Time-to-digital converter (TDC) based on startable ring oscillators and successive approximation

This paper presents a time-to-digital converter (TDC) architecture based on startable ring oscillators (SRO) and the cyclic time domain successive approximation principle. A ring oscillator is first used as a coarse interpolator within the cycle of the reference clock, after which the ring oscillator is used as a phase memory for the time domain successive approximation. The LSB resolution is ~42 ps which matches the applications using single photon avalanche diode (SPAD) as the source of timing signals.