is this phase plot "WRONG"?

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020170

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last week I designed opamp, and I simulated amp using AC analysis.

this is amplitude and phase plot pictures

**broken link removed**

my phase plot is some weird. but phase margin is high.

I've never seen phase plot like mine.

is there any thing wrong in my picture? Could you tell me the reason?

thanks.
 

There seems to be some extra zero near the cross over frequency. Notice that the amplitude slope changes with an upward bias to make it more nearly horizontal.
 

thanks for the reply

is it right that zero just exist in LHP ? why is this phase plot wrong?

please explain the reason in detail.

thanks.
 

it should be a LHP zero, cause LHP zero will increase ur phase of transfer fucntion.
this LHP should come from ur compensation network. usually when we use miller compensation to spit the dominant and non-dominant pole it will introduce a extra zero, but a good compensation should not like this. cause there are always noise at high frequency . u had improved the phase margin but the gain margin is poor, cause the attenuation after the crossover frequency is not -20dB/decade.
 

One further thing to do is to do the plots again with the maximum frequency a few decades higher. This would reveal any additional poles and zeros at higher frequencies.
 

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