The purpose of this paper is to present the conception of a twofold modulation frequency laser range finder. The system is based on the phase-shift measurement method with two modulation frequencies, one giving the distance within a wide range and a second one leading to high resolution measurement. The measurement method is based on intermediate frequency sampling associating the under-sampling technique with digital synchronous detection. Its main advantage is a global simplification of the electronic system, leading to a quite simple development and low cost system. There is only one phase-shift measurement stage but the twofold modulation frequency is possible thanks to the heterodyne technique. The emission and detection parts are designed for wideband operation and are digitally controlled. The whole system has been designed with only one digital phase locked loop reducing the phase noise and improving the resolution. Because of the global structure and the different digitally controlled parts the necessary calibration process could be introduced. From the design of the prototype it is possible to move towards a smart laser range finder.

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