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What is the influence of complex poles on OP-amp stability?

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threekingtiger

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What's the influence of complex poles to OP-amp stability?
In "CMOS Analog Circuit Design 2nd Edition" by Phillip Allen, he pointed out that the complex poles may result in poor phase margin in section 7.1, more specifically Figure 7.1-5(a).
Can anyone tell me why the poles p2 and p3 in Figure 7.1-5(a) is bad for PM or recommend some paper which has sheded light on this problem?
 

Re: Complex poles

simply speaking, i think complex poles will cause peaking in magnitude plot in the frequency domain and oscillation in the time domain, which in turn reflects instability issue--less phase margin.
 

Re: Complex poles

In analog circuit designs we tend to keep as little poles as possible. Poles, in frequency response, pull the gain curve down to unity gain, thereby changing the frequency response or BW in undesirable format. Change in BW directly changes the phase margin which affects the stability of op amp. A phase margin of 30 to 70 degrees is fine.
 

Re: Complex poles

I don't think 30 deg is sufficient for stability requirement. 60 deg should be prefered considering the process variation and other factors' influences. Right?

---------- Post added at 02:23 PM ---------- Previous post was at 02:22 PM ----------

Thanks. It's helpful.
erikl said:
See e.g. here.
Click to expand...
 


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