Light receiver and ranging device

A light receiver includes a plurality of photoelectric conversion portions each of which includes a photoelectric conversion element configured to receive light, and a pulse generator configured to generate a pulse signal corresponding to an amount of light received by the photoelectric conversion element. The light receiver includes a plurality of bit counters each of which is configured to count the pulse signal of the pulse generator, and the plurality of bit counters are dispersed in the plurality photoelectric conversion portions.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2020-035067, filed on Mar. 2, 2020, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

BACKGROUND

Technical Field

The present disclosure relates to a light receiver and a ranging device.

Related Art

Currently, single photon avalanche diode (SPAD) sensors, which are single photon detection elements, are known. A SPAD sensor has a capability to operate in a Geiger mode in which a reverse voltage exceeding the breakdown voltage is applied to a p-n junction to drive the sensor. Therefore, a SPAD sensor can attain a much higher gain than that attained by an avalanche photo diode (APD) and can react with a very small signal unit of one photon. Note that the gain of the SPAD sensor is about 1E6, while the gain of the APD is about 100 to 200.

The SPAD sensor requires quenching after reacting to photons, to reduce the current due to the Geiger mode. Further, after reducing the current in the Geiger mode by the quenching, the SPAD sensor requires recharge control for supplying electric charges until the SPAD sensor returns to a steady mode. Both the quenching and recharge control are performed using a resistor connected in series with the SPAD sensor. The resistor is, for example, on-resistance of a metal-oxide semiconductor field-effect transistor (MOSFET). Further, since the output signal is a digital pulse, a counter circuit or the like is used for the SPAD sensor to maintain the signal for each pixel.

SUMMARY

According to an embodiment of this disclosure, a light receiver includes a plurality of photoelectric conversion portions each of which includes a photoelectric conversion element configured to receive light, and a pulse generator configured to generate a pulse signal corresponding to an amount of light received by the photoelectric conversion element. The light receiver includes a plurality of bit counters each of which is configured to count the pulse signal of the pulse generator, and the plurality of bit counters are dispersed in the plurality photoelectric conversion portions.

According to another embodiment, a ranging device includes a light source configured to emit light to an object, the above-described light receiver, and a control circuit. In response to a detection result that a phase difference between the output signal from the higher-bit counter circuit and the output signal from the lower-bit counter circuit in the first mode is 0, the control circuit calculates ½ of a time of emission of the light from the light source to the object as a time to reception of reflected light of the light emitted to the object.

DETAILED DESCRIPTION

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views thereof, embodiments according to the present disclosure are described. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Hereinafter, a description is given below of a laser imaging detection and ranging (LIDAR) apparatus according to an embodiment of the present disclosure with reference to the accompanying drawings. The LIDAR apparatus is configured to measure scattered light obtained by pulsed manner laser irradiation, thereby measuring the distance to an object, or analyzing the properties of the object. In other words, the LIDAR apparatus is an active ranging device including a light-emitting element.

A first embodiment is described below.

FIG.1is a block diagram illustrating a main part of a LIDAR apparatus100as a ranging device according to the first embodiment. InFIG.1, the LIDAR apparatus100according to the first embodiment includes a light projection device1that projects light from a light source11, a light-receiving device2that receives reflected light from an object40, and a control circuit3that controls the light projection device1and measures the distance based on a reflection signal.

The light projection device1and the light-receiving device2are disposed to detect an object in a detection direction (image capture direction), which is generally the forward direction of a mobile body such as a vehicle, an aircraft, or a ship. Alternatively, the light projection device1and the light-receiving device2may be disposed to detect an object in a direction other than the forward direction, such as a lateral direction or the backward direction of the mobile body.

The light projection device1includes the light source11, a coupling lens13, an optical scanner14, a light source drive circuit16, an optical scanner drive circuit17, and a scanning angle monitor18.

The light source11includes a plurality of light-emitting element groups separate from each other in an optical scanning direction. Each light-emitting element group is constructed of a plurality of vertical cavity surface-emitting lasers (VCSELs). The light source11is connected to the control circuit3via the light source drive circuit16. The control circuit3individually controls the respective light emission timings of the light-emitting element groups of the light source11.

The coupling lens13couples the laser beam emitted from the light source11to the optical scanner14. The optical scanner14performs scanning in the XZ plane by directing the laser beams from the plurality of light-emitting element groups of the light source11to the same detection area. With the deflection of the laser beam by the optical scanner14, an object present in a predetermined angular range is detected, and the distance to the detected object can be measured.

The scanning angle of the laser beams by the optical scanner14may be detected by the scanning angle monitor18and fed to the control circuit3. In this case, the control circuit3adjusts an optical-scanner drive signal based on the monitor result, and controls the scanning angle and the scanning frequency.

The light-receiving device2includes a single photon avalanche diode (SPAD) sensor21as an example of a light receiver and a light-receiving lens22. A detail description of the SPAD sensor21is deferred. The light-receiving lens22couples the laser beam reflected from an object in the beam scanning direction, to the SPAD sensor21(the light receiver). Other optical devices such as a mirror may be disposed between the light-receiving lens22and the SPAD sensor21(the light receiver).

The light projection device1and the light-receiving device2are disposed close to each other. From a position several meters or more away from the light projection device1and the light-receiving device2, respective optical axes of the light projection device1and the light-receiving device2can be regarded as coaxial. The laser beams are diffusely reflected from the object40. Such diffusely reflected light includes an optical component returning along the same optical path as the laser beam emitted from the LIDAR apparatus100, and the optical component passes through the light-receiving lens22and is received by the SPAD sensor21(the light receiver). The SPAD sensor21forms a reflection signal indicating the intensity of the received reflected light and supplies the reflection signal to the control circuit3.

The control circuit3measures the distance to the detected object40based on the period from when the drive timing signal of the light source11is output to when the reflection signal is supplied, that is, based on the difference between the time at which the laser beams are emitted and the time at which the reflected light is received.

In this configuration, the quality of the laser beams output from each light-emitting element group is ensured, and a high angular resolution thereof is maintained. In addition, irradiating the same detection area with a plurality of laser beams at different timings is advantageous in enhancing the light intensity in total and increasing the measurable distance. Further, the SPAD sensor21used as the light receiver has high sensitivity and can obtain a reflection signal having a high signal-to-noise (SN) ratio. Therefore, the distance can be measured with high accuracy.

The control circuit3may be implemented by an integrated circuit chip, such as a large-scale integrated (LSI) chip or a microprocessor; a logic device such as a field programmable gate array (FPGA); or a combination of the integrated circuit chip and the logic device.

External Configuration of SPAD Sensor

The SPAD sensor21, which serves as the light receiver of the LIDAR apparatus100according to the first embodiment, is a high-sensitivity image sensor capable of detecting a single photon. The SPAD sensor21is used to measure the time (time of flight) from emission of light to the object40to the return of reflected light from the object40. Thus, the SPAD sensor21is used as a rangefinder.

FIG.2is a diagram illustrating an external configuration of the SPAD sensor21serving as the light receiver. In the example illustrated inFIG.2, the SPAD sensor21has a pixel array of 16 pixels in total. The number of pixels in the pixel array can be greater than 16 or less than 16. Each of the pixels (e.g., SPADPIX0on the upper left) is an example of a photoelectric conversion portion and provided with a SPAD (e.g., SPAD0) including a light-receiving areas R (R0to R15). Each SPAD is an example of a photoelectric conversion element. Each pixel includes a pixel selection unit51, a pulse shaping unit52(an example of a pulse generator), a front end53, and a toggle flip flop (one of T flip-flops TFF0to TFF15). The signal from the SPAD has a spike shape and has a pulse width too small for a subsequent-stage counter circuit to count. The pulse shaping unit52increases the pulse width of the SPAD. Each of the T flip-flops TFF0to TFF15is examples of a bit counter.

InFIG.2, the 16 T flip-flops (0th to 15th T flip-flops TFF0to TFF15) of the SPAD sensor21(the light receiver) are given reference characters TFF0to TFF15. As illustrated inFIG.3, TFF0to TFF15are continuously arranged in a so-called zigzag shape (meandering shape) and are dispersed in the pixels. Specifically, inFIG.2, the 0th to 3rd T flip-flops TFF0to TFF3are disposed in order from the lower right pixel in the upward direction, and the 4th T flip-flop TFF4is disposed adjacent to the left of the 3rd T flip-flop TFF3. The 5th to 7th T flip-flops TFF5to TFF7are disposed in order from the 4th T flip-flop TFF4in the downward direction inFIG.2. The 8th T flip-flop TFF8is disposed adjacent to the left side of the 7th T flip-flop TFF7, and the 9th to 11th T flip-flops TFF9to TFF11are disposed in order from the 8th T flip-flop TFF8in the upward direction inFIG.2. The 12th T TFF12is disposed adjacent to the left of the 11th T flip-flop TFF11, and the 13th to 15th T flip-flops TFF13to TFF15are disposed in order downward from the 12th T flip-flop TFF12inFIG.2. Thus, the T flip-flops TFF0to TFF15are sequentially disposed adjacent pixels (photoelectric conversion portions) in an order from a bit counter (e.g., the TFF0) configured to output a count value of a lowest bit to a bit counter configured to output a count value of a highest bit (e.g., TFF15).

The SPAD sensor21illustrated inFIG.2includes 16 T flip-flops TFF0to TFF15to count photons. Specifically, each pixel is provided with one of the T flip-flops TFF0to TFF15. Therefore, the SPAD sensor21illustrated inFIG.2is a 16-bit counter. The number of bits of the entire SPAD sensor21determines the dynamic range of the amount of light that the SPAD sensor21can handle. Therefore, preferably, the number of bits of the entire SPAD sensor21is as large as possible (corresponding dynamic range becomes large).

Arranging the T flip-flops TFF0to TFF15adjacent to each other and continuous in this way is advantageous in keeping the wiring between the T flip-flops short, thereby reducing the wiring area. With the reduction of the wiring area, the aperture ratio of each pixel can be improved accordingly.

Further, as will be described later, the LIDAR apparatus100according to the first embodiment collectively detects the respective output signals of the pixels of the SPAD sensor21with one counter circuit (a 24-bit counter circuit60inFIG.4). Further, as an external light removing method of the LIDAR apparatus100, there is a method of regarding photons that are simultaneously incident on the pixels as signals, and removing the photons that are incident at random as external light. When such an external light removal method is used, collectively counting the outputs of the pixel of the SPAD sensor21with the 24-bit counter circuit60is useful.

Circuit Configuration of SPAD Sensor

FIG.4is a diagram illustrating a circuit configuration of the SPAD sensor21serving as the light receiver. In the example illustrated inFIG.4, 16 pixel signals in total are collectively supplied to the 24-bit counter circuit60(an example of a counter circuit) provided with T flip-flops TFF0to TFF23.

The 16 pixel signals are of:

the four pixels SPADPIX0to SPADPIX3respectively including the T flip-flops TFF0to TFF3illustrated inFIG.2;

the four pixels SPADPIX4to SPADPIX7respectively including the T flip-flops TFF4to TFF7;

the four pixels SPADPIX8to SPADPIX11respectively including the T flip-flops TFF8to TFF11; and

the four pixels SPADPIX12to SPADPIX15respectively including the T flip-flops TFF12to TFF15.

The 24-bit counter circuit60generates a collective light-receiving signal.

The SPAD of each pixel operates in the Geiger mode with voltage (reverse bias voltage) equal to or higher than the breakdown voltage applied to a VH terminal. Further, the MOSFET of the front end53having the drain connected to the anode side of the SPAD functions as a quench resistor. The gate bias of the MOSFET is controlled by the gate voltage applied to a quench terminal QNCH, and the quench resistance value can be changed from the outside.

The 24-bit counter60counts each pulse signal output from each pixel in response to one photon. In addition, each pixel can be selectively activated by the selection signal from a SELECT terminal. Only the pixel selected by the selection signal is activated via the SELECT terminal, and the count output pulse of the number of photons is output. As a result, the count value of only a given pixel out of 16 pixels can be obtained.

The count value of the 24-bit counter circuit60is reset to “0” by a reset pulse supplied via a reset terminal RESET. Further, the count value of the 24-bit counter circuit60is output to the outside via an output terminal OUT [0:23] by the read pulse supplied via a read terminal READ.

The first embodiments provides the following effects.

As is clear from the above description, the LIDAR apparatus100according to the first embodiment shares the single 24-bit counter circuit60among the plurality of pixels of the SPAD sensor21. While switching the outputs from the 0th to 15th T flip-flops TFF0to TFF15, which are allocated to the respective pixel of the SPAD sensor21, the LIDAR apparatus100inputs the outputs into the single 24-bit counter circuit60and sequentially reads out the outputs. As a result, the logic circuit area of each pixel can be reduced, and the aperture ratio of the light-receiving area of each pixel can be increased.

Next, a description is given of a LIDAR apparatus according to a second embodiment.

The LIDAR apparatus100according to the first embodiment described above is an example in which the respective T flip-flops of the pixels of the SPAD sensor21are continuously arranged in a zigzag (meandering) shape. By contrast, the LIDAR apparatus100according to the second embodiment is an example in which the T flip-flops of the pixels of the SPAD sensor21are continuously arranged in a spiral shape. The second embodiment is different from the first embodiment described above only in the arrangement of the T flip-flops of the pixels of the SPAD sensor21. Accordingly, only the difference is described below, and redundant description is omitted.

FIG.5is a diagram illustrating an external configuration of the SPAD sensor21(the light receiver) of the LIDAR apparatus according to the second embodiment. In the second embodiment, similar to the first embodiment described above, the SPAD sensor21has an array of 16 pixels in total. Further, as described above, each pixel also includes the light-receiving area R (one of R0to R15), the pixel selection unit51, the pulse shaping unit52, the front end53, and one of the T flip-flops TFF0to TFF15.

As illustrated inFIG.6, the 0th to 15th T flip-flops TFF0to TFF15are continuously arranged in a so-called spiral shape. Specifically, inFIG.5, the 0th to 3rd T flip-flops TFF0to TFF3are arranged in order from the lower right pixel in the upward direction. Further, the 3rd to 6th T flip-flops TFF3to TFF6are disposed in order from the right to the left on the top row of the SPAD sensor21in inFIG.5. As a result, the 4th T flip-flop TFF4is disposed adjacent to the left side of the 3rd T flip-flop TFF3inFIG.5.

Further, the 6th to 9th T flip-flops TFF6to TFF9are disposed in order from the upper left pixel in the downward direction inFIG.5. The 10th and 11th T flip-flops TFF10and TFF11are disposed in order adjacent to the right side of the 9th T flip-flop TFF9at the lower left on the bottom row of the SPAD sensor21inFIG.5.

Further, the 12th and the 13th T flip-flops TFF12and TFF13are sequentially arranged in the upward direction from the 11th T flip-flop TFF11in the bottom row of the SPAD sensor21. Further, the 14th T flip-flop TFF14is disposed adjacent to the left side of the 13th T flip-flop TFF13. Further, the 15th T flip-flop TFF15is disposed adjacent to the lower side of the 14th T flip-flop TFF14. As a result, the 0th to 15th T flip-flops TFF0to TFF15are arranged in a spiral shape as illustrated inFIG.6.

Arranging the 0th to 15th T flip-flops TFF0to TFF15adjacent to each other and continuous in a spiral shape is advantageous in keeping the wiring between the T flip-flops short and reducing the wiring area. Accordingly, the aperture ratio of each pixel can be improved. Thus, the second embodiment can attain effects similar to those attained by the first embodiment.

Next, a description is given of a LIDAR apparatus according to a third embodiment.

In the LIDAR apparatus according to the third embodiment, a color filter is provided on each of the pixels of the SPAD sensor21that includes the 0th to 15th T flip-flops TFF0to TFF15arranged continuously in a zigzag shape (serpentine shape) as described in the first embodiment.

FIG.7is a diagram illustrating an example of the SPAD sensor21including the color filter on each pixel. In the example illustrated inFIG.7, 16 pixels in total are divided into square grids each of which includes 4 pixels (2 columns×2 rows). Each pixel grid includes green, red, and blue color filters in a ratio of 2:1:1 (Bayer color filter array).

With the Bayer color filter array on the four pixels, red, green, and blue (RGB) signals can be acquired with the four pixels. As described above in the first embodiment, the SPAD sensor21of the LIDAR apparatus collectively outputs the signals from four pixels. Therefore, the delay of the output signal due to the arrangement of the RGB color filters can be reduced, and the same effects as those of each of the above-described embodiments can be obtained.

Next, a description is given of a LIDAR apparatus according to a fourth embodiment.

In the LIDAR apparatus according to the fourth embodiment, the 24-bit counter circuit of the SPAD sensor21can be switched between a first mode and a second mode. In the first mode, the 24-bit counter circuit is used as the 24-bit counter to count outputs of the T flip-flops TFF0to TFF23as described above. In the second mode, the 24-bit counter circuit is used as a counter that separately counts outputs of the lower 12-bit T flip-flops TFF0to TFF11and the higher 12-bit T flip-flops TFF12to TFF23.

As one example, a description is given of divided use of a 24-bit counter circuit into 12-bit counters, but the manner of division is not limited thereto. Alternatively, for example, a 36-bit counter circuit may be divided into three 12-bit counters, or a 36-bit counter circuit may be divided into two counters of a 24-bit counter and a 12-bit counter. The number of bits of the counter circuit, the number of divisions, and the number of bits of each of the divided counters can be arbitrarily set according to the design of the device.

An external configuration of the SPAD sensor21according to the fourth embodiment is described.

FIG.8is a diagram illustrating an external configuration of the SPAD sensor21(the light receiver) of the LIDAR apparatus according to the fourth embodiment. As illustrated inFIG.8, the SPAD sensor21according to the fourth embodiment includes the pixel selection unit51, the pulse shaping unit52, and the front end53in each pixel. Further, the SPAD sensor21according to the fourth embodiment includes the 0th to 23rd T flip-flops TFF0to TFF23, OR circuits (examples of a first-stage logic circuit), a two-input OR circuit, two-input AND circuits (examples of a second-stage logic circuit), and a multiplexer circuit, which are allocated to the plurality of pixels.

Specifically, of the 0th to 23rd T flip-flops TFF0to TFF23, the 0th and 1st T flip-flops TFF0and TFF1are disposed in the second pixel from the bottom in the right column, and the 2nd and 3rd T flip-flops TFF2and TFF3are disposed in the upper right pixel inFIG.8. The 4th and 5th T flip-flops TFF4and TFF5are in the pixel adjacent to the upper right pixel inFIG.8. In the three pixels continuously arranged downward from the pixel including the 4th and 5th T flip-flops TFF4and TFF5inFIG.8, the 6th and 7th T flip-flops TFF6and TFF7, the 8th and 9th T flip-flops TFF8and TFF9, and the 10th and 11th T flip-flops TFF10and TFF11are disposed, respectively.

Further, the 12th and 13th T flip-flops TFF12and TFF13are disposed in the second pixel from the bottom in the second row from the left, and the 14th and 15th T flip-flops TFF14and TFF15are disposed in the top pixel in the second column from the left inFIG.8. In the four pixels in the first column from left inFIG.8, the 16th and 17th T flip-flops TFF16and TFF17, the 18th and 19th T flip-flops TFF18and TFF19, the 20th and 21st T flip-flops TFF20and TFF21, and the 22nd and 23rd T flip-flops TFF22and TFF23are disposed, respectively.

That is, the 0th to 23rd T flip-flops TFF0to TFF23are arranged from the second pixel from the bottom in the right column inFIG.8sequentially in adjacent pixels such as the T flip-flop TFF0, the T flip-flop TFF1, the T flip-flop TFF2, . . . , and the T flip-flop TFF23in order. As a result, the wiring between the T flip-flops can be shortened, the wiring area can be reduced, thereby improving the aperture ratio of each pixel.

Further, in the case of the SPAD sensor21used in the fourth embodiment, an OR circuit A[3] (an example of a first-stage logic circuit), an OR circuit B[2:3], and two two-input AND circuits2AND are disposed in a pixel SPADCELL (an example of a third photoelectric conversion portion) at the lower right inFIG.8. In the second pixel from the top in the left column inFIG.8includes a reset circuit RESET and a read circuit READ. Further, the bottom pixel in the second column from the left inFIG.8includes an OR circuit A[2], an OR circuit B[0:1], a two-input OR circuit2OR, and a multiplexer MUX. Further, a pixel QUADSPAD0(an example of a second photoelectric conversion portion), which is the second pixel from the top in the second column from the left inFIG.8includes an OR circuit A[0].

In the fourth embodiment, in order to collectively supply the output of the 16 pixels to a common 24-bit counter circuit70(inFIG.9), the outputs of the 4 upper left pixels are collected to one OR circuit A[0]. Similarly, the outputs of the 4 upper right pixels are collected to one OR circuit A[1], the outputs of the 4 lower left pixels are collected to one OR circuit A[2], and the 4 outputs of the lower right pixels are collected to one OR circuit A[3]. Further, the outputs of the 4 upper left pixels and the 4 upper right pixels are collected to one OR circuit B[0:1], and the outputs of the 4 lower left pixels and the lower right 4 pixels are collected to one OR circuit B[2:3]. Then, the outputs of the OR circuit B[0:1] and the OR circuit B[2:3] are collected to the two-input OR circuit2OR. As a result, the outputs of 16 pixels are collected in the order of 4 outputs, 8 outputs, and 16 outputs and supplied to the 24-bit counter circuit70.

As in the SPAD sensor21illustrated inFIG.8, arranging the pixels including only the T flip-flops adjacent to each other and collecting the logic circuits, such as the OR circuit, in other pixels can eliminate unnecessary wiring. This configuration can prevent decreases in the aperture ratio of the light-receiving area due to the wiring, thereby preventing a delay of the output signal.

That is, in the fourth embodiment, the output signals are collected by the OR circuits A[0], A[1], A[2], and A[3] for each of the four grids of the upper left grid (the light-receiving areas R0, R1, R4, and R5), the upper right grid (the light-receiving areas R2, R3, R6, and R7), the lower left grid (the light-receiving areas R8, R9, R12, and R13), and the lower right grid (the light-receiving areas R10, R11, R14, and R15). As a result, the parasitic capacitance of the wiring can be reduced, and the delay of the output signal can be minimized.

Switching of Division of T Flip-Flops

In the fourth embodiment, as described above, the 24-bit counter circuit70of the SPAD sensor21can be switched between the first mode to count outputs of the T flip-flops TFF0to TFF23as the 24-bit counter, and the second mode to separately count outputs of the lower 12-bit T flip-flops TFF0to TFF11and the higher 12-bit T flip-flops TFF12to TFF23. The second mode is suitable when the SPAD sensor21is used as an indirect time-of-flight (ToF) sensor. Details will be described later.

FIG.9is a circuit diagram illustrating the above-mentioned switching between the first mode and the second mode. The configuration of each pixel is the same as that according to the first embodiment described above. The SPAD connected to the VH terminal operates in the Geiger mode, and the MOSFET of the front end53having the drain connected to the anode side of the SPAD functions as a quench resistor. The gate bias of the MOSFET is controlled via the QNCH terminal so that the quench resistance value can be changed from the outside.

The outputs of the above-mentioned four pixels on the upper left (SPADPIX0to SPADPIX3), the outputs of the four pixels on the upper right, the outputs of the four pixels on the lower left, and the outputs of the four pixels on the lower right are input to a four-input OR circuit81(an example of a first-stage logic circuit), and the output signals A[0] to A[3] in response to the reaction of each SPAD can be output collectively. The first-stage logic circuit collects the count values from at least two bit counters. Of the output signals A[0] to A[3], the output signal A[0] and the output signal A[1] are supplied to a two-input OR circuit82(B[0:1]). Further, of the output signals A[0] to A[3], the output signal A[2] and the output signal A[3] are supplied to a two-input OR circuit83(B[2:3]). A two-input OR circuit84collects the respective output signals of the two-input OR circuit82(B[0:1]) and the two-input OR circuit83(B[2:3]), and supplies the output signals to a first AND circuit91and a second AND circuit92.

In the fourth embodiment, the 24-bit counter circuit70is divided into a first 12-bit counter circuit71(an example of a lower-bit counter circuit) that counts the respective outputs of the 0th to 11th T flip-flops TFF0to TFF11, and a second 12-bit counter circuit72(an example of a higher-bit counter circuit) that counts the respective outputs of the 12th to 23rd T flip-flops TFF12to TFF23.

The first AND circuit91, to which the output signals collected by the two-input OR circuit84is supplied, is connected to the first 12-bit counter circuit71. The second AND circuit92, to which the output signals collected by the two-input OR circuit84is supplied, is connected to a multiplexer95(an example of a switching control circuit). The two-input OR circuits82to84, the first AND circuit91, and the second AND circuit92are examples of a second-stage logic circuits.

The first 12-bit counter circuit71is also connected to the multiplexer95. The multiplexer95selects one of the output signals from the second AND circuit92and the output signals counted by the first 12-bit counter circuit71and supplies the selected signals to the second 12-bit counter circuit72.

With such a circuit configuration, the pulse signal output by each pixel reacting to one photon can be counted by the 24-bit counter circuit70. Of the plurality of pixels, the pixel selected via the SELECT terminal becomes active and outputs the counted number of photons. As a result, the count value of only a given pixel among the 16 pixels can be obtained.

The count value is reset to “0” by a reset pulse supplied via the reset terminal RESET. Further, the count value is output via the output terminal OUT [0:23] based on the read pulse supplied via the read terminal READ.

Further, in the fourth embodiment, a high level “1” switching signal or a low level “0” switching signal is supplied from a switching control terminal CNTDIVIDE [0:1] to the first AND circuit91and the second AND circuit92. As a result, the first 12-bit counter circuit71and the second 12-bit counter circuit72can be used as one 24-bit counter (first mode), or the first 12-bit counter circuit71and the second 12-bit counter circuit72can be used as the lower 12-bit counter (TFF0to TFF11) and the higher 12-bit counter (TFF12to TFF23), respectively, (second mode).

Use of the SPAD sensor as an indirect ToF sensor requires detecting the phase difference of the output signals. Therefore, the circuit is configured to prepare an up counter and a down counter for detecting the difference. From this point, the configuration to detect the count value with the two divided counters of the higher 12-bits counter and the lower 12-bits counter is preferable.

FIG.10is a timing chart when a SPAD sensor having a function of 24-bit/12-bit counter circuit switching is used as an indirect ToF sensor as described above. As described above, use of the SPAD sensor as an indirect ToF sensor requires the circuit configuration for detecting the phase difference of the output signals. Accordingly, an up counter and a down counter are provided to detect the difference.

That is, in the fourth embodiment, as described with reference toFIG.9, the counter circuit is divided into two, namely, divided into the first 12-bit counter circuit71(TFF0to TFF11) and the second 12-bit counter circuit72(TFF12to TFF23), so that the SPAD sensor21can be used as an indirect ToF sensor.

That is, in the timing chart ofFIG.10, the pulse width of the light emission is synchronized with the timing of activating the 0th to 11th T flip-flops TFF0to TFF11. The active period of the 12th to 23rd T flip-flops TFF12to TFF23is started simultaneously with the end of the active period of the 0th to 11th T flip-flops TFF0to TFF11, and the length of the active periods are the same.

The reflected light signal is generated with a delay of ToF from the light emission signal. Therefore, the control circuit3calculates the ToF (time to reception of the reflected light of the light emitted to the object40) from the difference in signal amount between the first 12-bit counter circuit71(0th to 11th T flip-flops TFF0to TFF11) and the second 12-bit counter circuit72(12th to 23rd T flip-flops TFF12to TFF23).

For example, when the difference in signal amount between the first 12-bit counter circuit71and the second 12-bit counter circuit72is 0, the signal amount of the 0th to 11th T flip-flops TFF0to TFF11is the same as the signal amount of the 12th to 23rd T flip-flops TFF12to TFF23. In this case, the control circuit3calculates ½ of the light projection pulse width (light projection time) as the length of time (ToF) to when the reflected light of the light emitted to the object is received.

As is clear from the above description, the LIDAR apparatus according to the fourth embodiment includes the lower-bit counter circuit (the first 12-bit counter circuit71) and the higher-bit counter circuit (the second 12-bit counter circuit72), and calculates the phase difference of the output signals of the counter circuits. Thus, the LIDAR apparatus can calculate the time (ToF) to when the reflected light of the light emitted to the object is received. Therefore, the SPAD sensor can be used as an indirect ToF sensor, and the same effects as those of the above-described embodiments can be obtained.