Measurement method of time-of-flight in pulsed laser ranging

Abstract

Lidar(Light Detection And Ranging) is a remote sensing technology that measures distance by illuminating a target with a laser and analyzing the reflected light . The pulsed laser ranging precision depends on receiving channel bandwidth, SNR (Signal-to-Noise Ratio), time discrimination precision and TOF (Time of Flight) measurement precision. However, the ranging precision is mainly determined by the TOF measurement precision. Various methods are developed to realize the TOF measurement and can be classified into coarse counting method, analog method, and interpolator method. The interpolator method combined with the advantage of the former two methods is proved be effective, but its realization principle is complex and difficult to realize in hardware. Here, Similar to the interpolation method, a new TDC method based on a reference sine signal is introduced to measure the TOF and can attain high precision and wide measurement range. At first, in principle how to use a reference sine signal to realize TOF measurement is analyzed and proved in detail. The TOF measurement is converted to measure the phase shift of reference sine signal. Then the factors that affect the measurement precision are quantitatively analyzed, which indicates that the frequency and the noise of reference sine signal are the main factors which affect the TOF measurement precision. Finally, numerical simulation and confirmatory experiment are presented, both showing that the proposed method is feasible to realize high precision by using low frequency reference sine signal. This proposed TOF measurement method can be applied in pulsed laser ranging and Three-dimensional imaging system.