WO2025190818A1

WO2025190818A1 - System for time-of-flight measurement, method for time-of-flight measurement and sensor for time-of-flight measurement

Info

Publication number: WO2025190818A1
Application number: PCT/EP2025/056342
Authority: WO
Inventors: Robert Kappel; Sargis ABOVYAN
Original assignee: Ams Osram AG
Current assignee: Ams Osram AG
Priority date: 2024-03-15
Filing date: 2025-03-07
Publication date: 2025-09-18
Anticipated expiration: 2026-09-15

Abstract

According to the invention, a system for time-of-flight measurement, comprises: a plurality of Single-Photon Avalanche Diodes (SPAD) (2) configured to detect photons and generate electrical signals, a plurality of merging modules (4), wherein each merging module out of the plurality of merging modules (4) is coupled to one or more SPAD(s) (2) out of the plurality of SPADs (2) and to a Multiplexer (MUX) (6), wherein each merging module (4) is configured to receive the electrical signals from the SPAD (2), to merge the received electrical signals into a single pixel signal, and to forward the single pixel signal to the MUX (6), the Multiplexer (MUX) (6), which is coupled to the plurality of merging modules (4) and to a plurality of Time-to-Digital Converter (TDC) channels (8), and which is configured to receive the single pixel signal from each merging module (4) and to establish single pixel and TDC channel connections, and to output the respective single pixel signal to the respective TDC channel, and a plurality of Time-to-Digital Converter (TDC) channels (8), each TDC channel (8) being coupled to the MUX (6) and configured to convert the output signal from the MUX (6) to a time value and then to a digital value. Furthermore, a corresponding method for for time-of-flight measurement and a corresponding sensor for time-of-flight measurement is disclosed.

Description

DESCRIPTION

SYSTEM FOR TIME-OF-FLIGHT MEASUREMENT, METHOD FOR TIME-OF- FLIGHT MEASUREMENT AND SENSOR FOR TIME-OF-FLIGHT MEASUREMENT

TECHNICAL FIELD

The invention relates to a system for time-of-f light measurement, a method for time-of-f light measurement, and a sensor for time-of-f light measurement.

BACKGROUND

Time of Flight (ToF) refers to the process of calculating the time an object, particle, or wave (such as acoustic or electromagnetic) takes to traverse a certain distance within a medium. This data can be utilized to determine the velocity or the path length, or to gain insights into the properties of the particle or the medium, like its composition or flow rate .

E.g., in the realm of contemporary smartphones, Time of Flight (ToF) sensors play a crucial role in collecting depth data, enabling precise identification of structures, object distances, and movements. This is accomplished by emitting a pulse of light and recording the time it takes— known as the "time of flight"— for the light to travel to an object and bounce back to the sensor. This technology operates efficiently even under severe lighting conditions, such as near-complete darkness, and offers incredibly fast performance. These features are particularly of interest for e.g. smartphone development, tablet development and in the development of AR/VR glasses.

Time of Flight (ToF) measurements generally require several essential components. At the core of these is the ToF sensor and sensor module, which are tasked with gauging the time it takes for an obj ect , particle , or wave to traverse a certain distance within a medium . A light source , such as a laser or LED, is employed to emit a light pulse . Additionally, a delay line is utili zed to transmit the signal , and an oscillator is incorporated to generate a clock signal . A Time-to-Digital Converter ( TDC ) is responsible for trans forming the time measurement into a digital format , while the receiver channels serve to detect the signal at various points .

Typically, the information corresponding to individual pixels is then stored in distinct histograms . Each pixel has its own histogram, which represents the distribution of data values for that particular pixel .

Time-of-Flight ( ToF) is a broad term that refers to said technique , whereas direct Time-of-Flight ( dToF) , on the other hand, is a speci fic variant of ToF systems . In a dToF setup, the time is directly measured from the moment the light is emitted until the point it is detected after reflection . This allows for a straightforward and direct computation of distance . o ■©

In a Direct Time-of-Flight ( dToF) system, the time it takes for a signal to travel from a Single-Photon Avalanche Diode ( SPAD) to a Time-to-Digital Converter ( TDC ) is measured .

SPADs serve in this context as depth detectors in dToF range sensors . A photon striking the SPAD initiates an electron avalanche , resulting in a detectable current pulse . This pulse is then transmitted to the TDC . The TDC calculates the duration of the pulse ' s j ourney from the SPAD to the TDC, which is directly proportional to the distance between the sensor and the obj ect being measured . The precision of the depth measurement is constrained by the bin width of the histogram generated by the TDC .

Yet , ToF and also dToF have their drawbacks . As Time-of- flight measurement principle is based on time measurement , the propagation delay of the electrical signal from singlephoton avalanche diodes ( SPAD) to TDC is part of the measurement result and misalignment between the di f ferent pixels can occur . Said misalignment could occur due to a variety of factors , including variations in manufacturing, environmental conditions , or operational parameters . This misalignment could introduce errors or distortions in the data, which could af fect the accuracy and reliability of the resulting information .

Additionally, in case of a multi zone device , it could happen that propagation delay from SPAD to TDC of all pixels is not aligned so that in case of e . g . a flat wall as a target , not all pixels give the same distance measurement result .

The main challenge in this context is to make sure that the SPAD to TDC interconnect is well balanced . Since perfect matching is not possible , especially in case of logic gates in the signal path, there is always some kind of of fset present . This of fset is directly translated into a distance measurement error in di f ferent channels/ zones .

Previously, to address this issue , typically a postprocessing step to compensate for the misalignment was conducted . This step involved adj usting the gain and of fset for each pixel to bring them into alignment with each other . The gain adj ustment would scale the amplitude of the data values , while the of fset adj ustment would shi ft the data values up or down . This process helped to ensure that the data from di f ferent pixels could be accurately compared and combined .

Once the misalignment had been compensated for, the data from the individual histograms was merged into a single histogram . This combined histogram represented the distribution of data values across all the pixels . By merging the data in this way, a comprehensive overview of the information from all the pixels could be provided, while also ensuring that this information was accurately aligned and comparable .

This approach, while ef fective , was not without its limitations . The post-processing step could be computationally intensive , particularly for systems with a large number of pixels . Furthermore , the accuracy of the compensation depended on the precision of the gain and of fset adj ustments , which could be af fected by noise or other sources of error .

SUMMARY

Therefore , there exists a need for a system for time-of- flight measurement , a method for time-of- f light measurement and a sensor for time-of- f light measurement that allows to convert compensate for skew between the channels and provides a signi ficantly simpli fied data processing in one histogram .

These and other problems are solved by the subj ect matter of the attached independent claims .

DETAILED DESCRIPTION

The above obj ects of the invention are achieved by a system for time-of- f light measurement , a method for for a time-of- flight measurement , and a sensor for time-of- f light measurement according to the annexed claims .

Preferred embodiments may be taken from the dependent claims , and, beyond that , from the following description, in particular comprising various embodiments as covered and described in the annexed claims .

The skilled person will understand that any embodiment described in the following description is covered and comprised by the subj ect matter covered by the annexed claims .

The embodiments , features and combination of features as described herein in connection with the invention, as well as the combination of features as given in the annexed claims , but also any combination of features as mentioned and described in connection with the embodiments shall be considered as being disclosed herein, at least , however, shall be considered to be derivable by the skilled person .

In particular, each feature and each combination of features in the embodiments as described herein may for example be claimed in a di f ferent combination, in particular di f ferent claim category, at least because the skilled person will recogni ze that each and every combination of the features mentioned herein is suitable for contributing to solving the underlying problem .

Further, each feature and each combination of features in the claims and used in the description below may be used and claimed independently from the respective claimed subj ect matter, independently from claim dependencies and back- references , and independently from the claim category in which the feature is claimed . For example , in an arbitrary combination selected from one or more claims , one or more embodiments as set forth herein below and/or from the annexed figures may be envisaged .

Within the present application, terms such as " lateral" or "laterally" , "rear" , " frontal" , "upper" , " lower" , "bottom" , "opposite" , " inner" , "outer" or the like , as used herein, which de-scribe the position of a first obj ect relative to another obj ect , preferably refer to the relative position of a respective part or obj ect with regard to its position fully mounted for its intended use .

A system for time-of- f light measurement according to the present invention comprises a plurality of Single-Photon Avalanche Diodes ( SPAD) configured to detect photons and generate electrical signals , a plurality of merging modules , wherein each merging module out of the plurality of merging modules is coupled to one or more SPAD ( s ) out of the plurality of SPADs and to a Multiplexer (MUX ) , wherein each merging module is configured to receive the electrical signals from the SPAD, to merge the received electrical signals into a single pixel signal , and to forward the single pixel signal to the MUX, the Multiplexer (MUX ) , which is coupled to the plurality of merging modules and to a plurality of Time-to-Digital Converter ( TDC ) channels , and which is configured to receive the single pixel signal from each merging module and to establish single pixel and TDC channel connections , and to output the respective single pixel signal to the respective TDC channel , and a plurality of Time-to-Digital Converter ( TDC ) channels , each TDC channel being coupled to the MUX and configured to convert the output signal from the MUX to a time value and then to a digital value .

With this , the system has the capability to reduce the skew between channels of a multi-channel Time-to-Digital Converter ( TDC ) . Skew refers to the timing di f ferences that can occur between di f ferent channels . This skew can introduce errors in the time measurements , which can af fect the overall performance of the system .

Furthermore , the system is fit for dynamic element matching for the TDC channels . With this architecture , a compensation of skew between the channels is achieved .

Dynamic Element Matching ( DEM) is a method employed in Time- to-Digital Converters ( TDCs ) to enhance the converter' s performance . A TDC measures the time interval between two events by tallying the number of clock cycles that occur between them . However, discrepancies in the components can lead to measurement errors . DEM mitigates these errors by choosing the usage pattern of the elements , which results in the error from component mismatches mani festing as pseudorandom noise that is not correlated with the input sequence , rather than as nonlinear distortion . In DEM TDCs that use mismatch-scrambling, the noise is white , while in those that use mismatch-shaping, the noise is spectrally shaped . The outcome is that the error due to component discrepancies is dispersed and mani fests as random noise rather than systematic distortion, enhancing the accuracy of the TDC and the overall performance of the dToF system .

Moreover, the data from the TDC channels can be directly stored in a histogram memory . This eliminates the need for a post-processing architecture to compensate for the of fset in di f ferent channels . This signi ficantly simpli fies the data processing architecture as no processor is required .

As the system allows for the merging of data from multiple TDC channels into a single histogram, this can make the data easier to analyse and interpret . In summary, with this architecture , the system provides a comprehensive solution for reducing skew, simpli fying data processing, and merging data from multiple TDC channels .

In a preferred embodiment of the invention, the system is configured to establish connections between the single pixels and the TDC channels for a predetermined period and in a rotating manner, so that each pixel is connected to each TDC channel sequentially in a pixel-to-TDC channel connection .

This can help reduce the impact of variations between di f ferent TDC channels , thereby improving the accuracy of ToF measurements .

In addition, by establishing a connection between each pixel and every channel for a set duration, it guarantees an equal usage of all channels over time . This can result in a more evenly distributed signal intensity across the channels . In a Time of Flight ( ToF) system, this could lead to a more precise and accurate determination of particle flight times .

In a further preferred embodiment of the invention said predetermined period is the same for each pixel-to-TDC channel connection . By ensuring that each pixel is connected to every channel for an equal duration, the possibility of a single pixel monopoli zing a channel is avoided . This can result in a more equitable data distribution across the channels , potentially enhancing the system' s overall ef ficiency3

When the number of SPADs , which are coupled to one matching module may be the same for all merging modules , it is guaranteed that every module processes an equal amount of data . This uni form distribution of data across all merging modules leads to a balanced system where the workload is evenly spread, preventing any single module from being overloaded .

This balance in data handling not only optimi zes the system performance by preventing potential bottlenecks but also makes the system' s performance predictable . Predictability is crucial in system design as it allows for more accurate forecasting of system behaviour under di f ferent operating conditions , which in turn aids in ef ficient resource allocation and system planning .

In another embodiment of the invention, the number of merging modules is equal to the number of TDC channels . This one-to- one correspondence between merging modules and TDC channels can enhance the ef ficiency of data processing and trans fer . This is because each merging module is directly linked to a speci fic TDC channel . As a result , data can be trans ferred smoothly and promptly, improving the overall system performance .

In order to increase the ef fectiveness of the described arrangement , the MUX may be arranged beside or in close vicinity to the SPADs .

The placement of the MUX in close proximity to the SinglePhoton Avalanche Diode ( SPAD) has several advantages . One of the primary benefits is the minimi zation of the distance that signals need to travel . This reduced distance can signi ficantly decrease the signal delay .

A shorter signal path not only speeds up data trans fer but also enhances the overall ef ficiency of the system . Furthermore , this proximity can lead to a reduction in the chance of signal degradation . Signal degradation can occur over longer distances , and by minimi zing this distance , the integrity of the signal can be preserved .

Another advantage of this close placement is the reduction of potential interference . Interference can distort the signal , but a shorter path can lessen this risk . Lastly, having the MUX near or beside the SPAD contributes to a more compact and ef ficient system design . This compactness is particularly beneficial in applications where space is a constraint , allowing for optimal use of available space .

In a further preferred embodiment of the invention, the merging modules comprise at least one NAND or/and at least one NOR gate . NAND and NOR gates have the ability to implement any Boolean function . This characteristic grants a high degree of flexibility in the logic that can be incorporated into the merging modules .

The use of these universal gates can lead to a more streamlined circuit design . This is because they often require fewer components than other types of gates , simpli fying the overall system architecture .

Furthermore , NAND and NOR gates can enhance the system' s ef ficiency . They are capable of executing complex logic operations swi ftly, minimi zing delay .

Integrating a reference Single-Photon Avalanche Diode ( SPAD) array into a system provides numerous benefits , notably its role in system calibration . Calibration is vital in any measurement system to ensure data accuracy and reliability . Therefore , in a further preferred embodiment of the invention, the system further comprises a reference SPAD array, reference merging modules coupled to the SPADs of the reference SPAD array, and reference TDC channels .

The reference SPAD array acts as a benchmark for calibrating other system components . By comparing the system' s output with the known values from the reference SPAD array, discrepancies can be identi fied and corrected, ensuring accurate and reliable measurements .

Additionally, the reference SPAD array can help identi fy and correct potential error sources within the system, such as noise , signal interference , or performance variations among individual SPADs . Regular calibration using the reference SPAD array can identi fy and correct these issues , preventing them from impacting the system' s measurement accuracy .

In a preferred embodiment of the invention, the reference merging modules are coupled to the MUX, which is configured to receive the reference single pixel signal from each reference merging module and to establish reference single pixel and reference TDC channel connections and to output the respective reference single pixel signal to the respective reference TDC channel , wherein the system is configured to establish connections between the reference single pixels and the reference TDC channels for a predetermined period and in a rotating manner inbetween the reference single pixels and the reference TDC channels only, so that each reference pixel is connected to each reference TDC channel sequentially in pixel-to-TDC channel connection .

Similar to the advantage of having the ability to rotate connections in the main system, this configuration ensures that each reference channel is used equally over time , leading to a balanced distribution of data across the channels .

The above-described problems are also advantageously solved by a method for time-to-digital conversion of multiple single-photon avalanche diode ( SPAD) signals , wherein the method comprises the steps of providing a plurality of Single-Photon Avalanche Diodes ( SPAD) configured to detect photons and generate electrical signals , of the SPADs generating electrical signals , of providing a plurality of merging modules , wherein each merging module out of the plurality of merging modules is coupled to one or more SPAD ( s ) out of the plurality of SPADs and to a Multiplexer (MUX ) , wherein each merging module is configured to receive the electrical signals from the SPAD, to merge the received electrical signals into a single pixel signal , and to forward the single pixel signal to the MUX, of sending the electrical signals from the SPADs to the merging modules , of the merging modules merging the electrical signals into a single pixel signal , of providing the Multiplexer (MUX ) , which is coupled to the plurality of merging modules and to a plurality of Time-to- Digital Converter ( TDC ) channels , and which is configured to receive the single pixel signal from each merging module and to establish single pixel and TDC channel connections , and to output the respective single pixel signal to the respective TDC channel , of providing a plurality of Time-to-Digital Converter ( TDC ) channels , each TDC channel being coupled to the MUX and configured to convert the output signal from the MUX to a time value and then to a digital value , of forwarding the single pixel signal to the MUX, of the MUX establishing single pixel and TDC channel connections , of the MUX outputting the respective single pixel signal to the respective TDC channel , and of the TDC channels converting the output signal from the MUX to a time value and then to a digital value .

The method employs a technique known as dynamic element matching for the TDC channels . This technique allows for the compensation of skew between the channels . By dynamically adjusting the elements in the system, it can average out these mismatches over time, improving the overall performance of the system. Besides that, it can randomize mismatches.

This randomization process disperses the error throughout the system. As a result, the error manifests as random noise instead of systematic distortion.

Moreover, the data from the TDC channels can be directly stored in a histogram memory. This eliminates the need for a post-processing step to compensate for the offset in different channels. This significantly simplifies the data processing as no processor is required.

Furthermore, the system allows for the merging of data from multiple TDC channels into a single histogram. This can make the data easier to analyse and interpret. In summary, the system provides a comprehensive solution for reducing skew, simplifying data processing, and merging data from multiple TDC channels.

In a further preferred embodiment, the method for a time-of- flight measurement further comprises the step of establishing connections between the single pixels and the TDC channels for a predetermined period and in a rotating manner, so that each pixel is connected to each TDC channel sequentially in a pixel-to-TDC channel connection.

This approach offers a number of benefits, e.g. that it guarantees equal usage of all channels over time. This leads to a balanced dispersion of data across the channels, ensuring no single channel is overloaded. As a result, the load is evenly spread across all channels. Consequently, this can enhance the overall performance of the system.

Furthermore, in a preferred embodiment of the invention, in the method for a time-of-f light measurement, said predetermined period is the same for each pixel-to-TDC channel connection. This equal access results in a balanced dispersion of data across all channels .

Furthermore , this setup aids in minimi zing potential bias in the measurements . This is because each pixel is given an equal chance to contribute to the data that each channel collects . Lastly, by evenly distributing the load across all channels , the overall performance of the system can be signi ficantly enhanced .

In a further preferred embodiment of the invention, the step of establishing connections between the single pixels and the TDC channels in a rotating manner is controlled by a one-hot encoder .

One signi ficant benefit of using a one-hot encoder to control the rotating connections between the single pixels and the TDC channels is the substantial enhancement in data processing ef ficiency and accuracy . The one-hot encoding method ensures that at any given moment , only one connection is active . This unique feature of one-hot encoding helps to minimi ze signal interference , thereby boosting the precision of the measurements . Furthermore , the simplicity of one-hot encoding lies in its control logic, where j ust a single line is active at any time . This simplicity aids in making the system design and debugging processes more straightforward .

Furthermore , this setup simpli fies the control logic of the Multiplexer (MUX ) . This simplicity makes the system more straightforward to design and implement . Additionally, it eases the process of troubleshooting, should any issues arise .

Furthermore , in a further preferred embodiment of the invention, the method for a time-of- f light measurement further comprises the step of conducting Dynamic Element Matching on bins of the same system . The application of Dynamic Element Matching ( DEM) can also aid in minimi zing discrepancies between the Time to Digital Converter ( TDC ) channels and the bins . This reduction in mismatches is a signi ficant factor that contributes to the accuracy of the measurements . As a result , the data obtained are more reliable and precise .

Additionally, the system then has a high level of robustness . It is capable of withstanding variations in environmental conditions or component characteristics . This robustness ensures the system' s reliability and consistent performance , even under changing conditions .

It shall be noted that the steps given above do not necessarily have to be carried out in the given order . The provided steps may be carried out in any other suitable order .

However, the order as given above may apply for particular variants of the method .

It will be immediately acknowledged by a person skilled in the art that a feature , embodiment , ef fect , or advantage described herein in connection with the inventive system, may also be a feature , embodiment , ef fect or advantage of the inventive method or sensor, respectively, and vice versa .

The above-described problems are also advantageously solved by a sensor for time-of- f light measurement , the sensor comprising a plurality of Single-Photon Avalanche Diodes ( SPAD) configured to detect photons and generate electrical signals , a plurality of merging modules , wherein each merging module out of the plurality of merging modules is coupled to one or more SPAD ( s ) out of the plurality of SPADs and to a Multiplexer (MUX ) , wherein each merging module is configured to receive the electrical signals from the SPAD, to merge the received electrical signals into a single pixel signal , and to forward the single pixel signal to the MUX, the Multiplexer (MUX ) , which is coupled to the plurality of merging modules and to a plurality of Time-to-Digital Converter ( TDC ) channels , and which is configured to receive the single pixel signal from each merging module and to establish single pixel and TDC channel connections , and to output the respective single pixel signal to the respective TDC channel , and a plurality of Time-to-Digital Converter ( TDC ) channels , each TDC channel being coupled to the MUX and configured to convert the output signal from the MUX to a time value and then to a digital value .

It is understood by a person skilled in the art , that the advantages presented with the system for time-of- f light measurement equally apply to the sensor for time-of- f light measurement .

Thereby, the present invention is particularly useful , when applying dToF sensors in mobile devices , such as mobile phones , tablets , AR / VR glasses , or the like . In general , the present invention can be advantageously applied in proximity sensing, enhanced autofocus , 3D imaging, LiDAR, and other applications in the field .

BRIEF DESCRIPTION OF THE DRAWINGS

Expedient embodiments are now described with reference to the accompanying drawings , which show in

FIG . 1 an architecture of a system for time-of- flight measurement ,

FIG . 2 an example of 16 merging modules and a MUX with a respective muxing logic,

FIGs . 3a and 3b a rotation scheme for the muxing logic . In FIG . 1 , a system for time-of- f light measurement 1 is shown . Single photon avalanche diodes ( SPAD) are depicted with reference numeral 2 and are configured to detect photons and generate electrical signals .

A Single-Photon Avalanche Diode ( SPAD) 2 is a photodetector that has the ability to detect extremely low light levels , even down to the detection of individual photons . When a photon interacts with the SPAD 2 , it initiates an electron avalanche , resulting in a current pulse that can be measured . This pulse is useful in determining the time of arrival of the photon, thanks to the rapid build-up of the avalanche and the low timing j itter of the device .

In the embodiment shown in FIG . 1 several SPADs 2 are grouped together and are connected to a merging module 4 . Altogether, in FIG . 1 , four merging modules 4 are depicted .

The primary function of a merging module 4 is to take signals from various SPADs 2 and consolidate them into one single pixel . This consolidation process is particularly important because it contributes to the miniaturi zation of SPAD 2 pixels .

Each of those merging modules 4 is therefore connected to one or more SPADs and to a multiplexer MUX 6 . The number of SPADs 2 , which are coupled to one merging module 4 is the same for all merging modules 4 in this speci fic embodiment but can as well be di f ferent .

The Multiplexer (MUX ) 6 is designed to handle multiple input signals , which in this case , are from individual pixels from the merging modules 4 . Each pixel can be considered as an independent input source for the MUX 6 . The MUX 6 operates by selecting a speci fic pixel based on the control signals . Once a pixel is selected, the MUX 6 forwards the signal from this pixel into a single line . This single line is then connected to a respective Time-to-Digital Converter ( TDC ) channel 8 .

The TDC channel 8 is responsible for further processing of the signal. In essence, the MUX 6 acts as a bridge, connecting individual pixels to respective TDC channels 8.

Therefore, each merging module 4 is further configured to receive the electrical signals from the SPAD 2, merge the received electrical signals into a single pixel signal and forward the single pixel signal to the MUX 6.

The MUX 6 is coupled to the plurality of merging modules 4 and to a plurality of Time-to-Digital Converter (TDC) channels 8. As described above, it is configured to receive the single pixel signal from each merging module 4 and to establish single pixel and TDC channel 8 connections, and to output the respective single pixel signal to the respective TDC channel 8.

In FIG. 1, a plurality of time-to-digital converter (TDC) channels 8 is depicted. In the case of the embodiment of FIG. 1, there are four channels depicted, as well as 4 merging modules 4. In this specific embodiment of the invention, the number of merging modules 4 is equal to the number of TDC channels 8, but this number can as well differ.

Each TDC channel 8 is coupled to the MUX 6 and configured to convert the output signal from the MUX 6 to a time value and further to a digital value.

Time-to-Digital Converter (TDC) channels 8 operate by gauging the time interval between the initiation of a signal and its subsequent return after bouncing off an object. This time difference is employed to compute the distance between the signal source and the object. The process involves the emission of a signal, which travels, hits an object, and then returns .

The TDC channels 8 usually utilize a specific technique known as a tapped delay line (TDL) for the precise timestamping of the incoming signal. The TDL helps in capturing the exact time of the incoming signal. This timestamp information is then used to construct a histogram for each individual channel. The histogram is subsequently processed to derive the range information, which provides the distance measurement.

In FIG. 2 an example of 16 merging modules 4 and the MUX 6 with the respective muxing logic is depicted.

The merging modules 4 comprise at least one NAND or/and at least one NOR gate and in this specific embodiment three NAND gates 22 and one NOR gate 24 each.

A NAND gate, also known as a NOT-AND gate, functions as an AND gate followed by a NOT gate. It has multiple inputs and a single output. The output is '1' or true if any of the inputs are 'O' or false. Conversely, a NAND gate only outputs 'O' or false if all its inputs are '1' or true.

Conversely, a NOR gate, or NOT-OR gate, functions as an OR gate followed by a NOT gate. Like a NAND gate, a NOR gate also has multiple inputs and a single output. However, the output is '1' or true only if all the inputs are 'O' or false. A NOR gate outputs 'O' or false if any of its inputs are '1' or true.

A MUX 6 is a type of combinational logic circuit. Its primary function is to use control signals to select one of its many inputs and connect it to its output (s) . This operation is commonly referred to as muxing.

Therefore, the core of a MUX 6 is its muxing logic. This logic is responsible for the selection process that determines which input gets connected to the output (s) . The muxing logic receives information on a single line and then transmits that information on one of the possible output lines . In conclusion, the muxing logic in a MUX 6 controls the selection and routing of input signals to the outputs 12. This selection and routing are based on the state of the control signals.

The MUX 6 is arranged beside or in close vicinity to the SPADs 2, this is done to increase the effectiveness of the described setting and process and to compensate delay errors introduced by the (long) interconnect from SPADs 2 to the TDC channels 8.

An example of a MUX for a 16 TDC channel system is shown in the embodiment of FIG. 2. The output of 9 SPADs is combined to one pixel by a 9 to 1 compression tree in each of the merging modules 4. The compression tree is based on NAND 22 and NOR 24 gates acting as a logic 9 to 1 OR gate.

The muxing logic is connected to the 16 outputs 10 of the SPAD array and 16 enable signals. The 16 enable signals are controlled by a one-hot code and rotate the Pixel to TDC mapping .

The system uses a one-hot code to control the 16 enable signals. In a one-hot code, only one bit is "on" or "hot" at any given time. This code determines which of the 16 enable signals is active, and consequently, which output 10 of the SPAD array is selected.

In FIG. 3a a muxing logic is depicted. As shown in the figure, the selection signal 0, 1, 2 and 3 generated by the Mux 6 is defining the mapping of pixel to TDC channel. When the selection signal is 0, Pixel D is connected to channel I, Pixel C to channel II, Pixel B to channel III and Pixel A to channel IV. When changing the selection signal to 1, Pixel C is connected to channel 1, Pixel B to channel II, pixel A to channel III and pixel D to channel IV etc. When going through all settings , each of the pixels becomes connected to each of the channels for some time . As a result the overall skew is averaged out . In fact the individual skew is converted to j itter .

In a multi-channel system, each channel might experience a unique delay, resulting in a timing di f ference known as skew . The system is engineered to average out this skew, meaning it reduces the impact of these individual timing di f ferences over a period of time or across multiple data samples .

On the other hand, j itter is a term used to describe the fluctuation in the timing of a series of data packets or signals . The system can minimi ze skew, but it does not eliminate it completely but rather trans forms it into j itter .

In FIG . 3b an example of such a rotation scheme is shown . In order to average out mismatch, each Pixel to TDC channel combination need to be selected and an integration has to be applied for the same amount of time . 14 is the start of the frame , whereas 16 is the end of the frame and 18 is a VCSEL CLK signal and 20 the selection signal .

With this , connections between the single pixels and the TDC channels 8 are established for a predetermined period and in a rotating manner, so that each pixel is connected to each TDC channel 8 sequentially in a pixel-to-TDC channel connection .

Said predetermined period is the same for each pixel-to-TDC channel connection in this speci fic embodiment , but might as well be di f ferent for some or each pixel-to-TDC channel connection .

All delay errors introduced by the MUX 6 , interconnect , interconnect logic gates and channel to channel skew are compensated by rotating the pixel to channel interconnect as shown in FIG . 3a and 3b . Furthermore , the system for time-of- f light measurement according to the invention can comprise a reference SPAD array and reference merging modules coupled to the SPADs of the reference SPAD array, and reference TDC channels ( all not depicted in the Figures ) .

The reference merging modules are coupled to the MUX 6 , which is configured to receive the reference single pixel signal from each reference merging module and to establish reference single pixel and reference TDC channel connections and to output the respective reference single pixel signal to the respective reference TDC channel .

Furthermore , the connections between the reference single pixels and the reference TDC channels are established for a predetermined period and in a rotating manner in between the reference single pixels and the reference TDC channels only, so that each reference pixel is connected to each reference TDC channel sequentially in pixel-to-TDC channel connection .

An example of the implementation might comprise the TDC channels being connected to the main SPAD array and looking to the scene and the reference TDC channels being connected to the reference SPAD array, which is located close to a VCSEL ( all not depicted in the Figures ) .

The rotation scheme is applied independently to the main and reference channels in a way that each pixel to channel selection is applied for exactly the same amount of time ( e . g . 1000 VCSEL pulses ) .

In order to increase the ef fectiveness of dynamic element matching of TDC channels , the MUX 6 has to be implemented as close as possible to the SPAD array in order to compensate delay errors introduced by the interconnect from SPAD to the TDC .

Such a time-of- f light measurement could comprise the steps of the SPADs generating electrical signals , of sending the electrical signals from the SPADs to the merging modules , of the merging modules merging the electrical signals into a single pixel signal , of forwarding the single pixel signal to the MUX, of the MUX establishing single pixel and TDC channel connections , of the MUX outputting the respective single pixel signal to the respective TDC channel , and of the TDC channels converting the output signal from the MUX to a time value and then to a digital value . Furthermore , a step of establishing connections between the single pixels and the TDC channels for a predetermined period and in a rotating manner, which is controlled by a one-hot encoder, and wherein said predetermined period is the same for each pixel-to-TDC channel connection, so that each pixel is connected to each TDC channel sequentially in a pixel-to- TDC channel connection, can also be comprised, as well as a step of conducting Dynamic Element Matching on bins of the same system .

Claims

1. A system for time-of-f light measurement (1) , comprising: a plurality of Single-Photon Avalanche Diodes (SPAD) (2) configured to detect photons and generate electrical signals, a plurality of merging modules (4) , wherein each merging module out of the plurality of merging modules (4) is coupled to one or more SPAD(s) (2) out of the plurality of SPADs (2) and to a Multiplexer (MUX) (6) , wherein each merging module (4) is configured to:

- receive the electrical signals from the SPAD (2) ,

-merge the received electrical signals into a single pixel signal, and

- forward the single pixel signal to the MUX (6) , the Multiplexer (MUX) (6) , which is coupled to the plurality of merging modules (4) and to a plurality of Time-to-Digital Converter (TDC) channels (8) , and which is configured to receive the single pixel signal from each merging module (4) and to establish single pixel and TDC channel connections, and to output the respective single pixel signal to the respective TDC channel, and a plurality of Time-to-Digital Converter (TDC) channels (8) , each TDC channel (8) being coupled to the MUX (6) and configured to convert the output signal from the MUX (6) to a time value and then to a digital value.

2. The system for time-of-f light measurement (1) according to claim 1, wherein the system is configured to establish connections between the single pixels and the TDC channels (8) for a predetermined period and in a rotating manner, so that each pixel is connected to each TDC channel (8) sequentially in a pixel-to-TDC channel connection.

3. The system for time-of-f light measurement (1) according to claim 2, wherein said predetermined period is the same for each pixel-to-TDC channel (8) connection.

4. The system for time-of-f light measurement (1) according to any of the preceding claims, wherein the number of SPADs (2) , which are coupled to one merging module (4) is the same for all merging modules ( 4 ) .

5. The system for time-of-f light measurement (1) according to any of the preceding claims, wherein the number of merging modules (4) is equal to the number of TDC channels (8) .

6. The system for time-of-f light measurement (1) according to any of the preceding claims, wherein the MUX (6) is arranged beside or in close vicinity to the SPADs (2) .

7. The system for time-of-f light measurement (1) according to any of the preceding claims, wherein the merging modules (4) comprise at least one NAND (22) or/and at least one NOR (24) gate.

8. The system for time-of-f light measurement (1) according to any one of the preceding claims, further comprising a reference SPAD array, reference merging modules coupled to the SPADs of the reference SPAD array, and reference TDC channels.

9. The system for time-of-f light measurement (1) according to claim 8, wherein the reference merging modules are coupled to the MUX (6) , which is configured to receive the reference single pixel signal from each reference merging module and to establish reference single pixel and reference TDC channel connections and to output the respective reference single pixel signal to the respective reference TDC channel, wherein the system is configured to establish connections between the reference single pixels and the reference TDC channels for a predetermined period and in a rotating manner in between the reference single pixels and the reference TDC channels only, so that each reference pixel is connected to each reference TDC channel sequentially in pixel-to-TDC channel connection.

10. A method for a time-of-f light measurement, the method comprising the following steps: of providing a plurality of Single-Photon Avalanche Diodes (SPAD) (2) configured to detect photons and generate electrical signals, of the SPADs (2) generating electrical signals, of providing a plurality of merging modules (4) , wherein each merging module (4) out of the plurality of merging modules (4) is coupled to one or more SPAD(s) (2) out of the plurality of SPADs (2) and to a Multiplexer (MUX) (6) , wherein each merging module (4) is configured to:

- receive the electrical signals from the SPAD (2) ,

-merge the received electrical signals into a single pixel signal, and

- forward the single pixel signal to the MUX (6) , of sending the electrical signals from the SPADs (2) to the merging modules (4) , of the merging modules (4) merging the electrical signals into a single pixel signal, of providing the Multiplexer (MUX) (6) , which is coupled to the plurality of merging modules (4) and to a plurality of Time-to-Digital Converter (TDC) channels (8) , and which is configured to receive the single pixel signal from each merging module (4) and to establish single pixel and TDC channel (8) connections, and to output the respective single pixel signal to the respective TDC channel (8) , of providing a plurality of Time-to-Digital Converter (TDC) channels (8) , each TDC channel (8) being coupled to the MUX (6) and configured to convert the output signal from the MUX (6) to a time value and then to a digital value, of forwarding the single pixel signal to the MUX (6) , of the MUX (6) establishing single pixel and TDC channel (8) connections, of the MUX (6) outputting the respective single pixel signal to the respective TDC channel (8) , and of the TDC channels (8) converting the output signal from the MUX (6) to a time value and then to a digital value.

11. The method for a time-of-f light measurement according to claim 10, further comprising the following step: of establishing connections between the single pixels and the TDC channels (8) for a predetermined period and in a rotating manner, so that each pixel is connected to each TDC channel (8) sequentially in a pixel-to-TDC channel (8) connection.

12. The method for a time-of-f light measurement according to claim 11, wherein said predetermined period is the same for each pixel-to-TDC channel (8) connection.

13. The method for time-of-f light measurement according to any one of claims 10 to 12, wherein the step of establishing connections between the single pixels and the TDC channels (8) in a rotating manner is controlled by a one-hot encoder.

14. The method for a time-of-f light measurement according to any one of claims 10 to 13, further comprising the following step: of conducting Dynamic Element Matching on bins of the same system.

15. A sensor for time-of-f light measurement, the sensor comprising : a plurality of Single-Photon Avalanche Diodes (SPAD) (2) configured to detect photons and generate electrical signals, a plurality of merging modules (4) , wherein each merging module (4) out of the plurality of merging modules (4) is coupled to one or more SPAD(s) (2) out of the plurality of SPADs (2) and to a Multiplexer (MUX) (6) , wherein each merging module (4) is configured to:

- receive the electrical signals from the SPAD (2) , -merge the received electrical signals into a single pixel signal, and

- forward the single pixel signal to the MUX (6) , the Multiplexer (MUX) (6) , which is coupled to the plurality of merging modules (4) and to a plurality of Time-to-Digital Converter (TDC) channels (8) , and which is configured to receive the single pixel signal from each merging module (4) and to establish single pixel and TDC channel (8) connections, and to output the respective single pixel signal to the respective TDC channel (8) , and a plurality of Time-to-Digital Converter (TDC) channels (8) , each TDC channel (8) being coupled to the MUX (6) and configured to convert the output signal from the MUX (6) to a time value and then to a digital value.