🤖 AI Summary
To address the bottlenecks of low resolution, severe nonlinearity, and missing codes in time-to-digital converters (TDCs) implemented on 16 nm FPGAs, this paper proposes two hardware-agnostic post-processing techniques: Partial Order Reconstruction (POR) and Iterative Time-bin Interleaving (ITI). These methods effectively fuse multiple delay chains and reconstruct missing codewords. Integrated with code-density testing, directed acyclic graph (DAG)-based analysis, and tap-delay-line calibration, the approach achieves picosecond-level timing measurement accuracy: a minimum time resolution of 1.15 ps, an RMS time error of 3.38 ps, differential nonlinearity (DNL) within [−0.43, 0.24] LSB, and integral nonlinearity (INL) within [−2.67, 0.15] LSB. The proposed scheme significantly improves the linearity and completeness of usable time bins in FPGA-embedded TDCs, outperforming or matching state-of-the-art solutions, and is well-suited for high-precision delay measurement and timing calibration applications.
📝 Abstract
We present a Time-to-Digital Converter (TDC) implemented on a 16 nm Xilinx UltraScale Plus FPGA that achieves a resolution of 1.15 ps, RMS precision of 3.38 ps, a differential nonlinearity (DNL) of [-0.43, 0.24] LSB, and an integral nonlinearity (INL) of [-2.67, 0.15] LSB. This work introduces two novel hardware-independent post-processing techniques - Partial Order Reconstruction (POR) and Iterative Time-bin Interleaving (ITI) - that significantly enhance the performance of FPGA-based TDCs. POR addresses the missing code problem by inferring the partial order of each time bin through code density test data and directed acyclic graph (DAG) analysis, enabling near-complete recovery of usable bins. ITI further improves fine time resolution by merging multiple calibrated tapped delay lines (TDLs) into a single unified delay chain, achieving scalable resolution without resorting to averaging. Compared to state-of-the-art FPGA-based TDC architectures, the proposed methods deliver competitive or superior performance with reduced hardware overhead. These techniques are broadly applicable to high-resolution time measurement and precise delay calibration in programmable logic platforms.