Dynamic control of measurements from a time-of-flight sensor

Abstract

A control device for dynamically controlling measurements of a time-of-flight sensor (100) comprising an input interface (20) with a counter port (22) for receiving information about a detected event and with a histogram port (224) for receiving information about the current histogram content; a processing unit (30) for generating a measurement control signal; an event counter (40) connected to the counter port (22) to generate an event count representing all detected events based on the information about a detected event; a maximum value unit (50) connected to the histogram port (24) to determine and store a current maximum value of a histogram if it is greater than the maximum signal value stored in the maximum value unit (50); a measurement counter (60) to count the number of measurements and determine a measurement count value;an output interface (70) for outputting the measurement control signal for measuring events; wherein the processing unit (30) is configured to generate the measurement control signal based on a minimum measurement count, a maximum measurement count, a minimum SNR value, the measurement count value, the maximum signal value, and the number of events in order to initiate a measurement of the light time-of-flight sensor (100).

Description

[0001] The present invention relates to a control device for dynamically controlling measurements of a time-of-flight sensor such as a TOF sensor.

[0002] Time-of-flight sensors are used to perform distance measurements. These measuring systems can be used, for example, in a vehicle to detect objects near the vehicle or in its wider surroundings. Applications include, for example, detecting vehicles ahead to enable autonomous driving, or detecting the immediate surroundings within a range of up to 30 or 50 meters with a wider detection angle to allow vehicles to turn autonomously.

[0003] Other applications for such time-of-flight sensors can be found in robotics, where precise and reliable distance measurements are required, for example, to grasp, move, and position products or parts. In addition, robots can be used for environmental sensing to enable autonomous navigation. Object recognition and tracking are also desirable. In process automation, level measurement or quality assurance, such as dimensional control, can be performed. Further applications can be found in geodesy, for example, in height surveying and mapping.

[0004] Time-of-flight sensors often use photodiodes or avalanche diodes as receivers. The receiving diodes of these sensors can also be so-called SPADs (single-photon avalanche diodes) or arrays of SPADs. These can detect individual photons reflected from an object. Light sources or lasers are frequently used as photon sources. It is also possible to use photon sources in the non-visible optical range.

[0005] A key challenge in using time-of-flight sensors is matching the effective sensitivity to the dynamic range required in a given application. This is addressed by adjusting the accumulation time to achieve the optimal operating point. The accumulation time refers to the period during which the sensor collects photons to generate a signal. This time affects the sensor's effective sensitivity because the number of photons collected during the accumulation period is added together. A longer accumulation time can increase sensitivity but can also decrease the sensor's repetition rate and lead to saturation if the photon count rate becomes too high. Therefore, for optimal performance, a time-of-flight sensor must be designed to suit the application's specific requirements.The sensor must also have a sufficiently large dynamic range to accommodate variations in dynamic parameters, such as the influence of ambient light from sunlight or other bright light sources. At high ambient light intensities, the time-of-flight sensor can quickly reach its maximum photon target rate and become saturated. Adaptive sensitivity control would be desirable, for example, to adjust the accumulation time accordingly.

[0006] Furthermore, power consumption is an important criterion in many applications. A shorter accumulation time allows for a reduction in overall power consumption without affecting the sensor's performance.

[0007] Furthermore, current technology aims to enable individual adjustment of the accumulation time or the total measurement time for different scenes. This should make the sensor more effective, enabling it to measure very well both in darkness and with a high level of ambient light.

[0008] The requirements known from the state of the art are to be addressed by improving existing sensors, in particular time-of-flight sensors.

[0009] The tasks set out are solved by a control device for dynamically controlling measurements of a time-of-flight sensor with the features of claim 1, by a time-of-flight sensor for measuring time of light with a light source, a receiving diode and a control device with the features of claim 12 and by a distance measuring system with the features of claim 15.

[0010] In one aspect, the present invention relates to a control device for dynamically controlling measurements of a time-of-flight sensor. The control device comprises an input interface, a processing unit, an event counter, a maximum value unit, a measurement counter, and an output interface.

[0011] The input interface has a counter port for receiving information about a detected event and a histogram port for receiving information about the current histogram content of a histogram unit. The event counter is connected to the counter port of the input interface. It generates an event count that reflects the detected events. This event count is based on the information about a detected event. This information could, for example, be measured values ​​from a receiving diode, such as a SPAD diode.

[0012] The maximum value unit is connected to the histogram port of the input interface. The maximum value unit is configured to determine the current state of the histogram. The determined histogram value is stored in the maximum value unit if it is greater than the maximum signal value stored in the maximum value unit.

[0013] The measurement counter counts the number of measurements and determines a measurement count value, which is used by the processing unit to generate a measurement control signal. The output interface is configured to output the generated measurement control signal to the processing unit in order to initiate the measurement of events based on the measurement control signal.

[0014] The processing unit is further configured to generate the measurement control signal based on a minimum number of measurements, a maximum number of measurements, a minimum SNR value, the measurement count value, the maximum signal value of the maximum value unit, and the event count of the event counter. This measurement control signal is used to initiate a measurement by the time-of-flight sensor.

[0015] The control device can therefore be used and combined with an existing time-of-flight sensor to improve it.

[0016] In another aspect, the present invention relates to a time-of-flight sensor for measuring the time of flight of light. The time-of-flight sensor comprises a light source, for example a laser, a receiving diode, for example a SPAD diode or an avalanche diode, and a control device. The time-of-flight sensor further includes a TDC (Time-to-Digital Converter) unit and a histogram unit for histograming the detected events during a measurement. The control device of the time-of-flight sensor is configured to allow a dynamic termination of a time-of-flight measurement based on the measurement data and values ​​determined during a measurement. Simultaneously, it is configured to control whether a time-of-flight measurement is initiated and to control this measurement within predefined limits based on the detected signals, the receiving diode, and the histogram values ​​stored in the histogram unit.

[0017] In further aspects, the invention relates to a vehicle with a control device described above or to a robot with such a control device.

[0018] Further aspects of the invention relate to a corresponding method and a computer program product with program code for carrying out the steps of the method when the program code is executed on a computer, as well as a storage medium on which a computer program is stored which, when executed on a computer, causes the execution of the method described herein.

[0019] Preferred embodiments of the invention are described in the dependent claims. It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the present invention. In particular, the method and the computer program product can be implemented according to the embodiments described for the device in the dependent claims.

[0020] Within the scope of the invention, it was recognized that in time-of-flight measurements, an increased photon detection sensitivity (> 15%) of the individual photosensors, photodiodes, or SPADs is not desirable for all applications and areas of use. Firstly, increased photon detection sensitivity increases the sensor's power consumption; secondly, a high level of ambient light worsens the signal-to-noise ratio (SNR) of the measuring device. The measurement efficiency thus decreases, and the overall measurement time increases. The system can also reach saturation more quickly.

[0021] According to the invention, the control device, which is a dynamic measurement unit (DMU), monitors and determines (on the fly) the signal-to-noise ratio (SNR) of the time-of-flight measuring device or the time-of-flight sensor. The control device prompts the time-of-flight sensor to perform further measurements when the measured SNR value falls below a predetermined threshold. This improves measurement accuracy, particularly under adverse environmental conditions such as high levels of ambient light. Furthermore, measurement time is reduced because measurements are only taken until the desired SNR value is reached.

[0022] The processing unit of the control device determines a signal-to-noise ratio (SNR) based on the measurement count, the maximum signal value of the maximum value unit, and the number of events, and checks this SNR ratio or SNR value against predefined boundary conditions and limits. These limits include a minimum SNR value, which may be predefined.

[0023] For example, a minimum and a maximum number of measurements can be specified as boundary conditions for a dynamic measurement termination. Other limit values ​​are conceivable and possible.

[0024] Due to the dynamic termination of measurements, preferably only as many measurements as necessary are performed. Therefore, a light time-of-flight sensor with the control system according to the invention is fast and energy-efficient.

[0025] The control device according to the invention thus achieves several advantages. Firstly, it prevents the saturation of physical memory components on and within an integrated circuit (IC), which is used, for example, as a histogram memory. Typically, 9-bit memory is used here, which can store 511 values. In conventional time-of-flight sensors or devices, an increase in the number of measurements can lead to a memory overflow. Dynamically terminating the measurements prevents saturation.

[0026] According to the invention, the number of necessary measurements can be reduced or limited to achieve a sufficient signal-to-noise ratio (SNR). This allows for obtaining an SNR value suitable for distance measurement. Overall, power consumption can be significantly reduced. Furthermore, individual adjustments for different scenarios or applications are possible. In a time-of-flight sensor or a time-of-flight measuring device with multiple channels or pixels, i.e., with multiple photodiodes or SPAD diodes, the accumulation time (total measurement time) can be individually controlled. This makes it possible to adapt the sensitivity to different intensities of reflective objects and the level of ambient light. This results in optimized and rapid measurement.

[0027] According to the invention, the control device enables adaptive control of the effective sensitivity of SPAD sensors through real-time monitoring of the histogram data. Effective sensitivity can be optimally adjusted by means of the accumulation time, which results from the number of measurements performed in a measurement series. Performance is improved under varying conditions, current consumption is reduced, and saturation is avoided.

[0028] Within the scope of the invention, it was found that high photon sensitivity of the sensors enables very good measurement results in dark or relatively dark environments, e.g., with an ambient light level in the range of 10 kLux. However, in bright environments with high ambient light levels, for example, a light level of approximately 100 kLux or more, sensors with high photodetection sensitivity produce a much lower signal-to-noise ratio. The signal measured by the sensors becomes significantly worse. Within the scope of the invention, it was also recognized that this behavior is due to the fact that the typical receiving diodes, which are designed as SPADs, are in their respective dead-time phase for a larger portion of the accumulation time or total measurement time under higher ambient light conditions and higher ambient light levels, and thus cannot detect photons.Furthermore, it was found that with sensors of lower photodetection sensitivity, increasing the number of measurements leads to the same or better results. Therefore, when dynamically adjusting the number of measurements, receiving diodes or SPADs with lower photodetection sensitivity can be used. Since these SPADs also have the advantage of a better signal-to-noise ratio than those with high photodetection sensitivity, more reliable and faster measurements can be achieved overall.

[0029] This is based in particular on the fact that measurements are dynamically terminated as soon as a measured value or SNR value with a sufficiently large signal-to-noise ratio or signal-to-noise ratio is received, which allows for the detection of an object and the determination of the distance to the object.

[0030] Within the scope of the invention, it was also recognized that a certain minimum number of measurements must be performed to enable a statistical evaluation of the measurement results. This limit can be predetermined or defined by the minimum number of measurements.

[0031] In a preferred embodiment, the processing unit in the control device is configured to generate or estimate an SNR value (signal-to-noise ratio) from the measurement count, which represents the number of measurements performed, the maximum signal value, and the number of events. Processing only these three values ​​allows the generation of an SNR value. The maximum signal value is the highest value occurring in the digital output signal of the time-of-flight sensor or SPAD, which is also visible in the histogram.

[0032] Preferably, to determine the SNR value, an average of the number of events, a so-called mean event value, is first calculated from the measurement count and the event count of the event counter. Based on the mean event value and the maximum signal value, the SNR value is then calculated. This SNR value is checked against the predefined minimum SNR value (min-SNR value) as a lower limit. As soon as the determined SNR value is greater than the min-SNR value (limit value), a sufficient signal value is present to allow the determination of a distance value within the measurement series. Further measurement is then unnecessary. The raw histogram data can be output by the time-of-flight sensor to an analysis unit or an evaluation unit, which determines a distance to an object based on the data in the histogram and enables further processing of this determined distance value.For example, the distance value can serve as a basis for analyzing and adjusting the driving strategy or for the movement status of a vehicle.

[0033] The SNR value cannot be calculated solely from the maximum signal value and the ratio of event count to measurement count. SNR value = Maximum signal value / Number of events / Measurement count

[0034] If the number of bins of a histogram unit or histogram memory is known, the SNR value can preferably also be determined from the max signal value and the ratio of event count to bin count. SNR value = Maximum signal value / Number of events / Number of bins

[0035] In a preferred embodiment of the control device, the processing unit always generates a measurement control signal as long as the measurement count of the counter is less than the minimum number of measurements. This ensures that a minimum number of measurements are performed before the measurements are aborted. This is necessary to obtain a sufficient number of measurements to perform a statistical evaluation.

[0036] In a preferred embodiment of the control device, the measurement control signal is generated as long as the measurement count of the counter is greater than the minimum number of measurements and less than the maximum number of measurements. The measurement count must therefore lie between the minimum and maximum numbers of measurements, i.e., between the two predefined limits. As a further criterion, the SNR value determined by the processing unit must be below the minimum SNR value. These conditions thus stipulate that the minimum number of measurements has already been performed, but the maximum number of measurements has not yet been reached. Simultaneously, no signal has been detected that meets the criterion of the predefined minimum signal-to-noise ratio. As long as these conditions are met, the measurement control signal is generated, and further measurements of the time-of-flight sensor are initiated.

[0037] A preferred embodiment of the control device provides that the output of the measurement control signal is aborted, prevented, or suppressed as soon as the measurement count of the counter exceeds the maximum number of measurements. Thus, a maximum number of measurements is specified, upon reaching which the measurements are aborted and no further measurements are taken. In this case, the detection of signals that would allow for distance determination was unsuccessful. However, performing further measurements is not advisable, as no corresponding measured values ​​are expected due to saturation or an excessively low signal-to-noise ratio (SNR).

[0038] In a preferred embodiment of the control device, the generated measurement control signal is transmitted to a TDC unit to initiate and perform a measurement by the sensor. The measurement control signal thus triggers the time-of-flight sensor to measure photons reflected by an object within the sensor's field of view.

[0039] In a preferred embodiment, the processing unit is configured and configured to reset the event counter, the measurement counter, or the maximum value unit. For this purpose, a reset signal is sent to the respective component. The individual components can be reset individually, in combination, or together. This allows the system to start with new values ​​after the completion of a measurement cycle, i.e., after the accumulation time has elapsed.

[0040] In a preferred embodiment of the control device, the minimum number of measurements, the maximum number of measurements, and / or the minimum SNR value, all of which can be predefined, are stored in a memory. The individual values ​​can be stored in a common memory, in separate memory locations, or in sub-areas of a memory. They can be stored as non-volatile memory or in volatile memory. The memory can be overwritten, preferably either by the control device itself, by the processing unit, or externally.

[0041] An equally preferred embodiment of the control device provides a limit value interface for receiving limit values ​​such as the minimum number of measurements, the maximum number of measurements, and / or the minimum SNR value. These values ​​can be forwarded directly to the processing unit. Alternatively, and more preferably, the values ​​are fed into and stored in an optional memory.

[0042] Preferably, the control device includes an output interface comprising a measurement counter port for outputting the measurement count value and / or an event counter port for outputting the number of events counted. In this way, the corresponding values ​​can be output for further processing by the time-of-flight sensor, a higher-level distance measurement system, or other processing devices, for example, in a vehicle.

[0043] Preferably, the control device is designed such that the maximum value unit stores not only the highest signal value or SNR value, but a plurality of signal values ​​or SNR values. Preferably, the N highest signal values ​​are stored, where N is a natural number. For example, 2, 3, 5, 10, or 15 signal values ​​can be stored. The individual signal values ​​can be stored in one maximum value unit or in different maximum value units, which, for example, are arranged side by side and interconnected. The maximum value unit can also provide multiple memory areas in which the corresponding signal values ​​are stored. In this way, it is possible to output multiple SNR values ​​or signal values, or to directly output the N highest values ​​from the histogram memory. In various application areas or uses, the highest value is not of interest.For example, a pane of glass might be positioned directly in front of the sensor, causing reflections. In this case, the highest signal value would be recorded, but this provides no information about an object within the sensor's field of view or its distance. The multiple signal values ​​from each maximum value unit can be output and further processed by other evaluation units.

[0044] The time-of-flight sensor according to the invention for measuring time of flight has a light source, preferably a laser. The laser can operate, for example, in the range of 700 nanometers to 1000 nanometers. Preferably, lasers with a wavelength of 850 nanometers, 905 nanometers, or, more preferably, 940 nanometers are used. Particularly in the wavelength range around 940 nanometers (940 nanometers ± 20 nanometers), the sun emits very few photons, so that a measuring system tuned to this wavelength or a time-of-flight sensor can, for example, filter out extraneous light components from the sun by using a narrowband optical filter. Preferably, the photodetector or the receiving diode or SPAD is sensitive in a range corresponding to the wavelength range of the laser or the light source. Preferably, the wavelength range in which the SPAD is particularly sensitive is 940 nanometers.

[0045] A preferred embodiment of the time-of-flight sensor comprises a control device with the features specified above.

[0046] A time-of-flight sensor is particularly preferred if it comprises one or more receiving diodes or a receiving diode array. Preferably, a receiving diode comprises one or more SPADs; preferably, a time-of-flight sensor has an array of SPADs, for example, of 3 x 3 SPADs.

[0047] In a preferred embodiment, the histogram unit of the time-of-flight sensor includes a memory to store the determined values ​​in individual bins as a function of time and to be able to output them at the end of a measurement.

[0048] A preferred embodiment of a distance measurement system comprises a time-of-flight sensor, as described above, and an evaluation unit for determining the distance to an object within the field of view of the time-of-flight sensor. The distance is determined from histogram data after the measurements are completed. The histogram data is transmitted from the time-of-flight sensor to the evaluation unit. Additionally, the measurement count from the counter can be transmitted to the evaluation unit. It is also preferred that the event count from the event counter be output to the evaluation unit or to another higher-level unit or device.

[0049] Such a distance measuring system can be used, for example, in a vehicle or in a robot and for observing the surroundings.

[0050] The inventive method for controlling a time-of-flight measurement of a time-of-flight sensor comprises several steps. The method can be implemented in a distance measurement system, a time-of-flight sensor, or a control device, as described above. The method is used to dynamically adjust the number of measurements and thus the accumulation time, i.e., the total measurement time. This adjustment is made on the fly, i.e., during a series of measurements or a measurement cycle, and not, as is customary in the prior art, after a (completed) measurement cycle. The current measured values ​​can be used, allowing the environment and environmental conditions to be taken into account directly.

[0051] In one step of the process, the number of detected events, recorded by the receiving diode of the time-of-flight sensor, is counted. From this count, an event count is generated for further processing.

[0052] In a further step, the measurements taken by the light time-of-flight sensor are counted and stored as a measurement count value, which is generated in this step.

[0053] A further step involves reading the current value from the histogram unit of the time-of-flight sensor before the next measurement is taken. This histogram value is stored as the maximum signal value in a maximum value unit (a memory location) if the value stored in the maximum value unit is lower.

[0054] A further step involves determining an average event value from the target measurement value and the number of events generated. In a subsequent step, a signal-to-noise ratio (SNR) value is calculated as a signal value or signal-to-noise ratio value from the average event value and the maximum signal value of the maximum value unit. The SNR value is compared with a minimum SNR value stored in the processing unit when certain boundary conditions are met. A comparison always takes place when the number of measurements performed is above a lower limit defined by the minimum number of measurements, and when the maximum number of measurements defined by the maximum number of measurements has not yet been exceeded. In this case, it is checked whether the SNR value is below a limit defined as the minimum SNR value. If this is the case, a measurement control signal is generated in a further step, which is sent from the control device to the time-of-flight sensor.The signal is output to the TDC unit of the time-of-flight sensor. This initiates another measurement; the TDC unit is started.

[0055] The measurement control signal is generated even if the measured SNR value is below the minimum SNR value, provided the number of measurements is below a minimum. As long as the number of measurements is less than the specified minimum and therefore less than the specified limit, a measurement control signal is always generated to initiate and start another measurement.

[0056] If the current number of measurements exceeds an upper limit, i.e., an upper threshold defined by the maximum number of measurements, the measurement is aborted, regardless of whether a sufficiently high SNR value could be determined. No further measurement control signal is generated and / or no measurement control signal is output at the output interface.

[0057] The individual process steps are carried out until either the number of measurements exceeds the maximum number of measurements or the determined SNR value exceeds the minimum SNR value. The steps mentioned above can, at least partially, be performed in a different order and / or simultaneously and / or almost simultaneously.

[0058] In other words, a measurement control signal is generated to initiate a measurement of the time-of-flight sensor when the measurement count is below a minimum measurement count. A signal is also generated when the measurement count is between a minimum and a maximum measurement count, and the SNR value is below a minimum SNR value. The measurement is aborted when the measurement count is above a maximum measurement count or when the SNR value is above a minimum SNR value.

[0059] The invention is described and explained in more detail below with reference to some selected embodiments in conjunction with the accompanying drawings. These show: Fig. 1 Simulations of received signals from two different time-of-flight sensors at low brightness; Fig. 2 Simulations of the received signals of the same time-of-flight sensors under the influence of extraneous light; Fig. 3 Simulations of the received signals of a time-of-flight sensor in ambient light with different numbers of measurements; Fig. 4 a control device according to the invention for dynamically controlling measurements of a light time-of-flight sensor; Fig. 5 a time-of-flight sensor according to the invention with a control device; Fig. 6 Distance measuring system with a time-of-flight sensor with a control device; Fig. 7 a time-of-flight sensor with multiple measuring channels and a control device according to the invention; Fig. 8 an alternative embodiment of a time-of-flight sensor with multiple measurement channels; Fig. 9 a vehicle with a control device according to the invention; and Fig. 10 a robot with a distance measuring system according to the invention; and Fig. 11 a schematic representation of the method according to the invention.

[0060] Fig. Figure 1 shows two graphs with simulated histograms of received signals from a time-of-flight sensor with a SPAD receiver (SPAD = Single Photon Avalanche Diode). The simulations cover received signals in the absence of ambient light and in low ambient light conditions of 10 kLux. The y-axis represents the simulated number of detection results, while the x-axis shows the simulated time since a measurement was triggered.

[0061] The left graph shows a SPAD with a 20% photon detection sensitivity. The number of simulated measurements is 500.

[0062] The graph on the right shows the simulation result of a SPAD with 10% photon detection sensitivity. The number of measurements performed is 1000. In both cases, measurements under low ambient light conditions are simulated.

[0063] It can be seen that with a light receiver with twice the photon detection sensitivity (20%), but only half the number of measurements, approximately the same results can be achieved as with a receiver whose photon detection sensitivity is only half as high (10%), but the number of measurements has been doubled. It turns out that a receiver with a lower photon detection sensitivity can be used if the number of measurements is increased accordingly. This finding was one of the foundations for the present invention.

[0064] Fig. Figure 2 shows the result of a simulation of 500 measurements with a receiver with a 20% photon detection sensitivity.

[0065] The graph on the right shows the result of a simulation of 1000 measurements with a receiver having a photon detection sensitivity of 10%. Both simulations were performed for an increased ambient light level of 100 kLux.

[0066] Based on the in Fig. 1 and Fig. In the simulations shown, it was found that a high level of photon noise, which can be caused, for example, by ambient light, leads to an increase in the dead time in the SPAD diodes. Consequently, the proportion of dead time to the total measurement time increases. Within the scope of the invention, it was further found that the increased photon detection sensitivity in the presence of ambient light has a significant influence on the signal-to-noise ratio.

[0067] Within the scope of the invention, it was also recognized that the effective photon detection sensitivity of the SPAD must be adapted to the dynamic illumination conditions, such as ambient light and field of view per pixel, if saturation is to be avoided and accurate distance measurement is to be enabled. The effective sensitivity of the SPAD is the product of the photon detection sensitivity (photon detection efficiency) of the respective SPAD multiplied by the integration time. The integration time is proportional to the number of measurements, which typically always have a substantially similar measurement time per measurement.

[0068] The simulation shows that in low ambient light of 10 kLux, as in Fig. Figure 1 shows that a signal with a good signal-to-noise ratio is achieved when a SPAD diode with a photon detection sensitivity of 20% at a given dead time is used, and the number of measurements is 500. A similar signal is also obtained, however, when a SPAD diode with a photon detection sensitivity reduced by half (to 10%) is used, and the number of measurements is doubled (1000 instead of 500) to compensate for the reduced sensitivity. The overall longer integration time with more measurements compensates for the lower photon detection sensitivity. This is an economically important and surprising finding that has emerged within the scope of the invention.

[0069] The dead time considered for each simulated SPAD diode is the time after a photon event during which, due to its design, the SPAD diode cannot detect any further photons and consequently cannot output a signal. This also applies when irradiated with a larger quantity of photons. Within the scope of the invention, it was recognized that, for a given photon rate and a given SPAD diode dead time, a higher photon detection sensitivity directly leads to a higher number of events and thus also to a higher probability that the SPAD will be in a dead time at some point. In other words, the proportion of the dead time to the total measurement time is, to a first approximation, approximately inversely proportional to the photon detection sensitivity for small changes in this sensitivity.

[0070] These effects become even more pronounced at higher ambient brightness levels, such as in a simulated 100 kLux environment. Based on a comparison of the simulation results in Fig. Figure 2 shows that a SPAD with twice the photon detection sensitivity produces a signal with a much lower signal-to-noise ratio than a SPAD with half the photon detection sensitivity but twice the number of measurements. Evaluation of these simulations revealed that this behavior is due to the fact that the SPAD with the higher photon detection sensitivity spends most of the total measurement time in its respective dead time under brighter ambient light conditions. To counteract this effect, it was found that SPADs with reduced photon detection sensitivity are advantageous when the number of measurements is increased accordingly (right-hand graph in Figure 2). Fig. 2).

[0071] Fig. Figure 3 shows results from simulations of a SPAD diode with a photon detection sensitivity of 10% at a high ambient light level of 1000 kLux. In the left graph, the number of measurements performed is 3000, and in the right graph, the number is 2000.

[0072] In practice, the evaluation circuit of a measurement system with a time-of-flight sensor is implemented as a micro-integrated circuit, such as an IC. Histogram statistics data are preferably stored in the evaluation circuit's memory for later analysis. The maximum number of possible values ​​in a typical 9-bit memory is 512. This saturation limit is exceeded in the left graph. It shows that meaningful results can no longer be obtained after 3000 measurements. The saturation limit imposed by the physical memory is exceeded when the number of measurements increases. In contrast, the right graph shows the simulation with 2000 measurements. Here, successful detection of a value with a sufficiently good signal-to-noise ratio is achieved. The maximum value here is 350, which is significantly below the saturation limit.

[0073] From the simulations and the graphs according to Fig. As can be seen in Figure 3, a good signal-to-noise ratio can be achieved with as few as 2000 measurements. Further measurements are not necessary. Instead, the measurement series can be terminated, as implemented by the present invention. This results in lower power consumption and also prevents the saturation limit from being reached in the first place.

[0074] Fig. Figure 4 shows a control device 10 according to the invention, comprising an input interface 20 with a counter port 22 for receiving information about a detected event and a histogram port 24 for receiving information about the current histogram content of a histogram memory. The control device 10 further includes a processing unit 30 for generating a measurement control signal, an event counter 40, a maximum value unit 50, and a measurement counter 60. The control device 10 for dynamically controlling measurements of a time-of-flight sensor also has an output interface 70 for outputting the measurement control signal to initiate a new measurement.

[0075] The event counter 40 is connected to counter port 22 of input interface 20 and receives information about a detected event. This information can originate, for example, from a SPAD diode. Based on this information, the event counter 40 generates an event count representing the detected events. To do this, the counter value in the event counter 40 is incremented by the number of detected events. The event counter 40 thus serves to count all events of a measurement cycle and to continuously monitor the average photon rate of a SPAD. Preferably, the event counter 40 can be reset by the processing unit 30 before a new set of measurements, i.e., a measurement cycle, is incremented.

[0076] The maximum value unit 50 is connected to the histogram port 24 to determine the current state of the histogram, which is stored in a histogram memory. The maximum value unit stores the current state of the histogram if it is greater than the maximum signal value already stored in the maximum value unit. The maximum value unit stores the value of a bin in the histogram memory if this value is greater than the previously stored value. A series of cascaded maximum value units can be provided, in which the k largest values ​​from the histogram memory are stored.

[0077] Since it is updated with every event, the maximum value unit can also be used to continuously monitor the highest values, i.e., the peaks, in a histogram without having to query the entire histogram memory.

[0078] The measurement counter 60 counts the number of measurements initiated by the processing unit 30. It detects the measurement control signal generated by the processing unit 30 before outputting it at the output interface 70. The measurement counter 60 then generates the measurement count value, which is fed back to the processing unit 30 for comparison with a limit value. The measurement counter 60 is therefore configured to monitor how many measurements have already been performed in the current measurement cycle or series.

[0079] The processing unit 30 of the control device 10 is configured to generate the measurement control signal and output it at the output interface 70, thereby initiating a measurement by the time-of-flight sensor. For this purpose, a TDC unit of the time-of-flight sensor can be controlled, for example. The generation of the measurement control signal is based on a minimum number of measurements, a maximum number of measurements, and a minimum SNR value. Furthermore, the determination of the measurement control signal is based on the measurement count of the measurement counter 60, the maximum signal value stored in the maximum value unit 50, and the number of events provided by the event counter 40.

[0080] The processing unit 30 is a signal-to-noise ratio (SNR) calculator and uses the maximum signal value from the maximum value unit 50 and the number of events from the event counter 40 as input for an application-specific function to calculate a signal-to-noise ratio (SNR) value. The processing unit 30 outputs at least the minimum number of measurements multiplied by a "Go signal" to the output interface 70 for an optionally connected TDC (Time Data Computing) device. This ensures that a minimum number of measurements are taken and therefore a minimum number of events is recorded in the event counter 40.

[0081] If the minimum number of measurements is exceeded, each update of the maximum value unit (50) checks whether one or more values ​​within this unit are at least as large as the threshold of the minimum SNR value. If so, the event detection is considered successful. No further measurements are required, and no "go" signal is transmitted.

[0082] If this is not the case, measurements are initiated by outputting a measurement control signal at output interface 70 until the measurement count in the measurement counter 60 exceeds the maximum number of measurements. A detection attempt is then considered unsuccessful and the measurement cycle is terminated.

[0083] The processing unit 30 can preferably first determine an SNR value based on the measurement count, the maximum signal value, and the number of events. This determined SNR value is compared with the minimum SNR value, and a measurement control signal is generated as long as the calculated SNR value is less than this limit. However, this only occurs if the measurement count is less than the maximum measurement count, which is also checked in the processing unit 30. As long as the minimum measurement count has not been reached, i.e., the measurement count is less than this limit, a measurement control signal is generated regardless of whether the determined SNR value is greater or less than the minimum SNR value.

[0084] The calculation of the SNR value in processing unit 30 is preferably application-specific.

[0085] Optionally, the control device 10 can include a limit value interface 80, by means of which the limit values, namely the minimum number of measurements, the maximum number of measurements, and / or the minimum SNR value, are received. These values ​​can be stored in an optional intermediate memory or memory 32 of the processing unit 30 to be available to the processing unit 30. The memory 32 can also be arranged outside the processing unit 30 as an independent component.

[0086] Optionally, the control device 10 can also include an event port 42 to output the event count of the event counter 40, making it available for further processing in external devices. Alternatively, the event port 42 can also be integrated into the output interface 70.

[0087] The processing unit 30 is preferably configured to reset the event counter 40 and / or the measurement counter 60 and / or the maximum value unit 50. This preferably occurs before a new measurement series is started.

[0088] The Max value unit 150 replaces the Max signal value with the input value at histogram port 24 if the current input value (Bin(i)), which reflects the current state of the histogram, is greater than the Max signal value, i.e., if: Bin(i) > Max(k)

[0089] Alternatively, when multiple peaks are detected, i.e., with k > 1, the following can apply: Bin(i)=Max(k), if Bin(i)>Max(k) and if Bin(i) <Max(k+1).

[0090] Furthermore, other termination criteria can be defined. For example, the output of a measurement control signal can be prevented if the following applies: Bin(i)>f(average count rate of the event counter) =c+m*average count rate of the event counter

[0091] Here, Bin(i) is the value in the current bin of a histogram memory or histogram unit connected to histogram port 24, and f( ) is the function of an average count rate. The average count rate of the event counter is the number of events relative to the number of measurements (measurement count value). The variables c and m can be system-specific parameters of the time-of-flight sensor or of a system in which the control device 10 is used. They can be application-specific and, for example, take into account whether and how many false positive results or only false negative results are accepted.

[0092] Fig. Figure 5 shows a time-of-flight sensor 100 with the control device 10 according to the invention. The time-of-flight sensor 100 comprises an optical unit 130 with a receiving diode 132 and a light source 134. The receiving diode 132 is preferably configured as a SPAD 136. The time-of-flight sensor 100 further has a TDC unit 110 and a histogram unit 120, which may optionally include a histogram memory. The control device 10 controls and enables a dynamic termination of the time-of-flight measurement of the time-of-flight sensor 100 as soon as a predetermined signal value or a signal-to-noise ratio (SNR) value is determined or a maximum number of measurements has been performed.

[0093] The measurement control signal generated by the control device 10 is transmitted via output interface 70 to the TDC unit 10, which then starts a measurement and causes the light source 134 to emit light. This light is received by the SPAD 136 after reflection from an object. The events are transmitted to the control device 10 via input interface 20 and counted in the control device 10. Additionally, the corresponding bin in the histogram unit 120 is incremented, and the number of counted current events is passed to the measurement unit 50 of the control device 10. The control device 10 can output the number of measurements performed at its output interface 70 for further external processing. It is also possible to output the number of events via event port 42.The histograms determined in the histogram unit 120 can also be output by the light time-of-flight sensor 100 and further processed in another unit.

[0094] Fig. Figure 6 shows a distance measuring system 200 according to the invention, comprising a time-of-flight sensor 100, which can be configured as described above, and an evaluation unit 210 for determining a distance. The distance is preferably determined from the histogram data after completion of the measurements or a series of measurements. The time-of-flight sensor 100 outputs histogram data from an internal histogram unit 120 to the evaluation unit 210, which is further processed in the evaluation unit 210.

[0095] Fig. Figure 7 shows a schematic representation of the measurement principle of a time-of-flight sensor with multiple optical units 130. Several SPADs 136, which can be grouped into a single pixel, can be used. Each SPAD 136 typically has a digital output that generates a rising or falling edge, which is recognized as an event. As soon as a photon is detected by the SPADs 136, an event is output. The pixel can either output all individual events from the SPADs via dedicated lines or output only a digital sum of the events. In this case, only the number of SPADs 136 that have been triggered is determined. Each pixel group is assigned to a TDC unit 110. In the embodiment shown here, all SPAD channels are controlled simultaneously by the optical units 130 and the TDC units 110. This is done by a single control device 10.All TDC units 110 are assigned to one control device 10 and receive a global measurement control signal or “GO” signal from it.

[0096] Fig. Figure 8, however, shows a variant in which each group of optical units 130 is assigned a TDC unit 110 with a separate control device 10. The control device 10 does not have to be integrated into the TDC unit 110. It can also be implemented as an independent element. This allows for individually adapted triggering for each group of optical units 130, tailored to the environmental conditions. For example, in a monitored scene observed by the time-of-flight sensor 100, very bright objects, such as reflectors or traffic signs, and very dark objects, such as black vehicles or people dressed in black, may be present simultaneously. A pixel (group of optical units 130) directed at the dark object requires a higher number of measurements than another pixel directed at a bright object.While each control device 10 is subject to the same constraints, such as threshold functions, the number of minimum measurements (min measurement value), and the number of maximum measurements (max measurement value), it performs a different number of measurements for each pixel based on the determined maximum values ​​and counted events. This allows for a highly individualized and environment-specific measurement series for each pixel.

[0097] Fig. Figure 9 shows a vehicle 90 with a distance measuring system 200 according to the invention. The distance measuring system 200 comprises a light time-of-flight sensor 100 with a control device 10.

[0098] Fig. Figure 10 shows a robot 92, in particular an industrial robot, with a distance measuring system 200 according to the invention. The distance measuring system 200 comprises a time-of-flight sensor 100 with a control device 10.

[0099] Fig.Figure 11 shows the schematic sequence of a method according to the invention for controlling a time-of-flight measurement of a time-of-flight sensor 100, which allows dynamic adjustment of the accumulation time, or the total measurement time, and the number of measurements to be performed. The method comprises several steps, which can also be carried out in a different order or partially in a different order. It is not necessary to perform all steps of the method.

[0100] In step S10, the number of events detected by the light time-of-flight sensor 100 is counted and a value representing the number of events, the so-called event count, is generated.

[0101] Step S12 involves counting the measurements taken by the sensor and generating a measurement count value.

[0102] Step S14 involves reading the current value from a histogram unit, preferably before the next measurement and before the currently detected event is fed to the histogram unit. The individual events are stored in individual bins in a histogram memory of the histogram unit.

[0103] One step S16 involves determining a mean event value from the measurement count value and the number of events.

[0104] In step S18, an SNR value is determined from the mean event value and the read-out maximum signal value of the histogram unit.

[0105] In step S20, it is checked whether the measurement count value is below a minimum measurement count that is specified.

[0106] If this is the case, a measurement control signal is generated in step S22 to initiate a measurement of the light time-of-flight sensor. The measurement control signal is used to control a TDC unit of the sensor.

[0107] If the criterion in step S20 is not met, step S24 checks whether the measurement count value is above a maximum measurement count, which is also specified.

[0108] If this criterion is met, the measurement is terminated in step S26. A measurement control signal is neither generated nor output.

[0109] If the criterion in step S24 is not met, i.e., the maximum number of measurements has not yet been reached, step S28 checks whether the SNR value is below a minimum SNR value, which is specified and can be application-specific or system-specific.

[0110] If the criterion in step S28 is met, a measurement control signal is generated according to step S22. If the criterion in step S28 is not met, the measurement is aborted according to step S26.

[0111] Once a measurement control signal has been generated, it can be sent to the light time-of-flight sensor in step S30. Step S30 can optionally also include resetting all counters and count values.

[0112] This completes one measurement. For the next measurement, i.e., as long as no abort and thus end of a measurement cycle is initiated according to step S26, steps S10 to S30 are performed again.

[0113] The invention has been comprehensively described and explained with reference to the drawings and the description. The description and explanation are to be understood as examples and not as limiting. The invention is not limited to the disclosed embodiments. Other embodiments or variations will become apparent to a person skilled in the art when using the present invention and upon a detailed analysis of the drawings, the disclosure, and the subsequent claims.

[0114] In the patent claims, the words "comprise" and "with" do not preclude the presence of further elements or steps. The undefined article "a" or "an" does not preclude the presence of multiple elements. A single element or unit can perform the functions of several of the units mentioned in the patent claims. An element, unit, device, and system can be implemented partially or completely in hardware and / or software. The mere mention of some measures in several different dependent patent claims is not to be understood as precluding the advantageous use of a combination of these measures. A computer program can be stored / distributed on a non-volatile data carrier, for example, on optical storage media or on a solid-state drive (SSD).A computer program can be distributed together with hardware and / or as part of hardware, for example via the internet or via wired or wireless communication systems. Reference punctuation in the patent claims is not to be understood as limiting.

Claims

[1] Control device for dynamically controlling measurements of a time-of-flight sensor (100) comprising an input interface (20) with a counter port (22) for receiving information about a detected event and with a histogram port (224) for receiving information about the current histogram content; a processing unit (30) for generating a measurement control signal; an event counter (40) connected to the counter port (22) to generate an event count representing all recorded events based on the information about a recorded event; a maximum value unit (50) connected to the histogram port (24) to determine and store a current maximum value of a histogram when it is greater than the maximum signal value stored in the maximum value unit (50); a measurement counter (60) to count the number of measurements and to determine a measurement count value; an output interface (70) for outputting the measurement control signal for measuring events; wherein the processing unit (30) is configured to generate the measurement control signal based on a min measurement count, a max measurement count, a min SNR value, the measurement count value and the max signal value and the event count in order to initiate a measurement of the light time-of-flight sensor (100). [2] Control device according to claim 1, characterized by , that the processing unit (30) is set up to generate an SNR value from the measurement count value and the maximum signal value and the event count. [3] Control device according to any one of the preceding claims, characterized by , that the measurement control signal is generated when the measurement count value of the measurement counter (60) is less than the minimum measurement count. [4] Control device according to any one of the preceding claims, characterized by, that the measurement control signal is generated when the measurement count value of the measurement counter (60) is between the min measurement count and the max measurement count and an SNR value is below the min SNR value. [5] Control device according to any one of the preceding claims, characterized by , that the output of the measurement control signal is aborted if the measurement count value of the measurement counter (60) is above the max measurement count. [6] Control device according to any one of the preceding claims, characterized by , that the measurement control signal is transmitted to a TDC unit (110) to initiate a measurement of a sensor. [7] Control device according to any one of the preceding claims, characterized by , that the processing unit (30) is configured to reset the event counter (40), the measurement counter (60) and / or the maximum value unit (50). [8] Control device according to any one of the preceding claims, characterized by, that the min measurement count, the max measurement count and / or the min SNR value are stored in a memory (32). [9] Control device according to any one of the preceding claims, characterized by , that the control device (10) includes a limit value interface (80) to receive the min measurement count, the max measurement count and / or the min SNR value. [10] Control device according to any one of the preceding claims, characterized by , that the output interface (70) includes a measurement count port for outputting the measurement count value and / or an event count port for outputting the event count with the number of counted events. [11] Control device according to any one of the preceding claims, characterized by , that the maximum value unit (50) stores the n largest signal values, where n is a natural number and preferably n is at most 10, more preferably n is at most 5. [12] Light time-of-flight sensor for measuring light time of flight, comprising a light source (134), a receiving diode (132) and a control device (10), a TDC unit (110) and a histogram unit (120), wherein the control device (10) enables a dynamic termination of the light time-of-flight measurement. [13] Light time-of-flight sensor according to the preceding claim, characterized by that the control device (10) is designed according to one of the preceding claims. [14] Light time-of-flight sensor according to claim 12 or 13, characterized by , that the receiving diode (134) comprises one or more SPADs (136) and / or the histogram unit (120) comprises a memory. [15] Distance measuring system with a time-of-flight sensor (100) according to claims 12 to 14, and an evaluation unit (210) for determining a distance, wherein the time-of-flight sensor (100) transmits histogram data from a histogram unit (120) to the evaluation unit (210) for further processing. [16] Vehicle with a control device (10) according to one of claims 1 to 11 or with a light time-of-flight sensor (100) according to one of claims 12 to 14 or with a distance measuring system (200) according to claim 15. [17] Robot with a control device (10) according to one of claims 1 to 11 or with a time-of-flight sensor (100) according to one of claims 12 to 14 or with a distance measuring system (200) according to claim 15. [18] Method for dynamically controlling a time-of-flight measurement of a time-of-flight sensor comprising the following steps: Counting the number of events detected by the time-of-flight sensor and determining the event count; Counting the measurements taken by the light time-of-flight sensor and generating a measurement count value; Reading the current value from a histogram unit before the next measurement; Determining a mean event value from the measurement count and the number of events; Determining an SNR value from the mean event value and the maximum signal value; Check if the measurement count is below a minimum measurement count; If so, generate a measurement control signal to initiate a measurement of the light time-of-flight sensor; If no, check if the measurement count is above a maximum number of measurements and if yes, abort the measurement; If no, check if the SNR value is below a minimum SNR value; If so, generating a measurement control signal to initiate a measurement (to control a TDC unit) of the sensor; If no, cancel the measurement; Output the measurement control signal (to the TDC unit), if available; Repeat the previous steps. [19] Computer program product comprising code for carrying out the method according to the preceding claim.

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