Multi-Channel FPGA Time-to-Digital Converter With 10 ps Bin and 40 ps FWHM

We present a novel architecture for multi-channel time-to-digital converters (TDCs) to be implemented into low-cost field-programmable gate arrays (FPGAs), achieving 10-ps least significant bit (LSB), 164- $mu ext{s}$ full-scale range, and good linearity both in terms of differential nonlinearity (DNL) and integral nonlinearity (INL). The conceived architecture is based on the carry chain delay line model and wave union A method: the positions of both rising and falling edges that propagate in multiple parallel carry chains are recorded each time there is an HIT input. This technique effectively subdivides the ultrawide bins improving the measurement precision and, combined with the sliding-scale technique and continuous code density calibration, improves the TDC linearity. Employing the proposed architecture, we have implemented in a Xilinx Artix-7 FPGA a TDC with 20 timestamp units and validated the device in a time-correlated single photon counting (TCSPC) setup, when connected to an array chip with $5 imes 5$ single-photon avalanche diodes (SPADs).