H1RG readout procedures for MAJIS, the VIS/NIR imaging spectrometer of JUICE: impact on the performances

MAJIS is an imaging spectrometer operating in the visible and IR range which is part of the payload of the JUICE mission of ESA, dedicated to the study of the icy moons of Jupiter, Jupiter and the Jupiter environment, to be launched in April 2023. MAJIS implements two channels, one for the visible-near IR range (0.5 – 2.35 μm) and one for the IR range (2.25 – 5.52 μm). H1RG detectors from Teledyne where selected for these two channels. The specific constraints of MAJIS (very wide dynamic range, windowing, on-board de-spiking) required very significant adjustments to readout microcodes provided by Teledyne. The de-spiking approach implemented by MAJIS relies on on-board processing of series of consecutive sub-integrations5 . For reaching optimum performance, possible biases between successive CDS readouts of the same signal needed to be lower than the total noise. The first of the two detector readouts required for CDS had to be implemented very shortly after reset so as to benefit from the full well depth for dynamic range. This required coping with the reset anomaly which is specific to the HxRG family of detectors. The MAJIS team selected an approach based on drop frames and dark subtraction which minimized microcode adjustments so as to limit development and schedule risks. Detector characterization then instrument calibration showed that this approach was quite successful in terms of performances with no impact on the duty cycle for observations with short integration times.