Abstract: Present a design of a 64-channel, high time resolution, self-calibrating Time to Digital Converter (TDC) for biomedical imaging, especially the small animal PET imaging applications. Double 10-bit gray counters are designed for coarse conversion while a multiphase sampling technology based on array of Delay Locked Loops (DLLs) is proposed for fine conversion. 64 channels use a asynchronous First In First Out unit to store the timing data commonly. Fabricated in SMIC 0.18μm CMOS low voltage technology. The simulations indicate the resolution range is achieved from 71 ps to 143 ps and the dynamic range is 10~20μs. The differential nonlinearity is 0.8 LSB. The integral nonlinearity is 0.3 LSB.