FRONT-END ELECTRONICS FOR A VARIABLE FIELD PET CAMERA USING THE PMT-QUADRANT-SHARING DETECTOR ARRAY DESIGN

This is a front end electronic design for a PET camera with 8 arrays o f position sensitive detectors. Each array has 16 BGO blocks (each blo ck is composed of 49 crystals). The design goals are component and spa ce reduction. Each PMT has its fast amplifier and triggered integrator . Nine flash ADCs serve an array of 27 PMTs and 784 crystals. The fast signals from one or more PMT clusters are summed. The fast summed sig nals are thresholded and sent to a programmable logic to determines th e probable scintillation zone (4 blocks) and to turn on the associated 9 PMT integrators. After integration, the logic also drives a set of ultra-fast analog snitches to connect the flash ADC set to the PMT int egration channels in the scintillation zone. The 9 ADC outputs (integr ated pulses with good photon statistics) are latched and compared. The comparator result determines which block in the zone is firing and th e appropriate 4 ADCs are selected and bused into a position decoder. T he decoder outputs the image-slice address and the crystal address. Th e circuit is pipelined and driven by a 250 MHz master clock.