High-frequency phase measurement for optical rangefinding system

A phase measuring circuit has been designed and tested that is capable of accurately measuring phase differences (±0.5°) between transmitted and received signals having frequencies up to to 75 MHz. The measurement output rate was 100 phases per second and this allowed for a signal averaging of 50 consecutive measurements per output. The received signal level could be reduced by 30 dB without creating any additional phase delays. The system has been extensively tested with a time-of-flight optical rangefinding system using continuously modulated laser light transmitted to and received from a variety of targets