One problem facing a digitizing system consisting of more than one digitizer, where synchronicity is desired, is how to distribute the trigger signal. Regardless of method, the end goal is the same: to trigger all the channels at the same time. One naive solution many be to split the trigger signal and pass that to each digitizer through cables of equal length. However, this solution does not scale with the number of digitizers in the system—eventually the trigger signal is attenuated beyond the sensitivity of the analog input. Moreover, by attenuating the signal, the trigger edge is distorted and precision is lost. To address these issues this system features a daisy chain trigger mechanism. The idea is to pass the trigger signal from one device to the next . In order to keep track of the trigger point across all devices, the common time frame, the 10 MHz clock reference is distributed to all boards.
Fig. 1 presents a block diagram of a system consisting of two chassis in a daisy chain configuration. The trigger timing precision is measured to 50 ps over large arrays.
