vivkr
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Hi Yawei,
I am actually simulating the settling behavior. The gain-boosted opamps are expected to have a gain > 60 dB.
When I look at the settling behavior of these opamps, I see that the settling error (as defined by Bult to be the ratio of the differential inputs @ virtual ground nodes to the differential output voltage of the opamp) keeps on falling with a constant slope until it flattens out at a level < - 60 dB.
So, the gain-boosting opamps have done their job, and I expect that the overall settling error will be < -120 dB because my main opamp has > 60 dB. But, I see that the overall settling error starts falling off correctly, but suddenly, it changes slope and then on, it settles very slowly. I do not understand this.
The gain-boost opamps are finished settling, and I don't expect a doublet there. The output is not beyond the allowed swing level of my opamp.
In fact, I see that the settling is fine for the largest output swing levels, where I get < -120 dB accuracy, but for some inputs less than this peak swing value, I am seeing the slow settling. For a folded cascodes, this appears to be a strange behavior.
Regards Vivek
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