A new front-end ASIC for GEM detectors with time and charge measurement capabilities

A 32 channel CMOS front-end ASIC has been designed to read out the GEM detectors intended to be used for beam monitoring in a new proton-therapy facility currently under construction. In order to improve the spatial resolution by exploiting charge centroid algorithms, the analog channels, based on the classic CSA+shaper architecture, are equipped with a peak detector (PD) which works as an analog memory during the read-out phase. The outputs of the PDs are multiplexed towards an integrated 8-bit subranging ADC. An accurate trigger signal marks the arrival of a valid event and is generated by fast-ORing the outputs of 32 voltage discriminators which compare the shaper outputs with a programmable threshold. The digital part of the ASIC manages the read-out of the channels, the A/D conversion and the configuration of the ASIC. A 100Mbit/s LVDS serial link is used for data communication. The sensitivity of the analog channel is 15mV/fC and the dynamic range is 80fC. The simulated ENC is about 650e- for a detector capacitance of 10pF.