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Digital offset calibration method for fully differential amplifier

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Dear friends,

I am learning this technique for digitally treating the offset voltage, in the figure below the author used to comparators to detect the offset voltage

Circuit source : https://ieeexplore.ieee.org/document/9040131

Capture.PNG


The other authors used single comparator to perform the operation as shown below

Circuit source :

2.PNG


I observe two things from the second scheme,

1. It is easier since it employs one comparator,
2. it doesn't need to compare to Vref as in the first one

Now I will present the the third circuit, author used fully-differential comparator and he needed to compare to a reference voltage
Circuit source : https://www.computer.org/csdl/proceedings-article/isvlsi/2017/6762a655/12OmNwDj18z

3.PNG


Could you please tell me what are the differences in between all cases ? and which one should be better

Thank you very much
 

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I think 1 and 3 are pretty much the same. It is just a matter of how you represent the comparator symbol. And they both cancel offset that's around the Vref, although for example the 1st one would not care if both aoutputs are above Vref or below. So, comes the 2nd which only looks at the difference and can be done with only one comparator.
 
Thank you Suta for your reply

As you said, offset voltage is asymmetrical deviation of the outputs around the VCM. For example, consider positive offset voltage when Vo1 = 2.5 V and the other output = 0.8 V where VCM = 1.65 V which represent the Vos+
an opposite offset is vo1 = 0.8 V and Vo2 = 2.5 that represent Vos-

Practically both of them can not be together above or below the VCM

This address me other question, we can compare using one comparator from Vo1 to VCM or from Vo2 to Vcm, no need to compare Vo1 and Vo2 in this case
 

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