Photodetector and method for converting illumination charges

Abstract

A photodetector (112) is disclosed, comprising at least one photosensitive element (120) having a resistance depending on an illumination by light, wherein the photodetector (112) further comprises at least one readout circuit (124), the readout circuit (124) comprising: - at least one input circuit (126) configured for providing at least one bias voltage (128) to the photosensitive element (120), the bias voltage (128) being adaptable between at least one first voltage (130) in an illumination phase (132) and ground (134) in a dark phase (136); - at least one integrator circuit (142) for storing photoelectric charges generated by the photosensitive element (120), the integrator circuit (142) comprising at least one operational amplifier (144) and at least one capacitor (146), the photosensitive element (120) being connected to an inverting input (148) of the operational amplifier (144) and the capacitor (146) being connected to an output (150) of the operational amplifier (144), wherein the capacitor (146) is configured for storing dark current charges and illumination charges during the illumination phase (132), wherein the integrator circuit (142) is configured for reversing current flow of the dark current charges in the dark phase (136) thereby removing the dark current charges from the capacitor (146); - at least one trimmed voltage divider (152) connected to the input circuit (126) and to a non-inverting input (154) of the operational amplifier (144); and - at least one analog-to-digital converter (164) for converting the illumination charges stored in the integrator circuit (142) into one voltage value (182). Further disclosed is a system (110) comprising the photodetector (112), a method for converting illumination charges and a computer program and a computer-readable storage medium for performing the method.

Description

[0001] Photodetector and method for converting illumination charges

[0002] Technical Field

[0003] The present invention refers to a photodetector, to a system comprising the photodetector and to a method for converting illumination charges generated by at least one photosensitive element. The invention further relates to a computer program and a computer-readable storage medium for performing the method. The photodetector may, as an example, be used in spectroscopy systems, e.g. in spectrometer devices, for investigating or monitoring purposes, in particular, in the infrared (IR) spectral region, especially in the near-infrared (NIR) spectral region, and / or in the visible (VIS) spectral region. However, further applications are feasible.

[0004] Background art

[0005] Many sensors, such as sensors comprising one or more photosensitive elements, for example sensors of a spectrometer device comprising one or more photosensitive elements, which, upon illumination with light generate a photocurrent or a photocharge, are known to generate an analog sensor current which has to be readout for determining the sensor's readings. For example, in spectrometer devices, application-specific integrated circuits (ASIC) may be used, which use a capacitor counter, also known as “integrate-and-fire” (lAF)-counter to determine a raw current signal and which can be digitalized using analog-to digital converters (ADC).

[0006] US 2002 / 0074499 A1 discloses methods and apparatus for compensating a radiation sensor for temperature variations of the sensor. In one example, the radiation sensor is a thermal sensor having at least one property that varies as a function of temperature. The thermal sensor outputs signals based on thermal radiation of interest from a particular radiating body in its view. These signals may contain significant undesirable components due in part to changes in temperature of the sensor itself. The disclosed methods and apparatus account for temperature variations of the sensor that are not due to the radiation of interest, so as to reduce undesirable components in the instantaneous signals output by the sensor. In one example, this is accomplished without thermally stabilizing the sensor itself (i.e., dynamic temperature compensation). In another example, the sensor is thermally stabilized selectively at various predetermined temperatures as a function of the ambient temperature in the proximity of the sensor.

[0007] US 10,066,988 B2 describes a detection device comprising a photodetector configured to transform an electromagnetic signal into a representative electric signal. The detection device also comprises an amplifier having a first input terminal connected to a first terminal of the photodetector. An integration capacitor is connected to the output terminal of the amplifier and to the first input terminal of the amplifier. A first source of a reference voltage is connected to a second input terminal of the amplifier. A second source of a detector voltage is connected to a second input terminal of the photodetector. The first and second voltage sources are correlated so as to correlate the noise components. US 2022 / 0326075 A1 discloses a device including at least one photoconductor configured for exhibiting an electrical resistance RPhoto dependent on an illumination of a light-sensitive region of the photoconductor; and at least one photoconductor readout circuit, where the photoconductor readout circuit is configured for determining the electrical resistance RPhoto of the photoconductor, where the photoconductor readout circuit includes at least one bias voltage source configured for applying at least one modulated bias voltage to the photoconductor.

[0008] US 2009 / 0146048 A1 describes a photo detection apparatus including first and second photo detection elements which are connected in series to each other at a junction node. A spectral response characteristic of the first photo detection element is different than a spectral response characteristics characteristic of the second photo detection element. The photo detection apparatus further includes a signal generating circuit connected to the junction node and generating a light detection signal corresponding to a current extracted at the junction node.

[0009] Despite the advantages achieved in the prior art, various technical challenges still remain. Specifically, most ASIC only provide limited measurement range and require reskimming of dark currents. Reskimming may be particularly disadvantageously with uncooled photosensitive elements. Further, some sensors may not require skimming, but may alter their system response based on a temperature of the photosensitive element. Additionally, known sensors generally require sampling during measurement and, thus, require fast ADC readout and data handling, for example Fast-Fourier transform (FFT).

[0010] Problem to be solved

[0011] It is therefore desirable to provide methods and devices which at least partially address above- mentioned technical challenges. Specifically, a photodetector, a system comprising the photodetector and a method for converting illumination charges generated by at least one photosensitive element shall be proposed which allow reading out of photosensitive elements with low computational and low hardware requirements.

[0012] Summary

[0013] This problem is addressed by a photodetector, by a system comprising the photodetector, by a method for converting illumination charges generated by at least one photosensitive element and by a computer program and a computer-readable storage medium 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.

[0014] In a first aspect of the present invention, a photodetector is disclosed. 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 arbitrary device configured for qualitatively and / or quantitatively detecting, i.e. at least one of determining, measuring and monitoring, at least one parameter, such as at least one of a physical parameter, a chemical parameter and a biological parameter. The photodetector may be configured for generating at least one detector signal, more specifically at least one electric detector signal, such as an analogue and / or a digital detector signal, the detector signal providing information on the at least one parameter measured by the detector. The photodetector may specifically be configured for qualitatively and / or quantitatively detecting an illumination by light. The photodetector may further be configured for generating at least one detector signal comprising information on the illumination by light, such as by providing at least one digital detector signal indicating an intensity as a function of wavelength of the illumination by light. For the purpose of detecting light, the photodetector may comprise at least one photosensitive element.

[0015] The photodetector comprises at least one photosensitive element having a resistance depending on an illumination by light. The term “photosensitive element” 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 measurement device configured for detecting optical radiation, such as for detecting an illumination by light. The photosensitive element may comprise at least one light-sensitive region, specifically comprising at least one light-sensitive material. The photosensitive element may comprise at least one substrate, specifically an electrically insulating substrate. For example, a single photosensitive element may be a substrate having applied thereon or therein at least one single light-sensitive region, which generates a physical response to the illumination for a given wavelength range. The photosensitive element may be configured for generating photoelectric charges upon illumination of a light-sensitive region by light. The generation of photoelectric charges by the photosensitive element over a certain period of time may result in the generation of a photoelectric current if a voltage is applied to the photosensitive element. A photoelectric current generated by the photosensitive element may correspond to an amount of photoelectric charges generated by the photosensitive element upon illumination of the lightsensitive region by light in a certain period of time.

[0016] The term “photoelectric charge” 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 any electric charge generated by the photosensitive element. Specifically, the photosensitive element may be configured for generating electric charges by using the photoelectric effect, i.e. due to an illumination of a light-sensitive region by light. The photoelectric charges may comprise electric charges generated by the photosensitive element upon illumination by light using the photoelectric effect, which are denoted herein as “illumination charges”. The photoelectric charges may further comprise electric charges generated by the photosensitive element when no illumination is present, which are denoted herein as “dark current charges”. The dark current charges may be generated by the photosensitive element due to random generation of charges carriers, such as electrons or holes, in the light-sensitive region. The dark current charges may cause noise or background in the detector signal of the photodetector.

[0017] 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 a photosensitive area of the photosensitive element. As used herein, the term “light” may refer, without limitation, to electromagnetic radiation in one or more of the infrared spectral range, the visible spectral range and the ultraviolet spectral range. Herein, the term “ultraviolet spectral range”, generally, refers to electromagnetic radiation having a wavelength of 1 nm to 380 nm, preferably of 100 nm to 380 nm. Further, in partial accordance with standard ISO-21348 in a valid version at the date of this document, the term “visible spectral range”, generally, refers to a spectral range of 380 nm to 760 nm. The term “infrared spectral range” (IR) generally refers to electromagnetic radiation of 760 nm to 1000 pm, wherein the range of 760 nm to 1.5 pm is usually denominated as “near infrared spectral range” (NIR) while the range from 1.5 p to 15 pm is denoted as “mid infrared spectral range” (MidlR) and the range from 15 pm to 1000 pm as “far infrared spectral range” (FIR). Preferably, light used for the typical purposes of the present invention is light in the infrared (IR) spectral range, more preferred, in the near infrared (NIR) and / or the mid infrared spectral range (MidlR), especially the light having a wavelength of 1 pm to 5 pm, preferably of 1 pm to 3 pm. This is due to the fact that many material properties or properties on the chemical constitution of many objects may be derived from the near infrared spectral range. It shall be noted, however, that spectroscopy in other spectral ranges is also feasible and within the scope of the present invention.

[0018] The term “resistance” 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 measure indicating an opposition of an object to a flow of electric current. The resistance may specifically be a quantitative measure of the opposition of the object to a flow of electric current. The resistance of an object may be given by a ratio of a voltage drop V at the object and the flow of electric current I flowing through the object, specifically by R = V / I, wherein R denotes the resistance of the object. The resistance may depend on one or more external or internal quantities. For example, the resistance of an object may depend on a temperature of the object. Additionally or alternatively, the resistance of an object may depend on an illumination by light, thus rendering the object a “photoresistor”. As an example, the photosensitive element may comprise at least one photoresistor, specifically at least one of a PbS photoresistor and a PbSe photoresistor. The resistance of the photosensitive element, specifically of the photoresistor, may decrease upon illumination by light.

[0019] The photodetector further comprises at least one readout circuit. 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 electric circuit configured for quantifying and / or processing at least one physical property and / or a change in at least one physical property detected by at least one measurement device, such as by at least one photosensitive element. The readout circuit may be configured for reading out the at least one photosensitive element. Specifically, the readout circuit may be configured for reading out photoelectric charges generated by the photosensitive element upon illumination by light, specifically using the at least one photocurrent. The readout circuit may be or may comprise at least one integrated circuit. The readout circuit may be or may comprise at least one readout integrated circuit (ROIC).

[0020] The readout circuit comprises: at least one input circuit configured for providing at least one bias voltage to the photosensitive element, the bias voltage being adaptable between at least one first voltage in an illumination phase and ground in a dark phase; at least one integrator circuit for storing photoelectric charges generated by the photosensitive element, the integrator circuit comprising at least one operational amplifier and at least one capacitor, the photosensitive element being connected to an inverting input of the operational amplifier and the capacitor being connected to an output of the operational amplifier, wherein the capacitor is configured for storing dark current charges and illumination charges during the illumination phase, wherein the integrator circuit is configured for reversing current flow of the dark current charges in the dark phase thereby removing the dark current charges from the capacitor; at least one trimmed voltage divider connected to the input circuit and to a non-inverting input of the operational amplifier; and at least one analog-to-digital converter for converting the illumination charges stored in the integrator circuit into one voltage value.

[0021] The term “providing” 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 supplying at least one of a quantity, a parameter or a signal to one or more elements or devices. Specifically, the providing may comprise supplying at least one electric signal, e.g. a voltage or a current, to one or more components of the readout circuit. Consequently, the term “input 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 electric circuit configured for providing, i.e. for supplying at least one voltage or current to one or more components of the readout circuit. The input circuit may specifically form at least one interface between the one or more components of the readout circuit and other, external circuits or units, e.g. power sources or control units. Specifically, the input circuit may comprise at least one interface configured for receiving at least one input, such as at least one of a voltage or a current input, and for providing, i.e. for forwarding, at least one output, such as at least one of a voltage or a current output, to the one or more components of the readout circuit. The input circuit may be configured for alternately providing voltage or current to the one or more components of the readout circuit and absorbing voltage or current from the one or more components of the readout circuit. As an example, the input circuit may comprise active devices, specifically at least one pair of active devices, more specifically at least one complementary pair of transistors, for performing the providing and the absorbing. The input circuit may specifically be a switchable input circuit. The input circuit may be configured for being switched between two states, wherein, in a first state, the input circuit may be configured for providing the at least one output to the one or more components of the readout circuit, wherein, in a second state, the input circuit may be configured for absorbing from the one or more components of the readout circuit. As an example, the input circuit may comprise at least one push-pull output stage.

[0022] The term “bias 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 an operating voltage of the photosensitive element. Specifically, the bias voltage may be applied to the photosensitive element to obtain the photoelectric current being dependent on the illumination of the photosensitive element by light. The bias voltage may alternate between at least one non-zero voltage level, in the following denoted as “first voltage” or “supply voltage”, and a reference voltage level, also denoted as “ground”, the reference voltage level specifically being zero voltage. The bias voltage is adaptable between the first voltage and ground, specifically by using the input circuit, specifically by using the supply voltage. The bias voltage may be adapted to the first voltage in the illumination phase and to ground in the dark phase. The first voltage may be in a range of 1 V to 10V, specifically in a range of 2 V to 7 V, more specifically may be 5 V. Further, the first or supply voltage may be provided to the voltage divider. The input circuit may be configured for providing the first or supply voltage to the trimmed voltage divider. Thus, specifically, the input circuit may be configured for providing the bias voltage to the photosensitive element and the first or supply voltage to the voltage divider. For example, the bias voltage being adaptable between the first voltage in the illumination phase and ground in the dark phase may be provided to the photosensitive element, wherein the first or supply voltage may be provided to the trimmed voltage divider.

[0023] The term “illumination phase” 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 period of time with illumination of the photosensitive element by light, specifically with intentional illumination of the photosensitive element by light using one or more light sources. Specifically, in the illumination phase, at least one light source may be turned on to illuminate the photosensitive element. The illumination phase may comprise a phase of active illumination of the photosensitive element by light, e.g. using one or more light sources. In the illumination phase, the photosensitive element may have a decreased or increased resistance due to the illumination by light. In the illumination phase, the bias voltage adapted to the first voltage may be applied to the photosensitive element. In the illumination phase, photoelectric charges generated by the photosensitive element due to the illumination by light may result in the photoelectric current. The term “dark phase” 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 period of time without illumination of the photosensitive element by light, specifically without intentional illumination of the photosensitive element by light. Specifically, in the dark phase, the at least one light source illuminating the photosensitive element in the illumination phase may be turned off. In the dark phase, an active illumination of the photosensitive element present during the illumination phase may be avoided. However, other light sources may be present in the dark phase. As an example, light may be present in the dark phase even without having an active or intentional illumination of the photosensitive element by light, e.g. due to ambient light. In the dark phase, the bias voltage adapted to ground may be applied to the photosensitive element. In the dark phase, the current flow of the dark current charges may be reversed compared with the current flow in the illumination phase.

[0024] The term “storing” 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 accumulating at least one of a quantity, a parameter or a signal. Specifically, the storing may comprise accumulating at least one electric quantity, such as electric charges. Consequently, the term “integrator 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 electric circuit configured for storing, i.e. for accumulating at least one of a quantity, a parameter or a signal, specifically for accumulating at least one electric quantity, such as electric charges. The integrator circuit may be configured for integrating at least one input, such as at least one input current, specifically for integrating the input over time. The integrator circuit may be configured for accumulating the input, such as electric charges of the input current, over time. Specifically, the integrator circuit may be a current integrator.

[0025] The term “operational amplifier” 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 electric circuit having at least one output dependent on at least two inputs. The operational amplifier may be configured for outputting at least one output dependent on a difference between at least two inputs. The operational amplifier may specifically comprise a differential amplifier. The operational amplifier may comprise at least positive input, herein referred to as “inverting input”, and at least one negative input, herein referred to as “non-inverting input”, wherein the output of the operational amplifier may be dependent on the difference between the positive input and the negative input. The operational amplifier may specifically output at least one enhanced difference in voltage between the inverting input and the non-inverting input. Consequently, the “output” of the operational amplifier may refer, without limitation, to at least one voltage generated by the operational amplifier dependent on the at least two inputs of the operational amplifier. The term “capacitor” 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 electric device configured for storing electrical energy in an electric field by accumulating electric charges on at least two spaced surfaces, the surfaces being insulated from each other. The capacitor may have a capacitance determining a capacity of the capacitor for storing an amount of electric charges per voltage difference between the two surfaces. The capacitor may comprise the at least two surfaces in any physical form ensuring spaced surfaces, such as planar surfaces and / or rolled- up surfaces. The capacitor may comprise electrically conducting surfaces, such as metallic surfaces, e.g. metallic foils, thin films, sintered bead of metal, and / or solid-state electrolyte surfaces, the surfaces being optionally separated by a dielectric medium, such as glass, ceramic, plastic film, paper, mica, air, and oxide layers.

[0026] The term “voltage divider” 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 electric circuit configured for providing at least one output voltage being a fraction of an input voltage. The voltage divider may have at least one input, specifically for receiving the input voltage, and at least one output, specifically for providing the output voltage. The voltage divider may specifically be a passive linear electric circuit. For example, the voltage divider may comprise two or more resistors being arranged such that the output voltage is a fraction of the input voltage. The voltage divider may comprise further electric components, such as capacitors, switches and the like. The voltage divider may specifically be adaptable such that the output voltage of the voltage divider may be adjustable. The process of adjusting or adapting the output voltage may also be referred as “trimming”. Consequently, the term “trimmed voltage divider” may refer, without limitations, to an adjusted or adapted voltage divider. The trimmed voltage divider may be trimmed to provide a fraction of the supply voltage, specifically half of the supply voltage, to the non-in- verting input of the operational amplifier. The trimmed voltage divider may have at least one input being connected to the input circuit and at least one output being connected to the non-in- verting input of the operational amplifier. The trimmed voltage divider may specifically be configured for providing the fraction of the supply voltage to the operational amplifier, specifically via its output.

[0027] The trimmed voltage divider may be trimmed such that no photoelectric charges remain in the integrator circuit having no illumination light, specifically no intentional illumination light, on the photosensitive element in a measurement phase, specifically in the illumination phase of the measurement phase. The measurement phase may specifically comprise at least one cycle or sequence of illumination phase and dark phase. The measurement phase may specifically be part of a trimming process of the voltage divider. Thus, during the measurement phase for trimming the trimmed voltage divider, specifically during the illumination phase of the measurement phase, no intentional illumination, e.g. no illumination due to one or more light sources, may be present on the photosensitive element. The trimmed voltage divider may be trimmed prior to use, e.g. in a factory trimming process or at a first use at the customer site. A full bridge rectifying solution may be used to achieve the trimmed voltage divider. As an example, the voltage divider may be trimmed prior to use of the photodetector such that no photoelectric charges remain in the integrator circuit when no illumination light impinges on the photosensitive element during a whole measurement phase, i.e. illumination phase and dark phase, of a trimming process. Thus, if the voltage divider is trimmed in this way, any dark current charges may be removed from the capacitor during the dark phase when the photodetector is actually used for measuring illumination light.

[0028] As an example, the trimmed voltage divider may comprise at least one first resistor and at least one second resistor. The first resistor may have a first resistance and the second resistor may have a second resistance. The first resistance may be equal to the second resistance. For example, the first resistance and the second resistance may be in a range of 10 kQ to 10 MQ, specifically in a range of 100 kQ to 1 MQ, more specifically are 1 MQ. Alternatively or additionally, the trimmed voltage divider comprises at least one potentiometer. The potentiometer may be or may comprise at least one variable, specifically adjustable, resistor. For example, the second resistor may comprise the potentiometer, such as at least one variable resistor. Alternatively or additionally, the trimmed voltage divider comprises at least one full bridge, specifically at least one full H-bridge, with a low pass filter to provide half of the supply voltage to the noninverting input of the operational amplifier.

[0029] The term “converting” 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 changing at least one property of one or more of a quantity, parameter or signal. Specifically, the converting of the illumination charges may comprise changing at least one analog signal, such as an electric current of the illumination charges, into at least digital signal indicative of the illumination charges. Consequently, the term “analog-to-digital converter”, also denoted as “ADC”, 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 electric circuit configured for converting, i.e. for changing at least one property of one or more of a quantity, parameter or signal. The ADC may be configured for converting one analog input signal, specifically an electric current of the illumination charges, into at least one digital output signal. Any known ADC architecture may be used as ADC for converting the analog signal into the digital output signal. For example, the ADC may comprise at least one ADC architecture selected from the group consisting of: a counter type ADC; a single-slope ADC; a dual-slope ADC; a pipelined ADC; a successive approximation (SAR) ADC; a sigma-delta ADCs. With respect to embodiments of the ADC reference is made to “Analog-to-Digital Converter Architectures and Choices for System Design” by Brian Black, Analog Dialogue 33-8 (1999). The photodetector may comprise a plurality of photosensitive elements. For example, the photodetector may comprise an array of photosensitive elements, the array of photosensitive elements specifically comprising a matrix of 1 x N photosensitive elements or of M x N photosensitive elements, wherein, as an example, M may be < 10 and N may be in the range from 1 to 50, preferably from 2 to 20, more preferred from 5 to 10. The photodetector may comprise at least one photosensitive element-specific section and at least one generic section. Components of the photodetector associated with the photosensitive element-specific section may be comprised at least once for each photosensitive element. Components of the photodetector associated with the generic section may be comprised at least once for all of the photosensitive elements. As an example, the photosensitive element-specific section may comprise at least the photosensitive element and the integrator circuit. For each photosensitive element, the readout circuit may comprise at least one integrator circuit. The generic section may comprise at least the input circuit, the trimmed voltage divider and the analog-to-digital converter. Further, the generic section may comprise at least one at least one multiplexer for connecting each photosensitive element-specific section with the analog-to-digital converter.

[0030] In a further aspect of the present invention, a system is disclosed, the system comprising at least one photodetector according to the present invention, such as according to any one of the embodiments described above and / or according to any one of the embodiments disclosed in further detail below, the system further comprising at least one light source configured for emitting light and at least one control unit for controlling at least one of the light source and the photodetector.

[0031] For definitions of terms and possible embodiments of the photodetector, reference is made to the description of the photodetector above.

[0032] 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 system may comprise at least one two interacting or interdependent components. The at least two components may be handled independently or may be coupled or connectable.

[0033] As an example, the system may be or may comprise at least one spectrometer device, specifically at least one portable spectrometer device. The term “spectrometer device” 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 device configured for acquiring at least one item of spectral information on at least one object. Specifically, the at least one item of spectral information may refer to at least one optical property or optically measurable property which is determined as a function of a wavelength, for one or more different wavelengths. More specifically, the optical property or optically measurable property, as well as the at least one item of spectral information, may relate to at least one property characterizing at least one of a transmission, an absorption, a reflection and an emission of the at least one object, either by itself or after illumination with external light. The at least one optical property may be determined for one or more wavelengths. The spectrometer device specifically may form an apparatus which is capable of recording a signal intensity with respect to the corresponding wavelength of a spectrum or a partition thereof, such as a wavelength interval, wherein the signal intensity may, specifically, be provided as an electrical signal which may be used for further evaluation. The photodetector according to the present invention, such as according to any one of the embodiments described above and / or according to any one of the embodiments disclosed in further detail below, may specifically be used for recording the signal intensity with respect to the corresponding wavelength of a spectrum or a partition thereof. For this purpose, as an example, the spectrometer device may further comprise at least one wavelength-selective element for selectively transmitting, reflecting, diffracting or absorbing light to pass light of specific wavelength to the photodetector, specifically to the one or more photosensitive elements.

[0034] The spectrometer device, as an example, may be or may comprise a device which allows for a measurement of at least one spectrum, e.g. for the measurement of a spectral flux, specifically as a function of a wavelength or detection wavelength. The spectrum may be acquired, as an example, in absolute units or in relative units, e.g. in relation to at least one reference measurement. Thus, as an example, the acquisition of the at least one spectrum specifically may be performed either for a measurement of the spectral flux (unit W / nm) or for a measurement of a spectrum relative to at least one reference material (unit 1 ), which may describe the property of a material, e.g., reflectance over wavelength. Additionally or alternatively, the reference measurement may be based on a reference light source, an optical reference path, a calculated reference signal, e.g. a calculated reference signal from literature, and / or on a reference device.

[0035] Specifically, the at least one spectrometer device may be a diffusive reflective spectrometer device configured for acquiring spectral information from the light which is diffusively reflected by the at least one object, e.g. the at least one sample. Additionally or alternatively, the at least one spectrometer device may be or may comprise an absorption- and / or transmission spectrometer. In particular, measuring a spectrum with the spectrometer device may comprise measuring absorption in a transmission configuration. Specifically, the spectrometer device may be configured for measuring absorption in a transmission configuration. As outlined above, however, other types of spectrometer devices are also feasible.

[0036] The spectrometer device, specifically, may be a portable spectrometer device. The term “portable” 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 the property of at least one object of being moved by human force, such as by a single user. Specifically, the object characterized by the term “portable” may have a weight not exceeding 10 kg, specifically not exceeding 5 kg, more specifically not exceeding 1 kg or even not exceeding 500 g. Additionally or alternatively, the dimensions of the object characterized by the term “portable” may be such that the object extends by no more than 0.3 m into any dimension, specifically by no more than 0.2 m into any dimension. The object, specifically, may have a volume of no more than 0.03 m3, specifically of no more than 0.01 m3, more specifically no more than 0.001 m3or even no more than 500 mm3. In particular, as an example, the portable spectrometer device may have dimensions of e.g.

[0037] 10 mm by 10 mm by 5 mm. Specifically, the portable spectrometer device may be part of a mobile device or may be attachable to a mobile device, such as a notebook computer, a tablet, a cell phone, such as a smart phone, a smartwatch and / or a wearable computer, also referred to as “wearable”, e.g. a body borne computer such as a wrist band or a watch. In particular, a weight of the spectrometer device, specifically the portable spectrometer device, may be in the range from 1 g to 100 g, more specifically in the range from 1 g to 10 g.

[0038] The term “light source” 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 device configured for generating or providing light in the sense of the above-mentioned definition. The light source specifically may be or may comprise at least one electrical light source, such as an electrically driven light source. For example, the light source may comprise at least one light source selected from the group consisting of: a thermal emitter; an incandescent lamp; an arc lamp; a fluorescent lamp; a light emitting diode (LED); a laser; a laser diode; a solid-state laser; a gas laser; a quantum cascade laser; a plasma light source.

[0039] The term “control unit” 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 device or a combination of devices configured for performing at least one control operation, such as controlling the light source and / or controlling the photodetector. The control unit may comprise one or more processors. The term “control unit” may specifically refer 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 control unit may be configured for processing basic instructions that drive the computer or system. The control unit may comprise at least one element selected from the group consisting of: a microcontroller unit (MCU); a field-programmable gate array (FPGA); an application-specific integrated circuit (ASIC). As an example, the control unit 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 coprocessor, 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 control unit may be a multi-core processor. Specifically, the control unit may be or may comprise a central processing unit (CPU). Additionally or alternatively, the control unit may be or may comprise a microprocessor, thus specifically the control unit’s elements may be contained in one single integrated circuitry (IC) chip. Additionally or alternatively, the control unit 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.

[0040] In a further aspect of the present invention, a method for converting illumination charges generated by at least one photosensitive element having a resistance depending on an illumination by light is disclosed. The method comprising using the photodetector according to the present invention, such as according to any one of the embodiments described above and / or according to any one of the embodiments disclosed in further detail below. For definitions of terms and possible embodiments of the photodetector, reference is made to the description of the photodetector above.

[0041] The method comprises the following steps that may be performed in the given order. However, a different order may also be possible. In particular, one, more than one or even all of the method steps may be performed once or repeatedly. Further, the method steps may be performed successively or, alternatively, one or more of the method steps may be performed in a timely overlapping fashion or even in a parallel fashion and / or in a combined fashion. The method may further comprise additional method steps that are not listed.

[0042] The method comprises: a) at least one illumination phase comprising: a.1 ) illuminating, by using at least one light source, the photosensitive element of the photodetector; a.2) providing at least one bias voltage to the photosensitive element using the input circuit, the bias voltage being adapted to the first voltage; a.3) storing photoelectric charges generated by the photosensitive element, wherein, in the illumination phase, dark current charges and illumination charges are stored in the capacitor of the integrator circuit; b) at least one dark phase comprising: b.1 ) turning off the light source; b.2) providing at least one bias voltage to the photosensitive element using the input circuit, the bias voltage being adapted to ground; b.3) storing photoelectric charges generated by the photosensitive element, wherein, in the dark phase, current flow of the dark current charges in the integrator circuit is reversed thereby removing the dark current charges from the capacitor; c) converting, by using the analog-to-digital converter, the illumination charges stored in the integrator circuit into one voltage value.

[0043] The method may comprise driving the light source with at least one illumination frequency to switch between the illumination phase and the dark phase. The illumination frequency may be in a range of 1 Hz to 1 kHz, specifically in a range of 50 Hz to 500 Hz, more specifically is 100 Hz. The method may further comprise, specifically prior step a), trimming the trimmed voltage divider such that no photoelectric charges remain in the integrator circuit having no illumination light on the photosensitive element in the illumination phase.

[0044] The first voltage may be in a range of 1 V to 10V, specifically in a range of 2 V to 7 V, more specifically may be 5 V.

[0045] In the method, steps a) and b) may be performed consecutively. Specifically, the method comprises performing step a) at least once before performing step b). The method may specifically comprise illuminating the photosensitive element at least once before turning off the light source such that photoelectric charges may be present in the integrator circuit before reversing the current flow and removing the dark current charges from the integrator circuit, specifically from the capacitor.

[0046] Additionally or alternatively, steps a) and b) may be performed repeatedly, wherein step c) may be performed once after a final step b). Specifically, the method may comprise performing steps a) and b) multiple times, preferably in an alternating fashion. As an example, the method may comprise at least one measurement cycle comprising repeatedly performing steps a) and b) in an alternating fashion, specifically during a given time interval, e.g. for one second. The measurement cycle may be terminated by performing step c), specifically comprising converting the illumination charges stored in the integrator circuit accumulated over the multiple illumination phases.

[0047] Step c) may comprise a digital conversion, specifically at least one conversion selected from the group consisting of: SAR; delta-sigma; slope-ADC.

[0048] In a further aspect of the present invention, a computer program is disclosed, comprising instructions which, when the program is executed by the system according to the present invention, such as according to any one of the embodiments described above and / or according to any one of the embodiments 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 described above and / or according to any one of the embodiments disclosed in further detail below.

[0049] Similarly, a computer-readable storage medium, specifically a non-transient computer-readable storage medium, is disclosed, comprising instructions which, when the instructions are executed by the system according to the present invention, such as according to any one of the embodiments described above and / or according to any one of the embodiments 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 described above and / or according to any one of the embodiments disclosed in further detail below. 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 may be or may comprise a computer-readable data carrier. The computer-readable storage medium specifically may be or may comprise a storage medium such as a random-access memory (RAM) and / or a readonly memory (ROM).

[0050] Further disclosed and proposed herein is a computer program including computer-executable instructions for performing, controlling and / or at least supporting performing of 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 a computer network. Specifically, the computer program may be stored on a computer-readable data carrier and / or on a computer-readable storage medium.

[0051] Thus, specifically, one, more than one or even all of method steps a) to c) as indicated above may be performed, controlled and / or at least supported by using a computer or a computer network, preferably by using a computer program.

[0052] Further disclosed and proposed herein is a computer program product having program code means, in order to perform, control and / or at least support performing of the method according to the present invention in one or more of the embodiments enclosed herein when the program is executed on a system according to the present invention, such as according to any one of the embodiments described above and / or according to any one of the embodiments disclosed in further detail below. Specifically, the program code means may be stored on a computer-readable data carrier and / or on a computer-readable storage medium.

[0053] 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.

[0054] Further disclosed and proposed herein is a computer program product with program code means stored on a machine-readable carrier, in order to perform, control and / or at least support performing of 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.

[0055] Finally, disclosed and proposed herein is a modulated data signal which contains instructions readable by a computer system or computer network, for performing, controlling and / or at least supporting performing of the method according to one or more of the embodiments disclosed herein.

[0056] 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, controlled and / or at least supported 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.

[0057] Specifically, further disclosed herein are: a computer or computer network comprising at least one processor, wherein the processor is adapted to perform, control and / or at least support performing of the method according to one of the embodiments described in this description, a computer loadable data structure that is adapted to perform, control and / or at least support performing of 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, control and / or at least support performing of 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, controlling and / or at least supporting performing of 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, control and / or at least support performing of 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, controlling and / or at least supporting performing of 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.

[0058] The photodetector, the system comprising the photodetector and the method for converting illumination charges according to the present invention, in one or more of the above-mentioned embodiments and / or in one or more of the embodiments described in further detail below, may provide a large number of advantages compared with known methods and devices of similar kind. Specifically, the photodetector, the system and the method overcome above-identified technical challenges, specifically the need for skimming and / or sampling generally required in known devices. The photodetector, the system and the method may specifically provide advantages for small spectrometer devices having few channels, such as less than 10 photosensitive elements. Further, the photodetector, the system and the method may not require complex analysis, such as Fast-Fourier transform or skimming, for the converting of the illumination charges, and, thus, may specifically be used for applications with low computing power resources. The present invention may specifically enable realizing a photodetector with low hardware requirements thereby providing a cost-effective solution and, thus, may particularly used e.g. for low cost spectrometer devices.

[0059] The photodetector, the system and the method may specifically provide means for storing measured illumination charges being generated by the photosensitive element due to illumination by an incoming light source, e.g. by a sample LED. After a complete measurement cycle, the ADC may acquire one voltage value that represents the sum of all illumination charges that were generated by the photosensitive element during the measurement.

[0060] The light source may specifically be switched with a frequency, e.g. of 100Hz. During a first period, also referred to as illumination phase, the bias voltage may be switched to a known voltage, e.g. 5 V, and the light source may be turned on. During the illumination phase, the photosensitive element may be lower impedance due to the light effect allowing more photoelectric charges to be stored in the integrator circuit, specifically in the capacitor of the integrator circuit. The photoelectric charges stored in the capacitor at the end of the illumination phase may comprise both the dark current charges and the illumination charges. To remove the dark current charges, in a second phase, also referred to as dark phase, the light source may be turned off and the bias voltage may be adapted to ground, thereby effectively reversing the current flow in the integrator circuit. The light source may be turned off and only the dark current charges may be removed from the capacitor, thereby leaving the illumination charges behind. This measurement cycle may be repeated multiple times, e.g. for a given time interval, such as for one second. Subsequently, the remaining charges may be converted with the ADC, specifically obtaining a light signal.

[0061] The trimmed voltage divider may specifically comprise the first resistor and the second resistor being trimmed such that no photoelectric charges remain in the integrator circuit having no illumination light on the photosensitive element in the illumination phase. Alternatively or additionally, the voltage divider may comprise a full bridge with a low pass filter to get half of the supply voltage, e.g. 2.5V of the first voltage of 5 V, at the non-inverting input of the operational amplifier.

[0062] The photodetector and the system may specifically provide a cost-effective solution by comprising standard components, such as in the generic section, the input circuit, the trimmed voltage divider and the analog-to-digital converter and optionally the multiplexer, and, in the photosensitive element-specific section, the photosensitive element and the integrator circuit comprising the operational amplifier and the capacitor. The system further comprises the light source and the control unit.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] Summarizing and without excluding further possible embodiments, the following embodiments may be envisaged:

[0067] Embodiment 1 : A photodetector comprising at least one photosensitive element having a resistance depending on an illumination by light, wherein the photodetector further comprises at least one readout circuit, the readout circuit comprising: at least one input circuit configured for providing at least one bias voltage to the photosensitive element, the bias voltage being adaptable between at least one first voltage in an illumination phase and ground in a dark phase; at least one integrator circuit for storing photoelectric charges generated by the photosensitive element, the integrator circuit comprising at least one operational ampli- fier and at least one capacitor, the photosensitive element being connected to an inverting input of the operational amplifier and the capacitor being connected to an output of the operational amplifier, wherein the capacitor is configured for storing dark current charges and illumination charges during the illumination phase, wherein the integrator circuit is configured for reversing current flow of the dark current charges in the dark phase thereby removing the dark current charges from the capacitor; at least one trimmed voltage divider connected to the input circuit and to a non-in- verting input of the operational amplifier; and at least one analog-to-digital converter for converting the illumination charges stored in the integrator circuit into one voltage value.

[0068] Embodiment 2: The photodetector according to the preceding embodiment, wherein the trimmed voltage divider is trimmed such that no photoelectric charges remain in the integrator circuit having no illumination light on the photosensitive element in a measurement phase, specifically in the illumination phase of the measurement phase.

[0069] Embodiment 3: The photodetector according to any one of the preceding embodiments, wherein the trimmed voltage divider comprises at least one first resistor and at least one second resistor.

[0070] Embodiment 4: The photodetector according to the preceding embodiment, wherein the first resistor has a first resistance, wherein the second resistor has a second resistance, wherein the first resistance is equal to the second resistance.

[0071] Embodiment 5: The photodetector according to the preceding embodiment, wherein the first resistance and the second resistance are in a range of 10 kQ to 10 MQ, specifically in a range of 100 kQ to 1 MQ, more specifically are 1 MQ.

[0072] Embodiment 6: The photodetector according to any one of the preceding embodiments, wherein the trimmed voltage divider comprises at least one potentiometer.

[0073] Embodiment 7: The photodetector according to any one of the preceding embodiments, wherein the trimmed voltage divider comprises at least one full bridge, specifically at least one full H-bridge, with a low pass filter to provide half of the supply voltage to the non-in- verting input of the operational amplifier.

[0074] Embodiment 8: The photodetector according to any one of the preceding embodiments, wherein the photosensitive element comprises at least one photoresistor, specifically at least one of a PbS photoresistor and a PbSe photoresistor.

[0075] Embodiment 9: The photodetector according to any one of the preceding embodiments, wherein the photodetector comprises a plurality of photosensitive elements, wherein the photodetector comprises at least one photosensitive element-specific section and at least one generic section, wherein components of the photodetector associated with the photosensitive element-specific section are comprised at least once for each photosensitive element, wherein components of the photodetector associated with the generic section are comprised at least once for all of the photosensitive elements.

[0076] Embodiment 10: The photodetector according to the preceding embodiments, wherein the photosensitive element-specific section comprises at least the photosensitive element and the integrator circuit.

[0077] Embodiment 11 : The photodetector according to any one of the two preceding embodiments, wherein the generic section comprises at least the input circuit, the trimmed voltage divider and the analog-to-digital converter.

[0078] Embodiment 12: The photodetector according to any one of the three preceding embodiments, wherein the generic section comprises at least one at least one multiplexer for connecting each photosensitive element-specific section with the analog-to-digital converter.

[0079] Embodiment 13: The photodetector according to any one of the preceding embodiments, wherein the input circuit comprises at least one push-pull output stage.

[0080] Embodiment 14: A system comprising at least one photodetector according to any one of the preceding embodiments, the system further comprising at least one light source configured for emitting light and at least one control unit for controlling at least one of the light source and the photodetector.

[0081] Embodiment 15: The system according to the preceding embodiment, wherein the control unit comprises at least one element selected from the group consisting of: a microcontroller unit (MCU); a field-programmable gate array (FPGA); an application-specific integrated circuit (ASIC).

[0082] Embodiment 16: The system according to any one of the two preceding embodiments, wherein the light source comprises at least one light source selected from the group consisting of: a thermal emitter; an incandescent lamp; an arc lamp; a fluorescent lamp; a light emitting diode (LED); a laser; a laser diode; a solid-state laser; a gas laser; a quantum cascade laser; a plasma light source.

[0083] Embodiment 17: A method for converting illumination charges generated by at least one photosensitive element having a resistance depending on an illumination by light, the method comprising using the photodetector according to any one of the preceding embodiments referring to a photodetector, wherein the method comprises: a) at least one illumination phase comprising: a.1) illuminating, by using at least one light source, the photosensitive element of the photodetector; a.2) providing at least one bias voltage to the photosensitive element using the input circuit, the bias voltage being adapted to the first voltage; a.3) storing photoelectric charges generated by the photosensitive element, wherein, in the illumination phase, dark current charges and illumination charges are stored in the capacitor of the integrator circuit; b) at least one dark phase comprising: b.1) turning off the light source; b.2) providing at least one bias voltage to the photosensitive element using the input circuit, the bias voltage being adapted to ground; b.3) storing photoelectric charges generated by the photosensitive element, wherein, in the dark phase, current flow of the dark current charges in the integrator circuit is reversed thereby removing the dark current charges from the capacitor; c) converting, by using the analog-to-digital converter, the illumination charges stored in the integrator circuit into one voltage value.

[0084] Embodiment 18: The method according to the preceding embodiment, wherein the method comprises driving the light source with at least one illumination frequency to switch between the illumination phase and the dark phase.

[0085] Embodiment 19: The method according to the preceding embodiment, wherein the illumination frequency is in a range of 1 Hz to 1 kHz, specifically in a range of 50 Hz to 500 Hz, more specifically is 100 Hz.

[0086] Embodiment 20: The method according to any one of the preceding method embodiments, wherein the method comprises, specifically prior step a), trimming the trimmed voltage divider such that no photoelectric charges remain in the integrator circuit having no illumination light on the photosensitive element in the illumination phase.

[0087] Embodiment 21 : The method according to any one of the preceding method embodiments, wherein the first voltage is in a range of 1 V to 10V, specifically in a range of 2 V to 7 V, more specifically is 5 V.

[0088] Embodiment 22: The method according to any one of the preceding method embodiments, wherein steps a) and b) are performed consecutively.

[0089] Embodiment 23: The method according to any one of the preceding method embodiments, wherein steps a) and b) are performed repeatedly, wherein step c) is performed once after a final step b). Embodiment 24: The method according to any one of the preceding method embodiments, wherein step c) comprises a digital conversion, specifically at least one conversion selected from the group consisting of: SAR; delta-sigma; slope-ADC.

[0090] Embodiment 25: A computer program comprising instructions which, when the program is executed by the 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.

[0091] Embodiment 26: A computer-readable storage medium, specifically a non-transient computer- readable storage medium, comprising instructions which, when the instructions are executed by the 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.

[0092] Short description of the Figures

[0093] 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.

[0094] In the Figures:

[0095] Figure 1 shows an embodiment of a system and a photodetector;

[0096] Figure 2 shows an embodiment of the trimmed voltage divider;

[0097] Figure 3 shows a flow chart of a method for converting illumination charges; and

[0098] Figures 4A to 4E show diagrams of bias voltage (Fig. 4A), illumination (Fig. 4B), resistance (Fig. 4C), current flow (Fig. 4D) and ADC voltage (Fig. 4E) as a function of time.

[0099] Detailed description of the embodiments

[0100] Figure 1 shows an exemplary embodiment of a system 110 and a photodetector 112 according to the present invention. The system 110 comprises the at least one photodetector 112 according to the present invention. The system 110 further comprises at least one light source 114 configured for emitting light and at least one control unit 116 for controlling at least one of the light source 114 and the photodetector 112, as indicated by the arrows in Figure 1 . In the example of Figure 1 , the light source 114 may comprise at least one light emitting diode (LED) 118.

[0101] The photodetector 112 comprises at least one photosensitive element 120 having a resistance depending on an illumination by light. In the example of Figure 1 , the photosensitive element 120 may comprise at least one photoresistor 122, specifically at least one of a PbS photoresistor and a PbSe photoresistor. The resistance of the photosensitive element 120, specifically of the photoresistor 122, may decrease upon illumination by light, as will be outlined in further detail below.

[0102] The photodetector 112 further comprises at least one readout circuit 124. The readout circuit 124 may be configured for reading out the at least one photosensitive element 120. Specifically, the readout circuit 124 may be configured for reading out photoelectric charges generated by the photosensitive element 120 upon illumination by light, specifically using at least one photocurrent.

[0103] The readout circuit 124 comprises at least one input circuit 126 configured for providing at least one bias voltage 128 to the photosensitive element 120, the bias voltage 128 being adaptable between at least one first voltage 130 in an illumination phase 132 and ground 134 in a dark phase 136. In Figure 1 , an exemplary bias voltage 128 is shown as a function of time 138. The bias voltage 128 may specifically correspond to the diagrams shown in Figure 4. Thus, for a detailed description of the bias voltage 128, reference is made to the description of Figure 4. The input circuit 126 may, as an example, comprise at least one push-pull output stage 140.

[0104] The readout circuit 124 further comprises at least one integrator circuit 142 for storing photoelectric charges generated by the photosensitive element 120. The integrator circuit 142 comprises at least one operational amplifier 144 and at least one capacitor 146. As shown in Figure 1 , the photosensitive element 120 is connected to an inverting input 148 of the operational amplifier 144 and the capacitor 146 is connected to an output 150 of the operational amplifier 144.

[0105] The readout circuit 124 further comprises at least one trimmed voltage divider 152 connected to the input circuit 126 and to a non-inverting input 154 of the operational amplifier 144. Specifically, as shown in Figure 1 , the input circuit 126 may be connected to both the photosensitive element 120 and the trimmed voltage divider 152, specifically being configured for providing the bias voltage 128 to the photosensitive element 120 and the supply voltage 130 to the trimmed voltage divider 152. The trimmed voltage divider 152 may have at least one input being connected to the input circuit 126 and at least one output being connected to the non-inverting input 154 of the operational amplifier 144. The trimmed voltage divider 152 may specifically be configured for providing a fraction of the supply voltage 130 to the operational amplifier 144, specifically via its output. In the exemplary embodiment of Figure 1 , the trimmed voltage divider 152 may comprise at least one first resistor 156 and at least one second resistor 158. The first resistor 156 may have a first resistance and the second resistor 158 may have a second resistance. The first resistance may be equal to the second resistance. For example, the first resistance and the second resistance may be in a range of 10 kQ to 10 MQ, specifically in a range of 100 kQ to 1 MQ, more specifically are 1 MQ.

[0106] Alternatively or additionally, Figure 2 shows another embodiment of the trimmed voltage divider 152. In this example, the trimmed voltage divider 152 may comprise at least one full bridge 160, specifically at least one full H-bridge, with a low pass filter 162 to provide half of the supply voltage 128 to the non-inverting input 154 of the operational amplifier 144.

[0107] Turning back to Figure 1 , the trimmed voltage divider 152 may be trimmed such that no photoelectric charges remain in the integrator circuit 142 having no illumination light, specifically no intentional illumination light, on the photosensitive element 120 in a measurement phase, specifically in the illumination phase 132 of the measurement phase. The measurement phase may specifically comprise at least one cycle or sequence of illumination phase 132 and dark phase 136. Thus, during the measurement phase for trimming the trimmed voltage divider 152, specifically during the illumination phase 132 of the measurement phase, no intentional illumination, e.g. no illumination due to one or more light sources, may be present on the photosensitive element 120. The trimmed voltage divider 152 may be trimmed prior to use, e.g. in a factory trimming process or at a first use at the customer site.

[0108] Further, the capacitor 146 is configured for storing dark current charges and illumination charges during the illumination phase 132. The integrator circuit 142 is further configured for reversing current flow of the dark current charges in the dark phase 136 thereby removing the dark current charges from the capacitor 146. The readout circuit 124 further comprises at least one analog-to-digital converter 164 for converting the illumination charges stored in the integrator circuit 142 into one voltage value.

[0109] In the exemplary embodiment of Figure 1 , the photodetector 112 may comprise a plurality of photosensitive elements (denoted by reference number 166). For example, the photodetector 112 may comprise an array of photosensitive elements 120, the array of photosensitive elements 120 specifically comprising a matrix of 1 x N photosensitive elements 120 or of M x N photosensitive elements 120, wherein, as an example, M may be < 10 and N may be in the range from 1 to 50, preferably from 2 to 20, more preferred from 5 to 10. The photodetector 112 may comprise at least one photosensitive element-specific section and at least one generic section. Components of the photodetector 112 associated with the photosensitive element-specific section may be comprised at least once for each photosensitive element 120. Components of the photodetector 112 associated with the generic section may be comprised at least once for all of the photosensitive elements 120. In this example, the photosensitive element-specific section may comprise at least the photosensitive elements 120 and the integrator circuit 142. For each photosensitive element 120, the readout circuit 124 may comprise at least one integrator circuit 142. The generic section may comprise at least the input circuit 126, the trimmed voltage divider 152 and the analog-to-digital converter 164. Further, the generic section may comprise at least one at least one multiplexer 168 for connecting each photosensitive element-specific section with the analog-to-digital converter 164.

[0110] Figure 3 shows a flow chart of a method for converting illumination charges generated by at least one photosensitive element 120 having a resistance depending on an illumination by light. The method comprising using the photodetector 112 according to the present invention, such as according to any one of the exemplary embodiments described with respect to Figure 1 and 2. However, any other embodiments disclosed herein may also be used in the method.

[0111] The method comprises the following steps that may be performed in the given order. However, a different order may also be possible. In particular, one, more than one or even all of the method steps may be performed once or repeatedly. Further, the method steps may be performed successively or, alternatively, one or more of the method steps may be performed in a timely overlapping fashion or even in a parallel fashion and / or in a combined fashion. The method may further comprise additional method steps that are not listed.

[0112] The method comprises: a) at least one illumination phase 132 comprising: a.1) illuminating, by using the at least one light source 114, the photosensitive element 120 of the photodetector 112; a.2) providing the at least one bias voltage 128 to the photosensitive element 120 using the input circuit 126, the bias voltage 128 being adapted to the first voltage 130; a.3) storing photoelectric charges generated by the photosensitive element 120, wherein, in the illumination phase 132, dark current charges and illumination charges are stored in the capacitor 146 of the integrator circuit 142; b) at least one dark phase 136 comprising: b.1) turning off the light source 114; b.2) providing the at least one bias voltage 128 to the photosensitive element 120 using the input circuit 126, the bias voltage 128 being adapted to ground 134; b.3) storing photoelectric charges generated by the photosensitive element 120, wherein, in the dark phase 136, current flow of the dark current charges in the integrator circuit 142 is reversed thereby removing the dark current charges from the capacitor 146; c) (denoted by reference number 170) converting, by using the analog-to-digital converter 164, the illumination charges stored in the integrator circuit 142 into one voltage value.

[0113] The method may comprise driving the light source 114 with at least one illumination frequency to switch between the illumination phase 132 and the dark phase 136. The illumination frequency may be in a range of 1 Hz to 1 kHz, specifically in a range of 50 Hz to 500 Hz, more specifically is 100 Hz. The method may further comprise, specifically prior step a), trimming the trimmed voltage divider 152 such that no photoelectric charges remain in the integrator circuit 142 having no illumination light on the photosensitive element 120 in the illumination phase 132.

[0114] The first voltage 130 may be in a range of 1 V to 10V, specifically in a range of 2 V to 7 V, more specifically may be 5 V.

[0115] In the method, steps a) and b) may be performed consecutively. Specifically, the method comprises performing step a) at least once before performing step b). The method may specifically comprise illuminating the photosensitive element 120 at least once before turning off the light source 114 such that photoelectric charges may be present in the integrator circuit 142 before reversing the current flow and removing the dark current charges from the integrator circuit 142, specifically from the capacitor 146.

[0116] Additionally, as indicated by reference number 172 in Figure 3, steps a) and b) may be performed repeatedly, wherein step c) may be performed once after a final step b). Specifically, the method may comprise performing steps a) and b) multiple times, preferably in an alternating fashion. As an example, the method may comprise at least one measurement cycle comprising repeatedly performing steps a) and b) in an alternating fashion, specifically during a given time interval, e.g. for one second. The measurement cycle may be terminated by performing step c), specifically comprising converting the illumination charges stored in the integrator circuit 142 accumulated over the multiple illumination phases 132.

[0117] Step c) may comprise a digital conversion, specifically at least one conversion selected from the group consisting of: SAR; delta-sigma; slope-ADC.

[0118] Figures 4A to 4E show diagrams of the bias voltage 128 (Fig. 4A), illumination 174 (Fig. 4B), resistance 176 (Fig. 4C), current flow 178 (Fig. 4D) and ADC voltage 180 (Fig. 4E) as a function of time 138. Specifically, the diagrams of Figures 4A to 4E may be obtained by performing the method for converting illumination charges, e.g. according to the exemplary embodiment shown in Figure 3. As can be seen in Figure 4A, the bias voltage 128 may be adapted to the first voltage 130 in the illumination phase 132, wherein, in the dark phase 136, the bias voltage 128 may be adapted to ground 134. The illumination 174 of the light source 114 may be turned on in the illumination phase 132 and turned off in the dark phase 136, as shown in Figure 4B. As can be seen in Figure 4C, the resistance of the photosensitive element 120 may decrease upon illumination by light, and, thus, may be lower in the illumination phase 132 compared to the resistance 176 in the dark phase 136. Consequently, as shown in Figure 4D, the current flow 178 may be positive in the illumination phase 132 thereby storing dark current charges and illumination charges in the integrator circuit 142 and may be negative in the dark phase 136. Specifically, as outlined above, current flow of the dark current charges in the integrator circuit 142 is reversed thereby removing the dark current charges from the capacitor 146 in the dark phase 136. The illumination phase 132 and the dark phase 136 may be performed repeatedly in an al- ternating fashion. Thus, as shown in Figure 4E, the ADC output voltage may increase with increasing number of illumination phases 132 and dark phase 136. The ADC may convert only the illumination charges stored in the integrator circuit 142 into one voltage value (denoted by reference number 182), which may represent a total light signal accumulated in the illumination phases 132.

[0119] List of reference numbers system photodetector light source control unit light emitting diode photosensitive element photoresistor readout circuit input circuit bias voltage first I supply voltage illumination phase ground dark phase time push-pull output stage integrator circuit operational amplifier capacitor inverting input output trimmed voltage divider non-inverting input first resistor second resistor full bridge low pass filter analog-to-digital converter plurality of photosensitive elements multiplexer converting measurement cycle illumination resistance current flow 180 ADC voltage

[0120] 182 voltage value

Claims

Claims1 . A photodetector (112) comprising at least one photosensitive element (120) having a resistance depending on an illumination by light, wherein the photodetector (112) further comprises at least one readout circuit (124), the readout circuit (124) comprising: at least one input circuit (126) configured for providing at least one bias voltage (128) to the photosensitive element (120), the bias voltage (128) being adaptable between at least one first voltage (130) in an illumination phase (132) and ground (134) in a dark phase (136); at least one integrator circuit (142) for storing photoelectric charges generated by the photosensitive element (120), the integrator circuit (142) comprising at least one operational amplifier (144) and at least one capacitor (146), the photosensitive element (120) being connected to an inverting input (148) of the operational amplifier (144) and the capacitor (146) being connected to an output (150) of the operational amplifier (144), wherein the capacitor (146) is configured for storing dark current charges and illumination charges during the illumination phase (132), wherein the integrator circuit (142) is configured for reversing current flow of the dark current charges in the dark phase (136) thereby removing the dark current charges from the capacitor (146); at least one trimmed voltage divider (152) connected to the input circuit (126) and to a non-inverting input (154) of the operational amplifier (144), wherein the trimmed voltage divider (152) is trimmed such that no photoelectric charges remain in the integrator circuit (142) having no illumination light on the photosensitive element (120) in a measurement phase; and at least one analog-to-digital converter (164) for converting the illumination charges stored in the integrator circuit (142) into one voltage value (182).

2. The photodetector (112) according to the preceding claim, wherein the trimmed voltage divider (152) comprises at least one first resistor (156) and at least one second resistor (158), wherein the first resistor (156) has a first resistance, wherein the second resistor (158) has a second resistance, wherein the first resistance is equal to the second resistance.

3. The photodetector (112) according to any one of the preceding claims, wherein the trimmed voltage divider (152) comprises at least one potentiometer.

4. The photodetector (112) according to any one of the preceding claims, wherein the trimmed voltage divider (152) comprises at least one full bridge (160), specifically at least one full H-bridge, with a low pass filter (162) to provide half of the supply voltage (128) to the non-inverting input (154) of the operational amplifier (144).

5. The photodetector (112) according to any one of the preceding claims, wherein the photosensitive element (120) comprises at least one photoresistor (122), specifically at least one of a PbS photoresistor and a PbSe photoresistor.

6. The photodetector (112) according to any one of the preceding claims, wherein the photodetector (112) comprises a plurality of photosensitive elements (166), wherein the photodetector (112) comprises at least one photosensitive element-specific section and at least one generic section, wherein components of the photodetector (112) associated with the photosensitive element-specific section are comprised at least once for each photosensitive element (120), wherein components of the photodetector (112) associated with the generic section are comprised at least once for all of the photosensitive elements (120), wherein the photosensitive element-specific section comprises at least the photosensitive element (120) and the integrator circuit (142), wherein the generic section comprises at least the input circuit (126), the trimmed voltage divider (152) and the analog-to-digital converter (164), wherein the generic section comprises at least one at least one multiplexer (168) for connecting each photosensitive element-specific section with the analog- to-digital converter (164).

7. The photodetector (112) according to any one of the preceding claims, wherein the input circuit (126) comprises at least one push-pull output stage (140).

8. A system (110) comprising at least one photodetector (112) according to any one of the preceding claims, the system (110) further comprising at least one light source (114) configured for emitting light and at least one control unit (116) for controlling at least one of the light source (114) and the photodetector (112).

9. A method for converting illumination charges generated by at least one photosensitive element (120) having a resistance depending on an illumination by light, the method comprising using the photodetector (112) according to any one of the preceding claims referring to a photodetector (112), wherein the method comprises: a) at least one illumination phase (132) comprising: a.1 ) illuminating, by using at least one light source (114), the photosensitive element (120) of the photodetector (112); a.2) providing at least one bias voltage (128) to the photosensitive element (120) using the input circuit (126), the bias voltage (128) being adapted to the first voltage (130); a.3) storing photoelectric charges generated by the photosensitive element (120), wherein, in the illumination phase (132), dark current charges and illumination charges are stored in the capacitor (146) of the integrator circuit (142); b) at least one dark phase (136) comprising: b.1 ) turning off the light source (114);b.2) providing at least one bias voltage (128) to the photosensitive element (120) using the input circuit (126), the bias voltage (128) being adapted to ground (134); b.3) storing photoelectric charges generated by the photosensitive element (120), wherein, in the dark phase (136), current flow of the dark current charges in the integrator circuit (142) is reversed thereby removing the dark current charges from the capacitor (146); c) converting, by using the analog-to-digital converter (164), the illumination charges stored in the integrator circuit (142) into one voltage value (182).

10. The method according to the preceding claim, wherein the method comprises driving the light source (114) with at least one illumination frequency to switch between the illumination phase (132) and the dark phase (136), wherein the illumination frequency is in a range of 1 Hz to 1 kHz, specifically in a range of 50 Hz to 500 Hz, more specifically is 100 Hz.11 . The method according to any one of the preceding method claims, wherein the method comprises, specifically prior step a), trimming the trimmed voltage divider (152) such that no photoelectric charges remain in the integrator circuit (142) having no illumination light on the photosensitive element (120) in the illumination phase (132).

12. The method according to any one of the preceding method claims, wherein steps a) and b) are performed repeatedly, wherein step c) is performed once after a final step b).

13. A computer program comprising instructions which, when the program is executed by the system (110) according to any one of the preceding claims referring to a system (110), cause the system (110) to perform the method according to any one of the preceding claims referring to a method.

14. A computer-readable storage medium, specifically a non-transient computer-readable storage medium, comprising instructions which, when the instructions are executed by the system (110) according to any one of the preceding claims referring to a system (110), cause the system (110) to perform the method according to any one of the preceding claims referring to a method.

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