Test system of the front-end readout for an application-specific integrated circuit for the water Cherenkov detector array at the large high-altitude air shower observatory

Abstract

The water Cherenkov detector array (WCDA) is an important part of the large high-altitude air shower observatory (LHAASO), which is in a research and development phase. The central scientific goal of LHAASO is to explore the origin of high-energy cosmic rays of the universe and to push forward the frontier of new physics. To simplify the WCDA’s readout electronics, a prototype of a front-end readout for an application-specific integrated circuit (ASIC) is designed based on the time-over-threshold method to achieve charge-to-time conversion. High-precision time measurement and charge measurement are necessary over a full dynamic range [1–4000 photoelectrons (P.E.)]. To evaluate the performance of this ASIC, a test system is designed that includes the front-end ASIC test module, digitization module, and test software. The first module needs to be customized for different ASIC versions, whereas the digitization module and test software are tested for general-purpose use. In the digitization module, a field programmable gate array-based time-to-digital converter is designed with a bin size of 333 ps, which also integrates an inter-integrated circuit to configure the ASIC test module, and a universal serial bus interface is designed to transfer data to the remote computer. Test results indicate that the time resolution is better than 0.5 ns, and the charge resolution is better than 30% root mean square (RMS) at 1 P.E. and 3% RMS at 4000 P.E., which are beyond the application requirements.