Study of Systematic and Statistical Uncertainty in Offset, Noise, and Gain Determination of the DSSC Detector for the European XFEL

The DSSC (DEPFET Sensor with Signal Compression) is a new instrument with non-linear response and parallel signal processing (filtering, linear amplification, and 8-bit digitization) for all pixels. The DSSC will serve as ultra-fast megapixel imaging detector at the European XFEL (X-ray Free Electron Laser) in Schenefeld, Germany, which began science operation in September this year. The DSSC detector needs to be calibrated for each of a set of twelve predefined operation modes before being employed in scientific experiments. A crucial step in the calibration of the response of each individual detector pixel is the calibration of offset and gain. We present a study of both systematic and statistical uncertainty in the determination of offset, noise, and gain. The best possible calibration of offset and gain requires that these two quantities can be determined with an uncertainty that is less than half the finite resolution of the respective read-out ASIC calibration settings. The study is based on simulated calibration data, which were then analyzed using our calibration tools. Systematic and statistical uncertainty in offset, noise, and gain determination was quantified by comparing analysis results with the actual values employed in the simulations. A review of all results identified the most suitable calibration approaches. Their ability for providing the best possible offset and gain calibration is discussed.