Optical conductor readout circuit

Abstract

An apparatus (111) is proposed. The apparatus (111) includes: - at least one photoconductor (114), which is configured to exhibit a resistance R depending on the irradiation (116) of a photosensitive region (118) of the photoconductor (114). photo - At least one photoconductor readout circuit (112), wherein the photoconductor readout circuit (114) is configured to determine the resistance R of the photoconductor (114). photo The photoconductor readout circuit (112) includes at least one bias voltage source (152) configured to apply at least one modulated bias voltage to the photoconductor (114).

Description

TECHNICAL FIELD

[0001] The present invention relates to a photoconductor readout circuit, a detector and use of a photoconductor readout circuit for photoconductor readout. In particular, the photoconductor readout circuit can be used to determine a measurable voltage response of a photoconductor, such as a lead sulfide photoconductor sensor. BACKGROUND

[0002] Photoconductors such as lead sulfide photoconductors require a resistance measurement for readout. This can require a strong bias voltage and a circuit suitable for this voltage. The measurement is typically done in comparison to other resistors. Often the resistors or photoconductors are measured in a circuit similar to a Wheatstone bridge. For example, a voltage divider circuit for readout of a photoconductor is known. Typically, a voltage amplifier is used in combination with a voltage divider to measure the signal from the photoconductor, see for example https: / / www.hamamatsu.com / resources / pdf / ssd / e06_handbook_compound_semiconductor.pdf.

[0003] However, for such known readout circuits the resistance can drift due to electrochemical processes as a response to the unmodulated bias voltage. In combination with a wideband infrared light source, the modulation of the light source is a problem and is typically slow, resulting in high f-noise due to the longer measurement time. There is a need for a cheaper and more reliable readout electronics that allows to adjust the measurement frequency independently from the light modulation frequency.

[0004] CN 208 077 480 describes an LED flicker frequency controller for 555 integrated circuit teaching, belonging to the field of digital electronic technology. The oscillation circuit composed of 555 integrated circuit is the focus and difficulty in the teaching of digital electronic technology course, and the utility model discloses a 555 integrated circuit design square wave oscillation circuit, and the "frequency" is controlled by environmental illumination intensity, and then the function of illumination intensity control LED flicker frequency is realized. The utility model is applied to the 555 integrated circuit of digital electronic technology course experiment and imparts knowledge to students, can shift the interest of students in participating in experimental teaching, and improves the teaching effect. "555 timer IC" is described in "555 timer IC - Wikipedia", en.wikipedia.org / w / index.php?title=555 timer IC & oldid=919149415.

[0005] Problem solved by the invention

[0006] Therefore, the problem solved by the invention is to specify a photoconductor readout circuit and a detector that at least substantially avoid the drawbacks of this type of known circuits. In particular, an improved, in particular more reliable and cost-effective photoconductor readout would be desirable. Summary of the Invention

[0007] This problem is solved by the present invention, which features independent patent claims. Advantageous developments of the invention, which can be implemented individually or in combination, are presented in the dependent claims and / or in the following description and detailed embodiments.

[0008] As used herein, the expressions “have,” “include,” and “contain,” and their grammatical variations, are used in a non-exclusive manner. Thus, the expression “A has B” and the expressions “A includes B” or “A contains B” can refer to the fact that A contains one or more further components and / or elements in addition to B, and the situation where no other components, elements, or elements exist in A besides B.

[0009] In a first aspect of the invention, an apparatus is disclosed. The apparatus includes:

[0010] - At least one optical conductor, said optical conductor being configured to exhibit a resistance R depending on the irradiation of a photosensitive region of said optical conductor. photo ;

[0011] - At least one photoconductor readout circuit, wherein the photoconductor readout circuit is configured to determine the resistance R of the photoconductor. photo The photoconductor readout circuit includes at least one bias voltage source configured to apply at least one modulated bias voltage to the photoconductor.

[0012] As used herein, the term "photoconductor," also referred to as a photoresistor, is a broad term and should be given a meaning common and customary to those skilled in the art, and not limited to a particular or customary meaning. Specifically, the term may refer to, but is not limited to, a device capable of exhibiting a particular resistance R. photo The photosensitive element, the specific resistance R photo The resistance depends on the illumination of the photosensitive region of the photoconductor. Specifically, the resistance depends on the material of the photoconductor. As will be outlined in detail below, the photoconductor may include a photosensitive region comprising a "photoconductive material". For example, a photoconductor can be used in a photodetector circuit.

[0013] As used herein, the term "illumination" is a broad term and shall be given its ordinary and customary meaning to a person of ordinary skill in the art and shall not be limited to a special or customized meaning. The term specifically can refer, but is not limited to, electromagnetic radiation in one or more of the visible spectral range, the ultraviolet spectral range and the infrared spectral range. Therein, the term visible spectral range generally refers to a spectral range of 380 nm to 760 nm, partly according to standard ISO-21348. The term infrared (IR) spectral range generally refers to electromagnetic radiation in the range of 760 nm to 1000 pm, wherein the range of 760 nm to 1.4 pm is generally designated as near infrared (NIR) spectral range and the range from 15 pm to 1000 pm is designated as far infrared (FIR) spectral range. The term "ultraviolet spectral range" generally refers to electromagnetic radiation in the range of 1 nm to 380 nm, preferably in the range of 100 nm to 380 nm. In the following, the term "illumination" is also denoted as "light". Preferably, the illumination as used within the present invention is visible light, i.e. light in the visible spectral range, and / or infrared light, i.e. light in the infrared spectral range.

[0014] As used herein, the term "light-sensitive region of the photoconductor" generally refers to a region of the photoconductor which is sensitive to illumination, e.g. by an incident light beam. For example, the light-sensitive region can be a two- or three-dimensional region, which is preferably but not necessarily continuous, and can form a continuous region. The photoconductor can have one or more such light-sensitive regions. As used herein, the term "exhibiting a resistance R photo " which depends on the illumination" generally refers to the resistance of the photoconductor being adjusted and / or changed and / or varying depending on the illumination, in particular the illumination intensity, of the light-sensitive region. In particular, the resistance is adjusted and / or changed and / or varied in response to the illumination. The photoconductor can exhibit a decrease in resistance when illuminated. The photoconductor can decrease its resistivity when illuminated. In particular, the resistance of the photoconductor can decrease with increasing incident light intensity. The change between the dark resistance and the bright resistance is the quantity to be measured or to be read out. As used herein, the term "dark resistance" generally refers to the resistance of the photoconductor in the unlit state, i.e. without illumination. As further used herein, the term "bright resistance" refers to the resistance of the photoconductor under illumination. For the measurement and / or readout, a voltage divider circuit is generally known which has a non-linear characteristic. A linear change in the resistance of the photoconductor leads to a non-linear change in the voltage output. As will be outlined in more detail below, the present invention proposes a circuit feature with a linear behavior.

[0015] The photoconductor can comprise at least one photoconductive material. As the resistance is defined as the inverse value of the conductivity, alternatively, the term "photoresistive material" can also be used to name the same kind of material. The photoactive area can comprise at least one photoconductive material selected from the group comprising: lead sulfide (PbS); lead selenide (PbSe); mercury cadmium telluride (HgCdTe); cadmium sulfide (CdS); cadmium selenide (CdSe); indium antimonide (InSb); indium arsenide (InAs); indium gallium arsenide (InGaAs); extrinsic semiconductors, organic semiconductors doped with Ge, Si, GaAs. However, other materials are feasible. Further possible photoconductive materials are described, for example, in WO 2016 / 120392 Al. For example, the photoconductor can be a Hertzstueck® available from trinamiX GmbH, D-67056 Ludwigshafen am Rhein, Germany. TM commercially available photoconductor.

[0016] For example, the photoactive area can be illuminated by at least one illumination source. The illumination source can for example be or comprise an ambient light source and / or can be or can comprise an artificial illumination source. By way of example, the illumination source can comprise at least one infrared emitter and / or at least one visible light emitter and / or at least one ultraviolet light emitter. By way of example, the illumination source can comprise at least one light emitting diode and / or at least one laser diode. In particular, the illumination source can comprise one or more of the following illumination sources: a laser, in particular a laser diode, although in principle, alternatively or additionally, other types of lasers can also be used; a light emitting diode; an incandescent lamp; a neon lamp; a flame source; an organic light source, in particular an organic light emitting diode; a structured light source. Alternatively or additionally, other illumination sources can also be used. The illumination source can generally be adapted to emit light in at least one of the following: ultraviolet spectral range, infrared spectral range. Most preferably, the at least one illumination source is adapted to emit light in the NIR and IR range, preferably in the range of 800 nm and 5000 nm, most preferably in the range of 1000 nm and 4000 nm.

[0017] The illumination source can comprise at least one non-continuous light source. Alternatively, the illumination source can comprise at least one continuous light source. The light source can be any light source having at least one radiation wavelength having an overlap with the sensitive wavelength of the photosensitive detector. For example, the light source can be configured for generating Planckian radiation. For example, the light source can comprise at least one light emitting diode (LED) and / or at least one laser source. For example, the light source can be configured for generating the illumination by a heat releasing reaction, such as oxidation of a liquid or solid material or a gas. For example, the light source can be configured for generating the illumination from a fluorescence effect. The illumination source can be configured for generating at least one modulated light beam. Alternatively, the light beam generated by the illumination source can be non-modulated and / or can be modulated by a further optical device. The illumination source can comprise at least one optical chopper device configured for modulating the light beam from a continuous light source. The optical chopper device can be configured for periodically interrupting the light beam from a continuous light source. For example, the optical chopper device can be or can comprise at least one variable frequency rotating disc chopper and / or at least one fixed frequency tuning fork chopper and / or at least one optical shutter. The proposed device can measure and / or determine the resistance of the photoconductor independently from the light modulation frequency. Thus, the proposed device allows measuring the photoconductor resistance for an illumination source without modulated light intensity.

[0018] As used herein, the term "photoconductor readout circuit" is a broad term and shall be given its ordinary and customary meaning to a person of ordinary skill in the art and is not limited to a special or customized meaning. The term specifically can refer, without limitation, to an electronic circuit configured for the readout of at least one photoconductor and / or a plurality of photoconductors.

[0019] The photoconductor readout circuit can comprise:

[0020] at least one measurement voltage divider circuit, wherein the photoconductor is connected in series with at least one capacitor, wherein the capacitor is chargeable by the photoconductor,

[0021] at least one comparator circuit comprising at least one reference voltage divider circuit and at least one comparator, wherein the comparator comprises at least one input, wherein

[0022] the first input is electrically connected with the output of the measurement voltage divider circuit, wherein the comparator is configured for changing between

[0023] two output states when the input voltage at the first input is identical to at least one reference voltage;

[0024] at least one output terminal, wherein the resistance R photo of the photoconductor can be determined in dependence on the charge-discharge frequency at the output terminal.

[0025] As used herein, the term “voltage divider circuit”, also denoted voltage divider, is a broad term and shall be given its ordinary and customary meaning to a person of ordinary skill in the art and shall be interpreted as the meaning that would be given to an individual skilled in the art at the time of the priority date of this application. The term specifically can refer, but is not limited to, an electronic circuit configured for generating an output voltage signal that is a fraction of an input voltage signal of the voltage divider circuit. As used herein, the term “measurement voltage divider circuit” as used herein is a broad term and shall be given its ordinary and customary meaning to a person of ordinary skill in the art and shall be interpreted as the meaning that would be given to an individual skilled in the art at the time of the priority date of this application. The term specifically can refer, but is not limited to, a voltage divider circuit comprising at least one photoconductor to be measured. As used herein, the term “reference voltage divider circuit” as used herein is a broad term and shall be given its ordinary and customary meaning to a person of ordinary skill in the art and shall be interpreted as the meaning that would be given to an individual skilled in the art at the time of the priority date of this application. The term specifically can refer, but is not limited to, a voltage divider circuit comprising at least two reference resistors, each reference resistor having a known, such as a predefined or predetermined, resistance. The reference voltage divider circuit can comprise at least two reference resistors, each reference resistor having a predefined or predetermined resistance. As used herein, the term “reference resistor” is a broad term and shall be given its ordinary and customary meaning to a person of ordinary skill in the art and shall be interpreted as the meaning that would be given to an individual skilled in the art at the time of the priority date of this application. The term specifically can refer, but is not limited to, a resistor having a known resistance R i , wherein i is a natural number and denotes the name of the resistor.

[0026] As used herein, the term “capacitor” is a broad term and shall be given its ordinary and customary meaning to a person of ordinary skill in the art and shall be interpreted as the meaning that would be given to an individual skilled in the art at the time of the priority date of this application. The term specifically can refer, but is not limited to, at least one element configured for collecting and / or storing electrical energy, in particular electrons originating from the photoconductor. The capacitor is arranged in series with the photoconductor. The capacitor can be charged by the photoconductor. In particular, at least one output of the photoconductor can be electrically connected with at least one input of the capacitor. The resistance R photo The smaller the resistance R

[0027] As used herein, the term “comparator circuit” is a broad term and shall be given its ordinary and customary meaning to a person of ordinary skill in the art and shall not be limited to a special or customized meaning. The term specifically can refer, without limitation, to an electronic circuit configured for comparing at least one input voltage, specifically at least one measured voltage to be measured, with at least one reference voltage, specifically at least one known or predetermined reference voltage. The comparator circuit can be configured for outputting an output signal indicative of the comparison result. The comparator circuit can be implemented as an inverting Schmitt trigger. The inverting Schmitt trigger can comprise a comparator and positive feedback to the non-inverting input of the comparator implemented by a voltage divider circuit, in the present case a reference voltage divider.

[0028] The comparator circuit comprises at least one comparator. As used herein, the term “comparator” is a broad term and shall be given its ordinary and customary meaning to a person of ordinary skill in the art and shall not be limited to a special or customized meaning. The term specifically can refer, without limitation, to an electronic element configured for comparing at least one input voltage with at least one reference voltage and for producing an output signal indicative of the comparison result. The comparator, specifically the electronic comparator element, can be or can comprise one or more of the following: at least one operational amplifier; at least one Schmitt trigger; at least one logic element based on emitter coupled logic (ECL); at least one transistor-transistor logic (TTL), such as at least one advanced Schottky (ASTTL), at least one fast Schottky, at least one high-speed CMOS, and at least one CMOS; and at least one tri-state logic comparator. For example, the comparator can be or can comprise at least one operational amplifier and / or at least one further electronic element configured for performing a specified operation. As used herein, the term “compare” is a broad term and shall be given its ordinary and customary meaning to a person of ordinary skill in the art and shall not be limited to a special or customized meaning. The term specifically can refer, without limitation, to performing at least one mathematical operation, such as dividing or subtracting an input voltage from a reference voltage.

[0029] For the resistors in the reference voltage divider circuit, only the ratio of the resistors can be important. The ratio of the reference resistors in the reference voltage divider circuit can remain unchanged as long as the resistance values of the two resistors vary by the same factor, which allows for using resistors with a long range of resistance values.

[0030] The comparator can be driven by a supply voltage. For example, two identical direct current (DC) voltages, such as in the range from ±0.001 V to ±5000 V, preferably from ±1 V to ±500 V, more preferably from ±2 V to ±50 V, can be applied to the supply input of the comparator. The comparator can be driven with a single supply voltage, wherein the supply voltage can be from ±0.001 V to ±5000 V. Preferably, the supply voltage can be from ±0.1 V to ±500 V, and most preferably, the supply voltage can be from ±1 V to ±50 V. Alternatively, the comparator can be driven by a dual supply voltage, wherein it can be between ±0.001 V and ±5000 V. Preferably, the supply voltage can be from ±0.1 V to ±500 V, and most preferably, the supply voltage can be from ±1 V to ±50 V. The comparator dual supply voltage can be symmetric or asymmetric.

[0031] The comparator comprises at least one input. For example, the comparator comprises at least two inputs, such as two input terminals. The comparator can comprise at least a first input and at least a second input. In particular, the comparator can have an inverting input (-) and a non-inverting input (+). The output of the reference voltage divider can be connected to the non-inverting input of the comparator, while the output of the measurement voltage divider can be connected to the inverting input. Thus, the first input is electrically connected with the output of the measurement voltage divider circuit, and the second input is electrically connected with the output of the reference voltage divider circuit. The first input can be the inverting input, and the second input can be the non-inverting input. The reference voltage divider can be configured for providing positive feedback to the comparator. In particular, the reference voltage divider can be arranged such that a portion of the output voltage of the comparator is present at the non-inverting input. In other embodiments, the comparator can comprise only one input. In this case, the comparator can comprise an internal comparison voltage.

[0032] The output signal of the comparator, also denoted as output voltage, can depend on the comparison of the input voltage and the reference voltage. The voltage at the first input is denoted herein as input voltage, in particular as measurement voltage signal V meas The voltage at the second input or the internal reference voltage of the comparator, for example in case of a Schmitt trigger, is denoted as reference voltage V ref The comparator is configured for changing between two output states when the input voltage at the first input is the same as the reference voltage.

[0033] The output signal can be a digital signal, in particular a binary digital output with two states denoted as output states. The output state Vout can depend on which of the input voltage or the reference voltage is larger:

[0034]

[0035] When the measured voltage is less than the reference voltage, the output voltage will be "high". The "high" output state can be positive, in particular equal to the positive saturation voltage. When the measured voltage becomes equal to the reference voltage, i.e. by further charging of the capacitor, the comparator will change the output state to "low", which is in particular equal to the negative saturation voltage. In this case of switching from the high output state to the low output state, a negative voltage can occur at the non-inverting input due to the negative saturation voltage at the output of the comparator. Thus, in case of the same input signal, the output signal switches the potential at the output of the comparator to the opposite sign. Moreover, the inverting Schmitt trigger can exhibit a hysteresis. In case of a change of the output state, the reference voltage at the non-inverting input changes, resulting in two different reference voltage values and thus in two different values for switching the output state.

[0036] As long as V ref > V meas i.e. for the "high" output state, the capacitor will be charged by the photoconductor until the measured voltage and the reference voltage are the same. Then the output state can change to "low" and the capacitor will be charged to a voltage with opposite sign until the next switching of the output state. The resistance R photo of the photoconductor can be determined from the charge-discharge frequency at the output terminal of the photoconductor readout circuit. The charge-discharge speed of the capacitor can depend on the resistance R photo , and in particular, R photo is smaller, the charge-discharge speed will be higher. Thus, the charge-discharge frequency measured at the output terminal depends on the resistance R photo of the photoconductor. The photoconductor readout circuit comprises at least one output terminal. As used herein, the term "output terminal" is a broad term and shall be given its ordinary and customary meaning to a person of ordinary skill in the art and shall not be limited to a special or customized meaning. The term specifically can refer, without limitation, to any electronic element allowing to tap the voltage of the output of the comparator circuit. In particular, the output terminal can be connected in series with the output of the comparator. As used herein, the term "charge-discharge frequency" is a broad term and shall be given its ordinary and customary meaning to a person of ordinary skill in the art and shall not be limited to a special or customized meaning. The term specifically can refer, without limitation, to the time constant for charging or discharging the capacitor between two switches in terms of output state. Thus, the resistivity measurement of the photoconductor can be converted into a frequency measurement.

[0037] The photoconductor readout circuit can comprise at least one amplifier, in particular at least one impedance converter, configured to amplify the output signal of the comparator circuit.

[0038] The device, in particular the photoconductor readout circuit, can comprise at least one coupling to at least one evaluation device. The photoconductor readout circuit can comprise at least one rectifier and at least one further voltage divider for coupling to a low voltage evaluation system, such as at least one microcontroller for frequency measurement. The coupling can comprise at least one diode and at least one coupling voltage divider circuit. The coupling can be arranged at the output of the comparator circuit.

[0039] The photoconductor readout circuit comprises at least one bias voltage source configured for applying at least one modulated bias voltage to the photoconductor. As used herein, the term “bias voltage source” refers to at least one voltage source configured for generating a bias voltage. The bias voltage can be a voltage applied across the photoconductor material. Common readout circuits can be based on voltage dividers which are susceptible to fluctuations in the bias voltage. Any noise in the bias voltage can be measured as the measured voltage at the output of the voltage divider. In the circuit according to the present application, the reference voltage divider and the measurement voltage divider can be connected to the same potential, which is the output voltage of the comparator. This can allow for removing the susceptibility to fluctuations.

[0040] As used herein, the term "modulated bias voltage" refers to the fact that the bias voltage is a periodic time-dependent bias voltage and / or an alternating bias voltage. The bias voltage source can be configured to change the bias voltage with each charge and / or discharge. As used herein, the term "modulation" refers to changing the polarization of the bias voltage on the photoconductor in such a way that the net flow of charge carriers through the photoconductor during a measurement period is zero. In particular, the bias voltage is chosen such that the integral of the charge carriers, such as the total current flowing through the photoconductor during a measurement period, is zero. The measurement period can be the time between two successive transitions of the bias voltage polarization in the same direction, such as from a rising edge (e.g. positive edge) to a rising edge or from a falling edge (e.g. negative edge) to a falling edge. The change of the bias voltage with each charge or discharge can allow to protect the photoconductor from resistivity drift. Typically, photoconductors are measured with a DC bias voltage, which can cause a drift of ions in the photoconductive material or substrate, which changes the properties of the photoconductor. As proposed in the present invention, with an alternating bias voltage of appropriate frequency, the drift of the ions can be counteracted. The alternating bias voltage can reduce noise like flicker noise, 1 / f or pink noise. Due to the modulation of the measurement and the implementation of higher frequencies, the F noise can be significantly reduced. At the output, the frequency can be measured using one or more of the following operations: at least one Fourier transform; frequency counting, edge detection, period length measurement, etc. The bias voltage can be from ±0.001 V to ±5000 V. Preferably, the bias voltage can be from ±0.1 V to ±500 V, and most preferably, the bias voltage can be from ±1 V to ±50 V. The bias voltage can be switched between positive and negative. The photoconductor can be characterized by a resistance asymmetry for positive bias voltage and negative bias voltage. Due to the fact that the integral of the charge carriers over the measurement period in the proposed circuit is zero, the asymmetry can not affect the resistance measurement. The electric field across the photoconductive material due to the applied bias voltage can be about 50 V / mm.

[0041] The photoconductor readout circuit can comprise a plurality of photoconductors. The photoconductors can be arranged in an array. The photoconductor readout circuit can be configured to determine the resistance of each photoconductor of the plurality of photoconductors. The photoconductor readout circuit for reading out the plurality of photoconductors can comprise at least one logic gate, such as programmable logic, e.g. at least one field programmable gate array (FPGA), an integrated circuit with single or multiple input channels, a microprocessor with single or multiple inputs. The FPGA can be configured as a free running ring oscillator. Due to this, it is possible to produce a very high time resolution in the measurement of the output frequency of the comparator.

[0042] The photoconductor readout circuit can further comprise at least one analog-to-digital converter (ADC) configured for converting the output signal into a digital signal, in particular for further evaluation.

[0043] The photoconductor readout circuit can be implemented as an integrated circuit. As used herein, the term "integrated circuit" is a broad term and should be given its ordinary and customary meaning to a person of ordinary skill in the art and is not limited to a special or customized meaning. The term specifically can refer, without limitation, to an electronic circuit on a substrate, such as a semiconductor substrate. For example, the integrated circuit can be implemented as a microchip.

[0044] In an embodiment, the device can comprise at least one first electronic circuit. The first electronic circuit can be configured for generating at least one first output signal. The frequency of the first output signal can be a mathematical function of the measurement period of the photoconductor. The output of the photoconductor readout circuit can be a frequency that depends on the resistance of the photoconductor. A counter can be needed to measure the frequency as the output of the photoconductor readout circuit. Since a higher frequency is needed to reduce the 1 / f noise, the counter can be configured for sampling the high frequency with high precision and low noise, such as jitter.

[0045] The device can comprise at least one second photoconductor configured for exhibiting an electrical resistance R photo2 that depends on the illumination of its light-sensitive area. The device can comprise at least one second electronic circuit configured for generating a second measurement period. The second electronic circuit can be configured for generating at least one second output signal. The frequency of the second output signal can be a mathematical function of the measurement periods of the photoconductor and the second photoconductor.

[0046] The second electronic circuit can be a frequency mixer. For dual detector applications, such as non-dispersive infrared spectroscopy for gas analysis, where one detector measures the light intensity at one specific wavelength and one detector measures the light intensity at another wavelength, the two measurement signals need to be compared. Another example can be temperature measurements independent of the emissivity, where the radiated power of the measurement object can be measured at two different wavelengths and the signals compared. The second electronic circuit responsible for the frequency counting can be configured to sample both signals with the same accuracy and low noise. This can even increase the requirements and costs of the frequency counter. Alternatively, a period length counter can be used. The requirements for the period length and frequency counter can remain the same. The output signals of the two photoconductor readout circuits for dual applications can be digitized separately. Since the output signals of the two photoconductor readout circuits can be frequencies, both frequencies can be sampled with a frequency counter, which can be implemented in the form of a timer with a microcontroller, FPGA, time-to-digital converter (TDC). This approach can require two input channels for the microcontroller and FPGA or use two of these counters with very good time resolution. Additionally or alternatively, the frequencies of the two photoconductor readout circuits can be mixed at the analog level before digitization by means of a frequency mixer. The frequency mixer can be or can comprise a non-linear circuit configured to generate new frequencies from two signals applied to it. The frequency mixer can be configured to take both applied signals and generate a new signal equal to the sum and difference of the original frequencies. The sum of the original frequencies, i.e. the output signals of the photoconductor readout circuits, can be filtered by means of a simple low-pass filter, while the difference can be sampled.

[0047] For example, two frequencies f1 = 10000 Hz and f2 = 9960 Hz can be mixed and filtered to f Mixed = f1 - f2 = 40 Hz, which can also be measured with very good resolution using a normal period or frequency counter. In this way, the requirements and costs, in particular the number of counters, can be reduced, while the resolution is increased. The measurement resolution can be increased by the heterodyne factor, in particular the ratio f1 / f Mixed of the carrier f1 to the beat frequency f Mixed In the described example, the heterodyne factor is 10000 / 40 = 250. Thus, a period counter with a 100 nanosecond resolution can resolve a change in the period length of 400 picoseconds.

[0048] Frequency mixers are generally known to the skilled person. A wide variety of frequency mixers are available, in particular for different frequency ranges, noise levels, package forms, as integrated circuits or as discrete components, etc.

[0049] The device can comprise at least one temperature sensitive element. The signal of the temperature sensitive element can be used to correct one or both of the first output signal or the second output signal of the first electronic circuit.

[0050] The device can comprise at least one third resistor which is used to exhibit a radiation independent resistance with the same temperature dependence as the photoconductor and the second photoconductor. The third resistor can be a photoconductor which is darkened in such a way that it does not experience radiation, or a non-photosensitive resistor. The device can comprise at least one third electronic circuit which is configured to generate a third frequency. The third frequency can be used as a reference frequency. The reference frequency can be used to generate a frequency difference from the illuminated photoconductor by means of the at least two electronic circuits. The measurement resistance and the ratio detection at the measurement wavelength can drift due to thermal changes, for example environmental temperature influences, instabilities of the employed thermoelectric cooler, etc. Therefore, an additional darkened photoconductor can be employed which is covered in such a way that it cannot see any radiation in its active area. The output frequency of this detector can be used as a reference f Ref By using a double-mixer setup, the difference f Mixed1 = f1-f Ref and f Mixed2 = f2-f Ref can be measured with high precision. By calculating the quotient f Mixed1 / f Mixed2 , the temperature dependence of f1 and f2 can be eliminated. For example, if the temperature coefficient of the photoconductor is a, the quotient for a temperature T is and thus independent of temperature.

[0051] Furthermore, frequency dividers can be used in such a way that their frequency output is an integer power of 2 of the input signal, while the power can be chosen freely. For a power of 5, the output frequency would be 1 / 32 of the input frequency. An inexpensive temperature sensor, for example a negative temperature coefficient thermistor (NTC), can be established to measure the temperature of the photoconductor. The temperature dependence of the dark resistance can be factory calibrated, and the measurement value can be corrected with a temperature dependence calibration factor.

[0052] In a further aspect of the application, a detector comprising at least one photoconductor readout circuit according to the application is disclosed. Furthermore, the detector comprises at least one evaluation device which is configured to determine an output signal at at least one output of the device, in particular of the photoconductor readout circuit. The evaluation device is configured to determine the resistance R photo of the photoconductor by evaluating the output signal.

[0053] As used herein, the term "evaluation device" generally refers to any device designed to determine and / or generate at least one voltage output signal at a voltage output. As an example, the evaluation device can be or can comprise one or more integrated circuits, such as one or more application-specific integrated circuits (ASICs), and / or one or more data processing devices, such as one or more computers, preferably one or more microcomputers and / or microcontrollers. Additional components can be comprised, such as one or more preprocessing devices and / or data acquisition devices, such as one or more devices for receiving and / or preprocessing of the voltage signals, such as one or more AD converters and / or one or more filters. Further, the evaluation device can comprise one or more data storage devices. The evaluation device can comprise one or more interfaces, such as one or more wireless interfaces and / or one or more wired interfaces. The evaluation device can in particular comprise at least one data processing device, in particular an electronic data processing device, which can be designed to determine the at least one output voltage signal. The evaluation device can also be designed to fully or partially control the at least one illumination source and / or to control the at least one voltage source and / or to adjust the at least one load resistor. The evaluation device can further comprise one or more additional components, such as one or more electronic hardware components and / or one or more software components, such as one or more measurement units and / or one or more evaluation units and / or one or more control units. For example, the evaluation device can comprise at least one measurement device, e.g. at least one voltmeter, adapted to measure the at least one output voltage signal. The evaluation device can be configured for performing one or more of the following operations: at least one Fourier transform; frequency counting, edge detection, period length measurement, etc.

[0054] The detector can comprise at least one illumination source.

[0055] For further details regarding this aspect of the present application, in particular further details of the photoconductor readout circuit, the evaluation device and the optional illumination source, reference can be made to the description of the photoconductor readout circuit as provided above and in more detail below.

[0056] In a further aspect of the application, a use of a device according to the application is disclosed for the purpose of readout of one or more of at least one PbS sensor, at least one PbSe sensor, or at least one pixelated sensor array comprising a plurality of pixels, wherein each of the pixels comprises at least one PbS or PbSe sensor. In particular, the device according to the application can be used in medium or low bias voltage applications, for example in applications where the device is powered by a battery or needs to run on low power, for example sensor nodes, portable measurement devices, devices in explosive environments, allowing for an improved signal-to-noise ratio and thus for a high signal quality. For example, the voltage divider circuit can be used in a spectrometer, a moisture measurement instrument, a thickness measurement instrument, a gas analysis instrument or any other type of device using a photoresistor as a sensor element. The device can be used in an optical sensor. For example, the voltage divider circuit can be used in an optical sensor employing the so-called FiP effect, for example WO 2012 / 110924 A1, WO 2014 / 097181 A1 and WO 2016 / 120392 A1. Known voltage divider circuits cannot measure the change in resistance with high resolution without any light modulation, so that a spectrometer with a photoconductor detector can only be realized by a dispersive element and a plurality of pixels. Single-pixel spectrometers use photodiodes and other current generating detectors like InGaS, Si photodiodes etc. due to their stability allowing for measurements without light modulation. Since the device according to the application can measure the change in resistance of a photoconductor with high precision without any light modulation, a single-pixel spectrometer based on a Michelson interferometer or a Fabry-Perot interferometer etc. can also be realized by a photoconductor detector. The proposed device with all the mentioned advantages can be used to establish a single-pixel spectrometer.

[0057] In general, the following embodiments are considered to be particularly preferred in the context of the present application:

[0058] Embodiment 1 : A device comprising:

[0059] at least one photoconductor configured for exhibiting an electrical resistance R photo ;

[0060] at least one photoconductor readout circuit, wherein the photoconductor readout circuit is configured for determining the electrical resistance R photo of the photoconductor, wherein the photoconductor readout circuit comprises at least one bias voltage source configured for applying at least one modulated bias voltage to the photoconductor.

[0061] Embodiment 2: The device according to the previous embodiment, wherein the bias voltage is a periodic time-dependent bias voltage, wherein the bias voltage is chosen such that the integral of the charge carriers flowing through the photoconductor during a measurement period is zero, wherein the measurement period is defined by the time between two consecutive transitions of the bias voltage polarization in the same direction.

[0062] Embodiment 3: The device according to any of the previous embodiments, wherein the photoconductor readout circuit comprises:

[0063] at least one measurement voltage divider circuit comprising at least one photoconductor configured for exhibiting an electrical resistance R photo that depends on the illumination of a photoactive area of the photoconductor, and at least one capacitor in series with the photoconductor, wherein the capacitor is chargeable by the photoconductor;

[0064] at least one comparator circuit comprising at least one reference voltage divider circuit and at least one comparator, wherein the comparator comprises at least one input, wherein a first input is electrically connected with an output of the measurement voltage divider circuit, wherein the comparator is configured for changing between two output states when an input voltage at the first input is the same as at least one reference voltage;

[0065] at least one output terminal, wherein the electrical resistance R photo of the photoconductor is determinable from a charge-discharge frequency at the output terminal.

[0066] Embodiment 4: The device according to the previous embodiment, wherein the reference voltage divider circuit comprises at least two reference resistors, each reference resistor having a predefined or predetermined electrical resistance.

[0067] Embodiment 5: The device according to any of the two previous embodiments, wherein the comparator is or comprises one or more of: at least one operational amplifier; at least one Schmitt trigger; at least one logic element based on emitter coupled logic (ECL); at least one transistor-transistor logic (TTL), such as at least one advanced Schottky (ASTTL), at least one fast Schottky, at least one high-speed CMOS, and at least one CMOS; and at least one tri-state logic comparator.

[0068] Embodiment 6: The device according to any of the three previous embodiments, wherein the comparator is configured for comparing the input voltage with at least one reference voltage and for generating an output signal indicative of the result of the comparison.

[0069] Embodiment 7: The device according to any of the four preceding embodiments, wherein the charging-discharging speed of the capacitor depends on the resistance R photo .

[0070] Embodiment 8: The device according to any of the five preceding embodiments, wherein the photoconductor readout circuit comprises at least one amplifier configured for amplifying the output signal of the comparator circuit.

[0071] Embodiment 9: The device according to any of the preceding embodiments, wherein the device comprises at least one coupling to at least one evaluation device.

[0072] Embodiment 9: The device according to any of the preceding embodiments, wherein the photoactive area comprises at least one photoconductive material selected from the group consisting of: lead sulfide (PbS); lead selenide (PbSe); mercury cadmium telluride (HgCdTe); cadmium sulfide (CdS); cadmium selenide (CdSe); indium antimonide (InSb); indium arsenide (InAs); indium gallium arsenide (InGaAs); extrinsic semiconductors, organic semiconductors.

[0073] Embodiment 10: The device according to embodiment 2, wherein the device comprises at least one first electronic circuit, wherein the first electronic circuit is configured for generating at least one first output signal, wherein the frequency of the first output signal is a mathematical function of the measurement period of the photoconductor.

[0074] Embodiment 11: The device according to the preceding embodiment, wherein the device comprises at least one temperature sensitive element, wherein the signal of the temperature sensitive element is used for correcting the first output signal of the first electronic circuit.

[0075] Embodiment 12: The device according to any of the two preceding embodiments, wherein the device comprises at least one second photoconductor configured for exhibiting a resistance R photo2 , which depends on the illumination of its photoactive area, wherein the device comprises at least one second electronic circuit configured for generating a second measurement period, wherein the second electronic circuit is configured for generating at least one second output signal, wherein the frequency of the second output signal is a mathematical function of the measurement periods of the photoconductor and the second photoconductor.

[0076] Embodiment 13: The device according to the preceding embodiment, wherein the second electronic circuit is a frequency mixer.

[0077] Embodiment 14: The device according to any one of the preceding embodiments, wherein the device comprises at least one third resistor for exhibiting a radiation-independent resistance with the same temperature dependence as the photoconductor and the second photoconductor, wherein the third resistor is a photoconductor that is darkened in a manner that it is not subjected to radiation, or a non-photosensitive resistor, wherein the device comprises at least one third electronic circuit configured for generating a third frequency, wherein the third frequency is used as a reference frequency, wherein the reference frequency is used for generating a frequency difference from the photoconductor under illumination by means of the at least two electronic circuits.

[0078] Embodiment 15: A detector comprising at least one device according to any one of the preceding embodiments, wherein the detector comprises at least one evaluation device configured for determining an output signal at the at least one output of the device, wherein the evaluation device is configured for determining the resistance R of the photoconductor by evaluating the output signal. photo .

[0079] Embodiment 16: The detector according to the preceding embodiment, wherein the evaluation device is configured for performing one or more of the following operations: at least one Fourier transform; a frequency counting, an edge detection, a measurement of the period length, etc.

[0080] Embodiment 17: Use of a device according to any one of the preceding embodiments relating to a device for the purpose of readout of one or more of the following: at least one PbS sensor, at least one PbSe sensor, or at least one pixelated sensor array comprising a plurality of pixels, wherein each of the pixels comprises at least one PbS or PbSe sensor. BRIEF DESCRIPTION OF DRAWINGS

[0081] Further optional details and features of the application will become apparent from the following description of preferred exemplary embodiments in conjunction with the appended claims. In this context, specific features can be realized individually or in combination with features. The application is not limited to the exemplary embodiments. The exemplary embodiments are shown schematically in the drawings. The same reference numerals in the individual figures refer to the same elements or elements with the same function, or elements that correspond to each other in terms of their function.

[0082] In particular, in the figures:

[0083] Figure 1 Exemplary embodiments of a detector comprising a device according to the application are shown;

[0084] Figure 2 Further exemplary embodiments of a device comprising a photoconductor readout circuit are shown;

[0085] Figure 3 Further exemplary embodiments of the device are shown;

[0086] Figure 4 Further exemplary embodiments of the device are shown;

[0087] Figures 5A to 5C Further exemplary embodiments of the device are shown;

[0088] Figure 6 Further embodiments of the device and the photoconductor readout circuit are shown;

[0089] Figures 7A to 7C Embodiments of the device comprising a plurality of photoconductors are shown. DETAILED DESCRIPTION

[0090] Figure 1 An exemplary embodiment of a detector 110 comprising at least one device 111 according to the present application comprising at least one photoconductor readout circuit 112 is shown in a highly schematic manner. The device 111 comprises at least one photoconductor 114 configured for exhibiting an electrical resistance R photo .

[0091] The electrical resistance R photo may depend on an illumination of a material of the photoconductor 114. The photoactive region 118 of the photoconductor 114 can comprise a photoconductive material. The photoactive region 118 can comprise at least one photoconductive material selected from the group consisting of lead sulfide (PbS); lead selenide (PbSe); mercury cadmium telluride (HgCdTe); cadmium sulfide (CdS); cadmium selenide (CdSe); indium antimonide (InSb); indium arsenide (InAs); indium gallium arsenide (InGaAs); extrinsic semiconductors, e.g. doped Ge, Si, GaAs. However, other materials can be feasible. Further possible photoconductive materials are described, for example, in WO 2016 / 120392 Al. For example, the photoconductor can be a commercially available photoconductor available under the trade name Hertzstueck® from trinamiX GmbH, D-67056 Ludwigshafen am Rhein, Germany. TM

[0092] ​For example, the light-sensitive area 118 can be illuminated by at least one illumination source. The illumination source 120 can for example be or comprise an ambient light source and / or can be or can comprise an artificial illumination source. The detector 110 can comprise at least one illumination source 120 configured for illuminating the light-sensitive area 118. By way of example, the illumination source 120 can comprise at least one infrared emitter and / or at least one visible light emitter and / or at least one ultraviolet light emitter. By way of example, the illumination source 120 can comprise at least one light emitting diode and / or at least one laser diode. The illumination source 120 can in particular comprise one or more of the following illumination sources: a laser, in particular a laser diode, although in principle, alternatively or additionally, other types of lasers can also be used; a light emitting diode; an incandescent lamp; a neon lamp; a flame source; an organic light source, in particular an organic light emitting diode; a structured light source. Alternatively or additionally, other illumination sources can also be used. The illumination source 120 can generally be adapted to emit light in at least one of the following: the ultraviolet spectral range, the infrared spectral range.

[0093] Most preferably, the at least one illumination source is adapted to emit light in the NIR and IR range, preferably in the range of 800 nm and 5000 nm, most preferably in the range of 1000 nm and 4000 nm. The illumination source 120 can comprise at least one continuous or at least one non-continuous light source.

[0094] The photoconductor readout circuit 112 comprises at least one measurement voltage divider circuit 122 comprising at least one photoconductor 114 and at least one capacitor C 124 in series with the photoconductor 114. The capacitor C 124 can be charged by the photoconductor 114. In particular, at least one output of the photoconductor 114 can be electrically connected with at least one input of the capacitor 124. The resistance R photo The smaller, the faster the capacitor C will be charged. In a normal voltage divider, the maximum dynamic range of the output signal is reached when the resistance values of the two resistors are the same. The photoconductor can generally have a resistance value of > 100 kQ. A large resistance value can lead to a high thermal noise in the circuit. Low-noise, high-temperature-stable resistors based on metal foil technology can generally be found for lower resistance values and are therefore not suitable as voltage dividers. In the circuit according to the application, the resistance of the measurement voltage divider is replaced by the capacitor 124. Furthermore, the capacitor C 124 can be connected to ground.

[0095] The photoconductor readout circuit 112 comprises at least one comparator circuit 126 comprising at least one reference voltage divider circuit 128 and at least one comparator 130. The comparator circuit 126 can be configured for comparing at least one input voltage with at least one reference voltage and for outputting an output signal indicative of the comparison result. The comparator circuit 126 can be implemented as a non-inverting Schmitt trigger. The non-inverting Schmitt trigger can comprise the comparator 130 and a positive feedback to the non-inverting input of the comparator implemented by the voltage divider circuit, in the present case the reference voltage divider 128. The reference voltage divider circuit 128 can comprise at least two reference resistors 132, each reference resistor 132 having a predefined or predetermined resistance, denoted as R2 and R3 in Figure 1 The resistors R2 and R3 can be connected in series. The resistor R2 can be connected to the output of the comparator 130. Further, R3 can be connected to ground. The comparator 130 can be or can comprise one or more of the following: at least one operational amplifier; at least one Schmitt trigger; at least one logic element based on emitter coupled logic (ECL); at least one transistor-transistor logic (TTL), such as at least one advanced Schottky (ASTTL), at least one fast Schottky, at least one high-speed CMOS, and at least one CMOS; and at least one tri-state logic comparator.

[0096] For the resistors in the reference voltage divider circuit 128, only the ratio of the resistors can be important. The ratio of the reference resistors in the reference voltage divider circuit can remain unchanged as long as the resistance values of the two resistors vary by the same factor, which allows the use of resistors with a long range of resistance values.

[0097] The comparator 130 comprises at least one input 134, in particular two input terminals as shown in Fig. 134. The comparator can comprise at least one first input 136 and at least one second input 138. In particular, the comparator 130 can have a non-inverting input (+) and an inverting input (-). The output of the reference voltage divider 128 can be connected to the non-inverting input of the comparator, while the output of the measurement voltage divider 122 can be connected to the inverting input. Thus, the first input 136 is electrically connected with the output of the measurement voltage divider circuit 122, and the second input is electrically connected with the output of the reference voltage divider circuit 128. The first input 136 can be the inverting input, and the second input can be the non-inverting input. The reference voltage divider 128 can be configured for providing a positive feedback to the comparator 130. In particular, the reference voltage divider 128 can be arranged such that a portion of the output voltage of the comparator 130 is present at the non-inverting input.

[0098] The output signal of the comparator 130, also denoted as output voltage, can depend on the comparison result of the input voltage at the first input 136 with the at least one reference voltage. In particular, the output signal of the comparator 130 can be indicative of the comparison result of the input voltage at the first input 136 with the at least one reference voltage.Figure 1 In an embodiment of the application, the reference voltage can be the input voltage at the second input 138. The voltage at the first input 136 is denoted herein as the measurement voltage signal V meas , while the voltage at the second input 138 is denoted as the reference voltage signal V ref . The comparator 130 is configured to change between two output states when the input voltages at the first and second input are the same. The output signal can be a digital signal, in particular a binary digital output having two states denoted as output states. The output states V out may depend on which of the input voltages is larger:

[0099]

[0100] When the measurement voltage is smaller than the reference voltage, the output voltage will be "high". The "high" output state can be positive, in particular equal to a positive saturation voltage. When the measurement voltage becomes equal to the reference voltage, i.e. by further charging of the capacitor, the comparator changes the output state to "low", which is in particular equal to a negative saturation voltage. In this case of switching from a high output state to a low output state, a negative voltage can occur at the non-inverting input due to the negative saturation voltage at the output of the comparator 130. Thus, in case of the same input signals, the output signal switches the potential at the output of the comparator 130 to the opposite sign. Also, the inverting Schmitt trigger can exhibit a hysteresis. In case of a change of the output state, the reference voltage at the non-inverting input changes, resulting in two different reference voltage values and thus in two different values for switching the output state.

[0101] As long as V ref > V meas , i.e. for the "high" output state, the capacitor 124 will be charged by the photoconductor 114 until the measurement voltage and the reference voltage are the same. Then the output state can change to "low" and the capacitor 124 will be charged to a voltage having the opposite sign until the next output state switch. The resistance R photo of the photoconductor 114 can be determined from the charge-discharge frequency at the output terminal of the photoconductor readout circuit. The charge-discharge speed of the capacitor 124 can depend on the resistance R photo , and in particular, the smaller R photo , the higher the charge-discharge speed will be. Thus, the charge-discharge frequency measured at the output terminal 140 depends on the resistance R photoThe photoconductor readout circuit 112 includes at least one output terminal 140. Output terminal 140 can be connected in series with the output of comparator 130. The charge-discharge frequency can be a time constant used to charge or discharge capacitor 124 between two switching of output states. Therefore, the resistivity measurement of photoconductor 114 can be converted into a frequency measurement.

[0102] Furthermore, the detector 110 includes at least one evaluation device 142 configured to determine an output signal at at least one output 140 of the device, particularly the output signal of the photoconductor readout circuit 112. The evaluation device 142 is configured to determine the resistance R of the photoconductor 114 by evaluating the output signal. photo Evaluation device 142 may be or may include one or more integrated circuits, such as one or more application-specific integrated circuits (ASICs), and / or one or more data processing devices, such as one or more computers, preferably one or more microcomputers and / or microcontrollers. Additional components may be included, such as one or more preprocessing devices and / or data acquisition devices, such as one or more devices for receiving and / or preprocessing voltage signals, such as one or more AD converters and / or one or more filters. Further, evaluation device 142 may include one or more data storage devices. Evaluation device 142 may include one or more interfaces, such as one or more wireless interfaces and / or one or more wired interfaces. Evaluation device 142 may particularly include at least one data processing device, especially an electronic data processing device, which may be designed to determine at least one output voltage signal. Evaluation device 142 may also be designed to fully or partially control at least one illumination source and / or control at least one voltage source and / or adjust at least one reference resistor. Evaluation device 142 may also include one or more additional components, such as one or more electronic hardware components and / or one or more software components, such as one or more measurement units and / or one or more evaluation units and / or one or more control units. For example, the evaluation device 142 may include at least one measuring device, such as at least one voltmeter, adapted to measure at least one output voltage signal. The evaluation device 142 may be configured to perform one or more of the following operations: at least one Fourier transform; frequency counting, edge detection, period length measurement, etc.

[0103] Figure 2 Further embodiments of the device 111 and the photoconductor readout circuit 112 are shown. In addition to... Figure 1 In addition to the components shown, Figure 2In an embodiment of the light conductor readout circuit 112, the light conductor readout circuit 112 comprises at least one additional amplifier 144, in particular at least one impedance converter, configured for amplifying the output signal of the comparator circuit 126. The additional amplifier 144 can be connected to a further voltage divider comprising resistors R1 and R4. The resistor R1 can be connected to the output of the further amplifier 144 and to the resistor R4, wherein the resistor R4 can be connected to ground. The output of the further voltage divider can be connected to the non-inverting input of the additional amplifier 144.

[0104] Figure 3 Further embodiments of the device 111 and the light conductor readout circuit 112 are shown. In addition to the elements shown, in an embodiment of the light conductor readout circuit 112, the light conductor readout circuit 112 comprises at least one coupling 146 to at least one evaluation device 142. The light conductor readout circuit 112 can comprise at least one rectifier 148 and at least one further voltage divider 150 for coupling to a low voltage evaluation system, such as at least one microcontroller for frequency measurement. The coupling 146 can comprise at least one diode and at least one coupling voltage divider circuit. The coupling 146 can be arranged at the output of the comparator circuit 126. Figure 1 Figure 3 In an embodiment of the light conductor readout circuit 112, the light conductor readout circuit 112 comprises at least one coupling 146 to at least one evaluation device 142. The light conductor readout circuit 112 can comprise at least one rectifier 148 and at least one further voltage divider 150 for coupling to a low voltage evaluation system, such as at least one microcontroller for frequency measurement. The coupling 146 can comprise at least one diode and at least one coupling voltage divider circuit. The coupling 146 can be arranged at the output of the comparator circuit 126.

[0105] ​The photoconductor readout circuit 112 comprises at least one bias voltage source 152 configured for applying at least one modulated bias voltage to the photoconductor 114. Common readout circuits can be based on a voltage divider which is susceptible to bias voltage fluctuations. Any noise in the bias voltage can be measured as the measured voltage at the output of the voltage divider. In the circuit according to the present invention, the reference voltage divider 128 and the measurement voltage divider 122 can be connected to the same potential, which is the output voltage of the comparator. This can allow removing the susceptibility to fluctuations. The modulated bias voltage can be a periodic time-dependent bias voltage and / or an alternating bias voltage. The bias voltage source 152 can be configured for changing the bias voltage with each charge and / or discharge. The modulation can be changing the polarization of the bias voltage on the photoconductor 114 in such a way that the net flow of charge carriers through the photoconductor 114 is zero over the measurement period. In particular, the bias voltage is chosen such that the integral of charge carriers, such as the total current flowing through the photoconductor 114 over the measurement period, is zero. The measurement period can be the time between two consecutive transitions of the bias voltage polarization in the same direction, such as from a rising edge (e.g. positive edge) to a rising edge or from a falling edge (e.g. negative edge) to a falling edge. The change of the bias voltage with each charge or discharge can allow protecting the photoconductor 114 from resistivity drift. Typically, photoconductors are measured with a DC bias voltage, which can cause a drift of ions in the photoconductive material or substrate, which changes the properties of the photoconductor. As proposed in the present invention, with an alternating bias voltage of appropriate frequency, the drift of ions can be counteracted. The alternating bias voltage can reduce noise like flicker noise, 1 / f or pink noise. Due to the modulation of the measurement and the implementation of higher frequencies, the F noise can be significantly reduced. At the output, the frequency can be measured using one or more of the following operations: at least one Fourier transform; frequency counting, edge detection, etc. The bias voltage can be from ±0.001 V to ±5000 V. Preferably, the bias voltage can be from ±0.1 V to ±500 V, and most preferably, the bias voltage can be from ±1 V to ±50 V. The bias voltage can be switched between positive and negative. The photoconductor 114 can be characterized by a resistance asymmetry for positive and negative bias voltages. Since the integral of charge carriers over the measurement period is zero in the proposed circuit, the asymmetry can not affect the resistance measurement. The electric field across the photoconductive material due to the applied bias voltage can be about 50 V / mm.

[0106] Comparator 130 can be driven by a supply voltage 156. For example, two identical DC voltages, such as those in the range of ±0.001V to ±5000V, preferably ±1V to ±500V, and more preferably ±2V to ±50V, can be applied to the supply input 158 ​​of comparator 130. Comparator 130 can be driven by a single supply voltage 156, wherein the supply voltage 156 can range from ±0.001V to ±5000V. Preferably, the supply voltage 156 can range from ±0.1V to ±500V, and most preferably, the supply voltage 156 can range from ±1V to ±50V. Alternatively, comparator 130 can be driven by dual supply voltages, wherein the supply voltage can be between ±0.001V and ±5000V. Preferably, the supply voltage 156 can range from ±0.1V to ±500V, and most preferably, the supply voltage 156 can range from ±1V to ±50V. The comparator's dual supply voltages can be symmetrical or asymmetrical.

[0107] and, Figure 3 The child was shown Figure 1 ) to 4). Figure 1 The diagram shows an exemplary measured voltage signal V as a function of time (in milliseconds). meas (in units of V). Sub Figure 2 The example reference voltage V is shown as a function of time (in milliseconds). ref (in units of V). Sub Figure 3 The diagram shows an example output of comparator 130. Figure 4 The example input voltage (in V) of the evaluation device 142 as a function of time (in ms) is shown.

[0108] Figure 4 Further embodiments of the device 111 and the photoconductor readout circuit 112 are shown. In addition... Figure 1 In addition to the components shown, Figure 4 In one embodiment, the photoconductor readout circuit 112 includes at least one bias voltage source 152 configured to apply at least one bias voltage to the photoconductor 114. Figure 4 As shown, the photoconductor readout circuit 112 includes coupling 146. In Figure 4 In this context, coupling 146 may include at least one metal-oxide-semiconductor field-effect transistor (MOSFET) 154.

[0109] Figures 1 to 4The resistors R2 and R3 in the middle can additionally or alternatively be implemented as temperature dependent resistors, such as at least one negative temperature coefficient thermistor (NTC), or at least one temperature sensitive diode, or at least one positive temperature coefficient thermistor (PTC), or at least one additional dark photoconductor. This can allow to compensate for temperature dependencies of the photoconductor 114.

[0110] Figures 5A to 5C Further embodiments of the device 111 and the photoconductor readout circuit 112 according to the present application are shown. In Figure 5A the comparator 130 is implemented as a Schmitt trigger 160. The readout circuit works as explained with respect to Figures 1 to 4 but the comparator 130 comprises an internal comparison voltage which serves as the reference voltage. In Figure 5B the comparator 130 is implemented as an inverter. The inverter can work like a Schmitt trigger, wherein the threshold of the input voltage at the comparator is adapted to the used circuit technology. In case of transistor-transistor logic (TTL), the threshold can be U e <0.8 V for the low level and U e > 2 V for the high level. Alternatively, other digital circuit technologies can be used, such as CMOS. In Figure 5C the comparator 130 can be implemented as an inverting circuit comprising discrete components, such as two transistors. Alternatively, an integrated component embodiment is possible, wherein the circuit can comprise discrete components which are configured to generate an oscillation with a frequency which depends on the conductivity of the photoconductor 114.

[0111] Figure 6 Further embodiments of the device 111 and the photoconductor readout circuit 112 are shown. In addition to the elements shown in Figure 1 the photoconductor readout circuit 112 comprises at least one additional comparator 131 in the embodiment of Figure 6 the output of the first comparator 130 is connected to the inverting input of the additional comparator 131. The non-inverting inputs of the comparators 130 and 131 are connected to the same potential. Both comparators 130, 131 can be supplied with a single DC voltage source, such as a TTL power supply or a battery with a constant DC supply voltage of V supply In this embodiment, the bias voltage applied on the photoconductor is still modulated, changing its polarization between V supply and -V supply in such a way that the net flow of charge carriers through the photoconductor 114 is zero over the measurement period. The Figure 1 subfigure (a) shows an exemplary bias voltage (in V) on the photoconductor 114 as a function of time (in s). The Figure 2Fig. 6 shows an exemplary output of the comparator 130 as a function of time in s. The sub Figure 3 Fig. 7 shows an exemplary output of the additional comparator 131 as a function of time in s. The output of the additional comparator 131 can be phase delayed by at least half a period compared to the output of the comparator 130. Alternatively, the comparator 130 and the additional comparator 131 can be replaced by a single comparator with two inputs and two outputs, while the outputs are differential to each other, which means that the output voltages are opposite in polarity with respect to the common mode operating point of the circuit.

[0112] Fig. 7 shows an embodiment in which the device 111 comprises a plurality of photoconductors. Figure 7A Fig. 7 shows an embodiment in which the device 111 comprises at least one second electronic circuit 162. In this embodiment, the device 111 comprises two photoconductors, the photoconductor 114 and a second photoconductor 164. The second electronic circuit 162 can be or can comprise a mixer. The frequencies f1 and f2 of the two photoconductor readout circuits 112 can be mixed at the analog level before digitization by means of the mixer. The mixer can be or can comprise a non-linear circuit configured for generating new frequencies from two signals applied to it. The mixer can be configured for taking the two applied signals and generating new signals equal to the sum and the difference of the original frequencies. The sum of the original frequencies, i.e. the sum of the output signals of the photoconductor readout circuits 112, can be filtered by means of a simple low-pass filter, while the difference can be sampled, as Figure 7A The sampled difference can be measured by at least one counter 164.

[0113] For example, two frequencies f1 = 10000 Hz and f2 = 9960 Hz can be mixed and filtered to f Mixed = f1 - f2 = 40 Hz, which can also be measured with very good resolution using a common period or frequency counter. In this way, the requirements and costs, in particular the number of counters, can be reduced, while the resolution is increased. The measurement resolution can be increased by a heterodyne factor, in particular the ratio f1 / f Mixed of the carrier f1 to the beat frequency f Mixed In the described example, the heterodyne factor is 10000 / 40 = 250. Thus, a period counter with a resolution of 100 nanoseconds can resolve a change in the period length of 400 picoseconds.

[0114] Mixers are generally known to the skilled person. A wide variety of mixers is available, in particular for different frequency ranges, noise levels, package forms, as integrated circuits or as discrete components, etc.

[0115] As Figure 7BAs shown, device 111 may include at least one third resistor 166 for exhibiting radiation-independent resistance with the same temperature dependence as the photoconductor 114 and the second photoconductor 164. The third resistor 166 may be a photoconductor that is darkened in a manner unaffected by radiation, or a non-photosensitive resistor. Device 111 may include components configured to generate a third frequency f. Ref At least one third electronic circuit 168. The third frequency can be used as a reference frequency. The reference frequency can be used to generate the frequency difference from the irradiated photoconductor by means of at least two electronic circuits 162, 168. The measured resistance and specific detection rate at the measurement wavelength may drift due to thermal variations, such as the influence of ambient temperature, instability of the thermoelectric cooler used, etc. Therefore, an additional darkening photoconductor can be used, which is covered in a way that its active region is free of radiation. The output frequency of the detector can be used as a reference frequency f. Ref By using Figure 7B The dual mixer setup shown allows for high-precision measurement of the difference f. Mixed1 =f1-f Ref and f Mixed2 =f2-f Ref By calculating the quotient f Mixed1 / f Mixed2 This eliminates the temperature dependence of f1 and f2. For example, if the temperature coefficient of a photoconductor is α, then the quotient with respect to temperature T is... Therefore, it is unrelated to temperature.

[0116] In addition, such as Figure 7C As shown, a frequency divider 170 can be used such that its output frequency is an integer power of 2 of the input signal, where the power can be freely selected. For a power of 5, the output frequency will be 1 / 32 of the input frequency. Inexpensive temperature sensors, such as negative temperature coefficient thermistors (NTCs), can be built to measure the temperature of the photoconductor. The temperature dependence of the dark resistance can be factory calibrated, and the measured value can be corrected using a temperature dependence calibration factor.

[0117] Reference tag list

[0118] 110 detector

[0119] Device 111

[0120] 112 Photoconductor readout circuit

[0121] 114 Optical Conductor

[0122] 116 Irradiation

[0123] 118 Photosensitive areas

[0124] 120 Irradiation Source

[0125] 112 measuring voltage divider circuit

[0126] 124 capacitor

[0127] 126 comparator circuit

[0128] 128 reference voltage divider circuit

[0129] 130 comparator

[0130] 131 comparator

[0131] 132 reference resistor

[0132] 134 input

[0133] 136 first input

[0134] 138 second input

[0135] 140 output terminal

[0136] 142 evaluation device

[0137] 144 additional amplifier

[0138] 146 coupled

[0139] 148 rectifier

[0140] 150 further voltage divider

[0141] 152 bias voltage source

[0142] 154 MOSFET

[0143] 156 supply voltage

[0144] 158 supply input

[0145] 160 schmitt trigger

[0146] 162 second electronic circuit

[0147] 164 counter

[0148] 166 third resistor

[0149] 168 third electronic circuit

[0150] 170 frequency divider

Claims

1. An apparatus (111), comprising: - At least one photoconductor (114), said at least one photoconductor (114) being configured to exhibit a resistance R depending on the illumination (116) of the photosensitive region (118) of said photoconductor (114). photo ; - At least one photoconductor readout circuit (112), wherein the photoconductor readout circuit (114) is configured to determine the resistance R of the photoconductor (114). photo The photoconductor readout circuit (112) includes at least one bias voltage source (152), which is configured to apply at least one modulation bias voltage to the photoconductor (114). The device (111) includes at least one first electronic circuit configured to generate at least one first output signal, wherein the frequency of the first output signal is a mathematical function of the measurement period of the photoconductor (114). The device (111) includes at least one second photoconductor (164), which is configured to exhibit a resistance R depending on the illumination of its photosensitive region. photo2 The device (111) includes at least one second electronic circuit (162) configured to generate a second measurement cycle, wherein the second electronic circuit is configured to generate at least one second output signal, wherein the frequency of the second output signal is a mathematical function of the measurement cycle of the photoconductor (114) and the second photoconductor (164). The second electronic circuit (162) is a mixer.

2. The apparatus (111) according to claim 1, wherein, The bias voltage is a periodic time-dependent bias voltage, wherein the bias voltage is selected such that the integral of charge carriers flowing through the photoconductor (114) during the measurement period is zero, wherein the measurement period is defined by the time between two consecutive transitions of bias voltage polarization in the same direction.

3. The apparatus (111) according to claim 1 or 2, wherein, The photoconductor readout circuit (112) includes: - At least one measuring voltage divider circuit (122), wherein the photoconductor (114) is connected in series with at least one capacitor (124), wherein the capacitor (124) can be charged by the photoconductor (114). - At least one comparator circuit (126), which includes at least one reference voltage divider circuit (128). and at least one comparator (130), wherein the comparator (130) includes at least one input (134), wherein a first input (136) is electrically connected to the output of the measuring voltage divider circuit (122), wherein the comparator (130) is configured to change between two output states when the input voltage at the first input (136) is the same as at least one reference voltage; - At least one output terminal (140), wherein the resistance R of the optical conductor (114) photo It can be determined based on the charging-discharging frequency at the output terminal (140).

4. The apparatus (111) according to claim 3, wherein, The reference voltage divider circuit (128) includes at least two reference resistors (132), each of which has a predefined or predetermined resistance.

5. The apparatus (142) according to claim 3, wherein, The comparator (130) is or includes one or more of the following: at least one operational amplifier; at least one Schmitt trigger; at least one logic element based on emitter-coupled logic (ECL); at least one transistor-to-transistor logic (TTL), such as at least one advanced Schottky (ASTTL), at least one fast Schottky, at least one high-speed CMOS, and at least one CMOS; and at least one tri-state logic comparator, wherein the comparator (130) is configured to compare the input voltage with at least one reference voltage and to generate an output signal indicating the result of the comparison.

6. The apparatus (110) according to claim 3, wherein, The charging-discharging rate of the capacitor (124) depends on the resistor R. photo .

7. The apparatus (110) according to claim 3, wherein, The photoconductor readout circuit (112) includes at least one amplifier (144) configured to amplify the output signal of the comparator circuit.

8. The apparatus (111) according to claim 1 or 2, wherein, The device includes at least one coupling (146) to at least one evaluation device (142).

9. The apparatus (111) according to claim 1 or 2, wherein, The photosensitive region (118) includes at least one photoconductive material selected from the following: lead sulfide (PbS); lead selenide (PbSe); mercury cadmium telluride (HgCdTe); cadmium sulfide (CdS); cadmium selenide (CdSe); indium antimonide (InSb); indium arsenide (InAs); indium gallium arsenide (InGaAs); intrinsic semiconductor; organic semiconductor.

10. The apparatus (111) according to claim 1 or 2, wherein, The device (111) includes at least one temperature-sensitive element, wherein the signal of the temperature-sensitive element is used to correct the first output signal of the first electronic circuit.

11. The apparatus (142) according to claim 1 or 2, wherein, The device (111) includes at least one third resistor (166) for exhibiting radiation-independent resistance with the same temperature dependence as the photoconductor (114) and the second photoconductor, wherein the third resistor (166) is a photoconductor darkened in a manner unaffected by radiation, or a non-photosensitive resistor, wherein the device (111) includes at least one third electronic circuit (168) configured to generate a third frequency, wherein the third frequency serves as a reference frequency, wherein the reference frequency is used to generate a frequency difference from the irradiated photoconductor by means of at least two electronic circuits (162, 168).

12. A detector (110) comprising at least one means (111) according to any one of claims 1-11, wherein, The detector (110) includes at least one evaluation device (142) configured to determine an output signal at at least one output of the photoconductor readout circuit (112) of the device (111), wherein the evaluation device (142) is configured to determine the resistance R of the photoconductor (114) by evaluating the output signal. photo .

13. The detector (110) according to claim 12, wherein, The evaluation device (142) is configured to perform one or more of the following operations: at least one Fourier transform; frequency counting; edge detection; period length measurement.

14. Use of the device (111) according to any one of claims 1-11, relating to the apparatus (111), for the purpose of reading out at least one optical conductor, wherein, The device (111) includes at least one photoconductor (114), the at least one photoconductor (114) being configured to exhibit a resistance R depending on the illumination (116) of the photosensitive region (118) of the photoconductor (114). photo At least one photoconductor readout circuit (112), wherein the photoconductor readout circuit (114) is configured to determine the resistance R of the photoconductor (114). photo The photoconductor readout circuit (112) includes at least one bias voltage source (152) configured to apply at least one modulated bias voltage to the photoconductor (114), wherein the photoconductor includes one or more of the following: at least one PbS sensor, at least one PbSe sensor, or at least one pixelated sensor array including a plurality of pixels. Each of the pixels includes at least one PbS or PbSe sensor.

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