Design and Performance of the GEMROC ASIC for 2-D Readout of Gas Electron Multiplier Detectors

In this paper we report on the development of an Application Specific Integrated Circuit (ASIC) being a key component for two-dimensional readout of Gas Electron Multiplier (GEM) detectors in the Proton Range Radiography (PRR) system. The GEMROC ASIC consists of 32 independent channels, allowing for simultaneous recording of the amplitudes and time of incoming signals. Thanks to the implemented token-based read out of derandomizing buffers, the ASIC also provides data sparsification and full zero suppression. Reconstruction of the hit positions is performed in an external FPGA based data acquisition system by matching the time stamps of signals recorded in X- and Y-strips. The amplitude information is used for finding centers of gravity for clusters of signals on neighboring strips belonging to the same detection events. Such a readout architecture provides capability of working with high count rates up to 10(6)/s. The circuit has been designed in 0.35 mu m CMOS process. The basic functionality and parameters have been evaluated using the testability functions implemented in the ASIC design. A fully equipped GEM detector module has been built and tested with X-rays and electrons from radioactive sources.