Distance measuring system and distance measuring method

A rangefinding system comprising:

• a light-emitting device for emitting pulsed light toward an object;
• a light-detecting device for detecting reflected light from the pulsed light, and producing an output signal depending on the energy of reflected light that is detected;
• a control device for controlling the light-emitting device and the light-detecting device;
• and
• an arithmetic device for calculating a distance up to the object according to a time-of-flight process using the output signal from the light-detecting device;
• the light-detecting device further comprising:
• a photodetector for detecting the reflected light and generating photoelectrons by the detected reflected light;
• first through fourth capacitors for storing the photoelectrons from the photodetector;
• a photoelectron discharger for discharging the photoelectrons from the photodetector;
• first through fourth gate electrodes disposed between the photodetector and the first through fourth capacitors, for allotting the photoelectrons with respect to the first through fourth capacitors in synchronism with emission of the pulsed light;
• and
• a fifth gate electrode disposed between the photodetector and the photoelectron discharger, for controlling supply of the photoelectrons from the photodetector and the photoelectron discharger;
• wherein, if it is assumed that a time at which the pulsed light starts to be emitted is referred to as time Teu,
• a time at which the pulsed light stops being emitted is referred to as time Ted,
• a time at which the reflected light stops being exposed to the photodetector is referred to as time Trd,
• respective times at which the first through fourth gate electrodes are opened are referred to as times Tg1u, Tg2u, Tg3u, and Tg4u,
• respective times at which the first through fourth gate electrodes are closed are referred to as times Tg1d, Tg2d, Tg3d, and Tg4d,
• a period from the time Tg1u to the time Tg1d is referred to as period P1,
• a period from the time Tg2u to the time Tg2d is referred to as period P2,
• a period from the time Tg3u to the time Tg3d is referred to as period P3,
• a period from the time Tg4u to the time Tg4d is referred to as period P4,
• a period from the time Tg4d to the time Trd is referred to as period Psr,
• a photoelectron quantity stored in the first capacitor during the period P1 is referred to as photoelectron quantity Q1,
• a photoelectron quantity stored in the second capacitor during the period P2 is referred to as photoelectron quantity Q2,
• a photoelectron quantity stored in the third capacitor during the period P3 is referred to as photoelectron quantity Q3,
• a photoelectron quantity stored in the fourth capacitor during the period P4 is referred to as photoelectron quantity Q4,
• a period during which the pulsed light is emitted, reflected by the object, and returned as the reflected light is referred to as round trip time ΔP, and
• a distance between the rangefinding system and the object is referred to as distance D,
• then the control device controls emission of the pulsed light from the light-emitting device and opening and closing of the first through fourth gate electrodes so as to satisfy the following relationships:
• (1) P1=P3;
• (2) P2=P4;
• and
• (3) Tg1u<Tg1d≦Tg2u<Tg2d≦Teu<Tg3u<Tg3d≦Tg4u≦Ted<Tg4d, or Teu<Tg3u<Tg3d≦Tg4u≦Ted<Tg4d<Tg1u<Tg1d≦Tg2u<Tg2d;
• and
• the control device opens the fifth gate electrode to discharge the photoelectrons when all of the first through fourth gate electrodes are closed;
• the arithmetic device acquires light energy information of the reflected light during the period P3 based on the difference between the photoelectron quantity Q3 stored in the third capacitor corresponding to ambient light and the reflected light, and the photoelectron quantity Q1 stored in the first capacitor corresponding to the ambient light;
• the arithmetic device acquires light energy information of the reflected light during the period Psr based on the difference between the photoelectron quantity Q4 stored in the fourth capacitor corresponding to the ambient light and the reflected light, and the photoelectron quantity Q2 stored in the second capacitor corresponding to the ambient light;
• the arithmetic device calculates the round trip time ΔP based on a ratio of the light energy information of the reflected light during the period P3 and the light energy information of the reflected light during the period Psr, and a ratio of the period P3 and the period Psr;
• and
• the arithmetic device measures the distance D based on the round trip time ΔP.