CASTOR A VLSI CMOS MIXED ANALOG-DIGITAL CIRCUIT FOR LOW-NOISE MULTICHANNEL COUNTING APPLICATIONS

In this paper we present the design and first experimental results of a VLSI mixed analog-digital 1.2 microns CMOS circuit (CASTOR) for mult ichannel radiation detectors applications demanding low noise amplific ation and counting of radiation pulses. This circuit is meant to be co nnected to pixel-like detectors. Imaging can be obtained by counting t he number of hits in each pixel during a user-controlled exposure time . Each channel of the circuit features an analog and a digital part. I n the former one, a charge preamplifier is followed by a CR-RC shaper with an output buffer and a threshold discriminator. In the digital pa rt, a 16-bit counter is present together with some control logic. The readout of the counters is done serially on a common tri-state output. Daisy-chaining is possible. A 4-channel prototype has been built. Thi s prototype has been optimised for use in the digital radiography Syrm ep experiment at the Elettra synchrotron machine in Trieste (Italy): i ts main design parameters are: shaping time of about 850 ns, gain of 1 90 mV/fC and ENC (e(-) rms) = 60 + 17 C (pF). The counting rate per ch annel, limited by the analog part, can be as high as about 200 kHz. Ch aracterisation of the circuit and first tests with silicon microstrip detectors are presented. They show the circuit works according to desi gn specification and can be used for imaging applications.