
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Quote:
Originally posted by DarkOne
You have feedback attached only to "negative" half of the circuit
Yes ! Is it "feedback" ? !


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Old 19th June 2004, 09:11 AM   #7
thanh is offline thanh  Viet Nam
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Quote:
You have feedback attached only to "negative" half of the circuit
Ok! I have a agreement with Darkone
Skychu! you have to feedback attached only to "negaitve" half of the circuit
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