| 摘要 |
PURPOSE:To achieve reception with the highest sensitivity by dividing a reception time zone, selectively extracting plural received pulses by the emission of one laser light, counting a final extracted received pulse train, and then varying the sensitivity of a receiver according to the magnitude of the pulses. CONSTITUTION:A counting circuit 8 counts a basically final received pulse train. While laser light is reflected repeatedly, a range measurement limiting circuit 9 couples with the circuit 8 to generate gate pulses at time which corresponds to a point predetermined distance before a last measured distance value. A gate circuit 10 sends out a received pulse together with a gate pulse command from the circuit 9. A peak holding circuit 11 holds the peak value of the received pulse fo a certain time. A bias control circuit 12 controls the bias voltage of a photodetector 5 according to the amplitude value of the received pulse from the circuit 11. When a disturbing light pulse due to a scatter by raindrops and reflected light from a target are distant, separation by a distance-classified limiting function is carried out and when the separation from the scattered light is impossible because the target is too close, an AGC function is put in operation. |
