Digital laser range finder: phase-shift estimation by undersampling technique

The purpose of this paper is to present the conception and the first realization of a new laser range finder which is a digital system. Based on the flight time measurement principle, it uses a phase-shift conversion method which is achieved by the undersampling technique. Firstly, the authors remind readers of the synchronous demodulation principle and present the undersampling technique. Then the corresponding phase-shift measurement unit working at a 10 MHz modulation frequency is described. The choice of the sampling frequency, related to the modulation frequency, is important and leads to a very interesting simplification of the digital process. Performance evaluation of this unit shows a good accuracy in phase-shift estimation. The system is designed to be integrated in a complete autonomous device. An important evolution of the system is introduced in order to feature a high second modulation frequency at 240 MHz, which is required for high accuracy measurement. Nevertheless the new system keeps a rather simple architecture.