Do you mean 2channel ADC ?
Generally "Gain Error" and "Offset Error" are characteristics of 2channel ADC, e.g. for I/Q ADC.
If so, why don't you use high speed word buffer for capturing ADC output code, then analyze by computer ?

Is there any merit in using Sinusoidal Histogram method for Gain and Offset ?

Sinusoidal Histogram method is suitable for evaluation of missing code and dynamic DNL.

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