Automated out-of-line pixel detection

Abstract

A method and a system (118) for automated out-of-line pixel detection of at least one photodetector (120) are disclosed. The photodetector (120) comprises a plurality of pixels (122), wherein each pixel (122) comprises at least one photosensitive region (124), wherein each pixel (122) is configured for generating a signal in response to illumination by optical radiation of its respective photosensitive region (124), wherein the photodetector (120) further comprises at least one readout circuit (126) configured for readout of the plurality of pixels (122). The method comprises the following steps: a) applying a skimming voltage Vskimming to each pixel (122) of the plurality of pixels (122) and measuring an initial signal value Sinitial for each pixel (122) of the plurality of pixels (122) without illumination of the photodetector (120) by using the readout circuit (126) of the photodetector (120); b) changing the skimming voltage Vskimming,j for at least one pixel j (130) of the plurality of pixels (122) and measuring an actual signal value Sactual,k of at least one further pixel k (132) of the plurality of pixels (122) with k ≠ j; c) comparing the initial signal value of the further pixel k (132) and the actual signal value of the further pixel k (132), by using at least one processor (134), wherein the further pixel k (132) is detected as out-of-line pixel (116) in case the initial signal value and the actual signal value differ by more than at least one predefined tolerance.

Description

[0001] AUTOMATED OUT-OF-LINE PIXEL DETECTION

[0002] Technical Field

[0003] The present invention relates to a method and a system for automated out-of-line pixel detection of at least one photodetector comprising a plurality of pixels. The invention further relates to a computer program and a computer-readable storage medium for performing the method.

[0004] Such methods and devices can, in general, be used for testing and / or preparing photodetectors for investigation or monitoring purposes, in particular in the infrared (IR) spectral region, especially in the near-infrared (NIR) spectral region, e.g. for a detection of heat, flames, fire, or smoke. However, further kinds of applications are possible

[0005] Background art

[0006] Photodetectors having a plurality of pixels arranged in an array or a matrix can be used in the field of optical investigation or monitoring. Errors or inaccuracies during manufacturing of these photodetectors may result in neighboring pixels providing implausible signals, e.g. due to unwanted electrical or optical connections or an instability of electrical or optical properties of the respective pixels over time or ambient conditions, such as temperature. Usually, these pixels can be identified using optical setups to generate and analyze spectral measurement.

[0007] US 6,118,482 A describes a method and apparatus for electrical testing of CMOS pixel sensors which involves electrically writing a pattern into the CMOS pixel sensors for the detection of adjacent cell shorts or stuck at faults as well as verification of read-channel circuit functionality and performance.

[0008] US 2008 / 0106602 A1 discloses an on chip test method for determining the photon transfer curve (PTC) and dark current in an image sensor. The method comprises a snap shot mode where a first plurality of pixel rows are exposed for a time ti , a second plurality of pixel rows are exposed for a time t2, and so forth up to an nth plurality of pixel rows exposed for a time tnwhere the total number of pixel rows equals a frame and tn>t2>ti . The resulting image has "n" regions each with a different brightness that become progressively brighter from top to bottom of the image.

[0009] US 2005 / 0041242 A1 describes methods and apparatuses for testing image sensors. The apparatuses include image sensor testing devices comprising a digital light projection system capable of projecting static or dynamic images onto an image sensing device under test and an image sensor signal detection means for analyzing the output of said image sensing device under test. The digital light projection system comprises a light source, collimating optics, a digital micromirror device, and focusing optics. Other example methods and apparatuses include image sensor testing devices employing a digital light projection system capable of simultaneously testing a plurality of image sensors. The light source is calibrated and converted to a desired test image by the digital micromirror device. The test image is then focused onto an image sensor, the output of which is read by a detector and correlated with the input digital test image.

[0010] US 6,489,798 B1 discloses a method and apparatus for testing an image sensor array such as a CMOS imager which has sensing circuits arranged in rows and columns and wherein the sensing circuits include photosensitive devices. A reset voltage is applied to the photosensitive device in each of the sensor circuits such that at least adjacent circuits are reset to different voltage levels. The voltage on each photosensitive device is detected and compared to an expected level to determine if and where any faults may exist in the sensing circuits or lines in the array. A different reset voltage may be applied to each of the sensor circuits, however in one embodiment, a supply with only two voltage levels may be used. One voltage level is applied to every second column to provide a supply voltage to the photosensitive devices and to every second row to generate a reset enable signal for the photosensitive devices. The second voltage level is applied to the remaining columns and rows resulting in different reset voltage levels on adjacent sensing circuits.

[0011] JP 2000 244005 A describes a photoelectric transfer device. To output a correct signal in a short time after the power of the photoelectric transfer device is turned on by injecting the same type of charge carrier as the one generated by casting light. Immediately after the power of a photoelectric transfer device having pixels is turned on, the potential of a terminal is increased much higher than the reference voltage at a terminal to turn a diode into a forward biased state and a photo transistor into an on state and thereafter the potential of the terminal is lowered. The charge carrier which is the same type as the one generated by light injected into the photo transistor of a photoelectric transfer element from the diode is immediately discharged by the forward bias current of a diode, and thereby the base of the photo transistor reaches a stationary state wherein the base current is equal to the current generated by light. By injecting the charge carrier into the pixels, the instability of the output when the power of the photoelectric transfer device is turned on can be removed in a short time to obtain the correct output.

[0012] EP 3 637 135 A1 discloses a solid-state optical receiver system, particularly for automotive applications, comprising at least two optical receiver circuits, each optical receiver circuit comprising an optical receiver for detecting an optical input signal, and a signal processing unit for processing the signal of the optical receiver, which is characterized in that the solid-state optical receiver system comprises a short-circuit detection unit for detecting a short-circuit between optical receiver circuits. Further describes is a method for detecting a short-circuit between optical receiver circuits of a solid-state optical receiver system, particularly for automotive applications.

[0013] Despite the advantages achieved by known methods and devices, several technical challenges remain. Specifically, generating, analyzing and verifying spectral measurements of manufactured photodetectors may only be possible in a late phase of manufacturing. For example, during manufacturing, the photodetector can generally not measure any spectral information without additional hardware setup, such optical filters, e.g. a linear variable filter (LVF), or gratings. Thus, checking for defective or out-of-line pixel at an early stage of manufacturing may only be possible in a limited way and with high effort, e.g. by performing resistance measurements having the pixels mechanically contacted to a wafer prober. The resistance measurement may generally be performed before the read out electronics is bonded to the photodetector. However, short circuits may especially arise after bonding. Further, spectral measurements may require additional hardware setup. For example, a LVF may be used to split light generated by an additional light source into spectral constituents over the pixels. The defective or out-of-line pixel may only be found reliably when measuring a spectrum having dynamic ranges. Thus, summarizing, there is a need for checking photodetector having a plurality of pixels with the array itself and without using light signals, specifically without spectral measurements.

[0014] Problem to be solved

[0015] It is therefore desirable to provide methods and devices which at least partially address above- mentioned technical challenges. Specifically, a method and a system for automated out-of-line pixel detection of at least one photodetector shall be proposed which enable detection of out-of- line pixels at any early stage of manufacturing and without the need for additional hardware setup.

[0016] Summary

[0017] This problem is addressed by a method and a system for automated out-of-line pixel detection of at least one photodetector with the features of the independent claims. Advantageous embodiments which might be realized in an isolated fashion or in any arbitrary combinations are listed in the dependent claims as well as throughout the specification.

[0018] In a first aspect of the present invention, a method for automated out-of-line pixel detection of at least one photodetector comprising a plurality of pixels is disclosed. Each pixel comprises at least one photosensitive region. Each pixel is configured for generating a signal in response to illumination by optical radiation of its respective photosensitive region. The photodetector further comprises at least one readout circuit configured for readout of the plurality of pixels.

[0019] The term “photodetector” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an optical detector or optical sensor configured for detecting optical radiation, such as for detecting an illumination by light and / or a light spot generated by at least one light beam. The photodetector may specifically be configured for detecting optical radiation in one or more of the visible spectral range, the infrared spectral range and the ultraviolet spectral range. The pixels of the photodetector may be responsive to incident illumination and may be configured for generating an electrical signal indicating an intensity of the illumination, such as a detector current. The photodetector may be sensitive in one or more of a visible spectral range, an ultraviolet spectral range or the infrared spectral range, specifically a near infrared spectral range (NIR). The photodetector may specifi- cally be an infrared photodetector. The photodetector may be sensitive for electromagnetic radiation in wavelength range from 600 nm to 1000 pm, specifically in a wavelength range from 760 nm to 15 pm, more specifically in a wavelength range from 1 pm to 5 pm, more specifically in a wavelength range from 1 pm to 3 pm, preferably from 1 .3 pm to 2.5 pm, more preferably from 1 .5 pm to 2.2 pm.

[0020] The term “pixel” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a single optical detecting or sensing device configured for detecting optical radiation. Specifically, the pixel may be a single unit of a photodetector configured for being illuminated by light. The pixel may be configured for receiving optical radiation and for generating at least one output signal, such as an electronic signal, e.g. a detector current, in response to the illumination by the optical radiation. The pixel may be or may comprise a single photosensitive element. The pixel may have at least one lightsensitive property such that illumination of the pixel by light causes at least one change in the light-sensitive property.

[0021] As used herein, the term “light”, also denoted as “optical radiation”, refers, without limitation, to a partition of electromagnetic radiation which is, usually, referred to as “optical spectral range” and which comprises one or more of a visible spectral range, an ultraviolet spectral range and an infrared spectral range. The terms “ultraviolet spectral” or “UV”, generally, refer to electromagnetic radiation having a wavelength of 1 nm to 380 nm, preferably of 100 nm to 380 nm. The term “visible”, generally, refers to a wavelength of 380 nm to 760 nm. The terms “infrared” or “I R”, generally, refer to a wavelength of 760 nm to 1000 pm, wherein a wavelength of 760 nm to 3 pm is, usually, denominated as “near infrared” or “NIR” while the wavelength of 3 pm to 15 pm is, usually, denoted as “mid infrared” or “Midi R” and the wavelength of 15 pm to 1000 pm as “far infrared” or “FIR”.

[0022] The term “photosensitive region” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an element adapted for interacting with optical radiation. The photosensitive region may be located on a surface of the photodetector, specifically on a surface of the pixels of the photodetector. The photosensitive region may specifically be a single, closed, uniform photosensitive region. However, other options may also be feasible. The photosensitive region may form part of the pixel, specifically may provide the light-sensitive part of the pixel. The photodetector comprises a plurality of pixels. The plurality of pixels, specifically the photosensitive regions of the plurality of pixels, may be arranged in at least one of an array or a matrix. For example, the plurality of pixels, specifically the photosensitive regions of the plurality of pixels, may be arranged in a linear array. As another example, the plurality of pixels, specifically the photosensitive regions of the plurality of pixels, may be arranged in a 2D distribution. The plurality of pixels, specifically the photosensitive regions of the plurality of pixels, may be arranged in a pattern. The pattern may be periodical or non-periodical. The pattern may be a rectangular, a hexagonal or otherwise shaped pattern. The pixel may comprise at least one substrate. A single pixel may be a substrate with at least one single photosensitive region disposed therein or thereon, the photosensitive region generating a physical response to the illumination by light for a given wavelength range. However, other options may also be feasible.

[0023] The photosensitive region may comprise at least one photoconductive material. The photocon- ductive material may be selected from the group consisting of: lead sulfide (PbS); lead selenide (PbSe); mercury cadmium telluride (HgCdTe); cadmium sulfide (CdS); cadmium selenide (CdSe); indium antimonide (InSb); indium arsenide (InAs); indium gallium arsenide (InGaAs); silicon (Si); Silicon Germanium (SiGe); lithium tantalate (LiTaO3); triglycine sulfate (TGS); platinum silicide (PtSi); quantum well infrared photodetector (QWIP); extrinsic semiconductors, organic semiconductors. For example, the photodetector may be or may comprise at least one line sensor comprising a one-dimensional array of pixels, e.g. a CCD line sensor, a CMOS line sensor and the like. For example, the photodetector may be or may comprise a two-dimensional array of pixels, e.g. a CCD sensor, a CMOS sensor and the like.

[0024] The photodetector may specifically comprise at least one detector array comprising the plurality of pixels, wherein, optionally, each of the pixels may be configured to detect at least a portion of at least one constituent wavelength component. The photodetector may comprise the plurality of pixels arranged in the detector array. For example, the photodetector may comprise the plurality of pixels arranged in a linear array. Alternatively or additionally, the photodetector may comprise the plurality of pixels arranged in two-dimensional array. The detector array, specifically the linear array of pixels, may comprise a number of 2 to 1000 pixels, specifically a number of 10 to 500 pixels, more specifically a number of 200 to 300 pixels, most specifically a number of 256 pixels. Other numbers of pixels and / or other arrangements, however, may be feasible.

[0025] The term “signal” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a signal generated by the photodetector. The signal may specifically comprise the at least one output signal of the pixel. The at least one output signal may be least one electronic signal. The at least one output signal may be an analogue signal and / or a digital signal. The output signals for adjacent pixels can be generated simultaneously, or in a temporally successive manner. By way of example, during a row scan or a line scan, it can be feasible to generate a sequence of output signals which correspond to the series of the photosensitive elements which may be arranged in a line. In addition, the individual pixels may, preferably, be active pixel sensors which may be adapted to amplify the output signals prior to providing them as detector signals to an external processor, specifically to the readout circuit. For this purpose, each of the pixels may comprise one or more signal processing devices, such as one or more filters and / or analogue-digital-converters for processing and / or preprocessing the electronic signals. Each of the pixels may comprise at least one skimming circuit configured for skimming a detector current from the pixels generated in response to the illumination by optical radiation. As outlined above, the signal of each pixel may depend on the illumination by optical radiation of its respective photosensitive region. The signal may specifically depend on a detector current generated by the respective pixel in response to illumination by light, e.g. at least one photocurrent generated by the respective pixel in response to illumination by light. The pixel may also be configured for generating a signal without having illumination by optical radiation of its photosensitive region. The signal without having illumination on the photosensitive region may also be referred to as “dark current signal”. The signal, specifically the detector current, may comprise the dark current signal. The dark current signal may depend on operational parameters applied to the respective pixel, such as applied voltage or the like.

[0026] The term “illumination” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an amount or an intensity of light impinging a certain area, specifically the photosensitive region of the pixels.

[0027] As outlined above, the photodetector further comprises the at least one readout circuit configured for readout of the plurality of pixels. The term “readout” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an action or process of quantifying and / or processing at least one physical property and / or a change in at least one physical property detected by at least one device, specifically by the at least one photodetector or more specifically by the photosensitive region. The readout may comprise an individual readout of one device, such as of one photosensitive region of each pixel. Additionally or alternatively, the readout may comprise a readout of a group of devices, such as a group of photosensitive regions of the pixels.

[0028] The term “readout circuit” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an electronics unit configured for readout, i.e. for quantifying and / or processing at least one physical property and / or a change in at least one physical property detected by the photodetector or more specifically by the photosensitive region. The readout electronics unit may comprise at least one of an operational amplifier, an analog-to-digital converter, a voltage divider, and a current divider. The readout circuit may comprise at least one integrated circuit. The readout circuit may comprise at least one application-specific integrated circuit (ASIC), the ASIC specifically being configured for readout of one or more pixels, more specifically for readout of the plurality of pixels. The readout circuit may be or may comprise at least one readout integrated circuit (ROIC). The readout circuit may be configured for processing at least one detector current, specifically a part of the detector current, from a pixel and derive the signal value of the respective pixel therefrom.

[0029] The term “out-of-line pixel” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a pixel showing implausible signal behavior. Specifically, neighboring pixels of the photodetector may provide implausible signals, e.g. due to unwanted, electrically or optical connections, which may result in a non-resolvable spectral trend or deviation from the samples’ response in a reproducible way. For example, two or more pixels may be short-circuited. Said pixels showing implausible signals may be denoted as “out-of-line pixels”. The out-of-line pixel may be or may comprise at least one of a short-circuited pixel, a pixel having defective bonding wires, a pixel being electrically connected to another pixel or a crosstalk pixel. For example, the out-of-line pixel may have a systematic deviation in signal behavior from the signal behavior of the other pixels of the photodetector or of one or more other regions of the photodetector, e.g. a deviation in signal behavior from the signal behavior of the other pixels of the array or matrix of pixels or of one or more other regions of the array or matrix.

[0030] The term “detection” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to at least one process of determining if out-of-line pixels are present. Specifically, the detection of out-of-line pixels may comprise evaluating the signal behavior of each pixel of the plurality of pixels. The quality control may comprise classifying the pixels of the photodetector into reliable pixels and out-of-line pixels. A result of the detection may be stored in at least one Log-file. The detection may comprise masking all pixels of the plurality of pixels which are classified as out-of-line. The detection may be part of a quality control process. The detection may be performed on newly manufactured photodetectors. Alternatively or additionally, the detection may also be performed on photodetectors during usage, e.g. to determine if pixels of the plurality of pixels deteriorate to out-of- pixels during usage of the photodetector. The detection may comprise issuing at least one indication about the presence of out-of-line pixels, e.g. by using at least one user interface.

[0031] The term “automated” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a process which is performed completely by means of at least one computer and / or computer network and / or machine, in particular without manual action and / or interaction with a user. The method may be at least partially computer-implemented. The term "computer implemented method" as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a method involving at least one computer and / or at least one computer network. The computer and / or computer network may comprise at least one processor which is configured for performing at least one of the method steps of the method according to the present invention. Specifically, each of the method steps is performed by the computer and / or computer network. The method may be performed completely automatically, specifically without user interaction. The method steps may be performed in the given order. It shall be noted, however, that a different order is also possible. The method may comprise further method steps which are not listed. Further, one or more of the method steps may be performed once or repeatedly. Further, two or more of the method steps may be performed simultaneously or in a timely overlapping fashion.

[0032] The method comprises the following steps: a) applying a skimming voltage VSkimmingto each pixel of the plurality of pixels and measuring an initial signal value Sinitiai for each pixel of the plurality of pixels without illumination of the photodetector by using the readout circuit of the photodetector; b) changing the skimming voltage VSkimming,j for at least one pixel j of the plurality of pixels and measuring an actual signal value Sactuai,k of at least one further pixel k of the plurality of pixels with k * j; c) comparing the initial signal value of the further pixel k and the actual signal value of the further pixel k by using at least one processor, wherein the further pixel k is detected as out-of-line pixel in case the initial signal value and the actual signal value differ by more than at least one predefined tolerance.

[0033] The term “applying a voltage” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a process of providing a voltage to one or more elements or devices. The applying of a voltage to each pixel of the plurality of pixels may comprise using at least one voltage generator, such as at least one voltage source and / or at least one voltage regulator. The voltage may be applied to the pixel in a controlled manner, such as by controlling a strength, type, frequency and / or temporal evolve- ment of the applied voltage. The voltage may be applied to each pixel individually, such as by controlling the applied voltage to each pixel independent from the other pixels.

[0034] The term “skimming voltage” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a voltage applied to each pixel for the purpose of readout. The skimming voltage may be a voltage applied to the readout circuit for the purpose of charge skimming during the readout of the pixels. Specifically, the pixel, as outlined above, is configured for generating a signal in response to illumination by optical radiation of its respective photosensitive region. The signal may comprise at least one detector current, specifically one or more of a dark current signal and a photocurrent. As further outlined above, the pixel may comprise at least one skimming circuit configured for skimming the detector current. The skimming voltage may be applied to the skimming circuit. Specifically, the skimming voltage may be applied to the skimming circuit in order to control at least one skimming current through the skimming circuit. The detector current may be separated into the skimming current through the skimming circuit and a remainder which is processed by the readout circuit to derive the signal value of the respective pixel therefrom. The signal value of the pixel may be dependent on the skimming voltage applied to the skimming circuit of the respective pixel. The term “measuring” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a quantitative determination of at least one representative value using at least one measurement signal. Specifically, measuring a signal value of a pixel of the plurality of pixel may comprise processing the signal generated by the respective pixel and deriving the signal value therefrom. A result of the measuring may comprise, as an example, the signal value on a relative or dimensionless scale. Thus, the signal value may be measured in arbitrary units.

[0035] The term “initial signal value” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a signal value for a pixel under initial conditions. The initial signal value may be or may comprise a signal value for a pixel having an initial skimming voltage applied thereto. Specifically, the skimming voltage applied to each pixel in step a) may define the initial skimming voltage. The initial signal value may be a signal value obtained by using the readout circuit with the initial skimming voltage applied to each pixel. The initial signal value may be used as a reference value. Specifically, changes and / or deviation in the signal value of a pixel may be identified by using the initial signal value, specifically by comparing with the initial signal value. The initial signal value may be a single signal value and / or a mean or average value obtained by measuring the signal value of the pixel multiple times with the initial skimming voltage applied thereto.

[0036] The term “without illumination” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a situation having no illumination, specifically no intentional illumination, by optical radiation on the photosensitive region of the pixel. Specifically, in a phase without illumination, light sources illuminating the photosensitive region of the pixel may be turned off. In a phase without illumination, an active illumination of the photosensitive region of the pixel may be avoided. However, other light sources may be present, e.g. specifically ambient light sources.

[0037] The term “changing a voltage” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a process of varying a voltage applied to an element or device, specifically in order to induce a measurable change in an output of the element or device. The changing of the skimming voltage for a pixel of the plurality of pixels may comprise varying the skimming voltage applied to the pixel, specifically applied to the skimming circuit of the pixel. The changing of the skimming voltage may induce a change in the signal value of the pixel. For intact photodetectors, the changing of the skimming voltage for the pixel j may not induce a change in the signal value of other pixels with k * j. The changing of the skimming voltage may comprise tuning the skimming voltage from at least one initial skimming voltage. For example, the changing of the skimming voltage may comprise increasing the skimming voltage for pixel j from the at least one initial skimming voltage. The skimming voltage for the remaining pixels may be kept constant at the initial skimming voltage. Alternatively or additionally, a decrease of the skimming voltage may be also be feasible.

[0038] The term “actual signal value” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a signal value for a pixel under modified conditions. The actual signal value may be or may comprise a signal value for a further pixel k obtained during applying of at least one changed skimming voltage to at least one pixel j with k * j. Specifically, the actual signal value may comprise at least one signal value obtained for the further pixel k of the plurality of pixels in parallel with an application of a changed skimming voltage applied to the at least one pixel j being different from the first pixel. The skimming voltage for the further pixel k may be kept constant during measuring the actual signal value. The actual signal value may be a single signal value and / or a mean or average value obtained by measuring the signal value of the further pixel k multiple times with the changed skimming voltage applied to the pixel j. The actual signal value Sactuai,k may be measured without illumination of the photodetector, specifically without intentional illumination of the photodetector.

[0039] The actual signal value Sactuai,k may specifically be measured for each further pixel k of the plurality of pixels. The actual signal values of the plurality of pixels may be measured in a frame measurement through the plurality of pixels. The frame measurement may specifically be a coherent measurement of all pixels of the photodetector. The frame measurement may comprise a timely overlapping or parallel measurement of at least a part of the plurality of pixels, e.g. a parallel measurement of columns or rows of the pixels in the photodetector, more specifically of all of the pixels of the photodetector.

[0040] The term “further pixel” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a pixel differing from the pixel with the changed skimming voltage. The further pixel k may be different from the pixel j. The further pixel may specifically be different from the pixel having the changed skimming voltage applied thereto.

[0041] The further pixel k may be a pixel of the plurality of pixels with k = j ± n, wherein n e N. Specifically, the further pixel k may be at least one of a nearest neighboring pixel of the pixel j with k = j ± 1 and a next-nearest neighboring pixel of the pixel j with k = j ± 2.

[0042] The term “comparing” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a process of evaluating at least one first item of information with respect to at least one second item of information. The comparing may comprise evaluating the actual signal value with respect to the initial signal value. The comparing may comprised directly comparing the initial signal value and the actual signal value and / or indirectly comparing the initial signal value and the actual signal value, such as by comparing the initial signal value and the actual signal value with further preprocessing of the respective signal value. The comparing of the initial signal value and the actual signal value may comprise determining at least one quotient using the initial signal value and the actual signal value. Alternatively or additionally, the comparing of the initial signal value and the actual signal value may comprise determining at least one difference between the initial signal value and the actual signal value. The comparing may specifically comprise determining a difference between a maximum of the initial signal value and the actual signal value, and a minimum of the initial signal value and the actual signal value. The difference may be compared with the predefined tolerance to detect an out-of-line pixel.

[0043] Additionally or alternatively, the comparing of the initial signal value of the further pixel k and the actual signal value of the further pixel k may comprise at least one offset correction. The offset correction may be applied to both the initial signal value and the actual signal value. The offset correction may be applied prior to determining a difference in the initial signal value and the actual signal value. Alternatively or additionally, the offset correction may be applied to the determined difference of the initial signal value and the actual signal value. The offset correction may account for noise-induced fluctuation of the signal values at the pixels.

[0044] The comparing may be performed automatically, specifically by using the at least one processor. The term “processor” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an arbitrary logic circuitry configured for performing basic operations of a computer or system, and / or, generally, to a device which is configured for performing calculations or logic operations. In particular, the processor may be configured for processing basic instructions that drive the computer or system. The processor may be or may comprise at least one of an integrated circuit, in particular an application-specific integrated circuit (ASIC), or a data processing device, in particular at least one of a digital signal processor (DSP), a field programmable gate array (FPGA), a microcontroller, a microcomputer, a computer, or an electronic communication unit, specifically a smartphone or a tablet. As an example, the processor may comprise at least one arithmetic logic unit (ALU), at least one floating-point unit (FPU), such as a math co-processor or a numeric co-processor, a plurality of registers, specifically registers configured for supplying operands to the ALU and storing results of operations, and a memory, such as an L1 and L2 cache memory. In particular, the processor may be a multi-core processor. Specifically, the processor may be or may comprise a central processing unit (CPU). Additionally or alternatively, the processor may be or may comprise a microprocessor, thus specifically the processor’s elements may be contained in one single integrated circuitry (IC) chip. Additionally or alternatively, the processor may be or may comprise one or more application-specific integrated circuits (ASICs) and / or one or more field-programmable gate arrays (FPGAs) and / or one or more tensor processing unit (TPU) and / or one or more chip, such as a dedicated machine learning optimized chip, or the like. The processor specifically may be configured, such as by software programming, for performing one or more detection operations. Further components may be feasible, in particular at least one preprocessing device or data acquisition device. The processor may, preferably, be configured to perform at least one computer program, in particular at least one computer program performing or supporting the steps of the method according to the present invention.

[0045] The term “predefined tolerance” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a quantitative measure for evaluating a deviation between two values. Specifically, the predefined tolerance may be or may comprise a quantitative measure for evaluating a deviation of the actual signal value from the initial signal value. The deviation of the actual signal value from the initial signal value may be compared with the predefined tolerance. In case the deviation of the actual signal value from the initial signal value exceeds the predefined tolerance, the respective further pixel k may be detected as an out-of-line pixel. In case the deviation of the actual signal value from the initial signal value is equal to or below the predefined tolerance, the respective further pixel k may be detected as an intact pixel. The predefined tolerance may comprise an absolute quantitative measure, such as an absolute threshold, e.g. a threshold count, and / or a relative quantitative measure, such as a tolerance level being dependent on the initial signal value, e.g. a multiple of the initial signal value. The predefined tolerance may prevent biases in the out-of-line pixel detection, e.g. due to noise-induced fluctuation of the signal values at the pixels. The predefined tolerance may be defined and / or determined in advance of the method of automated out-of-line pixel detection and, thus, may be referred to as “predefined”.

[0046] The method may further comprise selecting at least one pixel sequence comprising a number of pixels selected from the plurality of pixels. The term “pixel sequence” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a group of pixels selected from the plurality of pixels. The pixel sequence may specifically comprise a group of non-neighboring pixels. The pixel sequence may comprise a regular pixel sequence, specifically a regular pixel sequence having the number of pixels spaced apart from each other by at least one predefined pixel spacing. For example, the predefined pixel spacing may be at least 5 pixels. Thus, in this example, the pixel sequence may comprise each 6thpixel of the plurality of pixels. However, any other pixel spacing of 2 or more pixels may also be feasible. In step b), the skimming voltage may be changed for each pixel of the pixel sequence simultaneously. The method may further comprise shifting the pixel sequence along the plurality of pixels. Specifically, the method may comprise shifting the pixel sequence along the plurality of pixels such that each pixel of the plurality of pixels is selected at least once for the pixel sequence. The pixel sequence may allow for testing many pixels at the same time. Further, performing the method with the shifted pixel sequence may ensure that no pattern of out-of-line pixels remains undetected. Additionally or alternatively, the pixel sequence may allow for multiple measurements of the actual signal value for the further pixels and, thus, may render the detection of out-of-line pixels more reliable.

[0047] The method may further comprises repeating step b) for each pixel j of the plurality of pixels. Specifically, each pixels of the plurality of pixel may be selected at least once to be the pixel j with the changed skimming voltage. The method may comprise repeating step b) for each pixel consecutively or repeating step b) for a number of pixels selected from the plurality of pixels simultaneously.

[0048] In a further aspect of the present invention, a system for automated out-of-line pixel detection of at least one photodetector is disclosed. The term “system” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an arbitrary set of interacting or interdependent components parts forming a whole. Specifically, the components may interact with each other in order to fulfill at least one common function. The at least two components may be handled independently or may be coupled or connectable.

[0049] The system comprises the at least one photodetector comprising a plurality of pixels j, with j being a pixel position and j > 2. Each pixel comprises at least one photosensitive region. Each pixel is configured for generating a signal in response to illumination by optical radiation of its respective photosensitive region. The photodetector further comprises at least one readout circuit configured for readout of the plurality of pixels. The system further comprises at least one voltage generator for applying a skimming voltage VSkimmingto each pixel of the plurality of pixels. The readout circuit is configured for measuring an initial signal value Sinitiai for each pixel of the plurality of pixels without illumination of the photodetector. The voltage generator is further configured for changing the skimming voltage VSkimming,j for one pixel j of the plurality of pixels. The readout circuit is configured for measuring an actual signal value Sactuai,k of at least one further pixel k of the plurality of pixels with k * j. The system further comprises at least one processor for comparing the initial signal value of the further pixel k and the actual signal value of the further pixel k. The further pixel k is detected as out-of-line pixel in case the initial signal value and the actual signal value differ by more than at least one predefined tolerance.

[0050] For definitions of terms and possible embodiments of the system or any part thereof, reference is made to the description of the method for automated out-of-line pixel detection above.

[0051] The term “voltage generator” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an electrical device configured for applying voltage. The voltage generator may be or may comprise at least one voltage source and / or at least one voltage regulator. The voltage generator may specifically be configured for applying the skimming voltage to the plurality of pixels, specifically in a controlled manner to control a strength, type, frequency and / or temporal evolvement of the applied voltage for each pixel separately.

[0052] The photodetector may specifically be an infrared photodetector.

[0053] The photosensitive region may comprise at least one photoconductive material selected from the group consisting of: lead sulfide (PbS); lead selenide (PbSe); mercury cadmium telluride (HgCdTe); cadmium sulfide (CdS); cadmium selenide (CdSe); indium antimonide (InSb); indium arsenide (InAs); indium gallium arsenide (InGaAs); silicon (Si); Silicon Germanium (SiGe); lithium tantalate (LiTaO3); triglycine sulfate (TGS); platinum silicide (PtSi); quantum well infrared photodetector (QWIP); extrinsic semiconductors, organic semiconductors.

[0054] The system may be configured for performing the method according to the present invention, such as according to any one of the embodiments disclosed above and / or according to any other embodiment disclosed in further detail below.

[0055] In a further aspect of the present invention, a computer program is disclosed, comprising instructions which, when the program is executed by a system according to the present invention, such as according to any one of the embodiments disclosed above and / or according to any other embodiment disclosed in further detail below, cause the system to perform the method according to the present invention, such as according to any one of the embodiments disclosed above and / or according to any other embodiment disclosed in further detail below.

[0056] In a further aspect of the present invention, a computer-readable storage medium, specifically a non-transient computer-readable storage medium, is disclosed, comprising instructions which, when the instructions are executed by a system according to the present invention, such as according to any one of the embodiments disclosed above and / or according to any other embodiment disclosed in further detail below, cause the system to perform the method according to the present invention, such as according to any one of the embodiments disclosed above and / or according to any other embodiment disclosed in further detail below.

[0057] As used herein, the term “computer-readable storage medium” specifically may refer to non- transitory data storage means, such as a hardware storage medium having stored thereon computer-executable instructions. The computer-readable storage medium specifically may be or may comprise a storage medium such as a random-access memory (RAM) and / or a read-only memory (ROM). The computer-readable storage medium may specifically be or may comprise a computer-readable data carrier.

[0058] Further disclosed and proposed herein is a computer program including computer-executable instructions for performing the method according to the present invention in one or more of the embodiments enclosed herein when the program is executed on a computer or computer network. Specifically, the computer program may be stored on a computer-readable data carrier and / or on a computer-readable storage medium. Thus, specifically, one, more than one or even all of method steps a) to c) as indicated above may be performed by using a computer or a computer network, preferably by using a computer program.

[0059] Further disclosed and proposed herein is a computer program product having program code means, in order to perform the method according to the present invention in one or more of the embodiments enclosed herein when the program is executed on a computer or computer network. Specifically, the program code means may be stored on a computer-readable data carrier and / or on a computer-readable storage medium.

[0060] Further disclosed and proposed herein is a data carrier having a data structure stored thereon, which, after loading into a computer or computer network, such as into a working memory or main memory of the computer or computer network, may execute the method according to one or more of the embodiments disclosed herein.

[0061] Further disclosed and proposed herein is a computer program product with program code means stored on a machine-readable carrier, in order to perform the method according to one or more of the embodiments disclosed herein, when the program is executed on a computer or computer network. As used herein, a computer program product refers to the program as a tradable product. The product may generally exist in an arbitrary format, such as in a paper format, or on a computer-readable data carrier and / or on a computer-readable storage medium. Specifically, the computer program product may be distributed over a data network.

[0062] Further, disclosed and proposed herein is a modulated data signal which contains instructions readable by a computer system or computer network, for performing the method according to one or more of the embodiments disclosed herein.

[0063] Referring to the computer-implemented aspects of the invention, one or more of the method steps or even all of the method steps of the method according to one or more of the embodiments disclosed herein may be performed by using a computer or computer network. Thus, generally, any of the method steps including provision and / or manipulation of data may be performed by using a computer or computer network. Generally, these method steps may include any of the method steps, typically except for method steps requiring manual work, such as providing the samples and / or certain aspects of performing the actual measurements.

[0064] Specifically, further disclosed herein are: a computer or computer network comprising at least one processor, wherein the processor is adapted to perform the method according to one of the embodiments described in this description, a computer loadable data structure that is adapted to perform the method according to one of the embodiments described in this description while the data structure is being executed on a computer, a computer program, wherein the computer program is adapted to perform the method according to one of the embodiments described in this description while the program is being executed on a computer, a computer program comprising program means for performing the method according to one of the embodiments described in this description while the computer program is being executed on a computer or on a computer network, a computer program comprising program means according to the preceding embodiment, wherein the program means are stored on a storage medium readable to a computer, a storage medium, wherein a data structure is stored on the storage medium and wherein the data structure is adapted to perform the method according to one of the embodiments described in this description after having been loaded into a main and / or working storage of a computer or of a computer network, and a computer program product having program code means, wherein the program code means can be stored or are stored on a storage medium, for performing the method according to one of the embodiments described in this description, if the program code means are executed on a computer or on a computer network.

[0065] The method and devices according to the present invention may provide a large number of advantages over known methods and devices. Specifically, the method and the system for automated out-of-line pixel detection may reliably detect any out-of-line pixel of photodetector, for example electrically connected pixels. The method and the system for automated out-of-line pixel detection may be configured for checking the photodetector with the array of pixel itself and without using light signals, specifically without spectral measurements. By changing the skimming voltage, connections between pixels can be detected that are not visible in a spectral measurement. Further, the method and the system for automated out-of-line pixel detection may allow for checking the photodetector for short-circuited pixels, pixels having defective bonding wires, pixels being electrically connected to another pixel and / or crosstalk pixels, specifically within an array or matrix of a plurality of pixels.

[0066] The method and the system for automated out-of-line pixel detection may specifically comprise tuning individual pixels by changing the skimming currents applied thereto. The further, remaining pixels may be measured and monitored. If a further pixel other than the tuned pixels is influenced, the further pixel can be detected as an out-of-line pixel, which may have an electrical connection to the tuned pixel. The method for automated out-of-line pixel detection may be part of a quality control, such as part of a test function testing the photodetector's functions. The skimming current of one pixel may be tuned by DAC value and the further pixels may be measured and monitored with respect to a change in their signal value. The tuning may specifically be done for every single pixel of the plurality of pixels multiple times. For example, every 6thpixel may be tuned. Then a frame measurement may be performed. If any pixel other than the tuned pixel shows a deviation from the frame DAC counts, this further pixel may have an electrical connection with the tuned pixel and an out-of-line pixel is detected. As used herein, the terms “have”, “comprise” or “include” or any arbitrary grammatical variations thereof are used in a non-exclusive way. Thus, these terms may both refer to a situation in which, besides the feature introduced by these terms, no further features are present in the entity described in this context and to a situation in which one or more further features are present. As an example, the expressions “A has B”, “A comprises B” and “A includes B” may both refer to a situation in which, besides B, no other element is present in A (i.e. a situation in which A solely and exclusively consists of B) and to a situation in which, besides B, one or more further elements are present in entity A, such as element C, elements C and D or even further elements.

[0067] Further, it shall be noted that the terms “at least one”, “one or more” or similar expressions indicating that a feature or element may be present once or more than once typically are used only once when introducing the respective feature or element. In most cases, when referring to the respective feature or element, the expressions “at least one” or “one or more” are not repeated, nonwithstanding the fact that the respective feature or element may be present once or more than once.

[0068] Further, as used herein, the terms "preferably", "more preferably", "particularly", "more particularly", "specifically", "more specifically" or similar terms are used in conjunction with optional features, without restricting alternative possibilities. Thus, features introduced by these terms are optional features and are not intended to restrict the scope of the claims in any way. The invention may, as the skilled person will recognize, be performed by using alternative features. Similarly, features introduced by "in an embodiment of the invention" or similar expressions are intended to be optional features, without any restriction regarding alternative embodiments of the invention, without any restrictions regarding the scope of the invention and without any restriction regarding the possibility of combining the features introduced in such way with other optional or non-optional features of the invention.

[0069] Summarizing and without excluding further possible embodiments, the following embodiments may be envisaged:

[0070] Embodiment 1 : A method for automated out-of-line pixel detection of at least one photodetector comprising a plurality of pixels, wherein each pixel comprises at least one photosensitive region, wherein each pixel is configured for generating a signal in response to illumination by optical radiation of its respective photosensitive region, wherein the photodetector further comprises at least one readout circuit configured for readout of the plurality of pixels, wherein the method comprises the following steps: a) applying a skimming voltage VSkimmingto each pixel of the plurality of pixels and measuring an initial signal value Sinitiai for each pixel of the plurality of pixels without illumination of the photodetector by using the readout circuit of the photodetector; b) changing the skimming voltage VSkimming,j for at least one pixel j of the plurality of pixels and measuring an actual signal value Sactuai,k of at least one further pixel k of the plurality of pixels with k * j; c) comparing the initial signal value of the further pixel k and the actual signal value of the further pixel k by using at least one processor, wherein the further pixel k is detected as out-of-line pixel in case the initial signal value and the actual signal value differ by more than at least one predefined tolerance.

[0071] Embodiment 2: The method according to the preceding embodiment, wherein an out-of-line pixel is at least one of a short-circuited pixel, a pixel having defective bonding wires, a pixel being electrically connected to another pixel or a crosstalk pixel.

[0072] Embodiment 3: The method according to any one of the preceding embodiments, wherein the further pixel k is a pixel of the plurality of pixels with k = j ± n, wherein n e N, specifically at least one of a nearest neighboring pixel of the pixel j with k = j ± 1 and a next-nearest neighboring pixel of the pixel j with k = j ± 2.

[0073] Embodiment 4: The method according to any one of the preceding embodiments, wherein the method further comprises repeating step b) for each pixel j of the plurality of pixels.

[0074] Embodiment 5: The method according to any one of the preceding embodiments, wherein the actual signal value Sactuai,k is measured for each further pixel k of the plurality of pixels.

[0075] Embodiment 6: The method according to the preceding embodiment, wherein the actual signal values of the plurality of pixels are measured in a frame measurement through the plurality of pixels.

[0076] Embodiment 7: The method according to any one of the preceding embodiments, wherein the method further comprises selecting at least one pixel sequence comprising a number of pixels selected from the plurality of pixels, wherein, in step b), the skimming voltage is changed for each pixel of the pixel sequence simultaneously.

[0077] Embodiment 8: The method according to the preceding embodiment, wherein the pixel sequence comprises a regular pixel sequence, specifically a regular pixel sequence having the number of pixels spaced apart from each other by at least one predefined pixel spacing.

[0078] Embodiment 9: The method according to any one of the two preceding embodiments, wherein the method further comprises shifting the pixel sequence along the plurality of pixels.

[0079] Embodiment 10: The method according to any one of the preceding embodiments, wherein the changing of the skimming voltage comprises tuning the skimming voltage from at least one initial skimming voltage.

[0080] Embodiment 11 : The method according to any one of the preceding embodiments, wherein the comparing comprises determining a difference between a maximum of the initial signal value and the actual signal value, and a minimum of the initial signal value and the actual signal value.

[0081] Embodiment 12: The method according to any one of the preceding embodiments, wherein the comparing of the initial signal value of the further pixel k and the actual signal value of the further pixel k comprises at least one offset correction.

[0082] Embodiment 13: The method according to any one of the preceding embodiments, wherein the actual signal value Sactuai,k is measured without illumination of the photodetector.

[0083] Embodiment 14: The method according to any one of the preceding embodiments, wherein the method is at least partially computer-implemented.

[0084] Embodiment 15: A system for automated out-of-line pixel detection of at least one photodetector, wherein the system comprises the at least one photodetector comprising a plurality of pixels j, with j being a pixel position and j > 2, wherein each pixel comprises at least one photosensitive region, wherein each pixel is configured for generating a signal in response to illumination by optical radiation of its respective photosensitive region, wherein the photodetector further comprises at least one readout circuit configured for readout of the plurality of pixels, wherein the system further comprises at least one voltage generator for applying a skimming voltage VSkimmingto each pixel of the plurality of pixels, wherein the readout circuit is configured for measuring an initial signal value Sinitiai for each pixel of the plurality of pixels without illumination of the photodetector, wherein the voltage generator is further configured for changing the skimming voltage VSkimming,j for one pixel j of the plurality of pixels, wherein the readout circuit is configured for measuring an actual signal value Sactuai.k of at least one further pixel k of the plurality of pixels with k * j, wherein the system further comprises at least one processor for comparing the initial signal value of the further pixel k and the actual signal value of the further pixel k, wherein the further pixel k is detected as out-of-line pixel in case the initial signal value and the actual signal value differ by more than at least one predefined tolerance.

[0085] Embodiment 16: The system according to the preceding embodiment, wherein the photodetector is an infrared photodetector.

[0086] Embodiment 17: The system according to any one of the preceding embodiments referring to a system, wherein the photosensitive region comprises at least one photoconductive material selected from the group consisting of: lead sulfide (PbS); lead selenide (PbSe); mercury cadmium telluride (HgCdTe); cadmium sulfide (CdS); cadmium selenide (CdSe); indium antimonide (InSb); indium arsenide (InAs); indium gallium arsenide (InGaAs); silicon (Si); Silicon Germanium (SiGe); lithium tantalate (LiTaO3); triglycine sulfate (TGS); platinum silicide (PtSi); quantum well infrared photodetector (QWIP); extrinsic semiconductors, organic semiconductors. Embodiment 18: The system according to any one of the preceding embodiments referring to a system, wherein the system is configured for performing the method according to any one of the preceding claims referring to a method.

[0087] Embodiment 19: A computer program comprising instructions which, when the program is executed by a system according to any one of the preceding embodiments referring to a system, cause the system to perform the method according to any one of the preceding embodiments referring to a method.

[0088] Embodiment 20: A computer-readable storage medium, specifically a non-transient computer- readable storage medium, comprising instructions which, when the instructions are executed by a system according to any one of the preceding embodiments referring to a system, cause the system to perform the method according to any one of the preceding embodiments referring to a method.

[0089] Short description of the Figures

[0090] Further optional features and embodiments will be disclosed in more detail in the subsequent description of embodiments, preferably in conjunction with the dependent claims. Therein, the respective optional features may be realized in an isolated fashion as well as in any arbitrary feasible combination, as the skilled person will realize. The scope of the invention is not restricted by the preferred embodiments. The embodiments are schematically depicted in the Figures. Therein, identical reference numbers in these Figures refer to identical or functionally comparable elements.

[0091] In the Figures:

[0092] Figure 1 shows a diagram of a spectral measurement using a photodetector;

[0093] Figure 2 shows an embodiment of a system for automated out-of-line pixel detection in a schematic view;

[0094] Figure 3 shows a flow chart of an embodiment of a method for automated out-of-line pixel detection;

[0095] Figure 4 shows a diagram of a frame measurement with changed skimming voltage applied to each 6thpixel;

[0096] Figure 5 shows a diagram of a result of the method for automated out-of-line pixel detection; and Figure 6 shows a diagram with measured actual signal values and spectral measurements.

[0097] Detailed description of the embodiments

[0098] Figure 1 shows a diagram of a spectral measurement using a photodetector having a plurality of pixels. Specifically, the diagram shows a relative amplitude 110 of a signal value of each pixel in relative units as a function of pixel position 112. The diagram of Figure 1 shows a dynamic spectrum measured with the photodetector. As indicated in Figure 1 by reference numbers 114, the spectrum shows implausible signal behavior for some pixels. The pixels with the implausible signal behavior can be classified as out-of-line pixels 116.

[0099] In Figure 2, an exemplary embodiment of a system 118 for automated out-of-line pixel detection is shown in a schematic view. The system 118 comprises the at least one photodetector 120 comprising a plurality of pixels j (denoted by reference number 122), with j being a pixel position 112 and j > 2. Each pixel 122 comprises at least one photosensitive region 124. Each pixel 122 is configured for generating a signal in response to illumination by optical radiation of its respective photosensitive region 124. The photodetector 120 may specifically be an infrared photodetector. As an example, the photosensitive region 124 may comprise at least one photoconduc- tive material selected from the group consisting of: lead sulfide (PbS); lead selenide (PbSe); mercury cadmium telluride (HgCdTe); cadmium sulfide (CdS); cadmium selenide (CdSe); indium antimonide (InSb); indium arsenide (InAs); indium gallium arsenide (InGaAs); silicon (Si); Silicon Germanium (SiGe); lithium tantalate (LiTaO3); triglycine sulfate (TGS); platinum silicide (PtSi); quantum well infrared photodetector (QWIP); extrinsic semiconductors, organic semiconductors.

[0100] The photodetector 120 comprising the plurality of pixels 122 is shown schematically in Figure 2 with a small number of pixels 122. As an example, the photodetector 120 may comprise the plurality of pixels 112 arranged in a linear array. The linear array of pixels 122 may comprise e.g. a number of 256 pixels 122. However, other numbers and / or arrangements of the pixels 122 are also feasible.

[0101] The photodetector 120 further comprises at least one readout circuit 126 configured for readout of the plurality of pixels 122. As shown in Figure 2, the readout circuit 126 may be at least partially integrated into the photodetector 120. For example, the readout circuit 126 at least one application-specific integrated circuit (ASIC), the ASIC specifically being configured for readout of one or more pixels 122, more specifically for readout of the plurality of pixels 122. The readout circuit 126 may be or may comprise at least one readout integrated circuit (ROIC).

[0102] As shown in Figure 2, the system 118 further comprises at least one voltage generator 128 for applying a skimming voltage VSkimmingto each pixel 122 of the plurality of pixels 122. As an example, the voltage generator 128 may be or may comprise at least one voltage source and / or at least one voltage regulator. Further, the readout circuit 126 is configured for measuring an initial signal value Sinitiai for each pixel 122 of the plurality of pixels 122 without illumination of the photodetector 120. The voltage generator 128 is further configured for changing the skimming voltage VSkimming,j for one pixel j (denoted by reference number 130) of the plurality of pixels 122. The readout circuit 126 is configured for measuring an actual signal value Sactuai,k of at least one further pixel k (denoted by reference number 132) of the plurality of pixels 122 with k * j.

[0103] The system 118 further comprises at least one processor 134 for comparing the initial signal value of the further pixel k 132 and the actual signal value of the further pixel k 132. The further pixel k 132 is detected as out-of-line pixel 116 in case the initial signal value and the actual signal value differ by more than at least one predefined tolerance.

[0104] The system 118 may be configured for performing the method according to the present invention, such as according to the exemplary embodiment of Figure 3 and / or according any other embodiment disclosed herein. Thus, for a description of the method, reference is made to the description of Figure 3.

[0105] Figure 3 shows a flow chart of an exemplary embodiment of a method for automated out-of-line pixel detection of at least one photodetector 120 comprising a plurality of pixels 122. The photodetector 120 may be embodied according to the exemplary embodiment of the photodetector 120 shown in Figure 2. Thus, for a detailed description of the photodetector 120, reference is made to the description of Figure 2.

[0106] The method steps may be performed in the given order. It shall be noted, however, that a different order is also possible. The method may comprise further method steps which are not listed. Further, one or more of the method steps may be performed once or repeatedly. Further, two or more of the method steps may be performed simultaneously or in a timely overlapping fashion.

[0107] The method comprises the following steps: a) (denoted by reference number 136) applying a skimming voltage VSkimming to each pixel 122 of the plurality of pixels 122 and measuring an initial signal value Sinitiai for each pixel 122 of the plurality of pixels 122 without illumination of the photodetector 120 by using the readout circuit 126 of the photodetector 120; b) (denoted by reference number 138) changing the skimming voltage VSkimming,j for at least one pixel j 130 of the plurality of pixels 122 and measuring an actual signal value Sactuai,k of at least one further pixel k 132 of the plurality of pixels 122 with k * j; c) (denoted by reference number 140) comparing the initial signal value of the further pixel k 132 and the actual signal value of the further pixel k 132, by using the at least one processor 134, wherein the further pixel k 132 is detected as out-of-line pixel 116 in case the initial signal value and the actual signal value differ by more than at least one predefined tolerance. The method may further comprise selecting at least one pixel sequence comprising a number of pixels selected from the plurality of pixels 122. The pixel sequence may comprise a regular pixel sequence, specifically a regular pixel sequence having the number of pixels spaced apart from each other by at least one predefined pixel spacing. For example, the predefined pixel spacing may be at least 5 pixels. Thus, in this example, the pixel sequence may comprise each 6thpixel 122 of the plurality of pixels 122. However, any other pixel spacing may also be feasible.

[0108] In step b), the skimming voltage may be changed for each pixel 122 of the pixel sequence simultaneously. This is shown in Figure 4. Figure 4 shows a diagram of a frame measurement through the plurality of pixels 122. Specifically, Figure 4 shows the measured signal value 142 for each pixel 122 as a function of the pixel position 112. As shown in Figure 4, the skimming voltage for each 6thpixel 122 is changed and, thus, the signal value 142 of the pixels 122 having the changed skimming voltage applied thereto is enhanced.

[0109] The method may further comprise shifting the pixel sequence along the plurality of pixels 122. Specifically, the method may comprise shifting the pixel sequence along the plurality of pixels 122 such that each pixel 122 of the plurality of pixels 122 is selected at least once for the pixel sequence. The pixel sequence may allow for testing many pixels 122 at the same time. Further, performing the method for the shifted pixel sequence may ensure that no pattern of out-of-line pixels remains undetected. Additionally or alternatively, the pixel sequence may allow for multiple measurements of the actual signal value for the further pixels and, thus, may render the detection of out-of-line pixels more reliable.

[0110] Figure 5 shows a diagram of an exemplary result of the method for automated out-of-line pixel detection. Specifically, Figure 5 shows the measured actual signal value 144 of the further pixels k 132 for each pixel 122 as a function of the pixel position 112. By changing the skimming voltage of a pixel j 130, some of the further pixels k 132 show increased actual signal values compared to the initial signal value, which is, in the example of Figure 5, approximately 10.000 counts. As can be seen in Figure 5, the measured photodetector 120 has pairs of two and three short-circuited pixels for which the actual signal values exceeds the initial signal value by more than the predefined threshold. These pixels can be detected as out-of-line pixels 116. In the example of Figure 5, the out-of-line pixels 116 are short-circuited with different resistances such that their respective actual signal value differs with respect to the measured signal counts. However, even short-circuited pixels having higher resistance can be detected by using the method for automated out-of-line pixel detection.

[0111] Figure 6 shows a diagram with measured actual signal values and spectral measurements. Specifically, Figure 6 shows two dynamic spectral measurements with a photodetector 120 having out-of-line pixels 116 (denoted by reference number 146). For the spectral measurements, on the left y-axis of the diagram of Figure 6, the relative amplitude 110 of the signal value of each pixel 122 is shown in relative units as a function of the pixel position 112. Further, Figure 6 shows an exemplary result of the method for automated out-of-line pixel detection performed with the same photodetector 120 used for the spectral measurements 146 (denoted by reference number 148). These results are shown on the right y-axis of Figure 6 with the measured actual signal value 144 of the further pixels k 132 as a function of the pixel position 112. As can be seen in Figure 6, pixels 122 of the photodetector 120 which show implausible signal behavior 114 in the spectral measurements can also be detected as out-of-line pixels 116 by performing the method for automated out-of-line pixel detection according to the present invention. Further, even pixels 122 which show only small signal implausibility in the spectral measurement (denoted by reference number 150) can be detected as out-of-line pixel 116 by using the method for automated out-of-line pixel detection according to the present invention.

[0112] List of reference numbers relative amplitude pixel position implausible signal behavior out-of-line pixel system photodetector pixel photosensitive region readout circuit voltage generator pixel j further pixel k processor applying a skimming voltage changing the skimming voltage comparing the initial signal value and the actual signal value signal value measured actual signal value spectral measurements result of the method for automated out-of-line pixel detection pixel with small signal implausibility in the spectral measurement

Claims

Claims1 . A method for automated out-of-line pixel detection of at least one photodetector (120) comprising a plurality of pixels (122), wherein each pixel (122) comprises at least one photosensitive region (124), wherein each pixel (122) is configured for generating a signal in response to illumination by optical radiation of its respective photosensitive region (124), wherein the photodetector (120) further comprises at least one readout circuit (126) configured for readout of the plurality of pixels (122), wherein the method comprises the following steps: a) applying a skimming voltage VSkimmingto each pixel (122) of the plurality of pixels (122) and measuring an initial signal value Sinitiai for each pixel (122) of the plurality of pixels (122) without illumination of the photodetector (120) by using the readout circuit (126) of the photodetector (120); b) changing the skimming voltage VSkimming,j for at least one pixel j (130) of the plurality of pixels (122) and measuring an actual signal value Sactuai,k of at least one further pixel k (132) of the plurality of pixels (122) with k * j, wherein the further pixel k (132) is at least one of a nearest neighboring pixel of the pixel j (130) with k = j ± 1 and a next-nearest neighboring pixel of the pixel j (130) with k = j ± 2; c) comparing the initial signal value of the further pixel k (132) and the actual signal value of the further pixel k (132) by using at least one processor (134), wherein the further pixel k (132) is detected as out-of-line pixel (116) in case the initial signal value and the actual signal value differ by more than at least one predefined tolerance.

2. The method according to the preceding claim, wherein an out-of-line pixel (116) is at least one of a short-circuited pixel, a pixel having defective bonding wires, or a crosstalk pixel.

3. The method according to any one of the preceding claims, wherein the method further comprises repeating step b) for each pixel j (130) of the plurality of pixels (122).

4. The method according to any one of the preceding claims, wherein the actual signal value Sactuai.k is measured for each further pixel k (132) of the plurality of pixels (122), wherein the actual signal values of the plurality of pixels (122) are measured in a frame measurement through the plurality of pixels (112).

5. The method according to any one of the preceding claims, wherein the method further comprises selecting at least one pixel sequence comprising a number of pixels selected from the plurality of pixels (122), wherein, in step b), the skimming voltage is changed for each pixel (122) of the pixel sequence simultaneously.

6. The method according to the preceding claim, wherein the pixel sequence comprises a regular pixel sequence, specifically a regular pixel sequence having the number of pixels spaced apart from each other by at least one predefined pixel spacing.

7. The method according to any one of the two preceding claims, wherein the method further comprises shifting the pixel sequence along the plurality of pixels (122).

8. The method according to any one of the preceding claims, wherein the changing of the skimming voltage comprises tuning the skimming voltage from at least one initial skimming voltage.

9. The method according to any one of the preceding claims, wherein the comparing comprises determining a difference between a maximum of the initial signal value and the actual signal value, or a minimum of the initial signal value and the actual signal value.

10. The method according to any one of the preceding claims, wherein the comparing of the initial signal value of the further pixel k (132) and the actual signal value of the further pixel k (132) comprises at least one offset correction.

11. A system (118) for automated out-of-line pixel detection of at least one photodetector (120), wherein the system (118) comprises the at least one photodetector (120) comprising a plurality of pixels j (122), with j being a pixel position and j > 2, wherein each pixel (122) comprises at least one photosensitive region (124), wherein each pixel (122) is configured for generating a signal in response to illumination by optical radiation of its respective photosensitive region (124), wherein the photodetector (120) further comprises at least one readout circuit (126) configured for readout of the plurality of pixels (122), wherein the system (118) further comprises at least one voltage generator (128) for applying a skimming voltage VSkimmingto each pixel (122) of the plurality of pixels (122), wherein the readout circuit (126) is configured for measuring an initial signal value Sinitiai for each pixel (122) of the plurality of pixels (122) without illumination of the photodetector (120), wherein the voltage generator (128) is further configured for changing the skimming voltage VSkimming, j for one pixel j (130) of the plurality of pixels (122), wherein the readout circuit (126) is configured for measuring an actual signal value Sactuai,k of at least one further pixel k (132) of the plurality of pixels (122) with k * j, wherein the system (118) further comprises at least one processor (134) for comparing the initial signal value of the further pixel k (132) and the actual signal value of the further pixel k (132), wherein the further pixel k (132) is detected as out-of-line pixel (116) in case the initial signal value and the actual signal value differ by more than at least one predefined tolerance.

12. The system (118) according to the preceding claim, wherein the system (118) is configured for performing the method according to any one of the preceding claims referring to a method.

13. A computer program comprising instructions which, when the program is executed by a system (118) according to any one of the preceding claims referring to a system (118), cause the system (118) to perform the method according to any one of the preceding claims referring to a method.

14. A computer-readable storage medium comprising instructions which, when the instructions are executed by a system (118) according to any one of the preceding claims referring to a system (118), cause the system (118) to perform the method according to any one of the preceding claims referring to a method.

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