A CMOS time-to-digital converter based on a ring oscillator for a laser radar

An integrated ring oscillator based time-to-digital converter (TDC) for a pulsed time-of-flight laser rangefinder has been designed and tested. The time-to-digital conversion is based on counting the pulses of this eight-stage differential ring oscillator and additionally registering the state of its 16 phases at the arrival moment of the timing signals. The single-shot precision and the nonlinearity of the TDC are better than 78.5 ps and +/-37 ps, respectively and the current consumption of the time-to-digital converter is < 24 mA from a +3 V power supply. The time-to-digital converter was fabricated on the same chip with a receiver channel in a 0.35 mum CMOS process.