Patent Description:
A light detection and ranging (LiDAR) which is a distance measuring system irradiates a laser beam to an object to be measured, senses an intensity of a reflection light reflected from the object to be measured by a sensor, detects a point of time at which the reflection light reaches the LiDAR, and measures a distance between the LiDAR and the object to be measured based on time difference between the point of time at which the reflection light reaches and a point of time at which the laser beam is irradiated.

This LiDAR technology is expected to be applied to a part mounted on an automobile such as a sensor for automated driving. In the LiDAR which is required to perform a long distance measurement, an optical sensor having high sensitivity is necessary. That is, a photomultiplier which can even detect single photons, particularly, a silicon photo multiplier (hereinafter referred to as SiPM) has been used. At the same time, the LiDAR is also required to have high resolution, and a multi-pixel SiPM which adopts a one-dimensional or two-dimensional array configuration has been proposed (for example, Japanese <CIT> or Japanese <CIT>).

Although the SiPM has high sensitivity, the SiPM has a drawback that the recovery after detection of light takes time. As a means for alleviating this problem, an active quenching technique which uses an active element has been proposed. For example, see <NPL>, or <NPL>.

However, in the conventional multi-pixel SiPM, a sensor area is restricted and hence, it is difficult to ensure both high resolution and a dynamic range. Further, the LiDAR is required to be operated various situations such as a bright environment, a dark environment, a high-temperature environment and a low-temperature environment, the LiDAR has various problems in practical use. For example, in a conventional multi-pixel SiPM, a large current flows in a bright environment so that power consumption is increased. Conversely, if an amount of current is restricted, recovery is delayed so that a defect occurs in distance measurement. Furthermore, in an environment where sensor fusion is indispensable, LiDAR also should complement the functions of other sensors and is required to be multifunctional.

<NPL>, describes the design of a <NUM> × <NUM> photon-counting avalanche photodiode array with fully integrated active bias controlling circuit.

<NPL>, describes an integrated active quenching circuit that drives an avalanche photodiode above its breakdown voltage, in order to detect single photons.

<CIT> describes a photodetection circuit including an avalanche photodiode and a mode switching circuit that may be configured to selectively switch an operating mode of the photodetection circuit between linear mode and Geiger mode.

A embodiment of the present invention has been made in view of the above-mentioned circumstances, and it is an object of thereof to provide a LIDAR which uses a multi-pixel SiPM where both high resolution and expansion of a dynamic range can be acquired, and tasks such as the reduction of power consumption can be realized.

A photodetector of the embodiment is a photodetector which includes a plurality of channels each having a plurality of SPAD units, each SPAD unit having an avalanche photodiode, the photodetector being capable of selecting outputting or non-outputting of the channels, wherein the SPAD unit includes: an active quenching circuit which performs active quenching of the avalanche photodiode; and a control circuit which brings the active quenching circuit which corresponds to the channel where non-outputting is selected into an operable state.

Next, preferred embodiments will be described with reference to drawings.

<FIG> is a block diagram of a schematic configuration of a distance measuring device according to an embodiment.

The distance measuring device <NUM> according to the embodiment is configured as a LiDAR which measures a distance using a SiPM.

The distance measuring device <NUM> is configured to be able to measure a distance between the distance measuring device <NUM> and a distance measuring object OBJ. The distance measuring device <NUM> is configured as a vehicle mounted LiDAR, for example.

In this case, the distance measuring object OBJ is an object such as another vehicle, a pedestrian, or an obstacle which exists in front of, on sides, or behind a vehicle on which the distance measuring device <NUM> is mounted, for example.

The distance measuring device <NUM> includes a control measurement circuit <NUM>, a laser light source <NUM>, a scanner and optical system <NUM>, and a photodetector <NUM>.

The control measurement circuit <NUM> controls the operation of the entire distance measuring device <NUM>. More specifically, the control measurement circuit <NUM> sends an oscillation signal SP to the laser light source <NUM>, and controls the emission of a pulsed laser beam PLT by the laser light source <NUM>. Further, the control measurement circuit <NUM> sends a scanning control signal SC to the scanner and optical system <NUM> so as to drive the scanner and optical system <NUM>, and controls the scanning direction of a laser irradiated to the object OBJ. The control measurement circuit <NUM> sends a selection signal SL to the photodetector <NUM> to select channels (a plurality of SiPMs) which detect a light received by the photodetector <NUM> (including a reflection light of a pulsed laser beam PLT). Further, when an output signal SO is inputted to the control measurement circuit <NUM> as a result of detection of a light from the photodetector <NUM>, the control measurement circuit <NUM> calculates a distance between the distance measuring device <NUM> and the distance measuring object OBJ based on the output signal SO, and outputs distance data DD which includes the calculated distance.

The laser light source <NUM> emits a pulsed laser beam PLT (infrared light) having a predetermined pulse width and a predetermined cycle based on an oscillation signal SP from the control measurement circuit <NUM>, and the pulsed laser beam PLT is outputted to the scanner and optical system <NUM>.

<FIG> is an explanatory diagram of a first example of the scanner and optical system.

In the optical system illustrated in <FIG>, an optical axis of a projection light and an optical axis of a reflection light coincide with each other by a pinhole (perforated) mirror or the like. Accordingly, the optical system is called a coaxial optical system.

The scanner and optical system <NUM> illustrated in <FIG> includes, for example, a scanner, a light projecting optical system, and a light receiving optical system.

More specifically, in the example of <FIG>, the scanner and optical system <NUM> includes: a scanner unit which constitutes a one-dimensional scanning system and includes a polygon mirror <NUM> where respective mirror surfaces have different tilt angles and a polygon drive unit <NUM> which rotationally drives the polygon mirror <NUM>; a light projecting optical system which includes a lens <NUM> which condenses a laser emitted from a laser diode <NUM>,and a pinhole mirror <NUM> which projects the laser beam condensed by the lens <NUM> onto a scanning object via the polygon mirror <NUM>; and a light receiving optical system which includes a mirror <NUM> which receives a laser beam reflected on by the scanning object by way of the polygon mirror <NUM> and the pinhole mirror <NUM> and reflects the received light, and a one-dimensional sensor <NUM> which receives a laser reflected by the mirror <NUM>.

Then, the scanner and optical system <NUM> drives the scanner based on a scanning control signal SC from the control measurement circuit <NUM> so that the emission direction of a laser emitted to the outside of the distance measuring device <NUM> via the light projecting optical system can be changed. More specifically, for example, the scanner and optical system <NUM> includes a one-dimensional scanning system (capable of performing scanning in the horizontal direction, for example). A laser can be emitted to an entirety of a predetermined two-dimensional range by repeating laser scanning by the one-dimensional scanning system plural times (in directions different from each other little by little with respect to the vertical direction, for example).

<FIG> is a schematic diagram of a laser emission direction in the optical system illustrated in <FIG>.

As illustrated in <FIG>, the laser scanning is performed in the x direction from one end (a left side in the drawing) to the other end (a right side in the drawing) of a scanning object. When the laser scanning reaches the other end of the scanning object, then, at the position displaced from the above scanning position in the y direction by a predetermined distance, the laser scanning is performed in the x direction from the other end (the right side in the drawing) to one end (the left side in the drawing) of the scanning object. The predetermined two-dimensional range can be scanned by repeating such laser scanning plural times in the same manner.

In this case, the scanner which constitutes the scanner and optical system <NUM> mirror may be configured such that laser scanning can be performed by rotating a stage (not illustrated in the drawing) on which the light projecting optical system is mounted or laser scanning may be performed by driving a mirror which constitutes the light projecting optical system.

Further, the light receiving optical system which constitutes the scanner and optical system <NUM> condenses a received light including a reflection light generated when an emitted pulsed laser beam PLT is reflected by the object <NUM> (such a received light also including an ambient light and a stray light besides the reflection light) on the photodetector <NUM>. Here, an ambient light and a stray light form a noise.

Although the detailed configuration of the photodetector <NUM> is described later, when the received light is incident on the photodetector <NUM> from the scanner and optical system <NUM>, for example, electrons the number of which corresponds to the number of photons included in the reflection light are generated at each cycle of the pulsed laser beam PLT emitted from the laser light source <NUM>. The photodetector <NUM> is configured to generate, for example, about <NUM>,<NUM> electrons with respect to one photon. The photodetector <NUM> generates an output signal SO corresponding to the number of generated electrons and outputs the output signal SO to the control measurement circuit <NUM>. In the optical system illustrated in <FIG>, a reflection light is irradiated to basically the same position regardless of the scanning direction. As illustrated in <FIG>, the projection light has a shape elongated in one direction (for example, the vertical direction), and a one-dimensional sensor which is elongated in one direction is used.

<FIG> is an explanatory diagram of a second example of the scanner and optical system.

The optical system illustrated in <FIG> is called a non-coaxial optical system because an optical axis of an emitted light and an optical axis of a reflection light are different from each other.

In the optical system of <FIG>, a laser emitted from the laser diode <NUM> is condensed by a lens <NUM>, and the laser is reflected in a desired irradiation direction via, for example, a micro electro mechanical systems (MEMS) <NUM> which functions as a scanner. As the scanner, a small polygon mirror may be used besides the MEMS.

In the non-coaxial optical system having the above-mentioned configuration, a reflection light is irradiated to different positions in accordance with the scanning directions. Accordingly, the actual sensing position must be changed according to the scanning direction.

Accordingly, when a distance measurement is performed in the two-dimensional direction by a unit such as a two-dimensional scanner, as illustrated in <FIG>, it is necessary to condense a reflection light from a scanning object by the lens <NUM> and, thereafter, to selectively receive a light in accordance with scanning by the two-dimensional sensor array <NUM>.

Next, the configuration of the photodetector will be described.

<FIG> is an explanatory diagram of the configuration of the photodetector.

First, the configuration of the photodetector according to the first embodiment will be described with reference to <FIG>.

As illustrated in <FIG>, the photodetector <NUM> is configured as a two-dimensional array sensor having a plurality of channels <NUM> which are arranged two-dimensionally.

As illustrated in <FIG>, each channel <NUM> includes a plurality of (for example, <NUM> × <NUM> = <NUM>) cell units <NUM> arranged two-dimensionally. The reason why the number of cell units <NUM> which form the channel <NUM> is small in this manner is that an active quenching is fast so that a dynamic range can be increased due to its high speed property.

Next, a configuration example of another photodetector will be described.

<FIG> is an explanatory diagram of the configuration of another photodetector.

<FIG> is a typical arrangement example of the channels <NUM> in the two-dimensional array, and black dots represent the channels <NUM> respectively. Each square frame represents a SPAD unit.

Here, the number of channels <NUM> and the number of pixels are the same, and six SPAD units <NUM> correspond to one pixel which corresponds to one channel <NUM>.

That is, when the channel of interest is a channel <NUM>-<NUM> (= pixel G1), the sum of outputs of the six SPAD units surrounded by a bold line frame B1 is used as an output of the pixel G1.

Similarly, when the channel of interest is a channel <NUM>-<NUM> (= pixel G2), the sum of the outputs of the six SPAD units surrounded by a bold line frame B2 is used as an output of the pixel G2.

By adopting such a configuration, it is possible to provide a photodetector having a desired number of pixels (for example, <NUM> × <NUM> pixels) using a certain number of SPAD units <NUM>.

<FIG> is a schematic diagram of a typical channel in a one-dimensional array.

In <FIG>, description will be made assuming that each channel <NUM> includes <NUM> cell units <NUM> (cell units <NUM>-<NUM> to <NUM>-<NUM>).

In the channel <NUM>, a plurality of cell units <NUM>-<NUM> to <NUM>-<NUM> are connected in parallel, and outputs of the cell units <NUM>-<NUM> to <NUM>-<NUM> are respectively connected to an output terminal <NUM> via selection switches <NUM>-<NUM> to <NUM>-<NUM> corresponding to the respective cell units <NUM>-<NUM> to <NUM>-<NUM> and an integrator <NUM>. When the sensor is a current output type sensor, for example, the integrator <NUM> is realized by simply joining output lines to each other.

In the description made hereinafter, when it is not necessary to distinguish the cell units <NUM>-<NUM> to <NUM>-<NUM> from each other, the cell units <NUM>-<NUM> to <NUM>-<NUM> are expressed as the cell units <NUM>.

Accordingly, the output signals of the cell units <NUM>-<NUM> to <NUM>-<NUM> are outputted from the output terminal <NUM> in an integrated manner.

By the way, not all of the plurality of two-dimensionally arranged channels <NUM> which form the photodetector <NUM> perform outputting simultaneously. That is, by designating the position (or the position range) in the first direction (for example, the vertical direction in <FIG>) and the second direction (for example, the Y direction in <FIG>) based on a position designation signal, output signals of the channels <NUM> included in a region having a predetermined shape (a rectangular area, a circular area, an elliptical area or the like) designated based on the position designation signal are separately outputted to a subsequent output stage circuit.

<FIG> is an explanatory diagram of an example of a sensor which selects an outputting region.

<FIG> schematically illustrates the selection of an output region in the one-dimensional sensor. In <FIG>, a portion in a bold line frame indicates the selected region.

In general, a one-dimensional sensor is often used with a coaxial optical system, and has an output selection function such that, when the irradiation position is displaced due to individual difference between distance measuring devices, a temperature or aging, the position can be adjusted.

On the other hand, <FIG> schematically shows the selection of an output region in a two-dimensional sensor, and a portion in a bold line frame indicates a selected region in <FIG>.

In the case of a two-dimensional sensor, the position of the output region is generally selected in accordance with the scanning direction of the light projecting system.

In this embodiment, as described above, the output signals of the channels <NUM> are outputted separately, and the signals are not outputted after being coupled so that the lowering of S/N can be avoided.

Further, since the outputting from a plurality of channels <NUM> is used instead of the outputting from one channel <NUM>, no problem occurs even if the synchronization is loose, and the configuration strongly resist against the displacement of the light receiving position.

Further, even when the received light is irradiated across the channels <NUM>, the received light can be detected.

In the case where the respective cell units <NUM>-<NUM> to <NUM>-<NUM> are in a measuring allowable state, regardless of whether or not the measuring is actually performed, even when one photon is incident, a large amount of current generated by the Geiger phenomenon (a current generated by one photon generates a current approximately <NUM>,<NUM> times as large as the current generated by one photon) flows and hence, power consumption is also increased.

In particular, when the photodetector <NUM> is configured as a two-dimensional array sensor, the number of cell units <NUM> is enormous and hence, the power consumption becomes very large, and in the worst case, the wiring may be disconnected.

In view of the above, in the embodiment described hereinafter, when the outputting to a subsequent stage is not performed, the power consumption of the cell unit <NUM> corresponding to a non-outputting portion is suppressed. As a result, the power consumption of the entire photodetector <NUM> which constitutes a two-dimensional array sensor is suppressed.

<FIG> is a block diagram showing a schematic configuration of the cell unit.

The cell unit <NUM> includes: a plurality of SPAD units <NUM> which are connected in parallel and each have an output terminal <NUM>; and an integrator <NUM> which integrates outputs of the SPAD units <NUM> and output an integrated output.

Next, a specific configuration of the SPAD unit will be described.

<FIG> is a diagram illustrating a schematic function and configuration of a SPAD unit according to the first embodiment.

The SPAD unit <NUM> includes: a resistor <NUM> having one end connected to a high-potential side power source PH; a silicon avalanche photo diode (SiAPD) <NUM> having a cathode connected to the other end of the resistor <NUM> and an anode connected to a low-potential side power source PL; a current limiting resistor <NUM> connected in parallel to the SiAPD <NUM>; a quenching switch <NUM> connected between the current limiting resistor <NUM> and a second low-potential side power source PL2; a sensing unit <NUM> configured to detect a change of a potential caused by a Geiger current of the SiAPD <NUM> and to output a detection signal SEN in an insulated state; a selection switch <NUM>; an OR (logical sum) circuit <NUM>; and a holding circuit <NUM>. The resistor <NUM> may be substituted by a transistor as described later, and the SPAD unit <NUM> may not include the resistor <NUM>.

In this embodiment, a potential VPL2 of the second low-potential side power source PL2 is set lower than a voltage described below due to an operating voltage PH, a breakdown voltage Vbd, and an over voltage Vov of the SiPM (this potential setting being also applicable hereinafter). That is, the following relationship is established.

The quenching switch <NUM> is realized by a MOS transistor, for example.

In this embodiment, the photodetector <NUM> controls each SPAD unit <NUM> based on a selection signal SL outputted from the control measurement circuit <NUM>.

In the above-mentioned configuration, when a Geiger current is detected, a logical value of a detection signal SEN is changed from "<NUM>" (for example, "L" level) to "<NUM>" (for example, "H" level), and the logical value of a detection signal SEN is held at "<NUM>" for a predetermined time by the holding circuit <NUM>.

As a result, during the period in which the logical value of the detection signal SEN is "<NUM>", an output of the OR circuit <NUM> becomes "<NUM>".

Accordingly, the quenching switch <NUM> is always in an ON state (closed state) during the period in which the logical value of the detection signal SEN is "<NUM>". When the logical value of the detection signal SEN is set to "<NUM>", the quenching switch <NUM> is brought into an OFF state (open state) during a period in which a detection signal SEN is outputted from the SPAD unit <NUM> in response to a control signal Cs, and the quenching switch <NUM> is brought into an ON state (closed state) during a period in which a detection signal SEN is not outputted from the SPAD unit <NUM> in response to the control signal Cs.

On the other hand, when a detection signal SEN of the SPAD unit <NUM> is outputted in response to a control signal Cs, the selection switch <NUM> is brought into an ON state (closed state), and when the detection signal SEN from the SPAD unit <NUM> is not outputted in response to a control signal Cs, the selection switch <NUM> is brought into an OFF state (open state).

Further, a resistance value R2 of the current limiting resistor <NUM> is set to be very small compared to a resistance value R1 of the quenching resistor <NUM> (R2 << R1).

The manner of operation of the first embodiment will be described hereinafter.

As described above, outputting or non-outputting of an output signal of the channel <NUM> is selectable. When non-outputting where outputting is not performed via the output terminal <NUM> (see <FIG>) is selected, the selection switch <NUM> of the SPAD unit <NUM> which constitutes the channel <NUM> where non-outputting is selected is brought into an OFF state (open state), and the active quenching switch <NUM> is brought into an ON state (closed state).

As a result, a predetermined reverse bias voltage generated due to a high-potential side power source PH and a low-potential side power source PL is not applied between an anode and a cathode of the SiAPD42 and hence, the voltage is not biased to a breakdown voltage of avalanche breakdown of the SiAPD42 (for example, -<NUM> V). Accordingly, a Geiger phenomenon does not occur in the SiAPD <NUM> even when light enters the SiAPD <NUM> from the scanner and optical system unit <NUM>, and a Geiger current generated by a Geiger discharge does not flow into the SiAPD <NUM>.

That is, according to the first embodiment, when the outputting of the channel <NUM> is not selected (during non-outputting), a Geiger current (approximately <NUM>,<NUM> times as large as a normal current) does not flow unnecessarily into the plurality of SiAPDs <NUM> which form the non-selected channel <NUM>. Accordingly, the lowering of power consumption of the photodetector <NUM> and, eventually, the lowering of power consumption of the distance measuring device <NUM> can be realized.

Further, for such a configuration, the active quenching switch <NUM> for performing active quenching is diverted when the channel <NUM> is selected and hence, it is possible to suppress an increase of a circuit scale.

In this example, for the sake of brevity, an output of the sensing unit <NUM> is directly outputted to the output terminal <NUM>, however, the output of the sensing unit <NUM> may be outputted to the output terminal <NUM> via an output buffer. In the output buffer, a time for holding "<NUM>" may be set different from a holding time which corresponds to the detection signal SEN described above.

In the case where the number of channels <NUM> is large, when the SPAD unit <NUM> does not perform outputting via the output terminal <NUM>, there is a possibility that a through current which flows from a high-potential side power source PH to a low-potential side power source PL via the quenching resistor <NUM>, the current limiting resistor <NUM>, and the active quenching switch <NUM> brings about considerable power consumption of the entire photodetector <NUM>.

In view of the above, a modification of the first embodiment is provided for suppressing this through current thus suppressing the power consumption of the entire photodetector <NUM>.

<FIG> is a diagram illustrating a schematic functional configuration of a SPAD unit according to the modification of the first embodiment.

In the modification of the first embodiment, as illustrated in <FIG>, a through-current prevention switch <NUM> is provided between a resistor <NUM> and the high-potential side power source PH. Note that the resistor <NUM> may not be provided.

When the outputting from the channel <NUM> is not selected (non-outputting time), that is, when the SPAD unit <NUM> does not perform outputting via an output terminal <NUM>, a selection switch <NUM> and the through-current prevention switch <NUM> are brought into an OFF state (open state), and an active quenching switch <NUM> is brought into an ON state (closed state).

As a result, it becomes possible to prevent a through current flowing from the high-potential side power source PH to the low-potential side power source PL via the resistor <NUM>, the current limiting resistor <NUM>, and the active quenching switch <NUM>. Accordingly, power consumption can be further reduced.

As described above, according to the modification of the first embodiment, with respect to the SPAD units <NUM> corresponding to the channels <NUM> in an outputting non-selected time, it is possible to eliminate a Geiger current and hence, it is possible to reduce or eliminate a through current which flows from the high-potential side power source PH to the low-potential side power source PL. Therefore, power consumption can be reduced without affecting the intended distance measurement.

<FIG> is an explanatory diagram of an example of a circuit configuration of the SPAD unit according to the first embodiment.

<FIG> and <FIG> described above are provided for functionally describing the SPAD unit <NUM> of the first embodiment. As an actual circuit configuration of the SPAD unit <NUM>, for example, a configuration illustrated in <FIG> is adopted.

In the SPAD unit <NUM> illustrated in <FIG>, a transistor M4 corresponds to a quenching switch, and a transistor M3 corresponds to a reset switch which recovers a cathode potential of a SiAPD <NUM> while preventing a through current.

In order to hold a signal for a predetermined time, four inverters are used as a holding circuit <NUM> (delay circuit). On the other hand, the holding circuit <NUM> (delay circuit) is not connected to gate terminals (inputting) of a transistor M1 and the transistor M4 which are required to exhibit a high-speed response in quenching. Accordingly, a quick quenching operation is expected with respect to the transistor M1 and the transistor M4.

Further, a transistor M5 is added compared to a conventional active quenching circuit. Accordingly, when a selection signal SL is "<NUM>" (= "L" level), a logic value of a connection point MP is fixed to "<NUM>" (= "H" level) by the transistor M5. As a result, the quenching switch M4 is brought into an ON state (closed state), and the SiAPD <NUM> is held at a voltage equal to or below a breakdown voltage Vbd. At the same time, a transistor M3 is in an OFF state (open state), there is no possibility that a through current flows.

When a conventional circuit which is not provided with the transistor M5 is used, when a selection signal SL is "<NUM>" (= "L" level), the transistor M2 and the transistor M3 are always in an OFF state (open state), and the connection point MP is in a floating state. In particular, when the power source is supplied, a plurality of SiAPDs <NUM> are brought into an ON state at a time and hence, there is a possibility that a large current flows.

<FIG> is an explanatory diagram of a functional circuit for preventing a selection signal SL from becoming "<NUM>" (= "H" level) when the power source is supplied.

In the above circuit, it is assumed that an output of the JK flip-flop 14B never fails to become "<NUM>" (= "L" level) after the power source is supplied. The selection signal SL is held at <NUM> (L) until a Start signal is inputted. By using the circuit together with the circuit illustrated in <FIG>, there is no possibility that the SiAPDs <NUM> are brought into an ON state at a time until a start signal SSTRT is inputted after the power source is supplied.

In the first embodiment, the configuration is adopted where whether or not a Geiger current is generated by the incidence of light is digitally detected. The second embodiment, however, is an embodiment where an amount of Geiger current generated by the incidence of light is measured simply and in an analog manner, SPAD units <NUM> are effectively used as analog elements, and the SPAD units <NUM> are used as an infrared camera when the SPAD units <NUM> are not used for distance measurement.

<FIG> is a schematic configuration diagram of a SPAD unit according to the second embodiment.

In <FIG>, parts similar to the corresponding parts in the first embodiment illustrated in <FIG> are denoted by the same reference numerals, and the detailed description of the parts used in the first embodiment are used also in this embodiment.

The SPAD unit <NUM> of the second embodiment differs from the SPAD unit <NUM> of the first embodiment with respect to a point that the SPAD unit <NUM> includes: an integrator <NUM> which integrates detection signals SEN outputted from a sensing unit <NUM> and outputs an integral signal SINT via the output terminal <NUM>; a timer <NUM> which counts a time from reset timing of the integrator <NUM> to a point of time that the integrator <NUM> reaches a maximum value (saturation) and outputs a count value TIM; and an AND circuit <NUM> which outputs a control signal for bringing an active quenching switch <NUM> into a closed state when the integrator <NUM> reaches the maximum value (saturation) and the SPAD unit <NUM> is in a non-distance measuring state.

<FIG> is an explanatory diagram of a specific circuit example of the integrator.

In the above configuration, as illustrated in <FIG>, as the integrator <NUM>, an integrator which uses a capacitor C1 and an operational amplifier OP and includes an input resistor R1 and a reset switch RSW is generally adopted.

However, a digital circuit such as a counter may be used as the integrator <NUM>. In a case where resetting (recharging) of active quenching is performed by a current source, the integrator can be realized simply by connecting one capacitor to the current source.

The reason that the timer <NUM> is provided to the SPAD unit <NUM> will be described.

With respect to the integrator <NUM>, since the number of SPAD units <NUM> is large, the number of integrators <NUM> becomes also large. Therefore, from the viewpoint of an installation area, a capacity of the integrator <NUM> cannot be increased so much that there is a possibility that a full capacity charge will be stored in the integrator <NUM> during a sensing period.

In view of the above, by counting a time until a capacity of the integrator <NUM> becomes full due to storing of a charge in the integrator <NUM> by the timer <NUM>, an amount of a charge which is considered to be stored in the integrator <NUM> if the integrator <NUM> is operated during a sensing period is estimated so that an effective dynamic range can be increased.

As a result, it is possible to perform processing which prevents the occurrence of a saturated state similar to a so-called whiteout phenomenon that occurs in a normal digital camera, and an effective dynamic range of the SPAD unit <NUM> can be substantially expanded.

Accordingly, it is possible to use the SPAD units <NUM> which do not perform distance measurement, that is, the SPAD units <NUM> in a non-selected state as imaging pixels. On the other hand, it is possible to make a photodetector <NUM> which constitutes a two-dimensional array sensor function as an infrared camera by using an integral signal SINT or a count value TIM which is outputted via an output terminal <NUM> as an imaging signal.

Furthermore, in the case where neither a distance measuring operation nor an infrared camera operation is performed based on a control signal Cs and an output from the integrator <NUM>, by bringing an active quenching switch <NUM> of an AND circuit <NUM> into an ON state (closed state), in the same manner as the first embodiment, with respect to the SPAD units <NUM> which do not perform outputting via an output terminal <NUM> after an integral function is used, a Geiger current can be eliminated and a through current which flows from a high-potential side power source PH to a low-potential side power source PL can be reduced. Accordingly, power consumption can be reduced without affecting the intended distance measurement.

Details of the manner of operation of the second embodiment will be described hereinafter.

<FIG> is an explanatory diagram of the manner of operation the second embodiment.

<FIG> is an explanatory diagram of the manner of operation when the integrator <NUM> is not saturated.

In this case, the active quenching switch <NUM> can be brought into an ON state (closed state) depending on the sensing unit <NUM>. Assume that the selection switch <NUM> is in an ON state (closed state).

As a result, during a period from a point of time t1 to a point of time t2, when the SiAPD <NUM> receives a reflection light of an emitted pulsed laser beam PLT, a Geiger current flows. Accordingly, the sensing unit <NUM> outputs a detection signal SEN via an output terminal <NUM>. As a result, the distance measurement is performed based on the difference (time) between a point of time that a pulsed laser beam PLT is emitted and a timing that a reflection light of the pulsed laser beam PLT is received.

The distance measurement is finished when the point of time t2 comes and hence, the selection switch <NUM> is brought into an OFF state (open state), the SPAD unit <NUM> is brought into an infrared camera operation mode, and the integrator <NUM> and the timer <NUM> are reset.

In an infrared camera operation mode, the SiAPD <NUM> receives an ambient light. When a Geiger current flows, the sensing unit <NUM> outputs a detection signal SEN to the integrator <NUM>.

As a result, the integrator <NUM> performs an integration operation, and the timer <NUM> performs a time measuring operation.

Then, at a point of time t3 that a predetermined imaging time has elapsed, in a case where the integrator <NUM> has not yet reached a saturation state, the integrator <NUM> outputs an integral signal SINT having a value proportional to an amount of received light (intensity of an ambient light) via the output terminal <NUM>.

Therefore, the control measurement circuit <NUM> in a subsequent stage constitutes an infrared imaged image based on the integral signal SINT.

Thereafter, at a timing that neither distance measurement nor infrared imaging is performed, the control measurement circuit <NUM> sets the control signal Cs to "<NUM>" via the controller 14A.

As a result, when an output of the AND circuit <NUM> becomes "<NUM>", the active quenching switch <NUM> is brought into an ON state (closed state).

Accordingly, it is possible to eliminate a through current flowing from a high-potential side power source PH to a low-potential side power source PL via the resistor <NUM>, the current limiting resistor <NUM>, and the active quenching switch <NUM> and hence, power consumption can be reduced.

<FIG> is an explanatory diagram of an operation of the integrator <NUM> when the integrator <NUM> reaches a saturated state.

Also in this case, the active quenching switch <NUM> can be brought into an ON state (closed state) depending on the sensing unit <NUM>. Assume that the selection switch <NUM> is in an ON state (closed state).

During the period from the point of time t1 to the point of time t2, when the SiAPD <NUM> receives a reflection light of an emitted pulsed laser beam PLT, a Geiger current flows. Therefore, the sensing unit <NUM> outputs a detection signal SEN via the output terminal <NUM>. As a result, the distance measurement is performed based on the difference (time) between a point of time that a pulsed laser beam PLT is emitted and a timing that a reflection light of the pulsed laser beam PLT is received.

In the case where the integrator <NUM> reaches a saturated state at the point of time t3 that a predetermined imaging time has not elapsed (the point of time that the predetermined imaging time has elapsed t4> t3), the integrator <NUM> notifies the timer <NUM> accordingly.

Further, the integrator <NUM> sets an output to the AND circuit <NUM> to "<NUM>" (corresponding to the output when the integrator <NUM> is saturated).

As a result, the timer <NUM> stops time measurement and holds a count value.

Then, at the point of time t4 that a predetermined imaging time has elapsed, the timer <NUM> outputs a count value TIM which corresponds to a time until the integrator <NUM> is saturated (= t3-t2) via the output terminal <NUM>.

Accordingly, the control measurement circuit <NUM> in the subsequent stage constitutes an infrared imaged image based on the count value TIM.

Specifically, the control measurement circuit <NUM> constitutes an infrared imaged image by estimating the intensity of an ambient light by increasing the intensity of an ambient light corresponding to a saturation time of the integrator <NUM> by (t4-t2)/(t3-t2) times using the point of time t2, the point of time t3 and the point of time t4.

Therefore, according to the second embodiment, distance measurement and infrared image imaging can be performed exclusively.

Further, according to the second embodiment, in the same manner as the first embodiment, with respect to the SPAD unit <NUM> which do not perform outputting via the output terminals <NUM>, a Geiger current is eliminated and hence, a through current flowing from the high-potential side power source PH to the low-potential side power source PL can be reduced or eliminated. Accordingly, the power consumption can be reduced without affecting the intended distance measurement and infrared image imaging.

Further, in the same manner as the modification of the first embodiment, a through-current prevention switch <NUM> is provided between the resistor <NUM> and the high-potential side power source PH and hence, a through current flowing from the high-potential side power source PH toward the low-potential side power source PL via the resistor <NUM>, the current limiting resistor <NUM>, and the active quenching switch <NUM> can be eliminated whereby the power consumption can be further reduced.

In the above description, two output terminals, that is, the output terminal <NUM> and the output terminal <NUM> are provided as output terminals. However, a changeover switch may be disposed in the SPAD unit <NUM> and one output terminal may be shared in common.

In the first embodiment described above, an output of the sensing unit <NUM> is directly outputted from the output terminal <NUM>. The third embodiment is, however, an embodiment where an output selected from outputs of a sensing unit <NUM> is time-integrated in an output stage of the photodetector <NUM> after multi-valuing.

<FIG> is a diagram showing a schematic configuration of a SPAD unit according to the third embodiment.

The SPAD unit <NUM> of the third embodiment differs from the SPAD unit <NUM> of the first embodiment illustrated in <FIG> with respect to a point that an integrator <NUM> is provided between a selection switch <NUM> and an output terminal <NUM>.

The reason that the integrator <NUM> is provided will be described hereinafter.

The SPAD unit <NUM> only outputs whether or not a Geiger current has flowed, and basically can only respond to binary values of "<NUM>" and "<NUM>".

In view of the above, in the third embodiment, an active quenching operation is performed by bringing an active quenching switch <NUM> into an ON state (closed state) plural times during a predetermined integration period. Since the active quenching SPAD can be operated at a high speed, the active quench SPAD can be operated plural times. However, it is possible to increase an operating speed of the active quench SPAD also by downsizing of the SPAD. By combining the operation of the active quenching SPAD plural times during a predetermined integration period and downsizing of the SPAD, it is possible to expect an operation of the SPAD at a higher speed of GHz level.

On the other hand, a photodetector <NUM> and an analog/digital circuit in a subsequent stage (included in a control measurement circuit <NUM>) differ from each other in required process technique and the like. Accordingly, it is desirable that the photodetector <NUM> and the analog/digital circuit are realized as different integrated circuits. In this case, the output terminal <NUM> performs data transfer between chips and hence, impedance such as parasitic capacitance is increased. If a high-speed transfer at a GHz level is intended between chips as described above, data may not be transferred correctly due to problems on impedance.

The reason that the integrator <NUM> is provided is that the SPAD unit <NUM> is effectively realized as a multi-value (n-value) sensor by performing detection plural times (n times) so that the above problems are solved.

In this case, with the use of the integrator <NUM>, reliable data transfer between the chips can be realized.

The reason is that although the SPAD unit <NUM> can perform a high-speed response operation by performing an active quenching operation, by transmitting a high-speed response result as a multi-value analog value at a low speed rather than directly transferring the high-speed response result, it is possible to realize stable data transfer.

That is, it is possible to easily perform interchip communication between the control measurement circuit <NUM> which is usually formed as a separate chip in a subsequent stage of the chip which constitutes the photodetector <NUM>. Further, data can be directly processed by the A/D converter which the control measurement circuit <NUM> has.

As the integrator <NUM>, a digital circuit using a counter and analog integration using a capacitor can be used.

<FIG> is a schematic explanatory diagram of an example where a low-pass filter is applied.

As schematically illustrated in <FIG>, a peak value of a low-pass filter output (indicated by an arrow in the drawing) is proportional to an addition result of low-pass filter input values. The simplest low-pass filter is a filter where a resistor and capacitor are connected in series.

Further, the integrators <NUM> are included in an output stage and it is sufficient to provide the integrators <NUM> only for outputs selected from outputs of a sensing unit <NUM>, it is sufficient to mount the integrators <NUM> the number of which corresponds to the number of output channels.

Further, the number of output channels is much smaller than the number of pixels in multiple pixels, especially in a two-dimensional sensor. Accordingly, by providing the integrators <NUM> in an output stage after a selection switch <NUM>, area efficiency can be increased whereby a multi-valued function can be realized.

Furthermore, by providing the integrator <NUM> illustrated in <FIG> with the same function as the integrator <NUM>, it is possible to cause a plurality of SPAD units <NUM> to function as multi-value sensors.

By adopting such a configuration, it is sufficient to provide the integrators the number of which is equal to the number of cell units <NUM> and hence, a multi-value sensor can be realized with a realistic circuit scale.

As described above, according to the third embodiment, it is possible to form a multi-value sensor without significantly changing the configuration of a conventional photodetector <NUM>.

Also in this case, in the same manner as the first embodiment, with respect to the SPAD units <NUM> which do not perform outputting via output terminals <NUM>, a Geiger current is eliminated and hence, a through current flowing from a high-potential side power source PH to a low-potential side power source PL can be reduced or eliminated. Accordingly, the power consumption can be reduced without affecting the intended distance measurement.

Further, in the same manner as the modification of the first embodiment, a through-current prevention switch <NUM> which constitutes a first switch is provided between a resistor <NUM> and the high-potential side power source PH. Accordingly, a through current flowing from the high-potential side power source PH toward the low-potential side power source PL via a resistor <NUM>, a current limiting resistor <NUM>, and an active quenching switch <NUM> can be eliminated and hence, the power consumption can be further reduced.

There may be a case where the SiAPD <NUM> receives a large amount of light and the return of a cathode of the SiAPD <NUM> to an initial state is not completed within a predetermined time. In this case, for example, in the circuit illustrated in <FIG>, M3 is brought into an OFF state at a predetermined time and hence, it takes a long time before a carrier of APD42 is released. Accordingly, there arises a drawback that the measurement cannot be performed at next measuring timing so that measurement performance is deteriorated.

<FIG> is a schematic configuration diagram of a SPAD unit according to the fourth embodiment.

The SPAD unit <NUM> of the fourth embodiment differs from the SPAD unit <NUM> of the first embodiment illustrated in <FIG> with respect to following points. A current limiting resistor <NUM> and a cathode reset switch <NUM> which constitutes a second switch are connected in series between a high-potential side power source PH and a current limiting resistor <NUM>. The SPAD unit <NUM> includes an AND circuit <NUM> which brings a cathode reset switch <NUM> into an ON state (closed state) in the case where an SiAPD <NUM> receives a large amount of light during an output period which is an ON state (closed state) of a selection switch <NUM> so that a sensing unit <NUM> detects that the return of the cathode of the SiAPD <NUM> is to an initial state is not completed within a predetermined time.

In this case, a resistance value R3 of the current limiting resistor <NUM> is set to be very small compared to a resistance value R1 of the resistor <NUM> (R3 << R1).

Next, the manner of operation of the fourth embodiment will be described.

Assume that, in an initial state of the SPAD unit <NUM>, the cathode of the SiAPD <NUM> is in an initial state, and the cathode reset switch <NUM> is in an OFF state (open state).

In this state, when the SPAD unit <NUM> performs outputting via an output terminal <NUM>, the selection switch <NUM> is brought into an ON state (closed state) and an active quenching switch <NUM> is brought into an OFF state (open state).

As a result, a predetermined reverse bias voltage generated by a high-potential side power source PH and a low-potential side power source PL is applied between an anode and the cathode of the SiAPD42 and hence, a voltage is biased to a breakdown voltage (for example, -<NUM> V) of an avalanche breakdown of the SiAPD42.

Therefore, when a light enters the SiAPD <NUM> from a scanner and optical system unit <NUM>, a Geiger phenomenon occurs, and a Geiger current caused by Geiger discharge flows.

Accordingly, the sensing unit <NUM> outputs a detection signal SEN indicating that the Geiger current is detected via the selection switch <NUM> and the output terminal <NUM>.

Thereafter, since a control signal Cs is at "<NUM>", the sensing unit <NUM> is at "<NUM>" and hence, the active quenching switch <NUM> is held in an ON state for a predetermined time. Accordingly, a quenching operation is performed, and the SiAPD <NUM> is returned to an initial state at a high speed.

When a predetermined time elapses after the active quenching switch <NUM> is brought into an ON state, the active quenching switch <NUM> is brought into an OFF state (opened state).

In this case, in the case where an SiAPD42 receives a large amount of light so that a sensing unit <NUM> detects that the return of the cathode of the SiAPD <NUM> to an initial state is not completed within a predetermined time, "<NUM>" is outputted to an AND circuit <NUM>.

At this time, since a control signal Cs which brings the selection switch <NUM> into an ON state is also "<NUM>", the AND circuit <NUM> brings the cathode reset switch <NUM> into an ON state (closed state).

As a result, the cathode reset current IRST flows via the cathode reset switch <NUM> and the current limiting resistor <NUM> from the cathode of the SiAPD <NUM> toward the high-potential side power source PH.

As a result, the cathode of the SiAPD <NUM> returns to an initial state at a high speed.

As described above, according to the fourth embodiment, even when a large amount of light is irradiated to the SiAPD <NUM> which constitutes the cell unit <NUM>, the distance measuring device is restored quickly and hence, measurement is performed again. <FIG> illustrates a functional implementation of the present embodiment. As a circuit, the SPAD unit <NUM> can be realized by a method such as inserting a NAND gate into an input of the gate of the transistor M3 illustrated in <FIG> and forming the other input by an MP.

Claim 1:
A photodetector (<NUM>) comprising a plurality of channels (<NUM>) each having a plurality of SPAD units (<NUM>), each SPAD unit having an avalanche photodiode (<NUM>), the photodetector (<NUM>) being controlled and supplied with a second selection signal (SL) by a control circuit (<NUM>) to select the channels, wherein
the photodetector (<NUM>) being controlled to be capable of selecting outputting or non-outputting of the channels (<NUM>),
each of the SPAD units (<NUM>) further includes an active quenching circuit (<NUM>, <NUM>) which performs active quenching of the avalanche photodiode (<NUM>),
the control circuit (<NUM>) brings the active quenching circuit (<NUM>, <NUM>), which corresponds to the channel where non-outputting is selected, into an operable state by the first selection signal (SL) from the control circuit (<NUM>), and
the photodetector (<NUM>) further includes a selection-signal generator (14B, 14C) which generates and outputs, to the plurality of SPAD units (<NUM>), the second selection signal (SL) obtained by taking a logical product of a first selection signal and a signal that turns to a logical value of zero upon power-on, so as not to bring the avalanche photodiodes (<NUM>) of the plurality of SPAD units (<NUM>) into an ON state at a time until a start signal is inputted.