Operating method of an acquisition module for a motor vehicle detection light system.

Abstract

A method for operating an acquisition module (39) comprising an arrangement of photodetectors (32), each comprising a set of photodiodes (321) capable of detecting photons from a scene (S), a data transmission bus (B), and a processing unit (4). The method comprises, for each photodetector, iterations of the following steps at different times, in particular at different times separated by a regular time interval: - a first step of determining a first number of photodiodes (321) that have detected one or more photons for a predetermined duration; - a second step of determining a second number by subtracting a third number from the first number in order to limit the flow of data processed downstream of the acquisition module (39); and - a step of transmitting the second number to the processing unit by means of the data transmission bus. Figure for the abstract: Fig. 1

Description

Title of the invention: Method of operation of an acquisition module for a vehicle detection light system.

[0001] The present invention relates to a method of operating an acquisition module for a motor vehicle detection lighting system. The invention also relates to an acquisition module for a motor vehicle detection lighting system. The invention also relates to a detection lighting system for a motor vehicle. The invention further relates to a lighting device, in particular a headlight, comprising such a detection lighting system and / or such an acquisition module. Finally, the invention also relates to a motor vehicle equipped with such a detection lighting system.

[0002] In order to improve the autonomous behavior of a motor vehicle, in particular cars, the number of sensors that equip said motor vehicle increases.

[0003] Various driver assistance lighting systems for motor vehicles are known in the prior art. Some of these driver assistance lighting systems take the form of optical sensor arrangements. These arrangements generally include one or more sensor lighting devices such as scanning lidar sensors. Such a sensor lighting device makes it possible to monitor an area surrounding the motor vehicle and, for example, to detect objects in the surrounding area and provide a driver assistance system with information about the detected object, such as the distance between the object and the motor vehicle or the object's geometric dimensions.

[0004] In the case of scanning lidar sensors, an infrared laser beam is emitted onto a deflection device, for example a reflecting mirror, and reflected by the deflection device into the surrounding area. The deflection device is generally movably mounted around an axis of rotation and can be driven by a means to rotate about said axis of rotation. The laser beam is thus deflected by a deflection angle at predefined scan steps or scan times, and the surrounding area is thus scanned in a given direction.

[0005] The laser beam reflected by the object in the surrounding area is then detected by a receiving device of the light detection device comprising an optical sensor.

[0006] These devices are nevertheless complex and bulky. Furthermore, they must be positioned strategically on the vehicle for effective observation. the environment. Their integration into a motor vehicle is therefore generally delicate. Moreover, the digital signals provided by these light detection systems can, in some cases, provide a false perception of the environment, which can endanger vehicle users.

[0007] To address these problems, it has been conceived to implement a similar alternative or complementary system using visible light instead of laser radiation. However, this alternative system solution presents a computing resource problem. Indeed, particularly in very bright environments, a large amount of data is generated. Therefore, substantial hardware resources are required to process all this data.

[0008] The object of the invention is to provide a method for operating an acquisition module that addresses the problems mentioned above and improves upon known acquisition modules. In particular, the invention proposes a method for operating an acquisition module that reduces the need for hardware computing and memory resources.

[0009] According to the invention, the method governs the operation of an acquisition module comprising an arrangement of photodetectors, each comprising a set of photodiodes capable of detecting photons from a scene, a data transmission bus, and a processing unit. The method comprises, for each of the photodetectors, iterations of the following steps at different times, in particular at different times separated by a regular time interval: - a first step of determining an initial number of photodiodes that have detected one or more photons for a predetermined duration, and - a second step of determining a second number by subtracting a third number from the first number in order to limit the flow of data processed downstream of the acquisition module, and - a step of transmitting the second number to the processing unit by means of the data transmission bus.

[0010] The second step may include a substep of calculating the third number as an average, in particular an equally weighted or unweighted average, of the first n numbers determined during the previous n first steps, with n a natural number, in particular n=3 or n=4 or n=5.

[0011] The second step may include a sub-step of calculating the third number as a minimum of the first n numbers determined during the previous n first steps, with n a natural number, in particular n=3 or n=4 or n=5.

[0012] The n previous first steps of determining the first n numbers can be implemented while the light emission module is inactive.

[0013] Each iteration may include a third step, before the transmission step of the second number to the arithmetic unit, the third step being a transformation step from a first P-bit encoding of the second number to a second M-bit encoding of the second number, with M <P, par exemple P=5 ou P=6 ou P=7 ou P=8 et M=3 ou M=4.

[0014] The third transformation step may include saturation, for example the transformation of the first coding into a second coding, comprising: - all bits set to the value "1", if one of the most significant PM bits in the first encoding contains at least one "1", and - all bits to the value "0", if the second number is negative, and - the values ​​of the M least significant bits of the first encoding.

[0015] The second step of determining the second number by subtracting the third number from the first number can be carried out by transforming the P-bit binary encoding of the first number by removing its PM least significant bits to obtain the M-bit binary encoding of the second number, with M <P, par exemple P=5 ou P=6 ou P=7 ou P=8 et M=3 ou M=4.

[0016] The first step in determining the first number may include an analog count or a digital count.

[0017] The regular time interval can be on the order of a nanosecond or on the order of 10 nanoseconds.

[0018] According to the invention, the acquisition module comprises hardware elements designed to implement the process defined above.

[0019] According to the invention, the light detection system comprises an acquisition module defined above, a control module and a light emission module, said control module being configured to determine a sequence of data to be emitted, said emission module being capable of providing emitted light in the form of a train of light pulses corresponding to the data sequence, the calculation unit of the acquisition module being configured to determine, by correlation operations between the data sequence and photon detection data comprising the second number, a time corresponding to a time of flight of the light emitted from the emission module to an object illuminated by the emitted light, and a time of flight of the emitted light, reflected by the object, to the acquisition module.

[0020] According to the invention, the lighting device comprises a previously defined lighting detection system and / or a previously defined acquisition module.

[0021] According to the invention, the motor vehicle, in particular the autonomous motor vehicle, comprises an acquisition module defined previously and / or a light detection system defined previously and / or a light device defined previously.

[0022] Fig. 1 schematically illustrates an embodiment of a motor vehicle according to the invention comprising a light device according to an embodiment of the invention comprising a light detection system according to an embodiment of the invention comprising an acquisition module according to an embodiment of the invention.

[0023] Fig. 2 schematically represents a pulse train emitted by a light detection system according to one embodiment of the invention.

[0024] Fig. 3 schematically represents a pulse train received by a light detection system according to an embodiment of the invention.

[0025] Fig. 4 schematically represents the obtaining of correlation values ​​by the light detection system according to an embodiment of the invention.

[0026] Figure 5 schematically illustrates an acquisition module according to one embodiment of the invention.

[0027] Fig. 6 schematically illustrates a time diagram of a signal obtained at the output of a summing circuit of an acquisition module according to an embodiment of the invention.

[0028] Fig. 7 schematically illustrates a time diagram of a signal obtained at the output of a calculation circuit for an average of an acquisition module according to an embodiment of the invention.

[0029] Fig. 8 schematically illustrates a time diagram of a signal obtained at the output of a subtractor circuit of an acquisition module according to an embodiment of the invention.

[0030] Figure 9 schematically illustrates a time diagram of a signal obtained at the output of an acquisition module according to an embodiment of the invention.

[0031] In the automotive field, it is known to use a pulsed light beam emitted by a light module of a vehicle's headlight system to perform a given photometric function. Conventionally, the light source emitting this beam is controlled by a pulse-width modulated (PWM) electrical signal. The light source is thus periodically switched on and off by this PWM signal, so that the emitted light beam consists of successive light pulses occurring at a frequency high enough that the human eye cannot distinguish them. The intensity of the emitted light beam is a function of the duty cycle of this PWM signal, making it possible to control it by adjusting this duty cycle and thus achieve a photometric signaling or lighting function, such as a daytime running light, a low beam, or a high beam.Various functions can be implemented by this type of lighting module.

[0032] According to the embodiment of the invention, such a lighting system is also used to fulfill a second telemetry function, thus enabling the formation of a light detection system. Indeed, the light source of the light module can be controlled so that the pulses of the emitted light beam carry a data sequence. The light detection system is further equipped with a receiver module to receive a reflected beam of the emitted light beam, the reflection occurring on an object O in a scene S in the vicinity of the vehicle. A computing unit of the motor vehicle can then, after detecting the data sequence in the received reflected beam, determine the time of flight of the light beam and thus evaluate the distance separating the vehicle from the object. The invention proposes an optimized light detection system using this detection principle

[0033] . Figure 1 shows in detail a light detection system 1 for a motor vehicle according to an embodiment of the invention.

[0034] The light detection system 1 comprises: - a control module 19 configured to determine a sequence of data to be transmitted, - a light emission module 2 arranged to emit a light beam Fl, and an acquisition module 39. Acquisition module 39 includes: - a receiving module 3 intended to receive a light beam F2, in particular a light beam reflected by an object O positioned for example at the front of a motor vehicle, in order to detect this object O, - a data transmission bus (B), and - a calculation unit (4). The receiving module 3 includes an arrangement of photodetectors 32, each comprising a set of photodiodes 32) capable of detecting photons from a scene S.

[0035] In the embodiment, the transmission module 2 and the reception module 3 are arranged in the same lighting and / or signaling device, such as a front headlight of a motor vehicle, the detection light system being thus combined with a lighting and / or signaling device, such as a front headlight intended for the function of lighting at the front of a motor vehicle, which is advantageous in terms of size.

[0036] The lighting and / or signaling device thus combines the two functions: - traditional lighting and / or signaling on the one hand, and - object detection, on the other hand. Alternatively, the light detection system according to the embodiment of the invention could naturally be separate from the lighting and / or signaling system of the motor vehicle. Furthermore, the transmitting module 2 and the receiving module 3 could then be arranged in different locations within the motor vehicle.

[0037] According to the embodiment, the emission module 2 comprises a light module 21 and a modulation unit 22. The light module 2 is arranged so that the light beam Fl it emits has an electromagnetic spectrum, at least a portion of which lies within the visible spectrum. For the purpose of fulfilling the rangefinding function of the invention, this visible spectrum may include an intensity peak PI, or line, in the blue at 450 nm. This is advantageous because natural light generally exhibits a minimum of light in this blue spectrum, thus minimizing its impact, which represents noise in the system of the invention. Alternatively, the spectrum of the light beam Fl may have other intensity peaks in the visible and / or infrared ranges.

[0038] In order to emit this light beam Fl, the light module 21 comprises a light source 23, capable of emitting light rays, and an optical unit 24 arranged to project these light rays to form the light beam Fl. By way of example, the optical unit 24 may indifferently comprise one or more reflectors, one or more lenses, one or more diaphragms or one or more collimators or a combination of several of these optical elements.

[0039] The light source 23 comprises, for example, a semiconductor generator (not shown). This light source 23 simultaneously emits blue and yellow light beams when electrically powered, the light thus formed appearing white to the human eye. Only the blue portion of the spectrum will, for example, be used for the rangefinding function according to the embodiment of the invention, the yellow portion serving as a complement to fulfill the second lighting and / or signaling function, which is optional according to the invention as mentioned above.

[0040] The receiving module 3 comprises an optical unit 31, downstream of which are provided a plurality or arrangement of photodetectors 32. Each photodetector 32 forms a pixel. The receiving module 3 also includes a demodulation unit 33 connected to each photodetector. The light beam F2 received by the receiving module 3 is thus focused by the optical unit 31 onto one or more of the photodetectors 32. The photodetectors are preferably identical and each is formed by several photodiodes, for example at least 4 photodiodes, typically fewer than 100 photodiodes, typically about 15 photodiodes. The photodiodes are single-photon avalanche photomultiplier diodes (SPADs). These photodiodes are arranged in a matrix. The photodiodes of the same photodetector can be electrically connected in parallel.

[0041] The arrangement of photodetectors can be in the form of an array of less than 100 photodetectors, typically around 1,000 to 100,000 photodetectors. It should be noted that the dimensions of the photodetectors 32 are on the order of a micrometer in one embodiment. The assembly thus forms a sensor whose spatial reception resolution, according to one embodiment of the invention, is on the order of 1°, or even 0.1°, and whose detection capabilities, due to the use of avalanche photodiodes, are particularly high, even under degraded acquisition conditions. The receiving module 3 may further include a filter disposed upstream of the photodetector arrangement, the filter having a bandwidth configured to allow the transmission of the spectrum corresponding to the pulse trains of the emitted light beam, in particular blue light, according to the embodiment.

[0042] The light detection system 1 further includes a computing unit 4, connected by means of communication to the transmission module 2 and the reception module 3, this computing unit being configured to implement a method of detecting an object, which can be integrated into a driving assistance method for a motor vehicle, in particular semi-autonomous, or even autonomous.

[0043] The light detection system 1 comprises all the hardware and / or software means for implementing the method according to the invention. Advantageously: - Control module 19 is configured to determine a sequence of data to be transmitted, - the emission module 2 is capable of providing emitted light in the form of a train of light pulses corresponding to the data sequence, and - the computing unit 4 of the acquisition module 39 is configured to determine, by correlation operations between the data sequence and photon detection data including the second number, a time corresponding to a time of flight of the light emitted from the emission module to an object illuminated by the emitted light, and a time of flight of the emitted light, reflected by the object, to the acquisition module 39.

[0044] An execution method of an object detection method or an execution method of an object detection light system will now be described.

[0045] In a first phase, the control module 19, in particular the processing unit 4, generates an initial data sequence Seql. This initial sequence Seql is, in the example described, a binary sequence composed of "0"s and "1"s, pseudo-random. This sequence Seql can be stored in a memory of the processing unit 4. This processing unit 4 can generate such a sequence periodically and continuously (during operation).

[0046] In a second phase, the modulation unit 22 modulates the light beam Fl emitted by the light module 21, from this data sequence Seql, for example by controlling the power supply provided to the light source 23. In this embodiment, the modulation unit 22 includes a generator of a pulse-frequency modulated control signal. This control signal allows control of a switched-mode power supply (not shown) to the light source 23. Conventionally, the frequency setpoint of this control signal, determined by the modulation unit 22, thus allows control of the average electrical power supplied to the light source 23, and therefore control of the luminous intensity of the light beam Fl, so as to satisfy the requirements of the photometric function it performs. More precisely, the modulation unit 22 converts the data sequence Seql into an emitted light beam Fl, composed of pulse trains resulting from the conversion of the data sequence Seql.The pulses follow one another at a sufficiently high variable frequency, for example greater than 10 MHz, specifically between 50 MHz and 100 MHz, so that the human eye can no longer distinguish them. Furthermore, the amplitude, width, and / or position of each pulse, relative to the period, allows for the characterization of a particular sequence of the light beam Fl. According to the described embodiment, each light pulse corresponds to a bit with the value "1" in the modulating sequence Seql, the pulse width corresponding to a chosen pulse duration Tp, which can be predefined, and its light intensity corresponding to a chosen peak power, which can also be predefined. The light beam Fl thus comprises a succession of elementary pulse trains, each train resulting from the conversion of the data sequence Seql.

[0047] The light beam Fl is thus emitted until it reaches the object O, located in the environment of the vehicle, which reflects it towards the receiving module 3. The light beam F2 received by the receiving module 3 is thus composed of a part of the light beam Fl reflected by the object O and noise, for example generated by sources of parasitic light such as urban lighting, car lighting, or even the sun.

[0048] In a third phase, each of the photodetectors 32 of the receiving module 3 converts the portion of the light beam F2 that it receives into an electrical signal Sel, which it transmits to the demodulation unit 33. The demodulation unit can then extract a demodulated data sequence Seq2 from this signal. For example, the demodulation unit 33 can count, from the electrical signal Sel, the number of photons received by a photodetector 32 during a time interval corresponding to a pulse duration Tp, and then determine by thresholding, based on a value determined from the peak power Pp, whether this quantity of photons corresponds to a pulse of the light beam Fl, and therefore to a bit with a value of "1" or a bit with a value of "0". If the number of photons detected by the photodetector is less than one If the number of photons detected by the photodetector exceeds a certain threshold, it is highly probable that these photons originate primarily from ambient light, such as sunlight or light from an artificial light source, such as streetlights. Conversely, if the number of photons detected by the photodetector is greater than a certain threshold, it is more likely that these detected photons originate primarily from the light beam F2 emanating from the emission module 2 and reflected by an object O. The electrical signal Sel is thus transformed into a received demodulated data sequence Seq2.As a note, if the demodulated data sequence Seq2 obtained does indeed come from the emitted and reflected light beam Fl, then it must correspond to the initial data sequence Seql, shifted in time by a travel time r which corresponds to the travel time of the beam from its emission by the transmitting module 2 to its reception by the receiving module 3. This travel time allows us to deduce the distance of the object O to the vehicle.

[0049] The computing unit 4 then implements the final part of the calculation, which consists of determining this transit time. To do this, the computing unit 4 first calculates values ​​of a correlation function Fcorr between the initial data sequence Seql and the received demodulated data sequence Seq2, for several time-shift values. The correlation values ​​are obtained by means of a cyclic convolution product between the received demodulated data sequence Seq2 and the modulating data sequence Seql, delayed according to each of the time-shift values.

[0050] Given the autocorrelation and cross-correlation properties of pseudo-random binary sequences, the correlation function Fcorr will thus be maximum for a time shift value corresponding to the time of flight of the light beam, separating the instant when it is emitted by the emission module 2 and the instant when it is received by the reception module 3. The computing unit 4 therefore searches for this maximum value of the correlation function Fcorr, in order to estimate the value r of this time of flight of the light beam Fl between the object O and the vehicle, associated with this maximum value.

[0051] According to one embodiment, the autocorrelation value Fcorr of a sequence of The pseudo-random binary type is given by the following equation:

[0052] Fcor if v = 0 (mod N) -r, smon

[0053] where Fcorr(v) is the autocorrelation function of the received demodulating data sequence for a time shift v, ml being the number of bits with a value of "1" in the sequence and N is the total number of bits in the sequence.

[0054] Figures 2 to 4 summarize the process of constructing the correlation function. Figure 2 represents the pulse train Sseq generated by the transmitting device 2 and contained within the light beam FL. Figure 3 represents the pulse train Sel received by the receiving device 3 and contained within the incident light beam F2. This received light train corresponds to the transmitted one, with a time shift T, which corresponds to the time of flight, as explained previously. Furthermore, it should be noted that this received pulse train exhibits some differences compared to the transmitted pulse train, due to noise from ambient light. Some pulses present in the Sseq pulse train are not found in the Sel pulse train. Conversely, some pulses present in the Sel pulse train were not present in the Sseq pulse train.

[0055] The correlation function is implemented for different offset values, and should allow reaching a peak at the time offset T, and thus allow determining the time of flight, as shown in [Fig.4].

[0056] This detection method presents the following practical problems related to the volume of data to be processed. In particular, correlation must be performed for the signals emitted for each pixel 32 or photodetector 32. Furthermore, since the detection method uses visible radiation, in a daytime environment, the method must process a large volume of data due to solar radiation.

[0057] To remedy this problem, the invention relates in particular to a specific photodetector 32.

[0058] In a particular embodiment of a photodetector 32 shown in [Fig. 5], the photodetector 32 comprises: - a plurality of 321 photodiodes, for example 30 photodiodes, - a 322 summing circuit, - a calculation circuit with an average of 323, - a 324 subtractor circuit, and - a 325 transformation circuit that converts a P-bit signal into an M-bit signal, with M <P.

[0059] The photodetector 32 further includes a clock providing a clock signal or an input receiving a clock signal. The clock signal allows the calculations and / or processing of the elements 322 to 325 listed above to be timed. The clock signal is, for example, clocked at approximately 1 GHz (period of approximately 1 ns) or clocked at 100 MHz (period of approximately 10 ns). Other clock frequencies are possible. However, as the clock frequency decreases, the measurement uncertainty of the distance of the detected object O to the vehicle increases.

[0060] The summing circuit 322 allows counting the photodiodes that are in the conducting state, that is, those that have recently been impacted by a photon. This count or The calculation is performed at each period of the clock signal. To do this, the photodiodes are preferably all connected to the summing circuit 322.

[0061] Summation can be performed analogically. To do this, the photodiodes can be connected in parallel and connected to the summing circuit 322, in which the sum of the currents flowing through the photodiodes is measured. The number of photodiodes in the conducting state is deduced from the value of this current.

[0062] Alternatively, the summation can be performed digitally in the summing circuit 322.

[0063] At the output of the summing circuit 322, we obtain, for example, a signal as shown in [Fig. 6], indicating the evolution of the number of photodiodes in the conducting state as a function of time. This signal is a P-bit signal, for example P=5, allowing the return of values ​​from 0 to 31 and thus providing information on the number of photodiodes in the conducting state among 30 photodiodes. This signal drives: - on the one hand, the calculation circuit for an average of 323, and - on the other hand, a first input of the subtractor circuit 324.

[0064] The averaging circuit 323 calculates an average, specifically an equally weighted or unweighted average, of the last n values ​​of the signal from the summing circuit 322, where n is a natural number, in particular n=3, n=4, or n=5. The output of the averaging circuit 323 produces, for example, a signal as shown in [Fig. 7], with n on the order of 10 to 15 and an equally weighted average implemented. This signal is a P-bit signal. This signal feeds into a second input of the subtractor circuit 324. The signal from the averaging circuit 323 is a signal representative of the noise generated by the illumination of the scene S by light sources other than the emitting module 2, typically by solar radiation. The signal from the averaging circuit 323 is also a P-bit signal.

[0065] Alternatively, the circuit 323 can be a circuit for calculating the minimum value of the last n values ​​of the signal from the summing circuit 322, with for example n a natural number, in particular n=3 or n=4 or n=5.

[0066] Any other solution is still conceivable in order to obtain at the output of the circuit 323 a signal representative of the noise generated by the ambient lighting of the scene S.

[0067] At the output of the subtractor circuit 324, we obtain for example a signal as shown in [Fig.8] giving the difference in values ​​of the signals feeding the first and second inputs of the subtractor circuit 324. This P-bit signal feeds the transformation circuit 325.

[0068] In the transformation circuit 325, the input signal of P bits is transformed into an output signal of M bits. In this transformation circuit, the values ​​are transformed bits of the signals as follows: - all bits of the M-bit output signal are set to the value "1", if one of the PM most significant bits of the input signal contains at least one "1", and - all bits of the M-bit output signal are set to the value "0" if the value of the signal from the summing circuit 322 is less than the value of the signal from the circuit 323, and - otherwise, the output signal is assigned the values ​​of the M least significant bits of the input signal. For example, we obtain the signal shown in [Fig.9].

[0069] For example, for P=5 and M=3: - if we have a negative value at the input of the transformation circuit 325, we obtain the value "000" at the output. - if we have the value "01001" at the input of the transformation circuit 325, we obtain the value "111" at the output. - if we have the value "00101" at the input of the transformation circuit 325, we obtain the value "101" at the output.

[0070] The signal from the transformation circuit is the signal coming out of the receiving module, that is to say a signal such as that shown in [Fig.3].

[0071] Preferably, all the acquisition modules 32 are similar and each provide their output signal to the demodulation unit.

[0072] As an alternative to the circuits 323, 324, and 325 described above, an alternative transformation circuit can be used to transform the input signal of P bits into an output signal of M bits according to the following logic. In this alternative transformation circuit, the bit values ​​of the signals are transformed as follows: the least significant bits PM are removed from the input signal feeding into the alternative transformation circuit to form the output signal of the alternative transformation circuit. For example, for P=5 and M=3, if the input to the alternative transformation circuit is the value "00101", the output is the value "001". This operation corresponds to a subtraction of a variable number depending on the value of the signal feeding into the alternative transformation circuit. This alternative is particularly economical in terms of computational resources.

[0073] In the given example, where a 5-bit signal is reduced to 3 bits, the volume of data to be processed is reduced by 40%. In particular, it is noted that such a reduction in data volume does not impair the quality of the correlation operation mentioned above. Indeed, the reduction in data volume only affects information regarding the quantity of light received. However, to implement the correlation and thus perform the rangefinding function mentioned above, it is sufficient to know the times when the pulses of the light beam F2 are received. This reduction of The volume of data does not affect this determination of moments in any way.

[0074] The invention also relates to a method of operating the acquisition module 39 implemented in the third phase mentioned above. This operating method is therefore more broadly part of: - of a method for detecting an object, and / or - of a method for operating the light detection system 1, and / or - of a method for operating the luminous device 100, and / or - of a method of operation of the motor vehicle 200.

[0075] One execution method of the operating process of the acquisition module 39 comprises, for each of the photodetectors, iterations of the following steps at different times, in particular at different times separated by a regular time interval: - a first step of determining an initial number of photodiodes 321 that have detected one or more photons for a predetermined duration, and - a second step of determining a second number by subtracting a third number from the first number in order to limit the flow of data processed downstream of acquisition module 39, and - a step of transmitting the second number to the processing unit by means of the data bus.

[0076] The first number can be obtained at the output of the summing circuit 322. The third number can be obtained at the output of the averaging circuit 323. The second number can be obtained at the output of the subtracting circuit 324 or at the output of the transformation circuit 325.

[0077] Preferably, the second step includes a sub-step of calculating the third number as an average, in particular an equally weighted or unweighted average, of the first n numbers determined during the previous n first steps, with n a natural number, in particular n=3 or n=4 or n=5.

[0078] Alternatively, the second step may include a substep of calculating the third number as a minimum of the first n numbers determined during the previous n first steps, with n a natural number, in particular n=3 or n=4 or n=5.

[0079] Preferably, the iterations of the first n steps are carried out while the light emission module 2 is inactive. This makes it possible to disregard the consequences of the illumination of scene S by the light beam Fl when determining the noise due to the ambient illumination of scene S.

[0080] Preferably, the method includes, in each iteration, a third step before the step of transmitting the second number to the processing unit 4. The third step is a transformation step of the second number obtained, coded on P bits, into a second encoding on M bits, with M <P, par exemple P=5 ou P=6 ou P=7 ou P=8 et M=3 ou M=4. Comme vu précédemment, ceci est mis en œuvre par le circuit de transformation 325.

[0081] This transformation preferably includes saturations. Thus, as seen previously, in addition to transforming the first encoding into a second encoding comprising the values ​​of the M least significant bits of the first encoding, - all bits of the second encoding are set to the value "1", if one of the most significant PM bits of the first encoding contains at least one "1", and / or - we set all the bits of the second encoding to the value "0", if the second number is negative.

[0082] As an alternative mentioned above, the second step of determining the second number by subtracting the third number from the first number can be carried out by transforming the binary encoding of the first number by removing its PM bits of least weight to obtain the binary encoding of the second number.

[0083] Advantageously, the first step in determining the first number includes an analog count or a digital count.

[0084] Advantageously, the regular time interval is on the order of a nanosecond or on the order of 10 nanoseconds.

Claims

Demands

1. Method of operating an acquisition module (39) comprising an arrangement of photodetectors (32) each comprising a set of photodiodes (321) capable of detecting photons from a scene (S), a data transmission bus (B) and a computing unit (4), the method comprising, for each of the photodetectors, iterations of the following steps at different times, in particular at different times separated by a regular time interval: - a first step of determining a first number of photodiodes (321) having detected one or more photons for a predetermined duration, and - a second step of determining a second number by subtracting a third number from the first number in order to limit the flow of data processed downstream of the acquisition module (39), and - a step of transmitting the second number to the computing unit by means of the data transmission bus.

2. Method according to claim 1, characterized in that the second step comprises a substep of calculating the third number as an average, in particular an equally weighted or unweighted average, of the first n numbers determined during the previous n first steps, with n a natural number, in particular n=3 or n=4 or n=5.

3. Method according to claim 1, characterized in that the second step comprises a substep of calculating the third number as a minimum of the first n numbers determined during the previous n first steps, with n a natural number, in particular n=3 or n=4 or n=5.

4. A method according to any one of claims 2 and 3, characterized in that the previous n first steps of determining the first n numbers are carried out while the light emission module is inactive.

5. A method according to any one of the preceding claims, characterized in that each iteration comprises a third step, prior to the step of transmitting the second number to the processing unit (4), the third step being a transformation step of a first P-bit encoding of the second number into a second M-bit encoding of the second number, with M <P, par exemple P=5 ou P=6 ou P=7 ou P=8 et M=3 ou M=4.

6. A method according to the preceding claim, characterized in that the third transformation step includes a saturation, for example the transformation of the first coding into a second coding, comprising: - all bits with the value "1", if one of the PM most significant bits of the first coding includes at least one "1", and - all bits with the value "0", if the second number is negative, and - the values ​​of the M least significant bits of the first coding.

7. The method according to claim 1, characterized in that the second step of determining the second number by subtracting the third number from the first number is carried out by transforming the P-bit binary encoding of the first number by removing its PM least significant bits to obtain the M-bit binary encoding of the second number, with M <P, par exemple P=5 ou P=6 ou P=7 ou P=8 et M=3 ou M=4.

8. A method according to any one of the preceding claims, characterized in that the first step of determining the first number includes an analog counting or a digital counting.

9. A method according to any one of the preceding claims, characterized in that the regular time interval is on the order of nanoseconds or on the order of 10 nanoseconds.

10. Acquisition module (39) comprising hardware elements (32, 321, 322, 323, 324, 325) designed to implement the method according to any one of the preceding claims.

11. Light detection system (1) comprising an acquisition module (39) according to the preceding claim, a control module (19) and a light emission module (2), said control module (19) being configured to determine a data sequence to be emitted, said emission module (2) being capable of providing emitted light in the form of a train of light pulses corresponding to the data sequence, the computing unit (4) of the acquisition module (39) being configured to determine, by correlation operations between the data sequence and photon detection data comprising the second number, a time corresponding to a time of flight of the light emitted from the emission module to an object illuminated by the emitted light, and a time of flight of the emitted light, reflected by the object, to the acquisition module (39).

12. Light device (100) comprising a light detection system (1) according to the preceding claim and / or an acquisition module (39) according to claim 10.

13. Motor vehicle (200), in particular autonomous motor vehicle, comprising an acquisition module (39) according to claim 10 and / or a light detection system (1) according to claim 11 and / or a light device (100) according to the preceding claim.

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