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This paper presents the design of a wide-range multi-channel time-to-digital converter (TDC) for high-energy physics and biomedical imaging applications. The TDC architecture is based on coarse-fine two-level conversion scheme. Double 10-bit gray counters are designed for coarse conversion while a multiphase sampling technology based on array of delay-locked loops is proposed for fine conversion. The resolution range is achieved from 71 ps to 142 ps by use of a reference clock from 100 MHz to 50 MHz. The measured range of the TDC is 10 mus. A prototype chip of 3-channel TDC for PET imaging system is designed and fabricated in AMS 0.35 mum CMOS technology. The area of the chip is 8.4 mm2 in size. The differential nonlinearity is plusmn0.1 LSB. The integral nonlinearity is plusmn0.1 LSB. The circuits will be extended to 64 channels for small animal PET imaging system.