A 2-channel CMOS time-to-digital converter for time-of-flight laser rangefinding

A time-to-digital converter (TDC) based on a free running ring oscillator and timing signal interpolators has been fabricated in a 0.13 μm CMOS process for the receiver of a pulsed time-of-flight laser rangefinder (TOF). The time-to-digital conversion is based on counting the pulses of this eighth-stage, differential ring oscillator and additionally registering the state of its 16 phases at the arrival moment of the timing signals and their delayed replicas. The temperature and supply voltage dependences of the ring oscillator are compensated for by measuring its frequency by means of an accurate time generator. The single-shot precision standard deviation value and the nonlinearity of the TDC are less than 20 ps (3 mm) and ±16 ps (2.4 mm), respectively, in the distance range of 0 to 15 m. The power consumption is less than 16 mW.