Design of high-speed and high-resolution time-to-digital converter using time arithmetic circuits

Abstract

Time-to-digital converter (TDC) has become increasingly more important with the advent of digital-friendly mixed-signal and analog circuits such as all-digital PLL/DLLs and time-domain ADCs. In a all-digital PLL(ADPLL) and a time-domain ADC, many analog-intensive circuits are replaced by TDC and digital intensive circuits. These circuits are well suited for nanometer CMOS technology, and even can be synthesis like digital circuits. Compared with a ADC, a TDC quantizes input time-signal and conducts signal processing in time-domain, which has benefits from nano-scale CMOS technology with fast transition but low supply voltage. In order to improve the performance of digital-friendly mixed-signal and analog circuits, much effort was put into improving the TDC’s time resolution to below sub-gate delay and conversion rate to above tens of Msps, resulting in a high-speed and high-resolution TDC. Recent innovations in achieving high-speed and high-resolution TDC include time-amplifiers (TAs). The function of TA is same as the amplifier in voltage-domain, amplifying small time-input with large enough to process further. Using these TAs, two-step, pipelined, and cyclic TDC are introduced. However, the gain of these TAs is unpredictable due to meta-stability and thus requires calibration for improved linearity. Although there exists a TA that does not use meta-stability but use different propagation delay in variable delay cells, it still suffers from linearity and requires calibration. Employing these time-amplifiers (TAs), many TDCs have recently been proposed, such as two-step [22,29], cyclic [25], and asynchronous pipeline [30] TDCs. While these methods look to mimic the operations of their ADC counterparts, a critical flaw is that register in time- domain is absent and thus pipelining cannot be achieved. For example, [21-29] are all based on an asynchronous operation, where input propagates through the delay cells without being stopped and thus they cannot operate ...