BES III Time-of-Flight readout system

A Time-of-Flight (TOF) readout system has been developed for BES III, this paper will present a brief overview of the system´s development and performance. A total of 448 Photo-Multiplier Tube (PMT) channels are distributed over the spectrometer. The signals formed from the anode of the PMTs are fed through the corresponding 448 channel preamplifiers which drive the differential signals over 18 meters of cable to the two TOF VME64xP crates, located on the 1^st and 3^rd floor respectively. Each crate consists of 14 ldquoFEErdquo Modules, 14 ldquoFEE_Rearrdquo Modules, 1 ldquoFastCtrlrdquo Module, a Clock Module, and a Power PC card which interfaces the FEE modules to DAQ over Ethernet. Each FEE module contains 16 channels analog front end electronics to digitalize the accurate arrival time of the PMT signal, with the resolution of better than 25 ps, as well as with the pulse height with the dynamic range of 180~5000 mV and the resolution of better than 10 mV for the amplified signal. After the successful electronics and cosmic ray test with the expected result, the mass production has been processed with commission, followed by the aging work. The whole system has been assembled to the spectrometer and in operation steadily.