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Abstract

The wide field imager (WFI) for the ATHENA mission will enable the spectroscopic investigation of solid angles up to 40’ in the x-ray regime between 0.2 keV to 15 keV. The required sensors are planed as DEPFET (DEpleted P-channel field-effect transistor) active pixel matrices. These are readout by custom-designed ASICs called VERITAS in a rolling shutter mode. After column parallel processing of the analog signals row-by-row, the resulting pulse heights are multiplexed onto a differential analog line pair. Thus a transmission undisturbed from external influences is achieved. But successive signals can be affected by the limited rise-time of the VERITAS output stage, depending on the signal height, the multiplexing time and the cable length. In order to investigate the impact on the measurements a dedicated cable harness is used during the characterization of a prototype device. The characterizations are performed using either test pulses applied to the VERITAS or with a ⁵⁵Fe calibration source illuminating the whole sensor. Different cable lengths and multiplexing times are tested to determine the influences. In order to deal with this effect a crosstalk correction algorithm is implemented for the analysis of the photon data. The determined crosstalk factors range up to 2.8% for the longest measured cablings of 2 m with the shortest multiplexing time. Using shorter cables and longer multiplexing times these factors can be reduced to below 1%. In all cases the accompanying effects in the data analysis can be corrected using the developed algorithm.