On-Chip Voltage Reference-Based Time-to-Digital Converter for Pulsed Time-of-Flight Laser Radar Measurements

A fully integrated time-to-digital converter (TDC) for a pulsed time-of-flight laser rangefinder has been designed and fabricated by a standard 0.18-mum CMOS process. The time-to-digital conversion is realized by counting the full clock cycles of an on-chip ring oscillator between timing signals and by recording the state of its 12 phases at the moment of arrival of the timing signals and their delayed replicas. The frequency of the oscillator is stabilized to an on-chip voltage reference by means of a frequency-to-voltage-converter-based feedback loop. The resolution and single-shot precision (standard deviation) of the TDC are ~ 60 ps and less than ~ 50 ps, respectively, in a range of 80 ns. The worst-case temperature dependence of the TDC is less than 50 ppm/
^deg
C in the temperature range of 0
^deg
C to 70
^deg
C, corresponding to 0.6 mm/
^deg
C at a distance of 12 m (80 ns). The power consumption of the TDC is less than 18 mW.