An FPGA-Based Time-to-Digital Converter With Online Dual-Chain Calibration

This paper introduces an FPGA-based time-to-digital converter with an online dual-chain calibration method to address time resolution and linearity issues arising from the non-uniformity of FPGA internal delay elements. The aim is to enhance the stability and accuracy of time-to-digital converters under varying environmental conditions. We employ an external high-precision clock to generate start-stop calibration signals for real-time monitoring of signal propagation time changes within FPGA components. Two identical delay chains in the time-to-digital converter are managed by a Finite State Machine to switch their roles, ensuring continuous data acquisition and online calibration. Experimental results show that the proposed time-to-digital converter significantly outperforms traditional time interval counter in terms of time linearity, maximum integral nonlinearity, and differential nonlinearity. Within a temperature range of 20°C to 80°C, post-online temperature calibration maintains the root mean square of the TDC below 20 ps, substantially improving performance across different temperature conditions.