Optical concentration measuring device and signal processor

Abstract

To provide an optical concentration measuring device and a signal processor in which a suppression effect of a leakage current is enhanced.SOLUTION: An optical concentration measuring device includes a light source, detectors (21, 22) that detect a signal based on light emitted from the light source, and output a detection signal, a signal processor (50) that acquires the detection signal and converts the detection signal to a digital signal, and a substrate (30) on which the detector and the signal processor are provided. The signal processor has a terminal array in which a plurality of signal terminals being input and output terminals of signal lines connected to the detectors is sandwiched between a plurality of voltage terminals supplying a voltage other than 0 V. In plan view of the substrate from the front, the signal processor and wiring connecting the plurality of voltage terminals surround the signal lines.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to an optical concentration measuring device and a signal processing unit. [Background technology]

[0002] In recent years, development of gas sensors (gas measurement devices) has been progressing. The gas sensors (gas measurement devices) are equipped with a light source that emits infrared rays, and are configured so that the infrared rays pass through gases containing the target gas, and detect the concentration of the target gas by utilizing the absorption characteristics of the infrared rays by the target gas. For example, an infrared sensor module has been proposed that includes an infrared sensor, an integrated circuit (IC) that processes the output signal of the infrared sensor, and a package that houses the infrared sensor and the IC. In compact infrared sensor modules, the IC may perform signal processing based on minute currents, for example, on the order of nA, and it is necessary to suppress leakage currents to improve detection accuracy. For example, Patent Document 1 discloses an output current detection IC for a diode-type sensor that is designed to reduce the effects of leakage current. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2015 / 105048 Summary of the Invention [Problem to be solved by the invention]

[0004] The technology in Patent Document 1 reduces leakage current in the protection circuit, but is difficult to apply directly to normal gas sensor measurements. Another known conventional method for suppressing leakage current is to surround the infrared sensor with ground potential on the gas sensor substrate. However, this conventional method only has limited effectiveness in suppressing leakage current, and a more effective method is needed.

[0005] In view of the above circumstances, an object of the present disclosure is to provide an optical concentration measurement device and a signal processing unit that are more effective in suppressing leakage current. [Means for solving the problem]

[0006] (1) An optical concentration measurement device according to an embodiment of the present disclosure, a light source that emits light toward a gas detection space into which a gas to be detected is introduced; a detection unit that detects a signal based on at least a part of the light that has been emitted from the light source and passed through the target gas, and outputs a detection signal; a signal processing unit that acquires the detection signal and converts it into a digital signal; a substrate on which the detection unit and the signal processing unit are provided, the detection unit includes a first detection unit and a second detection unit, the signal processing unit supplies a constant voltage other than 0 V to a plurality of signal terminals, which are input / output terminals of signal lines electrically connected to the detection unit, and forms a terminal arrangement in which the signal terminals are sandwiched between a plurality of voltage terminals that are not electrically connected to the detection unit; the plurality of voltage terminals include a first voltage terminal, a second voltage terminal, and a third voltage terminal; In a planar view of the substrate from the front, the wiring connecting the first voltage terminal and the second voltage terminal and the signal processing unit surround the signal line connecting the first detection unit and the signal processing unit, and the wiring connecting the second voltage terminal and the third voltage terminal and the signal processing unit surround the signal line connecting the second detection unit and the signal processing unit.

[0007] (2) As one embodiment of the present disclosure, in (1), The plurality of signal terminals are composed of at least two signal terminals sandwiched between the first voltage terminal and the second voltage terminal for connecting to the first detection unit, and at least two signal terminals sandwiched between the second voltage terminal and the third voltage terminal for connecting to the second detection unit.

[0008] (3) As one embodiment of the present disclosure, in (2), The plurality of signal terminals are composed of two signal terminals sandwiched between the first voltage terminal and the second voltage terminal for connecting to the first detection unit, and two signal terminals sandwiched between the second voltage terminal and the third voltage terminal for connecting to the second detection unit.

[0009] (4) As an embodiment of the present disclosure, in any one of (1) to (3), In a plan view of the substrate from the front, all of the voltage terminals and the signal terminals are provided on one side of the rectangular signal processing unit.

[0010] (5) As an embodiment of the present disclosure, in any one of (1) to (4), A part of the wiring connecting the first voltage terminal and the second voltage terminal is common to a part of the wiring connecting the second voltage terminal and the third voltage terminal.

[0011] (6) As an embodiment of the present disclosure, in any one of (1) to (5), The wiring length from the signal processing unit to the first detection unit is shorter than the wiring length from the signal processing unit to the second detection unit.

[0012] (7) As an embodiment of the present disclosure, in any one of (1) to (6), The wiring has a cut portion in a part thereof, and the length of the cut portion is 1 / 10 or less of the length of the signal line connecting the signal terminal to the detection unit.

[0013] (8) A signal processing unit according to an embodiment of the present disclosure includes: It is used in any of the optical density measuring devices (1) to (7). [Effects of the Invention]

[0014] According to the present disclosure, it is possible to provide an optical concentration measurement device and a signal processing unit that have an improved effect of suppressing leakage current. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a gas sensor according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a plan view of the substrate seen from the front, with a portion of the gas sensor in FIG. 1 being transparent. DETAILED DESCRIPTION OF THE INVENTION

[0016] A gas sensor 10 (see FIG. 1) and a signal processing unit 50 (see FIG. 2) according to an embodiment of the present disclosure will be described below with reference to the drawings.

[0017] (Gas Sensor 10) FIG. 1 is a diagram illustrating the configuration of a gas sensor 10 according to this embodiment. The gas sensor 10 measures the presence or concentration of a target gas in a gaseous medium. In this embodiment, the gas sensor 10 is described as a device for measuring the concentration of the target gas. Although the gas sensor 10 is an NDIR (non-dispersive infrared) sensor, the present invention is not limited to this and may be, for example, a photoacoustic sensor. The NDIR gas sensor 10 measures the concentration of the target gas using an infrared receiving element that receives infrared light in an absorption wavelength band corresponding to the target gas and an infrared emitting element that emits infrared light in the absorption wavelength band. When the gas sensor 10 is a photoacoustic sensor, the concentration of the target gas is measured by detecting the vibrations of gas molecules that absorb light as sound (pressure changes) using a high-performance microphone. The gas sensor 10 according to this embodiment can be applied to various devices. For example, it can be used for environmental measurement in buildings, as a portable, compact measuring device installed in mobile communication devices such as smartphones, or for gas detection inside vehicles such as automobiles, trains, and airplanes.

[0018] The configuration of the gas sensor 10 in this embodiment allows its application as a light-emitting and receiving device for purposes other than gas detection. In other words, the disclosure derived by replacing the above-described "gas sensor 10" with "optical concentration measuring device," "optical physical quantity measuring device," "light-emitting and receiving device," "optical device," or the like is within the scope of the present disclosure. For example, it becomes possible to detect the state of the optical path space (e.g., the presence or concentration of a specific component of a fluid, as an example other than gas). For example, it can be used as a component detector or component concentration measurer for a substance (e.g., water or body fluid) present in the optical path space between the light-emitting unit and the light-receiving unit. For example, when the substance present in the optical path space is blood, the component detector or component concentration measurer can be used to measure the glucose concentration in blood.

[0019] The component detection device or component concentration measurement device can measure the glucose concentration in blood glucose by measuring the absorption of light with wavelengths of 1 to 10 μm. When measuring the glucose concentration in blood glucose, it is preferable to measure the absorption of light in the 1.6 μm, 2.0 μm, and 10.0 μm bands. A small, highly accurate, and highly reliable non-invasive glucose concentration measurement device can be realized. Such a glucose concentration measurement device allows, for example, a diabetic patient to accurately check their own blood glucose level without causing damage to the skin, which would occur with invasive methods. Furthermore, more accurate medication (e.g., insulin) management can be achieved based on the measured blood glucose level.

[0020] The gas sensor 10 includes a light source 11, a detection unit 20, a signal processing unit 50 (see FIG. 2), and a substrate 30. In this embodiment, the detection unit 20 includes a first detection unit 21 and a second detection unit 22. The gas sensor 10 also includes a gas cell 40. The detection unit 20 detects a signal based on the light emitted from the light source 11 and outputs a detection signal. The signal detected by the detection unit 20 may be the light itself (the above-mentioned NDIR method) or may include vibrations of gas molecules that have absorbed the light (the above-mentioned photoacoustic method).

[0021] The gas cell 40 has a hole 43 through which a gas (e.g., ambient air) passes, and the gas is introduced into the gas detection space 42 through the hole 43. The gas sensor 10 measures the concentration of a detection gas in the introduced gas. The detection gas may be a flammable gas such as carbon dioxide, breath alcohol (e.g., ethanol), methane, propane, hydrogen, ethylene, or MCH (methylcyclohexane). The detection gas may also be a toxic gas such as carbon monoxide, hydrogen sulfide, formaldehyde, or ammonia. The detection gas may also be a greenhouse gas such as nitrous oxide or a refrigerant gas (e.g., chlorofluorocarbon, chlorofluorocarbon substitute, R32, or R1234y) used in air conditioners or refrigerators. The gas sensor 10 measures the concentration of the detection gas in the gas introduced into the gas detection space 42 and outputs the measurement result.

[0022] The gas sensor 10 includes a gas cell 40 on a main surface 30a of a substrate 30. The main surface 30a is one of the surfaces of the substrate 30 having the largest area. As shown in FIG. 1, a Cartesian coordinate system is set so that the xy plane is parallel to the main surface 30a of the substrate 30. The z-axis direction is perpendicular to the main surface 30a of the substrate 30. The z-axis direction is sometimes referred to as the up-down direction. Here, the positive direction of the z-axis corresponds to the upward direction. The planar view is a view looking in the negative direction of the z-axis (downward). In this embodiment, the light source 11, the detection unit 20, and the signal processing unit 50 are provided on the main surface 30a of the substrate 30 and disposed inside the gas detection space 42 above the main surface 30a.

[0023] In this embodiment, the second detection unit 22 is integrated with the light source 11. More specifically, the light source 11 and the second detection unit 22 are sealed on one surface of the light source substrate 12 by a sealing unit 23. In other words, the light source substrate 12, the light source 11, the second detection unit 22, and the sealing unit 23 are integrated to form a light source module. FIG. 1 is a cross-sectional view showing a cross section of the gas sensor 10 including these components. Here, for the first detection unit 21, a detection substrate may be present on the light incident side so as to correspond to the light source substrate 12, but this is not shown in FIG. 1 for ease of viewing.

[0024] 2 is a plan view of the substrate 30 seen from the front, with a portion of the gas sensor 10 in FIG. 1 being see-through. More specifically, FIG. 2 is a plan view of the substrate 30 on which the detection unit 20 (the first detection unit 21 and the second detection unit 22) and the signal processing unit 50 are provided, with the gas cell 40, the light source substrate 12, the light source 11, and the sealing unit 23 being see-through. Below, the components of the gas sensor 10 will be described in detail, followed by a description of the layout of the signal processing unit 50 and the substrate 30 shown in FIG. 2.

[0025] (Substrate 30) The substrate 30 has a function of holding the gas cell 40, the light source module, the first detection unit 21, and the signal processing unit 50. In this embodiment, the substrate 30 is a PCB (printed circuit board) on which the light source module, the first detection unit 21, and the signal processing unit 50 are mounted and electrically connected. The substrate 30 is made of a material such as paper, glass cloth, ceramics, polyimide, or liquid crystal polymer.

[0026] (Gas Cell 40) As described above, the gas cell 40 has a gas detection space 42 for detecting a gas to be detected. The gas detection space 42 is an internal space surrounded by the outer wall of the gas cell 40 and the substrate 30. The outer wall of the gas cell 40 may be made of, for example, metal, glass, resin, or a composite material thereof. The resin may be, for example, phenolic resin, epoxy resin, polyimide resin, bismaleimide triazine resin, fluororesin, polyphenylene oxide resin, LCP (liquid crystal polymer), PP (polypropylene), or PEEK (polyether ether ketone). The resin may also be PA (polyamide), PPE (polyphenylene ether), PC (polycarbonate), PPS (polyphenylene sulfide), PMMA (polymethyl methacrylate resin), or PAR (polyarylate resin). The resin may also be a hard resin made by mixing two or more of these materials. Furthermore, the gas cell 40 is preferably made of a material with a low optical absorption coefficient and high reflectance in order to efficiently confine the light emitted from the light source 11 within the gas cell 40. Specifically, the material of the gas cell 40 is preferably a resin housing coated with an alloy containing aluminum, gold, or silver, a dielectric, or a laminate thereof. From the viewpoints of high productivity and weight reduction, the inner surface of the gas cell 40 is preferably formed by vapor deposition or plating on the resin housing. Furthermore, the gas cell 40 may be formed by cutting, but from the viewpoint of productivity, it is preferably formed by injection molding or press working. Furthermore, the gas cell 40 and the substrate 30 may be mechanically joined by adhesive, screws, claws, fittings, grommets, welding, soldering, or the like.

[0027] Here, when the gas cell 40 is made of a conductive material such as metal and the substrate 30 and the gas cell 40 are electrically connected by solder or the like, the gas cell 40 may be fixed to a reference potential. Fixing the gas cell 40 to the reference potential allows the gas cell 40 to function as an electromagnetic wave shield, thereby improving the measurement performance of the gas to be detected. The reference potential is, for example, the ground potential.

[0028] (Light source 11) The light source 11 emits light having a wavelength that is absorbed by the gas to be detected. The light source 11 is also referred to as a light-emitting unit. The light source 11 may be provided on the main surface 30a of the substrate 30 inside the gas detection space 42. In this embodiment, the light is infrared. That is, the light source 11 is composed of a light-emitting element that emits infrared. The light-emitting element is preferably driven at high speed by a voltage pulse or a current pulse. The light-emitting element may be, for example, an LED (Light Emitting Diode), a laser (Light Amplification by Stimulated Emission of Radiation), a MEMS heater, a lamp, or the like. The LED includes, for example, a resonant-type light-emitting diode. The laser includes, for example, a vertical-cavity surface-emitting laser. In this embodiment, the light source 11 is an LED (infrared LED) that emits infrared light. Furthermore, the light source 11 is preferably a quantum-type infrared LED that emits infrared light using electrons or holes in a semiconductor so that it can be driven at a high frequency.

[0029] Here, the gas sensor 10 may further include a drive source that outputs a drive signal to drive the light-emitting element. In this embodiment, the drive source is included in the signal processing unit 50. In other words, a part of the signal processing unit 50 functions as the drive source.

[0030] Furthermore, the light source 11 may include auxiliary members having auxiliary optical functions such as wavelength selection, light collection, scattering, wavelength conversion, etc. Specifically, the auxiliary members include wavelength selection filters, lenses, phosphors, diffraction gratings, etc.

[0031] The light source 11 emits light from a light-emitting surface 11a. The light-emitting surface 11a is a surface of the light source 11 that contacts the light source substrate 12. The light-emitting surface 11a corresponds to one of the surfaces of the light source 11 that has the largest area.

[0032] Here, the wavelength of the infrared light may be 2 μm to 12 μm. The 2 μm to 12 μm region contains many absorption bands specific to various gases, making it a wavelength range particularly suitable for use in the gas sensor 10. For example, methane has an absorption band at 3.3 μm, carbon dioxide at 4.3 μm, and alcohol (ethanol) at 9.5 μm.

[0033] A part of the light emitted by light source 11 may be directed toward the gas detection space into which the target gas is introduced. The other part of the light emitted by light source 11 does not have to be directed toward the gas detection space into which the target gas is introduced. The light emitted by light source 11 may be directed directly toward the gas detection space into which the target gas is introduced, or may be directed toward the gas detection space into which the target gas is introduced via a reflecting part (light guiding part) such as a mirror.

[0034] (Sealing portion 23) The sealing unit 23 is made of, for example, a molded resin, but is not limited to this as long as it seals the light source 11 and the second detection unit 22. When the sealing unit 23 is made of a molded resin, the light source 11 and the second detection unit 22 can be integrated together with the light source substrate 12 while maintaining their positional relationship. As the material for the molded resin, for example, an epoxy resin or a phenol resin may be used.

[0035] (light source substrate 12) The light source substrate 12 may be, for example, a semiconductor substrate. Examples of the semiconductor substrate that can be used include a Si substrate, an InP substrate, and a GaAs substrate. The light source substrate 12 may also include an auxiliary member having auxiliary optical functions such as wavelength selection, light collection, scattering, and wavelength conversion. Specific examples of the auxiliary member include a wavelength selection filter, a lens, a phosphor, and a diffraction grating.

[0036] (Second detection unit 22) The second detection unit 22 functions as a photodetector that detects the amount of light emitted from the light source 11. The second detection unit 22 may be configured to include a light-receiving element sensitive to the wavelength band of light emitted from the light source 11. Specific examples of the light-receiving element include a quantum sensor such as a photodiode with a PIN structure. Other examples of the light-receiving element include a phototransistor, a thermopile, a pyroelectric sensor, and a bolometer. In this embodiment, the light-receiving element is a quantum infrared sensor. The second detection unit 22 is disposed at a position where light emitted from the light source 11 is reflected by a surface of the light source substrate 12 that contacts the gas detection space 42 and passes through the interior of the light source substrate 12. By disposing the second detection unit 22 at such a position, it becomes possible to detect the amount of light emitted from the light source 11 regardless of the usage environment.

[0037] Here, the gas sensor 10 has an analog-to-digital converter that converts the analog signal (detection signal) output by the second detection unit 22 into a digital signal. The analog signal (detection signal) output by the first detection unit 21 is also converted into a digital signal. In this embodiment, the analog-to-digital converter is included in the signal processing unit 50. That is, the signal processing unit 50 has a function of acquiring the detection signal output from the detection unit 20 and converting it into a digital signal.

[0038] (First detection unit 21) The first detection unit 21 detects a change in the amount of the target gas present in the gas (air) in the gas detection space 42. The first detection unit 21 is provided on the main surface 30a of the substrate 30 inside the gas detection space 42. In this embodiment, the first detection unit 21 may include a light-receiving element sensitive to the wavelength band of light emitted from the light source 11. Specific examples of the light-receiving element include a quantum sensor such as a photodiode with a PIN structure. Other examples of the light-receiving element include a phototransistor, a thermopile, a pyroelectric sensor, and a bolometer. In this embodiment, the light-receiving element is a quantum infrared sensor. The first detection unit 21 is disposed at a position where light emitted from the light source 11 that has passed through the gas detection space 42 enters the first detection unit 21. Here, a reflecting unit (light guide unit) that reflects the light emitted from the light source 11 so that the light enters the first detection unit 21 may be provided in the gas detection space 42. The reflecting portion may be, for example, a concave mirror, and the reflecting surface may be made of a metal having a high reflectivity, such as aluminum or gold.

[0039] First detection unit 21 may receive, of the light emitted by light source 11, light that has passed through the gas detection space into which the target gas is introduced. First detection unit 21 may receive, of the light emitted by light source 11, both light that has passed through the gas detection space into which the target gas is introduced and light that has not passed through the gas detection space into which the target gas is introduced.

[0040] As another example, when the gas sensor 10 is a photoacoustic type, the first detection unit 21 may be, for example, a microphone, an air pressure sensor, or a pressure sensor.

[0041] (Gas detection space 42) The gas detection space 42 is separated by an outer wall and has a function of storing a gas such as air in the inner space. The gas stored in the gas detection space 42 is replaced through the hole 43.

[0042] (hole 43) The hole 43 is provided in a part of the outer wall (side wall and ceiling) that defines the gas detection space 42 of the gas cell 40. Gas passes through the hole 43, replacing the gas in the gas detection space 42. There may be a plurality of holes 43. Here, the hole 43 may be equipped with a dust filter for dust prevention. The dust filter may be, for example, a nonwoven fabric, a Teflon (registered trademark) sheet, or the like.

[0043] (signal processing unit 50) The signal processing unit 50 may control the entire gas sensor 10. For example, the signal processing unit 50 may perform calculations to obtain the concentration of the target gas. That is, the signal processing unit 50 may calculate the concentration of the target gas based on the detection signal from the detection unit 20. As described above, in this embodiment, the signal processing unit 50 has at least the function of acquiring the detection signal output from the detection unit 20 and converting it into a digital signal. Also, in this embodiment, the signal processing unit 50 functions as a drive source for driving the light-emitting element. The signal processing unit 50 may be configured to include one or more processors. The processor may be, for example, a general-purpose processor or a dedicated processor specialized for a specific process, but is not limited to these and may be any processor. The signal processing unit 50 may be a small signal processing device configured by an IC including one or more processors.

[0044] (Design of gas sensor 10) In the gas sensor 10 according to this embodiment, the layout of the signal processing unit 50 and the substrate 30 shown in FIG. 2 is adopted in order to effectively suppress leakage current and improve the measurement accuracy of the gas to be detected.

[0045] First, the signal processing unit 50 has a terminal arrangement in which multiple signal terminals, which are input / output terminals of signal lines (thin solid lines in FIG. 2 ) connected to the detection unit 20, are sandwiched between multiple voltage terminals that supply voltage. The voltages supplied by the multiple voltage terminals may be constant voltages other than 0 V. Here, the constant voltage includes voltages that can be considered to be approximately constant when errors such as voltage fluctuations due to the operation of peripheral circuits, voltage fluctuations due to element variations, and voltage fluctuations due to temperature characteristics are taken into account. In the example of FIG. 2 , the multiple voltage terminals are composed of a first voltage terminal (TP1), a second voltage terminal (TP2), and a third voltage terminal (TP3). In this embodiment, the multiple voltage terminals supply an analog reference voltage used in an analog signal processing circuit, rather than a ground potential (i.e., not 0 V). The analog signal processing circuit amplifies or reduces noise from the detection signal, which is an analog signal. 2, the multiple signal terminals include two signal terminals (TS1, TS2) for connection to the first detection unit 21 and two signal terminals (TS3, TS4) for connection to the second detection unit 22. The two signal terminals (TS1, TS2) are sandwiched between a first voltage terminal (TP1) and a second voltage terminal (TP2). The two signal terminals (TS3, TS4) are sandwiched between a second voltage terminal (TP2) and a third voltage terminal (TP3). Here, the number of signal terminals sandwiched between the first voltage terminal (TP1) and the second voltage terminal (TP2) needs to be at least two, and may be, for example, three or more. Similarly, the number of signal terminals sandwiched between the second voltage terminal (TP2) and the third voltage terminal (TP3) needs to be at least two, and may be, for example, three or more.

[0046] In addition, in the gas sensor 10, in a plan view, the wiring connecting the multiple voltage terminals (thick solid lines in FIG. 2) and the signal processing unit 50 surround the signal line (thin solid lines in FIG. 2) connecting the detection unit 20 and the signal processing unit 50. In other words, the wiring layout of the substrate 30 is designed so that the signal line (thin solid lines in FIG. 2) is shielded by the wiring of the analog reference voltage (thick solid lines in FIG. 2). In the example of FIG. 2, in a plan view, the wiring connecting the first voltage terminal (TP1) and the second voltage terminal (TP2) and the signal processing unit 50 surround the signal line connecting the first detection unit 21 and the signal processing unit 50. In addition, the wiring connecting the second voltage terminal (TP2) and the third voltage terminal (TP3) and the signal processing unit 50 surround the signal line connecting the second detection unit 22 and the signal processing unit 50. Here, "surrounding" does not necessarily mean that the wiring connecting the multiple voltage terminals (thick solid lines in FIG. 2 ) completely surrounds the signal line (thin solid lines in FIG. 2 ). "Enclosing" means that the wiring connecting the multiple voltage terminals (thick solid lines in FIG. 2 ) and the signal processing unit 50 surround the signal line (thin solid lines in FIG. 2 ). The wiring connecting the multiple voltage terminals surrounding the signal line may have a disconnected section. A disconnected section is a section where the wiring is not connected (a disconnected section). However, to effectively suppress leakage current and improve the measurement accuracy of the detected gas, the length of the disconnected section is preferably 1 / 10 or less of the length of the signal line connecting the signal terminal to the detection unit 20. In FIG. 2 , the wiring connecting the multiple voltage terminals (thick solid lines in FIG. 2 ) overlaps with the first detection unit 21 or the second detection unit 22, as indicated by dashed lines. The wiring indicated by the dashed lines means that it passes below the first detection unit 21 or the second detection unit 22 (in the negative z-axis direction) in a plan view of the substrate 30 seen from the front. As another example, the wiring connecting multiple voltage terminals may extend in the xy plane direction so as to pass around the first detection unit 21 or the second detection unit 22, rather than passing below the first detection unit 21 or the second detection unit 22 (in the negative z-axis direction).

[0047] Here, if the voltage of the signal line connecting the detection unit 20 and the signal processing unit 50 is Vsig and the analog reference voltage is Vref, a large difference between Vsig and Vref will result in a leakage current. R in FIG. 2 is the insulation resistance of the substrate 30. The leakage current is given by |Vref-Vsig| / R. Although R is generally on the order of gigaohms, the wiring on the substrate 30 is not completely insulated from each other. During operation of the gas sensor 10 (i.e., during measurement of the gas to be detected), the value of Vsig (i.e., the level of the detection signal output by the detection unit 20) is closer to Vref than 0 V. Therefore, in the configuration of the gas sensor 10 according to this embodiment, |Vref-Vsig| approaches zero during operation of the gas sensor 10, thereby suppressing the leakage current during operation of the gas sensor 10.

[0048] For example, in the prior art, the detection unit 20 is surrounded by a ground potential. In such a prior art, a leakage current given by Vsig / R occurs during operation of the gas sensor 10. Therefore, the gas sensor 10 according to the present embodiment can suppress the leakage current more effectively than the prior art.

[0049] In the example of FIG. 2 , the signal processing unit 50 is rectangular in plan view, and all of the multiple voltage terminals and multiple signal terminals are provided on one side of the signal processing unit 50. However, the signal processing unit 50 may be configured such that some of the multiple voltage terminals and multiple signal terminals are provided on another side. Furthermore, depending on the arrangement of the multiple voltage terminals and multiple signal terminals, it may be difficult to make the distance from the signal processing unit 50 to the first detection unit 21 equal to the distance from the signal processing unit 50 to the second detection unit 22. In this case, as shown in FIG. 2 , it is preferable to arrange the first detection unit 21, which is directly related to measuring the concentration of the target gas, closer to the signal processing unit 50 than the second detection unit 22. In other words, it is preferable that the wiring length from the signal processing unit 50 to the first detection unit 21 be shorter than the wiring length from the signal processing unit 50 to the second detection unit 22. This is to minimize the influence of noise on the detection signal from the first detection unit 21.

[0050] In addition, in order to miniaturize the gas sensor 10, it is preferable that a portion of the wiring connecting the first voltage terminal (TP1) and the second voltage terminal (TP2) is common to a portion of the wiring connecting the second voltage terminal (TP2) and the third voltage terminal (TP3).

[0051] As described above, the optical concentration measurement device and signal processing unit 50 according to this embodiment can enhance the effect of suppressing leakage current during measurement by virtue of the above-described configuration.

[0052] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications or alterations based on the present disclosure, and therefore, it should be noted that these modifications and alterations are included within the scope of the present disclosure.

[0053] In the above embodiment, a configuration having two detectors 20 has been described, but the number of detectors 20 may be only one (first detector 21), or may be three or more. Furthermore, in the above embodiment, when a configuration having multiple detectors 20 is described, a common voltage terminal (i.e., TP2) exists between signal terminals for connecting the detectors, but a configuration without a common voltage terminal is also possible. That is, in the above embodiment, the signal processing unit 50 has a terminal arrangement of seven terminals (TP1, TS1, TS2, TP2, TS3, TS4, TP3). Here, TP2 may be separated into two terminals (TP2A, TP2B), and the signal processing unit 50 may have a terminal arrangement of eight terminals (TP1, TS1, TS2, TP2A, TP2B, TS3, TS4, TP3). [Explanation of symbols]

[0054] 10 Gas Sensor 11 Light source 11a Light-emitting surface 12 Light source board 20 Detector 21 First detection unit 22 Second detection unit 23 Sealing part 30 boards 30a Main surface 40 Gas Cell 42 Gas detection space 43 holes 50 Signal processing section

Claims

1. a light source that emits light toward a gas detection space into which a gas to be detected is introduced; a detection unit that detects a signal based on at least a part of the light that has been emitted from the light source and passed through the target gas, and outputs a detection signal; a signal processing unit that acquires the detection signal and converts it into a digital signal; a substrate on which the detection unit and the signal processing unit are provided, the detection unit includes a first detection unit and a second detection unit, the signal processing unit supplies a constant voltage other than 0 V to a plurality of signal terminals, which are input / output terminals of signal lines electrically connected to the detection unit, and forms a terminal arrangement in which the signal terminals are sandwiched between a plurality of voltage terminals that are not electrically connected to the detection unit; the plurality of voltage terminals include a first voltage terminal, a second voltage terminal, and a third voltage terminal; In a plan view of the substrate from the front, the wiring connecting the first voltage terminal and the second voltage terminal and the signal processing unit surround the signal line connecting the first detection unit and the signal processing unit, and the wiring connecting the second voltage terminal and the third voltage terminal and the signal processing unit surround the signal line connecting the second detection unit and the signal processing unit.

2. 2. The optical concentration measurement device according to claim 1, wherein the plurality of signal terminals are composed of at least two signal terminals sandwiched between the first voltage terminal and the second voltage terminal for connecting to the first detection unit, and at least two signal terminals sandwiched between the second voltage terminal and the third voltage terminal for connecting to the second detection unit.

3. 3. The optical concentration measurement device according to claim 2, wherein the plurality of signal terminals are composed of two signal terminals sandwiched between the first voltage terminal and the second voltage terminal for connecting to the first detection unit, and two signal terminals sandwiched between the second voltage terminal and the third voltage terminal for connecting to the second detection unit.

4. 4. The optical concentration measuring device according to claim 1, wherein, in a plan view of the substrate from the front, all of the plurality of voltage terminals and the plurality of signal terminals are provided on one side of the rectangular signal processing unit.

5. 4. The optical concentration measurement device according to claim 1, wherein a portion of a wiring connecting the first voltage terminal and the second voltage terminal is common to a portion of a wiring connecting the second voltage terminal and the third voltage terminal.

6. 4. The optical concentration measurement device according to claim 1, wherein a wiring length from the signal processing unit to the first detection unit is shorter than a wiring length from the signal processing unit to the second detection unit.

7. 4. The optical concentration measurement device according to claim 1, wherein the wiring has a cut portion in a part thereof, and the length of the cut portion is 1 / 10 or less of the length of the signal line connecting the signal terminal to the detection unit.

8. A signal processing unit used in the optical concentration measuring device according to claim 1 .

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