Explain me the Bode plot, why it goes from 180 to -180 degree suddenly

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joehwang

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Hi,

From the attachment, why the red line (the phase) go to 180 degree form -180 degree suddenly? Is it because the zaro or some other reasons?

Thanks!
 

Re: Bode plot

this depends on the software you use. in your case the phase is restricted within +/- 180 degree, so the phase jump to 180 degree from -180 degree.
 

Re: Bode plot

I believe that a zero would increase the phase gradually. Can I see your circuit?
 

Re: Bode plot

I am using HSPICE to simulate the two stage op-amp as shown in the attachment.
So, it is caused from the HSPICE which limited the phase in +- 180 degree?

Thanks!
 

Re: Bode plot

As phase measurement is generally ambiguous with a period of 360 degrees, no information is missing here. You see the phase wrap around with most simulators, to my opinion.
 

Re: Bode plot

Yes, most simulation software displays phase in the range -180 to +180 degrees. That is also a normal way to display phase data in datasheets, documentation, etc.
 

Re: Bode plot

180° = -180°, so there is no "sudden" change in phase. as FvM noticed, your phase is simply wrapped up between -180° and 180°. For example, 180°+20° is equivalent to -160°.
 

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