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The Gas Electron Multiplier (GEM) detector technology allows building large area position sensitive detectors though 2-D readout of such detectors at high rate is a challenging task. In the paper we report on the design and performance of the prototype GEMROC2 ASIC designed for high count rate applications of GEM detectors. The primary application of the ASIC is readout of 10$\times$10cm$^2$ GEM detector. However, it could also be used for read out of other types of Micro Pattern Gas Detectors (MPGDs).
The GEMROC2 design follows the concept of the previously designed GEMROC ASIC [1]. It consists of 64 independent channels, allowing for simultaneous recording of the amplitudes (energy channel) and time stamps (timing channel) 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 data acquisition system by matching the time stamps of signals recorded in X- and Y-strips. The amplitude information is used for centres of gravity finding in clusters of signals on neighbouring strips belonging to the same detection events. The ASIC could work in one of eight gain modes and one of two speed modes. In a slower mode the maximum count rate is 10$^5$/s while in a faster mode it is three times higher.
Any front-end electronics for readout of MPGDs requires an input protection circuit against possible random discharges inside active detector volume. Input protection circuits built of discrete Surface Mount Device (SMD) components are used as a standard. In case of a high density readout with a pitch of the readout strips below 1mm the very first problem with such a solution is caused by the assembly area needed for SMD components. The GEMROC2 provides integrated, silicon proven [2], input protection circuits so it could be used without any additional input components.
The ASIC 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. The ASIC has been also tested in a fully equipped GEM detector module with X-rays source.
This work was supported by the National Science Centre (NCN) Poland, grant number DEC2013/10/M/ST7/00568.
[1] T. Fiutowski et al., Design and performance of the GEMROC ASIC for 2-D readout of Gas Electron Multiplier detectors, IEEE Nucl. Sci. Symp. Conf. Rec. (2011) 1540.
[2] T. Fiutowski et al., Integrated input protection against discharges for Micro Pattern Gas Detectors readout ASICs. 2017 JINST 12 C02021.
