A simple and reliable counting and display circuit for laser rangefinder

A digital counting and display circuit for long distance laser rangefinder is presented. The laser rangefinder uses a pulsed Nd:YAG laser emitting in the near-infrared spectral region at the wavelength of 1.06 micrometer to measure distances to targets with a resolution of 5 m, an accuracy of +/- 1.5 m, and a maximum range of 15 km based on a direct time-of-flight method. The detection is achieved with a probability of detection of 0.99 and a probability of false alarm of 1.5X10^-7. The digital circuit is characterized by its simplicity, versatility and reliability. It is placed at the end of an optoelectronic detection chain formed by a silicon avalanche photodiode, a low-noise and fast multistage amplifier, and a fast analog-to-digital converter.