JP2014169921A - Distance sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the maximum measurable range of a distance sensor 1 without increasing circuit scale.SOLUTION: A capacitor C1 accumulates negative charges transferred from a photodiode 30 upon reception of light by the photodiode 30 during a divided period t1. A capacitor C2 accumulates negative charges transferred from the photodiode 30 upon reception of light by the photodiode 30 during a divided period t3. A capacitor C3 accumulates negative charges transferred from the photodiode 30 upon reception of light by the photodiode 30 during a divided period t5. A capacitor C4 accumulates negative charges transferred from the photodiode 30 upon reception of light by the photodiode 30 during a divided period t7. A distance computation circuit 15 computes a distance d between the distance sensor 1 and a detection target 20 on the basis of the amount of negative charges accumulated in each of the capacitors C1, C2, C3, and C4.

Description

  The present invention relates to a distance sensor that measures a distance to a detected object.

  2. Description of the Related Art Conventionally, a distance sensor includes a light emitting source that emits pulsed light at a constant frequency, and a light receiving element that receives reflected light reflected by a detection object out of the light emitted from the light emitting source. Finds the phase difference φ between the timing of emitting the emitted light from the light and the timing of receiving the reflected light by the light receiving element, and calculates the distance between the distance sensor and the object to be detected by this phase difference φ, frequency, etc. (For example, see Patent Document 1).

JP 2010-32425 A

  The inventor examined the distance sensor of Patent Document 1 in order to increase the maximum measurable distance.

  First, in the measurement circuit, the first, second, third, and fourth divided periods are set by dividing the light emission cycle in which the light source emits the pulsed light into, for example, four equal parts. A first capacitor that stores a negative charge moved from the light receiving element as the light receiving element receives light in the first divided period, and a light receiving element that receives light in the second divided period after the first divided period. Accordingly, a second capacitor for storing a negative charge moved from the light receiving element is provided. A third capacitor for storing a negative charge moved from the light receiving element in response to light reception by the light receiving element in a third divided period after the second divided period, and a fourth divided part after the third divided period A fourth capacitor is provided for storing a negative charge moved from the light receiving element as the light receiving element receives light during the period.

  Further, the measurement circuit obtains negative charge amounts Q1, Q2, Q3, and Q4 accumulated in the first to fourth capacitors, and based on the obtained negative charge amounts Q1, Q2, Q3, and Q4. The phase difference φ is calculated.

  Here, the maximum distance that can be measured by the distance sensor is determined by the light emission period (= 1 / frequency) at which the light source emits the pulsed light. That is, it is necessary that the phase difference φ is shorter than the light emission period, and if the phase difference φ is longer than the light emission period, the distance cannot be detected.

  For example, if the light emission period is lengthened, the first, second, third, and fourth divided periods are lengthened. For this reason, the negative charge accumulated in the first to fourth capacitors overflows, and the amount of negative charge accumulated for each capacitor cannot be detected accurately, and the phase difference φ cannot be calculated.

  Further, if the light emission period is lengthened and the number of divisions for equally dividing the light emission period is increased, it is possible to avoid the negative charge from overflowing in the first to fourth capacitors. However, as the number of divisions increases, the capacitor It is necessary to increase the number of. For this reason, the circuit scale of the measurement circuit increases.

  An object of the present invention is to provide a distance sensor that makes it possible to increase the maximum distance that can be measured while suppressing an increase in circuit scale.

In order to achieve the above object, according to the first aspect of the present invention, a period obtained by adding a light emission period in which light is emitted from the light source (12) and a stop period in which light emission from the light source is stopped is defined as one cycle. A light source control means (11) for controlling the light source so as to periodically and alternately repeat the light emission period and the stop period;
A light receiving element (30) for receiving the reflected light reflected by the detection object out of the light emitted from the light emitting source,
N divided periods obtained by dividing the one period into N (≧ 5) equal parts on the time axis are set,
A first capacitor (C1) for accumulating negative charges moved from the light receiving element in response to light reception by the light receiving element in the first divided period among the N divided periods;
A second capacitor (C2) for accumulating negative charges moved from the light receiving element in response to light reception by the light receiving element in a second divided period after the first divided period among the N divided periods. When,
A third capacitor (C3) for accumulating negative charges moved from the light receiving element in response to light reception by the light receiving element in a third divided period after the second divided period among the N divided periods. When,
A fourth capacitor (C4) that accumulates negative charges moved from the light receiving element in response to light reception by the light receiving element in a fourth divided period after the third divided period among the N divided periods. When,
Distance calculating means (15) for calculating the distance between the distance sensor and the detected object based on the amount of negative charge accumulated in each of the first, second, third and fourth capacitors; It is characterized by providing.

  According to the first aspect of the present invention, it is not necessary to increase the number of capacitors used for accumulating negative charges even if the period is lengthened and the number of divisions for equally dividing one period is increased. For this reason, it is possible to increase the number of divisions while suppressing an increase in circuit scale. Therefore, even if the period is lengthened and the number of divisions is increased, it is possible to prevent the negative charge from overflowing in the first to fourth capacitors while suppressing an increase in circuit scale. Therefore, it is possible to provide a distance sensor that can increase the maximum distance that can be measured while suppressing an increase in circuit scale.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

It is a figure which shows the circuit structure of the distance sensor in 1st Embodiment of this invention. It is a figure which shows the detail of the circuit structure of the pixel of FIG. It is a timing chart which shows operation of a distance sensor in a 1st embodiment. It is a graph for calculating | requiring the angle in 1st Embodiment. It is a graph which shows the relationship between the angle and phase difference in 1st Embodiment. It is a graph which shows the relationship between the angle and phase difference in 1st Embodiment. 6 is a timing chart for obtaining the angle θ in FIG. 5. It is a figure for demonstrating the modification of 1st Embodiment. It is a timing chart which shows the action | operation of the distance sensor in 2nd Embodiment of this invention. It is a timing chart which shows the action | operation of the distance sensor in 3rd Embodiment of this invention. It is a timing chart which shows the action | operation of the distance sensor in 4th Embodiment of this invention. It is a timing chart which shows operation of a distance sensor in a 5th embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are given the same reference numerals in the drawings in order to simplify the description.

(First embodiment)
FIG. 1 shows a configuration of a first embodiment of a distance sensor 1 of the present invention. The distance sensor 1 in FIG. 1 includes an oscillation circuit 10, a light source control circuit 11, a light source 12, a pixel 13, a pixel control circuit 14, and a distance calculation circuit 15.

  The oscillation circuit 10 outputs an oscillation signal that oscillates at a constant frequency and changes the amplitude at a constant frequency. The light emission source control circuit 11 controls the light emission source 12 based on the oscillation signal output from the oscillation circuit 10. The light emission source 12 is a source that emits light to the detection target 20. As the light source 12 of this embodiment, a laser diode (LD) and a light emitting diode (LED) are used.

  The pixel 13 receives reflected light reflected by the detection target 20 out of the emitted light emitted from the light emitting source 12 by the light receiving diode 30 (see FIG. 2), and according to the amount of reflected light received by the light receiving diode 30. The negative charges are accumulated in the capacitors C1, C2, C3 and C4. The details of the circuit configuration of the pixel 13 will be described later.

  The pixel control circuit 14 controls the pixel 13 based on the oscillation signal output from the oscillation circuit 10. The distance calculation circuit 15 calculates the distance between the distance sensor 1 and the detection target 20 based on the output voltage of the pixel 13.

  Next, the circuit configuration of the pixel 13 of the present embodiment will be described with reference to FIG. FIG. 2 is a circuit diagram showing details of the circuit configuration of the pixel 13.

  The pixel 13 includes a light receiving diode 30 and power storage circuits 31, 32, 33, and 34.

  The light receiving diode 30 and the reset transistor 35 are connected in series between the power supply VB and the ground. The light receiving diode 30 is disposed on the ground side. The reset transistor 35 is disposed on the power supply VB side. The reset transistor 35 is used to reset the amount of negative charge accumulated in the capacitors C1 to C4.

  The storage circuit 31 includes a capacitor C1, a transfer transistor 40a, an amplification transistor 41a, and a selection transistor 42a.

  The capacitor C1 and the transfer transistor 40a are connected in series between the common connection terminal 50 and the ground. The common connection terminal 50 is a common connection terminal between the light receiving diode 30 and the reset transistor 35. The capacitor C1 is disposed on the ground side. The transfer transistor 40a is disposed on the common connection terminal 50 side.

  The amplification transistor 41 a and the selection transistor 42 a are connected in series between the power supply VB and the distance calculation circuit 15. The amplification transistor 41a is arranged on the power supply VB side. The selection transistor 42a is disposed on the distance calculation circuit 15 side. The amplification transistor 41a operates in accordance with the output voltage of the common connection terminal 51a between the capacitor C1 and the transfer transistor 40a. The selection transistor 42a is controlled by the distance calculation circuit 15 to be turned on / off.

  The storage circuit 32 includes a capacitor C2, a transfer transistor 40b, an amplification transistor 41b, and a selection transistor 42b.

  The capacitor C2 and the transfer transistor 40b are directly connected between the common connection terminal 50 and the ground. The capacitor C2 is disposed on the ground side. The transfer transistor 40b is disposed on the common connection terminal 50 side.

  The amplification transistor 41b and the selection transistor 42b are connected in series between the power supply VB and the distance calculation circuit 15. The amplification transistor 41b is arranged on the power supply VB side. The selection transistor 42b is disposed on the distance calculation circuit 15 side. The amplification transistor 41b operates in accordance with the output voltage of the common connection terminal 51b between the capacitor C2 and the transfer transistor 40b. The selection transistor 42b is controlled by the distance calculation circuit 15 to be turned on / off.

  The storage circuit 33 includes a capacitor C3, a transfer transistor 40c, an amplification transistor 41c, and a selection transistor 42c.

  The capacitor C3 and the transfer transistor 40c are connected in series between the common connection terminal 50 and the ground. The capacitor C3 is disposed on the ground side. The transfer transistor 40c is disposed on the common connection terminal 50 side.

  The amplification transistor 41 c and the selection transistor 42 c are connected in series between the power supply VB and the distance calculation circuit 15. The amplification transistor 41c is disposed on the power supply VB side. The selection transistor 42c is disposed on the distance calculation circuit 15 side. The amplification transistor 41c operates according to the output voltage of the common connection terminal 51c between the capacitor C3 and the transfer transistor 40c. The selection transistor 42c is controlled by the distance calculation circuit 15 to be turned on / off.

  The storage circuit 34 includes a capacitor C4, a transfer transistor 40d, an amplification transistor 41d, and a selection transistor 42d.

  The capacitor C4 and the transfer transistor 40d are connected in series between the common connection terminal 50 and the ground. The capacitor C4 is disposed on the ground side. The transfer transistor 40d is disposed on the common connection terminal 50 side.

  The amplification transistor 41d and the selection transistor 42d are connected in series between the power supply VB and the distance calculation circuit 15. The amplification transistor 41d is disposed on the power supply VB side. The selection transistor 42d is disposed on the distance calculation circuit 15 side. The amplification transistor 41d operates in accordance with the output voltage of the common connection terminal 51d between the capacitor C4 and the transfer transistor 40d. The selection transistor 42d is controlled by the distance calculation circuit 15 to be turned on / off.

  In the present embodiment, the reset transistor 35, the transfer transistors 40a, 40b, 40c, and 40d, the amplification transistors 41a, 41b, 41c, and 41d, and the selection transistors 42a, 42b, 42c, and 42d are each configured by an nMOS transistor.

  The transfer transistor 40a corresponds to the first switch, the transfer transistor 40b corresponds to the second switch, and the transfer transistor 40c corresponds to the third switch. The transfer transistor 40d corresponds to the fourth switch. The reset transistor 35 corresponds to the fifth switch.

  Next, the operation of the distance sensor 1 of the present embodiment will be described with reference to FIG. FIGS. 3A, 3B, 3C, 3D, 3E, and 3F are timing charts. (A) shows the timing when the emitted light is emitted from the light emitting source 12, and (b) shows the timing when the reflected light is received by the light receiving diode 30. (C) shows the timing when the transfer transistor 40a (transfer TR40a in the figure) is turned on (ON), and (d) shows the timing when the transfer transistor 40b (transfer TR40b in the figure) is turned on (ON). (E) shows the timing when the transfer transistor 40c (transfer TR40c in the figure) is turned on (ON), and (f) shows the timing when the transfer transistor 40d (transfer TR40d in the figure) is turned on (ON).

  The light source control circuit 11 controls the light source 12 to blink at a constant period. Specifically, the light source control circuit 11 sets the light emission period ta for emitting light from the light source 12 to a certain time (for example, 75 nsec), and sets the stop period tb for stopping light emission from the light source 12 to a certain time ( For example, 125 nsec). Then, the light emission source control circuit 11 periodically alternates the light emission period ta and the stop period tb with the light emission period T (= ta + tb) as a fixed period (for example, 200 nsec) obtained by adding the light emission period ta and the stop period tb. The light emission source 12 is controlled to blink so as to repeat. Such blinking control of the light source 12 is repeated by the light source control circuit 11 over M cycles (M is an integer of 2 or more).

  For this reason, a part of the reflected light reflected by the detection target 20 out of the emitted light emitted from the light emission source 12 for each light emission period ta is received by the pixel 13. A symbol ts in FIG. 3 indicates a light reception period in which reflected light is received by the pixel 13.

  In the present embodiment, eight divided periods (t1, t2, t3, t4, t5, t6, t7, t8) are set by dividing the light emission cycle T into 8 (= N ≧ 5) equally on the time axis. ing.

  First, the pixel control circuit 14 controls the pixel 13 to store the negative charge transferred from the light receiving diode 30 in response to the light reception of the light receiving diode 30 in the first divided period t1 among the divided periods t1 to t8. It accumulates in 31 capacitors C1.

  Specifically, the pixel control circuit 14 turns on the transfer transistor 40a and turns off the reset transistor 35, the transfer transistors 40b, 40c, and 40d, and the selection transistors 42a, 42b, 42c, and 42d in the divided period t1. To do. For this reason, the negative charge moved from the light receiving diode 30 as the light receiving diode 30 receives light is accumulated in the capacitor C1 through the transfer transistor 40a.

  Next, in the divided period t2, the pixel control circuit 14 turns on the reset transistor 35, and turns off the transfer transistors 40a, 40b, 40c, and 40d and the selection transistors 42a, 42b, 42c, and 42d. Therefore, in the divided period t2, the negative charge moved from the light receiving diode 30 as the light is received by the light receiving diode 30 is discarded to the power source VB through the reset transistor 35 while maintaining the amount of charge accumulated in the capacitor C1.

  Next, in the division period t3, the pixel control circuit 14 turns on the transfer transistor 40b and turns off the reset transistor 35, the transfer transistors 40a, 40c, and 40d, and the selection transistors 42a, 42b, 42c, and 42d. For this reason, the negative charge moved from the light receiving diode 30 as the light receiving diode 30 receives light is accumulated in the capacitor C2 through the transfer transistor 40b.

  Next, in the divided period t4, the pixel control circuit 14 turns on the reset transistor 35, and turns off the transfer transistors 40a, 40b, 40c, and 40d and the selection transistors 42a, 42b, 42c, and 42d. Therefore, in the divided period t4, the negative charge transferred from the light receiving diode 30 with the light reception of the light receiving diode 30 is discarded to the power source VB through the reset transistor 35 while maintaining the charge amount accumulated in the capacitors C1 and C2. The

  Next, in the division period t5, the pixel control circuit 14 turns on the transfer transistor 40c and turns off the reset transistor 35, the transfer transistors 40a, 40b, and 40d, and the selection transistors 42a, 42b, 42c, and 42d. For this reason, the negative charge moved from the light receiving diode 30 as the light receiving diode 30 receives light is accumulated in the capacitor C3 through the transfer transistor 40c.

  Next, in the divided period t6, the pixel control circuit 14 turns on the reset transistor 35 and turns off the transfer transistors 40a, 40b, 40c, and 40d and the selection transistors 42a, 42b, 42c, and 42d. Therefore, in the divided period t6, while maintaining the amount of charge accumulated in the capacitors C1, C2, and C3, the negative charge moved from the light receiving diode 30 as the light is received by the light receiving diode 30 is transferred to the power source VB through the reset transistor 35. Discarded.

  Next, in the divided period t7, the pixel control circuit 14 turns on the transfer transistor 40d, and turns off the reset transistor 35, the transfer transistors 40a, 40b, and 40c, and the selection transistors 42a, 42b, 42c, and 42d. For this reason, the negative charge moved from the light receiving diode 30 as the light receiving diode 30 receives light is accumulated in the capacitor C4 through the transfer transistor 40d.

  Next, in the divided period t8, the pixel control circuit 14 turns on the reset transistor 35 and turns off the transfer transistors 40a, 40b, 40c, and 40d and the selection transistors 42a, 42b, 42c, and 42d. Therefore, in the divided period t8, while maintaining the amount of charge accumulated in the capacitors C1 to C4, the negative charge moved from the light receiving diode 30 as the light is received by the light receiving diode 30 is discarded to the power source VB through the reset transistor 35. The

  As described above, the pixel control circuit 14 repeatedly performs an operation including accumulation of negative charges in the capacitors C1 to C4 and discarding the negative charges to the power source VB over M cycles.

  In the divided period t1, the capacitor C1 accumulates the negative charge moved from the light receiving diode 30 with the light reception of the light receiving diode 30 every cycle. In the divided period t3, the capacitor C2 accumulates negative charges that are moved from the light receiving diode 30 in response to light reception by the light receiving diode 30 every cycle. In the divided period t5, the capacitor C3 accumulates the negative charge moved from the light receiving diode 30 with the light reception of the light receiving diode 30 every cycle. In the divided period t7, the capacitor C4 accumulates the negative charge moved from the light receiving diode 30 with the light reception of the light receiving diode 30 every cycle. In the divided periods t2, t4, t6, and t8, the negative charges moved from the light receiving diode 30 as the light receiving diode 30 receives light are discarded by the power supply VB every cycle.

  Thereafter, the pixel control circuit 14 turns off the reset transistor 35, the transfer transistors 40a, 40b, 40c, and 40d, and the selection transistors 42b, 42c, and 42d, and turns on the selection transistor 42a.

  The amplification transistor 41a outputs a current from the power supply VB to the distance calculation circuit 15 through the selection transistor 42a according to the output voltage of the common connection terminal 51a.

  The output voltage of the common connection terminal 51a decreases as the amount of negative charge accumulated in the capacitor C1 increases. For this reason, the larger the amount of negative charge stored in the capacitor C1, the smaller the current flowing from the power source VB to the distance calculation circuit 15 through the amplification transistor 41a and the selection transistor 42a. Thus, the distance calculation circuit 15 can detect the negative charge amount Q1 accumulated in the capacitor C1 by the current flowing from the power supply VB through the amplification transistor 41a and the selection transistor 42a.

  Next, the pixel control circuit 14 turns off the reset transistor 35, the transfer transistors 40a, 40b, 40c, and 40d, and the selection transistors 42a, 42c, and 42d, and turns on the selection transistor 42b. The amplification transistor 41b outputs a current from the power supply VB to the distance calculation circuit 15 through the selection transistor 42b according to the output voltage of the common connection terminal 51b.

  The output voltage of the common connection terminal 51b decreases as the amount of negative charge accumulated in the capacitor C2 increases. For this reason, as the amount of negative charge stored in the capacitor C2 increases, the current flowing from the power source VB to the distance calculation circuit 15 through the amplification transistor 41b and the selection transistor 42b decreases. Thus, the distance calculation circuit 15 can detect the negative charge amount Q2 accumulated in the capacitor C2 by the current flowing from the power supply VB through the amplification transistor 41b and the selection transistor 42b.

  Next, the pixel control circuit 14 turns off the reset transistor 35, the transfer transistors 40a, 40b, 40c, and 40d, and the selection transistors 42a, 42b, and 42d, and turns on the selection transistor 42c. The amplification transistor 41c outputs a current from the power supply VB to the distance calculation circuit 15 through the selection transistor 42c according to the output voltage of the common connection terminal 51c.

  The output voltage of the common connection terminal 51c decreases as the amount of negative charge accumulated in the capacitor C3 increases. For this reason, as the amount of negative charge stored in the capacitor C3 increases, the current flowing from the power source VB to the distance calculation circuit 15 through the amplification transistor 41c and the selection transistor 42c decreases. Thus, the distance calculation circuit 15 can detect the negative charge amount Q3 accumulated in the capacitor C3 by the current flowing from the power source VB through the amplification transistor 41c and the selection transistor 42c.

  Next, the pixel control circuit 14 turns off the reset transistor 35, the transfer transistors 40a, 40b, 40c, and 40d, and the selection transistors 42a, 42b, and 42c, and turns on the selection transistor 42d. The amplification transistor 41d outputs a current from the power supply VB to the distance calculation circuit 15 through the selection transistor 42d according to the output voltage of the common connection terminal 51c.

  The output voltage of the common connection terminal 51d decreases as the amount of negative charge accumulated in the capacitor C4 increases. For this reason, the larger the amount of negative charge stored in the capacitor C4, the smaller the current flowing from the power supply VB to the distance calculation circuit 15 through the amplification transistor 41d and the selection transistor 42d. Thus, the distance calculation circuit 15 can detect the negative charge amount Q4 accumulated in the capacitor C4 by the current flowing from the power supply VB through the amplification transistor 41d and the selection transistor 42d.

  Thereafter, the pixel control circuit 14 turns on the reset transistor 35 and the transfer transistors 40a, 40b, 40c, and 40d, respectively.

  At this time, the light receiving diode 30 and the power supply VB are connected through the reset transistor 35. As a result, the potential of the light receiving diode 30 is reset.

  In addition, the capacitor C1 and the power supply VB are connected through the reset transistor 35 and the transfer transistor 40a. The capacitor C2 and the power supply VB are connected through the reset transistor 35 and the transfer transistor 40b. The capacitor C3 and the power supply VB are connected through the reset transistor 35 and the transfer transistor 40c. The capacitor C4 and the power supply VB are connected through the reset transistor 35 and the transfer transistor 40d. As a result, the potentials of the capacitors C1, C2, C3, and C4 are reset.

  Further, as described above, the distance calculation circuit 15 detects the negative charge amounts Q1, Q2, Q3, and Q4 accumulated in the capacitors C1, C2, C3, and C4. Then, the distance calculation circuit 15, as described below, based on the negative charge amounts Q 1, Q 2, Q 3, and Q 4, the timing when the emitted light is emitted from the light source 12 and the timing when the reflected light is received by the light receiving diode 30. Is obtained, and the distance between the distance sensor 1 and the detected object 20 is calculated from the phase difference φ.

  Specifically, the distance calculation circuit 15 calculates the angle θ by substituting the negative charge amounts Q1, Q2, Q3, and Q4 into the following formula 1.

なお、（Ｑ１−Ｑ３）を縦軸（第１の軸）とし、（Ｑ２−Ｑ４）を横軸（第２の軸）とする図４の直交座標上において、グラフＧ１が（Ｑ１−Ｑ３）および（Ｑ２−Ｑ４）の関係を示している。上述の如く検出される負電荷量Ｑ１、Ｑ２、Ｑ３、Ｑ４から規定される点Ａをプロットし、直交座標の原点０とＡ点とを結ぶ線分を線分Ｓ１とする、この線分Ｓ１と横軸とが成す角度が角度θとなる。

Note that the graph G1 is (Q1-Q3) on the orthogonal coordinates of FIG. 4 where (Q1-Q3) is the vertical axis (first axis) and (Q2-Q4) is the horizontal axis (second axis). And the relationship of (Q2-Q4) is shown. The point A defined from the negative charge amounts Q1, Q2, Q3, and Q4 detected as described above is plotted, and the line segment connecting the origin 0 and the point A of the orthogonal coordinates is defined as a line segment S1. Is the angle θ.

  The relationship between the angle θ and the phase difference φ thus obtained is as shown by graphs G2a, G2b, and G2c in FIG. Graphs G2a, G2b, and G2c are graphs in which the vertical axis represents the angle θ and the horizontal axis represents the phase difference φ.

  Therefore, in this embodiment, one graph is selected from the graphs G2a, G2b, and G2c according to the negative charge amounts Q1, Q2, Q3, and Q4.

  When −45 ≦ θ ≦ 90 and Q2> Q4, the graph G2a is selected. When −90 ≦ θ ≦ 90 and Q2 <Q4, the graph G2b is selected. When −90 ≦ θ ≦ −45 and Q2> Q4, the graph G2c is selected.

  The phase difference φ is obtained from the graph thus selected and the angle θ. Accordingly, the distance d is obtained by substituting the phase difference φ and the modulation frequency fm into the equation (2).

ここで、ｃは光の速度であり、ｆｍは変調周波数である。ｆｍは、（１／Ｔ）で表される周波数であって、発光源１２の発光期間ｔａおよび停止期間ｔｂを繰り返す周波数を規定している。

Here, c is the speed of light, and fm is the modulation frequency. fm is a frequency represented by (1 / T), and defines a frequency at which the light emission source 12 repeats the light emission period ta and the stop period tb.

  According to the present embodiment described above, the light emission source control circuit 11 uses the period obtained by adding the light emission period ta and the stop period tb as one light emission period T, and the light emission period ta and the stop period tb are alternately alternated periodically. The light emission source 12 is controlled to blink so as to be repeated. The light receiving diode 30 receives the reflected light reflected by the detected object 20 out of the light emitted from the light emitting source 12. Divided periods t1 to t8 in which one light emission period T is divided into eight equal parts on the time axis are set.

  The capacitor C1 accumulates negative charges that are moved from the light receiving diode 30 as the light receiving diode 30 receives light in the divided period t1 of the divided periods t1 to t8. The capacitor C2 accumulates negative charges that are moved from the light receiving diode 30 as the light receiving diode 30 receives light in the divided period t3 of the divided periods t1 to t8. The capacitor C3 accumulates negative charges that are moved from the light receiving diode 30 as the light receiving diode 30 receives light in the divided period t5 in the divided periods t1 to t8. The capacitor C4 accumulates negative charges that are moved from the light receiving diode 30 as the light receiving diode 30 receives light in the divided period t7 of the divided periods t1 to t8. The distance calculation circuit 15 calculates the distance d between the distance sensor 1 and the detection target 20 based on the negative charge amount accumulated in each of the capacitors C1, C2, C3, and C4.

  As described above, the number of capacitors (C1 to C4) used for accumulating negative charges remains four even if the light emission period T is lengthened and the division number N (= 8) for equally dividing the light emission period T is increased. It is constant. For this reason, it is possible to increase the number of divisions while suppressing an increase in circuit scale. Therefore, even if the light emission period T is increased and the number of divisions N is increased, it is possible to prevent the negative charges from overflowing in the capacitors (C1 to C4) while suppressing an increase in circuit scale. Therefore, it is possible to provide the distance sensor 1 that makes it possible to increase the maximum distance that can be measured while suppressing an increase in circuit scale.

  In the first embodiment, the example in which the phase difference φ is calculated using the graph of FIG. 4 and the graph of FIG. 5 has been described, but instead of this, the graph G3 of FIG. The phase difference φ is calculated using the flowchart of FIG.

  The graph G3 shows a relationship in which the angle θ and the phase difference φ are specified on a one-to-one basis. The graph G3 is obtained by converting the graphs G2a, G2b, and G2c in FIG. 5 according to the magnitude relationship between the negative charge amounts Q1, Q2, Q3, and Q4. The flowchart of FIG. 7 shows a process for obtaining the angle θ used in the graph G3.

  First, in step S100 in FIG. 7, (Q1-Q3) and (Q2-Q4) are substituted into the equation 1 to obtain the angle θ.

  When the negative charge amount Q2 is greater than or equal to the negative charge amount Q4 (Q2 ≧ Q4), YES is determined in step S110. In this case, an angle (θ + 45) obtained by adding 45 degrees to the angle θ is set as the angle θ (step S120).

  Here, when the angle θ (= θ + 45) is larger than zero, the phase difference φ is obtained using the angle θ obtained in step S120 and the graph G3 in FIG.

  When the angle θ (= θ + 45) is smaller than zero, an angle (θ + 360) obtained by adding 360 degrees to the angle θ obtained in step S100 is set as an angle θ (= θ + 360) (step S140). The phase difference φ is obtained using this angle θ (= θ + 360) and the graph G3 in FIG.

  When the negative charge amount Q2 is less than the negative charge amount Q4 (Q2 <Q4), NO is determined in step S110. In this case, an angle (θ + 225) obtained by adding 225 degrees to the angle θ is set as the angle θ (step S121).

  Here, when the angle θ (= θ + 45) is larger than zero, the phase difference φ is obtained using the angle θ obtained in step S121 and the graph G3 in FIG.

  When the angle θ (= θ + 225) is smaller than zero, an angle (θ + 360) obtained by adding 360 degrees to the angle θ obtained in step S100 is set as the angle θ (step S140). The phase difference φ is obtained using this angle θ (= θ + 360) and the graph G3 in FIG.

  Thus, the phase difference φ can be obtained based on the negative charge amounts Q1, Q2, Q3, and Q4.

  In the first embodiment, negative charge is accumulated in the capacitor C1 in the divided period t1, negative charge is accumulated in the capacitor C2 in the divided period t3, and negative charge is accumulated in the capacitor C3 in the divided period t5. Although an example in which negative charge is accumulated in the capacitor C4 during the period t7 has been described, the following may be performed.

  That is, when the condition of the next light emission period (light emission pulse width) ta is satisfied, if the division number N for dividing the light emission period is 5 or more (N ≧ 5), it may be other than 8, and the capacitor C1 , C2, C3, and C4 are not limited to the divided periods (t1, t3, t5, and t7) described above.

  Hereinafter, the conditions of the light emission period ta will be described with reference to FIG. The conditions of the light emission period ta are expressed by the following formulas 1 to 8. For this reason, when Formula 1-Formula 8 are materialized, the conditions of the light emission period ta are materialized. That is, if Equations 1 to 8 are established, the angle θ is obtained by substituting the negative charge amounts Q1, Q2, Q3, and Q4 into the equation 1 above, and the phase difference φ is obtained from the obtained angle θ. Further, the distance d can be obtained by substituting the phase difference φ into the equation (2). Hereinafter, it is assumed that N division periods are set by equally dividing the light emission period T into N pieces.

  In FIG. 8, an exposure period S1 is a divided period in which negative charges are accumulated in the capacitor C1 among N divided periods. The exposure period S2 is a divided period in which negative charges are accumulated in the capacitor C2 among the N divided periods. The exposure period S3 is a divided period in which negative charges are accumulated in the capacitor C3 among the N divided periods. The exposure period S4 is a divided period in which negative charges are accumulated in the capacitor C4 among the N divided periods.

Light emission period ta ≧ (start time S3a of exposure period S3−end time S1b of exposure period S1)
Light emission period ta ≧ (start time S4a of exposure period S4−end time S2b of exposure period S2)
Light emission period ta ≧ (start time S1a of exposure period S1−end time S3b of exposure period S3)
Light emission period ta ≧ (start time S2a of exposure period S2−end time S4b of exposure period S4) Expression 4
Light emission period ta ≦ (End time S3b of exposure period S3−Start time S1a of exposure period S1) Equation 5
Light emission period ta ≦ (End time S4b of exposure period S4−Start time S2a of exposure period S2) Equation 6
Light emission period ta ≦ (end time S1b of exposure period S1−start time S3a of exposure period S3) Equation 7
Light emission period ta ≦ (end time S2b of exposure period S2−start time S4a of exposure period S4) Expression 8
Here, (the start time S3a of the exposure period S3−the end time S1b of the exposure period S1) in Expression 1 is within the start time S3a of the exposure period S3 within the Lth light emission period T and within the Lth light emission period T. The period between the exposure time S1 and the end time S1b is shown. L is an integer satisfying 1 <L ≦ M.

  In Expression 2, (the start time S4a of the exposure period S4−the end time S2b of the exposure period S2) is the start time S4a of the exposure period S4 within the Lth light emission period T and the exposure period within the Lth light emission period T. The period between the end time S2b of S2 is shown.

  In Expression 3, (the start time S1a of the exposure period S1−the end time S3b of the exposure period S3) is the start time S1a of the exposure period S1 within the (L + 1) th light emission period T and the light emission period T within the Lth light emission period T. The period between the exposure time S3 and the end time S3b is shown.

  In Expression 4, (the start time S2a of the exposure period S2−the end time S4b of the exposure period S4) is equal to the start time S2a of the exposure period S2 within the (L + 1) th light emission period T and the light emission period T within the Lth light emission period T. The period between the exposure time S4 and the end time S4b is shown.

  In Expression 5, (end time S3b of exposure period S3−start time S1a of exposure period S1) is the end time S3b of the exposure period S3 within the Lth light emission period T and the exposure period within the Lth light emission period T. The period between the start time S1a of S1 is shown.

In Expression 6, (end time S4b of exposure period S4−start time S2a of exposure period S2)
Indicates a period between the end time S4b of the exposure period S4 within the (L + 1) th light emission cycle T and the start time S2a of the exposure period S2 within the (L + 1) th light emission cycle T.

  In Expression 7, (end time S1b of the exposure period S1−start time S3a of the exposure period S3) is equal to the end time S1b of the exposure period S1 within the (L + 1) th light emission period T and within the Lth light emission period T. The period between the start time S3a of the exposure period S3 is shown.

  In Expression 8, (the end time S2b of the exposure period S2−the start time S4a of the exposure period S4) is the end time S2b of the exposure period S2 within the (L + 1) th light emission period T and the light emission period T within the Lth light emission period T. The period between the start time S4a of the exposure period S4 is shown.

  The start time S3a is the time when the exposure period S3 is started. The end time S1b is the time when the exposure period S1 ends. The start time S4a is the time when the exposure period S4 starts. The end time S2b is the time when the exposure period S2 ends.

  The start time S2a is the time when the exposure period S2 starts. The end time S4b is the time when the exposure period S4 ends. The start time S2a is the time when the exposure period S2 starts. The end time S4b is the time when the exposure period S4 ends. The start time S3a is the time when the exposure period S3 starts. The end time S1b is the time when the exposure period S1 ends. The end time S2b is the time when the exposure period S2 ends. The start time S4a is the time when the exposure period S4 starts.

(Second Embodiment)
In the first embodiment, the capacitor C1 accumulates negative charges in the divided period t1, the capacitor C2 accumulates negative charges in the divided period t3, and the capacitor C3 accumulates negative charges in the divided period t5. Although the example in which the capacitor C4 stores negative charges in the period t7 has been described, instead of this, in the second embodiment, as shown in FIG. 9, the capacitors C1 to C4 are as follows. Accumulate negative charge.

  In the present embodiment, the light emission source control circuit 11 sets the light emission period ta and the stop period tb to the same time (for example, 100 nsec). Further, eight divided periods (t1, t2, t3, t4, t5, t6, t7, t8) are set by dividing the light emission period T into 8 (= N ≧ 5) equally on the time axis.

  In the divided period t1, the capacitor C1 accumulates negative charges moved from the light receiving diode 30 as the light receiving diode 30 receives light. In the divided period t3, the capacitor C2 accumulates negative charges moved from the light receiving diode 30 as the light receiving diode 30 receives light. In the divided period t6, the capacitor C3 accumulates negative charges that are moved from the light receiving diode 30 as the light receiving diode 30 receives light. In the divided period t8, the capacitor C4 accumulates negative charges moved from the light receiving diode 30 as the light receiving diode 30 receives light. Then, in the divided periods t2, t3, t4, t5, and t7, the negative charge moved from the light receiving diode 30 as the light receiving diode 30 receives light is discarded to the power supply VB.

  In this way, the negative charge amounts Q1, Q2, Q3, and Q4 are accumulated in the capacitors C1, C2, C3, and C4.

  Accordingly, the distance calculation circuit 15 detects the negative charge amounts Q1, Q2, Q3, and Q4. Further, the distance calculation circuit 15 obtains an angle θ by substituting the negative charge amounts Q1, Q2, Q3, and Q4 into the equation 1 as in the first embodiment, and calculates a phase difference based on the angle θ. φ is obtained, and the distance d is calculated by substituting this phase difference φ into the above equation (2). Therefore, as in the first embodiment, it is possible to provide the distance sensor 1 that makes it possible to increase the maximum distance that can be measured while suppressing an increase in circuit scale.

(Third embodiment)
In the first embodiment, the example in which the light emission period T is divided into eight and eight division periods are set has been described. Instead, in the third embodiment, the light emission period T is divided into six. An example in which six division periods are set will be described with reference to FIG.

  As shown in FIG. 10, the light emission period T of the present embodiment is a period in which the light emission period ta and the stop period tb are in a ratio of 1: 1. As the light emission period T, division periods t1 to t6 divided into six equal parts are set. For example, 75 nsec is set as the light emission period ta and the stop period tb in the present embodiment, respectively.

  In the divided period t1, the capacitor C1 accumulates negative charges moved from the light receiving diode 30 as the light receiving diode 30 receives light. In the divided period t2, the capacitor C2 accumulates negative charges moved from the light receiving diode 30 as the light receiving diode 30 receives light. In the divided period t3, the capacitor C3 accumulates the negative charge moved from the light receiving diode 30 as the light receiving diode 30 receives light. In the divided period t4, the capacitor C4 accumulates negative charges moved from the light receiving diode 30 as the light receiving diode 30 receives light. Then, in the divided periods t5 and t6, the negative charge moved from the light receiving diode 30 as the light receiving diode 30 receives light is discarded to the power supply VB.

  In this way, the negative charge amounts Q1, Q2, Q3, and Q4 are accumulated in the capacitors C1, C2, C3, and C4. Further, the distance calculation circuit 15 detects the negative charge amounts Q1, Q2, Q3, and Q4 as in the first embodiment, and the detected negative charge amounts Q1, Q2, Q3, and Q4 are expressed by the above equation (1). To obtain the angle θ. Then, the phase difference φ is obtained based on the angle θ, and the distance d is calculated by substituting the phase difference φ into the above formula 2. Therefore, as in the first embodiment, it is possible to provide the distance sensor 1 that makes it possible to increase the maximum distance that can be measured while suppressing an increase in circuit scale.

(Fourth embodiment)
In the first embodiment, the example in which the light emission period T is equally divided into eight to provide eight divided periods has been described. Instead, in the fourth embodiment, the light emission period T is equally divided into five. An example in which five division periods are set will be described with reference to FIG.

  In the present embodiment, as shown in FIG. 11, the light emission period ta and the stop period tb are set so that the light emission period ta is 2 and the stop period tb is 3. As the light emission period T, division periods t1 to t5 divided into five equal parts are set.

  In the divided period t1, the capacitor C1 accumulates negative charges moved from the light receiving diode 30 as the light receiving diode 30 receives light. In the divided period t2, the capacitor C2 accumulates negative charges moved from the light receiving diode 30 as the light receiving diode 30 receives light. In the divided period t3, the capacitor C3 accumulates the negative charge moved from the light receiving diode 30 as the light receiving diode 30 receives light. In the divided period t4, the capacitor C4 accumulates negative charges moved from the light receiving diode 30 as the light receiving diode 30 receives light. Then, in the divided period t5, the negative charge moved from the light receiving diode 30 as the light receiving diode 30 receives light is discarded to the power supply VB.

  In this way, the negative charge amounts Q1, Q2, Q3, and Q4 are accumulated in the capacitors C1, C2, C3, and C4.

  Further, the distance calculation circuit 15 detects the negative charge amounts Q1, Q2, Q3, and Q4 as in the first embodiment, and the detected negative charge amounts Q1, Q2, Q3, and Q4 are expressed by the above equation (1). To obtain the angle θ. Then, the phase difference φ is obtained based on the angle θ, and the distance d is calculated by substituting the phase difference φ into the above formula 2. Therefore, the same effect as the first embodiment can be obtained.

  In FIG. 11, S1 is a divided period in which the capacitor C1 accumulates negative charges. S2 is a divided period in which the capacitor C2 accumulates negative charges. S3 is a divided period in which the capacitor C3 accumulates negative charges. S4 is a divided period in which the capacitor C4 accumulates negative charges.

(Fifth embodiment)
In the fourth embodiment, the example in which the light emission period ta and the stop period tb are set so that the light emission period ta is 2 and the stop period tb is 3 has been described. In the embodiment, as shown in FIG. 12, the light emission period ta and the stop period tb may be set so that the light emission period ta is 3 and the stop period tb is 2. As the light emission period T, division periods t1 to t5 divided into five equal parts are set. In the present embodiment, except for the ratio between the light emission period ta and the stop period tb, it is the same as that of the fourth embodiment, and the description thereof is omitted.

  In FIG. 12, S1 is a divided period in which the capacitor C1 accumulates negative charges. S2 is a divided period in which the capacitor C2 accumulates negative charges. S3 is a divided period in which the capacitor C3 accumulates negative charges. S4 is a divided period in which the capacitor C4 accumulates negative charges.

(Other embodiments)
In the first to fifth embodiments, the example in which the negative charges moved from the light receiving diode 30 over a plurality of cycles are accumulated in the capacitors C1 to C4 has been described. Instead, the negative charge is moved from the light receiving diode 30. The negative charge is accumulated in the capacitors C1 to C4 for one cycle, and the distance between the distance sensor 1 and the detection target 20 is determined based on the negative charge amounts Q1, Q2, Q3, and Q4 accumulated in the capacitors C1 to C4. You may ask for it.

  In the first to fifth embodiments, the example in which the distance calculation circuit 15 detects the negative charge amounts Q1, Q2, Q3, and Q4 by time division for each capacitor has been described. The negative charge amounts Q1, Q2, Q3, and Q4 may be detected in parallel for each capacitor.

  In the first to fifth embodiments, the example in which the nMOS transistor is used as the reset transistor 35 and the transfer transistors 40a, 40b, 40c, and 40d has been described. Instead, the reset transistor 35 and the transfer transistors 40a, 40b are used. 40c and 40d may be semiconductor switching elements such as pMOS transistors and bipolar transistors other than nMOS transistors.

  Similarly, semiconductor switching elements such as pMOS transistors and bipolar transistors other than nMOS transistors may be used as the amplification transistors 41a, 41b, 41c, and 41d and the selection transistors 42a, 42b, 42c, and 42d.

  The present invention is not limited to the first to fifth embodiments described above, and can be appropriately changed within the scope described in the claims. In the first to fifth embodiments, when numerical values such as the number of components of the embodiment are mentioned, it is particularly limited to a specific number when clearly indicated as essential and in principle. Except in some cases, the number is not limited.

DESCRIPTION OF SYMBOLS 1 Distance sensor 10 Oscillation circuit 11 Light source control circuit (light source control means)
12 light source 13 pixel 14 pixel control circuit (first to fifth control means)
15 Distance calculation circuit (distance calculation means)
30 Light-receiving diode (light-receiving element)
C1, C2, C3, C4 capacitors (first to fourth capacitors)
35 Reset transistor (5th transistor)

Claims (8)

The light emission period and the stop period are alternately repeated periodically with a period obtained by adding a light emission period for emitting light from the light emission source (12) and a stop period for stopping emission of light from the light emission source as one period. A light source control means (11) for controlling the light source;
A light receiving element (30) for receiving the reflected light reflected by the detection object out of the light emitted from the light emitting source,
N divided periods obtained by dividing the one period into N (≧ 5) equal parts on the time axis are set,
A first capacitor (C1) for accumulating negative charges moved from the light receiving element in response to light reception by the light receiving element in the first divided period among the N divided periods;
A second capacitor (C2) for accumulating negative charges moved from the light receiving element in response to light reception by the light receiving element in a second divided period after the first divided period among the N divided periods. When,
A third capacitor (C3) for accumulating negative charges moved from the light receiving element in response to light reception by the light receiving element in a third divided period after the second divided period among the N divided periods. When,
A fourth capacitor (C4) that accumulates negative charges moved from the light receiving element in response to light reception by the light receiving element in a fourth divided period after the third divided period among the N divided periods. When,
Distance calculating means (15) for calculating the distance between the distance sensor and the detected object based on the amount of negative charge accumulated in each of the first, second, third and fourth capacitors; A distance sensor comprising: Each time length of the light emission period and the stop period is set at a ratio of 5 when the light emission period is 3;
Eight division periods are set by dividing the one period into eight equal parts,
Of the eight divided periods, the first divided period is the first divided period, the third divided period is the second divided period, and the fifth divided period is the third divided period. The distance sensor according to claim 1, wherein the seventh divided period is the fourth divided period. The light emission period and the stop period are set to the same period,
Eight division periods are set by dividing the one period into eight equal parts,
Of the eight divided periods, the first divided period is the first divided period, the third divided period is the second divided period, and the sixth divided period is the third divided period. The distance sensor according to claim 1, wherein the eighth divided period is set as the fourth divided period. The light emission period and the stop period are set to the same period,
Six divided periods are set by dividing the one period into six equal parts,
Of the six divided periods, the first divided period is the first divided period, the second divided period is the second divided period, and the third divided period is the third divided period. The distance sensor according to claim 1, wherein a fourth divided period is the fourth divided period. Each time length of the light emission period and the stop period is set at a ratio of 3 when the light emission period is 2,
Five division periods are set by dividing the one period into five equal parts,
Of the five divided periods, the first divided period is the first divided period, the second divided period is the second divided period, and the third divided period is the third divided period. The distance sensor according to claim 1, wherein a fourth divided period is the fourth divided period. Each time length of the light emission period and the stop period is set at a ratio of 2 when the light emission period is 3,
Five division periods are set by dividing the one period into five equal parts,
Of the five divided periods, the first divided period is the first divided period, the second divided period is the second divided period, and the third divided period is the third divided period. The distance sensor according to claim 1, wherein a fourth divided period is the fourth divided period. A first switch (40a) disposed between the light receiving element and the first capacitor;
A second switch (40b) disposed between the light receiving element and the second capacitor;
A third switch (40c) disposed between the light receiving element and the third capacitor;
A fourth switch (40d) disposed between the light receiving element and the fourth capacitor;
A fifth switch (35) disposed between the light receiving element and a power source;
In the first divided period, the first switch among the first to fifth switches is turned on, and the negative charge from the light receiving element is moved to the first capacitor through the first switch. 1 control means;
The second switch among the first to fifth switches is turned on in the second divided period, and the negative charge from the light receiving element is moved to the second capacitor through the second switch. Two control means;
The third switch among the first to fifth switches is turned on in the third divided period, and the negative charge from the light receiving element is moved to the third capacitor through the third switch. 3 control means;
In the fourth division period, the fourth switch among the first to fifth switches is turned on, and the negative charge from the light receiving element is moved to the fourth capacitor through the fourth switch. 4 control means;
The fifth switch among the first to fifth switches is turned on in the other divided period other than the first to fourth divided periods in the one cycle, and the negative charge from the light receiving element is Fifth control means for moving to the power supply side through a fifth switch;
The distance sensor according to claim 1, further comprising: a distance sensor.   The distance calculating means receives the reflected light by the light receiving element and the timing of emitting the emitted light from the light emitting source based on the negative charge amount accumulated in the first, second, third and fourth capacitors. A phase difference (φ) between the distance sensor and the detected object is calculated based on the calculated phase difference (φ). The distance sensor as described in any one.

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