Development of a High Counting Rate Waveform-Sampling Readout Electronics Based on DRS4 for TOF-PET Detector

The high-sensitivity and high-time-resolution time-of-flight positron emission tomography (TOF-PET) systems place significant demands on the performance of readout electronics, including the number of channels, counting rate, time precision, and so on. Although waveform sampling electronics based on the switched capacitor array (SCA) chip combined analog-to-digital converter (ADC) have an advantage in time resolution, the long dead time limits its application in TOF-PET systems. To break through the limit of dead time, a 64-channel waveform sampling electronics module with a sampling rate of 5.12 GSPS based on the DRS4 chip (using SCA technology) is designed. By reducing the number of read sampling cells and utilizing a hardware-level precoincidence trigger design, efficient readout dead time reducing and valid coincidence events filtering are accomplished, increasing the system counting rate. The readout electronics test results show that after dc offset correction and time interval nonuniformity calibration, the time precision of the electronics is about 18-ps full-width half-maximum (FWHM). When the DRS4 chip reads out less than 50 sampling cells, the single-channel counting rate is higher than 100 kc/s, three times higher than the theoretical maximum counting rate. Based on the electronic module, a 64-channel TOF-PET detector module was constructed, and the counting rate reached 900 kc/s, which meets the requirements of a PET system. Particularly, the precoincidence trigger design can also enhance the valid event rate of the detection system, further improving the sensitivity of the system. This electronic system addresses the system-level challenge of achieving high time precision and high counting rate simultaneously. It shows the tremendous potential in the application of waveform digitization electronics based on SCA + ADC technology to large-scale coincidence time measurement systems, such as TOF-PET, positronium annihilation lifetime spectroscopy (PALS), and particle TOF measurement systems.