A CMOS mini-SiPM detector with in-pixel data compression for PET applications

A new architecture for PET photodetectors based on small-area SiPMs (mini-SiPMs) with individual SPAD digitization and in-pixel data compression is presented. The main goal of this architecture is to reduce the electronics area occupation per SPAD and thus improve the fill factor. Two compression schemes are described, spatial and temporal compression, and a combination of both is implemented in the pixel. Our first chip using this architecture is described, where each pixel contains a mini-SiPM with 32 SPADs, a 4-bit digital counter and individual SPAD SRAMs for disabling high DCR devices. The sensor contains a 14 × 10 pixel array for a total of 4480 SPADs, and the achieved fill factor is about 29%. The sensor also contains column-level TDCs, which acquire the time of arrival of the first photon in each column. The expected compression response of this sensor is presented.