The readout electronics and the DAQ system of the DRAGO Anger Camera

The aim of the DRAGO project is the development of a compact, high resolution gamma ray imager, based on the Anger Camera principle, with sub-millimeter spatial resolution. The imager is composed by a monolithic array of 77 silicon drift detectors, with an active area of 26 times 29 mm, coupled to a CsI(Tl) scintillator. The position of interaction of the photon, inside the crystal is obtained by a digital centroid identification algorithm. In this work we describe the electronic readout system of the camera, which is composed by an analog front end and an acquisition board. The analog front end is composed of 80 readout channels divided in 10 CMOS chips, built in 0.35 mum CMOS technology, each one processing 8 channels. Each analog channel of the circuit includes a low-noise preamplifier, a 6th order semi Gaussian shaping amplifier with four selectable peaking times from 1.8 mus up to 6 mus, a peak stretcher and a baseline holder. The acquisition board converts all the data coming from the 77 detectors, with a resolution of 13 bits, and sends them to the host PC via a USB interface. The two system have been experimentally characterized alone and working together, also during Anger Camera operation.