Method for measuring photocurrent considering electronic circuits and temperature dependence, and optical gas sensor

Abstract

This invention relates to an electronic circuit 1 for measuring photocurrent while considering temperature dependence. Furthermore, this invention relates to an optical gas sensor and a method for measuring photocurrent while considering temperature dependence. [Solution] The photodetector 10 has an anode terminal 11 and a cathode terminal 12, and the operational amplifier 20 has a first input section 21, a second input section 22 and an output section 23, the anode terminal 11 of the photodetector 10 and the first input section 21 of the operational amplifier 20 are electrically connected to each other, the cathode terminal 12 of the photodetector 10 and the second input section 22 of the operational amplifier 20 are electrically connected to each other, and the bias voltage terminal 50 is electrically connected to the anode terminal 11 of the photodetector 10 and the first input section 21 of the operational amplifier 20 via a first path 41. In this case, the electronic circuit 1 further includes a voltage divider 30 located in the first path 41 between the anode terminal 11 of the photodetector 10 and the bias voltage terminal 50.

Description

Technical Field

[0001] The present invention relates to a method for measuring a photocurrent in consideration of an electronic circuit and temperature dependence. Further, the present invention relates to an optical gas sensor having an electronic circuit.

Background Art

[0002] It is known from the prior art to use a photodetector, for example a photodiode made of InSb or InAsSb, in an optical gas sensor. Such a photodetector makes it possible, in addition to measuring the light rays of the light not absorbed by the gas (and from this measurement, for example, measuring the carbon dioxide concentration of the gas), to determine to what extent the specific temperature of each photodetector affects the measurement of the light rays. This determination is necessary to compensate for the temperature dependence of the measurement of each light ray.

[0003] European Patent Application Publication No. 3581898 describes an electronic circuit including a photodetector and a transimpedance amplifier, which can be selectively switched between a photocurrent measurement mode and a temperature measurement mode. In this case, in the photocurrent measurement mode, the anode terminal of the photodiode is connected to the first input part of the operational amplifier (op-amp) of the transimpedance amplifier, the cathode terminal of the photodiode is connected to the second input part of the operational amplifier, and the first bias voltage terminal is connected to the first input part and the anode terminal. In the temperature measurement mode, the anode terminal is connected to the ground terminal of the electronic circuit, the cathode terminal is connected to the second input part, the first bias terminal is connected to the first input part, and is separated from the anode terminal.

[0004] To enable switching between photocurrent measurement mode and temperature measurement mode, the electronic circuit described in European Patent Application Publication No. 3581898 includes three switches. In photocurrent measurement mode, two of the three switches are closed. As a result, no voltage is applied to the photodiode, and it operates in a pseudo-short circuit. In this case, the photocurrent of the photodiode is generated solely by the detection of a light ray. This photocurrent is amplified by a transimpedance amplifier and converted into a voltage. In temperature measurement mode, the two previously closed switches are opened, and only the third switch is closed. As a result, a bias voltage is applied to the photodiode. This allows a temperature-dependent (reverse) current to flow without the detection of a light ray. This current is amplified by a reduced amplification factor. In this case, since the voltage applied to the bias voltage terminal is generally in the range of 150-200mV, a reduction in the amplification factor is necessary. Generally, lower values ​​cannot be set directly. Therefore, the amplification factor must be appropriately reduced so that the amplified current is within a detectable range that can be digitally detected, for example, by an analog-to-digital converter.

[0005] However, implementing multiple switches to actively switch between different measurement modes carries the risk of malfunctions due to factors such as failure and / or wear effects. Therefore, there is a further need for improved solutions, in particular, for simplified electronic circuits that can measure photocurrent while taking temperature dependence into account, while reducing the number of possible malfunction factors. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] European Patent Application Publication No. 3581898 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Therefore, the object of the present invention is to provide an improved, and in particular simplified, electronic circuit for measuring photocurrent, in which at least some of the known drawbacks are beneficially avoided. In this case, for example, the most accurate and reliable measurement possible, taking into account the temperature dependence of the photodetector, is further guaranteed. [Means for solving the problem]

[0008] This problem is solved by the features described in the independent claim. Other preferred configurations are described in the dependent claims and the specification.

[0009] According to a first overall feature of the present invention, an electronic circuit is provided for measuring photocurrent with respect to temperature dependence.

[0010] The electronic circuit includes a photodetector having an anode terminal and a cathode terminal.

[0011] The electronic circuit includes a (voltage-controlled) operational amplifier having a first input, a second input, and an output. The anode terminal of the photodetector and the first input of the operational amplifier are electrically connected to each other (for example, via a second path). The cathode terminal of the photodetector and the second input of the operational amplifier are electrically connected to each other.

[0012] The electronic circuit includes a bias voltage terminal. This bias voltage terminal is electrically connected to the anode terminal of the photodetector and the first input of the operational amplifier via a first path.

[0013] The electronic circuit includes a voltage divider. This voltage divider is located in a first path between the anode terminal and the bias voltage terminal of the photodetector.

[0014] Within the scope of this specification, a photodetector, also called an optical detector and / or light sensor, means an electronic component that converts a ray of light into an electrical signal based on the internal photoelectric effect. This electrical signal is also called a photocurrent and / or optical signal. Therefore, a photodetector is a component that measures a ray of light. The ray of light is not limited to visible light, but may also be infrared or ultraviolet light. For example, a photodetector may be a photodiode, that is, a semiconductor diode that converts a ray of light into an electric current, i.e., a photocurrent, based on the internal photoelectric effect at a pn junction or pin junction.

[0015] A photodetector has a variety of applications for detecting light rays incident on it. For example, a photodetector or electronic circuit can be used to measure the content of a specific gas, such as carbon dioxide, in the vicinity of the photodetector. For this purpose, a light source may be activated so that a light ray is emitted in the direction of the photodetector. In this case, the gas to be tested is present between the light source and the photodetector. The gas content, for example, the gas concentration, can be measured based on the intensity of the light ray detected by the photodetector (i.e., the generated photocurrent) relative to the expected light ray intensity (i.e., the expected photocurrent). In this case, some of the light rays that did not reach the photodetector were absorbed or scattered by the gas. Therefore, the electronic circuit can be configured, for example, as part of a gas sensor.

[0016] A (reverse) current can be generated to power a photodetector by applying a bias voltage, independent of illumination to the photodetector. In this case, the bias voltage is generated via a first path by a voltage supplied to the bias terminal. This (reverse) current or bias voltage is temperature-dependent and can therefore be used to determine the effect of temperature on the photodetector or the effect of temperature on the current powering the photodetector. This is done, for example, by supplying a voltage to the bias terminal and measuring the output voltage of the photodetector, without the photodetector itself detecting a ray of light or without illumination to the photodetector.

[0017] Within the scope of this specification, an operational amplifier means, for example, a DC-coupled amplifier having a very high gain. Thus, an operational amplifier is an electronic component that takes the difference between two input voltages, amplifies this difference, and outputs it as an output voltage relative to a reference potential or ground. Accordingly, the input to the operational amplifier is, for example, high impedance, and the output of the operational amplifier is low impedance.

[0018] In this case, the first input voltage is supplied to the first input section of the operational amplifier via the bias voltage terminal, and the second input voltage is supplied to the second input section of the operational amplifier via the photodetector. Thus, the operational amplifier is configured to supply an output voltage that depends in particular on the input voltage supplied by the photodetector and amplifies this input voltage by a certain amplification factor. Therefore, for example, the photocurrent generated by the photodetector's reception can be appropriately amplified and detected by an ammeter and / or voltmeter at the output section of the operational amplifier.

[0019] Within the scope of the disclosure of this specification, a voltage divider means an electrical component configured to produce at least one output voltage which is a fraction of the input voltage of the voltage divider. In this case, the voltage divider can divide one input voltage into a plurality of partial voltages. These partial voltages can be taken out as output voltages at the voltage divider (or the output section of the voltage divider).

[0020] For example, a voltage divider can be implemented by a series circuit consisting of two or more resistors. In this case, at least one partial voltage can be taken out between these resistors. Particularly preferably in this case, the voltage divider is configured to generate and provide a bias voltage for a photodetector (as the output voltage of the voltage divider). This bias voltage is a fractional or partial voltage of the voltage applied to the bias voltage terminal (as the input voltage of the voltage divider).

[0021] Within the scope of the disclosure of this specification, a path, for example a first path, can mean any suitable connection between two or more terminals or any suitable electrical conductor. Thus, a path can also be referred to as an electrical connection and / or an electrical conductor. One path can have a plurality of sub-paths. In this case, at least one electrical component can be arranged between two of the plurality of sub-paths, for example, a voltage divider can be arranged within the first path.

[0022] Within the scope of the disclosure of this specification, a resistor preferably means an electronic component having a constant ohmic resistance.

[0023] The electronic circuit according to the present invention described above has several advantages. That is, the implementation of the voltage divider can measure the photocurrent generated when irradiating the photodetector and the (reverse) current (also called dark current) that can be measured to analyze the temperature dependence of the photodetector when applying a bias voltage without irradiating the photodetector in the same measurement mode. Therefore, the measurement combining temperature and photocurrent becomes possible in a common measurement mode. As a result, a switch becomes unnecessary.

[0024] In the development of the present invention, fortunately and accidentally, it has been found that the temperature dependence of photodetectors of different detector types is not qualitatively affected by the applied bias voltage, that is, the temperature behavior of the reverse current is not qualitatively affected by the applied (bias) voltage. Furthermore, the photodetector behaves linearly, like an ohmic resistance, especially in the case of a particularly low bias voltage. That is, the (reverse) current flowing through each photodetector changes almost linearly with respect to the bias voltage. Non-linearities (for example, step-like or edge-like during the transition) due to the special structure of the photodetector appear only at high bias voltages exceeding 10V, especially in the range of 12V.

[0025] Furthermore, fortunately and by chance, it has been found that the photocurrent does not depend on the applied bias voltage when the bias voltage is at least present in a sufficiently low voltage range (depending in particular on the detector type of the photodetector). In other words, for at least a low bias voltage (e.g., less than 2 mV), the generated reverse current does not qualitatively affect the photocurrent detected by detecting light rays based on the internal photoelectric effect.

[0026] Therefore, as long as this bias voltage is in a sufficiently low voltage range (e.g., less than 2 mV), the measurement of the photocurrent and the measurement for analyzing the temperature dependence by the (reverse) current can be carried out at the same bias voltage.

[0027] According to the present invention, such a sufficient reduction of the input voltage applied to the bias voltage terminal is ensured by a voltage divider, and the input voltage provides the bias voltage to the photodetector via a first path. This makes it possible for the measurement of the photocurrent and the measurement of the (reverse) current to be performed at the same bias voltage. Therefore, as described in the above prior art, it is no longer necessary to switch the electronic circuit between different measurement modes, especially to switch to a pseudo-short circuit for measuring the photocurrent.

[0028] Accordingly, the electronic circuit does not need to have a switching element. The omission of the switching element is not only beneficial for further improvement of the measurement principle, such as development into an integrated circuit, but also reduces the required space, further reduces the component cost and the manufacturing cost, and reduces the number of failure factors.

[0029] According to one embodiment, the anode terminal of the photodetector, the first input part of the operational amplifier, and the bias voltage terminal are electrically connected to each other fixedly and / or without a switch, that is, in particular, without a switching element between the anode terminal of the photodetector, the first input part of the operational amplifier, and the bias voltage terminal and / or without a switching element in the first path.

[0030] As described above, the voltage divider eliminates the need to switch the electronic circuit between different measurement modes. As a result, preferably, there is no need to provide a breaker between electrical connections, and therefore no need to provide the necessary switching elements in the first path, nor even throughout the entire electronic circuit.

[0031] According to one embodiment, the voltage divider is configured to provide a bias voltage for a photodetector when a voltage is applied to the bias voltage terminal. The bias voltage may have a value of 2mV or less, particularly 1mV or less. Alternatively, or in addition to this, the bias voltage may be at least 100 times, particularly at least 200 times, less than the voltage applied to the bias voltage terminal. Thus, the voltage divider is usefully configured to reduce the applied input voltage to a bias voltage of a desired value or range. In this case, for example, a normal current source and / or voltage source may be used to supply the input voltage, and a normal photodetector may be used to realize the electronic circuit.

[0032] The voltage applied to the bias voltage terminal may be 500mV or less, for example, 200mV. Therefore, a normal current source and / or voltage source can be usefully used to supply voltage to the bias voltage terminal.

[0033] According to one embodiment, the bias voltage terminal is further electrically connected to the cathode terminal of the photodetector and the second input section of the operational amplifier.

[0034] According to one embodiment, the second input of an operational amplifier is configured as the inverting input of the operational amplifier. The inverting input may be configured to adapt and / or control the potential of the second input of the operational amplifier to at least approximate the value of the potential applied to, for example, the first input of the operational amplifier. This makes it possible to generate a virtual ground at the second input of the operational amplifier. Alternatively or in addition, the operational amplifier may be configured as part of a transimpedance amplifier. In other words, the electronic circuit may include a transimpedance amplifier having an operational amplifier.

[0035] According to one embodiment, the electronic circuit further includes a negative feedback path that electrically connects the second input and output sections of the operational amplifier. This negative feedback path may extend in parallel with the operational amplifier. The negative feedback path may have resistors, particularly two resistors connected in series.

[0036] According to one embodiment, the electronic circuit further includes a branch path. This branch path electrically connects a negative feedback path and a bias voltage terminal to each other within the region between two resistors connected in series. The branch path may have branch resistors.

[0037] Branch paths and, optionally, negative feedback paths can be configured without switches, that is, they can be configured within branch paths without any switch elements, and optionally within negative feedback paths.

[0038] A transimpedance amplifier may have an operational amplifier, a negative feedback path, and a branch path. The transimpedance amplifier may have two series-connected resistors in the negative feedback path and / or a branch resistor in the branch path. The negative feedback path and optionally the branch path, particularly the two series-connected resistors in the negative feedback path and optionally the branch resistor, can be used to beneficially set the desired high amplification factor of the operational amplifier or transimpedance amplifier.

[0039] The operational amplifier and / or transimpedance amplifier shall have at least 100·10 6 Ω, for example, at least 200.10 6 It may have an amplification factor of Ω. The amplification factor may be constant.

[0040] The amplification factor may depend on and / or be adjustable by the resistance values ​​of the two series-connected resistors in the negative feedback path and / or the branch resistors in the branch path. This can be beneficially ensured that the current transmitted from the photodetector, i.e., the photocurrent and / or (reverse) current, is amplified as desired. As a result, for example, measurements can be made within the desired voltage range. Furthermore, since the amplification factor can be optionally made invariant, the configuration of the operational amplifier or transimpedance amplifier can be beneficially simplified. In this case, for example, a switching element for changing the amplification factor is not required.

[0041] An operational amplifier and / or transimpedance amplifier may be configured to convert a current transmitted from a photodetector, such as a photocurrent generated by the photodetector, into a current with a voltage of at least 1V, for example, about 2V or more. Furthermore, the operational amplifier and / or transimpedance amplifier may be configured to convert a current transmitted from a photodetector into a current with a voltage of up to 5V, for example, 3V or less. This allows the measured current to be beneficially amplified. This current can be measured by a normal ammeter and / or voltmeter. In this case, the converted voltage may be within a voltage range that can be digitized, for example, by an analog-to-digital converter.

[0042] The photodetector may be configured to generate a photocurrent having a current intensity of 50 nA or less, particularly 20 nA or less. Therefore, for example, ordinary photodetectors, such as semiconductor detectors or photodiodes, can be usefully used for electronic circuits.

[0043] According to one embodiment, the electronic circuit further includes a capacitor. This capacitor is placed in parallel with resistors, in particular two resistors connected in series in a negative feedback path, to constitute a low-pass filter.

[0044] According to one embodiment, the voltage divider has an input section, a first output section, and a second output section. The input section of the voltage divider may be electrically connected to a bias voltage terminal. The first output section of the voltage divider may be electrically connected to the anode terminal of a photodetector. It is conceivable that the voltage supplied to the first output section of the voltage divider can be at least 100 times, and particularly at least 200 times, smaller than the voltage applied to the input section of the voltage divider. Thus, the voltage divider can beneficially provide a bias voltage of a desired value or range via the first output section.

[0045] According to one embodiment, the voltage divider has a first resistor and a second resistor. The first resistor may be located between the input and first output of the voltage divider. The first resistor and the second resistor may be located between the input and second output of the voltage divider.

[0046] According to one embodiment, the electronic circuit further includes a grounding terminal electrically connected to the anode terminal and bias voltage terminal of the photodetector. For example, the second output section of a voltage divider may be electrically connected to the grounding terminal.

[0047] According to one embodiment, an output voltage, which depends, for example linearly and / or proportionally, to the current applied to the photodetector and / or the current generated within the photodetector, is measurable and / or extractable between the output of an operational amplifier and a bias voltage terminal. The output voltage may depend, for example linearly and / or proportionally, to the photocurrent and / or (reverse) current. This allows the temperature dependence of the light detected by the photodetector and the photodetector to be usefully inferred by measuring the output voltage.

[0048] An ammeter and / or voltmeter, such as an analog-to-digital converter and / or microcontroller, may or may not be connected to the output of an operational amplifier and optionally to a bias voltage terminal. An electronic circuit may have an ammeter and / or voltmeter, for example, to measure the output current and / or output voltage of the electronic circuit.

[0049] A current source and / or voltage source may be connected to or be connected to the bias voltage terminal. The electronic circuit may include a current source and / or voltage source. For example, the voltage supplied by the current source and / or voltage source may be adjustable or controllable by a voltage regulator and / or microcontroller.

[0050] According to one embodiment, the light detector may be a photodiode. At least a portion of the light detector and / or photodiode may consist of indium antimonide (abbreviated as InSb) and / or indium arsenide antimonide (abbreviated as InAsSb).

[0051] According to other common features of the present invention, an optical gas sensor is provided. The optical gas sensor may be configured to optically detect a gas, for example carbon dioxide, and in particular to measure the gas content of a gas, for example, the gas concentration.

[0052] An optical gas sensor includes a measuring cell for containing the gas.

[0053] An optical gas sensor includes a light source for emitting light rays in the direction of the measurement cell. For example, the light source may be an infrared source that emits infrared rays, particularly in the mid-infrared region. When the gas is carbon dioxide, infrared rays can be particularly useful for measuring the gas content, e.g., gas concentration, because carbon dioxide absorbs infrared light of specific wavelengths.

[0054] An optical gas sensor includes an electronic circuit as disclosed herein. The photodetector of the electronic circuit is arranged to detect at least a portion of the light rays that have passed through a measuring cell and the gas contained within the measuring cell.

[0055] Therefore, electronic circuits such as those disclosed herein can be usefully used to optically detect gases present in a measurement cell. In this case, the optical detection can be easily performed by using an optical gas sensor and detecting a ray of light by measuring or evaluating the output voltage of a photodetector and the electronic circuit. In this case, for example, the gas content or gas concentration of the gas can be measured.

[0056] According to one embodiment, at least a portion of the measuring cell may be placed between the light source and the photodetector of the electronic circuit and / or between the light source and the electronic circuit.

[0057] The measuring cell may have at least one external opening for gas to flow in from around the optical gas sensor.

[0058] According to another common feature of the present invention, a method for measuring photocurrent with respect to temperature dependence is provided.

[0059] This method is carried out by electronic circuits and / or optical gas sensors as disclosed herein.

[0060] This method includes providing a bias voltage for a photodetector by applying a voltage to a bias voltage terminal.

[0061] This method involves measuring a first output voltage of an electronic circuit and / or an optical gas sensor when providing a bias voltage. The photodetector is not illuminated by light rays, and / or the light source for emitting light rays, such as the light source of the optical gas sensor, is stopped.

[0062] This method involves measuring a second output voltage of an electronic circuit and / or optical gas sensor when providing a bias voltage. The photodetector is illuminated by a light ray and / or the light source is activated.

[0063] Therefore, electronic circuits and optical gas sensors such as those disclosed herein can be usefully used to measure photocurrent with regard to temperature dependence without changing the configuration or measurement mode of the electronic circuit. Instead of modification, it is sufficient to perform measurements without illumination of the photodetector and measurements with illumination of the photodetector. For this reason, it is sufficient to measure a first output voltage that depends on the (reverse) current generated by the applied bias voltage alone, and a second output voltage that depends on the (reverse) current and the photocurrent generated by the detected light ray, simply by stopping and then operating (or operating and then stopping) the light source.

[0064] According to one embodiment, the method can be carried out using an optical gas sensor. In this case, the gas content in the measuring cell, for example, the gas concentration, can be measured from the difference between a second output voltage and a first output voltage.

[0065] This difference may depend linearly and / or proportionally to the photocurrent of the photodetector, i.e., the light rays and / or light intensity detected by the photodetector. Therefore, it is usefully possible to estimate the gas around the photodetector or electronic circuit, i.e., within the measurement cell, based solely on the measured output voltage. Thus, optical detection of gas can be easily performed by an optical gas sensor. In this case, the gas content or gas concentration can be measured by simply calculating the difference in the measured output voltages.

[0066] According to one embodiment, the start-up phase may be the initiation of providing bias voltages prior to the measurement of the first and second output voltages. In this case, a low-pass filter formed by a capacitor produces a particularly slow time constant.

[0067] The first output voltage may depend, for example, linearly and / or proportionally, on the (reverse) current of the photodetector. The second output voltage may depend, for example, linearly and / or proportionally, on the sum of the photocurrent and (reverse) current of the photodetector.

[0068] The measurement of the first output voltage and the measurement of the second output voltage can be performed consecutively in less than 2 seconds, especially less than 1 second.

[0069] The first and second output voltages can be measured and / or taken between the output section of the operational amplifier and the bias voltage terminal.

[0070] To avoid repetition, the features disclosed above in relation to the apparatus (relating to electronic circuits and / or optical gas sensors) may also be claimed as features disclosed in relation to the method, and the features disclosed above in relation to the method may also be claimed as features disclosed in relation to the apparatus (relating to electronic circuits and / or optical gas sensors).

[0071] The embodiments, variations in implementation, and features of the present invention described above can be combined in any way. Further features and advantages of the present invention are described below and in the accompanying drawings. [Brief explanation of the drawing]

[0072] [Figure 1] This is a schematic diagram of an electronic circuit according to an embodiment of the present invention. [Figure 2] This is a schematic diagram of a gas sensor having an electronic circuit according to an embodiment of the present invention. [Figure 3] The processing procedure of the method according to an embodiment of the present invention is shown. [Figure 4] The following illustrates the change in output voltage during the process. [Figure 5] This example illustrates the change in the (reverse) current flowing through the photodetector in the electronic circuit, depending on the temperature of the photodetector, for various bias voltages. [Figure 6] This illustrates the progression of the "pseudo" signal of this photodetector, which depends on the bias voltage of the photodetector. [Figure 7] This example illustrates the temperature-dependent change in the output voltage of a photodetector. [Modes for carrying out the invention]

[0073] Figure 1 schematically shows an electronic circuit 1 for measuring photocurrent while considering temperature dependence, according to an embodiment of the present invention.

[0074] The electronic circuit 1 includes a photodetector 10 having an anode terminal 11 and a cathode terminal 12. Preferably, the photodetector 10 may be configured as a photodiode, and may be a semiconductor photodetector in which at least a portion is made of InSb and / or InAsSb. Thus, the photodetector 10 may be configured to detect infrared light in particular.

[0075] The electronic circuit 1 includes an operational amplifier 20 having a first input section 21, a second input section 22, and an output section 23. The second input section 22 may be configured, for example, as an inverting input section of the operational amplifier 20.

[0076] Preferably, the operational amplifier 20 and the photodetector 10 are electrically connected to each other. For this reason, it has been proposed that the anode terminal 11 of the photodetector 10 and the first input section 21 of the operational amplifier 20 are electrically connected to each other via a first path 41, and the cathode terminal 12 of the photodetector 10 and the second input section 22 of the operational amplifier 20 are electrically connected to each other via a second path 42.

[0077] Furthermore, the electronic circuit 1 includes a bias voltage terminal 50, which is electrically connected via a first path 41 to the anode terminal 11 of the photodetector 10 and the first input section 21 of the operational amplifier 20 in order to apply an input voltage.

[0078] The voltage divider 30 is configured to provide a bias voltage to the photodetector 10 when a voltage is applied at the bias voltage terminal 50. In other words, even when the photodetector 10 is not illuminated, a (reverse) current can be supplied to the photodetector 10.

[0079] The bias voltage may have a value of 2mV or less, particularly 1mV or less, and / or may be at least 100 times, particularly 200 times, less than the voltage applied to the bias voltage terminal 50. Therefore, current can be supplied to the bias voltage terminal 50 by, for example, a normal current source and / or voltage source. In this case, this current may have a voltage of 500mV or less, for example, in the range of 150mV to 200mV.

[0080] Furthermore, the electronic circuit 1 includes a voltage divider 30, which is located in the first path 41 between the anode terminal 11 and the bias voltage terminal 50 of the photodetector 10. The voltage divider 30 is used to reduce or divide the input voltage applied to the bias voltage terminal 50 into a desired bias voltage along the first path 41 toward the photodetector 10.

[0081] In the illustrated embodiment, the voltage divider 30 has an input section 31, a first output section 32, and a second output section 33. The input section 31 of the voltage divider 30 is electrically connected to a bias voltage terminal 50, and the first output section 32 of the voltage divider 30 is electrically connected to the anode terminal 11 of the photodetector 10. The voltage supplied to the first output section 32 of the voltage divider 30 is, for example, at least 100 times, and particularly at least 200 times, less than the voltage applied to the input section 31 of the voltage divider 30.

[0082] The voltage divider 30 has a first resistor R1 and a second resistor R2. The first resistor R1 is located between the input section 31 and the first output section 32 of the voltage divider 30, and the first resistor R1 and the second resistor R2 are located between the input section 31 and the second output section 33 of the voltage divider 30.

[0083] Furthermore, the electronic circuit 1 includes a grounding terminal 60, which is electrically connected to the anode terminal 11 and bias voltage terminal 50 of the photodetector 10. In this case, the second output section 33 of the voltage divider 30 is electrically connected to the grounding terminal 60.

[0084] The operational amplifier 20 is a voltage-controlled operational amplifier and is configured as part of a transimpedance amplifier. Accordingly, the electronic circuit 1 or the transimpedance amplifier includes a feedback section as a negative feedback path 43, which electrically connects the second input section 22 and the output section 23 of the operational amplifier 20. This negative feedback path 43 has two resistors R3 and R4 connected in series as a resistor.

[0085] Furthermore, the electronic circuit 1 or transimpedance amplifier has a branch path 44. This branch path 44 electrically connects the negative feedback path 43 and the bias voltage terminal 50 to each other within a region 45 between two series-connected resistors R3 and R4. The branch path 44 has a branch resistor R5.

[0086] Therefore, the bias voltage terminal 50 is not only electrically connected to the anode terminal 11 of the photodetector 10 and the first input section 21 of the operational amplifier 20, but is also electrically connected to the cathode terminal 12 of the photodetector 10 and the second input section 22 of the operational amplifier 20 via the negative feedback path 43 and the branch path 44.

[0087] In this case, preferably, the negative feedback path 43 and the branch path 44 are configured without switches. That is, no switch elements are provided in particular in the negative feedback path 43 and the branch path 44. As a result, a fixed electrical connection is provided.

[0088] The negative feedback path 43 and branch path 44, including resistors R3, R4, and R5, together with the operational amplifier 20 constitute a transimpedance amplifier. This transimpedance amplifier has a capacity of at least 100 × 10⁻¹⁶ 6 It may have an amplification factor G of Ω, for example, 200 × 10⁶ Ω or more. In this case, this amplification factor depends on the resistance values ​​of resistors R3, R4, and R5.

[0089]

number

[0090] Therefore, compared to the prior art described in European Patent Application Publication No. 3581898, the embodiment of the electronic circuit 1 shown in Figure 1 does not have any switching elements. In European Patent Application Publication No. 3581898, two switching elements are used to selectively connect the anode terminal of the photodiode to the first input and first bias voltage terminal of the operational amplifier in photocurrent measurement mode, and to the ground terminal in temperature measurement mode. On the other hand, the electronic circuit 1 of the present invention includes a voltage divider 30. Accordingly, the voltage divider 30 is not configured to selectively isolate or switch the electrical connection to the anode terminal 11 of the photodetector 10, but rather ensures that a sustained, sufficiently low bias voltage can be supplied to the photodetector 10 via the bias voltage terminal 50.

[0091] Furthermore, in European Patent Application Publication No. 3581898, a single switch element is used to selectively connect the negative feedback path to the second bias voltage terminal in photocurrent measurement mode and to disconnect it from the second bias voltage terminal in temperature measurement mode. On the other hand, the negative feedback path 43 and branch path 44 of the electronic circuit 1 of the present invention are configured without switches.

[0092] In this case, in particular, the branch path 44 is fixedly connected to the bias voltage terminal 50. As a result, the amplification factor of the operational amplifier 20 or the transimpedance amplifier is kept constant. On the other hand, in European Patent Application Publication No. 3581898, the amplification factor of the transimpedance amplifier is reduced in the temperature measurement mode by electrically isolating the negative feedback path and the second bias voltage terminal.

[0093] Figure 2 schematically shows an optical gas sensor 100 according to one embodiment. In this case, the optical gas sensor 100 includes an electronic circuit 1.

[0094] Furthermore, the optical gas sensor 100 includes a measuring cell 110 for containing the gas. The measuring cell 110 may have, for example, at least one external opening to allow the gas to flow in from around the optical gas sensor 100.

[0095] Furthermore, the optical gas sensor 100 includes a light source 120 to emit light rays in the direction of the measurement cell 100. In particular, the light source 120 may be an infrared source for emitting infrared rays, especially those in the mid-infrared region.

[0096] The photodetector 10 of the electronic device 1 is arranged to detect at least a portion of the light rays that have passed through the measuring cell 110. In this case, at least a portion of the measuring cell 110 may be placed between the light source 120 and the photodetector 10 or the electronic circuit 1.

[0097] Thus, the optical gas sensor 100 can be suitably configured to optically detect a gas (e.g., carbon dioxide) in the measuring cell 110. In particular, the gas content in the measuring cell 110, for example, the gas concentration, may be measurable based on detecting at least a portion of the light rays that have passed through the measuring cell 110 and the gas. In this case, the detectable intensity of the light rays that reach the photodetector 10 and are not absorbed and / or reflected by the gas in the measuring cell 110 depends on the type and content of the gas.

[0098] Therefore, the light ray detected by the photodetector 10 generates a photocurrent based on the internal photoelectric effect. The current intensity, which is the magnitude of the internal photoelectric effect, depends on the light intensity of the detected light ray. This photocurrent can be amplified by the operational amplifier 20 and then extracted, for example, between the output section 23 of the operational amplifier 20 and the bias voltage terminal 50.

[0099] Figure 3 illustrates a method 200 for measuring photocurrent while considering temperature dependence. This method 200 can be performed, at least in part, by an electronic circuit 1 and / or an optical gas sensor 100.

[0100] In the first method step S1, the bias voltage of the photodetector 10 is supplied by applying a voltage to the bias voltage terminal 50.

[0101] Step S1 of the first method can be the startup phase. In this case, for example, a low-pass filter configured by capacitor C may already have a slow time constant from the start of the 200 method.

[0102] In step S2 of the second method, the first output voltage of the electronic circuit 1 and / or the optical gas sensor 100 is measured when the bias voltage is supplied. In this case, the photodetector 10 is not illuminated by light rays, and / or the light source 120 is not operating to emit light rays.

[0103] Therefore, in step S2 of the second method, no photocurrent is generated by the detection of the light ray. Instead, only the (reverse) current generated by the bias voltage energizes the photodetector 10. Accordingly, the first output voltage may depend, for example, linearly and / or proportionally, on the (reverse) current of the photodetector 10.

[0104] In step S3 of the third method, the second output voltage of the electronic circuit 1 and / or the optical gas sensor 100 is measured when the bias voltage is supplied. In this case, the photodetector 10 is illuminated by a light ray and / or the light source 120 is operating.

[0105] The irradiation generates a photocurrent, an electrical signal on the order of several nanoamperes, for example, about 10 nA. The photocurrent (combined with the reverse current) is energized through the second path 42 and then amplified by the operational amplifier 20 or a transimpedance amplification factor, for example, 200 × 10⁻¹⁶ 6 The high amplification factor of Ω amplifies the current, converting it into a current with a voltage of, for example, on the order of approximately 2V.

[0106] Therefore, in step S3 of the third method, the sum of the generated photocurrent and the (reverse) current is supplied to the photodetector 10. Accordingly, the second output voltage depends linearly on the sum of the photocurrent and the (reverse) current of the photodetector 10, for example.

[0107] The first output voltage and the second output voltage can be measured and / or extracted between the output section 23 of the operational amplifier 20 and the bias voltage terminal 50.

[0108] Figure 4 illustrates the progression of the output voltage during the process of Method 200. In the startup phase of the first method step S1, the output voltage U rises to the first output voltage, i.e., to the temperature-dependent (reverse) current. In this case, a high amplification factor acts from the start by the operational amplifier 20 or the transimpedance amplifier, and optionally, a slow time constant is significantly acted by the low-pass filter.

[0109] After the startup phase, the first output voltage can be measured in the second method step S2. In this case, the photodetector 10 is not irradiated or the light source is not operating.

[0110] Finally, the photodetector 10 is irradiated in the third method step S3 or the light source is activated. As a result, the output voltage U rises until it reaches another plateau, namely the second output voltage.

[0111] Therefore, unlike the prior art described in European Patent Application Publication No. 3581898, there is no need to switch between different measurement modes between the second method step S2 and the third method step S3. In particular, it is not necessary to deactivate the bias voltage again and simulate short-circuit the photodetector 10 in the third method step S3.

[0112] Therefore, in electronic circuit 1, a switch element may be omitted. In particular, the anode terminal 11, the first input section 21 of the operational amplifier 20, and the bias voltage terminal 50 may be electrically connected to each other in a fixed manner and / or without a switch. In other words, a switch element is not provided in the first path 41 or between the anode terminal 11, the first input section 21 of the operational amplifier 20, and the bias voltage terminal 50.

[0113] Furthermore, a negative feedback path 43, i.e., the feedback section of the operational amplifier 20 or the transimpedance amplifier, can be permanently electrically connected to the bias voltage terminal 50 via a branch path 44. In this case, the branch path 44 can be configured without a switch. Moreover, it is conceivable that the entire electronic circuit 1 can be configured without a switch, i.e., without any switching elements.

[0114] Alternatively, steps S2 and S3 of both methods can be performed sequentially in the same measurement mode, i.e., with the same bias voltage applied. Changing the amplification factor by the operational amplifier 20 or the transimpedance amplifier is also unnecessary, as in the case of European Patent Application Publication No. 3581898 (where the amplification factor in the temperature measurement mode is reduced to about 1 / 700th compared to the photocurrent mode). Therefore, the amplification factor can be kept constant.

[0115] The voltage divider 30 ensures that the voltage applied to the bias voltage terminal 50 is reduced as needed to supply a sufficiently low bias voltage to the photodetector 10.

[0116] Therefore, a sufficiently low bias voltage, for example, in the range of up to 2mV, can be achieved by appropriately selecting the two resistors R1 and R2 of the voltage divider 30. For example, if a voltage of 200mV, adjusted or controlled by a typical microcontroller, is applied to the bias voltage terminal 50, a bias voltage of approximately 0.5mV can be obtained by selecting R1=2.43kΩ and R2=1MΩ.

[0117]

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[0118] Furthermore, in this low voltage range, the temperature dependence is qualitatively unaffected by the applied voltage. In other words, the temperature-dependent (reverse) current of the photodetector 10 is hardly affected by the low bias voltage. As a result, the reverse current remains almost constant regardless of the bias voltage, depending on the temperature.

[0119] Figure 5 illustrates the temperature T-dependent transition of the reverse current (referenced to 1000 at 25°C) supplying power to the photodetector 10 for different bias voltages ranging from 0.001V (i.e., 1mV) to 0.2V (200mV). As can be seen, the transition is nearly equal and therefore qualitatively unaffected by lower bias voltages. Thus, small fluctuations in the voltage applied to the bias voltage terminal 50, i.e., the bias voltage, have little effect on the temperature dependence. Therefore, temperature measurement, i.e., measurement of the temperature-dependent (also called quiescent current) (reverse) current or the (reverse) current-dependent first output voltage, can be performed at low bias voltages in step S2 of the second method.

[0120] Furthermore, at least within the low bias voltage range described above, the photocurrent Ip is little to no dependent on the applied voltage or the generated (reverse) current, or this dependence is at least negligibly small. In other words, when the photodetector 10 is irradiated, a low bias voltage has little to no effect on the magnitude and transition of the photocurrent Ip generated by the photodetector 10.

[0121] Therefore, Figure 6 illustrates the transition of the "pseudo" signal S of the photodetector 10 output from the photodetector 10 during two method steps S2 and S3, depending on the bias voltage V of the photodetector 10. In this case, the measured output signal depends on the "pseudo" signal S after amplification by the operational amplifier 20. Transition I corresponds to the temperature-dependent (reverse) current that flows through the photodetector 10 when the bias voltage is applied without illumination of the photodetector 10. On the other hand, transition II corresponds to the current that flows through the photodetector 10 when the photodetector 10 is further illuminated. Therefore, transition II includes an additional component of photocurrent. As a result, transition I is shifted.

[0122] Both transitions I and II demonstrate the operation of the photodetector 10, such as the ohmic resistor described above. That is, in the low bias voltage range shown, both transitions I and II are approximately linear between the bias voltage and the corresponding current intensity of the "pseudo" signal.

[0123] Transition III corresponds to the difference between Transition II and Transition I, i.e., the pure photocurrent that does not include the component due to the temperature-dependent (reverse) current. As can be seen, the pure photocurrent is hardly dependent on the low bias voltage applied and therefore transitions almost horizontally with respect to the bias voltage. Studies have shown that this dependence is extremely small, for example, 0.005% per 1 mV of bias voltage. For reference, Transition IV illustrates the difference between Transition I and Transition II (i.e., the inverse of Transition III). Therefore, this difference is also hardly dependent on the bias voltage.

[0124] In other words, the actual photocurrent, i.e., the current generated from the photodetector 10 by irradiation, can be calculated, for example, by the simple difference between the measured second output voltage and the measured first output voltage. Therefore, the photocurrent can be measured even if the applied bias voltage is low. As a result, unlike the prior art described in European Patent Application Publication No. 3581898, it is not necessary to switch the measurement mode between steps S2 and S3 of the two methods. In this case, the voltage applied to the bias voltage terminal 50 remains constant during both measurements.

[0125] In practice, the second method step S2 and the third method step can be performed consecutively within less than 2 seconds, particularly less than 1 second, for example, 0.6 seconds. Therefore, it is considered that rapid temperature changes will not degrade the measurement accuracy within this short period.

[0126] To measure a photocurrent or an output voltage that depends solely on the photocurrent, Method 200 may further include calculating the difference between a second output voltage and a first output voltage. This difference may depend, for example, linearly and / or proportionally to the photocurrent of the photodetector 10 and / or linearly and / or proportionally to the ray intensity detected by the photodetector 10.

[0127] When method 200 is performed using an optical gas sensor 100, the gas content, for example, the gas concentration, can be calculated from the difference between the second output voltage and the first output voltage in the measuring cell 110. If the gas to be measured is carbon dioxide, an infrared source can be used as the light source 120, because carbon dioxide absorbs at least a portion of infrared radiation for certain wavelengths, particularly in the mid-infrared region. Depending on the gas concentration, more or less infrared radiation reaches the photodetector 10. As a result, a larger or smaller photocurrent is generated accordingly. Therefore, the difference between the second output voltage and the first output voltage can be used to measure the gas concentration.

[0128] In measuring or gauging the output voltage, the electronic circuit 1 may include an ammeter and / or voltmeter, such as an analog-to-digital converter (ADC). Of particular note here is that the ADC's range is, for example, up to 2.8V. That is, this range can be digitized by the analog-to-digital converter.

[0129] Due to the characteristics of the photodetector 10, and especially if the photodetector 10 is a semiconductor-based infrared detector (e.g., InSb or InAsSb), the temperature-dependent (reverse) current, i.e., the (reverse) current level, increases with increasing temperature. However, since the photosensitivity decreases with increasing temperature, the photocurrent, i.e., the voltage level, in the irradiated state also decreases at the same time.

[0130] Figure 7 illustrates the change in output voltage U, which depends on temperature T. Change I corresponds to the first output voltage, which increases with increasing temperature.

[0131] Transition II corresponds to the component of the second output voltage that is solely attributable to the photocurrent. As can be seen, this transition II decreases with increasing temperature, unlike the first output voltage which depends solely on the (reverse) current. As a result, as shown by transition III, the entire second output voltage, obtained from the sum of both transitions I and II, increases with increasing temperature, similar to transition I, but much more gradually.

[0132] This ensures that the output voltage is maintained within a voltage range (e.g., up to 2.8V) within the relevant temperature range. This output voltage can be digitized by a corresponding analog-to-digital converter. Therefore, a given ADC range can be optimally utilized, for example, by appropriately selecting the components of electronic circuit 1.

[0133] The present invention is not limited to the preferred embodiments described above. Rather, numerous variations and modifications are possible that utilize the spirit of the invention and thus fall within the scope of protection. In particular, the present invention seeks protection for the subject matter and features of dependent claims, without relying on the cited claims. Specifically, each feature of an independent claim is disclosed independently of the others. Furthermore, the features of a dependent claim are also disclosed independently of all the features of an independent claim. [Explanation of symbols]

[0134] 1 Electronic circuit 10 Light detectors 11. Anode terminal of the light detector 12. Cathode terminal of the light detector 20 Operational Amplifiers 21 First input section of the operational amplifier 22 Second input section of the operational amplifier 23 Output section of the operational amplifier 30 voltage divider 31 Input section of the voltage divider 32. First output section of the voltage divider 33. Second output section of the voltage divider 41. First Route 42 Second Route 43 Negative feedback path 44 Branching Routes 45 Regions in the negative feedback path 50 Bias voltage terminal 60 Ground terminal 100 Optical Gas Sensors 110 measuring cells 120 light source 200 ways C Capacitor R1-R5 Resistors S1-S3 Method Steps

Claims

1. An electronic circuit (1) for measuring photocurrent while taking temperature dependence into consideration, comprising a photodetector (10), an operational amplifier (10), and a bias voltage terminal (50), The photodetector (10) has an anode terminal (11) and a cathode terminal (12), The operational amplifier (20) has a first input section (21), a second input section (22), and an output section (23), the anode terminal (11) of the photodetector (10) and the first input section (21) of the operational amplifier (20) are electrically connected to each other, and the cathode terminal (12) of the photodetector (10) and the second input section (22) of the operational amplifier (20) are electrically connected to each other. In the electronic circuit (1), the bias voltage terminal (50) is electrically connected to the anode terminal (11) of the photodetector (10) and the first input section (21) of the operational amplifier (20) via the first path (41), The electronic circuit (1) is further characterized by including a voltage divider (30) located in a first path (41) between the anode terminal (11) and the bias voltage terminal (50) of the photodetector (10).

2. The voltage divider (30) is configured such that when a voltage is applied to the bias voltage terminal (50), a) Having a value of less than 2 mV, especially less than 1 mV, and / or b) A voltage that is at least 100 times, and especially at least 200 times, smaller than the voltage applied to the bias voltage terminal (50), The electronic circuit (1) according to claim 1, characterized in that it is configured to supply a bias voltage to a light detector (10).

3. Furthermore, the electronic circuit (1) according to claim 1 or 2 is characterized in that the bias voltage terminal (50) is electrically connected to the cathode terminal (12) of the photodetector (10) and the second input section (22) of the operational amplifier (20).

4. The electronic circuit (1) according to any one of claims 1 to 3, characterized in that the second input section (22) of the operational amplifier (20) is configured as the inverting input section of the operational amplifier (20) and / or the operational amplifier (20) is configured as part of a transimpedance amplifier.

5. Furthermore, the electrical circuit (1) includes a negative feedback path (43), which electrically connects the second input section (22) of the operational amplifier (20) and the output section (23) of the operational amplifier (20). The electronic circuit (1) according to any one of claims 1 to 4, characterized in that the negative feedback path (43) has a resistor, in particular two resistors connected in series (R3, R4).

6. Furthermore, the electronic circuit (1) includes a branch path (44), which electrically connects the negative feedback path (43) and the bias voltage terminal (50) to each other within the region (45) between two series-connected resistors (R3, R4). In particular, the electronic circuit (1) according to claim 5 is characterized in that the branch path (44) has a branch resistor (R5).

7. Furthermore, the electronic circuit (1) includes a capacitor (C), which is arranged in parallel with the resistors of the negative feedback path (43), particularly two resistors (R3, R4) connected in series, to constitute a low-pass filter, as described in claim 5 or 6.

8. The voltage divider (30) has an input section (31), a first output section (32), and a second output section (33). The input section (31) of the voltage divider (30) is electrically connected to the bias voltage terminal (50), and the first output section (32) of the voltage divider (30) is electrically connected to the anode terminal (11) of the photodetector (10). In particular, the electronic circuit (1) according to any one of claims 1 to 7 is characterized in that the voltage supplied to the first output section (32) of the voltage divider (30) is at least 100 times, and especially at least 200 times, smaller than the voltage applied to the input section of the voltage divider (30).

9. The voltage divider (30) has a first resistor (R1) and a second resistor (R2), The electronic circuit (1) according to claim 8, characterized in that the first resistor (R1) is located between the input section (31) and the first output section (32) of the voltage divider (30), and the first resistor (R1) and the second resistor (R2) are located between the input section (31) and the second output section (33) of the voltage divider (30).

10. Furthermore, the electronic circuit (1) includes a grounding terminal (60), which is electrically connected to the anode terminal (11) and bias voltage terminal (50) of the photodetector (10), and in particular, the second input section (33) of the voltage divider (30) is electrically connected to the grounding terminal (60), as described in any one of claims 1 to 9.

11. The electronic circuit (1) according to any one of claims 1 to 10, characterized in that an output voltage dependent on the current applied to the photodetector (10) is measurable and / or extractable between the output section (23) of the operational amplifier (20) and the bias voltage terminal (50).

12. The electronic circuit (1) according to any one of claims 1 to 11, characterized in that the light detector (10) is a photodiode.

13. An optical gas sensor (100) includes a measuring cell (110) for containing a gas and a light source (120) for emitting light rays in the direction of the measuring cell (110), Furthermore, the optical gas sensor (100) includes the electronic circuit (1) described in any one of claims 1 to 12. The optical gas sensor (100) is characterized in that the photodetector (10) of the electronic device (1) is arranged to detect at least a portion of the light rays that have passed through the measuring cell (110).

14. In a method (200) for measuring photocurrent while taking temperature dependence into consideration, This method (200) is carried out using the electronic circuit (1) described in any one of claims 1 to 12 and / or the optical gas sensor (100) described in claim 13, and this method (200) is Step (S1) is to provide a bias voltage to the photodetector (10) by applying a voltage to the bias voltage terminal (50), Step (S2) of measuring the first output voltage of the electronic circuit (1) and / or optical gas sensor (100) when providing a bias voltage, when the light detector (10) is not illuminated by light rays and / or the light source (120) for emitting light rays is not operating, Step (S3) of measuring the second output voltage of the electronic circuit (1) and / or optical gas sensor (100) when supplying a bias voltage, when the photodetector (10) is illuminated by a light ray and / or the light source (120) is operating, The method (200) is characterized by including the following:

15. The method (200) is performed using an optical gas sensor (100), The method according to claim 14, wherein the gas content in the measuring cell (110) is measured from the difference between the second output voltage and the first output voltage.

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