US Patent 7315355 Method and device for optical distance measurement

A method and a device for optically measuring a distance by emitting an amplitude modulated and bundled optical signal and by receiving the signal reflected from a target object. The modulation frequency is continuously regulated by means of a regulating loop in such a manner that between the emitted and the received signal a fixed phase difference prevails that is independent of the distance. For reducing the circuitry required for a distance evaluation circuit, while maintaining a high accuracy and for increasing the attainable regulation speed, the detection of the phase difference occurs with a phase comparator.