ARTROC—a readout ASIC for GEM-based full-field XRF imaging system

In the paper we report on development of an Application Specific Integrated Circuit (ASIC), called ARTROC, being part of a full-field X-ray fluorescence spectroscopy (XRF) imaging system equipped with a standard three stage Gas Electron Multiplier (GEM) detector of 10×10 cm2 area. The ARTROC consists of 64 independent channels, allowing for simultaneous recording of the amplitudes (energy sub-channel) and time stamps (timing sub-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 centre of gravity finding in clusters of signals on neighbouring strips belonging to the same detection events. The ASIC could work in one of six gain modes and one of two speed modes. In a slower mode the maximum count rate per channel is 105/s while in a faster mode it is three times higher. The ARTROC comprises also input protection circuits against possible random discharges inside active detector volume, so it can be used without any additional input components. The ASIC has been designed in 350 nm 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 set-up with X-rays source.