We have proposed a novel center-of-gravity (COG) time-over-threshold (TOT) method for PET detectors readout. In order to reduce the output channels it uses the charge division architecture and all the detector signals will be read out and multiplexed into 3 TOT outputs. The COG position can be decoded from the TOT information only without causing too much distortion. This method has very simple structure and can significantly reduce the complexity of the readout electronics and the number of channels for PET instruments, especially for SSPM detectors. Preliminary evaluation has validated the method but the nonuniformity of input channels can distort the position decoding results. A demostration16-channel ASIC chip has been developed using current mirrors and discriminators. Preliminary test results with signal generators and LYSO/SSPM detectors have shown the validation of the method.
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