What causes this 360 phase shift at ~20khz? - Page 3 - diyAudio
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Old 17th September 2012, 10:41 PM   #21
AndrewT is offline AndrewT  Scotland
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if you have a single pole, the phase shift is 90degrees. That difference only occurs right out at the infinitely far away frequencies from the midband.

If you cascade two single pole filters the total phase shift is 180degrees. Again the full 180 degrees is way out at infinite frequencies.

To save me typing and you reading, I'm jumping straight to 5 cascaded single pole filters.
The total phase shift is 450degrees.
If the phase starts at 0degrees and increases to 180 degrees part way along the passband you will see the plot (without any wrapping) showing 180.
Continue farther out and the phase goes on past 270 and on to 360.
The vertical scale will have to be compressed to get all the degrees to fit on the page.

Now go out to infinite frequency and you will see the phase at 450.

To get all that shown at a readable vertical scale and fit a conventional page shape, you can ask the plotter (either a person or the software) to wrap the vertical scale at prescribed intervals. 0 to 360 is quite common. -180 to +180 is possibly slightly less common. But the wrapping to fit the page can be any value. 0 to 100 could be used if you had a need.

The plot in post1 has a wrap set to +180 to -180 (top to bottom) simply to allow a short vertical page height AND be readable.
You could unwrap it, but the vertical axis would be twice as high. You would need very tall paper to plot that.
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Old 18th September 2012, 01:59 AM   #22
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I did some research and you guys were right, it was wraping nice call guys.

there is a way to turn it off in ngspice, the result is attached.

Thanks guys!
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Old 18th September 2012, 12:29 PM   #23
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Quote:
Originally Posted by Dave Zan View Post
In some software you can show the phase with(out) this display artefact with a check box called "Wrap phase" or some similar option.
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Originally Posted by Fusion916 View Post
I did some research and you guys were right, it was wraping nice call guys.
Nice to read you sorted it out.

Quote:
there is a way to turn it off in ngspice, the result is attached.
Was it a check box called "Wrap phase"?

Best wishes
David

Last edited by Dave Zan; 18th September 2012 at 12:33 PM.
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Old 18th September 2012, 09:37 PM   #24
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Originally Posted by Enzo View Post
When your clock on the wall moves from 11:59 to 12:01, there is an instantaneous 24-hour change. The time line instantly switches from the positive end of one day to the exact opposite end of the next day. This is the same idea.
Most logical and humorous explanation. Absolutely right
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Old 19th September 2012, 08:17 PM   #25
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Default And solution was so simple ...

In ngspice just use cph() function instead ph() (see current documentation, page 265)
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Last edited by wojtek5001; 19th September 2012 at 08:20 PM.
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Old 19th September 2012, 08:47 PM   #26
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Originally Posted by wojtek5001 View Post
In ngspice just use cph() function instead ph() (see current documentation, page 265)
Thats exactly what I did
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