The vernier-based TDC employing soft-injection-locked ring oscillators

A time-to-digital converter (TDC) plays an important role in time interval measurement. Among various TDC structures, the vernier-based TDC is promising because it can possess high time resolution. However, the oscillators used in the conventional vernier-based TDC require complicated calibration procedure. This makes the TDC difficult in use. In this paper, we purpose a new soft-injection-locked ring oscillator for the vernier-based TDC. The proposed oscillator can oscillate immediately and accurately right after the trigger signal arrives. The TDC structure employing the purposed oscillators is verified by the off-the-shelf 40- and 74-series ICs. Experimental results show that the equivalent resolution less than ±1.5 LSB can be achieved.