Evaluation of the Prototype Front End Electronics of WCDA in LHAASO

The Water Cherenkov Detector Array (WCDA) is one of the key parts of the Large High Altitude Air Shower Observatory (LHAASO). In WCDA, the high precision time and charge measurement are required for 3600 Photomultiplier Tubes (PMTs) scattered over a 90000 m(2) area. With a distributed architecture, the 400 Front End Electronics (FEEs) placed near the PNITs are responsible for the time and charge measurement over a large dynamic range. The time measurement resolution is required to he better than 0.5 ns RIMS and the required resolution for the charge measurement is better than 30% @ 1 Photo Electron (P.E.) and 3% @ 4000 P.E. Considering the large scale of the detector area, high precision clock distribution and automatic phase compensation over long distances is required. To simplify the electronics structure, clock, data and commands are transmitted together over the same optical fiber media. To evaluate the prototype FEE performance, we conducted a series of tests, including performance tests both with constant and changing ambient temperature. Test results indicate that time and charge measurement resolution and clock synchronization satisfy the application requirement.