Optimization and performance of H2RG detectors and SIDECAR ASICs for SWIMS

摘要

SWIMS (Simultaneous-color Wide-field Infrared Multi-object Spectrograph) is one of the first-generation instruments for the University of Tokyo Atacama Observatory 6.5-m telescope which is now under construction in northern Chile. This instrument incorporates 4 (and maximum 8 in future) HgCdTe HAWAII-2RG detectors, from which images are acquired by SIDECAR ASICs. Characterization and validation of performances of these detectors are carried out using a test dewar at 80K using liquid nitrogen. Bias voltages such as reset level and substrate level and reference voltages are optimized to minimize readout noise with keeping output levels within proper range for ADC inputs. ADU-electron conversion gain g_c is measured by photon-transfer method, incorporating IPC (Inter-Pixel Capacitance) correction. IPC coefficient is measured to be about 1.4%, which result in overestimation of g_c by about 13%. After this correction, g_c is measured to be about 2.4 e~-/ADU with normal preamplifier gain setting in the ASICs. Correlated double sampling (CDS) readout noise is about 16 e~-rms, and is reduced to about 4 e~- rms by Multi Fowler sampling. The noise is different by 30% at most between channels of the ASIC. We also separate noise sources into those come from detector pixels, from a flat cable between the detector and the ASIC, and from preamps and from ADCs, and found that the detector pixels are the major sources of readout noise. Fitting of linearity curve is also obtained. The next step is to study the effects of driving multiple detectors to the performances and to install the detectors into SWIMS.