PROGRAMMABLE TRIGGER FOR ELECTRON PAIRS IN RING IMAGE CHERENKOV COUNTERS

This paper describes a programmable trigger processor for the recognition of Cherenkov rings in a RICH counter. It identifies open electron pairs and suppresses close conversion and Dalitz pairs within 20µs. More generally, the system can be used for correlating pixel images with pattern masks in order to locate all relatively well defined patterns of a certain type. The trigger processor consists of a systolic processor array of 160×176, i.e. 28,160 identical processing elements (PEs) that filter out open electron pairs, and a pseudo adder array that determines whether there was at least one such pair. The processor array is assembled of 20×22 VLSI chips containing 8×8 PEs each. The semi-custom chip has been developed in 2μ CMOS standard cell technology. Ring identification is done by a two-dimensional correlation of the input image with a circle, yielding the probability to find circles at certain locations. An intermediate image containing single bits at circle centers is obtained by a parallel thinning method. To drop open pairs, this image is correlated with a disk. By computing the logical AND of counters with content =1 and the intermediate image, open pairs are deleted. All PEs run synchronously at a clock frequency of 30 MHz. The total computing power therefore amounts to 844,800 million operations/s, where a typical operation is the combination of a 6 bit addition and a shift. The PEs are controlled by a freely programmable sequencer. Its program determines, e.g., the patterns searched for, how relatively well defined objects are located, or how relations between found objects are identified. Copyright © 1990 by The Institute of Electrical and Electronics Engineers, Inc.