Large format X-ray imager with mega-frame readout capability for XFEL, based on the DEPFET active pixel sensor

We propose a new detector system capable to fulfil the requirements of the future XFEL in Hamburg. The instrument will be able to record X-ray images with a maximum frame rate of 5MHz and to achieve a high dynamic range. The system is based on a pixel-silicon sensor with a new designed non-linear-DEPFET as a central amplifier structure. The detector chip is bump-bonded to a set of mixed signal readout ASICs that provide full parallel readout. The signals coming from the detector, after having been processed by an analog filter, are immediately digitized by a series of 8-ENOB ADCs and locally stored in a custom designed memory also integrated in the ASICs designed in the 130nm CMOS technology. During the time gap of 99ms of the XFEL machine, the digital data are sent off the focal plane to a DAQ electronics that acts as an interface to the back-end of the whole instrument. The pixel sensor has been designed so as to combine high energy resolution at low signal charge with high dynamic range. This has been motivated by the desire to be able to be sensitive to single low energy photons and, at the same time, to measure at other positions of the detector signals corresponding to up to 10⁴ photons of 1keV. In order to fit this dynamic range into a reasonable output signal swing, achieving at the same time single photon resolution, a strongly non linear characteristics is required. The new proposed DEPFET provides the required dynamic range compression at the sensor level, considerably facilitating the task of the electronics. At the same time the DEPFET charge handling capacitance is enormously increased with respect to standard DEPFETs. The Pixel matrix will have a format of 1024×1024 with a pixel size of 200×200 µm².