SENSROC4: An multichannel low-noise front-end readout ASIC dedicated to CZT detectors for PET imaging

In this paper, we present the design of a novel low-noise front-end readout application-specific integrated circuit for our small animal PET systems which objective is to achieve the following performances, the spatial resolution of 1 mm³, the detection efficiency of 15 % and the time resolution of 1 ns. A cascode amplifier based on the PMOS input transistor is selected to realize the charge-sensitive amplifier (CSA) for the sake of good noise performances. The output of the CSA is split into two branches. One is connected to a slow shaper for energy measurements. The other is connected to a fast shaper for time acquisition. A novel monostable circuits is designed to adjust the time delay of the trigger signals so that the peak value of the shaped voltages can be sampled and stored. Based on the above topology, an eight-channel front-end readout prototype chip is designed and implemented in 0.35 μm CMOS process. The die size is 2.286 mm × 2.282 mm. The input range of the ASIC is from 2000 e- to 180000 e-, reflecting to the energy of the gamma ray from 11.2 keV to 1 MeV. The gain of the readout channel is 65 V/pC. The best test result of ENC is 86.5 e- at zero farad plus 9.3 e- per picofarad. The nonlinearity is less than 3 %. The crosstalk is less than 2 %. The power dissipation is about 3 mW/channel.