A CUSTOM HIGH DENSITY VLSI CIRCUIT FOR TIME PROJECTION (TPC)READOUT

THE NEW GENERATION OF TIME PROJECTION CHAMBERS (TPCS), SUCH AS THE TELATIVISTIC HEAVY ION COLLIDER AT BROOKHAVEN NATIONAL LABORATORY, PRODUCE LARGE AMOUNTS OF DATA ON EVERY EVENT. AS A RESULT, A NEW GENERATION OF TPC ELECTRONICS, EMPLOYING A FRONT-END DATA COMPACTION SCHEME, IS REQUIRED TO EXTRACT THE INTERESTING DATA FROM THE ENORMOUS TOTAL DATA SET. TWO APPROACHES ARE BEING STUDIED IN PHASE I. IN BOTH CASES, SIGNAL CAPTURE UTILIZES AN ANALOG SAMPLING ARRAY, WHICH IS A TECHNOLOGY DEVELOPED ESPECIALLY FOR PHYSICS LABORATORY USE, AND IS NOW THE BASIS OF A UNIQUE LINE OF COMMERCIAL MEASURING INSTRUMENTS. THE FIRST VARIATION STUDIED IS THE DETECTION OF VALID DATA WITH A FRONT-END DISCRIMINATOR ON EVERY CHANNEL; THE DISCRIMINATOR,WORKING IN CONJUNCTION WITH A TIMING CLOCK, RECORDS THE TIME AT WHICH THE EVENT BEGINS, THEN TAKES A SPECIFIED NUMBER OF SAMPLES, WHICH ARE STORED IN AN ANALOG MEMORY. THE TIME VALUES ARE STORED SEPARATELY. AFTER THE DRIFT PERIOD IS OVER, THE ANALOG SAMPLES ARE READ OUT AND CONVERTED IN AN ANALOG-TO-DIGITAL CONVERTOR; THE AMPLITUDE VALUES AND TIME STAMP ARE STORED IN A LOCAL MEMORY FOR FURTHER COLLECTION AND PROCESSING. IN THE SECOND APPROACH, THE ENTIRE DRIFT PERIOD IS DIGITIZED, AND THE SAMPLES OF INTEREST ARE DETECTED ON READOUT. AT THIS TIME, SIGNALS BELOW THRESHOLD ARE DISCARDED, AND THE VALID DATA ALONG WITHTHE CALCULATED TIME VALUE(S) ARE STORED AS BEFORE. IN BOTH APPROACHES, ONLY THE DATA OF INTEREST ENTER THE NEXT STAGE OF PROCESSING.