Method for stabilizing voltage of photodetector diode, photodetector, program and medium

Abstract

The invention relates to a method for stabilizing the voltage of one or more groups of single photon avalanche diodes of a photoelectric detector, and the downstream of each diode is connected with a digital converter. Comprising the steps of: detecting one or more signals of a signal path comprising a diode and a digital converter of the photodetector with the same reverse voltage applied to the diode; determining a respective magnitude spectrum of the detected one or more signals; determining a respective local minimum of the determined one or more magnitude spectra; the applied reverse voltage is adjusted based on the determined one or more local minimums. The invention also relates to a photodetector, a computer program and a machine-readable storage medium.

Description

Technical Field

[0001] The present invention relates to a method for stabilizing one or more groups of single photon avalanche diodes of a photodetector, a photodetector, a computer program and a machine-readable storage medium. Background Art

[0002] Document WO 2021 / 111766 A1 discloses a single-photon avalanche diode.

[0003] Document WO 2020 / 013815 A1 discloses an avalanche diode. Summary of the invention

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

[0005] This object is achieved by means of a method for stabilizing one or more groups of single photon avalanche diodes of a photodetector, a photodetector, a computer program and a machine-readable storage medium. Advantageous embodiments of the invention are described below.

[0006] According to a first aspect, a method for stabilizing a group or multiple groups of single photon avalanche diodes of a photodetector is provided, wherein a digital converter is respectively connected downstream of the diodes, the method comprising the following steps:

[0007] detecting one or more signals of a signal path of the photodetector including the diode and the digitizer with the same reverse voltage applied to the diode,

[0008] determining a corresponding amplitude spectrum of the detected signal or signals,

[0009] determining corresponding local minima of the determined one or more magnitude spectra,

[0010] The applied reverse voltage is adjusted based on the determined one or more local minima.

[0011] According to a second aspect, there is provided a photodetector comprising:

[0012] One or more groups of single photon avalanche diodes,

[0013] Among them, the downstream of the diode is connected with a digital converter.

[0014] a detection device arranged to detect one or more signals of a signal path of the photodetector comprising the diode and the digitizer under the condition that the same reverse voltage is applied to the diode,

[0015] determining means arranged to determine a corresponding amplitude spectrum of the detected one or more signals,

[0016] wherein the determining means is arranged to determine a corresponding local minimum of the determined one or more amplitude spectra,

[0017] A regulating device is arranged to regulate the applied reverse voltage based on the determined one or more local minima.

[0018] According to a third aspect, there is provided a computer program comprising instructions which, when executed by a computer (eg by a photodetector according to the second aspect), cause the computer to perform the method according to the first aspect.

[0019] According to a fourth aspect, there is provided a machine-readable storage medium having stored thereon a computer program according to the third aspect.

[0020] The invention is based on and includes the recognition that the above-mentioned task is solved by regulating the reverse voltage applied to the diode using one or more determined local minima of one or more amplitude spectra. These amplitude spectra are determined from one or more signals of a signal path of a photodetector, wherein the signal path comprises a diode and a digital converter.

[0021] Since the dead time of a single photon avalanche diode depends strongly on the reverse voltage applied to the diode, the dead time can be efficiently adjusted by adjusting the applied reverse voltage as described in the concept proposed in this article. Therefore, it can be efficiently ensured that the diode can always operate at an optimal operating point. In addition, tolerances of the applied reverse voltage and, for example, aging effects can be effectively compensated in an advantageous manner. Therefore, early saturation of the photodetector can be advantageously and efficiently avoided, and the sensitivity to low photon rates can further be advantageously increased.

[0022] Therefore, in particular, the following technical advantages are brought about: a concept for efficiently stabilizing one or more groups of single photon avalanche diodes of a photodetector is provided.

[0023] The term “single photon avalanche diode” may also be abbreviated to “SPAD” within the framework of the description.

[0024] If only diode is written in the framework of the description, it should always be read together with the fact that this is a single-photon avalanche diode.

[0025] If only the word detector is written in the description, this should always be interpreted as a photoelectric detector.

[0026] If only the amplitude spectrum is written in the description, it should always be interpreted as a transformation of the time signal into the frequency space. For example, not all frequencies occurring in the signal are taken into account during the transformation in order to reduce the computational effort of the transformation.

[0027] In an embodiment of the method, it is provided that the respective digital output signals of the digitizer are quantized in time by means of a predetermined clock to obtain respective quantized output signals, wherein one of the quantized output signals is detected as a signal of one or more signals of the signal path.

[0028] For example, this results in the technical advantage of being able to measure the dead time of each individual SPAD. This can be particularly advantageous if the dead times of the SPADs of the detector have a large dispersion. If the dead time exceeds a certain threshold due to an incorrectly set reverse voltage, a SPAD with a particularly long dead time can fall into saturation and become "blind". Conversely, if the dead time is below a certain threshold due to an incorrectly set reverse voltage, a SPAD with a particularly short dead time can become insensitive to small amounts of light. Therefore, the regulation that includes the extreme values ​​of the measured dead time together ensures that the greatest possible number of SPADs always has optimal light sensitivity.

[0029] In an embodiment of the method, it is provided that one of the respective digital output signals of the digitizer is detected as a signal of one or more signals of the signal path.

[0030] This also brings the technical advantage of being able to measure the dead time of each individual SPAD, for example. However, time quantization distorts the dead time measurement. Signal paths that work with non-quantized or analog input signals do not suffer from this disadvantage. However, the implementation of such a signal path will be more complex than an implementation based on a quantized signal.

[0031] In an embodiment of the method, it is provided that respective histograms of the quantized output signals of one or more groups of diodes are calculated to generate respective histogram signals representing the respective calculated histograms.

[0032] The histogram serves as the basis for measuring the reflections (= "echoes") of the emitted laser pulses. The unit for calculating the histogram is therefore a typical component of a detector according to the prior art. Therefore, no additional logic unit needs to be implemented for calculating the histogram.

[0033] In one embodiment of the method, it is provided that one of the generated histogram signals is detected as a signal of one or more signals of the signal path. The dead time determined by the histogram corresponds to an average value of the dead times of all SPADs of the relevant group.

[0034] This results in the following technical advantages, for example: fewer logic cells and therefore less chip area are required to measure the average dead time of all pixels of the detector. The disadvantage is that the distribution of the dead time within the SPAD group remains unknown. It can therefore happen that individual SPADs with particularly high or low dead times no longer have optimal light sensitivity when regulation is based on the dead time average.

[0035] In an embodiment of the method, it is provided that a mean value of the generated histogram signal is determined to generate an averaged histogram signal representing the determined mean value, wherein the averaged histogram signal is detected as a signal of one or more signals of the signal path.

[0036] This results in the technical advantage that even fewer logic cells and therefore even less chip area are required to calculate the average dead time of all pixels of the detector. The method is particularly suitable for detectors whose SPADs have a low statistical dispersion of the dead time.

[0037] In one embodiment of the method, it is provided that the averaged histogram signals to be detected are calculated only from those histogram signals whose histogram averages are similar.

[0038] 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 light (Hintergrundbeleuchtung) on ​​one area of ​​the detector has a significantly higher intensity than on another area, the associated histogram mean will be very different. If the histogram mean is not included in the calculation of the dead time, this will lead to measurement errors. However, the dependence of the dead time on the histogram mean is so small that the histogram means of the histogram signals to be averaged can deviate from each other by, for example, + / -5%. Therefore, 10 dead times are obtained - each of the 10 quantiles has a dead time, and these quantiles have a width of 10% each. The average dead time of all SPADs of the detector is then obtained from the average of these 10 dead times.

[0039] For example, this provides the technical advantage of being able to measure the dead time in any background light situation. The accuracy is higher than a measurement based on an averaged histogram signal from histograms whose histogram means differ from each other by, for example, more than + / -5%.

[0040] Histogram mean values ​​which differ from each other by a maximum of a predetermined distance threshold, for example + / -x%, in particular + / -5%, are referred to as being similar or similar.

[0041] In one embodiment of the method, it is provided that a corresponding average value of the generated histogram signal is determined to generate a corresponding histogram average value signal representing the corresponding average value of the corresponding histogram, wherein the generated histogram signal to be detected is selected from the generated histogram signal based on the corresponding histogram average value signal.

[0042] For example, it is provided that histogram signals whose histogram mean is, for example, smaller than 2% of the maximum possible signal level are discarded.

[0043] This results in the following technical advantage, for example: if very intense laser pulses occur in a histogram signal with a very low histogram mean (less than 2% of the maximum possible signal level), no dead time measurement is performed, since this would be inaccurate in this case.

[0044] In one embodiment of the method, it is provided that the corresponding average value and the maximum value of the generated histogram signal are determined to generate a corresponding histogram average value signal and a histogram maximum value signal representing the corresponding average value and the maximum value of the corresponding histogram, wherein the generated histogram signal to be detected is selected from the generated histogram signal based on the corresponding histogram average value signal and the corresponding histogram maximum value signal.

[0045] This results in the following technical advantage, for example: histogram signals in which laser pulses with high intensity occur at very low histogram average values ​​of less than 2% of the maximum possible signal level can be discarded in a very targeted manner. Histogram signals in which the intensity of the laser pulses is comparably low despite the histogram average value being less than 2% of the maximum possible signal level can still be used for dead time measurement.

[0046] In one embodiment of the method, it is provided that, based on the determined one or more local minima, the corresponding dead time of the following one or more diodes is determined: the signal of the signal path for determining one or more local minima is based on the one or more diodes, wherein the applied reverse voltage is adjusted based on the one or more dead times respectively determined.

[0047] This results in the technical advantage that the reverse voltage can be efficiently regulated, for example. In particular, a particularly suitable parameter (in this case the dead time) is used to regulate the applied reverse voltage.

[0048] Determining the corresponding dead time may, for example, include reading the dead time from a lookup table.

[0049] The method is, for example, a computer-implemented method.

[0050] For example, the method according to the first aspect is performed by means of the photodetector according to the second aspect.

[0051] The photodetector according to the second aspect is arranged, for example, to perform all steps of the method according to the first aspect.

[0052] The photodetector according to the second aspect is arranged to execute a computer program, for example by programming techniques.

[0053] The statements made in connection with the method apply analogously to the photodetector and vice versa. This means that the technical functions and features of the method are analogously derived from the corresponding features and technical functions of the photodetector and vice versa.

[0054] For example, the method according to the first aspect explicitly comprises the step of applying the same reverse voltage to the diodes.

[0055] The local minimum value of the amplitude spectrum is, for example, the first local minimum value. The other local minimum values ​​are, for example, integer multiples of the first local minimum value.

[0056] The local minimum is defined in particular by its frequency. Therefore, determining the local minimum comprises in particular determining the frequency of the local minimum.

[0057] Calculating a histogram of the signals may include or be, for example, adding the signals.

[0058] The exemplary embodiments and embodiments described herein may be combined with one another to any extent, even if not explicitly stated to this effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The invention will be explained in more detail below by means of preferred exemplary embodiments.

[0060] The accompanying drawings show:

[0061] Figure 1 A flow chart showing a method according to the first aspect,

[0062] Figure 2 A photodetector according to the second aspect is shown,

[0063] Figure 3 A machine-readable storage medium according to a fourth aspect is shown,

[0064] Figure 4 A single photon avalanche diode is shown.

[0065] Figure 5 shows the signal path of the photodetector,

[0066] Figure 6 A first block diagram is shown,

[0067] Figure 7 shows the amplitude spectrum,

[0068] Figure 8 A second block diagram is shown, and

[0069] Fig. 9 A third block diagram is shown. DETAILED DESCRIPTION

[0070] Figure 1 A flow chart showing a method for stabilizing one or more groups of single photon avalanche diodes of a photodetector, wherein a digital converter is connected downstream of each diode, the method comprising the following steps:

[0071] detecting 101 one or more signals of a signal path of a photodetector including a diode and a digitizer under the condition that the same reverse voltage is applied to the diode,

[0072] determining 103 a corresponding amplitude spectrum of the detected one or more signals,

[0073] determining 105 corresponding local minima of the determined one or more amplitude spectra,

[0074] The applied reverse voltage is adjusted 107 based on the determined one or more local minima.

[0075] Figure 2 A photodetector 201 is shown which comprises a group 203 of single-photon avalanche diodes 205. A digitizer 207 is connected downstream of the single-photon avalanche diodes 205, respectively.

[0076] This means that the output signal of the diode 205 is digitized by the digitizer 207. The digitizer 207 thus outputs a digital output signal.

[0077] according to Figure 2 The photodetector 201 exemplarily shows a group of single photon avalanche diodes. In an exemplary embodiment not shown, the photodetector 201 includes a group of a plurality of such single photon avalanche diodes.

[0078] The photodetector 201 comprises a detection device 209 arranged to detect one or more signals of a signal path of the photodetector 201 comprising the diode 205 and the digitizer 207 in case the same reverse voltage is applied to the diode.

[0079] The photodetector 201 comprises a determining means 211 arranged to determine a respective amplitude spectrum of the detected one or more signals, wherein the determining means 211 is arranged to determine a respective local minimum of the determined one or more amplitude spectra.

[0080] The photodetector 201 comprises an adjusting means 213 arranged to adjust the applied reverse voltage based on the determined one or more local minima.

[0081] Figure 3 A machine-readable storage medium is shown having stored thereon a computer program 303. The computer program 303 comprises instructions which, when the computer program 303 is executed by a computer, cause the computer to perform the method according to the first aspect.

[0082] Figure 4 A circuit diagram 401 of a single photon avalanche diode 403 and a digital converter 405 connected downstream of the diode 403 is shown. The arrangement can be included, for example, by a photodetector according to the second aspect. The photodetector according to the second aspect is based on a single photon avalanche diode, which can detect single photons, for example, with a sub-nanosecond time resolution. The SPAD operation is characterized in particular by the diode operating in Geiger mode. This means that the absorption of a photon triggers an avalanche breakdown of an electron, which generates an electrically measurable signal. Figure 4 An exemplary structure of a single photon avalanche diode 403 with a digitizer 405 connected downstream is shown. N1 The voltage curve at is digitized by the digital converter 405, and the digital converter 405 outputs a corresponding digitized output signal. BD The reverse voltage V A , then avalanche breakdown occurs when a photon is absorbed. Therefore, the following applies Figure 4 The circuit shown in: V N1 –V A >V BD In the dark state, the diode has high resistance. Node V N1 Then the voltage V N1 =VE. If a photon triggers avalanche breakdown, the diode becomes conductive and the potential V N1 will drop to V min =VA+VBD. At this point, the diode becomes high impedance again, and the node V N1 The capacitance on the resistor R Quench It is charged to voltage VE again. With threshold V th The electronic component of the SPAD acts as a digital converter in that it generates binary pulses from the voltage drop. The states of the SPAD can be named "breakdown" (= "high") and "ready to break down" (= "low") using this signal. The pulse width or duration in the "breakdown" state is usually expressed as the dead time t d . Dead time t dAs the value of the voltage VA decreases, the probability of a photon causing an avalanche breakdown decreases, thereby reducing the quantum yield (PDE) of the SPAD.

[0083] Figure 5 The signal path 500 of a photodetector according to the concepts described here is shown in a simplified schematic diagram. The signal path 500 comprises a group 501 of a plurality of single photon avalanche diodes, each of which is connected downstream with a digital converter. The SPADs with a digital converter connected downstream are symbolically represented by a quadrilateral with reference numeral 503.

[0084] The digital output signals of the digitizer are time-quantized according to functional block 505. Based on the time-quantized signals, a histogram calculation is performed according to functional block 507. Here, for example, all time-quantized signals are added.

[0085] Figure 5 A number of exemplary time courses of individual signals or time clocks are also shown in FIG. 1 . The time is plotted on the abscissa. The amplitude of the signal or clock is plotted on the ordinate.

[0086] Reference numeral 509 refers to the time course of a clock, based on which the output signal of the digitizer is quantized.

[0087] Reference numerals 511 , 513 each refer to the time course of an output signal of the digitizer.

[0088] Reference numerals 515 and 517 refer to the time course of the time-quantized signal, which is the result of time-quantizing the signal according to processes 511 , 513 according to the clock shown in process 509 .

[0089] Reference numeral 519 refers to the time course of a histogram signal which shows the calculated histogram of the two signals according to the course 515 , 517 , in this case added together.

[0090] For the purposes of the following explanations, the following abbreviations are defined:

[0091] The digital output signal of the digitizer is S SP,i Represents, where i=[1...N].

[0092] Use S TDC,i Represents the time quantized output signal.

[0093] Use S Hist The histogram signal represents the calculated histogram. In particular, N SPAD pixels are grouped in a SPAD group. The digitized output signal S of the SPAD SP,i(i = [1..N]) is first time-quantized by a clock. The result is a signal S TDC,i For example, in the histogram calculation, all signals S of the SPAD group are then TDC,i Add together to get S Hist =S TDC,1 +…+S TDC,N . Histogram mean μ Hist Indicates the average number of SPADs that are in the "breakdown" state and provides information about the intensity of the background light. When operating the detector outdoors on a sunny day, for example, background light with comparably high intensity occurs. In SPAD-based detectors, for example, the histogram is used to detect reflections (= "echoes") of an emitted laser pulse.

[0094] In order to obtain the most reproducible possible behavior of the SPAD, the parameters PDE and dead time t d must be kept within the given limits. This is to set the voltage V as accurately as possible A As a condition. Usually choose V A =-V BD However, V BD V varies with temperature, due to manufacturing tolerances between SPADs, and through aging. In the current prior art, after a SPAD-based detector is produced, V BD is 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 A has a tolerance which, combined with aging effects, results in a dead time t d and PDE vary over a wide range. For a photodetector, this may mean that if the voltage |V A | Too high, the dead time t d and PDE increases to a certain extent, so that the detector falls into saturation at a certain photon rate and becomes "blind". A If | is too low, the PDE will decrease to a certain extent, so that the small amount of light can no longer be detected.

[0095] Through the dead time t d The measurement result is used to adjust the voltage V A It can ensure that the SPAD always works at the optimal working point. Therefore, it can effectively compensate the voltage V A The tolerances, aging effects and SPAD-to-SPAD variations of the detector can thus be reduced in the photodetector and the sensitivity to low photon rates can be improved.

[0096] Therefore, the dead time t ddepends largely on the reverse voltage V A This property is exploited in the framework of the concept described in this article in order to obtain a d The value of the reverse voltage V A : One or more minima of the amplitude spectrum as used in this paper.

[0097] Figure 6 A first block diagram 601 is shown, according to which the concepts described herein are explained in more detail by means of a photodetector 603 with an exemplary conditioning device 607 according to the second aspect.

[0098] The diodes are provided with the same reverse voltage by the adjustable voltage source 605. This means that the same reverse voltage is applied to the diodes by means of the adjustable voltage source 605.

[0099] It should be noted that the adjustment device 607 can be fully or partially implemented in the hardware of the photodetector.

[0100] The set value of the dead time is provided as input to the regulating device 607. This set value is symbolically identified by the block with the reference number 609. The set value of the dead time can also be denoted as T d,soll .

[0101] Furthermore, the control device 607 receives a signal 611 of the signal path as an input variable, for example S TDC,i,j , where j ranges from 1 to M and represents the index of one of the groups of single photon avalanche diodes of the photodetector 603. Hist,j Can also be used as input variable 611.

[0102] According to function block 613, the dead time is calculated based on input variable 611. Then, according to function block 615, the calculated dead time t d and setting value t d,soll Calculation and ideal voltage V a Deviation ΔV a Then, the logic unit 617 adjusts the adjustable voltage source 605 so that the deviation ΔV a minimize.

[0103] Therefore, it is provided that all SPAD groups are powered by a single voltage V A The regulator uses the time quantization signal S TDC,i,j Or histogram S Hist,j i∈[1..N] and j∈[1..M] apply. Dead time scalar t d The calculation can be based on one or more signals. When selecting the signal, for example, the dead time t of each SPAD pixel should be taken into account. dMay vary due to manufacturing tolerances.

[0104] For example, the dead time is calculated based on a local minimum value of the amplitude spectrum of the corresponding signal.

[0105] For example, then according to the calculated dead time t d and its setting value t d,soll To calculate the ideal voltage V a Deviation ΔV a For example, the logic unit adjusts the adjustable voltage source so that the deviation ΔV a minimize.

[0106] According to the signal S SP,i , S TDC,i or S Hist Each of the two is used to calculate the magnitude spectrum 701, which is Figure 7 As shown in FIG.

[0107] The frequency of the signal of the signal path is plotted on the abscissa 703. The amplitude of the signal of the signal path is plotted on the ordinate 705.

[0108] A plurality of local minima of the magnitude spectrum 701 are denoted by reference numerals 707 , 709 , 711 .

[0109] The first local minimum is identified by reference numeral 707. The second local minimum of the magnitude spectrum is identified by reference numeral 709. The third local minimum is identified by reference numeral 711.

[0110] The first local minimum 707 can also be represented by f d The other local minimum values ​​709 and 711 are located at f d An integer multiple of .

[0111] A particular feature of the amplitude spectrum 701 is that, for a given detector, the frequency f of the first local minimum is d It depends largely on the dead time t d , and only slightly depends on the corresponding signal S SP,i , S TDC,i or S Hist The average value of d There are other local minima at integer multiples of .

[0112] The frequency of the average value and the local minimum is a function of the dead time t for a low background light intensity and a high intensity due to the received laser pulse. d The relationship between is too complex to be evaluated in the detector logic. To prevent the resulting measurement errors, for example, the signal S SP,i , S TDC,i or SHist is filtered out from the mentioned cases. For example, for this purpose, use is made of the fact that the laser pulse duration is proportional to the passing signal S SP,i , S TDC,i or S Hist The ratio of the mapped measurement times is only about 1 to 100. Therefore, the laser pulses have only a negligible effect on the average value. For example, a very simple filter is based on the following: SP,i , S TDC,i or S Hist If the average value is less than 2% of the maximum possible signal level, it is discarded. SP,i , S TDC,i or S Hist A high-intensity laser pulse is determined by a maximum value in . Signals in which a maximum value close to the maximum possible signal level and a very low average value occur simultaneously are identified, wherein such signals are, for example, discarded.

[0113] The following example assumes that: the average value is μ Hist,j The signal S of SPAD group j Hist,j Serves as the basis for calculating dead time.

[0114] Calculate the dead time t d The method is Figure 8 As shown in FIG.

[0115] Figure 8 A second block diagram 801 is shown which explains the dead time t d An exemplary calculation of .

[0116] Used to calculate the dead time t d The unit 803 obtains, for example, a signal or a plurality of signals S Hist,j As input variable 805. According to functional block 807, one of the signals 805 is selected, for example by its average value. The average value of that histogram whose histogram signal is used to determine the amplitude spectrum and thus ultimately the local minimum is denoted as μ Hist and is provided as an input variable to the function block 811. According to the function block 809, the amplitude spectrum of the selected signal is determined and the frequency f is determined d This is provided as an input variable to the function block 811, according to which the function block calculates the average value μ Hist and f d To determine or calculate the dead time t d 813.

[0117] For example, using only its mean and μ Hist,j This is achieved, for example, by selecting the histogram accordingly.

[0118] Frequency f d , 2f d 、3f d …can be found by searching for local minima. The minimum search becomes particularly robust if a model function is fit to the magnitude spectrum beforehand.

[0119] Relationship d =F(t d ,μ Hist ) is determined, for example, by firstly directly measuring the dead time t beforehand during the production of the photodetector, for example d On the other hand, for different average values ​​μ Hist Determine the frequency f d For example, the relationship f d =F(t d ,μ Hist ) can now be implemented as a lookup table or fitting function. The inverse relationship t d =F(f d ,μ Hist ), according to the frequency f d and the histogram mean μ Hist Determine the dead time t at any time d .

[0120] For example, an exemplary embodiment of the adjustment is, according to Figure 6 According to the measured dead time t d and setting value t d,soll To calculate the deviation ΔV a , the deviation is to reach the set value t d,soll To do this, the relationship ΔV is used a =F(t d ,t d,soll ), which relationship can be determined, for example, by characterization.

[0121] The logic unit adjusts the target voltage V of the adjustable voltage source A,Soll , the purpose is to make ΔV a As close to 0 as possible.

[0122] exist Fig. 9 In the embodiment shown in FIG. , the dead time t is omitted. d Only the frequency f d Determined by the amplitude spectrum, such as Figure 7 According to the relationship A err =F(f d ,f d,soll ) Calculate the error variable A err , for example A err =B(f d,max-f d,soll ), where B is a constant. The logic unit adjusts the target voltage V of the adjustable voltage source A,Soll , the purpose is to make A err =0.

[0123] Frequency setting value f d,soll It can be selected by a strategy that does not only seek to achieve a certain dead time set value t or does not seek to achieve it at all d,soll The prerequisite is to pre-characterize the SPAD-based detector, where f d According to the corresponding parameters (such as PDE, V a For example, this can realize the following control strategies, which can be combined with each other, in particular partially combined with each other:

[0124] 1. Achieve the maximum possible PDE.

[0125] 2. Achieve a constant PDE within a given temperature range.

[0126] 3. Operate the photodetector at an operating point defined by the voltage VBD given in the new state.

[0127] therefore, Fig. 9 A third block diagram 901 is shown, which shows the frequency f d The applied reverse voltage V a Example adjustments of .

[0128] The logic unit 903 obtains, for example, a signal S Hist As input variable 905, it is used to determine the deviation ΔV a The frequency setting value f d,Soll 907 is used as another input variable. Hist , according to function block 909, the frequency f is calculated d , which is the frequency of the first local minimum. Frequency f d As input variable it is used for the function block 911, which also receives the set value f of the frequency d,soll 907.

[0129] For example, the error variable A err It can be defined as follows: A err =F(f d ,f d,Ssoll ).

[0130] The error variable is provided as an input variable to the logic unit 913, which outputs a target voltage 915 to the adjustable voltage source based on the error variable, in order to make A err =0.

Claims

1. A method for stabilizing a voltage of one or more groups (203) of single photon avalanche diodes (205) of a photodetector (201), wherein: A digital converter (207) is connected downstream of each diode (205), and the method comprises the following steps: detecting (101) one or more signals of a signal path of the photodetector (201) including the diode (205) and the digitizer (207) with the same reverse voltage applied to the diode (205), determining (103) a corresponding amplitude spectrum (701) of the detected one or more signals, determining (105) corresponding local minima (707, 709, 711) of the determined one or more amplitude spectra, The applied reverse voltage is adjusted (107) based on the determined one or more local minima (707, 709, 711).

2. The method according to claim 1, wherein: The corresponding digital output signal of the digital converter (207) is quantized in time by a predetermined clock to obtain a corresponding quantized output signal, wherein one of the quantized output signals is detected as a signal of one or more signals of the signal path.

3. The 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 according to claim 3, wherein: One of the generated histogram signals is detected as a signal of one or more signals of the signal path.

5. The method according to claim 3 or 4, wherein: An average value of the generated histogram signal is determined to generate an averaged histogram signal representing the determined average value, wherein the averaged histogram signal is detected as a signal of one or more signals of the signal path.

6. The method according to claim 4 or 5, wherein: A respective average of the generated histogram signals is determined to generate a respective histogram average signal representing a respective average of the respective histogram, wherein the generated histogram signal to be detected is selected from the generated histogram signals based on the averaged histogram average signal.

7. The method according to any one of claims 4 to 6, wherein: Determine a corresponding average value and a corresponding maximum value of the generated histogram signal to generate a corresponding histogram average value signal and a corresponding histogram maximum value signal representing the corresponding average value and the corresponding maximum value of the corresponding histogram, wherein the generated histogram signal to be detected is selected from the generated histogram signal based on the corresponding histogram average value signal and the corresponding histogram maximum value signal.

8. The method according to claim 6 or 7, wherein: The generated histogram signal to be detected is calculated from those histogram signals having similar histogram means.

9. A method according to any one of the preceding claims, wherein: Based on the determined one or more local minima (707, 709, 711), the corresponding dead time of the following one or more diodes (205) is determined: one or more signals of the signal path for determining the one or more local minima (707, 709, 711) are based on the one or more diodes, wherein the applied reverse voltage is adjusted based on the one or more respectively determined dead times.

10. A method according to any one of the preceding claims, wherein: One of the respective digital output signals of the digitizer is detected as a signal of one or more signals of the signal path.

11. A photodetector (201), comprising: one or more groups (203) of single photon avalanche diodes (205), Wherein, the downstream of the diode (205) is respectively connected with a digital converter (207), a detection device (209) arranged to detect one or more signals of a signal path of the photodetector (201) including the diode (205) and the digitizer (207) when the same reverse voltage is applied to the diode (205), determining means (211) arranged to determine a corresponding amplitude spectrum (701) of the detected one or more signals, wherein the determining means (211) is arranged to determine corresponding local minima (707, 709, 711) of the determined one or more amplitude spectra, A regulating device (213) is arranged to regulate the applied reverse voltage based on the determined one or more local minima (707, 709, 711).

12. A computer program (303) comprising instructions which, when the computer program (303) is executed by a computer, cause the computer to perform the method according to any one of claims 1 to 10.

13. A machine-readable storage medium (301) having stored thereon a computer program (303) according to claim 12.

Images