A high resolution FPGA TDC converter with 2.5 ps bin size and −3.79∼6.53 LSB integral nonlinearity

As a traditional digital platform, Field Programmable Gate Array (FPGA) is seldom used for analog applications. Since there is no way to fine tune the gate property or circuit structure, the performance of FPGA analog application is usually inferior to its counterparts based on full-custom or even cell-based design. Nevertheless, a high performance FPGA time-to-digital Converter (TDC) is proposed in this paper to expand the FPGA territory into high-end analog applications. The test time signal is sampled by a serious timing references generated by feeding the original clock into a tapped delay line. According to periodicity, the delays among those timing references are wrapped into a single reference period and the effective TDC resolution can be made much smaller than the clock period to compete even with the state-of the art full-custom TDCs in performance. After measurement, the effective resolution is as fine as 2.5 ps. The corresponding differential nonlinearity (DNL) is -1.90~1.66 LSB and the integral nonlinearity (INL) is -3.79~6.53 LSB only.