RUA: read-out unit ASIC for gamma ray detector readout

The gamma-ray imaging detectors proposed for the last generation of astronomical space missions show a trend of constant increase in the number of required detection pixels, each one corresponding to an individual detector. As example the IBIS imager of the INTEGRAL satellite, uses 20k pixels, 16k made of CdTe and 4k made of scintillator crystals with photo-diode read out. In this case the front-end electronics is realized using application specific integrated circuit (ASIC) that includes 16 complete spectroscopic chains. RUA (read-out unit ASIC) is a prototype developed with the aim to have a very versatile circuit. The first stage of RUA charge pre-amplifier is external to the ASIC, thus allowing a good matching of the input FET with the characteristics of whatever detector. For each channel RUA has the possibility to modify the main parameters of the analog block, such as shaping time, duration of rise time protection, gain, polarity and threshold discrimination level; this is done changing the value contained in external addressable registers. RUA will execute a number of logic and digital functions on the signal detected including: A/D conversion, event time marking, flagging coincidence with external events, digital data output via serial bus. The first prototype of one RUA channel that includes the analog blocks and part of the digital ones has been realized and tested. The results of the test are presented and discussed.