Resolution improvements on the novel VCO based time measurements technique

The precise measurement of time intervals is a primary goal in a growing number of applications and the challenge to achieve increasingly higher resolutions is a main topic of research. In this sense, time-of-flight measurements and time-correlated photon counting are two milestones. Since the intrinsic resolution of the sensors used today is in the order of tens of picoseconds, the measurement systems must guarantee performance at least of this order. The choice of making digital a part or the totality of the measurement electronic systems exploits well-known advantages from the adaptivity, to the versatile calibration, to the easiness of implementation of powerful processing algorithms, but also new methods must be put in place to significantly improve the resolution of the measurements. The well-established method for high-accuracy time interval measurements is the time-to-amplitude conversion (TAC). Another diffused method is the time-to-digital conversion (TDC), which has the advantage of easy integration. Methods based on phase measurements have also been proposed in literature. This work concerns a strategy of time measurement, with resolution of the order of few picoseconds, based on the additional features of very limited analog hardware, easy integrability in contexts where computation power is already present, no need of intensive calibration procedures, and minimizing the necessity of a-priori information. We present an improvement on time resolution of the VCO based time measurement technique. The improved analog frontend improves the time resolution with no effects on linearity, full scale range and event rate. The new method achieves the resolution of 8 ps rms.