Method and apparatus for time-of-flight sensing of a scene

Abstract

Embodiments of the present disclosure generally relate to methods and apparatuses for time-of-flight sensing of a scene. A method for time-of-flight (ToF) sensing of a scene is provided. The method includes performing, by a ToF sensor, a plurality of first ToF measurements using a first modulation frequency to obtain first measurement values. A respective correlation function of each of the plurality of first ToF measurement values is periodic and exhibits an amplitude that increases with distance over a measurement range of the ToF sensor. The method further includes determining a distance to an object in the scene based on the first measurement values.

Description

Technical Field

[0001] This disclosure relates to time-of-flight (ToF) sensing. In particular, examples relate to methods and apparatus for ToF sensing of a scene. Background Technology

[0002] ToF cameras measure distance by emitting near-infrared light. For long-distance measurements (e.g., up to 50m), a strong light source is used (e.g., using 2.5kW output power). Problems arise if an object is present near the ToF camera, as it can cause glare, affecting adjacent pixels. Furthermore, issues can occur because ToF camera pixels saturate when receiving excessive light.

[0003] Therefore, improved ToF sensing may be required. Summary of the Invention

[0004] This requirement can be satisfied by the subject matter of the appended claims.

[0005] One example relates to a method for Time-of-Flight (ToF) sensing of a scene. The method includes performing a plurality of first ToF measurements by a ToF sensor using a first modulation frequency to obtain first measurement values. The corresponding correlation function for each of the plurality of first ToF measurements is periodic and exhibits an amplitude increasing with distance within the measurement range of the ToF sensor. The method also includes determining the distance to objects in the scene based on the first measurement values.

[0006] Another example relates to an apparatus for Time-of-Flight (ToF) sensing of a scene. The apparatus includes a ToF sensor configured to perform a plurality of first ToF measurements using a first modulation frequency to obtain first measurement values. The corresponding correlation function for each of the plurality of first ToF measurements is periodic and exhibits an amplitude that increases with distance within the measurement range of the ToF sensor. Furthermore, the apparatus includes processing circuitry configured to determine the distance to an object in the scene based on the first measurement values. Attached Figure Description

[0007] The following will describe some examples of apparatus and / or methods by way of example only and with reference to the accompanying drawings, in which...

[0008] Figure 1 A flowchart illustrating an example of a ToF sensing method for a scene is shown;

[0009] Figure 2 An example of a device for ToF sensing of a scene is shown;

[0010] Figure 3 Exemplary related functions are shown;

[0011] Figure 4 An exemplary sequence is shown;

[0012] Figure 5 An example of a modulation code is shown;

[0013] Figure 6 An exemplary sequence is shown;

[0014] Figure 7 Exemplary related functions are shown;

[0015] Figure 8 Exemplary related functions are shown;

[0016] Figure 9 An example of phase expansion is shown; and

[0017] Figure 10 An example related function is shown. Detailed Implementation

[0018] Some examples will now be described in more detail with reference to the accompanying drawings. However, other possible examples are not limited to the features of these embodiments described in detail. Other examples may include modifications of features, as well as equivalents and alternatives to features. Furthermore, the terminology used herein to describe certain examples should not be used to limit other possible examples.

[0019] Throughout the description of the accompanying drawings, the same or similar reference numerals refer to the same or similar elements and / or features, which may be implemented identically or in modified form while providing the same or similar functions. For clarity, the thickness of lines, layers, and / or regions in the drawings may also be exaggerated.

[0020] When two elements A and B are combined using "or", this should be understood to disclose all possible combinations, i.e., only A, only B, and A and B, unless otherwise explicitly defined in individual cases. As alternative wording for the same combination, "at least one of A and B" or "A and / or B" can be used. This is equivalent to combinations of more than two elements.

[0021] If the singular form, such as "a," "an," and "the," is used, and the use of a single element is not explicitly or implicitly defined as mandatory, then other examples may use several elements to achieve the same functionality. If the functionality is described below as being implemented using multiple elements, then other examples may use a single element or a single processing entity to achieve the same functionality. It should also be understood that the terms "include," "including," "comprise," and / or "comprising" describe the presence of a specified feature, whole, step, operation, process, element, component, and / or a group thereof when used, but do not preclude the presence or addition of one or more other features, wholes, steps, operations, processes, elements, components, and / or a group thereof.

[0022] Figure 1 A flowchart illustrating an example of a ToF sensing method 100 for a scene is shown below. (Refer to the following...) Figure 2 Method 100 is described further. Figure 2 An exemplary device 200 for ToF sensing of a scene is shown.

[0023] Device 200 includes a ToF sensor 210. The ToF sensor 200 includes an illumination element (circuit, device) 230 for emitting modulated light pulses (i.e., modulated light) 202 into the scene. An object 201 is located in the scene and reflects the emitted light pulses 202. The ToF sensor 200 further includes a light-capturing element (circuit, device) 220 for capturing light 203 received from the scene. The light 203 includes reflections of the emitted light pulses 202 from the object 201.

[0024] The illumination element 230 generates modulated light pulses 202. The illumination element 230 may include any number of light sources. The illumination element 230 may include, for example, one or more light-emitting diodes (LEDs) and / or one or more laser diodes (e.g., one or more vertical cavity surface-emitting lasers, VCSELs) that are excited based on an illumination signal.

[0025] The light-capturing element 220 may include various components, such as optics (e.g., one or more lenses) and electronic circuitry. Specifically, the electronic circuitry includes an image sensor comprising at least one photosensitive element or pixel (e.g., a photonic mixing device (PMD) or a charge-coupled device (CCD)). For example, the image sensor may include multiple photosensitive elements or pixels. At least one photosensitive element or pixel is driven based on a reference signal.

[0026] Method 100 includes performing 102 first ToF measurements using a first modulation frequency by a ToF sensor 210 to obtain first measurement values. An illumination element 230 emits a corresponding modulated light pulse sequence into the scene during each corresponding first ToF measurement. Furthermore, during each corresponding first ToF measurement, a corresponding reference signal is used to drive at least one photosensitive element or pixel of a light-harvesting element 220. The first modulation frequency represents the modulation frequency of the reference signal and the modulated light pulse sequence emitted into the scene for the multiple first ToF measurements.

[0027] The parameters of the ToF sensor 210 are adjusted such that the corresponding (light intensity-independent) correlation function for each of the plurality of first ToF measurements is periodic and exhibits an amplitude that increases with distance within the measurement range of the ToF sensor. Without considering (i.e., ignoring) the intensity of light 203, the corresponding (light intensity-independent) correlation function gives the distance-dependent correlation between the received light 203 and the corresponding reference signal. In other words, the corresponding (light intensity-independent) correlation function only describes the distance dependence of the output of the ToF sensor 210, and does not describe the dependence of the output of the ToF sensor 210 on the intensity of the received light 203.

[0028] First modulation frequency f mod1 The period length d of a correlation function (independent of light intensity) that can be measured by the speed of light c and multiple first-Time-of-Flight (ToF) measurements. period1 definition:

[0029]

[0030] Figure 3 Two exemplary (light intensity-independent) correlation functions 310 and 320 are shown for two first ToF measurements performed by the ToF sensor 210. Figure 3 The horizontal axis represents the distance between the ToF sensor 210 and the object 201. The vertical axis represents the value of each correlation function. Figure 3 The exemplary measurement range 330 of the ToF sensor 210 is further shown in the figure.

[0031] Within the measurement range 330 of the ToF sensor 210, both correlation functions 310 and 320 exhibit a sinusoidal (i.e., periodic) curve (shape) with amplitude increasing with distance. However, it should be noted that the correlation function according to the proposed technique does not need to exhibit a sinusoidal curve with amplitude increasing with distance within the measurement range of the ToF sensor 210. In general, the correlation function can exhibit any type of periodic curve with amplitude increasing with distance within the measurement range of the ToF sensor 210. For example, alternatively, the correlation function can exhibit a triangular curve with amplitude increasing with distance within the measurement range of the ToF sensor 210.

[0032] Correlation functions 310 and 320 exhibit the same period length.

[0033] Because the amplitudes of correlation functions 310 and 320 increase within the measurement range 330 of the ToF sensor 210, the first ToF measurement is less sensitive to light 203 from the vicinity of the ToF sensor 210. In other words, correlation functions 310 and 320 are shaped such that larger correlation intensities are assigned to distances (regions) farther from the ToF sensor 210. As a result, closer distances (regions) acquire less correlation and farther distances (regions) acquire higher correlation.

[0034] The intensity of reflected light received from object 201 in the scene decreases with the distance between the ToF sensor 210 and object 201. For example, it can be assumed that the light intensity decreases according to the inverse square law. That is, the distance-dependent light intensity of light 203 received at the ToF sensor 210 can be assumed as follows:

[0035]

[0036] I represents the light intensity received at the ToF sensor 210, and d represents the distance between the ToF sensor 210 and the object 201 that reflects the emitted light pulse 202 back to the ToF sensor 210.

[0037] As the sensitivity of the ToF sensor 210 to light from its vicinity decreases, saturation of one or more photosensitive elements or pixels of the light-trapping element 220 due to strong reflections from the vicinity of the ToF sensor 210 can be avoided. Furthermore, glare effects caused by reflections of emitted light pulses 202 from objects near the ToF sensor 210 can be omitted or at least reduced.

[0038] The output of the ToF sensor 210 used for ToF measurement is proportional to the intensity of reflected light received from the object 201. For example, a first measurement value of one of a plurality of first ToF measurements output by the ToF sensor 210 can be determined by multiplying the intensity of reflected light received from the object 201 during the ToF measurement with the value of a (light intensity-independent) correlation function of the ToF measurement at the distance from the object 201 that caused the received reflection.

[0039] Furthermore, the periodic curve of the correlation function allows the distance between the ToF sensor 210 and the object 201 to be determined using standard methods. (See again...) Figure 1 Method 100 also includes determining the distance from 104 to object 201 in the scene based on the first measurement.

[0040] Specifically, the first measurement allows for the determination of a corresponding reference signal for at least one photosensitive element or pixel used to drive the light-capturing element 220 during the corresponding first ToF measurement, and a corresponding phase shift between the light 203 received by the light-capturing element 230 from the scene during the corresponding first ToF measurement (i.e., reflection of the emitted light pulse 202 caused by the object 201).

[0041] For example, in the case of performing two first ToF measurements, the phase shift This can be determined as follows:

[0042]

[0043] Where C1 and C2 represent the first measurements of the two first ToF measurements.

[0044] In the case of performing four first ToF measurements, the phase shift This can be determined as follows:

[0045]

[0046] C1, C2, C3, and C4 represent the first measurements of the four first ToF measurements.

[0047] It should be noted that different time offsets are used for each of the multiple first ToF measurements between the corresponding modulated light pulse 202 sequence emitted to the scene during the corresponding first ToF measurement and the corresponding reference signal used to drive the light-harvesting element 220 of the ToF sensor 210 during the corresponding first ToF measurement. The time offset used for the first ToF measurement is determined by the first modulation frequency f. mod1 The reciprocal of the first period length T1 is an integer multiple of the fraction given by the first period length T1, that is:

[0048]

[0049] For example, when performing two first ToF measurements, a time offset of n·T1 / 4 can be used, where n = 0 and 1. Similarly, when performing four first ToF measurements, a time offset of n·T1 / 4 can be used, where n = 0, 1, 2, and 3. The sequence of modulated light pulses 202 emitted into the scene during the first ToF measurements can be the same. Therefore, the reference signal used for the first ToF measurements can be time-shifted by n·T1 / 4. The first measured value C i Related to the parameter n, as follows:

[0050] i = n + 1 (6)

[0051] Due to different time offsets Figure 3 The correlation functions 310 and 320 shown are offset relative to each other.

[0052] Performing four first ToF measurements instead of two allows for the omission of errors associated with at least one photosensitive element or pixel of the light-capturing element 220. For example, gain errors or errors due to background light can be compensated. Error compensation is possible because performing two pairs of ToF measurements using inverted reference signals (reference signals for n=0, 2 reversed relative to each other, and reference signals for n=1, 3 reversed relative to each other) causes the differences C2-C4 and C1-C3 to cancel out these errors. However, it should be noted that this technique is not limited to performing two or four first ToF measurements. Generally, any number of ToF measurements l≥2 can be performed.

[0053] The distance d from the ToF sensor 210 to the object 201 can be based on the phase shift. To confirm, as follows:

[0054]

[0055] Device 200 includes a correspondingly configured processing circuitry 240 coupled to the ToF sensor 210. For example, the processing circuitry 240 may be a single dedicated processor, a single shared processor, or multiple individual processors, some or all of which may be shared, including digital signal processor (DSP) hardware, application-specific integrated circuit (ASIC), or field-programmable gate array (FPGA). The processing circuitry 240 may optionally be coupled to, for example, read-only memory (ROM), random access memory (RAM), and / or non-volatile memory for storing software. The processing circuitry 240 is configured to determine the distance to object 201 in the scene based on a first measurement.

[0056] For example, the processing circuit 240 can also output data indicating the distance to the object 201 (e.g., a two-dimensional depth image or a three-dimensional point cloud).

[0057] Device 200 may include additional hardware—traditional and / or custom-made.

[0058] Method 100 and apparatus 200 can allow the distance to object 201 in the scene to be determined while omitting glare and saturation of one or more photosensitive elements or pixels of light-capturing element 220. In other words, method 100 and apparatus 200 can improve ToF sensing.

[0059] The shape of the curves (independent of light intensity) of multiple first ToF measurements' correlation functions can be adjusted using the emitted modulated light pulses and a reference signal used to drive the light-trapping element 220. This will be discussed below regarding... Figures 4 to 7 This is described in one of the first ToF measurements. It should be noted that the aspects described below can also be used for other first ToF measurements.

[0060] As described above, when performing a ToF measurement, a modulated light pulse sequence 202 is emitted into the scene. The modulated light pulse sequence is a succession of first-type and second-type light pulse sub-sequences based on a modulation code. The first-type and second-type light pulse sub-sequences are distinct from each other. Specifically, each of the first-type light pulse sub-sequences includes a light pulse at a first position of its corresponding first-type light pulse sub-sequence. Each of the second-type light pulse sub-sequences includes light pulses at positions other than the first position of its corresponding second-type light pulse sub-sequence. For example, each of the first-type light pulse sub-sequences may include light pulses at odd-numbered positions of its corresponding first-type light pulse sub-sequence, while each of the second-type light pulse sub-sequences may include light pulses at even-numbered positions of its corresponding second-type light pulse sub-sequence, and vice versa.

[0061] Figure 4 Subgraph (a) illustrates an exemplary first sequence 410 of illumination signals, according to which illumination element 230 emits light pulses 202 to the scene. Each high pulse in the first sequence 410 of the illumination signal corresponds to a light pulse in a first type of light pulse subsequence. Similarly, Figure 4 Subgraph (b) illustrates an exemplary second sequence 420 of illumination signals, according to which illumination element 230 emits light pulses 202 to the scene. Each high pulse in the second sequence 420 of the illumination signal corresponds to a light pulse in a second type of light pulse subsequence. Figure 4As can be seen from subgraphs (a) and (b), the first sequence 410 of the illumination signal includes high pulses only at odd positions (i.e., pulses at positions / time slots 1, 3, 5, ... are high pulses), and the second sequence 420 of the illumination signal includes high pulses only at even positions (i.e., pulses at positions / time slots 2, 4, 6, ... are high pulses), such that the corresponding emitted light pulse subsequence of the first type includes light pulses only at odd positions, while the corresponding emitted light pulse subsequence of the second type includes light pulses only at even positions. In other words, the second type of light pulse subsequence includes light pulses only at positions different from those in the first type of light pulse subsequence. Figure 4 In the example, the second type of optical pulse subsequence is inverted relative to the first type of optical pulse subsequence.

[0062] Each of the first sequence 410 and the second sequence 420 of the illumination signal exhibits a corresponding alternating series of high and low pulses of equal duration (length). Therefore, each of the first type and the second type of optical pulse subsequence is a corresponding optical pulse sequence with equal pulse length (duration) and equal pulse interval. Thus, the sequences 410 and 420 of the illumination signal, and consequently the individual optical pulse subsequences of the first and second types, can be understood as continuous wave (CW) segments.

[0063] As described above, the first type of optical pulse subsequence and the second type of optical pulse subsequence are transmitted sequentially according to the modulation code. Figure 5 An exemplary modulation code 500 is shown. Modulation code 500 is a Barker code (sequence). However, the proposed technique is not limited to this. Other modulation codes can also be used, such as pseudo-random sequences, such as Kasami code sequences or maximum-length sequences (m-sequences).

[0064] Figure 1 The Barker code shown is 1110010. Each "1" in the Barker code represents a first type of optical pulse subsequence (i.e., the first sequence 410 of the illumination signal), and each "0" in the Barker code represents a second type of optical pulse subsequence (i.e., the second sequence 420 of the illumination signal). Accordingly, the first type of optical pulse subsequence is transmitted three times consecutively, then the second type of optical pulse subsequence is transmitted twice consecutively, then the first type of optical pulse subsequence is transmitted once, and finally, the second type of optical pulse subsequence is transmitted once. In other words, the first type of optical pulse subsequence and the second type of optical pulse subsequence are concatenated according to the modulation code selected for ToF measurement.

[0065] The first and second types of optical pulse subsequences exhibit the same duty cycle. The duty cycle can be selected as needed. For example, the duty cycle can be 25%. However, lower or higher duty cycle values ​​can also be used. The duty cycle of a signal represents the proportion of time the signal is active within one cycle. For example, the duty cycle of a first-type optical pulse subsequence represents the ratio of the total duration of the optical pulses in the first-type optical pulse subsequence to the total period (duration) of the first-type optical pulse subsequence. Similarly, the duty cycle of a second-type optical pulse subsequence represents the ratio of the total duration of the optical pulses in the second-type optical pulse subsequence to the total period (duration) of the second-type optical pulse subsequence.

[0066] Refer again Figure 4 The light-harvesting element 220 of the ToF sensor 210 is driven based on a reference signal when performing ToF measurements. Similar to the description above for the emitted modulated light pulse sequence, the reference signal comprises a series of first-type and second-type electrical pulse sequences according to a modulation code. The first-type and second-type electrical pulse sequences are different from each other. Specifically, each of the first-type electrical pulse sequences includes a high pulse at a second position of the corresponding first-type electrical pulse sequence. Each of the second-type electrical pulse sequences includes a high pulse only at positions different from the second position of the corresponding second-type electrical pulse sequence. For example, each of the first-type electrical pulse sequences may include a high pulse only at odd positions of the corresponding first-type electrical pulse sequence, while each of the second-type electrical pulse sequences may include a high pulse only at even positions of the corresponding second-type electrical pulse sequence, or vice versa. Figure 4 Subgraph (c) shows an exemplary electrical pulse sequence 430 of the first type, and subgraph (d) shows an exemplary electrical pulse sequence 440 of the second type. Figure 4 As can be seen from subgraphs (c) and (d), the first type of electrical pulse sequence 430 includes high pulses only at odd-numbered positions (i.e., pulses at positions / time slots 1, 3, 5, ... are high pulses), and the second type of electrical pulse sequence 440 includes high pulses only at even-numbered positions (i.e., pulses at positions / time slots 2, 4, 6, ... are high pulses). In other words, the second type of electrical pulse sequence 440 includes high pulses only at positions different from the high pulses in the first type of electrical pulse sequence 430. Figure 4 In the example, the second type of electrical pulse sequence 440 is reversed relative to the first type of electrical pulse sequence 430.

[0067] The light-harvesting element 220 of the ToF sensor 210 is sequentially driven according to a modulation code based on a first type of electrical pulse sequence 430 and a second type of electrical pulse sequence 440. (See again...) Figure 5For example, in the Barker code, a "1" represents a first type of electrical pulse sequence 430, and a "0" represents a second type of electrical pulse sequence 440. Therefore, the light-harvesting element 220 of the ToF sensor 210 is driven three times consecutively based on the first type of electrical pulse sequence 430, then twice consecutively based on the second type of electrical pulse sequence 440, then once based on the first type of electrical pulse sequence 430, and finally once based on the first type of electrical pulse sequence 430. In other words, the first type of electrical pulse sequence 430 and the second type of electrical pulse sequence 440 are concatenated according to the modulation code selected for ToF measurement.

[0068] It should be noted that the lengths of the illumination signal sequences 410 and 420, the lengths of the electrical pulse sequences 430 and 440, and the length of the modulation code 500 are merely exemplary. The number of optical pulses in the first and second type optical pulse subsequences, the number of electrical pulses in the first and second type electrical pulse sequences, and the length of the modulation code used may be longer or shorter than, for example, the lengths of the first and second type optical pulse subsequences and the lengths of the modulation codes used. Figure 4 and Figure 5 The length shown. For example, the number of optical pulses in the first type and / or the second type or the exemplary exemplary optical pulse subsequence and / or the number of electrical pulses in the first type and / or the second type of exemplary electrical pulse sequence can be... Figure 4 The number of pulses shown is u times the number of pulses. Similarly, the length of the exemplary modulation code can be v times the length of modulation code 500.

[0069] according to Figure 4 For example, the first type of optical pulse subsequence and the second type of optical pulse subsequence comprise the same number of optical pulses. In other examples, each of the first type of optical pulse subsequence may comprise a first number of optical pulses, while at least one of the second type of optical pulse subsequences may comprise a second number of optical pulses different from the first number. Other second type of optical pulse subsequences may comprise the first number of optical pulses. For example, one or more of the second type of optical pulse subsequences may comprise more or fewer optical pulses than the first type of optical pulse subsequence. In other words, at least some of the second type of optical pulse subsequences may have a different length than the first type of optical pulse subsequence. Changing the length of at least some of the second type of optical pulse subsequences, together with the design of the modulation code, can allow shaping an increase in the amplitude of the correlation function (independent of light intensity). For example, the increase in the amplitude of the correlation function (independent of light intensity) can be adjusted to counteract the decrease in light intensity with distance. In other words, the amplitude of the periodic correlation function can increase quadratically with distance.

[0070] The number of optical pulses in each optical pulse subsequence of the first type can be the same as the number of high pulses in the first type of electrical pulse sequence, similar to... Figure 4 As shown. In Figure 4 In this context, the first sequence 410 of the illumination signal corresponding to the first type of optical pulse subsequence exhibits the same number of pulses as the first type of electrical pulse sequence 430. Similarly, the number of optical pulses in each optical pulse subsequence of the second type can be the same as... Figure 4 The second type of electrical pulse sequence shown has the same number of high pulses. Figure 4 In this context, the second sequence 420 of the illumination signal corresponding to the second type of light pulse subsequence exhibits the same number of pulses as the second type of electrical pulse sequence 440.

[0071] In other examples, at least one optical pulse subsequence of the first type may include a number of optical pulses that is less than the corresponding number of high pulses in the first type of electrical pulse sequence. Additionally or alternatively, at least one optical pulse subsequence of the second type may include a number of optical pulses that is less than the corresponding number of high pulses in the second type of electrical pulse sequence. This is in Figure 6 As shown in the image.

[0072] Similar to Figure 4 , Figure 6 Subfigure (a) illustrates an exemplary first sequence 610 of illumination signals, according to which illumination element 230 emits light pulses 202 to the scene. Each high pulse in the first sequence 610 of the illumination signal corresponds to a light pulse in a first type of light pulse subsequence. Similarly, Figure 6Subgraph (b) illustrates an exemplary second sequence 620 of illumination signals, according to which illumination element 230 emits light pulses 202 to the scene. Each high pulse in the second sequence 620 of the illumination signal corresponds to a light pulse in a second type of light pulse subsequence. Similar to sequences 410 and 420 of the illumination signals, sequences 610 and 620 of the illumination signals are also different from each other, such that the corresponding emitted light pulse subsequences of the first type and the corresponding emitted light pulse subsequences of the second type are also different from each other. Specifically, the first sequence 610 of the illumination signals includes high pulses only at odd positions (i.e., pulses at positions / time slots 3 and 5 are high pulses), and the second sequence 420 of the illumination signals includes high pulses only at even positions (i.e., pulses at positions / time slots 4 and 6 are high pulses), such that the corresponding emitted light pulse subsequences of the first type include light pulses only at odd positions and the corresponding emitted light pulse subsequences of the second type include light pulses only at even positions. In other words, the second type of optical pulse subsequence includes optical pulses only at positions that differ from the positions of optical pulses in the first type of optical pulse subsequence.

[0073] Compared to the lighting signal sequences 410 and 420, in the lighting signal sequences 610 and 620, the first high pulse and the last high pulse are skipped (omitted).

[0074] Similar to Figure 4 , Figure 6 An exemplary electrical pulse sequence 630 of the first type is shown in subfigure (c), and an exemplary electrical pulse sequence 640 of the second type is shown in subfigure (d). Figure 6 The electrical pulse sequences 630 and 640 shown are... Figure 4 The electrical pulse sequences 430 and 440 shown are the same.

[0075] The number of pulses in the first sequence 610 of the illumination signal, and therefore the number of light pulses in the first type of light pulse subsequence, is less than the number of high pulses in the first type of electrical pulse sequence 630. Similarly, the number of pulses in the second sequence 620 of the illumination signal, and therefore the number of light pulses in the second type of light pulse subsequence, is less than the number of high pulses in the second type of electrical pulse sequence 640.

[0076] Therefore, the time span from the beginning of the first type of optical pulse subsequence to the first optical pulse in the first type of optical pulse subsequence is longer than the time span from the beginning of the first type of electrical pulse sequence 630 to the first high pulse in the first type of electrical pulse sequence 630. Similarly, the time span from the last optical pulse in the first type of optical pulse subsequence to the end of the first type of optical pulse subsequence is greater than the time span from the last high pulse in the first type of electrical pulse sequence 630 to the end of the first type of electrical pulse sequence 630. The same applies to the second type of optical pulse subsequence and the second type of electrical pulse sequence 640.

[0077] Using this relationship between optical pulse subsequences and electrical pulse sequences allows for shaping a correlation function (independent of light intensity) for ToF measurements. This is in Figure 7 As exemplarily shown in the figure.

[0078] Figure 7 Two exemplary (light intensity-independent) correlation functions 710 and 720 are shown for two first ToF measurements performed by the ToF sensor 210. (See also:) Figure 6 The optical pulse subsequence and electrical pulse sequence shown are used for two first ToF measurements. Figure 7 The horizontal axis represents the distance between the ToF sensor 210 and the object 201. The vertical axis represents the value of the corresponding correlation function. The measurement range of the ToF sensor 210 is within... Figure 7 It is not explicitly shown, but the range is from 0 to approximately 6.1 on the vertical axis.

[0079] and Figure 3 Similar to correlation functions 310 and 320, correlation functions 710 and 720 also exhibit a sinusoidal (i.e., periodic) curve (shape) with amplitude increasing with distance within the measurement range of the ToF sensor 210.

[0080] However, compared to correlation functions 310 and 320, correlation functions 710 and 720 exhibit a full cycle (oscillation) of maximum correlation. Within the distance region 730, each of correlation functions 710 and 720 exhibits a full cycle of maximum correlation. Using a correlation function that provides maximum correlation within a full cycle may be advantageous, for example, for long-range ToF sensing, since the received light intensity may be limited over a longer range. Therefore, skipping the first and last light pulses in at least some of the first and second type light pulse subsequences can achieve improved ToF sensing over longer distances.

[0081] However, it should be noted that the proposed technique is not limited to skipping only the first and last light pulses in one or more light pulse subsequences of the first and second types of light pulse subsequences. Other pulses in one or more light pulse subsequences of the first and second types of light pulse subsequences may also be skipped. Regarding the light intensity of the emitted light pulse 202, the illumination element used for ToF sensing becomes increasingly powerful. To comply with, for example, eye safety regulations, the amount of light emitted per unit time by an illumination element such as illumination element 230 for ToF measurement may be limited. Therefore, pulses in the first and second types of light pulse subsequences can be skipped to limit the amount of emitted light. For example, 10% to 90% of the pulses can be skipped.

[0082] Similarly, in this case, each of the first and second type of optical pulse subsequences exhibits a corresponding series of optical pulses with equal pulse lengths. However, the pulse interval between directly adjacent optical pulses is (2·m+1) times the pulse length of one or more optical pulses in the corresponding series, where m≥1. The pulse interval between directly adjacent optical pulses is equal to the pulse length of other optical pulses in the corresponding series (i.e., m=0).

[0083] Another aspect of ToF sensing is the ambiguity of ToF measurement. The maximum definite distance range d in ToF measurement... u With modulation frequency f mod Inversely proportional:

[0084]

[0085] Measurements beyond this distance are surrounded to fall within [0, d]. u Within a certain range, it appears closer than the actual distance. Lowering the modulation frequency f... mod This will allow for the expansion of the explicit distance range d u However, this will reduce the accuracy of distance measurement.

[0086] The ambiguity of distance measurement can be overcome by performing additional Time-of-Flight (ToF) measurements at different second modulation frequencies. (See again...) Figure 1 and Figure 2Method 100 may optionally further include performing 106 multiple second ToF measurements by the ToF sensor 210 using a second modulation frequency to obtain second measurement values. The second modulation frequency differs from the first modulation frequency (e.g., higher or lower). Similar to that described above for the first ToF measurement, the corresponding correlation function of each of the multiple second ToF measurements is periodic and exhibits an amplitude that increases with distance within the measurement range of the ToF sensor 210. The step of determining 104 the distance from the ToF sensor 210 to the object 201 in the scene is therefore further based on the second measurement values.

[0087] Similar to the mathematical expression (1) above, the second modulation frequency f mod2 The period length d of a correlation function (independent of light intensity) that can be measured by the speed of light c and multiple second-Time-of-Flight (ToF) methods. period2 definition:

[0088]

[0089] Figure 8 Subfigure (a) shows two exemplary (light intensity-independent) correlation functions 810 and 820 for two first ToF measurements performed by the ToF sensor 210. Furthermore, Figure 8 Subgraph (b) shows two exemplary (light intensity-independent) correlation functions 830 and 840 for two second ToF measurements performed by the ToF sensor 210. Figure 8 The horizontal axis in each subgraph represents the distance between the ToF sensor 210 and the object 201. Figure 8 The ordinate of each subplot represents the value of the corresponding related function. Figure 8 The exemplary measurement range 850 of the ToF sensor 210 is further shown in the figure.

[0090] For the first modulation frequency f mod1 The related functions 810 and 820 and the function for the second modulation frequency f mod2 Correlation functions 830 and 840 exhibit a sinusoidal (i.e., periodic) curve (shape) with amplitude increasing with distance within the measurement range 850 of the ToF sensor 210. Correlation functions 810 and 820 exhibit the same first period length. Correlation functions 830 and 840 exhibit the same second period length.

[0091] Similar to the description above for multiple first ToF measurements, different time offsets are used for each of the multiple second ToF measurements between the corresponding modulated light pulse 202 sequence emitted into the scene during the corresponding second ToF measurement and the corresponding reference signal used to drive the light-harvesting element 220 of the ToF sensor 210 during the corresponding second ToF measurement. The time offset used for the second ToF measurement is determined by the second modulation frequency f. mod2 The reciprocal of the second period length T2 is an integer multiple of the fraction, i.e.:

[0092]

[0093] For example, when performing two second ToF measurements, a time offset of n·T2 / 4 can be used when n = 0 or 1. Similarly, when performing four second ToF measurements, a time offset of n·T2 / 4 can be used when n = 0, 1, 2, or 3. The sequence of modulated light pulses 202 emitted into the scene during the second ToF measurements can be the same. Therefore, the reference signal used for the second ToF measurements can be time-shifted by n·T1 / 4.

[0094] As described above, if object 201 is beyond the defined distance d measured by the first ToF, u1 Then it is surrounded to fall within the defined distance range [0, d] measured by the first ToF. u1 Within. Similarly, if object 201 is beyond the specified distance d measured by the second ToF. u2 Then it is surrounded to fall within the defined distance range [0, d] measured by the second ToF. u2 Therefore, object 201 appears to be closer than it actually is.

[0095] In other words, multiple first ToF measurements and multiple second ToF measurements each give several possible distances to object 201.

[0096] For the first ToF measurement, the possible distance from object 201 to ToF sensor 210 is given by the following formula:

[0097]

[0098] This represents the phase value determined from the first measurement value according to, for example, one of the mathematical expressions (3) and (4). The first term of the mathematical expression (11) corresponds to the aforementioned mathematical expression (7). The second term of the mathematical expression (11) is based on the aforementioned mathematical expression (8) and describes that the actual distance of object 201 can be the explicit distance d measured by the first ToF. u1 It is k1 times greater than the distance determined by the mathematical expression (7) due to phase entanglement, where k1 = 0, 1, 2, ...

[0099] Similarly, for the second ToF measurement, the possible distance from object 201 to ToF sensor 210 is given by the following formula:

[0100]

[0101] This represents the phase value determined from the second measurement value according to, for example, one of the mathematical expressions (3) and (4). The first term of mathematical expression (12) corresponds to the aforementioned mathematical expression (7). The second term of mathematical expression (12) is based on the aforementioned mathematical expression (8) and describes that the actual distance of object 201 can be the explicit distance d measured by the second ToF. u2 The distance is k2 times greater than the distance determined by the mathematical expression (7), where R2 = 0, 1, 2, ...

[0102] This is Figure 9 As exemplarily shown in the figure. Figure 9 The diagram illustrates the possible distances from object 201 to ToF sensor 210 for ToF measurements with two different modulation frequencies. The first modulation frequency is approximately 150 MHz, resulting in a definite distance d for the first ToF measurement. u1 The distance is 1m. The second modulation frequency is approximately 100MHz, which allows the second ToF to measure a precise distance d. u2 It is 1.5m.

[0103] The phase value determined based on the first measurement value according to the mathematical expression (7) This ensures that the distance between object 201 and ToF sensor 210 is 1m. This distance is... Figure 9 The distance d is represented in the middle. 1_0 However, as shown in mathematical expression (11), the distance from object 201 to ToF sensor 210 can also be 1.1m, 2.1m, ... and larger. The possible distances for k1=1 and k1=2 are... Figure 9 The middle is represented as d 1_1 and d 1-2 .

[0104] Similarly, according to mathematical expression (7), the phase value is determined based on the second measurement value. This ensures that the distance between object 201 and ToF sensor 210 is 1.5m. This distance is... Figure 9 The distance d is represented in the middle. 2_0 However, as shown in mathematical expression (12), the distance from object 201 to ToF sensor 210 can also be 1.1.5m, 2.1.5m, ... and larger. For the possible distance of k2=1, ... Figure 9 The middle is represented as d 2_1 .

[0105] Mathematical expressions (11) and (12) apply only to a specific distance, i.e., to a specific pair of values ​​for consistent parameters k1 and k2. For example, it can be determined which integer values ​​of distances d1 and d2 according to mathematical expressions (11) and (12) are identical to each other or differ from each other by less than a threshold (to account for limited measurement precision). Thus, a first distance estimate d1 can be determined based on the first measurement according to mathematical expression (11). Similarly, a second distance estimate d2 can be determined based on the second measurement according to mathematical expression (12).

[0106] exist Figure 9 In the example, mathematical expressions (11) and (12) are consistent only when k1 = 2 and k2 = 1, such that the first distance estimate d1 = 3m and the second distance estimate d2 = 3m.

[0107] The distance d to object 201 can be determined based on a first distance estimate d1 and a second distance estimate d2. For example, these two distance estimates can be averaged to account for measurement errors from multiple first ToF measurements and multiple second ToF measurements.

[0108]

[0109] In other examples, a weighted average can be used:

[0110] d = w1·d1 + w2·d2 (14)

[0111] The weights w1 and w2 can be based on various parameters, such as the first modulation frequency and the second modulation frequency, or the amplitude of the first measurement and the amplitude of the second measurement.

[0112] The curves (shapes) of the correlation functions (independent of light intensity) for multiple second ToF measurements can be adjusted, similar to those described for the correlation functions for multiple first ToF measurements, by means of the emitted modulated light pulses and the reference signal used to drive the light-trapping element 220. This will be described below for one of the second ToF measurements. It should be noted that the aspects described below can also be applied to other first ToF measurements.

[0113] Similar to the description above, when performing a second ToF measurement, another sequence of modulated optical pulses 202 is emitted into the scene. This other sequence of modulated optical pulses is a series of third-type and fourth-type optical pulse subsequences based on a different modulation code. The third-type and fourth-type optical pulse subsequences are distinct from each other, as described above. Specifically, each of the third-type optical pulse subsequences includes a light pulse at a third position (e.g., an odd-numbered position) of the corresponding third-type optical pulse subsequence, and each of the fourth-type optical pulse subsequences includes a light pulse at a position different from the third position (e.g., an even-numbered position) of the corresponding fourth-type optical pulse subsequence. Due to the different modulation frequencies used for the multiple first ToF measurements and the multiple second ToF measurements, the pulse lengths and pulse intervals of the third-type and fourth-type optical pulse subsequences differ from those of the first-type and second-type optical pulse subsequences. Furthermore, the same principles described above for the first-type and second-type optical pulse subsequences can be applied to the third-type and fourth-type optical pulse subsequences.

[0114] Furthermore, when performing a second ToF measurement, the light-harvesting element 220 of the ToF sensor 210 is driven based on another reference signal, similar to the description above. This other reference signal comprises a series of third-type and fourth-type electrical pulse sequences according to another modulation code. The third-type and fourth-type electrical pulse sequences are different from each other, similar to the description above. Specifically, each of the third-type electrical pulse sequences includes a high pulse at a fourth position (e.g., an odd-numbered position) of the corresponding third-type electrical pulse sequence, and each of the fourth-type electrical pulse sequences includes a high pulse only at positions different from the fourth position (e.g., even-numbered positions) of the corresponding fourth-type electrical pulse sequence. Due to the different modulation frequencies used for the multiple first ToF measurements and the multiple second ToF measurements, the pulse lengths of the high and low pulses in the third-type and fourth-type electrical pulse sequences differ from the pulse lengths of the high and low pulses in the first-type and second-type electrical pulse sequences. Furthermore, the same principles described above for the first-type and second-type electrical pulse sequences can be applied to the third-type and fourth-type electrical pulse sequences.

[0115] The modulation code used for multiple first ToF measurements and another modulation code used for multiple second ToF measurements can be the same as or different from each other. The same other modulation code is used for multiple second ToF measurements. For example, in... Figure 8In the example, the same modulation code was used for multiple first ToF measurements and multiple second ToF measurements. As a result, in a distance region that is slightly different from the correlation functions 810 and 820 of the two first ToF measurements, the correlation functions 830 and 840 of the two second ToF measurements exhibit their highest amplitudes.

[0116] For the phase unfolding described above, it may be advantageous to have the highest amplitude of the correlation function of both the first and second ToF measurements within substantially the same distance region. The corresponding location of the highest amplitude can be adjusted via corresponding modulation codes for the multiple first ToF measurements and the multiple second ToF measurements. In other words, the modulation codes for the multiple first ToF measurements and another modulation code for the multiple second ToF measurements can be different from each other to shift the highest amplitude of the corresponding correlation functions, making them substantially the same distance region. For example, the correlation function of the multiple first ToF measurements may exhibit its corresponding maximum amplitude at a first distance, and the correlation function of the multiple second ToF measurements may exhibit its corresponding maximum amplitude at a second distance, such that the difference between the first and second distances is less than 20%, 10%, or 5%.

[0117] This is Figure 10 As exemplarily shown in the figure. Figure 10 Subfigure (a) shows two exemplary (light intensity-independent) correlation functions 1010 and 1020 for two first ToF measurements performed by the ToF sensor 210. Furthermore, Figure 10 Subgraph (b) shows two exemplary (light intensity-independent) correlation functions 1030 and 1040 for two second ToF measurements performed by the ToF sensor 210. Figure 10 The horizontal axis in each subgraph represents the distance between the ToF sensor 210 and the object 201. Figure 10 The vertical axis in each subplot represents the value of the corresponding correlation function. The measurement range of the ToF sensor 210 is within... Figure 10 It is not explicitly shown, but the range is from 0 to approximately 0.43 on the vertical axis.

[0118] First modulation frequency f mod1 The correlation functions 1010 and 1020 and the second modulation frequency f mod2 The correlation functions 1030 and 1040 exhibit sinusoidal (i.e., periodic) curves (shapes) with amplitude increasing with distance within the measurement range of the ToF sensor 210.

[0119] The first modulation code is used for two first ToF measurements, and a different second modulation code is used for two second ToF measurements. From Figure 10It can be seen that the correlation functions 1010 and 1020 of the two first ToF measurements and the correlation functions 1030 and 1040 of the two second ToF measurements exhibit their corresponding highest amplitudes at a distance of approximately 4 on the vertical axis (i.e., at essentially the same distance).

[0120] Furthermore, the modulation code used for the multiple first ToF measurements and another modulation code used for the multiple second ToF measurements can be chosen to be different from each other to ensure that the amplitude of the correlation function of the multiple first ToF measurements and the amplitude of the correlation function of the multiple second ToF measurements increase with distance in a similar manner.

[0121] The examples described in this article can be summarized as follows:

[0122] One example relates to a method for Time-of-Flight (ToF) sensing of a scene. The method includes performing a plurality of first ToF measurements by a ToF sensor using a first modulation frequency to obtain first measurement values. The corresponding correlation function of each of the plurality of first ToF measurements is periodic and exhibits an amplitude increasing with distance within the measurement range of the ToF sensor. The method further includes determining the distance to an object in the scene based on the first measurement values.

[0123] In some examples, different time offsets are used for the plurality of first ToF measurements between the respective modulated light pulse sequence emitted into the scene during the respective first ToF measurement and the respective reference signal used to drive the light-harvesting element of the ToF sensor during the respective first ToF measurement.

[0124] According to some examples, the time offset used for the ToF measurement is an integer multiple of a fraction of the first cycle length given by the reciprocal of the first modulation frequency.

[0125] In some examples, the sequence of modulated light pulses emitted into the scene during the first ToF measurement is the same.

[0126] According to some examples, performing a first ToF measurement in the first ToF measurement includes transmitting a modulated light pulse sequence into the scene, wherein the modulated light pulse sequence is a series of first-type light pulse subsequences and second-type light pulse subsequences according to a modulation code, and wherein each of the first-type light pulse subsequences includes a light pulse of the corresponding first-type light pulse subsequence at a first position, and each of the second-type light pulse subsequences includes a light pulse of the corresponding second-type light pulse subsequence at a position other than the first position.

[0127] In some examples, each of the first type of optical pulse subsequence includes a first number of optical pulses, wherein at least one of the second type of optical pulse subsequences includes a second number of optical pulses different from the first number of optical pulses.

[0128] According to some examples, performing one of the first ToF measurements further includes driving the light-harvesting element of the ToF sensor based on a reference signal, wherein the reference signal comprises a series of first-type electrical pulse sequences and second-type electrical pulse sequences according to the modulation code, and wherein each of the first-type electrical pulse sequences includes a high pulse of the corresponding first-type electrical pulse sequence at a second position, and each of the second-type electrical pulse sequences includes a high pulse of the corresponding second-type electrical pulse sequence only at a position different from the second position.

[0129] In some examples, at least one optical pulse subsequence of the first type includes a certain number of optical pulses, which is less than the corresponding number of high pulses in the electrical pulse sequence of the first type, and / or at least one optical pulse subsequence of the second type includes a certain number of optical pulses, which is less than the corresponding number of high pulses in the electrical pulse sequence of the second type.

[0130] According to some examples, the time span from the start of at least one optical pulse subsequence of the first type to the first optical pulse in the at least one optical pulse subsequence of the first type is longer than the time span from the start of one electrical pulse sequence of the first type to the first high pulse in one electrical pulse sequence of the first type, and / or wherein the time span from the last optical pulse in the at least one optical pulse subsequence of the first type to the end of the at least one optical pulse subsequence of the first type is longer than the time span from the last high pulse in one electrical pulse sequence of the first type to the end of one electrical pulse sequence of the first type.

[0131] In some examples, each of the first type of optical pulse subsequence and the second type of optical pulse subsequence exhibits a corresponding series of optical pulses with equal pulse lengths, wherein the pulse interval of a directly adjacent optical pulse is (2·m+1) times the pulse length of one or more optical pulses in the corresponding series of optical pulses, where m≥1, and wherein the pulse interval of the directly adjacent optical pulse is equal to the pulse length of the other optical pulses in the corresponding series of optical pulses.

[0132] According to some examples, the optical pulse subsequence of the first type and the optical pulse subsequence of the second type exhibit the same duty cycle.

[0133] In some examples, the method further includes performing a plurality of second ToF measurements by the ToF sensor using a second modulation frequency to obtain a second measurement value, wherein the corresponding correlation function of each of the plurality of second ToF measurements is periodic and exhibits an amplitude that increases with distance within the measurement range of the ToF sensor, and wherein the distance to the object in the scene is determined based on the second measurement value.

[0134] According to some examples, determining the distance to the object in the scene includes: determining a first distance estimate based on the first measurement; determining a second distance estimate based on the second measurement; and determining the distance to the object in the scene based on the first distance estimate and the second distance estimate.

[0135] In some examples, the correlation function measured by the first ToF exhibits its corresponding maximum magnitude at a first distance, wherein the correlation function measured by the second ToF exhibits its corresponding maximum magnitude at a second distance, and wherein the difference between the first distance and the second distance is less than 20%.

[0136] According to some examples, performing a second ToF measurement includes: transmitting another modulated optical pulse sequence to the scene, wherein the other modulated optical pulse sequence is a series of third-type and fourth-type optical pulse subsequences according to another modulation code, wherein each of the third-type optical pulse subsequences includes an optical pulse of the corresponding third-type optical pulse subsequence at a third position, and each of the fourth-type optical pulse subsequences includes an optical pulse of the corresponding fourth-type optical pulse subsequence at a position other than the third position.

[0137] In some examples, performing a second ToF measurement further includes driving the light-harvesting element of the ToF sensor based on another reference signal, wherein the other reference signal comprises a series of third-type and fourth-type electrical pulse sequences according to the other modulation code, wherein each of the third-type electrical pulse sequences includes a high pulse of the corresponding third-type electrical pulse sequence at a fourth position, and each of the fourth-type electrical pulse sequences includes a high pulse of the corresponding fourth-type electrical pulse sequence only at a position different from the fourth position.

[0138] Another example relates to an apparatus for Time-of-Flight (ToF) sensing of a scene. The apparatus includes a ToF sensor configured to perform a plurality of first ToF measurements using a first modulation frequency to obtain first measurement values. The corresponding correlation function of each of the plurality of first ToF measurements is periodic and exhibits an amplitude that increases with distance within the measurement range of the ToF sensor. Furthermore, the apparatus includes processing circuitry configured to determine the distance to an object in the scene based on the first measurement values.

[0139] The examples disclosed herein enable Time-of-Flight (ToF) measurements with increased correlation to reduce glare. Using a correlation function that increases with distance for ToF measurements allows glare from nearby objects to be ignored. This disclosure can enhance ToF sensing for many applications, such as long-range ToF sensing at the front of a vehicle (automobile).

[0140] Aspects and features described relative to a specific example in the previous examples may also be combined with one or more other examples to replace the same or similar features of that other example or to additionally introduce those features into another example.

[0141] It should also be understood that the disclosure of steps, processes, operations, or functions in the specification or claims should not be construed as implying that these operations must depend on the described order, unless explicitly stated in individual cases or required for technical reasons. Therefore, the foregoing description does not limit the execution of steps or functions to a specific order. Furthermore, in other examples, a single step, function, process, or operation may include and / or be decomposed into several sub-steps, sub-functions, sub-processes, or sub-operations.

[0142] If certain aspects have already been described for a device or system, these aspects should also be understood as descriptions of the corresponding methods. For example, a block, device, or functional aspect of a device or system may correspond to a feature of the corresponding method, such as method steps. Therefore, aspects described with respect to a method should also be understood as descriptions of corresponding blocks, elements, attributes, or functional features of the corresponding device or system.

[0143] The appended claims are incorporated herein by reference, wherein each claim may stand alone as a separate example. It should also be noted that while in the claims, a dependent claim refers to a specific combination with one or more other claims, other examples may also include combinations of dependent claims with the subject matter of any other dependent or independent claim. Such combinations are explicitly stated herein unless it is stated in individual cases that a particular combination is not intended. Furthermore, any other independent claim should also include the features of the claim, even if the claim is not directly defined as dependent on that other independent claim.

Claims

1. A method (100) for time-of-flight (ToF) sensing of a scene, the method (100) comprising: A plurality of first ToF measurements are performed by a ToF sensor using a first modulation frequency to obtain a first measurement value, wherein the corresponding correlation function of each of the plurality of first ToF measurements is periodic and exhibits an amplitude that increases with distance within the measurement range of the ToF sensor; as well as The distance to the object in the scene is determined based on the first measurement value (104).

2. The method (100) according to claim 1, wherein different time offsets are used for the plurality of first ToF measurements between the respective modulated light pulse sequence emitted to the scene during the respective first ToF measurement and the respective reference signal used to drive the light-harvesting element of the ToF sensor during the respective first ToF measurement.

3. The method (100) of claim 2, wherein the time offset for the ToF measurement is an integer multiple of a fraction of the length of the first cycle given by the reciprocal of the first modulation frequency.

4. The method (100) according to claim 2 or 3, wherein the sequence of modulated light pulses emitted to the scene during the first ToF measurement is the same.

5. The method (100) according to any one of claims 1 to 4, wherein performing a first ToF measurement in the first ToF measurement comprises: A modulated optical pulse sequence is transmitted to the scene, wherein the modulated optical pulse sequence is a series of first-type and second-type optical pulse subsequences based on a modulation code. The first type of optical pulse subsequence each includes an optical pulse at a first position of the corresponding optical pulse subsequence of the first type, and the second type of optical pulse subsequence each includes an optical pulse at a position different from the first position of the corresponding optical pulse subsequence of the second type.

6. The method (100) according to claim 5, wherein each of the first type of optical pulse subsequences comprises a first number of optical pulses, and wherein at least one of the second type of optical pulse subsequences comprises a second number of optical pulses different from the first number of optical pulses.

7. The method (100) according to claim 5 or 6, wherein performing one of the first ToF measurements further comprises: The light-harvesting element of the ToF sensor is driven by a reference signal, wherein the reference signal comprises a series of electrical pulse sequences of a first type and a second type according to the modulation code. The first type of electrical pulse sequence each includes a high pulse at a second position of the corresponding electrical pulse sequence of the first type, and the second type of electrical pulse sequence each includes a high pulse at a position other than the second position of the corresponding electrical pulse sequence of the second type.

8. The method (100) according to claim 7, wherein at least one optical pulse subsequence of the first type comprises a certain number of optical pulses, the certain number being less than the corresponding number of high pulses in the electrical pulse sequence of the first type, and / or wherein at least one optical pulse subsequence of the second type comprises a certain number of optical pulses, the certain number being less than the corresponding number of high pulses in the electrical pulse sequence of the second type.

9. The method (100) of claim 8, wherein the time span from the start of at least one optical pulse subsequence of the first type to the first optical pulse in at least one optical pulse subsequence of the first type is longer than the time span from the start of one electrical pulse sequence of the first type to the first high pulse in one electrical pulse sequence of the first type, and / or wherein the time span from the last optical pulse in at least one optical pulse subsequence of the first type to the end of at least one optical pulse subsequence of the first type is longer than the time span from the last high pulse in one electrical pulse sequence of the first type to the end of one electrical pulse sequence of the first type.

10. The method (100) according to any one of claims 5 to 9, wherein each of the first type of optical pulse subsequence and the second type of optical pulse subsequence exhibits a corresponding series of optical pulses with equal pulse lengths, wherein the pulse interval to the directly adjacent optical pulse is (2·m+1) times the pulse length of one or more optical pulses in the corresponding series of optical pulses, where m≥1, and wherein the pulse interval to the directly adjacent optical pulse is equal to the pulse length of the other optical pulses in the corresponding series of optical pulses.

11. The method (100) according to any one of claims 5 to 10, wherein the first type of optical pulse subsequence and the second type of optical pulse subsequence exhibit the same duty cycle.

12. The method (100) according to any one of claims 1 to 11, further comprising: The ToF sensor performs (106) a plurality of second ToF measurements using a second modulation frequency to obtain a second measurement value, wherein the corresponding correlation function of each of the plurality of second ToF measurements is periodic and exhibits an amplitude that increases with distance within the measurement range of the ToF sensor. The distance to the object in the scene determined by (104) is also based on the second measurement.

13. The method (100) of claim 12, wherein determining (104) the distance to the object in the scene comprises: A first distance estimate is determined based on the first measurement value; A second distance estimate is determined based on the second measurement value; as well as The distance to the object in the scene is determined based on the first distance estimate and the second distance estimate.

14. The method (100) according to claim 12 or 13, wherein the correlation function measured by the first ToF exhibits its corresponding maximum amplitude at a first distance, wherein the correlation function measured by the second ToF exhibits its corresponding maximum amplitude at a second distance, and The difference between the first distance and the second distance is less than 20%.

15. The method (100) according to any one of claims 12 to 14, wherein performing one of the second ToF measurements comprises: Another modulated optical pulse sequence is transmitted to the scene, wherein the other modulated optical pulse sequence is a series of third-type and fourth-type optical pulse sub-sequences based on another modulation code. The third type of optical pulse subsequence each includes an optical pulse at a third position of the corresponding optical pulse subsequence of the third type, and the fourth type of optical pulse subsequence each includes an optical pulse at a position different from the third position of the corresponding optical pulse subsequence of the fourth type.

16. The method (100) of claim 15, wherein performing one of the second ToF measurements further comprises: The light-harvesting element of the ToF sensor is driven by another reference signal, wherein the other reference signal comprises a series of third-type and fourth-type electrical pulse sequences according to the other modulation code. The third type of electrical pulse sequence each includes a high pulse at a fourth position of the corresponding electrical pulse sequence of the third type, and the fourth type of electrical pulse sequence each includes a high pulse at a position other than the fourth position of the corresponding electrical pulse sequence of the fourth type.

17. A device (200) for time-of-flight (ToF) sensing of a scene, the device (200) comprising: A ToF sensor (210) is configured to perform a plurality of first ToF measurements using a first modulation frequency to obtain a first measurement value, wherein the corresponding correlation function of each of the plurality of first ToF measurements is periodic and exhibits an amplitude that increases with distance within the measurement range of the ToF sensor; as well as The processing circuit (240) is configured to determine the distance to the object (201) in the scene based on the first measurement value.

Images