A 12 ps Precision Two-Step Time-to-Digital Converter Consuming 434 μW at 1 MS/s in 180 nm CMOS With a Dual-Slope Time Amplifier

A two-step time-to-digital converter (TDC) is designed for the high-precision time measurement of the DIRC-like TOF (DTOF) detector at the Super Tau-Charm Facility (STCF). Extending the measurement range by Nutt’s method, the TDC clock cycle is interpolated with two voltage-controlled tapped delay lines (TDL) connected by a dual-slope time amplifier (TA). By amplifying the residue from the first-step TDL-based interpolation with the TA and measuring it with the second TDL, the TDC resolution is significantly improved to sub-gate delay. Since the residue is extracted by a new method without the need of TA duplication or delay insertion, the TDC power consumption and conversion time are effectively reduced. By adopting the improved TA circuit into the TDC with a high gain, adjustable output offsets, and good linearity, the TDC measurement precision is guaranteed. In addition, a new DLL structure is proposed to stabilize the TDL against process, voltage, and temperature (PVT) variations with less power consumption. Benefiting from the proposed residue extraction method and DLL structure, the TDC exhibits low power consumption. To verify the TDC design, a prototype chip with two TDC channels is fabricated in GlobalFoundries (GF) 180 nm CMOS technology for performance evaluation. With a system clock of 150 MHz, it has a resolution (LSB) of 16.5 ps and a maximum sample rate of 6 MS/s. The differential nonlinearity (DNL) error ranges from −0.98 LSB to 0.87 LSB and the integral nonlinearity error (INL) ranges from −4.21 LSB to 2.83 LSB. With a bin-by-bin calibration method, the measured TDC precision is 12.1 ps on average within the 0–20 ns time interval measurement range. In addition, the TDC has low temperature sensitivity and does not require recalibration within a 20 ° C temperature range. Each TDC channel consumes $434~\mu $ W power at 1 MS/s sample rate. The test results confirm that the proposed TDC can achieve high precision with a moderate sample rate and low power consumption without highly scaled technologies, which can meet the requirements of the DTOF detector at STCF.