Measuring distance with optical time-of-flight method

Abstract

The present application relates to measuring distances with a light time-of-flight method. An optoelectronic sensor for measuring distances of objects in a detection region with a light time-of-flight method is provided, having a light emitter for emitting light signals into the detection region, a light receiver having a first plurality of light receiving elements for detecting received light from the detection region, and a second plurality of light time-of-flight measuring units for determining individual light time-of-flights from the light time-of-flight between the emitted light signals and the received light signals returned or reflected on the objects, a memory for collecting the individual light time-of-flights, a control and evaluation unit for determining a distance value by evaluating the individual light time-of-flights, and also for determining at least two distance values from the individual light time-of-flights of at least two groups of light time-of-flight measuring units. A readdressing unit writes the individual light time-of-flights to specific addresses in accordance with the allocation of the light time-of-flight measuring units to the groups, so that the control and evaluation unit can allocate the stored individual light time-of-flights to the groups and thus to the distance values by means of the addresses.

Description

[0001] The present application relates to an optoelectronic sensor and a method for distance measurement of an object in a detection region using the light time-of-flight method.

[0002] Distance sensors or distance scanners measure the time of flight of a light signal according to the light time-of-flight principle, which corresponds to a distance by the speed of light. Pulse-based measurements and phase-based measurements are distinguished. In the pulse time-of-flight method, a short light pulse is emitted and the time until the remission or reflection of the light pulse is received is measured. Alternatively, in the phase method, the amplitude of the emitted light is modulated and the phase shift between the emitted light and the received light is determined, wherein the phase shift is also a measure of the light time of flight.

[0003] Avalanche photo diodes (APD) are used in some optoelectronic sensors in order to also be able to detect lower reception intensities. Here, the incident light triggers a controlled avalanche effect. As a result, the charge carriers generated by the incident photons are multiplied and a photo current proportional to the light reception intensity, but significantly greater than a simple PIN diode, is generated.

[0004] Avalanche photo diodes (SPAD, Single Photon Avalanche Diode) operating in the so-called Geiger mode enable even higher sensitivity. Here, the avalanche photo diode is biased above the breakdown voltage, so that even a single charge carrier released by a single photon can trigger an uncontrolled avalanche, which then, due to the high field strength, absorbs all available charge carriers. Thereafter, the avalanche is stopped (passive quenching) and is not available for detection for a certain dead time. Alternatively, it is also known to detect the avalanche from the outside and to extinguish it (active quenching).

[0005] SPADs therefore count individual events like Geiger counters. SPADs are not only highly sensitive, but can also be integrated relatively inexpensively and efficiently in silicon semiconductors. In addition, SPADs can be easily integrated on printed circuit boards. The special thing is that even the smallest disturbing events, such as extraneous light photons or dark noise, produce the same maximum reception signal as a useful light signal.

[0006] Preferably, the SPAD-based distance sensor works in a pulse-based manner to ensure robust measurement even in the case of edge hits or Remissionssprüngen. This is also referred to as direct Time of Flight (dToF) measurement. In order to obtain reliable measurement results without the influence of disturbances, events can be collected by multiple SPADs or multiple emission pulses and evaluated together by searching for the maximum value in a histogram.

[0007] In order to implement this solution in practice, a histogram memory must be reserved. For this purpose, the memory compiler generates a region-optimized function block for a certain memory size, such as 1024 x 10 bits, and preferably extends this function block with a BIST (Built In Self Test) in order to achieve testability. This thus fixes the system to a histogram with a fixed resolution of a maximum of 1024 bins.

[0008] However, for certain sensors, the distance to multiple points or measurement regions (ROI, region of interest) is to be measured. Such a multi-segment evaluation can only be realized sequentially with a fixed histogram memory. Alternatively, a separate histogram memory must be reserved for the maximum number of possible measurement regions, which significantly increases the area consumption and raises the chip costs.

[0009] In principle, it is also conceivable to divide an existing one histogram memory into multiple measurement regions with a resolution loss, for example using four histograms with 256 bins instead of one histogram with 1024 bins. However, four histogram memories partitioned in this way, together with addressing logic, etc., take up more area than a single, larger histogram memory. In addition, the partitioning would be fixed, then only four histograms with a lower resolution could be recorded, but no longer one histogram with a higher resolution. Merging memory blocks into one larger memory block requires addressing logic and takes up area. These considerations play a significant role in particular for structures in the order of 100 nm and for the usual number of opto-electronic ASICs and similar digital components used in opto-electronic sensors, smaller structures can hardly afford.

[0010] EP 2 475 957 B1 discloses a SPAD-based optical distance meter. Therein, groups of SPADs are formed and with them the light time of flight is measured. By forming groups, the light time of flight measurement reacts to the special properties of the SPADs, since individual events of disturbances are intercepted by the group. However, no histogram is formed, so that the problem of storing multiple histograms does not arise at all.

[0011] Another optoelectronic sensor is known from EP 3 428 683 B1, which measures distances with SPADs and a dToF method. Therein, a switch matrix is provided to select specific SPADs for evaluation and to connect these SPADs one-to-one with a TDC (Time-to-Digital Converter). In this way, the SPADs selected collect a single common histogram. In EP 3 454 086 B1, this selection of SPADs is used to determine multiple distance values, thereby aligning a positioning system. This document explains the selection of SPADs from multiple measurement areas, but does not explain the specific implementation of the required multiple evaluations, as even the term histogram is not mentioned.

[0012] It is therefore the task of the present invention to obtain additional measurement information in an improved manner with a general-purpose sensor based on the direct light time-of-flight method.

[0013] This task is solved by an optoelectronic sensor and a method for distance measurement of objects in a detection area using the time-of-flight method, respectively. A light signal is emitted with at least one light emitter, and the light signal returned from the detection area is recorded in a light receiver. The light receiver has a first plurality of light receiving elements or pixels, for example arranged in a matrix. Individual light receiving elements or groups of light receiving elements are connected with a time-of-flight measurement unit, which measures the single time-of-flight of the light signal of the connected light receiving element or elements. Overall, there is a second plurality of time-of-flight measurement units, which is preferably smaller than the first plurality of light receiving elements. This means that only a fraction or even a small fraction of the light receiving elements in the active measurement area of the light receiver is selected. The single time-of-flights are collected in a memory, and a control and evaluation unit generates distance values from the collected single time-of-flights. The sensor provides at least the possibility to determine at least two distance values from the single time-of-flights of at least two groups of time-of-flight measurement units. Thus, depending on the number of groups, there are multiple measurement areas (ROI, region of interest), while a distance value is measured for each measurement area, respectively. In some embodiments, the sensor is switchable and provides, in addition to the simultaneous determination of multiple distance values, also a mode of only a single group, thereby providing a mode of a single measurement area.

[0014] The application is based on the basic idea of using the same memory for collecting single light flight times for multiple evaluations with multiple measurement regions and associated groups of light flight time measuring units. Thus, there is still only a single physical memory, uniformly addressed over the entire memory, in particular only a single function block generated by the memory compiler. The readdressing unit ensures that the single light flight times measured by the light flight time measuring units according to the measurement region are written into addresses in the memory from which the assignment to the group can be reconstructed. Thus, the membership to the group, and thus also to the measurement region, is encoded in the address. The memory is thus functionally partitioned, since the content of the memory cells is assigned to a specific group by their address. However, in the physical implementation of the memory, it is still a uniform, non-partitioned memory.

[0015] The advantage of the application is that multiple distance values can be obtained from multiple measurement regions while occupying a small amount of space, thus being low in manufacturing costs. There is no longer a need to make such multiple measurements one after the other in order to use only one memory. Thus, short measurement times and low costs can be reconciled. The processing of multiple groups in the same memory means a loss of resolution, how the multiple measurement regions and the appropriate resolution are appropriately selected is an application problem.

[0016] Preferably, the control and evaluation unit is designed to change the number of groups. The readdressing unit ensures that the single light flight times are stored in the addresses of the memory according to the new number of groups from which the new group membership of the light flight time measuring units can be reconstructed. Thus, the number of measurement regions can be adapted to the needs of the application. The conversion can be done by configuration or programming, even dynamically during operation. As already mentioned, a conversion to only a single group is not excluded. Since the division of the function of the uniform memory into multiple groups leads to a loss of resolution, it can be of interest to make the measurement with only one group at the highest possible resolution.

[0017] Preferably, the sensor has a selection unit which is designed to variably connect the light flight time units to the light receiving elements. This not only provides flexibility for how the light flight time units are divided into groups, i.e. which pixels are combined into a distance measurement value. It is also possible to select which pixel on the light receiver the light flight time unit is assigned to in order to determine or change the position of the measurement region (ROI). In general, it makes sense to connect the neighborhood of pixels to the light flight time units of the same group. However, in principle the assignment is free, a group can consist of pixels distributed over the light receiver. For example, in order to scan a larger region with fewer light flight time measuring units, it can be useful to cover the measurement region with a grid of only every Ith pixel connected to a light flight time measuring unit. Particularly preferably, the selection unit is a switch matrix.

[0018] Preferably, the memory is designed in such a way that the discrete functions can be stored in memory cells with consecutive addresses and can be stored therein and retrieved in this way with single light flight times, wherein in particular the addresses of the memory cells correspond to the definition regions and the associated function values are stored in the memory cells. In other words, the memory is organized in such a way that the addresses correspond to the X values and the contents of the memory cells correspond to the Y values of the discrete functions. Of course, the definition regions are usually shifted and rescaled with respect to the addresses: For example, the addresses 0, 1,... 15 correspond to the time values 15 ns, 30 ns,... 240 ns by multiplication by 15 ns and shifting by +15 ns. The same applies to the contents of the memory cells, provided that the memory cells are not used as pure counters.

[0019] Preferably, the readdressing unit is designed to assign at least one address bit of the address to the group. The at least one re-designated address bit no longer encodes the X value, but rather the group or the measurement region. By re-designating the m address bits in this way, the memory is functionally divided into 2 s sub-memory regions. At the same time, the X resolution is reduced by a factor of 2 s . The preferred cases are s = 1, in which the resolution of the two sub-memory regions is halved, and s = 2, in which the resolution of the four sub-memory regions is quartered. The case s = 0 remains adjustable, then only one measurement region has the highest resolution. Only a number of measurement regions corresponding to a power of 2 can be identified. However, other numbers can also be achieved by not using sub-memory regions or by the control and evaluation unit combining multiple sub-memory regions into one distance measurement value.

[0020] Preferably, the re-designated address bit is the most significant bit (MSB) or, preferably, the multiple re-designated address bits are the most significant bits. The advantage of this is that all single light flight times of the same group are stored at consecutive addresses. If other bits are used, this is conceivable in principle as well, the information would then be distributed to addresses of the memory that are separated from one another. This makes the subsequent evaluation and distance value calculation more cumbersome.

[0021] Preferably, the memory is designed as a histogram memory and the single light flight times are collected in at least one histogram. A histogram is a special case of a frequency distribution and a function stored in a memory which is discretized and is particularly suitable for suitably integrating the measurement information of the single light flight times. The addresses in the memory correspond to the bins of the histogram, wherein the bins discretize the time and the contents of the corresponding storage cells correspond to the frequency values (Count counts). In the case of a plurality of groups, a plurality of histograms is collected at the corresponding addresses of the memory which are assigned to the group.

[0022] Preferably, the histogram memory preferably has as many storage cells as bins of a histogram for only one group. Thus, the memory is designed to be sufficient to accommodate the single histogram with the highest resolution. It is still conceivable to have a small number of unused storage cells, for example when 1000 bins are required, but 1024 bins can be more easily implemented. For measurements with several measurement regions, instead, a plurality of histograms with a correspondingly reduced resolution is stored, in particular 2 s s histograms with a time resolution of 2

[0023] Preferably, the readdressing unit is designed to encode the group in at least one bit of the address, in particular in one or more most significant bits, and to encode the bin of the histogram in the remaining bits of the address. The address is then interpreted as two subblocks, wherein the first subblock serves for the membership to the group and the second subblock serves for the bin. If the light flight time measurement unit determines a single light flight time, this is rounded to the bin width and thus assigned to the bin. This can be particularly easily implemented if the bits of the measured single light flight time are directly interpreted as address bits of the second subblock. Depending on the number of groups, the readdressing unit ensures that the lowest bits of the single light flight time are ignored; this is a resolution loss which has to be accepted for a plurality of simultaneously evaluated measurement regions. Alternatively, the effective range of the measurement is reduced, then the reduced number of bins only covers a smaller region of uniqueness of the measurement. The readdressing unit also ensures that an address bit is set in the first subblock which corresponds to the assignment of the light flight time measurement unit to be measured to the group. At the resulting address, the memory content is incremented by 1.

[0024] ​Preferably, the light receiving elements each have an avalanche photodiode which is biased with a bias voltage above the breakdown voltage and thus operates in Geiger mode. The high sensitivity and dynamic compression of avalanche photodiode elements or SPADs in Geiger mode is particularly advantageous in distance measurements. Statistical evaluation by collecting single-photon time-of-flight, in particular in a histogram, is particularly suitable for SPADs and their properties.

[0025] Preferably, the time-of-flight measurement unit has a TDC (Time-to-Digital Converter). This is a well-known and relatively simple component which can determine the single-photon time-of-flight with high time resolution. The TDC can be directly monolithically integrated in the crystal of the light receiver. Preferably, the TDC is started at the emission time and stopped by the received single-photon pulse at the reception time. Other operating modes can be envisaged, for example starting the TDC each time an avalanche is triggered and then stopping at a known time, for example at the end of the measurement cycle.

[0026] The method according to the application can be further developed in a similar way and show similar advantages. Such advantageous features are described in the dependent claims following the independent claim, by way of example but not exhaustively. The application is further explained below on the basis of embodiments and with reference to the drawings. In the drawings: BRIEF DESCRIPTION OF DRAWINGS

[0027] Further features and advantages of the application will be explained in more detail below on the basis of embodiments and with reference to the drawings. In the drawings:

[0028] Figure 1 A schematic block diagram of a photoelectric sensor is shown;

[0029] Figure 2 A diagram showing the general measurement process is shown;

[0030] Figure 3 A diagram showing an exemplary allocation of measurement regions (ROIs) to time-of-flight measurement units is shown;

[0031] Figure 4 An exemplary addressing diagram of a histogram memory for a plurality of measurement regions (ROIs) is shown; and

[0032] Figure 5 A diagram showing an exemplary connection of time-of-flight measurement units, a readdressing unit and a histogram memory is shown.

[0033] Figure 1A simplified schematic block diagram of a photoelectric sensor 10 for distance measurement is shown. A light emitter 12, for example an LED or a laser source, emits a light signal 16 into a detection region 18 via emitter optics 14. The light emitter 12 is shown as an external component, but can equally be an integral part of the sensor 10. Preferably, the emitted light signal 16 has a light pulse, and the sensor 10 then measures the distance according to a pulse method or a direct time of flight (dToF) method. Preferably, a short light pulse of 100 ps is generated.

[0034] When the light signal 16 encounters an object 20 in the detection region 18, the returning or reflected light signal 22 is returned to a light receiver 26 via receiving optics 24. This light receiver 26 has a plurality of light receiving elements, which are preferably designed as Geiger-mode avalanche photodiode elements 28 or SPADs, and can be understood as pixels. The SPADs actually provide a digital signal, and therefore react extremely fast to incident light.

[0035] The received signals of selected avalanche photodiode elements 28 are read out and evaluated by light time of flight measurement units 30. Only four light time of flight measurement units 30 are shown, in practice there are usually more, for example approximately ten, but significantly fewer than the avalanche photodiode elements 28, which are usually in the hundreds, thousands or even significantly more. The light time of flight measurement units 30, in particular, each comprise a TDC (Time-to-Digital Converter) with a time resolution of, for example, 100 ps, and each measure the light time of flight from the emitted light signal 16 to the received returning light signal 22. It is also conceivable to not determine the individual light time of flight, but rather to determine the light time of flight of a plurality of receiving events, in particular in this way by continuing to operate the TDC after the detected light time of flight has been buffered. In this regard, a multi-echo capability is implemented, which can be used, for example, for measurements through a semi-transparent object or a glass pane, measurements in the presence of dirt or the like.

[0036] A selection unit 32, for example in the form of a switch matrix, is arranged between the light receiver 26 and the light time of flight measurement units 30. By means of the selection unit 32, a variably determined avalanche photodiode element 28 or pixel is connected to a light time of flight measurement unit 30, respectively. The connection between the avalanche photodiode elements 28 and the light time of flight measurement units 30 can be 1 : 1 or n: 1. By this selection determination, the active pixels for the measurement are determined. For example, pixels that are not selected, whose signals are not read out anyway, can be switched off by lowering the bias voltage below the breakdown voltage.

[0037] The single light flight times determined by the light flight time measurement units 30 are collected in a memory 34, preferably in the form of histograms. Here, the light flight time measurement units 30 are assigned to one or more groups, and each group generates its own histogram. By this group-wise assignment, the pixels connected with the light flight time measurement units 30 form a plurality of measurement regions (ROI, region of interest) with which a plurality of distance values can be determined simultaneously.

[0038] The histograms have n support points or bins which divide the time measurement region and thus the active range of the sensor 10 or a selected subregion thereof and then form the uniqueness region of the measurement. Preferably, the number of bins corresponds to the number range, and the bin width corresponds to the time resolution of the light flight time measurement units 30. In the bins, the frequency with which the single light flight times corresponding to the bin are measured is calculated. This statistic is assisted both by the plurality of light flight time measurement units 30 assigned to the same group and by repeated measurements. The maximum count value or maximum histogram height is predetermined by the bit depth of the storage cells of the memory 34. For example, 1024 storage cells with a depth of 10 bits can be provided.

[0039] If there is only a single measurement region (ROI), that is, if all single light flight times of all light flight time measurement units 30 are collected in one histogram, the maximum time resolution and the minimum bin width are achieved. In the case of a plurality of measurement regions, the available storage cells are distributed over a plurality of histograms, so that the bin width increases and thus the time resolution decreases, or the uniqueness region of the measurement is reduced. This will be discussed in more detail below with reference to Figures 2 to 5 The division of the memory 34 for the plurality of histograms by means of intelligent addressing is discussed in more detail.

[0040] Regardless of whether a single histogram or a plurality of histograms is collected in the memory 34, it is the same, single and uniform memory with a single address range or the same functional blocks, for example, generated by a memory compiler. There is no physical partitioning of the associated memory logic. Rather, the readdressing unit 36 ensures in the manner explained below that the light flight time measurement units 30 store their single light flight times at addresses of the single memory 34 from which the relationship of the respective light flight time measurement unit 30 to the group and to the measurement region can be reconstructed.

[0041] The control and evaluation unit 38 processes the histograms and searches for a peak value therein, for example caused by the returned light signal 22. The light flight time associated with the peak value corresponds to the sought distance value, converted into conventional units by the speed of light. The control and evaluation unit 38 can also be responsible for other control tasks in the sensor 10 and for this can be connected to other components of the sensor.

[0042] At least some or parts of the light flight time measuring unit 30, the selection unit 32, the memory 34, the readdressing unit 36 and / or the control and evaluation unit 38 can also be integrated together with the avalanche photodiode element 28 on a common chip, for example an ASIC, Application-Specific Integrated Circuit. It is also conceivable that the control and evaluation unit 38 is arranged on an additional component, for example a microprocessor, or that the readdressing unit 36 is implemented in the control and evaluation unit 38.

[0043] Figure 1 The arrangement of the sensor 10 should be understood as purely exemplary. Alternatively, other known optical solutions can be used, for example autocollimation, for example with a beam splitter and common optics, or the light emitter 12 is arranged in front of the light receiver 26. More complex sensors, such as a light raster or a laser scanner, are also conceivable.

[0044] Figure 2 A possible general measurement process is shown. After the start of the measurement, the light signal 16 is sent and received again in the actual measurement and the light flight time measuring unit 30 determines a single light flight time on the basis of the signal from the connected avalanche photodiode element 28. As soon as the measurement is finished, a flag MEAS_RDY is set and the k single light flight times can be transferred into the memory 34. Preferably, the process is then repeated I times, for example 1000 times, to produce a better statistical database by repeated measurements.

[0045] Figure 3An exemplary assignment of the measurement regions 40a-40d (ROI) to the light time-of-flight measurement units 30 is shown. Here, four measurement regions 40a-40d are exemplarily provided, which can be understood as a division of the light receiver 26 into quadrants. Each measurement region 40a-40d shall provide its own distance value at the same time and for this is connected with other groups of light time-of-flight measurement units 30. In this example, there are sixteen light time-of-flight measurement units 30 in total (here in the form of TDCs), and the first measurement region 40a is connected with TDC1...4, the second measurement region 40b with TDC5...8, the third measurement region 40c with TDC9-12, and the fourth measurement region 40d with TDC13-16. It should be noted that two types of assignment are distinguished. On the one hand, certain pixels or avalanche photodiode elements 28 are connected with certain time-of-flight measurement units 30 by means of the selection unit 32, here 1:1, alternatively n:1. On the other hand, the light time-of-flight measurement units 30 form groups corresponding to the measurement regions 40a-40d.

[0046] Figure 4 A memory 34 is shown, which is divided according to the four measurement regions 40a-40d or quadrants and stores four histograms. It should be remembered that the memory 34 is physically a single, unpartitioned memory, which is constructed and addressed in particular like a usual RAM. Thus, there are memory cells with addresses 0...23 n -1, each of which can store a value. In the histogram, this value serves as a counter.

[0047] In order to store multiple histograms in the memory, multiple address regions are distinguished, in the example four address regions 34a-34d corresponding to the four measurement regions 40a-40d. The readdressing unit 36 ensures that the single light time-of-flight is stored in the correct address region 34a-34d according to the resulting light time-of-flight measurement unit 30.

[0048] Figure 4 The corresponding address coding is shown on the right. Some address bits, in this case the two most significant bits (MSB, Most Significant Bit), are re-designated and no longer coded for the Bin, but for the group. These address bits and the memory cells are then lost from the single histogram, so that the time resolution is lost.

[0049] In particular, reference is made to the example of Figure 3 16 TDCs are used and connected with the four measurement regions 40a-40d labeled ROI1...4. Their coding is shown as Figure 4 for example:

[0050] ROI1 : TDC1...4 encoded with MSB 00

[0051] ROI2 : TDC5...8 encoded with MSB 01

[0052] ROI3 : TDC9...12 encoded with MSB 10

[0053] ROI4 : TDC13...16 encoded with MSB 11.

[0054] In the measurement sequence of Fig. 2, once the flag MEAS_RDY = 1 is set after the emission of the light signal 16 and the measurement time (e.g. 100 ns for an effective range of about 15 m), the single light flight time is written. Then, the TDCs 1...16 write the single light flight time in turn into the memory 34, i.e. increase the Bin determined by the measured single light flight time, respectively. For example, the correct MSB addressing as well as the selection of the appropriate address range 34a-34d is taken over by the state machine of the readdressing unit 36. Figure 3

[0055] By this form of histogram partitioning, the sensor 10 offers the option to collect multiple histograms from multiple measurement regions 40a-40d to measure multiple distance values simultaneously. The number of measurement regions 40a-40d can be changed, either by initial configuration or dynamically by reassigning more or less address bits while still running. A respective doubling of the number of measurement regions 40a-40d results in a halving of the time resolution or, alternatively, a halving of the effective range of uniqueness or measurement. Here, the unified and physically single memory 34 remains unchanged.

[0056] When the reduced address regions 34a-34d are compensated in this way, reducing the effective range has not only the disadvantage that it also shortens the measurement time and the sensor 10 thus has an improved response time. For example, measuring with one measurement region for an effective range of 15 m, with two measurement regions for an effective range of 7.5 m, with four measurement regions for an effective range of 3.8 m. At the same time, the measurement time is reduced from 100 ns to 50 ns and 25 ns. This offers comfortable flexibility for various applications. For example, for four-quadrant recording in motion detection and motion vector generation, a short response time is advantageous.

[0057] For example, if in total 1024 storage cells are available in the memory 34 and if still 16 TDCs are available, to keep the example, this can be used for:

[0058] 1 ROI with 1 x 16 TDCs writing on 1024 x 10 bits, ​

[0059] Two ROIs are written to 2 × 512 × 10 bits using a 2 × 8 TDC, or

[0060] Four ROIs are written on 4 × 256 × 10 bits using a 4 × 4 TDC.

[0061] If it's not just the two highest address bits that are reassigned, there could be even more histograms and measurement regions.

[0062] Figure 5 An exemplary architecture of the optical time-of-flight measurement unit 30, the readdressing unit 36, and the memory 34 is shown. In a preferred embodiment, the time region of the TDC corresponds exactly to the histogram width. Therefore, if the TDC uses 10 bits for measurement, a histogram memory with a 10-bit address region can also be used. The measurement result of the TDC can then be directly used as an address in memory 34, where the appropriate Bin is incremented. This describes the case where only one histogram is recorded.

[0063] In the case of multiple histograms, not all bins are available for a single histogram; one or more MSBs are reassigned, and the affiliation is encoded to a group or measurement region (ROI). The reassigned bits are set by the readdressing unit 36 ​​from the identifier of the corresponding TDC for measuring single-light time of flight and, for example, an internal allocation table from TDC to histogram and thus an internal allocation table from measurement regions 40a-40d to address regions 34a-34d.

[0064] If the smaller available storage space for each histogram is compensated for by reducing the effective range, the MSB of the TDC will become idle anyway, since only a short single-light flight time is measured, and the TDC represents this short single-light flight time without using the MSB. Therefore, the TDC initially only provides a value of 0 in the MSB, and the re-addressing unit 36 ​​can replace the appropriate measurement area in place of the MSB code.

[0065] Alternatively, the effective range can be preserved while reducing the time resolution. This effectively eliminates the least significant bit (LSB), the finest part of the time measurement, from the TDC. The re-addressing unit 36 ​​shifts the bit pattern used by the TDC to represent the measured single-light time of flight to the right by a histogram number of 2. s The corresponding s bits are used to discard the LSB and release the MSB, which is then replaced by the MSB code of the appropriate measurement region. Of course, the control and evaluation units must be configured with 2... s The calculation involves multiplying the Bin width by a factor of two, which results in a loss of temporal resolution. The reduction in effective range and temporal resolution can also be combined to divide the calculation across two variables.

[0066] Particular embodiments of neglecting LSBs or reducing the effective range can be conceived in many ways and methods. In one example, a 12-bit TDC measures the value of TDC_DATA[11:0] with a basic precision of 50 ps and addresses 10 bits in the histogram. Then optionally, TDC_DATA[9:0] is abgreifen to actually achieve the highest time resolution of 50 ps, but only over a distance range of 7.5 m, or by abgreifen TDC_DATA[10:1] or TDC_DATA[11:2], the distance range is doubled or quadrupled and the time resolution is halved or quartered accordingly. A corresponding data abgreifen can also be used to select the distance range. For example, TDC_DATA[0:9] is abgreifen with the highest resolution, two MSBs TDC_DATA[11:10] are used for the assignment of the distance range, for example, in the following form:

[0067] TDC_DATA[11:10] = b'00 ==> 0...7.5m,

[0068] TDC_DATA[11:10] = b'01 ==> 7.7...15m,

[0069] TDC_DATA[11:10] = b'10 ==> 15...22.5m,

[0070] TDC_DATA[11:10] = b'11 ==> 22.5...30m.

Claims

1. An optical-electrical sensor (10) for distance measurement of an object (20) in a detection region (18) using a light time-of-flight method, wherein the sensor (10) has a light emitter (12) for emitting a light signal (16) into the detection region (18), a light receiver (26) with a first plurality of light-receiving elements (28) for detecting a received light (22) from the detection region (18), a second plurality of light time-of-flight measurement units (30) for determining a respective single light time-of-flight from the light time-of-flight between the emission of the light signal (16) and the reception of the light signal (22) returned or reflected at the object (20), a memory (34) designed as a histogram memory for collecting the single light times-of-flight in at least one histogram, and a control and evaluation unit (38) designed to determine a distance value by evaluating the collected single light times-of-flight, wherein at least two distance values are also able to be determined from the single light times-of-flight of at least two groups of light time-of-flight measurement units (30), characterized in that the memory (34) is a single, unpartitioned memory, uniformly addressed over the entire memory (34), and the sensor (10) has a readdressing unit (36) designed to encode a group in at least one address bit of the address and to encode a Bin of a histogram in the remaining address bits, so that the address is interpreted as two subblocks, wherein the first subblock is used for the membership to a group and the second subblock is used for the Bin, in such a way that the single light times-of-flight are written to a specific address (34a-34d) of the same uniform memory (34) depending on the allocation of the light time-of-flight measurement units (30) to the groups, so that the control and evaluation unit (38) is able to assign the stored individual light times-of-flight to a group and thus to a distance value via the address, wherein the control and evaluation unit (38) is designed to change the number of groups, and wherein the readdressing unit (36) ensures that the single light times-of-flight are stored on the addresses of the memory (34) according to the new number of groups, from which the new group membership of the light time-of-flight measurement units (30) can be reconstructed.

2. The sensor (10) according to claim 1, the sensor (10) has a selection unit (32) designed to variably connect light time-of-flight measurement units (30) to light-receiving elements (28).

3. The sensor (10) according to any one of claims 1-2, wherein the memory (34) is designed in such a way that discrete functions can be stored in memory cells with consecutive addresses, and the single light times-of-flight are stored in the memory and retrieved in this way.

4. The sensor (10) according to any one of claims 1-2, wherein one or more address bits are the most significant bits.

5. The sensor (10) according to any one of claims 1-2, wherein, The histogram memory has as many storage locations as the bins of a histogram for only one group.

6. The sensor (10) according to any one of claims 1 to 2, wherein The readdressing unit (36) is designed to encode the groups in one or more most significant bits and to encode the bins of the histogram in the remaining bits of the address.

7. The sensor (10) according to any one of claims 1 to 2, wherein The light reception elements (28) each have an avalanche photodiode which is biased with a bias voltage above the breakdown voltage and thus operates in Geiger mode, and / or wherein the light time-of-flight measurement units (30) have TDCs.

8. The sensor (10) according to claim 3, wherein The addresses of the storage locations correspond to a defined range and the associated function value is stored in the storage location.

9. A method of distance measurement of an object (20) in a detection region (18) using a light time-of-flight method, wherein A light signal (16) is emitted into the detection region (18) and a light signal (22) which is returned or reflected in the detection region (18) is detected by a light receiver (26) having a first plurality of light reception elements (28), wherein a single light time-of-flight corresponding to a light time-of-flight measurement between emitting the light signal (16) and receiving the light signal (22) returned or reflected at the object (20) is determined with a second plurality of light time-of-flight measurement units (30) and the single light time-of-flights are collected in at least one histogram in a memory (34) designed as a histogram memory, and at least two distance values are determined from the single light time-of-flights of at least two groups of light time-of-flight measurement units (30), characterized in that The memory (34) is a single, unpartitioned memory which is uniformly addressed over the entire memory, and the single light time-of-flights are written into specific addresses (34a-34d) of the same uniform memory (34) by a readdressing unit (36) according to the allocation of the light time-of-flight measurement units (30) to the groups, wherein the groups are encoded in at least one address bit of the address and the bins of the histogram are encoded in the remaining address bits, so that the address is interpreted as two subblocks, wherein a first subblock is used for the membership to a group and a second subblock is used for the bin, and the stored single light time-of-flights are assigned to the groups and thus to the distance values via the address when determining the distance values, wherein the number of groups is changed to adapt to the requirements of the application, and wherein the readdressing unit (36) ensures that the single light time-of-flights are stored on the addresses of the memory (34) according to the new number of groups from which the new group membership of the light time-of-flight measurement units (30) can be reconstructed.

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