The H1 SPACAL time-to-digital converter system

This paper describes a pipelined 1400-channel Time-to-Digital Converter (TDC) system for the H1 Scintillating Fibre Calorimeter, which will soon be installed in the H1 experiment at DESY. The main task of the TDC system is to determine the time of arrival of energy depositions, and send this information from bunch crossings that satisfy the event trigger into the H1 data acquisition system. In addition, the TDC system must monitor the timing trigger, which vetoes bunch crossings that contain too much background energy. Products of the interaction are separated from background on the basis of their different times of arrival with respect to the bunch crossing clock. For this monitoring the TDC system uses automatic on-board histogramming hardware that produces a family of histograms for each of 1400 channels. The TDC function is performed by the TMC1004 ASIC. The system digitises over a range of 32 ns per bunch crossing with 1ns bins and a precision of 1ns. Because of the way the TMC1004 is designed, it is possible to vary the size of the bins between 0.6 ns and 3 ns by trading off measurement range for bin size. The system occupies two 9U VME crates