Time-to-Digital Converter based on an On-chip Voltage Reference Locked Ring Oscillator

A time-to-digital converter (TDC) based on an on-chip voltage reference locked ring oscillator has been fabricated in a 0.18 mum CMOS process for a pulsed time-of-flight laser rangefinder (TOF). The ring oscillator is stabilized by measuring its frequency by a frequency-to-voltage converter (FVC) and locking its output to a stable voltage reference. The time-to-digital conversion is based on counting the pulses of this six-stage, differential ring oscillator and additionally registering the state of its 12 phases at the arrival moment of the timing signals. The measured temperature dependence of the TDC is less than 0.34% in the temperature range of 0degC to 70degC corresponding to 34 mm in the distance of 10 m. The single-shot precision standard deviation value of the TDC is less than 46 ps (7 mm) in the distance range of 0 to 12 m and the power consumption is less than 18 mW