Multi-channel, low nonlinearity time-to-digital converters based on 20nm and 28nm FPGAs

Haochang Chen, David Day-Uei Li

Research output: Contribution to journalArticlepeer-review

40 Citations (Scopus)
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Abstract—This paper presents low nonlinearity, compact and multi-channel time-to-digital converters (TDC) in Xilinx 28nm Virtex 7 and 20nm UltraScale FPGAs. The proposed TDCs integrate several innovative methods that we have developed: 1) the sub-tapped delay line (TDL) 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 10.5ps 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.
Original languageEnglish
Number of pages9
JournalIEEE Transactions on Industrial Electronics
Early online date20 Jun 2018
Publication statusPublished - 30 Nov 2018


  • carry chains
  • field-programmable gate arrays (FPGA)
  • time-of-flight
  • time-to-digital converters (TDC)
  • FPGAbased TDCs
  • multichannel TDCs


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