ICnow
Newbie level 4
Hello!
While designing a SAR ADC i found out that Rail-to-Rail OpAmp that i used, have non-linear offset in relation to common mode. That has caused in high INL(though DNL is good).
I think that this happened because input make up from 2 differential pairs nfet and pfet. When common mode near gnd or vdd is working only one differential pair and offset only from this pair affecting ADC. When common mode in the middle of range, offsets from both pair adding to each other and overall offset through all common-mode range became non-linear. Could this be the cause of the bad INL?
If this the case, did somebody know what can i do about this? Except using dynamic offset compensation like auto-zero or chopper.
While designing a SAR ADC i found out that Rail-to-Rail OpAmp that i used, have non-linear offset in relation to common mode. That has caused in high INL(though DNL is good).
I think that this happened because input make up from 2 differential pairs nfet and pfet. When common mode near gnd or vdd is working only one differential pair and offset only from this pair affecting ADC. When common mode in the middle of range, offsets from both pair adding to each other and overall offset through all common-mode range became non-linear. Could this be the cause of the bad INL?
If this the case, did somebody know what can i do about this? Except using dynamic offset compensation like auto-zero or chopper.