Determine the functional form of the NIRISS ADC integral nonlinearity across the full count range

Derive an accurate, count-dependent functional form for the integral nonlinearity of the NIRISS analog-to-digital converter over the entire dynamic range, enabling full correction of periodic ramp-level residuals in up-the-ramp data.

Background

The authors identify a strong periodic residual in uncalibrated ramp data, likely due to amplifier power issues, and mitigate it with an ad hoc sinusoidal correction. They note that a fully accurate functional form for the ADC integral nonlinearity over all count levels remains undetermined, which limits comprehensive correction and could bias analyses relying on group-level behavior.