Abstract
This paper presents low nonlinearity, compact, and multichannel time-to-digital converters (TDC) in Xilinx 28 nm Virtex 7 and 20 nm UltraScale field-programmable gate arrays (FPGAs). The proposed TDCs integrate several innovative methods that we have developed: 1) the subtapped delay line averaging topology; 2) tap timing tests; 3) a direct compensation architecture; and 4) a mixed calibration method. The code density tests show that the proposed TDCs have much better linearity performances than previously reported ones. Our approach is cost-effective in terms of the consumption of logic resources. To demonstrate this, we implemented 96 channel TDCs in both FPGAs, using less than 25% of the logic resources. The achieved least significant bit (LSB) is 10.5 ps for Virtex 7 and 5.0 ps for UltraScale FPGAs. After the compensation and calibration, the differential nonlinearity (DNL) is within [–0.05, 0.08] LSB with σDNL = 0.01 LSB, and the integral nonlinearity (INL) is within [–0.09, 0.11] LSB with σINL = 0.04 LSB for the Virtex 7 FPGA. The DNL is within [–0.12, 0.11] LSB with σDNL = 0.03 LSB, and the INL is within [–0.15, 0.48] LSB with σINL = 0.20 LSB for the UltraScale FPGA.
Highlights
T IME-TO-DIGITAL converters (TDCs) are extremely high-precision stopwatches
Since the Virtex 7 field-programmable gate arrays (FPGA) are different from UltraScale FPGAs in the arrangements of logic modules, we will describe the proposed approaches, but with different configurations and methods selected for implementing our multichannel TDCs
When compensated TDC is compared with calibrated TDC, both the differential nonlinearity (DNL) and integral nonlinearity (INL) are improved significantly
Summary
T IME-TO-DIGITAL converters (TDCs) are extremely high-precision stopwatches. They are key components in many electronics systems and industrial products such as alldigital phase-locked loops, time-of-flight (ToF) mass spectrometers, and LIDAR or three-dimensional (3-D) ranging devices [1]–[6] used for robotics, self-driving vehicles, and solar photovoltaic deployment optimization. TDCs are widely applied in space sciences [7], biomedical applications, such as positron emission tomography and fluorescence lifetime imaging microscopy (FLIM) [8]–[12], nuclear and particle physics [13], [14], and quantum communications [15]. All results can be fully reproduced using the methods described in this paper. (Corresponding author: David Day-Uei Li.)
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