What causes this 360 phase shift at ~20khz? - diyAudio
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Old 16th September 2012, 07:43 PM   #1
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Default What causes this 360 phase shift at ~20khz?

In this simple common emitter stage there's an intentional pole at 10hz at the input and an intentional 180 phase shift due to the CE stage inverting gain stage but I want to understand what model parameter causes the 360 phase shift. Also, is this something I need to be concerned about? Rails are +/- 15V.

Here is the model:

.model mpsa18 npn (
+ Is=33.58f Xti=3 Eg=1.11 Vaf=100 Bf=2.365K Ne=1.579
+ Ise=166.7f Ikf=.1172 Xtb=1.5 Br=5.774 Nc=2 Isc=0 Ikr=0 Rc=1
+ Cjc=4.948p Mjc=.4109 Vjc=.75 Fc=.5 Cje=7.547p Mje=.3765 Vje=.75
+ Tr=800.3p Tf=310.1p Itf=.6 Vtf=6 Xtf=35 Rb=10)
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File Type: png ce.png (19.0 KB, 176 views)
File Type: png phase.png (43.3 KB, 176 views)
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Old 17th September 2012, 12:06 AM   #2
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Any guidance?
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Old 17th September 2012, 01:15 AM   #3
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If I understand your question correctly you mean the vertical line at ~20kHz?
This is just an artefact of the way the phase is displayed. It is not a problem.

Best wishes
David
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Old 17th September 2012, 01:30 AM   #4
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Quote:
Originally Posted by Dave Zan View Post
If I understand your question correctly you mean the vertical line at ~20kHz?
This is just an artefact of the way the phase is displayed. It is not a problem.

Best wishes
David
How is this an artifact on the way the phase is displayed? It goes from -180 to +180 instantaneously, so for some reason there is a +360 phase shift at this frequency.
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Old 17th September 2012, 01:57 AM   #5
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-180 is +180
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Old 17th September 2012, 02:03 AM   #6
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Quote:
Originally Posted by volume knob View Post
-180 is +180
The phasing is the same but a +360 degree phase shift is not "the same", its one full cycle of delay.

I would just like to know what is going on, calculation wise, in which there is a instantaneous 360 phase shift. I agree its not real, I just want to know where it comes from.
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Old 17th September 2012, 02:17 AM   #7
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Its a quirk in the way that degrees are displayed on graph, the + numbers are added to 0 degrees and the - numbers are subtracted from +360 degrees

If you can change you graph scale from -200 to +200, to a 0 to 360 scale it would make more sense
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Old 17th September 2012, 05:12 AM   #8
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In some software you can show the phase with(out) this display artefact with a check box called "Wrap phase" or some similar option.

Best wishes
David
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Old 17th September 2012, 05:21 AM   #9
JZatopa is offline JZatopa  United States
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Are you asking why isn't the phase flat all the way past 20k?
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Old 17th September 2012, 04:00 PM   #10
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Quote:
Originally Posted by DJNUBZ View Post
Are you asking why isn't the phase flat all the way past 20k?
Yes.

And this is not really a "graphing" issue, as it's displaying correctly, the simulation data points just change from negative to positive. This is what I would like an explanation on:

1.659587e+04 6.032661e-04 -3.14125e+00
1.698244e+04 5.895341e-04 -3.14127e+00
1.737801e+04 5.761147e-04 -3.14129e+00
1.778279e+04 5.630007e-04 -3.14131e+00
1.819701e+04 5.501853e-04 -3.14133e+00
1.862087e+04 5.376615e-04 -3.14135e+00
1.905461e+04 5.254229e-04 -3.14137e+00
1.949845e+04 5.134628e-04 -3.14138e+00
1.995262e+04 5.017750e-04 -3.14140e+00
2.041738e+04 4.903533e-04 -3.14142e+00
2.089296e+04 4.791915e-04 -3.14144e+00
2.137962e+04 4.682838e-04 -3.14146e+00
2.187762e+04 4.576244e-04 -3.14148e+00
2.238721e+04 4.472076e-04 -3.14150e+00
2.290868e+04 4.370279e-04 -3.14151e+00
2.344229e+04 4.270800e-04 -3.14153e+00
2.398833e+04 4.173585e-04 -3.14155e+00
2.454709e+04 4.078583e-04 -3.14157e+00
2.511886e+04 3.985743e-04 -3.14159e+00
2.570396e+04 3.895017e-04 3.141580e+00 <---change from - to +
2.630268e+04 3.806356e-04 3.141562e+00
2.691535e+04 3.719713e-04 3.141543e+00
2.754229e+04 3.635042e-04 3.141525e+00
2.818383e+04 3.552299e-04 3.141507e+00
2.884032e+04 3.471439e-04 3.141488e+00
2.951209e+04 3.392420e-04 3.141470e+00
3.019952e+04 3.315199e-04 3.141451e+00
3.090295e+04 3.239737e-04 3.141433e+00
3.162278e+04 3.165991e-04 3.141414e+00
3.235937e+04 3.093925e-04 3.141395e+00
3.311311e+04 3.023499e-04 3.141377e+00
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