| Laser ranging is a technology for precision measurement. It is developing along with the development of the laser technology. Laser rangefinders are widely used in the military field and the civil field profit from laser's high monochromaticity, high directionality, good coherence. The rangefinder deduces the range of a retroreflecting target by directing at the target an intensity-modulated laser beam and measuring the phase difference between the returned and transmitted modulation envelopes. Due to the excellent modulation characteristics of laser diode, the infused current of the laser diode is modulated to make the intensity of the laser beam change with the modulation signal. The distance information can be got from the phase difference of the laser signal before the emission and the reflected laser signal which is detected.On basis of analyzing the advantages and disadvantages of several usual method of multi-frequency modulation, a new method of multi-frequency modulation is proposed in this paper. Although it seems concise, it resolves the conflict between the larger rang bandwidth of multi-frequency and the narrow band pass of circuit. Using this as a foundation, a laser phase distance-measuring system is schemed out. The whole circuit system includes 7 parts as following: clock generator, circuit of laser diode driver, photoelectric detecting circuit, RF amplifier, mixer circuit, IF amplifier and IF low pass filter. All tests of them have been done. A satisfactory conclusion has been got, that the laser phase range finders has a long distance measuring range and high accuracy both with reflector and with reflectorless. |
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