TDC device, ranging device and ranging method

Abstract

To improve measurement accuracy while reducing the effect of fluctuation in the amount of voltage drop of a voltage supplied to a TDC circuit.SOLUTION: A TDC device 50 comprises: a TDC circuit 2 having a delay circuit including multi-stage delay elements configured to sequentially delay a measurement signal and multiple storage elements provided to correspond to the multi-stage delay elements and configured to retain outputs of the multi-stage delay elements in response to input measurement clocks; an edge detection unit 3 configured to detect a detection stage of the delay element that detected at least a rising edge of the measurement signal on the basis of switching of outputs of the multiple storage elements; a time computation unit 5 configured to output a delay time of the measurement signal on the bases of a delay conversion table pertaining to detection stages of the delay elements and amounts of delay of the multiple delay elements; and a delay unit 1 configured to delay the input measurement signal and then input the signal to the delay circuit of the TDC circuit 2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a TDC device, a ranging device, and a ranging method. [Background technology]

[0002] For example, the Time of Flight (TOF) method is used as a distance measurement method for measuring the distance to an object. In a distance measurement device using the TOF method, the distance to an object can be measured by detecting the flight time of light from the time when light is irradiated onto the object to the time when the reflected light is received.

[0003] Known distance measuring devices using the TOF method include devices that detect the time of flight of light using a TDC (time to digital converter) circuit. A TDC circuit is a circuit that digitizes time information. A delay element and a flip-flop are often used in this TDC circuit. In this TDC circuit, the delay amount (delay time) of the delay element varies due to variations in the manufacturing process, changes in the power supply voltage, and temperature changes during operation (so-called PVT (Process Voltage Temperature) fluctuations). If the delay amount of the delay element in the TDC circuit varies, it affects the measurement accuracy of the distance measuring device.

[0004] Therefore, in the past, a technique has been proposed for calibrating the TDC circuit when the distance measurement operation is not performed in a distance measuring device. For example, Patent Document 1 discloses a method for calibrating the variation in the delay amount of a delay element so that the TDC circuit operates normally against PVT fluctuations. In the method described in Patent Document 1, the delay amount of the delay element is adjusted by adjusting the bias current applied to the delay element. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2012-114716 A Summary of the Invention [Problem to be solved by the invention]

[0006] In a measurement device (e.g., a distance measuring device) equipped with a TDC circuit, a delay conversion table is generated or the delay amount of each delay element stored in the delay conversion table is calibrated by performing calibration, for example. However, when performing a calibration operation, it is desirable to complete the calibration operation in as short a time as possible because a distance measurement operation cannot be performed. For this reason, in a calibration operation, it is necessary to input many more pulses (calibration signals) to the TDC circuit in a short time than in a measurement operation.

[0007] When distance measurement and calibration operations are performed in a distance measuring device, a voltage drop occurs in which the power supply voltage of the TDC circuit becomes lower than a predetermined voltage value. In particular, during calibration operations in which pulses are input to the TDC circuit continuously in a short period of time, the voltage drop is greater than during measurement operations. In other words, the voltage drop of the TDC circuit differs between calibration operations and measurement operations. This difference in voltage drop causes the amount of delay of the delay element to differ between calibration operations and measurement operations. As a result, even if the TDC circuit is calibrated before the measurement operation, it is difficult to obtain a proper measurement. Distance measurement There is a risk that it will not be possible to do so.

[0008] Generally, the voltage drop of the power supply voltage of the TDC circuit during the measurement operation is smaller than the voltage drop of the power supply voltage of the TDC circuit during the calibration operation, so the delay amount of each delay element of the TDC circuit during the measurement operation is smaller than the delay amount of each delay element of the TDC circuit during the calibration operation. Therefore, a difference (error) occurs between the actual delay amount of each delay element during the measurement operation and the delay amount of each delay element during the calibration operation. Therefore, even if calibration is performed, it is difficult to accurately calibrate the delay amount of multiple delay elements. Note that, depending on the conditions, the voltage drop of the power supply voltage of the TDC circuit during the measurement operation may be larger than the voltage drop during the calibration operation, but in this case, a difference (error) occurs between the actual delay amount of each delay element during the measurement operation and the delay amount of each delay element during the calibration operation.

[0009] When calculating the delay time of the measurement signal in the TDC circuit during the measurement operation, for example, a cumulative delay amount obtained by accumulating the delay amounts of multiple delay elements calibrated by the calibration operation is used. As described above, due to the fluctuation in the voltage drop amount of the power supply voltage of the TDC circuit, an error occurs between the actual delay amount of each delay element during the measurement operation and the delay amount of each delay element during the calibration operation, so an error also occurs in the cumulative delay amount used when calculating the delay time of the measurement signal. Here, the error occurring when calculating the delay time of the measurement signal in the TDC circuit increases as the detection stage of the delay element that detects the rising edge of the measurement signal increases.

[0010] Therefore, an example of an object of the present invention is to provide a TDC device, a distance measuring device, and a distance measuring method that can improve measurement accuracy while reducing the effects of fluctuations in the amount of voltage drop in the power supply voltage of the TDC circuit. [Means for solving the problem]

[0011] (1) In order to achieve the above object, a TDC device according to one aspect of the present invention includes a TDC circuit having a delay circuit including multiple stages of delay elements that sequentially delay a measurement signal, and multiple memory elements that are provided corresponding to the multiple stages of delay elements and hold outputs of the multiple stages of delay elements in response to an input measurement clock, an edge detection unit that detects a detection stage of a delay element that has detected at least a rising edge of a measurement signal based on switching of the outputs of the multiple memory elements, and step The TDC circuit is characterized by having a time calculation unit that outputs the delay time of the measurement signal based on a delay conversion table relating to the delay amount of the delay element, and a delay unit that delays the input measurement signal and inputs it to the delay circuit of the TDC circuit.

[0012] In the present invention, the measurement signal input to the TDC device is delayed by the delay unit and then input to the TDC circuit. In this case, for example, depending on the delay amount of the measurement signal in the delay unit, the detection stage of the delay element that detects the rising edge of the measurement signal can be made smaller. This makes it possible to reduce the difference (error) between the actual accumulated delay amount of the multiple delay elements during the measurement operation and the accumulated delay amount of the multiple delay elements during the calibration operation. As a result, it is possible to improve the measurement accuracy while reducing the influence of the fluctuation in the voltage drop amount of the TDC circuit.

[0013] In addition, the following method can be considered as a method of reducing the error between the actual accumulated delay amount during the measurement operation and the accumulated delay amount during the calibration operation by utilizing the present invention. For example, it is possible to provide a plurality of measurement channels (channels that measure the delay time of the measurement signal by the TDC circuit, the edge detection unit, and the time calculation unit) in the TDC device, and provide a delay unit in at least one of them. In this case, by appropriately setting the delay amount in the delay unit, it is possible to provide a difference between the detection stage of the delay element that detects the rising edge of the measurement signal in one measurement channel and the detection stage of the delay element that detects the rising edge of the measurement signal in another measurement channel. As a result, even if the detection stage of the delay element in one measurement channel is large and the error included in the calculation result is large, it is expected that the detection stage of the delay element in the other measurement channels will be small and the error included in the calculation result will be small.

[0014] (2) The TDC device of (1) above includes a plurality of measurement channels, each having a TDC circuit, an edge detection unit, and a time calculation unit, an input unit that inputs the same measurement signal in parallel to the plurality of measurement channels, and a delay time determination unit that determines a delay time based on the delay times of the plurality of measurement signals calculated by the time calculation units of the plurality of measurement channels, and at least one of the plurality of measurement channels may have a delay unit that delays the measurement signal input from the input unit relative to the measurement signals input to the delay circuits of the TDC circuits of the other measurement channels.

[0015] In this TDC device, the input timing of a measurement signal input to the TDC circuit of one measurement channel can be shifted from that of a measurement signal input to the TDC circuit of another measurement channel. This shifts the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit of one measurement channel from that of the delay element that detects the rising edge of the measurement signal in the TDC circuit of another measurement channel. In addition, the delay time determination unit can determine one delay time based on the delay time of the measurement signal calculated by the time calculation unit of each measurement channel.

[0016] In this case, even if the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit of one measurement channel is large and the error included in the calculation result is large, it is expected that the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit of another measurement channel will be small and the error included in the calculation result will be small. Therefore, as described above, the delay time determination unit determines one delay time based on the delay time of the measurement signal calculated by the time calculation unit of each measurement channel, thereby making it possible to reduce the influence of errors.

[0017] (3) In the TDC device of (2) above, two or more of the multiple measurement channels may each have a delay unit, and each delay unit may delay the measurement signal input from the input unit by a time different from that of the other delay units, and input the signal to a delay circuit of the TDC circuit.

[0018] According to the TDC device of (3) above, even when three or more measurement channels are provided, the input timing of the measurement signal input to the TDC circuit of each measurement channel can be shifted from the input timing of the measurement signal input to the TDC circuit of the other measurement channels. As a result, even if the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit of one of the measurement channels is large and the error included in the calculation result is large, it is expected that the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit of the other measurement channels will be small, and the error included in the calculation result will be small.

[0019] (4) In the TDC device of (2) or (3) above, the delay time determination unit may output an average value of a plurality of delay times calculated by a plurality of measurement channels as a single delay time.

[0020] In this case, the influence of errors contained in the delay times calculated by the respective measurement channels can be reduced.

[0021] (5) In the TDC device of (2) or (3) above, the delay time determination unit may output, as one delay time, a delay time calculated by a measurement channel among a plurality of measurement channels, the measurement channel having the smallest detection stage of a delay element that detects a rising edge in the TDC circuit.

[0022] In this case, from among a plurality of delay times calculated by a plurality of measurement channels, a delay time that is considered to have the smallest error can be output as one delay time.

[0023] (6) Any of the TDC devices described above in (1) to (5) may be provided with a time correction unit that corrects the delay time of the measurement signal calculated by the time calculation unit or one of the delay times determined by the delay time determination unit in accordance with the delay in the delay unit, and outputs the corrected delay time of the measurement signal.

[0024] In this case, the time correction unit can remove the effect of the delay of the measurement signal in the delay unit from the delay time calculated by the time calculation unit or from one delay time determined by the delay time determination unit.

[0025] (7) Any of the TDC devices (1) to (6) above may be used in a distance measuring device that measures the distance to an object based on a measurement signal relating to reflected light of measurement light irradiated onto the object and a measurement clock, and may be equipped with a distance calculation unit that calculates the distance to the object using the delay time of the measurement signal as the time difference between the measurement light and the reflected light.

[0026] In this case, in the distance measuring device, the influence of fluctuations in the amount of voltage drop in the TDC circuit between the calibration operation and the measurement operation can be reduced, and the distance to the object can be measured with high accuracy.

[0027] (8) The TDC device of (7) above may include a distance correction unit that corrects the distance calculated by the distance calculation unit in accordance with the delay in the delay unit and outputs the corrected distance.

[0028] In this case, the distance correction unit can eliminate the effect of the delay of the measurement signal in the delay unit from the distance calculated by the distance calculation unit. Also, in the distance measuring device, the effect of the fluctuation in the voltage drop amount of the TDC circuit between the calibration operation and the measurement operation can be reduced and the distance to the object can be measured with high accuracy.

[0029] (9) The TDC device of (1) above is used in a distance measuring device that measures the distance to an object based on a measurement signal related to the reflected light of measurement light irradiated onto the object and a measurement clock, and is equipped with multiple measurement channels each having a TDC circuit, an edge detection unit, a time calculation unit, and a distance calculation unit that calculates the distance to the object using the delay time of the measurement signal output by the time calculation unit as the time difference between the measurement light and the reflected light, an input unit that inputs the same measurement signal in parallel to the multiple measurement channels, and a distance determination unit that determines one distance to the object based on multiple distances calculated by the distance calculation units of the multiple measurement channels, and at least one of the multiple measurement channels may have a delay unit that delays the measurement signal input from the input unit relative to the measurement signal input to the delay circuit of the TDC circuit of the other measurement channel.

[0030] In this TDC device, the input timing of the measurement signal input to the TDC circuit of one measurement channel can be shifted from the input timing of the measurement signal input to the TDC circuit of the other measurement channel. This changes the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit of one measurement channel from the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit of the other measurement channel. Then, the distance determination unit can determine one distance based on the distance to the object calculated by the distance calculation unit of each measurement channel.

[0031] In this case, even if the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit of one measurement channel is large and the error included in the calculation result is large, it is expected that the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit of another measurement channel will be small and the error included in the calculation result will be small. Therefore, as described above, the distance determination unit determines one distance based on the distance to the object calculated by the distance calculation unit of each measurement channel, thereby making it possible to reduce the effect of errors.

[0032] (10) In the TDC device of (9) above, two or more of the multiple measurement channels may each have a delay unit, and each delay unit may delay the measurement signal input from the input unit by a time different from that of the other delay units, and input the signal to a delay circuit of the TDC circuit.

[0033] According to the TDC device of (10) above, even when three or more measurement channels are provided, the input timing of the measurement signal input to the TDC circuit of each measurement channel can be shifted from the input timing of the measurement signal input to the TDC circuit of the other measurement channels. As a result, even if the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit of one of the measurement channels is large and the error included in the calculation result is large, it is expected that the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit of the other measurement channels will be small, and the error included in the calculation result will be small.

[0034] (11) In the TDC device of (9) or (10) above, the distance determination unit may output an average value of a plurality of distances calculated by a plurality of measurement channels as a single distance.

[0035] In this case, the influence of errors contained in the distance to the object calculated by each measurement channel can be reduced.

[0036] (12) In the TDC device of (9) or (10) above, the distance determination unit may output, as one distance, the distance calculated by the measurement channel among the multiple measurement channels, which has the smallest detection stage of the delay element that detected the rising edge in the TDC circuit.

[0037] In this case, from among a plurality of distances calculated by a plurality of measurement channels, the distance that is considered to have the smallest error can be output as one distance.

[0038] (13) In any of the TDC devices described in (9) to (12) above, the TDC device may be provided with a distance correction unit that corrects the distance calculated by the distance calculation unit or one distance determined by the distance determination unit in accordance with the delay in the delay unit and outputs the corrected distance.

[0039] In this case, the distance correction unit corrects the distance to the object calculated by the distance calculation unit or a distance determined by the distance determination unit in accordance with the delay in the delay unit, thereby eliminating the effect of delay in the measurement signal in the delay unit.

[0040] (14) In any of the TDC devices (9) to (12) above, the distance calculation unit may calculate the distance to a reference object based on a measurement signal related to reflected light from the reference object positioned at a specific distance, set a zero point for distance measurement based on the calculated distance, and calculate the distance to the target object based on the set zero point.

[0041] In this TDC device, the distance to the object can be properly calculated by the distance calculation unit without correcting the delay time of the measurement signal calculated by the time calculation unit. Therefore, since there is no need to provide a correction unit for correcting the delay time of the measurement signal calculated by the time calculation unit, the configuration of the TDC device can be simplified.

[0042] (15) In any one of the TDC devices described above in (1) to (14), the delay unit may be configured to be able to change the delay time by which the measurement signal is delayed.

[0043] In this case, the delay time provided by the delay section can be adjusted according to the environment in which the device is used, and the like, so that the effects of fluctuations in the amount of voltage drop in the TDC circuit can be more appropriately mitigated.

[0044] (16) In the TDC device of (1) above, the delay unit may be configured to be able to change the delay time by which the measurement signal is delayed, and a delay time determination unit may be provided that determines one delay time based on the multiple delay times calculated by the time calculation unit by performing multiple measurements while changing the delay time in the delay unit.

[0045] In this case, by changing the delay time in the delay section and performing multiple measurements, the effect of error can be reduced by taking the average value of the distances measured multiple times, or by using the distance measured multiple times with the smallest detection stage of the delay element that detected the edge, as in the case of providing multiple measurement channels.

[0046] (17) A distance measuring device according to one aspect of the present invention is characterized in that it comprises a TDC device according to any one of (1) to (16) above, a light-projecting unit that irradiates measurement light in synchronization with a measurement clock, and a light-receiving unit that receives reflected light of the measurement light reflected by an object and outputs a measurement signal related to the reflected light to the TDC device.

[0047] According to this distance measuring device, it is possible to accurately measure the distance to an object while reducing the influence of fluctuations in the amount of voltage drop in the TDC circuit between the calibration operation and the measurement operation.

[0048] (18) The distance measuring device of (17) above directs measurement light projected from a light projecting unit in a predetermined direction. deflection The measuring device may include at least one of a light deflection unit that deflects the measuring light in a predetermined direction and a light scanning unit that scans the measuring light in a predetermined direction.

[0049] In this case, the direction of the measurement light Deflecting Or, the measurement light can be scanned in a predetermined direction.

[0050] (19) A distance measuring method according to one aspect of the present invention is a method for measuring a distance to an object in a distance measuring device equipped with a TDC circuit having a delay circuit including multiple stages of delay elements that sequentially delay a measurement signal related to reflected light of measurement light irradiated onto the object, and multiple memory elements that are provided corresponding to the multiple stages of delay elements and hold the output of the multiple stages of delay elements in response to an input measurement clock, the method including: delaying the measurement signal and inputting it to the delay circuit of the TDC circuit; detecting a detection stage of the delay element that has detected at least a rising edge of the measurement signal based on switching of the outputs of the multiple memory elements; step The delay time of the measurement signal is calculated based on a delay conversion table relating to the delay amount of the delay element, and the distance to the object is calculated based on the delay time of the measurement signal as the time difference between the measurement light and the reflected light.

[0051] According to this distance measurement method, similar to the TDC device described above in (7), it is possible to accurately measure the distance to an object while reducing the effects of fluctuations in the voltage drop in the TDC circuit between the calibration operation and the measurement operation. Effect of the Invention

[0052] According to the present invention, it is possible to improve measurement accuracy while reducing the influence of fluctuations in the amount of voltage drop in the power supply voltage of a TDC circuit. [Brief description of the drawings]

[0053] [Figure 1] FIG. 1 is a block diagram showing the configuration of a distance measuring device including a TDC device according to the first embodiment. [Diagram 2] FIG. 2 is a diagram showing a TDC circuit. [Diagram 3] FIG. 3 is a diagram showing operation waveforms of the TDC circuit of FIG. [Figure 4] FIG. 4 is a diagram showing waveforms of the measurement signal and the measurement clock input to the TDC circuit. [Diagram 5] FIG. 5 is a diagram showing waveforms of a calibration signal and a measurement clock. [Figure 6] FIG. 6 is a histogram showing the results of detecting the rising edges of the calibration signal. [Figure 7] FIG. 7 is a diagram showing a cumulative histogram. [Figure 8] FIG. 8 is a diagram showing a delay conversion table. [Figure 9] FIG. 9 is a conceptual diagram showing an example of the relationship between the detection stage of the delay element at which the rising edge of the measurement signal is detected and the accumulated delay amount at each detection stage. [Figure 10] FIG. 10 is a diagram showing a modification of the distance measuring device according to the first embodiment. [Figure 11] FIG. 11 is a diagram showing another modified example of the distance measuring device according to the first embodiment. [Figure 12] FIG. 12 is a block diagram showing the configuration of a distance measuring device including a TDC device according to the second embodiment of the present invention. [Figure 13] FIG. 13 is a characteristic diagram showing the effect of the operation of the TDC device. [Figure 14] FIG. 14 is a diagram showing a modification of the TDC device according to the second embodiment. [Figure 15] FIG. 15 is a diagram showing another modified example of the TDC device according to the second embodiment. [Figure 16] FIG. 16 is a diagram showing yet another modified example of the TDC device according to the second embodiment. [Figure 17] FIG. 17 is a block diagram showing the configuration of a distance measuring device including a TDC device according to a third embodiment of the present invention. [Figure 18] FIG. 18 is a diagram showing a modification of the TDC device according to the third embodiment. [Figure 19] FIG. 19 is a diagram showing another modified example of the TDC device according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] Hereinafter, a TDC device and a distance measuring device according to an embodiment of the present invention will be described with reference to the drawings.

[0055] (First embodiment) FIG. 1 is a block diagram showing the configuration of a distance measuring device equipped with a TDC device according to a first embodiment of the present invention.

[0056] The distance measuring device 100 according to this embodiment is a device that irradiates a measurement light onto an object to be measured (hereinafter, referred to as the object), receives the measurement light reflected by the object, and calculates the distance to the object based on the timing of receiving the reflected light. In this embodiment, the distance measuring device 100 includes a TDC device 50, a light projecting unit 101, a light receiving unit 102, an optical deflection unit 103, an optical scanning unit 104, and a power supply unit 105. The details of the TDC device 50 will be described later.

[0057] The light projecting unit 101 includes, for example, a light source and a light source driving unit (not shown). The light source is, for example, a semiconductor laser or an LED. The light source driving unit is a circuit that drives the light emission of the light source. The light projecting unit 101 irradiates measurement light toward a reflecting unit of the light deflection unit 103 (described later). The measurement light is pulsed light having a pulse width of, for example, several nanoseconds to several tens of nanoseconds.

[0058] The light receiving unit 102 includes a light receiving element such as an avalanche photodiode, receives the measurement light reflected by the object, and converts the light intensity of the received reflected light into an electrical signal. When the light receiving unit 102 receives the reflected light, it outputs an electrical signal related to the reflected light (hereinafter, referred to as a measurement signal) to the TDC device 50.

[0059] The optical deflection unit 103 has a reflecting unit such as a mirror disposed therein, and deflects the measurement light from the light projecting unit 101 incident on the reflecting unit in a predetermined direction. The optical scanning unit 104 scans the measurement light deflected by the optical deflection unit 103 in a predetermined direction, for example, the horizontal direction or the vertical direction. The distance measuring device 100 may be configured to include only one of the optical deflection unit 103 and the optical scanning unit 104.

[0060] The power supply unit 105 outputs a predetermined power supply voltage to each of the TDC device 50, the light projecting unit 101, the light receiving unit 102, the light deflection unit 103, and the light scanning unit 104 included in the distance measuring device 100 in order to supply power for operating them. Note that the power supply unit 105 may include an input terminal to which power is supplied from outside the distance measuring device 100.

[0061] The TDC device 50 measures the time difference between the measurement light and the reflected light as a delay time from the time when a measurement start signal corresponding to the measurement light is input to the time when a measurement signal corresponding to the reflected light is detected. The TDC device 50 will be described in detail below.

[0062] In this embodiment, the TDC device 50 includes a delay unit 1, a TDC circuit 2, an edge detection unit 3, a table generation unit 4, a time calculation unit 5, and a distance calculation unit 6. These may be configured with dedicated hardware, or components that can be realized by software may be realized by a CPU executing a program.

[0063] The delay unit 1 delays the measurement signal input from the light receiving unit 102 to the TDC device 50, and inputs the delayed measurement signal to a first delay circuit 11 (see FIG. 2) of the TDC circuit 2. In this embodiment, the delay unit 1 includes a delay element (not shown), Light receiving section 102 The measurement signal input to the TDC device 50 from the optical fiber 1 is delayed by a time shorter than the period of the measurement clock, and then input to the TDC circuit 2. The measurement clock is a clock for detecting the time difference (delay time of the measurement signal) between the irradiation time of the measurement light (light projection time) and the reception time of the reflected light.

[0064] Fig. 2 is a diagram showing a TDC circuit 2. The TDC circuit 2 shown in Fig. 2 is a so-called Vernier type TDC circuit. The TDC circuit 2 includes a first delay circuit 11, a second delay circuit 12, a flip-flop row 13, and a synchronization circuit 14. Note that the TDC circuit 2 may be a flash type TDC circuit that does not include the second delay circuit 12. The flip-flop row 13 is an example of a memory element that can operate at high speed.

[0065] In the first delay circuit 11, a measurement signal is input to an input terminal Vref. The measurement signal is a signal of reflected light that is irradiated from a light projecting unit 101 and reflected by an object and received by a light receiving unit 102. The first delay circuit 11 includes n stages (n is an integer of 1 or more) of delay elements 11 n Each delay element 11 n The delay (also called delay time) of S Each delay element is set to n The output nodes of are denoted as S1, S2, S3, Sn.

[0066] In the second delay circuit 12, a measurement clock is input to an input terminal Vck. A light projector 101 (see FIG. 1) projects measurement light at the rising edge of the measurement clock. The second delay circuit 12, like the first delay circuit 11, includes n-stage delay elements 12 n Each delay element 12 n The delay of is τ C (<τ S ) is set for each delay element. n The output nodes of are denoted as C1, C2, C3, · · Cn.

[0067] A pair of delay elements 111 and 121, a pair of delay elements 112 and 122, etc. n and delay element 12 n For each pair of delay elements 111 and 121, the output terminals of each pair are connected to a flip-flop, which will be described later. In the following, the delay elements 111 and 121 are the first-stage delay elements, the delay elements 112 and 122 are the second-stage delay elements, and so on. n and delay element 12 n is called the nth stage delay element.

[0068] The flip-flop row 13 includes n D-flip-flops (hereinafter referred to as D-FF) 13. n (n is an integer equal to or greater than 1). In this embodiment, the D-FF 131 corresponds to the first-stage delay element, and the D-FF 13 n corresponds to the n-th delay element. For details, see D-FF13 nThe D terminal of the delay element 11 n The CK terminal is connected to the output node Sn of the delay element 12. n The output node Cn of D-FF13 is connected to the n The Q terminal of each D-FF 13 is connected to the synchronization circuit 14. n The output nodes of are denoted as D1, D2, D3, · · Dn.

[0069] The synchronization circuit 14 includes D-FF131 to D-FF133. n This is a circuit that outputs the output value of in sync with the measurement clock.

[0070] Fig. 3 is a diagram showing an example of the operation waveform of the TDC circuit 2 in Fig. 2. Fig. 4 is a diagram showing an example of the waveforms of the measurement signal and measurement clock input to the TDC circuit 2. In the example of Fig. 3, the measurement signal from the input terminal Vref rises from an L level (hereinafter referred to as L) to an H level (hereinafter referred to as H), and the measurement clock from the input terminal Vck rises from L to H with a delay of a time difference Δt. In the example shown in Fig. 3, "H, H, L, L" are obtained as data at the output nodes D1 to D4 of D-FFs 131 to 134.

[0071] When a measurement signal and a measurement clock are input to the TDC circuit 2, the edge detection unit 3 detects an edge (rising edge or falling edge) of the measurement signal based on the output value from the synchronization circuit 14. Here, in this embodiment, it is assumed that the total delay amount of the 12 stages of delay elements (i.e., n=12) in the TDC circuit 2 in FIG. 2 corresponds to one period of the measurement clock. In this case, D-FFs 131 to 13 12 4 are input so that "H, H, H, H, H, H, H, H, H, H, H, L, L" is obtained as data at output nodes D1 to D12. Edge detection unit 3 can detect the rising edge of the measurement signal by detecting a change from H to L in the data at output nodes D1 to D12.

[0072] In this embodiment, the edge detection unit 3 detects the detection stage of the delay element that detected the rising edge and falling edge of the measurement signal based on the switching of data at the output nodes D1 to Dn. Specifically, in this embodiment, the edge detection unit 3 determines, for example, the delay element (the 11th stage delay element in the example of FIG. 4) corresponding to the output node Di when the data changes from H to L among the output nodes D1 to Dn as the delay element that detected the rising edge of the measurement signal. Also, the edge detection unit 3 determines, for example, the delay element corresponding to the output node Di when the data changes from L to H among the output nodes D1 to Dn as the delay element that detected the falling edge.

[0073] In this embodiment, the edge detection unit 3 detects the rising edge of the measurement signal, and the time calculation unit 5 can measure the time interval from when the measurement signal rises to when the measurement clock A rises, as described later. The time interval is calculated by the delay amount of each delay element (in this embodiment, the delay elements 11 n Delay amount and delay element 12 n The difference between the delay and the delay: τ s -τ c ) (also called time resolution). In the example shown in Fig. 4, the rising edge of the measurement signal is detected by the 11th delay element. In this case, for example, the time interval from when the measurement signal rises to when measurement clock A rises can be found by accumulating the delay amounts of each delay element from the 1st delay element to the 10th delay element (the delay element immediately before the delay element that detected the rising edge).

[0074] In the example of Fig. 4, as described above, the total delay amount of 12 stages of delay elements (i.e., n=12) corresponds to one cycle of the measurement clock. Therefore, the time interval from the rising edge of measurement clock B, which is one stage before measurement clock A, to the rising edge of the measurement signal can be obtained by accumulating the delay amount of each delay element in the 11th and 12th stages. That is, in this embodiment, the time interval from the rising edge of the measurement clock to the rising edge of the measurement signal can be calculated as the cumulative delay amount from the delay element that detects the rising edge of the measurement signal (the 11th stage delay element in Fig. 4) to the last stage delay element (the 12th stage delay element in Fig. 4) among the multiple stages of delay elements corresponding to one cycle of the measurement clock.

[0075] The table generator 4 (see FIG. 1) generates a delay conversion table. s -τ c ) varies due to manufacturing variations. The delay conversion table varies (τ s -τ c ) is a table for calibrating the delay amount based on the delay time. In this embodiment, the delay conversion table is a table that indicates the relationship between the detection stage of the delay element that detects the rising edge of a calibration signal, which will be described later, when the calibration signal is input to the TDC circuit 2, and the accumulated delay amount of the delay element up to that detection stage. Hereinafter, the operation of generating the delay conversion table is referred to as a calibration operation. The table generating unit 4 performs the calibration operation when the distance measuring device 100 is not performing a distance measurement operation, that is, when a measurement signal is not input to the TDC circuit 2.

[0076] FIG. 5 is a diagram showing waveforms of the calibration signal and the measurement clock. In the calibration operation, the table generating unit 4 inputs a calibration signal to the input terminal Vref (see FIG. 2) from a clock generating circuit (not shown). The measurement clock is input to the input terminal Vck. The calibration signal is a signal whose period is slightly different from that of the measurement clock and is not synchronized with the measurement clock. The period of the calibration signal is variable, and the difference between the period of the calibration signal and the period of the measurement clock is the time resolution of the TDC circuit 2 (τ s -τ c For example, when the time resolution of the TDC circuit 2 is 10 [ps], and the period of the measurement clock is 4 [ns], the period of the calibration signal is preferably set in the range of more than 4 and less than 4.016 [ns].

[0077] When the calibration signal is input, the table generating unit 4 measures the number of rising edges of the detected calibration signal for each stage of delay elements (12 stages of delay elements in FIG. 5) in the TDC circuit 2, as shown in FIG. 5. In this embodiment, the rising edges of the calibration signal are detected by the edge detecting unit 3, similar to the rising edges of the measurement signal. Based on the detection result of the edge detecting unit 3, the table generating unit 4 measures the number of rising edges of the detected calibration signal for each stage of the delay elements.

[0078] FIG. 6 is a histogram showing the result of detecting the rising edge of the calibration signal. The table generating unit 4 generates a histogram showing the result of detecting the rising edge of the calibration signal. FIG. 6 shows the result of inputting a calibration signal so that the total number of rising edges of the calibration signal detected by the delay elements of each stage (hereinafter referred to as the total number of detections) is "36". In this figure, the number of rising edges of the calibration signal detected by the first stage delay element (hereinafter referred to as the number of detections) is "7". The number of detections at the eighth stage is "0". This represents the amount of delay possessed by the delay elements of each stage. For example, if the period of the measurement clock is 4 [ns], the total number of detections "36" corresponds to the period of the measurement clock of 4 [ns]. Therefore, the amount of delay possessed by the first stage delay element is 7 / 36×4 [ns].

[0079] Next, the table generating unit 4 generates a cumulative histogram from the histogram shown in Fig. 6 in order to estimate the cumulative delay amount of the delay elements up to each stage. Fig. 7 is a diagram showing a cumulative histogram. The cumulative histogram in Fig. 7 is generated by adding the detection number in the last stage, the 8th stage, to the detection number in the 7th stage in the histogram in Fig. 6, and then adding the added detection number in the 7th stage to the detection number in the 6th stage, in order from the last delay element to the 1st delay element. The result obtained by the above calculation is called the cumulative detection number (vertical axis in Fig. 7).

[0080] Next, the table generating unit 4 generates a table in which the cumulative detection count on the vertical axis of the cumulative histogram shown in Fig. 7 is converted into a cumulative delay amount. This table is called a delay conversion table. Fig. 8 is a diagram showing the delay conversion table. Fig. 8 shows a delay conversion table when the period of the measurement clock is set to 4 [ns].

[0081] The reason why the accumulation process is performed from the last delay element to the first delay element as described above is as follows. As described in FIG. 4, the delay amount from when the measurement clock B rises to when the measurement signal rises is the accumulated delay amount from the delay element that detected the rise of the measurement signal to the last delay element. In other words, by calculating the accumulated delay amount from the last delay element to the delay element that detected the rise of the measurement signal, it is possible to calculate the delay amount from when the measurement clock rises to when the measurement signal rises. Therefore, in this embodiment, the accumulated delay amount of the delay elements of each stage is calculated by accumulating the delay amounts from the last delay element to the first delay element.

[0082] When the distance measuring device 100 performs a distance measurement operation, the time interval between the rising edge of the measurement signal and the rising edge of the measurement clock immediately preceding that measurement signal is required in calculating the time difference between the measurement light and the reflected light (the delay time of the measurement signal). The time calculation unit 5 (see FIG. 1) calculates the time difference between the measurement light and the reflected light (the delay time of the measurement signal) based on the detection result of the edge detection unit 3 and the delay conversion table described above.

[0083] Specifically, the time calculation unit 5 acquires the cumulative delay amount corresponding to the detection stage of the delay element that detected the rising edge of the measurement signal as the time interval from the rising edge of the measurement clock to the rising edge of the measurement signal based on the detection result of the edge detection unit 3 (the detection stage of the delay element that detected the rising edge of the measurement signal) and the delay conversion table. For example, if the stage number of the delay element that detected the rising edge of the measurement signal is "4", the time calculation unit 5 acquires the cumulative delay amount corresponding to the stage number "4" as the time interval from the rising edge of the measurement clock to the rising edge of the measurement signal from the table of FIG. 8. Then, the time calculation unit 5 calculates the time difference between the measurement light and the reflected light from the number of clocks of the measurement clock from when the light projecting unit 101 irradiates the measurement light to the measurement clock immediately before the measurement signal rises (measurement clock B in FIG. 4) and the time interval acquired from the delay conversion table. The time calculation unit 5 outputs the calculated time difference between the measurement light and the reflected light to the distance calculation unit 6 (see FIG. 1).

[0084] The distance calculation unit 6 calculates the distance to the object from the time difference between the measurement light and the reflected light calculated by the time calculation unit 5. The distance calculation unit 6 may be configured, for example, by dedicated hardware, or may be realized by a CPU executing a program. In this embodiment, the distance calculation unit 6 calculates the distance d to the object by the following formula (1). In the following formula (1), C is the speed of light, and ΔT is the time difference between the measurement light and the reflected light (delay time of the measurement signal). d = (1 / 2) × C × ΔT (1)

[0085] (Effects of this embodiment) FIG. 9 is a conceptual diagram showing an example of the relationship between the detection stage of a delay element that detects the rising edge of a measurement signal and the accumulated delay amount at each detection stage. The solid line shows the relationship between the detection stage and the accumulated delay amount during a calibration operation, and the dashed line shows the relationship between the detection stage and the accumulated delay amount during a measurement operation.

[0086] When the voltage drop of the power supply voltage of the TDC circuit 2 during the measurement operation of the distance measuring device 100 is smaller than the voltage drop of the power supply voltage of the TDC circuit 2 during the calibration operation, the delay amount of each delay element during the measurement operation is smaller than the delay amount of each delay element during the calibration operation. As a result, the number of stages of delay elements corresponding to one cycle of the measurement clock during the measurement operation is greater than the number of stages of delay elements corresponding to one cycle of the measurement clock during the calibration operation.

[0087] As shown in Fig. 9, the actual cumulative delay amount of each detection stage during measurement becomes larger than the cumulative delay amount during calibration operation due to the increase in the number of stages of delay elements corresponding to one period of the measurement clock during measurement operation. As can be seen from Fig. 9, the difference (error) between the actual cumulative delay amount during measurement operation and the cumulative delay amount during calibration operation becomes larger as the detection stage of the delay element that detects the rising edge of the measurement signal becomes larger.

[0088] Depending on the conditions, the voltage drop of the power supply voltage of the TDC circuit 2 during the measurement operation may be larger than the voltage drop during the calibration operation, in which case the number of stages of delay elements corresponding to one cycle of the measurement clock during the measurement operation is smaller than the number of stages of delay elements corresponding to one cycle of the measurement clock during the calibration operation. In this case as well, the difference (error) between the actual accumulated delay amount during the measurement operation and the accumulated delay amount during the calibration operation becomes larger as the detection stage of the delay element that detects the rising edge of the measurement signal becomes larger.

[0089] Thus, when measuring the distance to an arbitrary object using the distance measuring device 100, the error contained in the measured distance increases if the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit 2 is large. In particular, the error increases as the difference between the amount of voltage drop of the power supply voltage of the TDC circuit 2 during measurement operation and the amount of voltage drop of the power supply voltage of the TDC circuit 2 during calibration operation increases.

[0090] Therefore, in this embodiment, the measurement signal input to the TDC device 50 is delayed by the delay unit 1 and then input to the TDC circuit 2. In this case, for example, the detection stage of the delay element that detects the rising edge of the measurement signal can be made smaller depending on the delay amount of the measurement signal in the delay unit 1. This makes it possible to reduce the difference (error) between the actual accumulated delay amount during measurement operation and the accumulated delay amount during calibration operation.

[0091] In this way, according to the distance measuring device 100 of this embodiment, the influence of fluctuations in the amount of voltage drop in the TDC circuit 2 between the calibration operation and the measurement operation can be reduced, while the distance to the target object can be measured with high accuracy.

[0092] In this embodiment, the measurement signal input to the TDC device 50 is delayed by the delay unit 1, and then the time calculation unit 5 calculates the time difference between the measurement light and the reflected light (the delay time of the measurement signal) based on the delayed measurement signal. Therefore, the delay time of the measurement signal calculated by the time calculation unit 5 is longer than the actual time difference between the measurement light and the reflected light by an amount corresponding to the delay amount in the delay unit 1. Therefore, if the delay time of the measurement signal calculated by the time calculation unit 5 is used as is to calculate the distance to the target, the calculated distance will be longer than the actual distance. That is, an error corresponding to the delay amount in the delay unit 1 occurs in the measurement result of the distance measuring device 100. In this regard, the distance measuring device 100 according to this embodiment calculates the distance to the target as follows, thereby making it possible to avoid the occurrence of such errors.

[0093] For example, the distance calculation unit 6 may calculate the distance (reference distance) to the reference object based on a measurement signal related to the reflected light from a reference object located at a specific distance, set a zero point of distance measurement based on the calculated reference distance, and calculate the distance to the target based on the set zero point. More specifically, for example, when the position of an arbitrary object in the distance measuring device 100 is set as the zero point of distance measurement, the distance calculation unit 6 may output a value obtained by subtracting the reference distance calculated by the measurement signal related to the reflected light from the reference object from the distance calculated by the measurement signal related to the reflected light from the target as the distance to the target. In this case, the distance calculated based on the measurement signal related to the reflected light from the target increases as the delay amount in the delay unit 1 increases, but the reference distance calculated based on the measurement signal related to the reflected light from the reference object also increases. Therefore, as described above, by subtracting the reference distance from the distance calculated based on the measurement signal related to the reflected light from the target, the influence of the delay amount in the delay unit 1 can be eliminated.

[0094] As another method, for example, it is possible to correct the delay time of the measurement signal calculated by the time calculation unit 5 or the distance calculated by the distance calculation unit 6. A specific description will be given below. Fig. 10 and Fig. 11 are diagrams showing modified examples of the distance measuring device 100.

[0095] In the distance measuring device 100 shown in FIG. 10, the TDC device 50 has a correction unit (time correction unit) 7a. In the distance measuring device 100 shown in FIG. 10, the delay time of the measurement signal calculated by the time calculation unit 5 is corrected in the correction unit 7a and then input to the distance calculation unit 6. Specifically, the correction unit 7a corrects the delay time of the measurement signal calculated by the time calculation unit 5 according to the delay amount of the measurement signal in the delay unit 1. For example, when the delay amount of the measurement signal in the delay unit 1 is 2 [ns], the correction unit 7a subtracts a time (2 [ns]) according to the delay amount of the measurement signal in the delay unit 1 from the delay time of the measurement signal calculated by the time calculation unit 5. The correction unit 7a outputs the delay time corrected in this way to the distance calculation unit 6. As a result, the distance calculation unit 6 can eliminate the influence of the delay of the measurement signal in the delay unit 1 and calculate the distance to the target object.

[0096] On the other hand, in the distance measuring device 100 shown in FIG. 11, the TDC device 50 has a correction unit (distance correction unit) 7b. In the distance measuring device 100 shown in FIG. 11, the distance to the object calculated by the distance calculation unit 6 is corrected by the correction unit 7b. Specifically, the correction unit 7b corrects the distance calculated by the distance calculation unit 6 according to the delay amount of the measurement signal in the delay unit 1. For example, when the delay amount of the measurement signal in the delay unit 1 is 2 [ns], the correction unit 7b subtracts a distance (about 300 mm) according to the delay amount of the measurement signal in the delay unit 1 from the distance calculated by the distance calculation unit 6. This makes it possible to remove the influence of the delay of the measurement signal in the delay unit 1 from the distance calculated by the distance calculation unit 6.

[0097] The correction units 7a and 7b may be configured with dedicated hardware, or may be realized by a CPU executing a program. The distance measuring device 100 may include the correction units 7a and 7b. In this case, since it is only necessary to activate either of the correction units 7a and 7b, even if a problem such as a failure occurs in one of the correction units 7a and 7b, the effect of the delay of the measurement signal in the delay unit 1 can be appropriately eliminated. The same applies to the embodiments described later.

[0098] The delay unit 1 may be configured to change the delay time (delay amount) for delaying the measurement signal, or may be configured to not change it. When the delay unit 1 is configured to change the delay time, for example, the delay unit 1 may be configured to adjust the delay time in the delay unit 1 according to the detection stage of the delay element that detected the rising edge of the calibration signal in the TDC circuit 2. According to this configuration, for example, when the detection stage of the delay element that detected the rising edge of the calibration signal in the TDC circuit 2 is large during the measurement operation of the distance measuring device 100, the delay time in the delay unit 1 may be adjusted so that the detection stage of the delay element that detected the rising edge of the calibration signal in the TDC circuit 2 becomes small from the next measurement operation onwards.

[0099] In addition, the following method can be considered as a method for reducing the difference (error) between the actual accumulated delay amount during the measurement operation and the accumulated delay amount during the calibration operation by using the configuration of the TDC device 50 according to this embodiment. For example, as in the distance measuring device according to the second embodiment described later (see FIG. 14), a plurality of measurement channels (channels for measuring the delay time of the measurement signal by the measurement unit 30) can be provided in the distance measuring device, and at least one of them can be provided with the delay unit 1. In this case, by appropriately setting the delay amount in the delay unit 1, a difference can be provided between the detection stage of the delay element that detects the rising edge of the measurement signal in one measurement channel and the detection stage of the delay element that detects the rising edge of the measurement signal in another measurement channel. As a result, even if the detection stage of the delay element in one measurement channel is large and the error included in the calculation result is large, it is expected that the detection stage of the delay element in the other measurement channels will be small and the error included in the calculation result will be small. Therefore, for example, the influence of the error can be reduced by calculating the distance based on the average value of the delay time of the measurement signal measured by each measurement channel. Also, for example, the influence of the error can be reduced by taking the average value of the distances measured by each measurement channel. Also, for example, by using the calculation result of the measurement channel in which the detection stage of the delay element that detected the rising edge of the measurement signal in the TDC circuit 2 is the smallest, among the multiple measurement channels, the influence of the error can be reduced.

[0100] In addition, when a delay unit 1 is provided in any of multiple measurement channels, it is preferable to set the delay amount of the measurement signal in the delay unit 1 so that when a rising edge of the measurement signal is detected in the first half of the delay element in the TDC circuit 2 of any of the measurement channels, a rising edge of the measurement signal is detected in the second half of the delay element in the TDC circuit 2 of any of the other measurement channels.

[0101] Furthermore, even if the TDC device 50 does not have multiple measurement channels, the delay time of the measurement signal in the delay unit 1 may be set to be changeable so that multiple measurements can be made for one measurement channel. By changing the delay time in the delay unit 1 and performing multiple measurements, the effect of errors can be reduced by taking the average value of the distances measured multiple times, or by adopting the distance measured multiple times in which the detection stage of the delay element that detected the edge is small, as in the case of providing multiple measurement channels. Specifically, the delay unit may be configured to be able to change the delay time for delaying the measurement signal, and may include a delay time determination unit that determines one delay time based on multiple delay times calculated by the time calculation unit by changing the delay time in the delay unit and performing multiple measurements. Note that, when the delay time of the measurement signal in the delay unit 1 is set to be changeable, it is preferable that the corresponding correction unit 7a or correction unit 7b be able to be corrected according to the changed delay time.

[0102] In the above embodiment, the TDC device 50 includes the distance calculation unit 6, but the distance calculation unit 6 may be provided in the distance measuring device 100 as a component separate from the TDC device 50. Similarly, the table generation unit 4 may be provided in the distance measuring device 100 as a component separate from the TDC device 50. The same applies to each embodiment described later.

[0103] In the above embodiment, the table generating unit 4 generates a delay conversion table indicating the relationship between the detection stage of the delay element that detected the rising edge of the calibration signal and the cumulative delay amount of the delay element up to that detection stage. However, the configuration of the delay conversion table is not limited to the above example. In this embodiment, a table indicating information on the delay amount of a plurality of delay elements of the TDC circuit 2 can be used as the delay conversion table. For example, the delay conversion table may be a table indicating the delay amount of each delay element of the TDC circuit 2. In this case, the time calculation unit 5 can calculate the delay time of the measurement signal based on the delay amount of each delay element indicated in the delay conversion table. The delay conversion table may be data input from outside the distance measuring device 100. The same applies to each embodiment described later.

[0104] Second embodiment 12 is a block diagram showing the configuration of a distance measuring device including a TDC device according to a second embodiment of the present invention. Note that, among the components of the distance measuring device according to the second embodiment, the description of parts having the same configuration as the distance measuring device according to the above-mentioned first embodiment will be omitted or simplified.

[0105] 12, the TDC device 50 according to this embodiment includes a plurality of measurement channels 20 (two in this embodiment), a distance calculation unit 6, a correction unit 7a, an input unit 8, and a delay time determination unit 9. Each measurement channel 20 includes a delay unit 1 and a measurement unit 30. The measurement unit 30 includes a TDC circuit 2, an edge detection unit 3, a table generation unit 4, and a time calculation unit 5. The TDC circuit 2, the edge detection unit 3, the table generation unit 4, the time calculation unit 5, and the distance calculation unit 6 have the same functions as those in the first embodiment described above.

[0106] In this embodiment, the light receiving unit 102 outputs a measurement signal related to the reflected light to the input unit 8 of the TDC device 50. The input unit 8 inputs the same measurement signal input from the light receiving unit 102 in parallel to the multiple measurement channels 20. In this embodiment, the input unit 8 inputs the same measurement signal to the delay unit 1 of each measurement channel 20. The input unit 8 is realized by hardware such as an electronic circuit, for example.

[0107] The delay unit 1 of each measurement channel 20 is configured similarly to the delay unit 1 of the first embodiment described above, and delays the measurement signal input from the input unit 8 and inputs it to the first delay circuit 11 (see FIG. 2) of the TDC circuit 2 of the measurement unit 30. In this embodiment, the delay amount in each delay unit 1 is set so that the delay amount of the measurement signal differs between the delay unit 1 of one measurement channel 20 and the delay unit 1 of the other measurement channel 20. In other words, each delay unit 1 delays the measurement signal input from the input unit 8 by a time different from that of the other delay units 1 and inputs it to the first delay circuit 11 of the TDC circuit 2. As a result, the measurement signal input to the TDC circuit 2 of one measurement channel 20 is delayed with respect to the measurement signal input to the TDC circuit 2 of the other measurement channel 20.

[0108] The time calculation unit 5 of each measurement unit 30, like the time calculation unit 5 of the first embodiment described above, calculates the delay time of the measurement signal (the time difference between the measurement light and the reflected light) and inputs the calculated delay time to the delay time determination unit 9.

[0109] The delay time determination unit 9 determines one delay time based on the delay time of the measurement signal calculated by the time calculation unit 5 of each measurement channel 20. In this embodiment, the delay time determination unit 9 outputs the average value of the delay times calculated by each measurement channel 20 as the one delay time. The delay time determination unit 9 may be configured by dedicated hardware, or may be realized by a CPU executing a program, for example.

[0110] The correction unit 7a corrects the delay time input from the delay time determination unit 9. Here, in this embodiment, the time calculation unit 5 of each measurement channel 20 calculates the delay time of the measurement signal based on the measurement signal delayed by the delay unit 1. Therefore, the delay time of the measurement signal calculated by each time calculation unit 5 is longer than the actual time difference between the measurement light and the reflected light by an amount corresponding to the delay amount in the delay unit 1. Therefore, the average value of the delay time calculated by each time calculation unit 5 is longer than the actual time difference between the measurement light and the reflected light. Therefore, in this embodiment, the correction unit 7a corrects the delay time input from the delay time determination unit 9 according to the delay amount in each delay unit 1 so that the influence of the delay amount in each delay unit 1 is eliminated. For example, in the distance measuring device 100 of FIG. 12, if the delay amount of the measurement signal in one delay unit 1 is 1 [ns] and the delay amount of the measurement signal in the other delay unit 1 is 3 [ns], the correction unit 7a subtracts a time corresponding to the delay amount of the measurement signal in each delay unit 1 (2 [ns] = (1 [ns] + 3 [ns]) / 2) from the delay time of the measurement signal input from the delay time determination unit 9. The correction unit 7a outputs the delay time corrected in this manner to the distance calculation unit 6. This allows the distance calculation unit 6 to remove the effect of the delay of the measurement signal in each delay unit 1 and calculate the distance to the target object.

[0111] (Effects of this embodiment) In the distance measuring device 100 according to this embodiment, each measurement channel 20 includes a delay unit 1. This allows the number of detection stages of the delay elements that detect the rising edge of the measurement signal in the TDC circuit 2 to be reduced depending on the delay amount in the delay unit 1. In this case, as described in the above first embodiment, the difference (error) between the actual accumulated delay amount of the multiple delay elements during the measurement operation and the accumulated delay amount of the multiple delay elements during the calibration operation can be reduced. As a result, the error included in the distance calculated by the distance calculation unit 6 can be reduced.

[0112] Furthermore, in the distance measuring device 100 according to this embodiment, the input timing (input timing with respect to the measurement clock) of the measurement signal input to the TDC circuit 2 of one measurement channel 20 is shifted from the measurement signal input to the TDC circuit 2 of the other measurement channel 20. This changes the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit 2 of one measurement channel 20 from the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit 2 of the other measurement channel 20.

[0113] Then, the delay time determination unit 9 determines the average value of the delay times of the measurement signals calculated by the time calculation unit 5 of each measurement channel 20 as one delay time. Furthermore, the one delay time determined by the delay time determination unit 9 is corrected by the correction unit 7a according to the delay amount of each delay unit 1, and the distance calculation unit 6 calculates the distance to the target object based on the corrected delay time.

[0114] In this case, even if the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit 2 of one measurement channel 20 is large and the error included in the calculation result is large, it is expected that the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit 2 of the other measurement channel 20 will be small and the error included in the calculation result will be small. Therefore, as described above, the delay time determination unit 9 can reduce the influence of the error by taking the average value of the delay times calculated by the time calculation unit 5 of each measurement channel 20. Note that the delay amount of each delay unit 1 that shifts the input timing is preferably set so that, for example, when the rising edge of the measurement signal is detected in the first half of the delay element in the TDC circuit 2 of one measurement channel 20, the rising edge of the measurement signal is detected in the second half of the delay element in the TDC circuit 2 of the other measurement channel 20.

[0115] In this way, the distance measuring device 100 according to this embodiment can measure the distance to the object while reducing the influence of the fluctuation in the amount of voltage drop between the calibration operation and the measurement operation.

[0116] Fig. 13 is a characteristic diagram showing the effect of the operation of the TDC device 50 according to this embodiment. The horizontal axis indicates the distance to the object (target) to be measured, and the vertical axis indicates the error between the calculated distance to the target and the actual distance to the target. Note that the characteristic diagram shown in Fig. 13 is a characteristic diagram obtained by measuring the distance to the target while changing the distance to the target in increments of 100 mm. Also, the values ​​on the vertical axis in Fig. 13 indicate standardized measurement errors, and do not directly indicate actual measurement errors.

[0117] In FIG. 13, the dashed line indicates the error when the distance to the object is calculated based on the delay time of the measurement time measured by one measurement channel 20 of the TDC device 50, and the dashed line indicates the error when the distance to the object is calculated based on the delay time of the measurement time measured by the other measurement channel 20. Also, the solid line indicates the error when the distance to the object is calculated based on the average value of the delay times of the measurement times measured by each measurement channel 20. Note that there is a difference of about half a period (2 ns) of the measurement clock between the delay amount in the delay unit 1 of one measurement channel 20 and the delay amount in the delay unit 1 of the other measurement channel 20. In calculating the distance to the object, the effect of the delay amount in the delay unit 1 is removed.

[0118] 13, the error in the distance to the object calculated based on the delay time measured by each measurement channel 20 increases or decreases with every 600 mm change in the distance to the object. This increase or decrease in error is considered to be caused by an error in the delay conversion table used in each measurement channel 20. On the other hand, when the distance to the object is calculated based on the average delay time of the measurement times measured by each measurement channel 20, the variation in error is reduced.

[0119] 13, it can be seen that the fluctuation of the measurement error can be reduced by changing the input timing of the measurement signal input to the TDC circuit 2 of each measurement channel 20 and calculating the distance to the target based on the average value of the delay time of the measurement signal measured by each measurement channel 20, as in the TDC device 50 according to this embodiment. By increasing the number of measurement channels 20 for which the delay amount of the measurement signal input to the TDC circuit 2 is adjusted, a greater effect can be expected.

[0120] In the TDC device 50 shown in Fig. 12, each measurement channel 20 includes a delay unit 1, but as in the TDC device 50 shown in Fig. 14, any of the measurement channels 20 may not include a delay unit 1. For example, in the TDC device 50 shown in Fig. 12, if any of the measurement channels 20 does not include a delay unit 1, it is preferable to set the delay amount of the measurement signal in the delay unit 1 so that when a rising edge of the measurement signal is detected in the first half of the delay element in the TDC circuit 2 of one measurement channel 20, a rising edge of the measurement signal is detected in the second half of the delay element in the TDC circuit 2 of the other measurement channel 20.

[0121] Further, the TDC device 50 shown in FIG. 12 includes two measurement channels 20, but as shown in FIG. 14, the TDC device 50 may include three or more measurement channels 20. As described above, it is expected that the effect of the present invention will be further enhanced by increasing the number of measurement channels 20. In addition, in the case where three or more measurement channels 20 are provided, each measurement channel 20 may include a delay unit 1 as in the TDC device 50 shown in FIG. 12, and as shown in FIG. 14, any measurement channel 20 may not include a delay unit 1. In the case where the TDC device 50 includes three or more measurement channels 20, the delay amount of the measurement signal in each delay unit 1 is adjusted so that the input timings of the measurement signals input to the TDC circuit 2 (see FIG. 12) of each measurement channel 20 are shifted from each other. In addition, the delay amount of each delay unit 1 is set, for example, according to the number of measurement channels 20 included in the TDC device 50. For example, the time equivalent to one period of the measurement clock divided by the number of measurement channels 20 provided in the TDC device 50 is used as a reference delay amount, and the delay amount of the delay section 1 of each measurement channel 20 can be set so that the input timing of the measurement signal input to the TDC circuit 2 of each measurement channel 20 is shifted by the reference delay amount.

[0122] In the TDC device 50 shown in FIG. 12 and FIG. 14, the distance to the object is calculated by the distance calculation unit 6 after the correction unit 7a corrects the one delay time output by the delay time determination unit 9, but the calculation method of the distance to the object is not limited to the above example. For example, as shown in FIG. 15, the correction unit 7a may be provided in the measurement unit 30 of each measurement channel 20 having the delay unit 1. In this case, the correction unit 7a corrects the delay time of the measurement signal calculated by the time calculation unit 5 according to the delay amount of the measurement signal in the delay unit 1, similar to the correction unit 7a of the TDC device 50 described in FIG. 10. This allows each measurement channel 20 to output the delay time of the measurement signal (the time difference from the reception time of the reflected light) from which the influence of the delay in the delay unit 1 has been removed. In this case, the one delay time determined by the delay time determination unit 9 is the delay time from which the influence of the delay in the delay unit 1 has been removed. Therefore, the distance calculation unit 6 can calculate the distance to the object by using the delay time output from the delay time determination unit 9 as it is without correction.

[0123] In the above embodiment, the delay time determination unit 9 determines the average value of the delay times calculated by the multiple measurement channels 20 as one delay time, but the method of determining one delay time by the delay time determination unit 9 is not limited to the above example. Specifically, the delay time determination unit 9 may determine, for example, the delay time of the measurement signal calculated by the measurement channel 20 having the smallest detection stage of the delay element that detected the rising edge of the measurement signal in the TDC circuit 2 among the multiple measurement channels 20 as one delay time. As described with reference to FIG. 9, the larger the detection stage of the delay element that detected the rising edge of the measurement signal, the larger the difference (error) between the actual accumulated delay amount during the measurement operation and the accumulated delay amount during the calibration operation. In other words, the smaller the stage of the delay element that detected the rising edge of the measurement signal, the smaller the difference (error) between the actual accumulated delay amount during the measurement operation and the accumulated delay amount during the calibration operation. Therefore, by the delay time determination unit 9 selecting as one delay time, from among the delay times calculated by the multiple measurement channels 20, the delay time calculated by the measurement channel 20 having the smallest detection stage of the delay element that detected the rising edge of the measurement signal in the TDC circuit 2, the influence of fluctuations in the amount of voltage drop between the calibration operation and the measurement operation can be sufficiently reduced.

[0124] 12 and 14, instead of the correction unit 7a that corrects the delay time of the measurement signal, a correction unit 7b that corrects the distance to the object calculated by the distance calculation unit 6 may be provided as shown in Fig. 16. Although a detailed description will be omitted, as described in Fig. 11, the correction unit 7b corrects the distance calculated by the distance calculation unit 6 in accordance with the delay amount of the measurement signal in the delay unit 1 so that the effect of the delay of the measurement signal in the delay unit 1 can be removed from the distance calculated by the distance calculation unit 6.

[0125] Third embodiment 17 is a block diagram showing the configuration of a distance measuring device including a TDC device according to a third embodiment of the present invention. Note that, among the components of the distance measuring device according to the third embodiment, the description of parts having the same configuration as those of the distance measuring devices according to the first and second embodiments described above will be omitted or simplified.

[0126] 17, the TDC device 50 according to this embodiment includes a plurality of (two in this embodiment) measurement channels 20, an input unit 8, a distance determination unit 10, and a correction unit 7b. Each measurement channel 20 includes a delay unit 1 and a measurement unit 30. The measurement unit 30 includes a TDC circuit 2, an edge detection unit 3, a table generation unit 4, a time calculation unit 5, and a distance calculation unit 6. The TDC circuit 2, the edge detection unit 3, the table generation unit 4, the time calculation unit 5, and the distance calculation unit 6 are configured in the same manner as the distance measuring device 100 described in FIG. 11.

[0127] In this embodiment, as in the second embodiment described in Figure 12, the light receiving unit 102 outputs a measurement signal related to the reflected light to the input unit 8 of the TDC device 50, and the input unit 8 inputs the same measurement signal input from the light receiving unit 102 in parallel to multiple measurement channels 20.

[0128] 12, the delay unit 1 of each measurement channel 20 delays the measurement signal input from the input unit 8 and inputs it to the first delay circuit 11 (see FIG. 2) of the TDC circuit 2 of the measurement unit 30. Also in this embodiment, each delay unit 1 delays the measurement signal input from the input unit 8 by a time different from that of the other delay units 1 and inputs it to the first delay circuit 11 of the TDC circuit 2.

[0129] 11, the distance calculation unit 6 of each measurement unit 30 calculates the distance to the object from the delay time (the time difference between the measurement light and the reflected light) of the measurement signal calculated by the time calculation unit 5. The distance calculation unit 6 inputs the calculated distance to the object to the distance determination unit 10.

[0130] The distance determination unit 10 determines one distance based on the distance to the object calculated by the distance calculation unit 6 of each measurement channel 20. In this embodiment, the distance determination unit 10 outputs the average value of the distances to the object calculated by each measurement channel 20 as the one distance. The distance determination unit 10 may be configured by dedicated hardware, or may be realized by a CPU executing a program, for example.

[0131] The correction unit 7b corrects the one distance determined by the distance determination unit 10 in accordance with the delay amount of the measurement signal in the delay unit 1 so that the influence of the delay of the measurement signal in the delay unit 1 can be removed from the one distance determined by the distance determination unit 10. For example, the correction unit 7b may subtract a distance (a value converted into an average value) corresponding to the delay amount of each delay unit 1 from the average value calculated by the distance determination unit 10. This makes it possible to remove the influence of the delay of the measurement signal in the delay unit 1 from the one distance determined by the distance determination unit 10.

[0132] (Effects of this embodiment) In the distance measuring device 100 according to this embodiment, each measurement channel 20 includes a delay unit 1, similarly to the distance measuring device 100 according to the second embodiment described above (see FIG. 12). This allows the number of detection stages of the delay elements that detect the rising edge of the measurement signal in the TDC circuit 2 to be reduced depending on the delay amount in the delay unit 1. In this case, as described above, it is possible to reduce the difference (error) between the actual accumulated delay amount of the multiple delay elements during measurement operation and the accumulated delay amount of the multiple delay elements during calibration operation. As a result, it is possible to reduce the error included in the distance calculated by the distance calculation unit 6.

[0133] Also in the distance measuring device 100 according to this embodiment, similarly to the distance measuring device 100 according to the second embodiment described above (see FIG. 12), the input timing (input timing with respect to the measurement clock) of the measurement signal input to the measurement unit 30 of one measurement channel 20 is shifted from the measurement signal input to the measurement unit 30 of the other measurement channel 20. This changes the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit 2 of one measurement channel 20 from the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit 2 of the other measurement channel 20.

[0134] Then, the distance determination unit 10 outputs the average value of the distances to the object calculated by the distance calculation unit 6 of each measurement channel 20 as one distance. In this case, even if the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit 2 of one measurement channel 20 is large and the error included in the calculation result is large, it is expected that the detection stage of the delay element that detects the rising edge of the measurement signal in the TDC circuit 2 of the other measurement channel 20 will be small and the error included in the calculation result will be small. Therefore, as described above, the distance determination unit 10 can reduce the influence of the error by taking the average value of the distances to the object calculated by the distance calculation unit 6 of each measurement channel 20. Note that, as in the above embodiment, the delay amount of each delay unit 1 that shifts the input timing is preferably set so that when the rising edge of the measurement signal is detected in the first half of the delay element in the TDC circuit 2 of one measurement channel 20, the rising edge of the measurement signal is detected in the second half of the delay element in the TDC circuit 2 of the other measurement channel 20.

[0135] In this way, the distance measuring device 100 according to this embodiment can measure the distance to the object while reducing the influence of the fluctuation in the amount of voltage drop between the calibration operation and the measurement operation.

[0136] 17, the distance determination unit 10 may determine, as one distance, the distance calculated by the measurement channel 20 having the smallest detection stage of the delay element that detected the rising edge of the measurement signal in the TDC circuit 2, among the multiple measurement channels 20. In this case, the correction unit 7b may subtract, from the one distance determined by the distance determination unit 10, the distance corresponding to the delay amount of the delay unit 1 of the measurement channel 20 that calculated the one distance.

[0137] In the TDC device 50 shown in FIG. 17, each measurement channel 20 is equipped with a delay unit 1, but as with the TDC device 50 shown in FIG. 14, any of the measurement channels 20 may not be equipped with a delay unit 1.

[0138] 17 includes two measurement channels 20, but the TDC device 50 may include three or more measurement channels 20, similar to the TDC device 50 shown in FIG 14. Even when three or more measurement channels 20 are provided, any of the measurement channels 20 may not include the delay unit 1.

[0139] In the TDC device 50 shown in FIG. 17, when calculating the distance to the object, the effect of the delay of the measurement signal in the delay unit 1 is removed by the correction unit 7b, but the method of removing the effect of the delay is not limited to the above example. For example, as in the TDC device 50 shown in FIG. 18, a correction unit 7a may be provided in each measurement channel 20 having a delay unit 1. The correction unit 7a corrects the delay time of the measurement signal calculated by the time calculation unit 5 according to the delay amount of the measurement signal in the delay unit 1, similar to the correction unit 7a described in FIG. 10, and outputs the corrected delay time to the distance calculation unit 6. In this way, the distance calculation unit 6 can calculate the distance to the object by removing the effect of the delay of the measurement signal in the delay unit 1. Although detailed description is omitted, in the distance measuring device 100 shown in FIG. 18, the distance determination unit 10 may output the average value of the distances to the object calculated by each measurement channel 20 as a single distance, or may output the distance calculated by the measurement channel 20 with the smallest detection stage of the delay element that detected the rising edge of the measurement signal in the TDC circuit 2 among the multiple measurement channels 20 as a single distance. The same applies to a distance measuring device 100 shown in FIG. 19, which will be described later.

[0140] 19, a correction unit 7b may be provided in each measurement channel 20 having a delay unit 1. Similar to the correction unit 7b described in FIG. 11, the correction unit 7b corrects the distance calculated by the distance calculation unit 6 according to the delay amount of the measurement signal in the delay unit 1, and outputs the corrected distance to the distance determination unit 10. As a result, a distance determined by the distance determination unit 10 is one in which the influence of the delay of the measurement signal in the delay unit 1 has been removed.

[0141] 17 to 19, the distance calculation unit 6 of each measurement unit 30 may calculate the distance to a reference object (reference distance) based on a measurement signal related to reflected light from a reference object positioned at a specific distance, set a zero point for distance measurement based on the calculated reference distance, and calculate the distance to the target object based on the set zero point, as in the first embodiment described in FIG. 1. In this case, the correction units 7a and 7b may not be provided. [Explanation of symbols]

[0142] 1 Delay section 2. TDC Circuit 3 Edge detection section 4 Table Generation Section 5 Time calculation section 6 Distance calculation section 7a,7b Correction section 8 Input section 9 Delay time determination section 10 Distance determination unit 11 First delay circuit 12 Second delay circuit 13 flip-flop row 14 Synchronization circuit 20 Measurement Channels 30 Measurement section 50 TDC device 100 Rangefinder 101 Light projector 102 Light receiving section 103 Light deflection section 104 Optical scanning unit 105 Power supply section

Claims

1. A plurality of measurement channels each having a TDC circuit, an edge detection unit, and a time calculation unit; an input unit that inputs the same measurement signal to the plurality of measurement channels in parallel; a delay time determination unit that determines a delay time based on the delay times of the measurement signals calculated by the time calculation units of the measurement channels, the TDC circuit includes a delay circuit including a plurality of stages of delay elements that sequentially delay the measurement signal, and a plurality of storage elements that are provided corresponding to the plurality of stages of delay elements and that hold outputs of the plurality of stages of delay elements in response to an input measurement clock; the edge detection unit detects a detection stage of the delay element that detects at least a rising edge of the measurement signal based on switching of outputs of the plurality of storage elements; the time calculation unit outputs a delay time of the measurement signal based on a detection stage of the delay element and a delay conversion table relating to the delay amounts of the delay elements of the multiple stages; A TDC device, wherein at least one of the plurality of measurement channels has a delay unit that delays the measurement signal input from the input unit relative to the measurement signal input to the delay circuit of the TDC circuit of the other measurement channels, and inputs the measurement signal to the delay circuit of the TDC circuit.

2. Two or more of the plurality of measurement channels each have the delay unit, and each delay unit delays the measurement signal input from the input unit by a time different from that of the other delay units, and inputs the measurement signal to the delay circuit of the TDC circuit.

2. The TDC device of claim 1.

3. The delay time determination unit outputs an average value of the plurality of delay times calculated by the plurality of measurement channels as the one delay time.

3. The TDC device according to claim 1 or 2.

4. The delay time determination unit outputs, as the one delay time, the delay time calculated by the measurement channel having the smallest detection stage of the delay element that detected the rising edge in the TDC circuit among the plurality of measurement channels.

3. The TDC device according to claim 1 or 2.

5. 5. The TDC device according to claim 1, further comprising a time correction section that corrects the delay time in accordance with a delay in the delay section and outputs the corrected delay time.

6. The TDC device is used in a distance measuring device that measures a distance to an object based on a measurement signal and a measurement clock related to reflected light of measurement light irradiated onto the object, a distance calculation unit that calculates a distance to the object based on the delay time of the measurement signal as a time difference between the measurement light and the reflected light, 6. A TDC device according to claim 1.

7. a distance correction unit that corrects the distance calculated by the distance calculation unit in accordance with the delay in the delay unit and outputs the corrected distance; 7. The TDC device of claim 6.

8. A distance measuring device for measuring a distance to an object based on a measurement signal and a measurement clock related to reflected light of measurement light irradiated onto the object, a plurality of measurement channels each having a TDC circuit, an edge detection unit, a time calculation unit, and a distance calculation unit; an input unit that inputs the same measurement signal in parallel to the plurality of measurement channels; a distance determination unit that determines a distance to the object based on the distances calculated by the distance calculation units of the plurality of measurement channels; the TDC circuit includes a delay circuit including a plurality of stages of delay elements that sequentially delay the measurement signal, and a plurality of storage elements that are provided corresponding to the plurality of stages of delay elements and that hold outputs of the plurality of stages of delay elements in response to an input measurement clock; the edge detection unit detects a detection stage of the delay element that detects at least a rising edge of the measurement signal based on switching of outputs of the plurality of storage elements; the time calculation unit outputs a delay time of the measurement signal based on a detection stage of the delay element and a delay conversion table relating to the delay amounts of the delay elements of the multiple stages; the distance calculation unit calculates a distance to the object based on the delay time of the measurement signal output by the time calculation unit as a time difference between the measurement light and the reflected light, At least one of the plurality of measurement channels has a delay unit that delays the measurement signal input from the input unit with respect to the measurement signal input to the delay circuit of the TDC circuit of the other measurement channel, and inputs the delayed measurement signal to the delay circuit of the TDC circuit. TDC device.

9. Two or more of the plurality of measurement channels each have the delay unit, and each delay unit delays the measurement signal input from the input unit by a time different from that of the other delay units, and inputs the measurement signal to the delay circuit of the TDC circuit.

9. The TDC device of claim 8.

10. The distance determination unit outputs an average value of the plurality of distances calculated by the plurality of measurement channels as the one distance.

10. A TDC device according to claim 8 or 9.

11. the distance determination unit outputs, as the one distance, the distance calculated by the measurement channel having the smallest detection stage of the delay element that detected the rising edge in the TDC circuit among the plurality of measurement channels.

10. A TDC device according to claim 8 or 9.

12. a distance correction unit that corrects the distance in accordance with the delay in the delay unit and outputs the corrected distance; A TDC device according to any one of claims 8 to 11.

13. the distance calculation unit calculates a distance to a reference object based on a measurement signal related to reflected light from the reference object located at a specific distance, sets a zero point for distance measurement based on the calculated distance, and calculates a distance to an object based on the set zero point. A TDC device according to any one of claims 8 to 11.

14. The delay unit is configured to be able to change a delay time for delaying the measurement signal.

14. A TDC device according to any one of claims 1 to 13.

15. A TDC device according to any one of claims 1 to 14; a light projecting unit that projects measurement light in synchronization with the measurement clock; a light receiving unit that receives the measurement light reflected by an object and outputs a measurement signal related to the reflected light to the TDC device; A distance measuring device comprising:

16. The measuring device further includes at least one of an optical deflection unit that deflects the measurement light projected from the light projecting unit in a predetermined direction and an optical scanning unit that scans the measurement light in a predetermined direction.

16. A distance measuring device according to claim 15.

17. A method for measuring a distance to an object in a distance measuring device including a TDC circuit having a delay circuit including multiple stages of delay elements that sequentially delay a measurement signal related to reflected light of measurement light irradiated onto an object, and a plurality of memory elements provided corresponding to the multiple stages of delay elements and that hold outputs of the multiple stages of delay elements in response to an input measurement clock, comprising: inputting the same measurement signal in parallel to a plurality of measurement channels each having the TDC circuit; a measurement signal input to at least one of the plurality of measurement channels is delayed with respect to the measurement signal input to the delay circuit of the TDC circuit of the other measurement channels, and the measurement signal is input to the delay circuit of the TDC circuit; In each of the plurality of measurement channels, a detection stage of the delay element that detected at least a rising edge of the measurement signal is detected based on switching of outputs of the plurality of memory elements, and a delay time of the measurement signal is calculated based on the detection stage of the delay element and a delay conversion table relating to the delay amounts of the plurality of stages of delay elements; determining a delay time based on the delay times of the measurement signals calculated by the plurality of measurement channels; a distance measuring method for calculating a distance to the object by using the one delay time as a time difference between the measurement light and the reflected light.

18. A method for measuring a distance to an object in a distance measuring device equipped with a TDC circuit having a delay circuit including multiple stages of delay elements that sequentially delay a measurement signal related to reflected light of measurement light irradiated onto the object, and multiple memory elements provided corresponding to the multiple stages of delay elements and holding outputs of the multiple stages of delay elements in response to an input measurement clock, comprising: inputting the same measurement signal in parallel to a plurality of measurement channels each having the TDC circuit; a measurement signal input to at least one of the plurality of measurement channels is delayed with respect to the measurement signal input to the delay circuit of the TDC circuit of the other measurement channels, and the measurement signal is input to the delay circuit of the TDC circuit; In each of the plurality of measurement channels, a detection stage of the delay element that detected at least a rising edge of the measurement signal is detected based on switching of outputs of the plurality of memory elements, a delay time of the measurement signal is calculated based on the detection stage of the delay element and a delay conversion table relating to delay amounts of the plurality of stages of delay elements, and a distance to the object is calculated by using the delay time of the measurement signal as a time difference between the measurement light and the reflected light, A distance measuring method, comprising: determining a distance to the object based on a plurality of the distances calculated by the plurality of measurement channels.

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