High resolution, multi-frequency laser range-finding for electronic imaging

The purpose of this paper is to present the conception of a twofold modulation frequency laser range finder. Such a system is required for high resolution measurement within a wide range. The system is based on phase shift measurement method. The implemented solution for phase shift measurement is the IF sampling method that means under-sampling technique, associated to digital synchronous detection. Its main advantage is a global simplification of the electronic system, leading to a quite simple development and low cost system. Both measurement frequencies are 10 MHz and 240 MHz but there is only one IF measurement unit working at 10 MHz, and the system is designed with only one digital PLL designed in order to reduce the phase noise. Most of the different sections of the prototype are digitally controlled leading to a kind of smart sensor.