Does the calibration function(either self or system) for this A/D has to be done for each individual channel?
This thread has been locked.
If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.
As you have already mentioned, there are 2 forms of calibration within the ADC. The self-offset calibration applies an internal short within the ADC itself and removes any offset with respect to only the ADC. The self-offset calibration applies to any selected input channel if the same PGA settings and data rate are used. When the calibration is run, the code value returned is stored in offset registers so that it can be subtracted from future conversions.
The system calibration works in a similar way and is meant to subtract system offset from sensor or circuitry prior to the ADC (such as an op amp or instrumentation amp) as well as the ADC and requires the system to provide the '0' input for the calibration. In other words this is an external offset calibration to remove external to the ADC offsets. This form of calibration may require different calibration for each set of input channels to the ADC.
There is another way to remove offset of the ADC and that is by using the global chop feature. The global chop swaps the input channel assignments to cancel the offset effects of the ADC.
Given the same configuration (PGA, data rate, etc.) the conversion result should be the same. Global chop improves the noise as the measurement requires two measurements and the result is an average. Global chop also greatly reduces offset drift of the measurement.
Note that global chop will not update the offset calibration registers and also takes two measurements to complete. Depending on the digital filter used, this could greatly extend the length of the conversion period. If the measurements require faster conversion rates, then self-offset calibration has an advantage. So there are pros and cons using each method.