A Simple Technique for Signal Compression in High Dynamic Range, High Speed X-ray Pixel Detectors

New X-ray pixel detectors are required to cope with the demanding requirements from XFEL sources, in terms of high speed and high dynamic range. Such detectors have to provide low electronics noise to allow single photon detection at low signal intensities. At high photons intensity, a signal compression technique may be introduced to allow the detection system to cope with the required dynamic range. In this work, we propose a very simple front-end (FE) solution based on an input PMOS transistor placed on the CMOS readout chip connected to the pixel detector. The FE is optimized for low-noise readout of X-ray photons at low intensities. A gain compression when the signal intensity increases is obtained by operating the PMOSFET in the triode regime thanks to a resistor placed between the transistor and the current-readout filter. The larger is the transistor signal, the larger is the voltage drop on the resistor which pushes the transistor to operate more in triode regime at lower gain, producing a compression in the overall FE response. The FE working principle and the first experimental results obtained with a first prototype realized in the 130 nm IBM technology are presented.