Method for voltage stabilization of diodes of a photodetector

Abstract

The invention relates to a method for voltage stabilization of one or more groups of single photon avalanche diodes of a photodetector, wherein a digitizer is connected downstream of each of the diodes, comprising the following steps: Detecting one or more signals of a signal path of the photodetector comprising the diodes and the digitizers with the same blocking voltage applied to the diodes, Determining a respective amplitude spectrum of the one or more detected signals, Determining a respective local minimum of the determined amplitude spectra, Control of the applied reverse voltage based on the determined local minima(s). The invention further relates to a photodetector, a computer program and a machine-readable storage medium.

Description

[0001] The invention relates to a method for voltage stabilization of one or more groups of single photon avalanche diodes of a photodetector, a photodetector, a computer program and a machine-readable storage medium. State of the art

[0002] The published patent application WO 2021 / 111766 A1 discloses a single-photon avalanche diode.

[0003] The published patent application WO 2020 / 013815 A1 discloses an avalanche diode. Disclosure of the invention

[0004] The object underlying the invention is to provide a concept for the efficient voltage stabilization of one or more groups of single photon avalanche diodes of a photodetector.

[0005] This object is achieved by means of the respective subject matter of the independent claims. Advantageous embodiments of the invention are the subject matter of the respective dependent subclaims.

[0006] According to a first aspect, a method is provided for voltage stabilization of one or more groups of single photon avalanche diodes of a photodetector, wherein a digitizer is connected downstream of each of the diodes, comprising the following steps: Detecting one or more signals of a signal path of the photodetector comprising the diodes and the digitizers with the same blocking voltage applied to the diodes, Determining a respective amplitude spectrum of the one or more detected signals, Determining a respective local minimum of the determined amplitude spectra, Control of the applied reverse voltage based on the determined local minima(s).

[0007] According to a second aspect, a photodetector is provided, comprising: one or more groups of single photon avalanche diodes, where each diode is followed by a digitizer, a detection device which is arranged to detect one or more signals of a signal path of the photodetector comprising the diodes and the digitizers when the same blocking voltage is applied to the diodes, a determination device which is configured to determine a respective amplitude spectrum of the one or more detected signals, wherein the determination device is configured to determine a respective local minimum of the determined amplitude spectra or spectra, a control device which is configured to control the applied blocking voltage based on the determined local minima or minima.

[0008] According to a third aspect, a computer program is provided which comprises instructions which, when the computer program is executed by a computer, for example by the photodetector according to the second aspect, cause the computer to carry out a method according to the first aspect.

[0009] According to a fourth aspect, a machine-readable storage medium is provided on which the computer program according to the third aspect is stored.

[0010] The invention is based on and incorporates the finding that the above object is achieved by using one or more determined local minima of one or more amplitude spectra to regulate the reverse voltage applied to the diodes. These amplitude spectra are determined from one or more signals of the signal path of the photodetector, which signal path includes the diodes and the digitizers.

[0011] Since the dead time of a single-photon avalanche diode depends significantly on the reverse voltage applied to the diode, the dead time can be efficiently controlled using the control of the applied reverse voltage according to the concept proposed here. This efficiently ensures that the diode can always be operated at an optimal operating point. Furthermore, a tolerance of the applied reverse voltage and, for example, aging effects can be effectively compensated. This advantageously prevents premature saturation of the photodetector and further advantageously increases sensitivity to low photon rates.

[0012] This results in the technical advantage that a concept for the efficient voltage stabilization of one or more groups of single photon avalanche diodes of a photodetector is provided.

[0013] The term “Single Photon Avalanche Diode” can also be abbreviated to “SPAD” in the description.

[0014] If the description only refers to a diode, it should always be understood that this is a single photon avalanche diode.

[0015] If the description only refers to a detector, it should always be understood that this is the photodetector.

[0016] Whenever the description refers only to an amplitude spectrum, it should always be understood that this is a transformation of a time signal into the frequency domain. To reduce the computational effort of the transformation, for example, not all frequencies occurring in the signal can be considered during the transformation.

[0017] In one embodiment of the method, it is provided that a respective digital output signal of the digitizers is quantized in time using a predetermined clock in order to obtain a respective quantized output signal, wherein one of the quantized output signals is detected as a signal of the one or more signals of the signal path.

[0018] This provides the technical advantage, for example, that the dead time of each individual SPAD can be measured. This can be particularly beneficial if the dead time of the SPADs in a detector is subject to considerable variation. SPADs with a particularly long dead time can saturate and become blind if the dead time exceeds a certain threshold due to an incorrectly set reverse voltage. SPADs with a particularly low dead time, on the other hand, can become insensitive to small amounts of light if the dead time falls below a certain threshold due to an incorrectly set reverse voltage. Control that takes the extreme values ​​of the measured dead times into account thus ensures that the largest possible number of SPADs always has optimal light sensitivity.

[0019] In one embodiment of the method, it is provided that one of respective digital output signals of the digitizers is detected as a signal of the one or more signals of the signal path.

[0020] This also provides the technical advantage, for example, of being able to measure the dead time of each individual SPAD. However, time quantization distorts the dead time measurement. A signal path that operates with a non-quantized or analog input signal is not subject to this disadvantage. However, the implementation of such a signal path would be more complicated than one based on quantized signals.

[0021] In one embodiment of the method, it is provided that a respective histogram of the quantized output signals of the one or more groups of diodes is calculated in order to generate a respective histogram signal which represents the respectively calculated histogram.

[0022] Histograms serve as the basis for measuring reflections (echoes) of emitted laser pulses. Therefore, histogram calculation units are a typical component of state-of-the-art detectors. Thus, no additional logic for calculating histograms needs to be implemented.

[0023] In one embodiment of the method, one of the generated histogram signals is detected as a signal of the one or more signals of the signal path. A dead time determined from a histogram corresponds to the average of the dead times of all SPADs in the respective group.

[0024] This results in the technical advantage, for example, that less logic and thus less chip area is required to measure the average dead time of all detector pixels. The disadvantage is that the distribution of dead times within the SPAD group remains unknown. Thus, when controlling based on the average dead time, individual SPADs with a particularly high or low dead time may no longer exhibit optimal light sensitivity.

[0025] In one embodiment of the method, it is provided that an average value of the generated histogram signals is determined in order to generate an averaged histogram signal which represents the determined average value, wherein the averaged histogram signal is detected as a signal of the one or more signals of the signal path.

[0026] This results in the technical advantage, for example, that even less logic and thus less chip area is required to calculate the average dead time of all detector pixels. This method is particularly suitable for detectors whose SPADs exhibit a low statistical dead time dispersion.

[0027] In one embodiment of the method, it is provided that the averaged histogram signal to be detected is calculated only from those histogram signals whose histogram mean values ​​are similar.

[0028] The reason is that the dead time is a nonlinear function of the frequency of the first local minimum of the amplitude density spectrum and the histogram mean. If the background illumination has a significantly higher intensity in one area of ​​the detector than in another area, the corresponding histogram mean will be very different. If the histogram mean is not included in the dead time calculation, this results in a measurement error. However, the dependence of the dead time on the histogram mean is so small that the histogram mean values ​​of the histogram signals to be averaged may deviate from each other by, for example, + / - 5%. This would result in 10 dead times - one dead time for each of the 10 quantiles, each with a width of 10%. The average dead time of all SPADs of the detector is then calculated from the average of these 10 dead times.

[0029] This provides the technical advantage, for example, that dead time measurement is possible under any background light situation. The accuracy is higher than compared to a measurement based on an averaged histogram signal from histograms with histogram mean values ​​that differ from each other by, for example, more than + / - 5%.

[0030] Histogram mean values ​​that differ from each other by a maximum of a predetermined distance threshold, for example + / - x%, in particular + / - 5%, are referred to as similar or are similar.

[0031] In one embodiment of the method, it is provided that a respective mean value of the generated histogram signals is determined in order to generate a respective histogram mean value signal which represents the respective mean value of the respective histogram, wherein the generated histogram signal to be detected is selected from the generated histogram signals based on the respective histogram mean value signal.

[0032] For example, it is intended to reject histogram signals with histogram mean values ​​of, for example, < 2% of the maximum possible signal level.

[0033] This results in the technical advantage, for example, that when laser pulses with a very high intensity occur in histogram signals with a very low histogram mean value of < 2% of the maximum possible signal level, no dead time measurement is carried out, since this can be inaccurate in such a situation.

[0034] In one embodiment of the method, it is provided that a respective mean value and a maximum value of the generated histogram signals are determined in order to generate a respective histogram mean value signal and a histogram maximum value signal which represents the respective mean value and the maximum value of the respective histogram, wherein the generated histogram signal to be detected is selected from the generated histogram signals based on the respective histogram mean value signal and the respective histogram maximum value signal.

[0035] This provides the technical advantage, for example, of being able to specifically reject histogram signals in which high-intensity laser pulses occur at a very low histogram mean value of < 2% of the maximum possible signal level. A histogram signal in which the histogram mean value is < 2% of the maximum possible signal level and the intensity of the laser pulses is comparably low can still be used for dead time measurement.

[0036] In one embodiment of the method, it is provided that, based on the determined local minima(s), a respective dead time of the diode(s) on which the signal(s) of the signal path used to determine the local minima(s) was / are based is determined, wherein the applied reverse voltage is regulated based on the respectively determined dead time(s).

[0037] This provides, for example, the technical advantage of efficiently controlling the reverse voltage. In particular, a particularly suitable parameter, in this case the dead time, is used to control the applied reverse voltage.

[0038] Determining the respective dead time can, for example, involve reading a dead time from a look-up table.

[0039] For example, the method is a computer-implemented method.

[0040] The method according to the first aspect is carried out, for example, by means of the photodetector according to the second aspect.

[0041] The photodetector according to the second aspect is, for example, configured to carry out all steps of the method according to the first aspect.

[0042] The photodetector according to the second aspect is, for example, programmed to execute the computer program.

[0043] Statements made in connection with the method apply analogously to the photodetector and vice versa. This means that technical functionalities and features of the method result analogously from corresponding features and technical functionalities of the photodetector and vice versa.

[0044] For example, the method according to the first aspect explicitly comprises the step of applying an equal reverse voltage to the diodes.

[0045] A local minimum of an amplitude spectrum is, for example, the first local minimum. Further local minima are, for example, integer multiples of the first local minimum.

[0046] A local minimum is defined, in particular, by its frequency. Determining a local minimum thus involves, in particular, determining the frequency of the local minimum.

[0047] Calculating a histogram of signals, for example, involves adding the signals.

[0048] The embodiments and forms of embodiment described here can be combined with each other to any extent, even if this is not explicitly described.

[0049] The invention is explained in more detail below using preferred embodiments.

[0050] Here we show: Fig. 1 a flowchart of a method according to the first aspect, Fig. 2 a photodetector according to the second aspect, Fig. 3 a machine-readable storage medium according to the fourth aspect, Fig. 4 a single photon avalanche diode, Fig. 5 a signal path of a photodetector, Fig. 6 a first block diagram, Fig. 7 an amplitude spectrum, Fig. 8 a second block diagram and Fig. 9 a third block diagram.

[0051] Fig. 1 shows a flowchart of a method for voltage stabilization of one or more groups of single photon avalanche diodes of a photodetector, wherein a digitizer is connected downstream of each of the diodes, comprising the following steps: Detecting 101 one or more signals of a signal path of the photodetector comprising the diodes and the digitizers with the same blocking voltage applied to the diodes, Determining 103 a respective amplitude spectrum of the one or more detected signals, Determining 105 a respective local minimum of the determined amplitude spectra, Rules 107 of the applied reverse voltage based on the determined local minima(s).

[0052] Fig. 2 shows a photodetector 201 comprising a group 203 of single photon avalanche diodes 205. A digitizer 207 is connected downstream of each of the single photon avalanche diodes 205.

[0053] This means that the output signals of the diodes 205 are digitized by the digitizer 207. The digitizers 207 thus output a digital output signal.

[0054] The photodetector 201 according to Fig. 2 shows an example of a group of single-photon avalanche diodes. In an embodiment not shown, the photodetector 201 comprises several such groups of single-photon avalanche diodes.

[0055] The photodetector 201 comprises a detection device 209 which is configured to detect one or more signals of a signal path of the photodetector 201 comprising the diodes 205 and the digitizers 207 when the same blocking voltage is applied to the diodes 205.

[0056] The photodetector 201 comprises a determination device 211 which is configured to determine a respective amplitude spectrum of the one or more detected signals, wherein the determination device 211 is configured to determine a respective local minimum of the determined amplitude spectra(s).

[0057] The photodetector 201 comprises a control device 213 which is configured to control the applied blocking voltage based on the determined local minima(s).

[0058] Fig. 3 shows a machine-readable storage medium on which a computer program 303 is stored. The computer program 303 comprises instructions that, when executed by a computer, cause the computer program 303 to execute a method according to the first aspect.

[0059] Fig. Figure 4 shows a circuit diagram 401 of a single-photon avalanche diode 403 and a digitizer 405 connected downstream of the diode 403. This arrangement can, for example, be comprised of a photodetector according to the second aspect. The photodetector according to the second aspect is based on single-photon avalanche diodes, which can, for example, detect individual photons with sub-nanosecond time resolution. SPAD operation is characterized in particular by the fact that the diode is operated in Geiger mode. This means that the absorption of a photon triggers an avalanche of electrons, which leads to an electrically measurable signal. Fig. 4 shows an exemplary structure of a single photon avalanche diode 403 with a downstream digitizer 405. The voltage curve at node V N1 is digitized by the digitizer 405, which provides a correspondingly digitized output signal. If a blocking voltage VA applied which is greater than a breakdown voltage V BD , the absorption of a photon results in an avalanche breakdown. Fig. The circuit shown in Figure 4 is therefore: V N1 - V A > V BD In the dark state, the diode has a high resistance. The node V N1 then has the voltage V N1 = VE. If a photon triggers an avalanche, the diode becomes conductive and the potential V N1 falls briefly to V min = VA + VBD. At this moment the diode becomes high-impedance again and the capacitances in the node V N1 are determined by the resistance R Quench recharged to the voltage VE. An electronic component with a threshold value V thserves as a digitizer by generating a binary pulse from this voltage drop. The SPAD state can be described with this signal as "breakthrough" (= "high") and "ready to break down" (= "low"). The width of the pulse, or the duration in the "breakdown" state, is usually referred to as the dead time t d The dead time t d decreases with the magnitude of the voltage VA. Furthermore, the probability with which a photon causes an avalanche breakdown decreases, thus decreasing the quantum efficiency (PDE) of the SPAD.

[0060] Fig. Figure 5 shows a signal path 500 of a photodetector according to the concept described here in a simplified representation. The signal path 500 comprises a group 501 of several single-photon avalanche diodes, each with a downstream digitizer. A SPAD with a downstream digitizer is symbolically represented by a square with the reference numeral 503.

[0061] The digital output signals of the digitizers are time-quantized according to function block 505. Based on the time-quantized signals, a histogram calculation is performed according to a function block 507. For example, all time-quantized signals are added together.

[0062] Further in Fig. Figure 5 shows several example temporal curves of the individual signals or a temporal clock. Time is plotted on the abscissa. The amplitude of the signal or clock is plotted on the ordinate.

[0063] Reference numeral 509 indicates a timing chart of a clock, based on which the output signals of the digitizers are quantized.

[0064] The reference numerals 511, 513 each point to a time course of an output signal of a digitizer.

[0065] The reference numerals 515 and 517 each point to a time profile of a time-quantized signal which results from a time quantization of the signals according to the profiles 511, 513 according to the clock shown in the profiles 509.

[0066] The reference numeral 519 points to a time course of the histogram signal, which shows the calculated histogram, in this case an addition, of the two signals according to the courses 515, 517.

[0067] For the following explanations, the following abbreviations are defined: The digital output signals of the digitizers are converted to S SP,i where i = [1...N].

[0068] With S TDC,i are the time-quantized output signals.

[0069] With S Histis the histogram signal representing the calculated histogram. In particular, N SPAD pixels are grouped within a SPAD group. The digitized output signals of the SPADs i = [1..N], S SP,i are first quantized in time using a clock pulse. The result is the signals S TDC,i . In the histogram calculation, for example, all signals S TDC,i the SPAD group added to S Hist = S TDC,1 +...+S TDC,N . The histogram mean µ Hist Denotes the average number of SPADs in the "breakthrough" state and provides information about the intensity of the background illumination. Background illumination of a comparably high intensity occurs, for example, when the detector is operated outdoors on a sunny day. In a SPAD-based detector, the histogram is used, for example, to detect the reflections (= "echoes") of emitted laser pulses.

[0070] In order to achieve the most reproducible behavior of the SPAD, the parameters PDE and dead time t d be kept within given limits. This requires the voltage V to be set as precisely as possible. A . Usually V A = -V SD However, V BD with temperature, by manufacturing tolerances from SPAD to SPAD, and by aging. With the current state of the art, after the production of a SPAD-based detector V BD measured as a function of temperature and stored for use in the product. However, aging effects cannot be taken into account with this method. In addition, the voltage V generated in the photodetector is subject to temperature variation. A a tolerance which, in combination with the aging effects, can lead to the dead time t dand the PDE changes over too wide a range. For the photodetector, this can mean that in case of too high a voltage |V A | the dead time t d and the PDE increase to such an extent that the detector saturates at a certain photon rate and thus becomes 'blind'. In the case of a voltage that is too low |V A | the PDE can decrease to such an extent that small amounts of light can no longer be detected.

[0071] A regulation of the voltage V A based on the measurement of the dead time t d ensures that the SPAD is always operated at the optimal operating point. The tolerance of the generated voltage V A Aging effects and SPAD-to-SPAD variation can thus be effectively compensated. This prevents premature saturation of the photodetector and increases sensitivity for low photon rates.

[0072] Thus, the dead time t d significantly depends on the blocking voltage V A This property is used in the concept described here to determine the blocking voltage V A based on a value that depends on the dead time t d depends on: the minimum or minima of the amplitude spectra used here.

[0073] Fig. 6 shows a first block diagram 601, according to which the concept described here is explained in more detail using a photodetector 603 according to the second aspect having an exemplary control device 607.

[0074] The diodes are supplied with an equal reverse voltage by an adjustable voltage source 605. This means that the adjustable voltage source 605 applies an equal reverse voltage to the diodes.

[0075] It is noted that the control device 607 may be implemented in whole or in part in the hardware of the photodetector.

[0076] A dead time setpoint is provided to the control device 607 as an input. This setpoint is symbolically identified by a block with the reference numeral 609. The dead time setpoint can also be expressed as T d,soll be referred to.

[0077] Furthermore, the control device 607 receives as input a signal 611 of the signal path, for example S TDC,i,j , where j ranges from 1 to M and denotes the index of one of the groups of single photon avalanche diodes of the photodetector 603. S Hist,j be used.

[0078] According to a function block 613, the dead time is calculated based on the input variable 611. From the calculated dead time t d and the setpoint t d,sollcan then be calculated according to a function block 615 a deviation ΔV A to the ideal voltage V a A logic 617 then controls the adjustable voltage source 605 so that the deviation ΔV a is minimized.

[0079] It is therefore intended that all SPAD groups are connected to a single voltage V A The controller uses either the time-quantized signals S TDC,i,j or the histograms S Hist,j . We have i ∈ [1.. N] and j ∈ [1.. M]. A dead-time scalar t d can be calculated from one or more signals. When selecting the signals, for example, it is taken into account that the dead time t d each SPAD pixel may vary due to manufacturing tolerances.

[0080] For example, a dead time is calculated based on a local minimum of an amplitude spectrum of the corresponding signal

[0081] From the calculated dead time td and its setpoint t d,soll For example, the deviation ΔV a to the ideal voltage V a For example, a logic controls the adjustable voltage source so that the deviation ΔV a is minimized.

[0082] From each of the signals S SP,i , S TDC,i or S Hist an amplitude spectrum 701 can be calculated, which can be used as an example in Fig. 7 is shown.

[0083] The frequency of the signal path is plotted on the abscissa 703. The amplitude of the signal path is plotted on the ordinate 705.

[0084] The reference numerals 707, 709, 711 denote several local minima of the amplitude spectrum 701.

[0085] The first local minimum is designated by reference numeral 707. The second local minimum of the amplitude spectrum is designated by reference numeral 709. The third local minimum is designated by reference numeral 711.

[0086] The first local minimum 707 can also be expressed with f d The other local minima 709, 711 are located at integer multiples of f d .

[0087] The special feature of the amplitude spectrum 701 is that for a given detector the frequency f d of the first local minimum depends significantly on the dead time t d and only slightly from the mean value of the respective signal S SP,i , S TDC,i or S Hist Further local minima are found at integer multiples of f d .

[0088] In situations with a very low intensity of the background light and at the same time a high intensity due to received laser pulses, the relationship between the mean value and the frequency of the local minimum at the dead time t d too complicated to implement a corresponding evaluation in the detector logic. To prevent resulting measurement errors, the signals S SP,i , S TDC,i or S Hist filtered out of the situation mentioned. For this purpose, for example, the ratio of the laser pulse duration to the measurement time determined by the signals S SP,i , S TDC,i or S Hist is only about 1 to 100. Thus, the laser pulses have only a negligible influence on the average. A very simple filter, for example, is based on the fact that the signals S SP,i , S TDC,i or S Histwith an average value of < 2 % of the maximum possible signal level are rejected. For example, laser pulses with a high intensity are rejected based on maximum values ​​in the signals S SP,i , S TDC,i or S Hist . Signals are detected in which maximum values ​​close to the maximum possible signal level and very low mean values ​​occur simultaneously, whereby such signals are, for example, rejected.

[0089] In the following, it is assumed that the signal S Hist,j of the SPAD group j with the mean µ Hist,j is used as the basis for calculating the dead time.

[0090] The method for calculating the dead time t d will be in Fig. 8 shown as an example.

[0091] Fig. 8 shows a second block diagram 801, which shows an exemplary calculation of a dead time t d explained.

[0092] A unit 803 for calculating the dead time td receives as input variable 805, for example, the signal or signals S Hist,j According to a function block 807, a selection of one of the signals 805 is made based, for example, on the mean value. The mean value of the histogram whose histogram signal is used to determine the amplitude spectrum and ultimately to determine the local minimum is referred to as µ Hist and is provided as an input variable to a function block 811. According to a function block 809, an amplitude spectrum of the selected signal is determined and the frequency f d This is provided as an input to function block 811, according to which, based on the mean value µ Hist and f d the dead time t d 813 is determined or calculated.

[0093] For example, to calculate the amplitude spectrum, only those histograms are used whose mean values ​​µHist,j are similar. This can be achieved, for example, by selecting the histograms accordingly.

[0094] The frequencies f d , 2f d , 3f d ...can be found by searching for local minima. The minima search becomes particularly robust if a model function is previously fitted to the amplitude spectrum.

[0095] The connection f d = F(t d , µ Hist ) is determined, for example, by determining the dead time t d for example, is measured directly and on the other hand the frequency f d for different mean values ​​µ Hist is determined. The relationship f d = F(t d , µ Hist ) can be implemented, for example, as a look-up table or as a fit function. The reverse relationship t d = F(f d , µ Hist) can now be used during operation of the photodetector to determine the dead time t d from the frequency f d and the histogram mean µ Hist to determine.

[0096] An exemplary embodiment of the regulation consists, for example, in Fig. 6 from the measured dead time t d and the setpoint t d,soll the deviation ΔV a which is necessary to achieve the setpoint t d,soll To achieve this, the relationship ΔV a = F(t d , t d,soll ), which can be determined, for example, by characterization.

[0097] A logic controls the target voltage V A,Soll the adjustable voltage source with the aim of ΔV a as close to 0 as possible.

[0098] At the Fig. 9, the calculation of the dead time t dOnly the frequency f d from an amplitude spectrum, as exemplified in Fig. 7. From the relationship A err = F(f d , f d,soll ) an error variable A err calculated, for example, to A err = B(f d,max - f d,soll ) with B as a constant. A logic controls the setpoint voltage V A,Soll the adjustable voltage source then with the target A err = 0.

[0099] The setpoint of the frequency f d,soll can be selected based on a strategy that does not only or not at all pursue the goal of achieving a certain dead time setpoint t d,soll to achieve. A prerequisite is a pre-characterization of the SPAD-based detector, in which f d depending on corresponding parameters such as PDE, V a, or temperature. This enables, for example, the following control strategies, which can be combined with each other, especially in part: 1. Achieving the maximum possible PDE. 2. Achieving a constant PDE in a given temperature range. 3. Operating the photodetector at operating points defined by the voltage VBD given in the new state.

[0100] Thus, Fig. 9 a third block diagram 901, which shows an exemplary control of the applied blocking voltage V a based on the frequency f d shows.

[0101] As input variable 905 a logic 903 receives to determine the deviation ΔV a for example the signal S Hist . The further input variable is the setpoint of the frequency f d,soll 907. Based on S Hist According to a function block 909, the frequency f dcalculated, i.e. the frequency of the first local minimum. The frequency f d is used as an input variable for a function block 911, which also determines the setpoint of the frequency f d,soll 907 receives.

[0102] The error variable A err can be defined, for example, as follows: A err = F(f d , f d,soll ).

[0103] The error variable is provided to a logic 913 as an input variable, which based on it outputs a target voltage 915 to the adjustable voltage source, with the target A err = 0. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2021 / 111766 A1

[0002] WO 2020 / 013815 A1

[0003]

Claims

[1] Method for voltage stabilization of one or more groups (203) of single photon avalanche diodes (205) of a photodetector (201), wherein a digitizer (207) is connected downstream of each of the diodes (205), comprising the following steps: detecting (101) one or more signals of a signal path of the photodetector (201) comprising the diodes (205) and the digitizers (207) with the same blocking voltage applied to the diodes (205), Determining (103) a respective amplitude spectrum (701) of the one or more detected signals, Determining (105) a respective local minimum (707, 709, 711) of the determined amplitude spectra, Control (107) of the applied reverse voltage based on the determined local minima(s) (707, 709, 711). [2] The method of claim 1, wherein a respective digital output signal of the digitizers (207) is time-quantized using a predetermined clock to obtain a respective quantized output signal, wherein one of the quantized output signals is detected as a signal of the one or more signals of the signal path. [3] A method according to claim 1 or 2, wherein a respective histogram of the quantized output signals of the one or more groups (203) of diodes (205) is calculated to generate a respective histogram signal representing the respective calculated histogram. [4] The method of claim 3, wherein one of the generated histogram signals is detected as a signal of the one or more signals of the signal path. [5] The method of claim 3 or 4, wherein an average value of the generated histogram signals is determined to generate an averaged histogram signal representing the determined average value, the averaged histogram signal being detected as a signal of the one or more signals of the signal path. [6] The method according to claim 4 or 5, wherein a respective mean value of the generated histogram signals is determined to generate a respective histogram mean value signal representing the respective mean value of the respective histogram, wherein the generated histogram signal to be detected is selected from the generated histogram signals based on the averaged histogram mean value signal. [7] Method according to one of claims 4 to 6, wherein a respective mean value and a respective maximum value of the generated histogram signals are determined in order to generate a respective histogram mean value signal and a respective histogram maximum value signal which represents the respective mean value and the respective maximum value of the respective histogram, wherein the generated histogram signal to be detected is selected from the generated histogram signals based on the respective histogram mean value signal and the respective histogram maximum value signal. [8] A method according to claim 6 or 7, wherein the generated histogram signal to be detected is calculated from those histogram signals whose histogram mean values ​​are similar. [9] Method according to one of the preceding claims, wherein, based on the determined local minima(s) (707, 709, 711), a respective dead time of the diode(s) (205) is determined on which the signal(s) of the signal path used to determine the local minima(s) (707, 709, 711) were based, wherein the applied reverse voltage is regulated based on the respectively determined dead time(s). [10] A method according to any one of the preceding claims, wherein one of respective digital output signals of the digitizers is detected as a signal of the one or more signals of the signal path. [11] Photodetector (201) comprising: one or more groups (203) of single photon avalanche diodes (205), wherein a digitizer (207) is connected downstream of each of the diodes (205), a detection device (209) which is arranged to detect one or more signals of a signal path of the photodetector (201) comprising the diodes (205) and the digitizers (207) when the same blocking voltage is applied to the diodes (205), a determination device (211) which is arranged to determine a respective amplitude spectrum (701) of the one or more detected signals, wherein the determining device (211) is arranged to determine a respective local minimum (707, 709, 711) of the determined amplitude spectra or spectra, a control device (213) which is configured to control the applied blocking voltage based on the determined local minima or minima (707, 709, 711). [12] Computer program (303) comprising instructions which, when the computer program (303) is executed by a computer, cause the computer to carry out a method according to one of claims 1 to 10. [13] Machine-readable storage medium (301) on which the computer program (303) according to claim 12 is stored.

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