This paper presents a high-resolution multi-channel Time-to-Digital Converter (TDC) for Positron Emission Tomography (PET) imaging system. The TDC using a two-level conversion scheme is proposed for obtaining high timing resolution. Double 10-bit gray counters are designed for coarse conversion while a multiphase sampling technology is presented for fine conversion. In order to achieve better timing resolution with either a faster technology, an array of Delay-locked loops is chosen as a timing generator. A prototype chip of 3-channel TDC is designed and fabricated in AMS 0.35µm CMOS technology. The area of the chip is 8.4 mm 2 in size. The measured range of the TDC is 10µs. The time tap is reduced to 71ps with a reference clock of 100MHz. The differential nonlinearity is ±0.1LSB. The circuits will be extended to 64 channels for small animal PET imaging systems.

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