Light receiver circuit and light sensor array comprising a light receiver circuit

Abstract

Light sensor array comprising a plurality of light receiver circuits (10), wherein the light receiver circuit (10) has a propagation time compensation and comprises at least one light sensor (12); a control circuit (14) for selecting and controlling the light sensor (12); a connecting line (16) to a TDC circuit (18) for evaluating a light signal received by the light sensor (12); and a test circuit (20) arranged between a test line (22) and the control circuit (14); where - the test line (22) is connected to a test signal source (24) for generating an electrical test signal; - the test circuit (20) is designed and configured to connect the test line (22) to the control circuit (14) and to forward the test signal to the control circuit (14); and - the control circuit is designed and configured to conduct a measurement signal of the light sensor (12) to the TDC circuit (18) and to conduct an electrical test signal to the connecting line (16) and further to the TDC circuit (18) in order to evaluate the electrical test signal and the propagation time of the electrical test signal from the test circuit (20) to the TDC circuit (18); and where - the light sensor array comprises two test signal sources (24, 24a, 24b), one of which is arranged at each end of the test line (22) and outputs a test signal into the test line (22).

Description

[0001] The present invention relates to a light receiver circuit for detecting optical events with a compensation of propagation times, with a light sensor, a control circuit and a connecting line to a time-digital converter circuit (TDC circuit) for evaluating a light signal received by the light sensor.

[0002] Electronic circuits typically require a clock or timing generator that delivers high-precision clock signals or timing signals to synchronize individual components within the electronic circuits. For example, in sensor circuits or distance measurement circuits, such as those used in motor vehicles and in the automotive sector, signal propagation times are determined to determine precise distances to objects. The surroundings of a vehicle, for example, are detected using such systems, and it is important that the timing is measured very precisely.

[0003] To provide a precise clock, synchronous electronic circuits operating at high clock frequencies are often used. Such circuits are generally expensive, prone to failure, not very robust, and only partially suitable for use in the automotive sector, although sufficiently high clock frequencies would be possible for good resolution in distance measurement. Asynchronous electronic circuits are also known for generating a clock or time code.

[0004] Furthermore, time generators based on the classic Vernier scheme are used, which allows for high-resolution time-to-digital conversion. However, scaling to multiple channels is limited, so high-resolution systems with many parallel measurement channels require a large number of time generators. This leads to significantly increased space requirements and power consumption, which is why such circuits are generally not used in the automotive sector.

[0005] Sensor arrays comprising a large number of sensors or photodiodes are often used as sensors for distance measurement or environmental detection. Well-known examples of such arrays are so-called single-photon avalanche diode detectors (SPAD detectors), in which several of these single-photon avalanche diodes are connected to form an array. Such avalanche diodes are used as lidar sensors, for example, in vehicles.

[0006] For photodiodes connected to an array, the connection of the individual photodiodes in the array to the surrounding readout electronics is particularly critical, as the resulting propagation time differences affect the absolute accuracy of the measurement. Even if the timing generator delivers two signals with the utmost precision, propagation time differences within the array can cause problems and incorrect measurements. Open or shorted connections can also represent a so-called single-point failure for one or more pixels, i.e., for one or more of the diodes.

[0007] DE 20 2013 105 389 U1 addresses a similar problem with an optoelectronic sensor operating in Geiger mode and proposes a solution in which an optical reference signal is routed to an additional optical reference receiver. This is intended to measure global propagation time differences that affect all photoreceivers and the reference receiver, such as propagation time differences from an evaluation unit to the drivers or delays in the transmitter drivers.

[0008] DE 10 2020 101 451 A1 relates to a time-of-flight light detection system for detecting hardware errors and degradations in a time-of-flight receiver. The system uses an evaluation circuit to compare a reference signal with an expected result after passing through a signal path to generate a comparison result and infer errors.

[0009] There is therefore a great need for a light receiver circuit that eliminates the known problems of time-of-flight differences and enables very precise measurement of distances or the environment of the sensor.

[0010] The present object is achieved by a light sensor array having the features of claim 1, a lidar receiver having the features of claim 11, a lidar system having the features of claim 12 and a method for compensating for runtime differences having the features of claim 14.

[0011] According to a first aspect, the present invention relates to a light sensor array comprising a light receiver circuit with at least one light sensor and a control circuit for selecting and controlling the light sensor. The light receiver circuit further comprises a connecting line to a time-to-digital converter (TDC) circuit for evaluating a light signal received from the light sensor. The light receiver circuit comprises a test line, each of which has an electrical test signal source at each of its ends for generating an electrical test signal, and a test circuit for forwarding the test signals to the control circuit of the light sensor. The test circuit is connected to the test line and the control circuit of the light sensor. A test signal generated by the test signal source is passed through the control circuit of the light sensor to the connecting line and further to the TDC circuit.In this way, the test signal and its propagation time from the test circuit to the TDC circuit are evaluated. This is the prerequisite for determining different propagation times of the test signal, so that any propagation time differences that occur during measurements with the light sensor can be compensated. Compensation of the propagation times of the measurement signals is desirable and necessary, particularly in a circuit for distance measurement or for environmental detection that includes multiple light receiver circuits with light sensors.

[0012] According to the invention, electrical test signals are used as reference signals. This allows local propagation time differences to be detected and measured, allowing the light receiver circuit to operate independently of its position in an array, and the measurement results are independent of the cable lengths used for its control and the cable lengths used for evaluating the measurement signals.

[0013] According to a further aspect, the invention relates to a method for compensating for propagation time differences in a light sensor array having a light receiver circuit. The light receiver circuit comprises at least one light sensor and a control circuit for selecting and controlling the light sensor, a connecting line to a TDC circuit for evaluating a light signal received by the light sensor, and a test circuit. Furthermore, the light receiver circuit includes a test line, at each end of which an electrical test signal source is arranged for generating an electrical test signal. According to the method, an electrical test signal is first generated for each test circuit and then fed to the test circuit of the light receiver circuit. The test signal is forwarded to a control circuit, which is also connected to the light sensor.An (electrical) output signal from the light sensor (measurement signal), which is based on a received light signal, is decoupled from the control circuit at the latest at the time at which the test signal is forwarded. After the output signal of the light sensor has been decoupled, the test signal is fed to an evaluation circuit. In a further step, the propagation times of the electrical test signals are determined by capturing and evaluating the test signal in the evaluation circuit. The determined propagation times of the test signals to the control circuit of the light receiver circuit, i.e. preferably from the electrical test signal source to the control circuit, are determined. In the case of multiple light sensors in multiple light receiver circuits, this is preferably done for each individual light receiver circuit.

[0014] A further step involves taking the determined propagation time into account when evaluating a light signal from the light sensor of the light receiver circuit. Using the information obtained from the propagation times of the test signal, propagation time differences due to the position of individual light receiver circuits in an array can be compensated and balanced. Compensating for propagation time differences between the individual pixels of an array within the array represents a major advantage over the prior art, for example, compared to DE 20 2013 105 389 U1.

[0015] Preferably, the measured propagation times of the test signal to the light receiver circuit are compensated for minus the measured propagation times of the test signal to the control circuit. This compensation makes it possible to process very precise measurement signals and clock signals in order to realize robust and reliable distance measurements or the determination of the surroundings of a light receiver circuit or a lidar receiver comprising the light receiver circuit.

[0016] The inventive light sensor array with multiple light receiver circuits can have a TDC circuit for evaluating the signals transmitted from a control circuit of the light receiver circuit via a connecting line, as well as a test signal source for generating a test signal for the test circuit. A basic version of the light sensor array can comprise only a plurality of light receiver circuits without the associated TDC circuits and test circuits.

[0017] The light sensor array preferably comprises a plurality of light receiver circuits, which are preferably arranged in a two-dimensional matrix with nxm light receiver circuits. Here, n and m are the number of respective light receiver circuits in the rows or columns of the array, respectively, where n and m are each greater than or equal to 2, preferably greater than or equal to 10. The light sensor array can be designed in a basic version without TDC circuits. The TDC circuits are then connected to the basic version of the array via the respective connecting lines of the light receiver circuits. For example, one TDC circuit can be provided per column of light receiver circuits in the array, which is preferably implemented with many light receiver circuits, for example when the array comprises more than 200 columns and more than 50 rows, or when m and n are greater than 50.

[0018] Particularly in large arrays with more than 20 columns and / or rows, different cable lengths inevitably arise between the individual light sensors and the evaluation unit, i.e., the TDC circuit. The effort required to make all cable lengths the same length is technically virtually impossible and economically impractical. The time difference between the reception of a light signal at an individual light sensor and the reception of the measurement signal at the TDC circuit is different for each light sensor (without compensation and without the inventive solution). The difference in the propagation times scales with the driver strength of the measurement signal. The resulting process, temperature, and voltage dependencies are compensated for by the invention, since the propagation time differences are determined and taken into account in real time using the test signal.The compensation, which is based on the electrical test signal, takes into account the propagation times from the light sensor to an evaluation unit (TDC circuit) and takes place directly in the evaluation unit, for example the TDC circuit.

[0019] Another aspect of the invention relates to a lidar receiver for receiving optical events. The lidar receiver has a light sensor array, preferably as described above and preferably with the associated TDC circuits, with a plurality of light receiver circuits, and includes a time code generator that generates a time code. The time code preferably changes in defined steps. The time code generator is connected to the control circuit of each lidar receiver circuit or to the respective TDC circuits such that the time code is transmitted to the respective control circuit or TDC circuit.

[0020] A preferred embodiment of the lidar system provides that it is classified according to a risk classification and has a corresponding classification. The risk classification is preferably an Automotive Safety Integrity Level (ASIL). Particularly preferably, the classification is at least ASIL A, more preferably ASIL B.

[0021] In a further aspect, the invention relates to a vehicle with a lidar system as described above, preferably with a lidas system with ASIL level.

[0022] Preferred embodiments of the invention are described in the dependent claims. It is understood that the features mentioned above and those to be explained below can be used not only in the respective combinations specified, but also in other combinations or alone, without departing from the scope of the present invention. In particular, the method can be implemented according to the embodiments described for the device in the dependent claims.

[0023] In a preferred embodiment of the light receiver circuit, it is designed such that the test circuit includes a test select switch for forwarding the test signal (of the test signal source) from the test line to the control circuit. The test select switch is preferably a transistor. A FET transistor is particularly preferred.

[0024] Within the scope of the invention, it was recognized that two critical aspects can arise when using large two-dimensional light sensor arrays. Light sensor arrays are typically designed such that the TDC circuits, i.e., the time-to-digital converter circuits, are arranged around the optical part of the array, i.e., the part containing the light sensors. The TDC circuits are thus arranged at the edge, preferably at the top and / or bottom edge, of the light sensor part.

[0025] In light sensor arrays with many light sensors, the length of the lines routed from the light receiver circuits to the TDC circuits varies depending on the position of the light sensor or the position of the light receiver circuit in the array. It can therefore be said that the line from each pixel to the TDC circuits arranged on the outside of the array is always different. This results in propagation time differences that can be significantly greater than the time resolution of the system. The TDCs and the readout transistors integrated in the light receiver circuit introduce further error components due to variations in process, voltage, and temperature. The present invention provides a way to measure and compensate for these effects during operation.

[0026] Furthermore, the present invention also addresses an aspect of functional safety. Here, the correct functioning of the TDCs, i.e., the integrated circuits used, must be regularly checked. The invention enables the detection of a large proportion of potential errors in the light receiver readout and in the timestamp or time code acquisition. The invention can be applied not only to the array, but also to one-dimensional line sensors (with light receiver circuits arranged in a row) and even to detectors with only a single pixel, i.e., a single light receiver circuit.

[0027] In contrast to the prior art, the present invention simplifies the layout, as less attention is paid to balanced line routing. Delay time shifts caused by different line routings are compensated for by the invention. This enables significantly more complex circuit designs in which a consistent line length guaranteed by the layout is technically impossible. This allows for simple and thus less expensive layouts to be implemented, resulting in robust circuits. The light receiver circuit according to the invention and the light sensor arrays constructed with it are thus more robust and less expensive overall.

[0028] In addition, the absolute accuracy of the light receiver circuits is increased by measuring, evaluating, and compensating for component-specific and IC-specific deviations, which are largely caused by the manufacturing process, the current temperature, or the voltage applied to the component, during operation. This allows for more consistent measurement results when multiple light sensor arrays or lidar receivers are used in a lidar system.

[0029] For all components of lidar systems, typically components in the detector ICs of lidar systems, as well as in ASICs, which are often considered critical and system-relevant, the invention additionally serves as a diagnostic tool and diagnostic option to realize functionally safe designs.

[0030] In a preferred embodiment, the light receiver circuit according to the invention comprises a test select switch in the test circuit. The test select switch has the function of forwarding the test signal to the control circuit. The so-called test select switch is preferably switched by a select signal that is present at the switch when it is selected for switching to test mode. The test select switch is preferably designed as a transistor; particularly preferably, an FET transistor is used.

[0031] In a further preferred embodiment of the light receiver circuit, the control circuit comprises a select switch to decouple and thus block the light sensor. The light sensor is decoupled when the test signal is applied to the control circuit so that only one signal reaches the control circuit, namely the test signal, which is passed through when the propagation times of the circuit are to be measured. The select switch is preferably switched to decouple the light sensor before the test signal is applied to the control circuit. This reliably prevents two signals from reaching the control circuit. The select switch is preferably switched by a select signal that is transmitted to the switch, for example, via a select line. The select signal is applied when the light receiver circuit is selected to receive a light signal by means of the light sensor.The select switch is preferably a transistor. It is particularly preferably designed as an nMOS transistor.

[0032] In a preferred embodiment of the light receiver circuit, the light sensor is a diode. This allows for very small designs. Light sensors that are avalanche diodes are particularly preferred. In practical use, single-photon avalanche diodes have proven to be very preferred as light sensors in a particular embodiment of the light receiver circuit. A light sensor array that has a TDC circuit for evaluating the signals transmitted via the connecting line and a test signal source for generating the test signal for the test circuit has, in a preferred embodiment, a plurality of light receiver circuits. Preferably, at least two of the light receiver circuits are arranged in a row, with the circuits arranged in a row being connected to the same test line.This way, only one test lead per row is required, reducing the number of test leads from the test signal source to the light receiver circuits. Of course, it is also possible to provide one test lead per column of the light sensor array.

[0033] According to the invention, the light sensor array comprises two test signal sources, one of which is arranged at each end of the test line. The test line thus connects the two test signal sources, whereby the light receiver circuits in a row (or column) can preferably also be connected to the test line. The test signal sources can be connected to several parallel test lines in order to route the test signals to several light receiver circuits.

[0034] The test signal sources are operated alternately, so that a test signal is alternately transmitted to the test line. Alternating in this case means that only one of the two test signal sources transmits a test signal to the test line at a time. However, test signals from the respective test signal sources do not have to be transmitted alternately. It is also possible for one test signal source to transmit multiple test signals in succession, for example, to be switched on and off several times before the other test signal source transmits a test signal to the test line.

[0035] However, alternating operation is preferred, whereby the test signal sources alternately (strictly alternating) emit a test signal into the test line.

[0036] A preferred embodiment of the light sensor array provides for an evaluation circuit, which is preferably integrated or included in the TDC circuit. The evaluation circuit evaluates the received test signals (and, if applicable, the measurement signals from the light sensors) and compensates for propagation time differences between the light signals from different light sensors when evaluating the light signals. The compensation of the propagation time differences is based on the propagation time of the received test signals from the respective light receiver circuits whose signal propagation times are to be compensated.

[0037] Preferably, the light sensor array comprises a matrix-like arrangement of the light receiver circuits, with multiple rows of light receiver circuits being present. Preferably, each of the rows is connected to its own test line, with the test line being connected at each of its ends to one of the two test signal sources.

[0038] The invention also encompasses a vehicle with a lidar system or with a light sensor array or a lidar receiver, as described above. The vehicle may be, among others, a motor vehicle, a two-wheeler or three-wheeler, a truck, a bus, or a passenger car. A vehicle may be a commercial vehicle, an agricultural machine, or a robot. The term "vehicle" in this case also includes a weapon system, a fire control system, a missile, a drone, a satellite, a rocket, an aircraft, a floating body (ship), or a submersible.

[0039] The invention is described and explained in more detail below using selected embodiments in conjunction with the accompanying drawings. They show: Fig. 1 shows a light receiver circuit according to an embodiment of the present invention; Fig. 2 a detailed view of the light receiver circuit; Fig. 3 a light sensor array with several light receiver circuits; Fig. 4 another detailed view of the light receiver circuit and array; Fig. 5a-c Measurement points of an array and corresponding signal curves of measurements; Fig. 6 a vehicle with a lidar system with light sensor array; and Fig. 7 a schematic diagram of the inventive method for compensating for propagation time differences in a light receiver circuit.

[0040] Fig. Figure 1 shows an embodiment of a light receiver circuit 10 of a light sensor array with propagation time compensation. The light receiver circuit 10 comprises at least one light sensor 12, a control circuit 14 for selecting and controlling the light sensor 12, and a connecting line 16 to a TDC circuit 18, which serves to evaluate a light signal received by the light sensor 12. The light receiver circuit 10 further comprises a test circuit 20, which is arranged between a test line 22 and the control circuit 14 and can connect a signal from the test line 22 to the control circuit 14.

[0041] The test line 22 is connected to a test signal source 24, wherein the test signal source 24 generates an electrical test signal and can output it to the test line 22. The test circuit 20 is designed and configured to establish a connection between the test line 22 and the control circuit 14 and to forward an electrical test signal generated by the test signal source 24 to the control circuit 14.

[0042] The control circuit 14 is connected to the light sensor 12 and is configured to transmit a measurement signal from the light sensor 12 to the TDC circuit 18. Furthermore, the control circuit 14 is configured to transfer an electrical test signal, which was forwarded by the test circuit 22, to the connecting line 16 and to transmit it further to the TDC circuit 18 via the connecting line. In this way, the test signal from the test signal source 24 reaches the TDC circuit 18 when the test circuit 20 is switched on, so that the propagation time of the electrical test signal from the test circuit 20 to the TDC circuit 18 can be determined and evaluated.

[0043] The prior art configuration of a light receiver circuit with a control circuit and a light sensor is thus expanded by the test circuit 20 to transmit a test signal from a test signal source 24 to the TDC circuit 18. Each light receiver circuit 10 is connected to a test line 22, so that if multiple light receiver circuits 10 are present, two or more of these circuits can be connected to a test line 22, allowing a test signal from a test signal source 24 to be transmitted to the individual light receiver circuits 10. In this way, it is possible to select individual light receiver circuits 10 whose propagation time to the TDC circuit 18 is to be measured. The propagation time of the test signal can then be compensated for when evaluating a light signal received by the light sensor 12, which is transmitted as a measurement signal to the control circuit 14.

[0044] Fig. 2 shows an extended embodiment of the light receiver circuit 10 from Fig. 1. The test circuit 20 includes a test select switch 26, which establishes a connection from the test line 22 to the control circuit 14 as soon as a signal is present on a test select line 28 connected to the test select switch 26 and switches the test select switch 26 on. In this way, the individual light receiver circuit 10 can be selected for test operation when a test select signal is applied to the test circuit 20 of the light receiver circuit 10 via the test select line 28. An electrical test signal from the test line 22 is then forwarded to the control circuit 14, since a connection from the test line 22 to the control circuit 14 is established.

[0045] In Fig. 2 shows that a test signal source 24 is arranged at both ends of the test line 22, each of which can generate a test signal. The electrical test signals are preferably fed alternately from the test signal source 24a at the first end of the test line 22 and the test signal source 24b at the other end of the test line, so that the propagation time of the test signal in the test line or up to the TDC circuit 18 can be determined.

[0046] Fig. 3 shows a lidar receiver 30 with a light sensor array 32 comprising a plurality of light receiver circuits 10 arranged in a matrix with columns 34. Each of the columns 34 containing a plurality of light receiver circuits 10 is assigned to a TDC circuit 18.

[0047] The lidar receiver 30 includes a time code generator 36 that generates a time code. The time code is changed in defined time steps so that a fixed point in time can be read from the code. The time code is transmitted to the TDC circuit 18 for each of the columns 34 of the light sensor array 32.

[0048] The lidar receiver 30 is constructed in such a way that the light sensor array 32 is arranged centrally and is arranged above and below in Fig. 3, a row of TDC circuits 18 is provided. An array of 256 x 80 light receiver circuits 10 is constructed, allowing the lidar receiver 30 to capture 256 x 80 pixels and, thanks to an integrated 448-byte SRAM memory, to quickly histogram them, for example. To construct the most compact lidar receiver possible, TDC circuits 18, 18a, 18b, 18c for the odd columns 34 of the light sensor array 32 are arranged above the light sensor array 32, while for the even columns 34, several TDC circuits 18 are arranged below the light sensor array.

[0049] Each of the rows of the array of light receiver circuits 10 in the individual columns 34 is connected to a test line 22, at each end of which a test signal source 24a, 24b is arranged. By alternately feeding an electrical test signal into the test lines 22 from the test signal source 24a and 24b, the propagation times of the measurement signals from the individual light receiver circuits 10 to the corresponding TDC circuits 18, 18a, 18b, 18c can be compensated.

[0050] The development of SPAD arrays with approximately 256 x 80 pixels and an integrated histogram can no longer be constructed in the conventional way with a 30 µm pixel pitch, in which the TDC circuits are each implemented with an SRAM memory of 448 bytes. Increasing the pixel pitch would result in a larger area and is unacceptable for many applications. In particular, compact circuitry cannot be realized this way. In order to achieve the most compact design possible, the TDC circuits are placed around the light sensor array, alternating above and below the optical surface. However, with a light detector that addresses one row at a time in "rolling shutter" mode, this leads to row-dependent "fixed pattern noise", which must be prevented. In particular, for the rows with light sensors at the edge of the light sensor array, one pixel orThe light sensor has a very short connecting cable to the associated TDC circuit, while the cable of the neighboring light sensor (pixel) is routed once through the light sensor array to the other side. With a time resolution of the TDC circuit of a few picoseconds, such an arrangement leads to significantly poorer absolute accuracy of the lidar receiver or the light sensor array. The light receiver circuit according to the invention also solves this problem, as it can compensate for the propagation time shifts caused by different cable lengths. As already described above, the invention thus allows the construction of lidar receivers and light sensor arrays that have very high accuracy and can also operate precisely and robustly in the picosecond range, while delivering reliable results.Sensors or detectors constructed in this way have the advantage that they can also be equipped with a safety cover (so-called FuSa (functional safety) cover). This further expands the range of applications for such circuits.

[0051] Furthermore, the test circuit of the light sensor arrays and lidar receivers can also be used for calibration purposes. This eliminates the need for pre-calibration of the system. Instead, calibration can be performed after the system has been installed (e.g., in a vehicle).

[0052] Calibrations can also be carried out at specific time intervals to further increase measurement accuracy.

[0053] Fig. 4 shows a detailed drawing of a portion of the light sensor array 32 with a plurality of light receiver circuits 10 and a plurality of TDC circuits 18 above and below the light sensor array 32. The respective TDC circuits 18 are shown only as a block.

[0054] In Fig. 4 also shows that each row of light receiver circuits 10 in the light sensor array 32 is connected to a test line 22, via which the electrical test signals from the two electrical test signal sources 24a, 24b can reach the respective light receiver circuits 10. Preferably, all light receiver circuits 10 in a row of the array are supplied with the test signals. Since the light receiver circuits 10 in the array are preferably interconnected column by column with a TDC circuit 18, electrical test signals can be sent to all light receiver circuits 10 in a row (row) simultaneously and evaluated simultaneously in the respective TDC circuits 18.

[0055] A detailed drawing of a light receiver circuit 10 is shown in the upper left area of Fig. 4. The test circuit 20 includes a test select switch 26, which is switched by a switching signal (test select signal) from the test select line 28. This closes the test select switch 26 and transmits an electrical test signal from the test line 22 to the control circuit 14.

[0056] In the embodiment shown here, the control circuit 14 includes a select switch 40 for switching or decoupling the light sensor 12, which can preferably be a photodiode. When a select signal is present on the select line 38, the select switch 40 is switched, so that a measurement signal at the output of the light sensor 12 is passed to a sense switch 42, which forwards the signal to the connecting line 16. The measurement signal from the light sensor 12 then reaches the TDC circuit 18. When an electrical test signal from the test circuit 20 is present at the control circuit 14, the select switch 40 is opened, so that the measurement signal from the light sensor 12 cannot reach the TDC circuit 18. Rather, the electrical test signal is applied to the sense switch 42 and can be connected via the connecting line 16 to the TDC circuit 18 connected to the connecting line 16.

[0057] The light receiver circuit 10 according to a preferred embodiment of Fig. 4 is configured such that the light sensor 12 is decoupled from the control circuit 14 as soon as the test signal is applied to the control circuit 14, preferably even before the test signal is applied to the control circuit 14. The select switch 40 can preferably be configured as a transistor, particularly preferably an nMOS transistor. The other switches of the light receiver circuit 10 can also be configured as transistors, preferably as nMOS or pMOS transistors.

[0058] The light sensor 12 is preferably a diode, such as a photodiode or an avalanche diode. The light sensor is particularly preferably a single-photon avalanche diode.

[0059] To reset the light receiver circuit 10 after receiving a light signal at the light sensor 12 and / or after forwarding a test signal from the test signal source 24, a reset switch 44 is provided. This connects the select switch 40 to ground, thus resetting the light receiver circuit. The reset switch 44 is triggered via a reset line 46. It can also be implemented as a transistor.

[0060] Based on the Fig. 5a to 5c, the compensation of the propagation times of the measurement signals from the light sensors 12 as a function of the location of the light receiver circuit 10 in the light sensor array 32 is explained.

[0061] Fig. 5a essentially shows the light sensor array 32 from Fig. 4 with the light receiver circuits 10 arranged as a matrix and the two banks of TDC circuits 18 above and below the array. Even-numbered TDC circuits 18 for the even-numbered columns of light receiver circuits 10 are arranged below the array, while the odd-numbered ones are arranged above the array.

[0062] The black dots shown in the array show measuring points or virtual measuring points for the signals in the circuit that are in the Fig. 5b, together with their running times in Fig. 5c. The test points T are measuring points at the input of the i-th TDC circuits 18. The measuring points R are reference points at the input of the i-th test circuit 20 of the light receiver circuits 10.

[0063] Fig. 5b shows that a select signal is no longer present at the select switch 40, thus decouples the light sensor 12 from the control circuit 14 even before a signal is present on the test select line 28. After decoupling, the test select signal is switched and remains present as long as electrical test signals are transmitted to the control circuit 14 by means of the test circuit 20. The test signal is generated in the respective test signal sources 24 and is then present at the outputs of the test signal sources 24 a short time later, as can be seen in the signal curves of T_in, A and T_in, B, respectively. After a certain runtime, the electrical test signals can then be applied to the virtual measuring points R are measured, while they are applied to the corresponding TDC circuit 18 a little later in the form of the measuring signals T for the i-th TDC circuit 18.

[0064] Fig. Figure 5c shows the propagation times of the individual measurement points depending on whether the test signal is fed into the test line 22 from the left test signal source 24a or the right test signal source 24b. The electrical test signals reach the inputs of the TDC circuits at different times, depending on which test signal source 24a, 24b generated the test signal and fed it into the test line, and depending on which TDC circuit 18 the signal is applied to. This graph can be created for each row of the array of light receiver circuits 10. Knowing these individual propagation times of the electrical test signals can be used to compensate for the propagation times of measurement signals from the individual light sensors 12 of the respective light receiver circuits 10.

[0065] In the preferred light receiver circuits 10 with light sensor 12, for example, as a photodiode or SPAD, with a select switch, reset switch, and sense switch, the test select switch 26 is arranged in parallel with the select switch 40. The test select switch 26 is designed to achieve a good match with the select switch 40, so that the switching times are similar. An electrical test signal switches this switch or transistor to Vcc, i.e., the supply voltage, so that a signal is generated at the sense switch 42 that resembles a photon detection by the light sensor 12 (for example, a SPAD). The light sensor 12 is not activated via the select switch 40 during the test to avoid false positive events due to optical activity.If the test signal is applied at a reference time, the delay of the signal chain and the function of the path from the sense switch 42 (or the test select switch) to the output of the TDC circuit, the so-called "TDC timestamp" (measured value at the output), can be measured. Thus, both the dynamic behavior (delay) and the static behavior (function) of the signal chain can be tested.

[0066] In an arrangement of light receiver circuits 10 in an array, one test line 22 is used for all simultaneously addressed light receiver circuits 10. To measure the propagation time of the electrical test signal in the test line, the test signal is fed in alternately from one or the other end of the test line.

[0067] Fig. 6 shows a vehicle 70 equipped with a lidar system for detecting optical events. The lidar system comprises a lidar receiver 30 with a light sensor array 32 and a driver circuit for a light source, as well as a light source for emitting electromagnetic light radiation in the visible or invisible range. A control unit initiates the light source and the time code generator of the lidar receiver and starts the lidar sensor array to evaluate optical events. The light radiation emitted by the light source (visible or invisible) is reflected by an object and detected by the light sensor, with the propagation times being compensated by the inventive light receiver circuits 10 and TDC circuits 18.

[0068] Fig. Figure 7 shows a schematic diagram of the sequence of the method according to the invention for compensating for propagation time differences in a light receiver circuit of a light sensor array. In a first generation step S10, an electrical test signal is generated in a test circuit 20. The method comprises a further step S12 of supplying the respective test signal via a test line, at each end of which a test signal is fed, to the test circuit 20 of a light receiver circuit 10, wherein the light receiver circuit 10 comprises a light sensor 12. A step S14 of decoupling a measurement signal from the light sensor 12 follows, wherein the decoupling takes place in a control circuit 14 of the light receiver circuit 10.A step S16 of forwarding the test signal from the test circuit 10 to the control circuit 14 is followed by a step S18 of supplying the test signal to an evaluation circuit by means of the control circuit 14, wherein the measurement signal is decoupled from the control circuit at the time the test signal is forwarded. The test signal is therefore only passed to the evaluation circuit once the decoupling step S14 has been completed. The evaluation circuit is preferably part of a TDC circuit 18, which is a component of a light sensor array 32. A step S20 of determining the propagation time of the test signal from the test circuit 20 to the evaluation circuit follows, wherein to carry out this step S20, the test signal is detected and evaluated in the evaluation circuit.A step of determining S22 the propagation time of the measurement signal from the light sensor 12 to a TDC circuit 18 serves to evaluate the measurement signal based on a light signal received by the light sensor 12. A step of taking into account S14 the determined propagation time of the electrical test signal when evaluating the propagation time of the measurement signal from the light sensor 12 of the light receiver circuit 10 follows, with the consideration being performed by compensating the propagation time of the electrical test signals from the test circuit 12 to the evaluation circuit.

[0069] The individual steps of the method according to the invention can also be performed in a different order or by adding further intermediate steps. The individual steps can be modified or adapted to existing features of a light receiver circuit if necessary.

[0070] In a preferred embodiment of the light sensor array 32, the TDC circuit 18 has the evaluation circuit that evaluates the electrical test signal. Alternatively, it is possible for the evaluation circuit to be a separate circuit or part of another component of a lidar system or lidar receiver or a light sensor array. The evaluation of the test signals and measurement signals, the determination of the propagation times, and the compensation of the propagation times during the evaluation and processing of the corresponding signals can also take place in the TDC circuit; alternatively, also in existing components of a circuit or assembly. For example, when using a lidar system with the light receiver circuit orThe light sensor array in a vehicle can be used to evaluate the signals and take them into account when detecting and recognizing objects and recording the vehicle's surroundings. Reference symbol 10 Light receiver circuit 12 Light sensor 14 Control circuit 16 connecting cable 18 TDC circuit 20 test circuit 22 Test line 24 Test signal source 26 test select switches 28 Testselect line 30 Lidar receivers 32 light sensor array 34 column 36 Timecode generator 38 Select line 40 Select switches 42 Sense switches 44 Reset switch 46 Reset line 70 vehicles

Claims

[1] Light sensor array comprising a plurality of light receiver circuits (10), wherein the light receiver circuit (10) has a propagation time compensation and comprises at least one light sensor (12); a control circuit (14) for selecting and controlling the light sensor (12); a connecting line (16) to a TDC circuit (18) for evaluating a light signal received by the light sensor (12); and a test circuit (20) arranged between a test line (22) and the control circuit (14); where - the test line (22) is connected to a test signal source (24) for generating an electrical test signal; - the test circuit (20) is designed and configured to connect the test line (22) to the control circuit (14) and to forward the test signal to the control circuit (14); and - the control circuit is designed and configured to conduct a measurement signal of the light sensor (12) to the TDC circuit (18) and to conduct an electrical test signal to the connecting line (16) and further to the TDC circuit (18) in order to evaluate the electrical test signal and the propagation time of the electrical test signal from the test circuit (20) to the TDC circuit (18); and where - the light sensor array comprises two test signal sources (24, 24a, 24b), one of which is arranged at each end of the test line (22) and outputs a test signal into the test line (22). [2] Light sensor array according to one of the preceding claims, characterized by that the test circuit (20) comprises a test select switch (26) for forwarding the electrical test signal to the control circuit (14), wherein the test select switch (26) is preferably a transistor, particularly preferably an FET transistor. [3] Light sensor array according to one of the preceding claims, characterized by in that the control circuit (14) comprises a select switch (40) for decoupling the light sensor (12) when the test signal is applied to the control circuit (14), preferably before the test signal is applied to the control circuit (14), wherein the select switch (40) is preferably a transistor, particularly preferably an nMOS transistor. [4] Light sensor array according to one of the preceding claims, characterized by that the light sensor (12) is a diode, preferably an avalanche diode, particularly preferably a single-photon avalanche diode (SPAD). [5] Light sensor array according to one of the preceding claims, characterized by that at least two of the light receiver circuits (10) are arranged in a series and the light receiver circuits (10) in a series are preferably connected to the same test line (22). [6] Light sensor array according to one of the preceding claims, comprising a TDC circuit (18) for evaluating the signals transmitted by the control circuit (14) via the connecting line (16) and a test signal source (24) for generating an electrical test signal for the test circuit (20). [7] Light sensor array according to one of the preceding claims, characterized by that the test signal sources (24, 24a, 24b) alternately output a test signal into the test line (22). [8] Light sensor array according to the preceding claim, characterized by that the test signal sources (24, 24a, 24b) alternately output a test signal into the test line (22). [9] Light sensor array according to one of the preceding claims, characterized bythat the light sensor array (32) comprises an evaluation circuit, which is preferably included in the TDC circuit (18) and which evaluates the received test signals and compensates for runtime differences of the measurement signals of different light sensors (12) when evaluating the measurement signals. [10] Light sensor array according to one of the preceding claims, characterized by that the light receiver circuits (10) of each row are connected to a test line (22), wherein the test lines (22) are each connected at their two ends to one of the two test signal sources (24). [11] Lidar receiver for detecting optical events, comprising a light sensor array (10) according to one of the preceding claims with a TDC circuit (18) and a test signal source (24) and comprising a time code generator which generates a time code which changes in defined time steps and which is connected to the control circuit (14) of each light receiver circuit (10) in such a way that the time code is transmitted to the respective control circuit (14). [12] Lidar system for detecting optical events comprising a lidar receiver (30) according to claim 11 and a driver circuit for a light source and a light source for emitting electromagnetic light radiation in the visible or invisible range, wherein a control unit initiates the light source and the time code generator and starts the light sensor array (32) to evaluate optical events. [13] A vehicle having a lidar system according to claim 12 or having a lidar receiver (30) according to claim 11 or a light sensor array according to any one of the preceding claims 1 to 10. [14] Method for compensating for transit time differences in a light sensor array (32) according to one of the preceding claims with a light receiver circuit (10), comprising the following steps: - generating two electrical test signals for a test circuit (20); - feeding the respective electrical test signal to the test circuit (20) of a light receiver circuit (10) comprising a light sensor (12) via a test line (22), at each end of which a test signal is fed; - decoupling a measurement signal of the light sensor (12) in a control circuit (14); - forwarding the respective test signal from the test circuit (20) to the control circuit (14); - feeding the respective test signal to an evaluation circuit by means of the control circuit (14), wherein the measurement signal is decoupled from the control circuit (14) at the time of forwarding the test signal; - determining the propagation time of the test signals from the test circuit (20) to the evaluation circuit by detecting and evaluating the test signal in the evaluation circuit; - determining the transit time of the measurement signal of the light sensor (12) to a TDC circuit (18) for evaluating the measurement signal based on a light signal received by the light sensor (12); and - Taking into account the determined propagation time of the electrical test signal when evaluating the propagation time of the electrical measurement signals of the light sensor (12) of the light receiver circuit (10) by compensating the propagation time of the test signals from the test circuit (20) to the evaluation circuit. [15] Method according to the preceding claim, characterized bythat the TDC circuit (18) includes the evaluation circuit.

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