Jiangmen Underground Neutrino observatory (JUNO) is a neutrino medium baseline experiment constructing in China, with the main goal to determine the neutrino mass hierarchy. A large liquid scintillator volume instrumented by around 20000 large photomultiplier tubes will detect the antineutrinos issued from nuclear reactors.The JUNO electronics system has mainly two parts: the front-end system inside water,the backend system outside water. For the front-end electronics, global control units (GCU) digitize the analog signals and send out event data as well as trigger requests. The BECs are used to collect the trigger requests from GCUs and process for next trigger decision step.
The JUNO experiment:
The Jiangmen Underground Neutrino Observatory (JUNO)  is a neutrino medium baseline experiment in construction in China, with the goal to determine the neutrino mass hierarchy and perform precise measurements of several neutrino mass and mixing parameters [2,3]. The experiment uses a large liquid scintillator detector aiming at measuring antineutrinos issued from nuclear reactors at a distance of 53 km. The 20 ktons of liquid scintillator contained in a 35 m diameter acrylic sphere is instrumented by more than 17000 20-inch photomultiplier tubes (PMT). Two vetoes are foreseen to reduce the different backgrounds: a 20 ktons ultrapure water Cerenkov pool around the central detector and a muon tracker installed on top of the detector.
The JUNO electronics readout:
One of the innovative aspects of JUNO is its electronics and readout concept . The JUNO electronics system can be separated into mainly two parts: (i) the front-end electronics system performing analog signal processing (the underwater electronics), and (ii) the back-end electronics system, sitting outside water, consisting of the DAQ and the trigger system. 2 100-meters Ethernet cables and 1 coaxial cable are used to link the two parts. One Ethernet cable as DAQ and slow control link, the other one as trigger link, and the coaxial cable is for the power delivery. At the front-end part, a custom designed PCB called GCU (global control unit)  will digitize the incoming analog signals from 3 PMTs with custom designed high speed ADC (analog to digital converter). . The GCU will store the data signals in a large local memory under the control of the FPGA (Field-Programmable Gate Array) waiting for trigger decision. The CGU will send and receive the trigger requests and acknowledgments to and from the outside-water system, and in case of positive trigger acknowledgment, it will also send out the corresponding event data to DAQ system.
The Back-End Cards:
The back-end card (BEC) is designed to handle the trigger link. Each BEC will receive the trigger request signals from 48 underwater boxes, and in total of about 150 back-end cards are needed. The BEC is used as a concentrator and the incoming differential trigger request signals will pass an equalizer for compensating the attenuation due to the long cable. An FPGA mezzanine card (FMC), called TTIM, sitting on the BEC will align the received trigger request signals to a certain system clock, make a sum, and send the result to the trigger system over an optical fiber. A 62.5 MHz system clock will be distributed to all the GCUs from the BECs. Besides, IEEE1588 is used to synchronize the two parts to a level of 8 ns.
 JUNO Collaboration, “Conceptual Design Report”, arXiv:1508.07166, Instrumentation and Detectors, 328 pages
 JUNO Collaboration, “Neutrino Physics with JUNO”, arXiv:1507.05613, J.Phys. G43 (2016) 030401
 Yu-Feng Li and al., “Unambiguous determination of the neutrino mass hierarchy using reactor neutrinos”,
arXiv:1303:6733, Phys. Rev. D88 (2013) 013008
 D. Pedretti , ”The Global Control Unit for the JUNO front-end electronics”, TIPP2017,