JP2017190978A - Distance sensor, electronic device, and manufacturing method for electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance sensor for measuring distance to a target object, which is capable of minimizing erroneous distance measurements caused by interference with other distance sensors.SOLUTION: A distance sensor 1 includes a light source 2, a light receiver 3, and a controller 40. The light source emits light toward a target object. The light receiver receives the light in synchronization with emission of the light by the light source and accumulates the amount of received light. The controller controls the light source and the light receiver to generate distance information indicative of a distance to the target object based on the amount of light received during every predetermined period of time. The predetermined period comprises a predetermined number of accumulation periods (Ta), each representing a period during which the light receiver accumulates the amount of received light in response to emission of the light by the light source. The distance sensor also includes a period setting unit 40b configured to modify length of the accumulation period such that a total period of the predetermined number of accumulation periods is shifted by one accumulation period or longer after the modification of length of the accumulation period.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a distance sensor, an electronic device including the distance sensor, and a method for manufacturing the electronic device.

  As a distance sensor that measures a distance to an object, there is a distance sensor that uses a TOF (Time-Of-Flight) method that measures light based on a propagation period of reflected light by irradiating an object including the object. In the distance sensor, a technique for reducing the possibility of causing operation interference between devices has been proposed.

  For example, Patent Document 1 discloses a distance measuring device that is intended to reduce the probability of interference between devices in a use environment such as an inter-vehicle distance sensor. The distance measuring device of Patent Document 1 includes a first delay unit that delays a distance measurement start signal by a first delay time having a random length synchronized with the reference clock, and a second delay that is equal to or less than the period of the reference clock. Second delay means for delaying by the delay time. In the distance measuring device of Patent Document 1, in order to reduce the probability of interference, transmission of an optical pulse is performed by a delayed ranging start signal by the first and second delay means, and the received signal is sampled by the first delay means. It starts with a delayed ranging start signal.

JP 7-325153 A

  An object of the present invention is to provide a distance sensor that can suppress erroneous measurement of distance due to interference between distance sensors in a distance sensor that measures a distance to an object.

  The distance sensor according to the present invention includes a light source unit, a light receiving unit, and a control unit. The light source unit emits light to the object. The light receiving unit receives light in synchronization with light emission from the light source unit, and accumulates the amount of received light. The control unit controls the light source unit and the light receiving unit to repeatedly generate distance information indicating the distance to the object based on the amount of received light for each predetermined period. The predetermined period includes a predetermined number of times that is an accumulation cycle, which is a cycle in which the light receiving unit accumulates the amount of received light according to the emission of light by the light source unit. The distance sensor further includes a cycle setting unit that changes the length of the accumulation cycle such that the total period of the accumulation cycle is shifted by one cycle or more of the accumulation cycle before and after the change of the length of the accumulation cycle. .

  According to the distance sensor of the present invention, the length of the accumulation cycle is changed so that the total period of the predetermined number of accumulation cycles is shifted by one cycle or more of the accumulation cycle. Thereby, in the distance sensor that measures the distance to the object, erroneous measurement of the distance due to interference between the distance sensors can be suppressed.

The block diagram which shows the structure of the distance sensor which concerns on Embodiment 1 of this invention. Schematic diagram showing a configuration example of the pixel circuit of the light receiving unit in the distance sensor Timing chart showing operation timing of emission and reception of pulsed light in distance sensor Schematic diagram for explaining a distance calculation method in the distance sensor according to the first embodiment. The figure for demonstrating the production | generation operation | movement of the distance image by the distance sensor which concerns on Embodiment 1. FIG. The figure for demonstrating the interference between the several distance sensors in Embodiment 1. FIG. Timing chart showing operation timing of distance sensor in non-interfering frame Timing chart showing the operation timing of the distance sensor in the interference frame The flowchart which shows the distance image generation process which concerns on Embodiment 1. The figure for demonstrating the accumulation cycle table in a distance sensor Timing chart showing the operation timing of the distance sensor in the distance image generation process Graph showing the measurement results of the distance sensor before and after the change of the accumulation cycle FIG. 6 is a block diagram illustrating a configuration of an electronic device according to a second embodiment. The block diagram which shows the structure of the distance sensor which concerns on Embodiment 3. The figure for demonstrating the calculation method of the distance of the distance sensor which concerns on Embodiment 3. FIG. Waveform diagram showing the operation of the distance sensor according to the third embodiment The figure for demonstrating the interference between the several distance sensors in Embodiment 3. FIG. The wave form diagram which shows the operation | movement before and behind the change of the accumulation cycle of the distance sensor which concerns on Embodiment 3. FIG.

  Hereinafter, a distance sensor according to the present invention, an electronic device including the distance sensor, and a method for manufacturing the electronic device will be described with reference to the accompanying drawings.

  Each embodiment is an exemplification, and needless to say, partial replacement or combination of configurations shown in different embodiments is possible. In the second and subsequent embodiments, description of matters common to the first embodiment is omitted, and only different points will be described. In particular, the same operational effects by the same configuration will not be sequentially described for each embodiment.

(Embodiment 1)
1. Configuration The configuration of the distance sensor according to the first embodiment will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of the distance sensor according to the first embodiment.

  As shown in FIG. 1, the distance sensor 1 according to the present embodiment includes a light source unit 2, a light receiving unit 3, and a TOF signal processing unit 4. The distance sensor 1 is a sensor module that measures a distance in a measurement method such as an indirect TOF method. The distance sensor 1 emits light from the light source unit 2, receives reflected light from the object 5 by the light receiving unit 3, and generates a distance image indicating the distance to the object 5 in the TOF signal processing unit 4. The indirect TOF method is a method in which reflected light is received a plurality of times in a time-sharing manner, and the distance to the object is measured by comparing the obtained amounts of received light.

  The distance sensor 1 generates a distance image indicating the distance to the user's hand or finger, for example, as the object 5. The distance sensor 1 is mounted on an information terminal device such as a mobile terminal, for example. The distance sensor 1 and the controller 6 that controls the operation of the mounted information terminal device constitute a user interface system in the information terminal device. In the user interface system, the controller 6 detects a user operation such as a gesture operation by a user's hand or finger movement based on the distance image from the distance sensor 1. In order to enable such detection, the distance sensor 1 outputs a distance image to the controller 6 in a detection range within a distance of 2000 mm, for example. The information terminal device on which the distance sensor 1 is mounted may be a mobile terminal such as a smartphone, a tablet terminal, or a mobile phone, or a wearable terminal such as a glasses type or a watch type, a notebook PC, a digital camera, or a portable game. It may be a machine.

  The light source unit 2 includes a light source such as an LED (light emitting diode) and a drive circuit that drives the light source. The light source of the light source unit 2 emits light having a wavelength band of, for example, 750 nm to 1500 nm. Based on the timing signal from the timing generation unit 42, the light source unit 2 performs pulse modulation of light from the light source and emits it. Hereinafter, the light emitted from the light source unit 2 by pulse modulation is referred to as “pulse light”. By configuring the light source with LEDs, the light source unit 2 can be easily driven at high speed. The light source unit 2 may include an LD (laser diode) as a light source.

  The light receiving unit 3 is configured by, for example, a CMOS (complementary metal oxide semiconductor) image sensor circuit. The light receiving unit 3 includes a plurality of pixel circuits 30 arranged in a matrix. The plurality of pixel circuits 30 have a light receiving surface that receives light including a wavelength band such as 750 nm or more and 1500 nm or less, and each stores a received light amount. The configuration of the pixel circuit 30 in the light receiving unit 3 will be described later. Further, although not particularly illustrated, the light receiving unit 3 converts the analog value of the received light amount accumulated in the pixel drive circuit that drives the pixel circuit 30 based on the timing signal from the timing generation unit 42 or the pixel circuit 30 into a digital value A. An A / D converter for / D (analog / digital) conversion is provided.

  The TOF signal processing unit 4 includes a circuit that performs various signal processing for generating a distance image in the TOF method, and includes a control unit 40, a reference clock generation unit 41, a timing generation unit 42, and a distance image output unit 43. And a storage unit 44. The TOF signal processing unit 4 is composed of, for example, one or a plurality of semiconductor integrated circuit chips.

  In the TOF signal processing unit 4, the control unit 40 is configured by, for example, an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The control unit 40 controls the overall operation of the distance sensor 1, for example, controls various circuits included in the TOF signal processing unit 4. The control unit 40 may be configured by a CPU or MPU, for example, a CPU that realizes a predetermined function in cooperation with software. The control unit 40 includes a distance calculation unit 40a and a cycle setting unit 40b.

  The distance calculation unit 40a is configured by an arithmetic circuit capable of performing four arithmetic operations. The distance calculation unit 40 a calculates a distance based on the propagation period of the received reflected light based on the detection result of the reflected light by the light receiving unit 3. A method for calculating the distance will be described later. The distance calculation unit 40a performs distance calculation for each pixel, and records distance data indicating the calculated distance for each pixel in the storage unit 44, for example. A distance image is generated by calculating distance data for all pixels by the distance calculation unit 40a. The distance calculation unit 40a is an example of a distance information generation unit that generates a distance image as distance information.

  The cycle setting unit 40b is constituted by, for example, a register circuit. The period setting unit 40b records the length of an accumulation period described later. The control unit 40 controls the timing generation unit 42 so that the distance image generation operation is performed for the length of the accumulation cycle recorded in the cycle setting unit 40b.

  Returning to FIG. 1, the reference clock generation unit 41 is configured by a crystal oscillator, for example. The reference clock generation unit 41 generates a reference clock signal having a predetermined clock frequency (for example, 38.4 MHz), and supplies the generated reference clock signal to the timing generation unit 42 and the like.

  The timing generation unit 42 includes an oscillation circuit and the like. The timing generator 42 generates a predetermined timing signal based on the reference clock signal. The predetermined timing signal is a timing signal for synchronously driving the light source unit 2 and the light receiving unit 3 in the distance image generation operation by the distance sensor 1. As the control unit 40 controls the timing generation unit 42, various settings of timing signals such as the number of pulses, duty ratio, and driving cycle are made together with the above-described accumulation cycle.

  The timing generation unit 42 supplies the generated timing signal to the light source unit 2 as a pulse light emission control signal for controlling light emission of the pulsed light by the light source unit 2. The timing generation unit 42 also supplies the generated timing signal to the light receiving unit 3, and synchronously drives emission of pulsed light from the light source unit 2 and reception of light by the light receiving unit 3. The operation timing of emission and reception of pulsed light in the distance sensor 1 will be described later. Note that the timing generation unit 42 may be integrated with the light receiving unit 3 to control the emission of the pulsed light from the light receiving unit 3 by the light source unit 2.

  The distance image output unit 43 includes an interface circuit that outputs information to an external device. The distance image output unit 43 outputs the distance image generated in the distance calculation unit 40a to an external device such as the controller 6. The distance image output unit 43 may output distance data for all the pixels recorded in the storage unit 44, or may output the distance data calculated by the distance calculation unit 40a as needed.

  The storage unit 44 is a storage medium that stores various information such as data and parameters for realizing the function of the distance sensor 1. The storage unit 44 is configured by a flash memory, for example. The storage unit 44 stores, for example, an accumulation cycle table D1 described later (see FIG. 10). The storage unit 44 may be configured as an internal memory of the control unit 40. The control unit 40 may include an internal register separately from the storage unit 44.

  The controller 6 in the information terminal device is composed of, for example, a CPU and an MPU. The controller 6 includes, for example, an internal memory composed of a flash memory or a ROM, and implements various functions by executing predetermined programs recorded in the internal memory. For example, the controller 6 performs display control of a device on which the controller 6 is mounted. Further, the controller 6 detects the object 5 such as a hand based on the distance image from the distance sensor 1 and determines the user's operation on the information terminal device such as a mobile device on which the controller 6 is mounted. The controller 6 is an example of an arithmetic processing unit that executes predetermined processing based on the distance image generated by the distance sensor 1.

1-1. Configuration of Pixel Circuit Next, the configuration of the pixel circuit 30 in the light receiving unit 3 will be described with reference to FIG. FIG. 2A is a schematic diagram showing a pixel circuit 30 stacked on a semiconductor chip. FIG. 2B is a circuit diagram showing an equivalent circuit of FIG.

  As illustrated in FIG. 2A, the pixel circuit 30 includes a photodiode PD and three floating diffusions FD1, FD2, and FD3. In the pixel circuit 30, a photodiode PD is provided in an embedded manner on a p-type semiconductor substrate, and three floating diffusions FD1, FD2, and FD3 are provided around the photodiode PD. Further, transistors M1, M2, and M3 are formed from the region where the photodiode PD is provided to the floating diffusions FD1, FD2, and FD3, respectively.

  In the present embodiment, a charge distribution method is employed in the light receiving unit 3. In the light receiving unit 3, a pixel driving circuit (not shown) drives signals (for example, first to first) for driving various MOS transistors included in the pixel circuit 30 based on a timing signal from the timing generation unit 42 (see FIG. 1). Third gate signals Sg1 to Sg3, reset signals Sr1 to Sr3, selection signal Ss) are generated.

  In the three floating diffusions FD1, FD2, and FD3, capacitors (charge storage units) C1, C2, and C3 are formed as shown in FIG. The three capacitors C1, C2, and C3 are connected to the photodiode PD through transistors M1, M2, and M3, respectively. The transistors M1, M2, and M3 are controlled to open and close by ON / OFF of the first, second, and third gate signals Sg1, Sg2, and Sg3 input to the respective gates. The first, second, and third gate signals Sg1, Sg2, and Sg3 open and close the gates of the transistors M1, M2, and M3 based on the timing signal, and sequentially store the charges accumulated in the photodiode PD in the capacitors C1, C2, and C3. It is a signal to distribute to.

  The photodiode PD receives light in a predetermined wavelength band and performs photoelectric conversion. In the pixel circuit 30, portions other than the photodiode are shielded from light. The electric charge generated by the photoelectric conversion is accumulated in any one of the three capacitors C1, C2, and C3 through the transistor that is controlled to be open among the transistors M1, M2, and M3. As described above, the capacitors C1, C2, and C3 accumulate charges corresponding to the amount of light received by the photodiode PD. The light receiving unit 3 acquires the amount of received light by accumulating charges in the capacitors C1, C2, and C3 for each pixel circuit 30.

  The amount of received light acquired by the capacitors C1, C2, and C3 of the pixel circuit 30 is read from the analog signal line when the pixel circuit 30 is selected by the selection signal Ss. The selection signal Ss is a signal for selecting a pixel circuit 30 to be read from the plurality of pixel circuits 30. Further, the capacitors C1, C2, and C3 are reset by releasing the accumulated charges when the reference voltage VR is applied by the reset signals Sr1, Sr2, and Sr3.

2. Operation Next, the operation of the distance sensor 1 according to the present embodiment will be described.

2-1. First, a method for calculating the distance to the object by the distance sensor 1 will be described with reference to FIGS. FIG. 3 is a timing chart showing the operation timing of emission and reception of pulsed light in the distance sensor 1. FIG. 3A shows the supply timing of the pulse emission control signal. FIG. 3B shows the arrival timing of the reflected light that reaches the distance sensor 1 from the object. 3C, 3D, and 3E show the output timings of the first, second, and third gate signals Sg1, Sg2, and Sg3 input to the pixel circuit 30, respectively. FIG. 4 is a schematic diagram for explaining a distance calculation method by the distance sensor 1.

  The pulse emission control signal shown in FIG. 3A is supplied from the timing generation unit 42 to the light source unit 2 (see FIG. 1). Based on the pulse emission control signal, the light source unit 2 emits pulsed light having a pulse width of a predetermined period Tp from time t1. The period Tp is, for example, 10 ns (nanoseconds) or more and 20 ns or less, for example, 13 ns. When the pulsed light is applied to the object, it is reflected by the object to generate reflected light. The reflected light from the object reaches the distance sensor 1 with a delay from the time of emission of the pulsed light according to the distance to the distance sensor 1.

  The reflected light from the object shown in FIG. 3B has a delay period Td from the emission of the pulsed light, and reaches the distance sensor 1 at time t2 after the period Td from time t1. The waveform of the reflected light has a pulse width of the same period Tp as that of the pulsed light. In the present embodiment, it is assumed that the period Td is less than the period Tp.

  In the light receiving unit 3 of the present embodiment, as shown in FIGS. 3C to 3E, based on the first to third gate signals Sg1 to Sg3, as shown in FIG. While receiving external light such as background light, the reflected light from the object is received in a time-sharing manner in synchronization with the emission of the pulsed light.

  Specifically, the first, second, and third gate signals Sg1, Sg2, and Sg3 are sequentially generated in the pixel circuit 30 on the light receiving surface in synchronization with the pulse light emission control signal. In the pixel circuit 30, charges generated according to the amount of light received by the photodiode PD based on the first, second, and third gate signals Sg1, Sg2, and Sg3 are accumulated in the capacitors C1, C2, and C3 (FIG. 2 (b)). Note that the charge generated in the photodiode PD during a period in which the charge corresponding to the amount of received light is not accumulated in the capacitors C1, C2, and C3 is discharged to the outside through a drain gate (not shown).

  The first gate signal Sg1 shown in FIG. 3C is turned on before the emission of the pulsed light and for the period Tp. While the first gate signal Sg1 is ON, a charge corresponding to the amount of light received by the photodiode PD is accumulated in the capacitor C1. FIG. 4A shows the received light amount Q1 based on the first gate signal Sg1 accumulated in the capacitor C1. The amount of received light Q1 is the amount of received external light acquired in a state where no reflected light of pulsed light is generated. The amount of received light Q1 is acquired in order to confirm the influence of external light that is not related to pulsed light such as background light.

  The second gate signal Sg2 shown in FIG. 3 (d) is turned ON from time t1 when emission of pulsed light is started to time t3 when it is stopped. While the second gate signal Sg2 is ON, a charge corresponding to the amount of light received by the photodiode PD is accumulated in the capacitor C2. FIG. 4B shows the received light amount Q2 based on the second gate signal Sg2 accumulated in the capacitor C2. The amount of received light Q2 includes a reflected light component derived from reflected light that arrives within a period Tp from the time t1 when pulsed light emission starts. The received light quantity Q2 also includes external light components such as background light (see FIG. 4).

  The third gate signal Sg3 shown in FIG. 3E is turned on for a period Tp from time t3 after stopping emission of pulsed light. While the third gate signal Sg3 is ON, a charge corresponding to the amount of light received by the photodiode PD is accumulated in the capacitor C3. FIG. 4C shows the received light amount Q3 based on the third gate signal Sg3 accumulated in the capacitor C3. The received light amount Q3 includes a reflected light component derived from reflected light that continuously arrives from time t3 when emission of pulsed light is stopped to time t4 after the delay period Td. In this way, the entire amount of reflected light received is time-divided and distributed as reflected light components of the amounts of received light Q2 and Q3 according to the delay period Td. Note that it is assumed that the delay period Td of the reflected light is less than the period Tp, and the time t4 when the arrival of the reflected light ends is within the range of the charging period Tp of the capacitor C3. The received light amount Q3 includes an external light component as in the received light amount Q2. Note that the length of the period in which the pulsed light is emitted and the length of the period in which the gate signals Sg1, Sg2, and Sg3 are ON do not have to be the same length.

  As described above, in the distance sensor 1, the light receiving unit 3 receives light during a predetermined time from the start of the pulsed light emission period, and the received light amounts Q2, Q3 in the capacitors C2, C3 (first charge storage unit). The electric charge according to is accumulated. Further, light is received during the stop period of emission of the pulsed light, and charges corresponding to the amount of received light Q1 are accumulated in the capacitor C1 (second charge accumulation unit). By detecting the charges accumulated in the capacitors C1, C2, and C3, the received light amounts Q1, Q2, and Q3 can be obtained. According to the received light amounts Q1, Q2, and Q3 corresponding to the charges accumulated in the capacitors C1, C2, and C3, the ratio of the delay period Td and the period Tp of the reflected light from the object is as shown in FIG. Furthermore, this corresponds to the ratio (hereinafter referred to as “distribution ratio”) distributed to the received light quantity Q3 in the total received light quantity of the reflected light. Therefore, the delay period Td can be obtained based on the distribution of the received light amounts Q2 and Q3, that is, the distribution ratio.

  Here, as shown in FIGS. 4B and 4C, the received light amounts Q2 and Q3 include not only reflected light components but also external light components. Since the received light amounts Q2 and Q3 are acquired in the period Tp having the same length as the received light amount Q1 of only the external light, the external light component included in the received light amounts Q2 and Q3 is considered to be approximately the same as the received light amount Q1. It is done. Therefore, in the present embodiment, the received light amount of the reflected light component excluding the external light component is calculated by appropriately subtracting the received light amount Q1 from the received light amounts Q2 and Q3. Since the received light amount Q1 is acquired immediately before acquiring the received light amounts Q2 and Q3, the external light component in the received light amounts Q2 and Q3 can be accurately removed by the received light amount Q1.

The delay period Td is the time taken for the pulsed light to reach the object and return to the distance sensor 1 as reflected light. That is, this is the time taken when the distance between the object and the distance sensor 1 reciprocates at the speed of light c. Therefore, if the distance to the object is L, Td = 2L / c is established, and therefore the distance L to the object can be calculated based on the following equation.
L = (c / 2) * Tp * {(Q3-Q1) / (Q2 + Q3-2 * Q1)} (1)

  In the distance sensor 1 according to the present embodiment, the distance calculation unit 40a performs a predetermined calculation based on the principle of the above equation (1), and calculates a distance based on the distribution ratio of the received light amount. The calculation formula of the distance calculation unit 40a is defined by, for example, various signal timings and parameter settings (calibration) performed in advance under a specific environment.

2-2. Distance Image Generation Operation A distance image generation operation according to the present embodiment will be described with reference to FIG. FIG. 5A is a diagram for explaining an operation for generating a distance image of one frame. FIGS. 5B, 5C, and 5D are timing charts of the first, second, and third gate signals Sg1, Sg2, and Sg3 during the integration period of FIG. 5A. FIG. 5E shows a timing chart of the drain gate during the integration period of FIG. The drain gate is a gate for discharging charges from the photodiode PD.

  The distance sensor 1 according to the present embodiment repeatedly performs the above-described series of operations of emitting pulsed light and receiving reflected light, and repeatedly generates a distance image each time the amount of received light is read. Hereinafter, a period in which the light receiving unit accumulates the received light amounts Q1, Q2, and Q3 with respect to one emission of the pulsed light from the light source unit 2 is referred to as an “accumulation cycle”. As shown in FIG. 5A, the period per one time (one frame) in which the distance image is repeatedly generated includes an integration period and a reading period. The integration period is a repetition period in which the light receiving unit 3 integrates the received light amounts Q1, Q2, and Q3 by repeating the above accumulation cycle a predetermined number of times. The reading period is a period in which the control unit 40 reads the amount of light received integrated from the light receiving unit 3 following the integration period.

  As shown in FIGS. 5B, 5C, and 5D, the first, second, and third gate signals Sg1, Sg2, and Sg3 are turned on for each accumulation cycle Ta that is included multiple times in the integration period. Including one light receiving period. As shown in FIG. 5E, the drain gate is in an open state during the light receiving stop period that is outside the light receiving period in the integration period, and discharges the charge photoelectrically converted by the photodiode PD. In the integration period, based on the first, second, and third gate signals Sg1, Sg2, and Sg3, the received light amounts Q1, Q2, and Q3 (see FIG. 4) are accumulated by repeatedly accumulating charges in the charge accumulating units C1, C2, and C3. ) Is accumulated. Hereinafter, the number of times each of the received light amounts Q1, Q2, and Q3 during the integration period is referred to as “the number of integrations”. The number of integration is, for example, 700 times or more and 70,000 times or less.

  In the readout period after the integration period, the control unit 40 of the TOF signal processing unit 4 reads out the digital values of the received light amounts Q1, Q2, and Q3 integrated by the pixel circuits 30 from the A / D converter of the light receiving unit 3. . In the control unit 40, the distance calculation unit 40a performs a calculation based on the formula (1) based on the digital values of the received light amounts Q1, Q2, and Q3 for each pixel circuit 30. By integrating the received light amounts Q1, Q2, and Q3, the statistical accuracy of the measured distance is increased, and the distance can be calculated with high accuracy.

  When the distance calculation unit 40a performs the above calculation on one pixel, distance data indicating the distance of the pixel is acquired. The TOF signal processing unit 4 generates a distance image of one frame by acquiring distance data for all pixels.

2-3. Interference between devices Hereinafter, operation interference between devices by the distance sensor 1 according to the present embodiment will be described with reference to FIGS. FIG. 6 is a diagram for explaining interference between the distance sensors 1 and 1A. FIG. 7 is a timing chart showing various operation timings of the distance sensor 1 in the non-interference frame F1. FIG. 8 is a timing chart showing various operation timings of the distance sensor 1 in the interference frame F2.

  FIG. 6A shows a state in which the two distance sensors 1 and 1A are adjacent to each other. The distance sensor 1 according to the present embodiment (hereinafter sometimes referred to as a first distance sensor) is mounted on a mobile device or the like in order to detect a gesture input by an object 50 such as a finger, for example. The second distance sensor 1 </ b> A has a configuration similar to that of the first distance sensor 1.

  When the mobile device is used, it is assumed that the first distance sensor 1 and the second distance sensor 1A are adjacent to each other in the vicinity of the object 50 as shown in FIG. In this case, the pulsed light from the light source unit 2 of the second distance sensor 1A is reflected not only by the object 50 and incident on the light receiving unit 3 of the second distance sensor 1A, but also by the first distance sensor 1. Is incident on the light receiving unit 3. Hereinafter, the pulsed light emitted from the second distance sensor 1A and incident on the first distance sensor 1 is referred to as “interference light”.

  FIG. 6B is a graph showing a measurement result of the distance of the first distance sensor 1 when the interference light from the second distance sensor 1A is incident. In FIG. 6B, the horizontal axis represents the number of frames of the distance image, and the vertical axis represents the measurement distance (mm). FIG. 6B shows the distance calculated by the first distance sensor 1 when the object 50 is disposed at a distance of 200 mm from the first distance sensor 1.

  In FIG. 6B, the interference frame F2 whose measurement distance is more than 20 mm away from the distance 200mm to the object 50 is periodically generated between the non-interference frames F1 calculating the measurement distance near 200mm. Yes. Such a situation is considered to be caused by a slight shift (for example, about several ppm) of the clock frequency between the two distance sensors 1 and 1A. Hereinafter, the non-interference frame F1 and the interference frame F2 in FIG. 6B will be described with reference to FIGS. 7 and 8, respectively.

  FIGS. 7A, 7B, 7C and 7D respectively show the light emission timing of the first distance sensor 1 and the gate signals Sg1, Sg2, and Sg3 in the non-interference frame F1 of FIG. 6B. The light reception timing by each of these is shown. FIGS. 7E, 7F, 7G, and 7H show the light emission timings of the second distance sensor 1A in the non-interference frame F1 and the light reception timings of the gate signals Sg1, Sg2, and Sg3, respectively. Show.

  In the non-interference frame F1 shown in FIGS. 7A to 7H, at time t10, as shown in FIGS. 7A and 7E, the light emission timings of the first and second distance sensors 1 and 1A are set. The time interval Ti is vacant. Since the time interval Ti is not less than the pulse width Tp and not more than the accumulation cycle Ta, as shown in FIGS. 7B to 7D, all the gate signals Sg1, Sg2, Sg3 of the first distance sensor 1 are in the closed state. During the period, the second distance sensor 1A emits light (FIG. 7E). At this time, the first distance sensor 1 performs distance measurement without receiving the interference light from the second distance sensor 1A.

  Further, as shown in FIGS. 7F to 7H, the first distance sensor 1 emits light while all the gate signals Sg1, Sg2, Sg3 of the second distance sensor 1A are closed. (FIG. 7A). Therefore, in the frames of FIGS. 7A to 7H, the first and second distance sensors 1 and 1A can measure the distance without causing mutual interference (FIG. 6B). ).

  Here, when the first and second distance sensors 1 and 1A are synchronized by a predetermined trigger signal or the like, the time interval Ti is always maintained, and it is considered that interference does not occur in other frames. However, there is usually a difference of, for example, about several ppm in the clock frequency of the reference clock generator 41 between the distance sensors 1 and 1A that are not particularly synchronized. Therefore, as shown in FIGS. 7A and 7E, at time t11 after time t10, the time interval Ti ′ between the operation timings of the two distance sensors 1 and 1A is from the time interval Ti at time t10. It is off. For example, the time interval Ti ′ between the operation timings of the two distance sensors 1 and 1A gradually shifts as time elapses over a period of a plurality of frames, and may be less than the pulse width Tp or exceed the accumulation cycle Ta. is assumed. FIGS. 8A to 8E show various operation timings in the interference frame in which the inter-device interference occurs due to the passage of time from the frames in FIGS. 7A to 7H.

  FIGS. 8A, 8B, 8C, and 8D respectively show the light emission timing of the first distance sensor 1 and the gate signals Sg1, Sg2, and Sg3 in the interference frame F2 in FIG. 6B. The light reception timing by each is shown. FIG. 8E shows the light emission timing of the second distance sensor 1A in the interference frame F2.

  In one frame period shown in FIGS. 8A to 8E, for example, at the initial time t12, in the light receiving period of the second gate signal Sg2 of the first distance sensor 1 (FIG. 8C), Interference light from the distance sensor 1A is emitted (FIG. 8 (e)). For this reason, the first distance sensor 1 receives the interference light based on the second gate signal Sg2, and accumulates it as the received light amount Q2.

  Further, as shown in FIGS. 8C and 8E, over the integration period of the first distance sensor 1, the light emission timing of the interference light is gradually shifted and superimposed on the light reception period of the second gate signal Sg2. doing. For this reason, the first distance sensor 1 continues to accumulate the influence of the interference light on the received light amount Q2 based on the second gate signal Sg2 during the integration period. As a result, in the first distance sensor 1, the received light amount Q2 based on the second gate signal Sg2 increases excessively, the distribution ratio of the received light amounts Q2 and Q3 is biased, and the distance calculated in this frame becomes abnormally short. (FIG. 6B).

  In the next frame, the light emission timing of the second distance sensor 1A is further delayed, and the interference light is emitted during the light receiving period of the third gate signal Sg3 of the first distance sensor 1 (FIG. 8D). (FIG. 8 (e)). For this reason, in the first distance sensor 1, the received light amount Q3 based on the third gate signal Sg3 is excessively increased, and the calculated distance becomes abnormally long (FIG. 6B).

  In order to suppress the erroneous measurement of the distance due to the interference between the distance sensors 1 and 1A as described above, in this embodiment, the total period (integration period) corresponding to the integration number of accumulation periods in one frame is one accumulation period. The length of the accumulation cycle is changed so as to shift by more than a minute. As a result, while the distance sensor 1 itself accepts the interference light, erroneous measurement of the distance can be suppressed even if the interference light is received. Hereinafter, details of the operation of the distance sensor 1 according to the present embodiment will be described.

2-4. Distance Image Generation Processing The distance image generation processing by the distance sensor 1 according to this embodiment will be described. The distance image generation process is a process in which the distance sensor 1 repeatedly generates a distance image at a predetermined frame rate (for example, 30 fps). In the present embodiment, an example will be described in which the distance sensor 1 automatically changes the length of the accumulation cycle Ta when interference between devices occurs during the execution of the distance image generation process. Hereinafter, the distance image generation processing will be described with reference to FIGS.

  FIG. 9 is a flowchart showing distance image generation processing according to the present embodiment. FIG. 10 is a diagram for explaining the accumulation cycle table D1 in the distance sensor 1. FIG.

  The distance image generation process shown in the flowchart of FIG. 9 is executed by the control unit 40 of the distance sensor 1. The storage unit 44 stores an accumulation cycle table D1 in advance. As will be described later, the accumulation cycle table D1 is a data table for managing the accumulation cycle Ta when executing the distance image generation process.

  In FIG. 9, first, the control unit 40 controls the light emission operation of the light source unit 2 and the light reception operation of the light receiving unit 3 in the length of the accumulation cycle Ta set in advance in the cycle setting unit 40 b by the control of the timing generation unit 42. On / off control is repeated for the number of integrations (step S1). In the period setting unit 40b, the length of the accumulation period Ta is set to, for example, 988 ns as a default (see FIG. 10). The number of integrations may be set freely, for example, 28,000 times.

  By the processing in step S1, the light source unit 2 irradiates the target with pulsed light for each accumulation period Ta, and the light receiving unit 3 receives reflected light and background light from the target (see FIG. 3). In step S1, the accumulation cycle Ta is repeated for the number of integrations during the integration period, and the light receiving units 3 integrate the received light amounts Q1, Q2, and Q3.

  Next, the control unit 40 reads the received light amounts Q1, Q2, and Q3 accumulated in the light receiving unit 3, performs distance calculation in the distance calculation unit 40a, and generates a distance image (step S2). In step S2, the light receiving unit 3 performs A / D conversion on the analog values of the integrated received light amounts Q1, Q2, and Q3 into digital values, and the control unit 40 receives the received light amounts Q1, Q2 of each pixel of the light receiving unit 3 in the digital values. , Q3 are read out. The control unit 40 performs calculation based on the formula (1) for the received light amounts Q1, Q2, and Q3 for each pixel in the distance calculation unit 40a. The control unit 40 outputs a distance image for each calculated pixel, for example, via the distance image output unit 43.

  Next, the control unit 40 determines whether interference between devices has occurred based on the distance data in the generated distance image (step S3). For example, the control unit 40 holds a part or all of each pixel of the distance image such as the past several frames in the storage unit 44, and whether the change rate of the distance data in the generated distance image exceeds a predetermined threshold value. The determination in step S3 is made based on whether or not. For example, the predetermined threshold value is set to a rapid change rate that is considered to be a motion of an object to be detected (for example, a human motion). Further, the control unit 40 may make the determination in step S3 based on the change rates of the various received light amounts Q1, Q2, and Q3.

  When the control unit 40 determines that no interference occurs between the devices (NO in S3), the control unit 40 returns to the process of step S1 without changing the setting of the accumulation cycle Ta in the cycle setting unit 40b.

  On the other hand, when the control unit 40 determines that interference between devices has occurred (YES in S3), the control unit 40 reads the accumulation cycle table D1 from the storage unit 44 and changes the length of the accumulation cycle Ta in the cycle setting unit 40b ( Step S4). The accumulation cycle table D1 will be described with reference to FIG.

  As shown in FIG. 10, the accumulation cycle table D1 records “mode” and “length of accumulation cycle” in association with each other. The mode is a mode for managing the length of the accumulation cycle set in the cycle setting unit 40b in multiple stages. In FIG. 10, a 10-stage mode is provided.

  In FIG. 10, mode 1 is a mode set as a default in the period setting unit 40b. In FIG. 10, mode 1 is associated with the accumulation cycle length “988 ns”. The mode 2 is associated with the accumulation cycle length “975 ns”, and the mode 10 is associated with the accumulation cycle length “858 ns”. In the accumulation cycle table D1, the lengths of the respective accumulation cycles are set so that the deviation of the integration period when the accumulation cycles of the lengths associated with the different modes are repeated is at least one accumulation cycle. Is set.

  Returning to FIG. 9, in step S <b> 4, the control unit 40 randomly selects one mode from modes other than the mode set in the cycle setting unit 40 b in the 10-step mode in the accumulation cycle table D <b> 1. The control unit 40 rewrites the length of the accumulation cycle Ta set in the cycle setting unit 40b to the length of the accumulation cycle associated with the mode selected in the accumulation cycle table D1. By randomly selecting the 10-step mode, the probability that the distance sensors 1 and 1A that cause interference select the same mode can be reduced to 1/10.

  The control unit 40 controls the timing generation unit 42 according to the updated setting of the cycle setting unit 40b, and repeats the processing after step S1 in the accumulation cycle Ta 'having the changed length. As a result, while the distance image is generated, the shift of the accumulation cycle is repeated until it is determined that no interference occurs.

  According to the above processing, when interference occurs in a specific frame while generating a distance image at a predetermined frame rate, the length of the accumulation period Ta is shifted (S4), and interference light is transmitted from the next frame. Can alleviate the effects. The influence of interference light in this distance image generation process will be described with reference to FIGS. 11 (a) to 11 (f) and FIGS. 12 (a) and 12 (b).

  FIG. 11A shows the light reception timing of the first gate signal Sg1 in the accumulation cycle Ta before the change by the distance image generation process. FIG. 11B shows the emission timing of the pulsed light in the accumulation cycle Ta ′ after the change by the distance image generation process. FIGS. 11C, 11D, and 11E show light reception timings of the gate signals Sg1, Sg2, and Sg3 in the changed accumulation cycle Ta ′. FIG. 11F shows the emission timing of the interference light by the second distance sensor 1A.

  FIGS. 11A to 11F show frames in the case where the light emission timing of the interference light overlaps the light reception period of the first gate signal Sg1 of the distance sensor 1 in the accumulation cycle Ta before the change (FIG. 11). (A), (f)). In this case, in step S4 in FIG. 9, it is assumed that the changed accumulation cycle Ta ′ is shortened from the accumulation cycle Ta before the change by a change width Δt having the same length as the pulse width Tp of the pulsed light (FIG. 9). 11 (b)-(e)).

  In one frame period illustrated in FIGS. 11A to 11F, in the first accumulation cycle Ta ′ during the integration period, as in the case before the change (FIG. 11A), the first change of the distance sensor 1 is performed. The light reception period by the 1 gate signal Sg1 overlaps the emission timing of the interference light (FIGS. 11C and 11F). However, in the subsequent accumulation cycle Ta ′, the operation timing of the distance sensor 1 with respect to the emission timing of the interference light is shifted by the change width Δt = Tp. For example, in the subsequent second accumulation cycle Ta ′, the light receiving period of the second gate signal Sg2 overlaps the emission timing of the interference light (FIGS. 11D and 11F). Further, in the third accumulation cycle Ta ′, the light receiving period of the third gate signal Sg3 overlaps the emission timing of the interference light (FIGS. 11 (e) and 11 (f)).

  As described above, the interference light is received by the gate signals Sg1, Sg2, and Sg3 in the plurality of accumulation periods Ta ′ included in the integration period in one frame after the change by changing the length of the accumulation period Ta at the time of interference. Light is received during the period. As a result, the influence of the interference light is dispersed in each of the light reception amounts Q1, Q2, and Q3, so that the influence of the interference light is included in a specific light reception amount among all the light reception amounts Q1, Q2, and Q3. Can be avoided. For this reason, the erroneous measurement of the distance by interference between the distance sensors 1 and 1A can be suppressed.

  As described above, in order to suppress the influence of the interference light, in this embodiment, the accumulation periods Ta and Ta ′ before and after the change are respectively equal to the number of accumulations, and the deviation between the repeated accumulation periods is equal to or more than one accumulation period. The length of the accumulation cycle Ta is changed using the change width Δt. As a result, during the repetition of the number of integrations, the interference light emitted at substantially the same period as the storage period Ta before the change makes at least one round within the storage period Ta ′ after the change, and the influence of the interference light is The amount of received light can be dispersed in Q1, Q2, and Q3.

  For example, in the case where the number of integrations is 28000, the pulse width Tp = 13 ns, and the accumulation period Ta = 988 ns (before change), if the change width Δt of the accumulation period Ta is set to 13 ns, which is the same as the pulse width Tp, The length of Ta ′ is 975 ns. Then, the difference between the integration periods before and after the change is 364000 ns, which is equal to or longer than 364 periods of the accumulation period Ta ′. In this case, the interference light having substantially the same period as the storage period Ta before the change circulates 364 times or more during the integration period in the storage period Ta ′ after the change, and the interference in each received light quantity Q1, Q2, Q3. The effect of light can be made statistically uniform. Further, by performing the distance calculation based on Expression (1) using the received light amounts Q1, Q2, and Q3, the influence of the interference light can be removed in the same manner as the influence of the background light.

  FIGS. 12A and 12B are graphs showing the measurement results of the distance of the distance sensor 1 before and after the change of the accumulation cycle Ta. 12A and 12B, distance measurement is performed on an object 200 mm away by the distance sensor 1 in each of the state where interference light is emitted and the state where interference light is not emitted. FIGS. 12A and 12B show the output distance of one central pixel in the distance image output in this case.

  In FIG. 12A, the length of the accumulation cycle Ta before the change is 988 ns, which is shifted by several ppm from the cycle of the interference light. FIG. 12B shows the output distances in the respective cases of 962 ns, 910 ns, and 858 ns shifted by the change width Δt = 13 ns as the changed accumulation cycle Ta ′. In this case, the difference between the integration periods before and after the change corresponds to 728 accumulation cycles, 2184 cycles, and 3620 cycles, respectively.

  As shown in FIG. 12A, in the accumulation cycle Ta before the change, the output distance in the state in which the interference light is emitted is severely disturbed compared to the state in which the interference light is not emitted. On the other hand, according to the changed accumulation cycle Ta ′, as shown in FIG. 12 (a), even when the interference light is emitted, the stable distance is equivalent to the state where the interference light is emitted. Output is obtained.

  The change width Δt of the accumulation cycle Ta may be set so that, for example, the difference between the integration periods before and after the change is equal to or greater than 10 accumulation cycles Ta from the viewpoint of stably dispersing the influence of the interference light. Further, the change width Δt of the accumulation cycle Ta is, for example, from the viewpoint of maintaining various performances such as the measurement range, measurement accuracy, or frame rate of the distance sensor 1, and the difference between the integration periods before and after the change is 10,000 cycles of the accumulation cycle Ta. It may be set to be less than or equal to minutes.

3. Summary As described above, the distance sensor 1 according to the present embodiment includes the light source unit 2, the light receiving unit 3, and the control unit 40. The light source unit 2 emits light to the object 50. The light receiving unit 3 receives light in synchronization with the emission of light from the light source unit 2, and accumulates received light amounts Q1, Q2, and Q3. The control unit 40 controls the light source unit 2 and the light receiving unit 3 to generate a distance image that is distance information indicating the distance to the object 50 based on the received light amounts Q1, Q2, and Q3 for each predetermined frame period. The frame period of the distance image includes an accumulation period Ta, which is a period in which the light receiving unit 3 accumulates the amount of received light according to the emission of light from the light source unit 2, for a predetermined number of integration times. The distance sensor 1 further changes the length of the accumulation cycle Tb so that the total period corresponding to the number of accumulations of the accumulation cycle Ta is shifted by one cycle or more of the accumulation cycle Tb before and after the change of the length of the accumulation cycle Tb. A period setting unit 40b is provided.

  According to the distance sensor 1 described above, the length of the accumulation cycle Ta is changed so that the total period of the accumulation cycle Ta is shifted by one cycle or more of the accumulation cycle Ta. As a result, the timing at which the interference light is received while the accumulation cycle Ta is repeated the number of times of accumulation makes at least one round of the accumulation cycle, and the influence of the interference light is dispersed between the received light amounts Q1, Q2, and Q3. For this reason, the erroneous measurement of the distance by interference between the distance sensors 1 and 1A can be suppressed.

  Further, in the present embodiment, the cycle setting unit 40b is configured so that the shift of the total period before and after the change of the length of the storage cycle Ta is 10 cycles or more and 10,000 cycles or less of the storage cycle Ta. Change the length. Thereby, the influence of the interference light is statistically evenly distributed between the received light amounts Q1, Q2, and Q3, and the erroneous measurement of the distance due to the interference can be stably suppressed.

  Further, in the present embodiment, the control unit 40 determines whether interference has occurred based on the generated distance image (S3), and when it is determined that interference has occurred (YES in S3), the storage period Ta The length is changed (S4). As a result, when interference occurs during the generation of a one-frame distance image, the distance sensor 1 can automatically determine the interference between devices and suppress erroneous measurement of distance due to interference from the next frame.

  In the present embodiment, whether or not interference has occurred is determined based on the distance image generated by the control unit 40 of the distance sensor 1 in step S3 of FIG. 9. However, the determination in step S3 is based on an electronic device such as a mobile device. It may be performed by the controller 6 in the device. The controller 6 compares the distance images of each frame output from the distance sensor 1 to determine whether or not interference has occurred. When it is determined that interference has occurred, the length of the accumulation cycle is changed. A predetermined command may be transmitted to the distance sensor 1.

  In the present embodiment, the light source unit 2 repeatedly emits light in pulse modulation. In the present embodiment, before and after the change of the accumulation cycle Ta, the light source unit 2 maintains the pulse width of the emitted pulsed light. Thereby, before and after the change of the accumulation cycle Ta, the total amount of received light is maintained, and a decrease in distance measurement accuracy can be avoided.

(Embodiment 2)
In the first embodiment, the example in which the distance sensor 1 automatically shifts the accumulation cycle when interference between devices occurs has been described. Embodiment 2 demonstrates the example which mounts a distance sensor so that the influence of interference may be suppressed beforehand. Hereinafter, Embodiment 2 will be described with reference to FIG.

  FIG. 13 is a block diagram illustrating a configuration of the electronic device 60 according to the present embodiment. The electronic device 60 includes two distance sensors 1, 1 </ b> A, a controller 6, and a display unit 61. The electronic device 60 is a mobile terminal, for example. The display unit 61 is configured by a liquid crystal display or an organic EL display, for example. The display unit 61 displays various images on the display surface under the control of the controller 6.

  In this embodiment, the cycle setting unit 40b of each distance sensor 1, 1A includes, for example, a switch or a selector, and is configured to be able to change the length of the accumulation cycle from the outside when the electronic device 60 is manufactured. The cycle setting unit 40b may be configured such that the length of the accumulation cycle cannot be changed from the outside when the electronic device 60 is used, for example, by a fuse circuit or the like. In the first embodiment, the control unit 40 of the distance sensor 1 determines whether interference has occurred during the generation of the distance image (S3 in FIG. 9), but each distance sensor 1, 1A according to the present embodiment. The controller 40 does not need to determine whether or not interference has occurred.

  In the present embodiment, as an example, in order to detect an input operation by a user's gesture on the display image of the display unit 61, two distance sensors 1 and 1A are disposed in the vicinity of the display unit 61 when the electronic device 60 is manufactured. Implemented. For example, the controller 6 of the electronic device 60 outputs a trigger signal to each of the distance sensors 1 and 1A for each frame in order to match the timing of acquiring the distance image from each distance sensor 1 and 1A.

  When using the electronic device 60, there is a concern that the two distance sensors 1, 1A in the electronic device 60 may interfere with each other. In order to avoid mutual interference, for example, in the method of synchronizing the distance sensors 1 and 1A using a trigger signal, synchronization for each frame is not sufficient, and it is necessary to generate a trigger signal for each accumulation cycle. For this reason, it is difficult to configure the trigger signal as a wireless signal from the viewpoint of signal delay, and even if it is configured as a wired signal, it must be designed with sufficient consideration for wiring and parasitic capacitance in order to adjust the signal delay. I will have to.

  Therefore, in the present embodiment, when the electronic device 60 is manufactured or shipped, a total number of times corresponding to the reference number of the respective storage cycles of the two distance sensors 1 and 1A at a predetermined number of reference times is each storage cycle. The accumulation cycle of each of the distance sensors 1 and 1A is set so as to shift by one cycle or more. At this time, the reference number is a number in a practically acceptable range as the cumulative number, for example, 100 times or more.

  For example, in the period setting unit 40b of each distance sensor 1, 1A, the default mode in the accumulation period table D1 (FIG. 10) is set to a different mode and the distance sensors 1, 1A are mounted. Instead of or in addition to this, the length of the accumulation cycle associated with each mode in the accumulation cycle table D1 of each distance sensor 1 and 1A is stored for the total number of times corresponding to the reference number of each accumulation cycle. You may set so that it may shift | deviate more than 1 period of a period.

  Thereby, the influence of mutual interference between the distance sensors 1 and 1A can be easily suppressed without requiring a complicated design for the trigger signal in consideration of the signal delay in the electronic device 60. In the above description, the controller 6 of the electronic device 60 outputs the trigger signal to each of the distance sensors 1 and 1A for each frame, but it is necessary to synchronize the timing for acquiring the distance image from each distance sensor 1 and 1A. In systems that do not, the trigger signal itself may be omitted.

  As described above, the electronic device 60 according to the present embodiment includes the two distance sensors 1 and 1A. In the electronic device 60, the accumulation cycle of each distance sensor 1, 1A is set such that the total period of a predetermined number of accumulation cycles of the distance sensors 1, 1A is shifted by one cycle or more of each accumulation cycle. . Thereby, the erroneous measurement of the distance by the interference between apparatuses of the distance sensors 1 and 1A in the electronic device 60 can be suppressed.

  The electronic device 60 is not limited to the two distance sensors 1 and 1A, and may include three or more distance sensors. In this case, the accumulation cycle of each distance sensor may be set so that the total period of the accumulation cycles of the plurality of distance sensors included in the electronic device 60 is shifted by one cycle or more of each accumulation cycle.

  The mounting method of the distance sensor 1 according to the present embodiment is a method for manufacturing the electronic device 60. In this manufacturing method, a plurality of distance sensors 1 and 1A are mounted on the electronic device 60, and a total period corresponding to the accumulated number of accumulation cycles of each of the plurality of distance sensors 1 and 1A is equal to or greater than one accumulation cycle. And a step of setting the accumulation cycle of each distance sensor 1, 1 </ b> A so as to be shifted to

  Further, the distance sensor 1 according to the present embodiment includes a cycle setting unit 40b that can set the length of the accumulation cycle from the outside. Thereby, when mounting on the electronic device 60 as described above, it is possible to suppress erroneous measurement of distance due to interference between devices by shifting the accumulation cycle.

(Embodiment 3)
In the first embodiment, the pulse modulation type distance sensor that repeatedly emits light from the light source unit in the pulse modulation has been described. However, the present invention is not limited to the pulse modulation method, and various modulation methods may be used. In Embodiment 3, a continuous wave type distance sensor that emits light in continuous wave modulation with a predetermined waveform will be described.

  FIG. 14 is a block diagram showing a configuration of the distance sensor 1B according to the present embodiment. The distance sensor 1B according to the present embodiment has the same configuration as the distance sensor 1 according to the first embodiment.

  In the present embodiment, the light source unit 2A of the distance sensor 1B emits light in continuous wave modulation having a predetermined waveform. Hereinafter, an example in which the light waveform in the continuous wave modulation is a sine waveform will be described. However, the predetermined waveform is not limited to a sine wave, and may be various waveforms such as a triangular wave and a sawtooth wave. Hereinafter, the light emitted from the light source unit 2A by continuous wave modulation is referred to as “modulated light”.

  The modulation frequency f of the modulated light is set by performing various adjustments in the timing generation unit 42 based on the clock frequency (for example, 50 MHz) of the reference clock generation unit 41. The cycle setting unit 40b according to the present embodiment changes the length of the accumulation cycle of the distance sensor 1B in the present embodiment by changing the setting of the modulation frequency f.

FIG. 15 is a diagram for explaining a method of calculating the distance of the distance sensor 1B according to the present embodiment. In the present embodiment, the distance to the object is calculated by the following equation based on the phase shift width Φ where the reflected light of the modulated light on the object is shifted from the phase of the modulated light at the time of emission and the modulation frequency f.
L = c × Φ / (4π × f) (2)

According to the above equation, by setting the modulation frequency f = 50 MHz, the reflected light returning within 20 ns per cycle can be detected, and a measurement range of 3 m can be obtained. Further, the phase shift width Φ in the above equation is calculated by the following equation.
Φ = tan ⁻¹ {(A1-A3) / (A2-A4)} (3)

  In the above equation, A1, A2, A3, and A4 are the amounts of received light including reflected light that are received at timings of π / 2, π, 3π / 2, and 2π, respectively, as shown in FIG. It is. As described above, the amount of received light when the light receiving unit 3A receives reflected light includes the influence of background light as well as the reflected light. According to the above equation, the influence of background light included when receiving reflected light is eliminated by using the difference (A1-A3) and (A2-A4) in the amount of received light. Therefore, by obtaining four types of received light amounts A1, A2, A3, A4, the two differences (A1-A3) and (A2-A4) are proportional to sinΦ and cosΦ, respectively, and the phase shift width of the reflected light Φ can be obtained.

  In the present embodiment, the distance calculation unit 40a in the control unit 40 reads out four types of received light amounts A1, A2, A3, and A4 for each pixel from the light receiving unit 3A, and performs calculations based on equations (2) and (3). By doing so, a distance image is generated.

  Returning to FIG. 14, in the present embodiment, the light receiving unit 3 </ b> A includes a pixel circuit 30 </ b> A having two charge storage units. Note that the pixel circuit 30A of the light receiving unit 3A is not limited to two charge storage units, and may include, for example, four or less charge storage units. Hereinafter, timing control performed by the control unit 40 via the timing generation unit 42 when the pixel circuit 30A of the light receiving unit 3A has two charge storage units will be described with reference to FIG.

  FIG. 16A is a waveform diagram showing the emission timing of modulated light when generating a one-frame distance image. In FIGS. 16A to 16C, the frame rate is 30 fps. As shown in FIG. 16A, the modulated light is emitted in two periods T11 and T12 at a predetermined time interval during one frame of 33 ms. Each period T11, T12 is, for example, 1.52 ms. In this case, 76000 cycles of modulated light are continuously emitted in each of the periods T11 and T12.

  FIG. 16B shows the light reception timing of the light reception amounts A1 and A3 in the period T11 based on the two gate signals Sa1 and Sa2. FIG. 16C shows the light reception timing of the light reception amounts A2 and A4 in the period T12. The two gate signals Sa1 and Sa2 are signals for storing charges in the two charge storage portions of the pixel circuit 30A in the light receiving portion 3A, respectively.

  As shown in FIG. 16B, in the period T11, the two gate signals Sa1 and Sa2 receive light in the same accumulation cycle Tb as the cycle of the modulated light (reflected light). Further, when the phase difference between the two received light amounts A1 and A3 corresponding to the phase π / 2 and 3π / 2 of the modulated light is π, the two gate signals Sa1 and Sa2 are half of the modulation frequency f. The light reception is repeated alternately with a shift of 10 ns for the period. As a result, the received light amounts A1 and A3 are accumulated in the respective charge accumulation portions of the pixel circuit 30A every accumulation cycle Tb. For example, in the period T11 of 1.52 ms, the received light amounts A1 and A3 are accumulated 76000 times, and the received light amounts A1 and A3 are integrated.

  In the period T12, the remaining two received light amounts A2, A4 of the received light amounts A1, A2, A3, A4 are received by the two gate signals Sa1, Sa2. As shown in FIG. 16C, the two gate signals Sa1 and Sa2 repeat light reception alternately in the accumulation cycle Tb, similarly to the light reception of the two light reception amounts A1 and A3 in the period T11. The light reception timing of the two gate signals Sa1 and Sa2 in the period T12 is such that the light reception amounts A2 and A4 corresponding to the phases π and 2π of the modulated light are received, so the light reception timing in the period T11 is 1 of the modulation frequency f. / 4 shift by 5ns.

  Even in the continuous wave modulation type distance sensor as described above, when a plurality of distance sensors exist, it is assumed that interference occurs between devices. A method for suppressing interference between the distance sensors 1B and 1C according to the present embodiment will be described with reference to FIGS. 17 (a) to 17 (d), 18 (a), and (b).

  FIG. 17A shows the light emission timing of the distance sensor 1B according to the present embodiment (hereinafter sometimes referred to as “first distance sensor”). FIG. 17 (b) shows the light emission timing of the second distance sensor 1C at the same point as FIG. 17 (a). FIGS. 17C and 17F show the light emission timings when the first and second distance sensors 1B and 1C interfere. The second distance sensor 1 </ b> C has the same configuration as the first distance sensor 1.

  FIGS. 17A and 17B show a frame period when no interference occurs between the first and second distance sensors 1B and 1C. In this case, there is a time interval between the light emission timings of the first and second distance sensors 1B and 1C so that the respective light emission periods do not overlap. Such a time interval gradually shifts due to a slight difference in clock frequency between the first and second distance sensors 1B and 1C.

  For example, it is assumed that there is a difference of 10 ppm between the first and second distance sensors 1B and 1C at the clock frequency f = 50 MHz of the reference clock generator 41. In this case, there is a difference of 500 clocks per second, and the relative timings of the first and second distance sensors 1B and 1C are shifted by 16.6 clocks (333 ns) every frame period of the frame rate of 30 fps. Go. For this reason, as time passes from the states of FIGS. 17A and 17B, as shown in FIGS. 17C and 17D, the light emission timings of the first and second distance sensors 1B and 1C overlap. Will occur. Hereinafter, the modulated light incident on the first distance sensor 1B from the second distance sensor 1C is referred to as “interference light”.

  FIG. 18 (a) shows the operation timing of the distance sensor 1B before the change of the accumulation cycle Tb in the states of FIGS. 17 (c) and 17 (d). When the interference light enters the first distance sensor 1B in the states of FIGS. 17C and 17D, the distance sensor 1B reflects the reflected light based on the gate signals Sa1 and Sa2, as shown in FIG. At the same time, the interference light is received. At this time, if the influence of the interference light continues to be accumulated to the same extent in each accumulation period Tb, the influence of the interference light is biased in the received light amounts A1, A2, A3, and A4, leading to erroneous distance measurement.

  Therefore, in the present embodiment, the accumulation period Tb is shifted by changing the modulation frequency f of the modulated light together with the light receiving timing of the gate signals Sg1 and Sg2 by the period setting unit 40b. At this time, the cycle setting unit 40b changes the modulation frequency f so that the number of accumulation cycles Tb repeated in the periods T11 and T12 is shifted by one or more. As a result, the number of times that the accumulation cycle Tb before the change is repeated during the period T11 (or period T12) is set as the reference number, and the period for repeating the accumulation cycles Tb and Tb ′ before and after the change is equal to the number of accumulation cycles. More than that.

  Then, as shown in FIG. 18B, during the repetition of the changed accumulation cycle Tb ′, the influence of the interference light received by the gate signals Sg1 and Sg2 becomes uneven for each accumulation cycle Tb ′. . For this reason, the influence of the interference light is statistically equally included between the received light amounts A1, A3 (or A2, A4) accumulated in the period T11 (or T12). For this reason, by the distance calculation based on Formula (3), the influence of interference light is removed similarly to the influence of background light. Thereby, erroneous measurement of the distance due to the influence of the interference light is suppressed.

  For example, the control unit 40 determines whether or not interference between devices has occurred in the same processing as the distance image generation processing (FIG. 9) of the first embodiment (S3), and determines that interference between devices has occurred. In this case, the modulation frequency is changed in the period setting unit 40b. Then, the control unit 40 controls the timing generation unit 41 so that the frequency newly set in the period setting unit 40b from the next frame is set as the modulation frequency of the modulated light.

  For example, in the period T1 and T2 of 1.52 ms, the control unit 40 increases the frequency of the accumulation cycle Tb from 76000 times to 76001 times, a frequency of 50000658 Hz or more, or decreases to 75999 times and 499342 Hz or less of 4999342 Hz or less. Is set in the period setting unit 40b. Further, in consideration of changes in the relative relationship between the distance sensors 1B and 1C due to the external environment, for example, a frequency of 500006579 Hz or higher may be set in the cycle setting unit 40b so that the accumulation cycle Tb is shifted by 10 cycles or more. Good.

  As described above, in the distance sensor 1B according to the present embodiment, the light source unit 2A emits modulated light in continuous wave modulation with a predetermined waveform. The period setting unit 40b sets the accumulation period Tb based on the frequency in continuous wave modulation. Thereby, the erroneous measurement of distance by interference between distance sensors 1B and 1C based on continuous wave modulation can be controlled.

  Further, in the present embodiment, the control unit 40 causes the light receiving unit 3A to repeat light reception at timings corresponding to the two phases π / 2, 3π / 2 (or π, 2π) of the modulated light waveform. Control. Thereby, it is possible to avoid the influence of the interference light from being biased between the received light amounts A1 and A3 (or A2 and A4), which are alternately received, and to prevent erroneous distance measurement.

(Other embodiments)
In the first embodiment, the pixel circuit 30 includes the charge storage unit C1 dedicated to external light. However, the pixel circuit in the distance sensor 1 is not limited thereto, and the charge storage unit C1 dedicated to external light may be omitted. . In this case, in reading from the pixel circuit, the received light amount including reflected light and the received light amount of external light may be acquired in different frames, and a one-frame distance image may be generated by reading out two frames. For example, in two consecutive frames, the emission of pulsed light is repeated in one frame, and the charge is accumulated by time division in two charge accumulating units, read out to the TOF signal processing unit 4, and the received light amount including reflected light is calculated. get. In the other frame, by receiving light while stopping the emission of pulsed light, the amount of external light received can be acquired. Even in this case, in the acquired amount of received light, the influence of the interference light can be subtracted in the same manner as the influence of the external light, and the erroneous measurement of the distance due to the inter-device interference can be suppressed.

  In the first embodiment, the light is continuously received twice in the first light receiving operation by the second and third gate signals Sg2 and Sg3. However, the number of times of continuous light receiving in the first light receiving operation. May be greater than twice. For example, the light reception period of the first gate signal Sg1 may be set immediately before the light reception period of the second gate signal Sg2. Further, a light receiving period for accumulating a predetermined amount of received light may be set after the light receiving period of the third gate signal Sg3. For example, the light receiving unit may include four or more charge storage units in the pixel circuit, and four or more types of received light amounts Q1, Q2,..., Qm (m is an integer of 4 or more) may be acquired in a time division manner.

  In each of the above embodiments, the example in which the cycle setting unit 40b is provided inside the control unit 40 has been described. However, the cycle setting unit 40b is provided outside the control unit 40 inside the distance sensors 1 and 1B. Also good. Further, the accumulation period table D1 may be incorporated in the period setting unit 40b.

  Further, in each of the above-described embodiments, the case where the distance measuring method of the distance sensors 1 and 1A to 1C is the indirect TOF method has been described. The distance measurement method of the distance sensor is not limited to this, and may be a direct TOF method that directly measures the propagation period of reflected light, for example. The direct TOF type distance sensor may be configured using, for example, a time digital converter or a single photon avalanche photodiode.

  Further, in each of the above embodiments, the case where the distance sensors 1 and 1A to 1C are mounted on the mobile device is illustrated. The device on which the distance sensors 1 and 1A are mounted is not limited to a mobile device, and may be various electronic devices such as a monitoring camera and an in-vehicle device. According to the distance sensor 1, for example, it is possible to suppress erroneous measurement of distance due to inter-device interference based on interference light incident from an oncoming vehicle in an in-vehicle device.

DESCRIPTION OF SYMBOLS 1 Distance sensor 2 Light source part 3 Light receiving part 30 Pixel circuit 40 Control part 40a Distance calculation part 40b Period setting part 42 Timing generation part 44 Storage part

Claims (9)

A light source unit for emitting light to an object;
A light receiving unit that receives light in synchronization with emission of light by the light source unit and accumulates a received light amount;
A control unit that controls the light source unit and the light receiving unit and generates distance information indicating a distance to the object based on the amount of received light for each predetermined period;
The predetermined period includes a predetermined number of times including an accumulation cycle, which is a cycle in which the light receiving unit accumulates an amount of received light according to emission of light by the light source unit,
Further, a cycle setting unit that changes the length of the accumulation cycle so that the total period of the predetermined number of the accumulation cycles is shifted by one cycle or more of the accumulation cycle before and after the change of the length of the accumulation cycle. Provided distance sensor. The cycle setting unit changes the length of the accumulation cycle so that the shift of the total period before and after the change of the length of the accumulation cycle is not less than 10 cycles and not more than 10,000 cycles of the accumulation cycle. Item 2. The distance sensor according to Item 1. The controller is
Based on the generated distance information, determine whether interference has occurred,
The distance sensor according to claim 1 or 2, wherein when it is determined that interference has occurred, a length of the accumulation cycle is changed. The distance sensor according to claim 1, wherein the light source unit repeatedly emits light in pulse modulation. The light source unit emits light in continuous wave modulation in a predetermined waveform,
The distance sensor according to claim 1, wherein the period setting unit sets the accumulation period based on a frequency in the continuous wave modulation. The distance sensor according to claim 5, wherein the control unit controls the light receiving unit so that light reception at a timing corresponding to at least two phases of the waveform is alternately repeated. The distance sensor according to any one of claims 1 to 6,
An arithmetic processing unit that performs predetermined arithmetic processing based on distance information generated in the distance sensor;
The arithmetic processing unit includes:
Based on the distance information, determine whether interference has occurred,
An electronic device that changes the length of the accumulation cycle when it is determined that interference has occurred. A plurality of the distance sensors according to any one of claims 1 to 6,
An electronic apparatus in which the accumulation cycle of each distance sensor is set such that the total period of the predetermined number of accumulation cycles of each of the plurality of distance sensors is shifted by one cycle or more of each accumulation cycle. A method of manufacturing an electronic device,
Mounting a plurality of the distance sensors according to any one of claims 1 to 6 on an electronic device;
A method for manufacturing an electronic device, comprising: setting an accumulation cycle of each distance sensor such that a total period of the predetermined number of accumulation cycles of each of the plurality of distance sensors is shifted to one cycle or more of each accumulation cycle.

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