Background on Time-to-Digital Converters

Abstract

For the first time, a third-order noise shaping concept has been successfully implemented in the design of time-to-digital converters (TDCs). Two 1-1-1 multistage noise shaping (MASH) $\Delta\Sigma$ TDCs are presented in this chapter. Third-order time domain noise shaping has been adopted by the TDCs to achieve better than 6 ps resolution. Following a detailed analysis of the noise generation and propagation in the MASH $\Delta\Sigma$ structure, the first prototyping TDC has been realized in 0.13 μm complementary metal–oxide–semiconductor (CMOS) technology. It achieves an effective number of bits (ENOB) of 11 bits and consumes 1.7 mW from a 1.2-V supply. Gamma radiation assessments with both a low dose rate of 1.2 kGy/h and a high dose rate of 30 kGy/h have been performed, proving the TDC’s radiation hardness. In the second MASH TDC, a delay-line-assisted calibration technique is introduced to mitigate the phase skew caused by the large comparator delay, which is the main limiting factor of the MASH TDC’s resolution. The demonstrated TDC achieves an ENOB of 13 bits and a wide input range of 100 ns.