A fast total energy trigger unit for a CsI calorimeter

A fast total energy trigger module for use with the CsI calorimeter of the Crystal Barrel experiment at LEAR is described. The unit intercepts and sums the data during the transfer of the digital output of the LeCroy FERA ADCs to the 1190 memory modules. Comparing the digital sum with two preset levels then generates outputs to the trigger logic in less than 40 μs from the start of the input gate signal to the FERA ADCs. This fast response allows the energy sum signals to be included in the level one trigger logic.