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Each pixel contains a pre-amplifier which integrates the current generated by X-ray absorption. The gain of the preamplifier is dynamically switched; when the integrated signal rises towards the preamplifier’s upper limit, the pixel switches to a lower gain setting.
This allows the detector to cope with the large dynamic range in the images produced by XFEL, while maintaining single-photon sensitivity in pixels with low illumination. Each pixel has an analogue pipeline which allows the detector store up to 500 images during the XFEL bunch train.
AGIPD (Adaptive Gain Integrating Pixel Detector)
Adaptive Gain Integrating Pixel Detector (AGIPD)
for the European X-ray Free Electron Laser in Hamburg
The AGIPD project is led by DESY and is a collaboration between DESY – PSI – University of Bonn and the University of Hamburg. It is a project to build a pixellated solid state detector for the European XFEL. The goal is a 1000 by 1000 pixel detector, with 200 micron pixel size and a central hole for the primary beam. The detector will be built with monolithic modules, as indicated in the figure below, which allows for even larger detectors in the future.
The analogue signals stored in the pipeline, are then read out and digitized during the intervals between bunch trains. This pixel circuitry is shown in the following picture.
