A Novel 550-fs Time-Resolution 7.5-bit Stochastic Time-to-Digital Converter Based on Two Arbiter Groups

Abstract

This paper presents a novel two arbiter groups based stochastic time-to-digital converter (STDC) to achieve a better linearity and larger measurement range compared to a traditional STDC. Traditional STDCs with one arbiter group have a bad linearity and narrow measurement range, for the nonlinear time-to-digital transfer function that described by a Gaussian cumulative distribution function (CDF). To improve the linearity, a basic two arbiter groups based STDC is proposed firstly. Through properly shifting the time offset distributions of the two arbiter groups away from each other by applying a global time offset reference to them, a virtual uniform distribution could be formed between the two shifted time offset mean values. To achieve a large measurement range, a dual-input dual-output periodic signal generator (DIDO-PSG) and a global time offset setting circuit (GTOSC) are further designed for the proposed STDC to obtain two pairs of time offset distributions with twice measurements for one input time interval. Through properly setting the mean values of the four time-offset distributions based on GTOSC, an overall transfer function with a large linear part that contributes to a good linearity could be achieved. Finally, a test chip prototype fabricated in a 0.18-μm CMOS technology demonstrates 550-fs time resolution and 0.105-ns measurement range with –1.81 LSB INL at 50MS/s, which is much better than traditional STDCs.