A Multichannel and Compact Time to Digital Converter for Time of Flight Positron Emission Tomography

This paper presents a novel multichannel time to digital converter (TDC) specifically designed for the digitization of photon time of flight (TOF) and energy in positron emission tomography (PET) scanners. A coarse-fine architecture based on a counter combined with a delay locked loop (DLL) is implemented using a fully synchronous approach exploiting the pipeline principle and dynamic logic. This makes the design particularly compact and suitable for multichannel applications. The converter is also able to reject the events generated by the dark noise of the photodetectors used in the PET modules. This significantly reduces the communication bandwidth required for reading the TDC outputs. The TDC has been designed in a 65 nm CMOS process and features 8 channels that provide the arrival time information of an event with an LSB of 102 ps. The core occupies an active area of $0.3~\hbox{mm}^2$ and consumes 230 mW.