A Hybrid MT-ToT Design for CdZnTe/SiPM in Biomedical PET Applications

In biomedical positron emission tomography (PET) applications, the main shortcomings of readout electronics based on simple time-over-threshold (ToT) method are non-linearity and time walk that lead to poor extraction of all relevant information from detectors. These problems can be solved using multi-channels ASIC chips with high-density of comparators according to the number of discrimination thresholds. That needs various field-programmable gate arrays (FPGAs) for accurate results in PET imaging systems, due to the on-chip integration of seral γ-photon sensors. In this work, the design concept of an analogue multi-threshold voltage time-over-threshold (MT-ToT) circuit for accurate data extraction in CdZnTe/SiPM based PET applications has been presented. The most concerning circuit building blocks are the latch type comparator and the multi-threshold voltage generator (MTVG). Implemented in 65nm CMOS technology from TSMC, the analogue MT-ToT is able to sense down to 1mV differential input voltage while ensuring up to 140µW of power budget from 1.2V supply voltage. With analogue pulse shapes varying from 250ns to 1us shaping time provided by a simulated CdZnTe detector, the proposed MT-ToT allows triggering signals with only 8.1ns timing resolution. Moreover, the hybrid MT-ToT can handle up to 1Gb/s count rate events from a modelled SiPM detector.