JP6476654B2 - Micro current detector - Google Patents

Description

  The present invention relates to a minute current detection device including a current detection unit that detects at least two or more minute currents disposed on a printed circuit board, and is particularly suitable for a gas detection device that detects a specific component in combustion exhaust gas of an internal combustion engine. It is a thing.

Conventionally, in a printed circuit board for high impedance operation including a circuit for handling a minute current such as a control circuit for controlling a sensor, in order to prevent leakage current from the board from entering an operational amplifier, for example, an inverting input terminal of an operational amplifier Generally, a guard ring connected to the non-inverting input terminal is provided so as to surround the periphery, or a guard ring is provided so as to surround the entire wiring path extending between the terminals.
Further, Patent Document 1 discloses a current path portion through which a current that becomes a noise source is supplied and signal detection in a sensor control circuit unit including a printed circuit board and a signal detection circuit to which a detection signal from a sensor is input. There is disclosed a control circuit unit in which a reference potential portion serving as a reference potential set in advance is provided between a circuit and a current path portion.

On the other hand, a general oxygen sensor or air-fuel ratio sensor detects milliampere current, whereas a gas sensor that detects a specific component in a gas to be measured, such as a NOx sensor or ammonia sensor, has a nanoampere micro current. Must be detected (see Patent Document 2).
In Patent Document 1, a signal detection circuit unit that detects a minute current and a current path unit that becomes a noise source are arranged in a region divided into two by a virtual line, and a signal detection circuit unit and a current path unit are arranged at a terminal unit. A sensor control circuit unit and a detection device in which a reference potential portion is provided between the two are disclosed.

JP 2007-171024 A JP 2009-222708 A

However, as disclosed in Patent Document 1, when the reference potential portion is provided between the signal detection portion and the current path portion in the terminal portion, it is possible to eliminate the entry of noise or the like from the current path portion to the signal detection portion. However, it is impossible to prevent a leakage current due to a potential difference between the reference potential portion and the signal detection portion.
In a minute current detection device that detects a very small current of several tens of nanoamperes, such as a NOx sensor, a slight leakage current between the reference potential unit and the signal detection unit Cannot be ignored.
Furthermore, even if the reference potential portion is disposed around the signal detection portion in the terminal portion, there is a possibility that noise may enter the wiring path to the detection circuit portion that detects a minute current.
On the other hand, even in the connector part that connects the current detection circuit formed on the printed circuit board to the outside, if the same reference potential part is provided between the current path part and the signal detection part, the size of the connector part increases. There is also a possibility that it becomes an obstacle to downsizing of the apparatus.

  Therefore, in the present invention, in view of such a situation, in a microcurrent detection device including at least two microcurrent detection means, a microcurrent detection device that improves the detection accuracy by reducing the influence of leakage current with a simple configuration. And providing a gas sensor that accurately detects a specific gas component in the measurement gas by comparing minute currents flowing in a plurality of current detection cells provided in a detection unit disposed in the measurement gas. Objective.

The present invention (5) is used in a gas sensor for detecting a specific component in a gas to be measured , and a plurality of minute currents (Is, Im) input from the sensor unit (4) are arranged on the printed circuit board (10). The difference between the first minute current (Is) and the second minute current (Im) detected by the minute current detection means (21, 22) while being detected by the plurality of minute current detection means (21, 22). A minute current detection device (5) for detecting a first minute current wiring portion (110) through which a first minute current flows, and a second minute current through which a second minute current flows, on the printed circuit board. A wiring portion (120) is provided and run in parallel, and the wiring length (L) is made equal, and a predetermined common voltage (Vcom) is supplied as a reference potential wiring portion having a predetermined reference potential. Voltage wiring part (100) Bei, and said first micro-current wiring portion and the second micro-current wiring portion and the spaced equal gap of (d1) brought adjacent the common voltage line unit for each Rutotomoni, the first minute A potential difference between each of the current wiring portion and the second minute current wiring portion and the common voltage wiring portion is smaller than a potential difference from the ground .

According to the present invention, the common voltage wiring section eliminates intrusion of leakage current from other wiring sections to the first micro current wiring section and the second micro current wiring section, and the common voltage wiring section. The first leakage current ( _IL1 ) flowing from the first portion to the first minute current outer line portion and the second leakage current (I _L2 ) flowing to the second minute current wiring portion are made equal to each other, and the first minute current When the difference between the current and the second minute current is calculated, the first leakage current and the second leakage current cancel each other, so that from the common voltage wiring portion provided as a reference potential portion It is possible to detect a minute current with high accuracy by eliminating the influence of the leakage current.

The block diagram which shows the outline | summary of the NOx sensor illustrated as a micro electric current detection circuit in the 1st Embodiment of this invention. The schematic diagram which shows the principal part of the micro electric current detection apparatus in the 1st Embodiment of this invention. The schematic diagram which shows the principal part of the micro electric current detection apparatus in the 2nd Embodiment of this invention. The principal part enlarged view which shows an example of a structure of the terminal part of the micro detection apparatus in the 1st Embodiment of this invention The top view which shows an example of the circuit wiring part of the micro electric current detection apparatus in the 2nd Embodiment of this invention Sectional drawing which shows the principal part of the micro electric current detection apparatus in the 3rd Embodiment of this invention. The perspective view which shows the principal part of the micro electric current detection apparatus in the 4th Embodiment of this invention.

In the present invention, when detecting a minute current of nanoampere level of 1 milliampere or less inputted from a high impedance circuit provided outside, two or more minute wiring paths are provided on a printed circuit board on which a minute current detection circuit is formed. Parallelize the minute current wiring parts through which current flows and equalize each wiring length, and at a certain distance outside at least both sides of the parallel minute current paths, a predetermined reference potential is set as a reference potential part. By having the reference potential wiring part adjacent to each other, the amount of leakage current between each minute current wiring part and the reference potential wiring part is constant, and by calculating the difference between the minute currents flowing through the respective minute current wiring parts, This is a minute current detection device that can accurately detect a minute current by offsetting the influence of leakage current.
Also, in the terminal part that connects the minute current path formed on the printed circuit board to the outside, the minute current terminal connected to the minute current wiring is adjacent, and the reference potential terminal of the reference potential is arranged on the outside of the terminal. On the other hand, by adjoining a terminal having a potential equal to or close to the reference potential, the influence of the leakage current in the external connection terminal portion having higher insulation than the substrate surface is suppressed, while the external connection terminal portion This is a miniaturization.

With reference to FIG. 1, a minute current detection device according to a first embodiment of the present invention will be described using a NOx sensor 5 as an example.
The NOx sensor 5 is used for detecting NOx contained in the combustion exhaust gas of the internal combustion engine.
The NOx sensor 5 includes a sensor unit 4 and a control circuit unit 1 that are disposed in the gas to be measured.
The sensor unit 4 forms an electrode layer at a predetermined position of an ion conductive solid electrolyte body such as zirconia, forms an insulating layer using a spacer made of an insulating material such as alumina, and generates heat when energized. This is a known NOx sensor element in which a plurality of detection cells are provided by burying a heater or the like.

The control circuit unit 1 includes at least an integrated circuit 2 mounted on the printed board 10, a circuit wiring unit P _CT for connecting the integrated circuit 2 and the sensor unit 4, and a heater control unit 3.
In the present embodiment, as a circuit wiring portion P _CT is an essential part of the present invention, at least, the common voltage line 100, sensor current wiring section 110 as a first input wiring portion, a first return line portion 112, the The second input wiring section includes a monitor current wiring section 120, a second feedback wiring section 122, a third input wiring section 130, a battery voltage wiring section 140, and a heater current wiring section 300.
In the present embodiment, the common voltage Vcom of the common voltage wiring unit 100 is set as a reference potential.

The integrated circuit 2 in the present embodiment includes at least a common voltage source unit 20, a sensor current detection unit 21 provided as a first minute current detection unit, and a monitor current detection unit 22 provided as a second minute current detection unit. And a pump current detector 23 provided as a third minute current detector.
The common voltage power supply unit 20 uses a known operational amplifier such as an operational amplifier, and a common voltage Vcom (for example, 5 V) divided by a predetermined voltage dividing resistor (R ₁ , R ₂ , R ₃ ). For example, it is configured to output 2.9V).
The common voltage Vcom is transmitted by the common voltage line 100 which is provided between the common voltage terminal unit T ₁₀₁ provided at an end portion of the common voltage output terminal 201 and the printed circuit board 10 of the integrated circuit 2, further common voltage terminal The signal is transmitted to the sensor unit 4 via the common voltage transmission line 400 connected via the unit T ₁₀₁ and applied to the sensor cell 41, the monitor cell 42, and the pump cell 42.

A known operational amplifier such as an operational amplifier is used for the sensor current detection unit 21, and the sensor current Is flowing in the sensor current detection resistor Rs provided as the first current detection means is detected by voltage conversion, and an unillustrated calculation is performed. It is configured to output to the circuit.
The non-inverting input terminal (+) 213 of the sensor current detection unit 21 has a sensor voltage Vs obtained by dividing the control voltage Vcc by a predetermined voltage dividing resistor (R ₁ , R ₂ , R ₃ ) in the integrated circuit 2. (For example, 2.5 V) is applied.
A sensor current wiring end portion 111 is formed at one end of the sensor current wiring portion 110, and the other end is connected to the inverting input terminal (−) 212 of the sensor current detection portion 21.
The sensor current wiring end portion 111 is connected to the sensor cell 41 of the NOx sensor 4 via the sensor terminal T _{111 and the} like.
The sensor current Is flowing in the sensor cell 41 is input to the inverting input terminal (−) 212 of the sensor current detection unit 21 via the sensor current wiring unit 110.
A sensor current detection resistor Rs is connected between the inverting input terminal 212 and the output terminal 211 of the sensor current detection unit 21 via the first feedback wiring unit 112 (negative feedback) and fed back to the output side. .

Similarly, a known operational amplifier such as an operational amplifier is used for the monitor current detection unit 22, and the monitor current Im flowing in the monitor current detection resistor Rm provided as the second current detection means is detected by voltage conversion. It is configured to output to an abbreviated arithmetic circuit.
A non-inverting input terminal (+) 223 of the monitor current detection unit 22 has a monitor voltage Vm obtained by dividing the control voltage Vcc by a predetermined voltage dividing resistor (R ₁ , R ₂ , R ₃ ) in the integrated circuit 2. (For example, 2.5 V) is applied.
A monitor current wiring end portion 121 is formed at one end of the monitor current wiring portion 120, and the other end is connected to the inverting input terminal (−) 222 of the monitor current detection portion 22.
The monitor current wiring end portion 121 is connected to the monitor cell 42 of the NOx sensor 4 through the monitor terminal T _{121 and the} like.
The monitor current Im flowing through the monitor cell 42 is input to the inverting input terminal (−) 222 of the monitor current detection unit 22 via the monitor current wiring unit 120.
A sensor current detection resistor Rs is connected between the inverting input terminal 222 and the output terminal 221 of the monitor current detection unit 22 via a second feedback wiring unit 122 (negative feedback) and fed back to the output side. .
In the present embodiment, the sensor voltage Vs and the monitor voltage Vm are configured to have the same potential.

A known operational amplifier such as an operational amplifier is used for the pump current detection unit 32, and the pump current Ip flowing through the pump current detection resistor Rp provided as the third current detection means is detected by voltage conversion and applied to the pump cell 43. The pump voltage Vp to be adjusted is adjusted.
A pump voltage Vp (for example, 2.9 V) applied to the pump cell 43 according to the oxygen concentration in the measurement gas introduced into the first space is applied to the non-inverting input terminal (+) 233 of the pump current detector 23. To) can be applied.
A pump current wiring end portion 131 is formed at one end of the pump current wiring portion 130, and the other end is connected to the inverting input terminal (−) 222 of the pump current detection portion 23.
The pump current wiring end 131 is connected to the pump cell 43 of the NOx sensor 4 via the pump terminal T _{131 and the} like.
The pump current Ip flowing through the pump cell 43 is input to the inverting input terminal (−) 232 of the pump current detection unit 23 via the pump current wiring unit 130.
A pump current detection resistor Rp is connected between the inverting input terminal 232 and the output terminal 231 of the pump current detection unit 23 via a third feedback wiring unit 132 (negative feedback), and is fed back to the output side. .

The common voltage wiring unit 100 has one end connected to the common voltage output terminal 201 of the integrated circuit 2 and the other end connected to the common voltage terminal T ₁₀₁ in the common voltage terminal unit 101 formed on the printed circuit board 10. ing.
One end of the sensor current wiring portion 110 is connected to the sensor current input terminal 212 of the integrated circuit 2, and the other end is connected to the sensor terminal T ₁₁₁ at the sensor current wiring end portion 111 formed on the printed circuit board 10. ing.
The first feedback wiring portion 112 connects the sensor current detection resistor _RS and the sensor current wiring portion 110.
One end of the monitor current wiring section 120 is connected to the monitor current input terminal 222 of the integrated circuit 2, and the other end is connected to the monitor terminal T ₁₂₁ at the monitor current wiring end section 121 formed on the printed circuit board 10. ing.
The second return line 122, which connects the monitor current detection resistor R _m and the monitor current wiring portion 120.

One end of the pump current wiring portion 130 is connected to the pump current input terminal 232 of the integrated circuit 2, and the other end is connected to the pump terminal T ₁₃₁ at the pump current wiring end portion 131 formed on the printed circuit board 10. ing.
The second feedback wiring portion 132 connects the pump current detection resistor _Rp and the pump current wiring portion 130.

One end of the battery voltage wiring unit 140 is connected to a power source + B (for example, 12 V), and the other end is connected to a battery terminal T ₁₄₁ provided in the power terminal unit 141 of the printed circuit board 10.
One end of the heater current wiring unit 300 is connected to the heater control unit 3, and the other end is connected to a heater terminal unit T ₃₀₁ provided in the heater energization terminal unit 301 of the printed circuit board 10.
The heater control unit 3 is provided with switching means (not shown) and controls a drive current for causing the heater 44 to generate heat to a predetermined temperature.

The sensor unit 4 and the control circuit unit 1 include a known heat resistant wiring member such as a wire harness (common voltage transmission line 400, sensor current transmission line 410, monitor current transmission line 420, pump current transmission line 430, heater conduction line 440. , Battery voltage transmission line 450) and connector terminal 17 of the connector structure provided at the end thereof (common voltage terminal T ₁₀₁ , sensor terminal T ₁₁₁ , monitor terminal T ₁₂₁ , pump terminal T ₁₃₁ , heater terminal T ₃₀₁ , battery terminal T ₁₄₁ ) is detachably connected.

  The sensor unit 4 has a three-cell structure including a sensor cell 41 provided as a first current detection unit, a monitor cell 42 provided as a third current detection unit, and a pump cell 43.

A plurality of detection cells having a pair of electrodes formed on both sides of a solid electrolyte body having conductivity with respect to specific ions such as zirconia are provided.
The pump cell 34 adjusts the oxygen concentration in the space by taking in and out oxygen present in the gas to be measured introduced into the first space partitioned at a predetermined position of the sensor unit 4, and a predetermined air passage. To discharge.
The pump cell 34 is applied with a voltage of a potential difference between the common voltage Vcom and the pump voltage Vp, and the amount of oxygen to be pumped is adjusted by changing the pump voltage Vp supplied from the variable power source.

The sensor cell 41 and the monitor cell 42 are partitioned at a predetermined position of the sensor unit 4 and are provided so as to face the second space communicated with the first space via a predetermined diffusion resistance.
A NOx active noble metal such as Pt and Rh is used for one electrode of the sensor cell 41, and a NOx inactive noble metal such as Au—Pt is used for one electrode of the monitor cell 42. The other electrode of the monitor cell 42 is configured as a common electrode.

A voltage corresponding to a potential difference between the common voltage Vcom and the monitor voltage Vm is applied to the monitor cell 42.
Since the monitor cell 42 has an oxygen discharge function like the pump cell, it is also referred to as a second pump cell or an auxiliary pump cell.
The monitor cell Im is generated between the electrodes of the sensor cell 41 due to the electromotive force or voltage applied to the monitor cell 42 according to the oxygen concentration remaining in the second space after the excess oxygen is discharged from the pump cell 43. NOx in the gas under measurement in the second space is reduced and decomposed by the applied sensor voltage Vs, and a sensor current Is is generated in the sensor cell 41.
In the NOx sensor, the amount of NOx in the gas to be measured can be accurately measured by calculating the difference between the sensor current Is flowing through the NOx active sensor cell 41 and the monitor current Im flowing through the NOx inactive monitor cell 42. it can.

In the integrated circuit 2 in the present embodiment, an example in which the sensor current detection resistor Rs and the monitor current detection resistor Rm are mounted on the printed circuit board 10 is shown, but a configuration in which the integrated circuit 2 is built in may be used.
In addition, although an example in which the common voltage source unit 20, the sensor current detection unit 21, the monitor current detection unit 22, and the pump current detection unit 23 are provided in one integrated circuit 2 is illustrated, each is configured by an independent integrated circuit. May be.

Furthermore, in this embodiment, the NOx sensor 4 having a three-cell structure is shown as an example. However, the present invention is not limited to this, and the sensor element may have a two-cell structure including a pump cell and a sensor cell. A known sensor element can be appropriately employed.
Further, the detection target is not limited to NOx, and HC or CO in the gas to be measured may be the detection target, or the concentration of ammonia may be detected.
Furthermore, in the present embodiment, an example is shown in which a so-called voltage follower type operational amplifier is used as the current detection means, but the current detection means is not limited in the present invention, and a non-inverting input amplifier is used. Instead of the current detection resistors Rs, Rm, and Rp, a capacitor, a capacitor and a resistor, a diode, or the like can be used in appropriate combination.

In the present invention, by forming the circuit wiring portion _PCT by the wiring method illustrated in FIGS. 2A, 2B, 3, 4, 5, and 6, the sensor current wiring portion 110 through which the sensor current Is flows and The first leakage current I _L1 flowing into the first feedback wiring section 112 is matched with the second leakage current I _L2 flowing into the monitor current wiring section 120 and the second feedback wiring section 122 through which the monitor current Im flows. be able to.
As a result, when the difference between the sensor current Is and the monitor current Im is calculated, the first leakage current I _L1 and the second leakage current I _L2 are offset, and a nanoampere-level minute current is detected. However, it is possible to eliminate the influence of the leakage current that inevitably occurs and to realize a highly accurate current detection device.

With reference to FIG. 2A, the wiring method used for the minute current detection device 5 in the first embodiment of the present invention will be described.
In the present embodiment, the sensor current wiring portion 110 through which the sensor current Is flows and the monitor current wiring portion 120 through which the monitor current Im flows run in parallel with the common voltage wiring portion 100 serving as a reference potential interposed therebetween, and The wiring lengths L are formed to be equal.
Further, in the present embodiment, the common voltage wiring unit 100 is disposed not only between the sensor current wiring unit 110 and the monitor current wiring unit 120 but also adjacent to the outside.
In addition, the gap d1 between the sensor current wiring unit 110 and the common voltage wiring unit 100 and the gap d1 between the monitor current wiring unit 120 and the common voltage wiring unit 100 are constant at any position in the wiring path. Thus, the wiring pattern of the common voltage wiring unit 100 is adjusted.

The common voltage wiring unit 100 provided adjacent to the outside of the sensor current wiring unit 110, the common voltage wiring unit 100 provided between the sensor current wiring unit 110 and the monitor current wiring unit 120, and the current wiring unit 120. The common voltage wiring part 100 provided adjacent to the outside is connected to each other in a board terminal part TME described later with reference to FIG.
By disposing the common voltage wiring unit 100 having the same potential adjacent to each of the sensor current wiring unit 110 and the monitor current wiring unit 120, a potential difference V between the sensor current wiring unit 110 and the common voltage wiring unit 100 is obtained. ₁ , the potential difference V ₂ between the monitor current wiring unit 120 and the common voltage wiring unit 100 becomes equal.

As a result, the first leakage current _IL1 flowing from the common voltage wiring section 100 to the sensor current wiring section 110 and the second leakage current _IL2 flowing from the common voltage wiring section 100 to the monitor current wiring section 210 become equal, and the sensor By taking the difference between the current signal _VSO and the monitor current detection signal _VMO , the influence of the leakage current can be offset.
In this embodiment, the common voltage Vcom is 2.9 V, the sensor voltage Vs is 2.5 V, the monitor voltage Vm is 2.5 V, the maximum value of the pump voltage Vp is 2.9 V, the heater voltage V _HTR is 12 V, the battery voltage An example in which + B is set to 12V is shown.
In the present embodiment, the pump current wiring unit 130, the battery wiring unit 140, and the heater wiring unit 300 are not adjacent to the sensor current wiring unit 110 and the monitor current wiring unit 120, but are guarded by the common voltage wiring unit 100. Therefore, a large leakage current does not enter.

With reference to FIG. 2B, a wiring method used in the minute current detection device 5a in the second embodiment of the present invention will be described.
In the following description, the same reference numerals are given to portions common to the above-described embodiments, and the characteristic portions of the respective embodiments are distinguished by attaching alphabetical branch numbers. Description will be omitted, and description will be made centering on characteristic portions in each embodiment.
In the above-described embodiment, an example in which the common voltage wiring unit 100 is disposed between the sensor current wiring unit 110 and the monitor current wiring unit 120 has been described. The difference is that the wiring part 110 and the monitor current wiring part 120 are adjacent to each other, and the common voltage wiring part 100 is disposed only outside the sensor current wiring part 110 and the monitor current wiring part 120.
Also in this embodiment, the distance L in which the sensor current wiring unit 110 and the monitor current wiring unit 120 run in parallel is made equal, the gap d ₁ between the sensor current wiring unit 110 and the common voltage wiring unit 100 and the monitor current wiring. the parts 120 and the gap d ₂ between the common voltage line 100 is disposed so as to be equal.

Also in the present embodiment, the first leakage current I _L1 and the second leakage current I _L2 can be equalized by wiring the common voltage wiring portion 100 having the same potential at an equal distance, similarly to the previous embodiment. it can.
In addition, in the present embodiment, the sensor voltage Vs and the monitor voltage Vm are equal, and the sensor current wiring unit 110 and the monitor current wiring unit 120 that are substantially equal to each other are adjacent to each other. Is substantially equal to 0, and no leakage current occurs between the two.
Further, since the common voltage wiring section 100 is not provided between the sensor current wiring section 110 and the monitor current wiring section 120, the actual wiring area can be reduced, and the apparatus can be reduced in size.

With reference to FIG. 3, the structure of the board | substrate terminal part TME and the connector 16 which aim at the connection of the electric current detection apparatus 1 and the exterior in the 1st Embodiment of this invention is demonstrated.
On the surface of the printed circuit board 10, as a circuit wiring portion _PCT , a common voltage wiring portion 100, a sensor current wiring portion 110, a monitor current wiring portion 120, a pump current wiring portion 130, a battery voltage wiring portion 140, and a heater energization wiring Part 300 is formed.
A land portion for connecting an integrated circuit terminal is formed at one end of the common voltage wiring portion 100, the sensor current wiring portion 110, the monitor current wiring portion 120, the pump current wiring portion 130, and the battery voltage wiring portion 140. The circuit 2 is connected to a common voltage output terminal 201, a sensor current input terminal 212, a monitor current input terminal 222, a pump current input terminal 232, and a battery voltage terminal 240.

One end of the heater energization wiring unit 300 is connected to the heater control unit 3.
The other end of the common voltage wiring unit 100, the sensor current wiring unit 110, the monitor current wiring unit 120, the pump current wiring unit 130, the battery voltage wiring unit 140, and the heater energization wiring unit 300 is connected to the terminal unit TME of the printed circuit board 10. Common voltage wiring end 101, sensor current wiring end 111, monitor current wiring end 121, pump current wiring end 131, battery voltage wiring end 141, and heater energization wiring end for connection to an NOx sensor provided outside A portion 301 is formed and connected to a connector terminal 17 including a common voltage terminal T ₁₀₁ , a sensor terminal T ₁₁₁ , a monitor terminal T ₁₂₁ , a pump terminal T ₁₃₁ , a battery terminal T ₁₄₁ , and a heater energization terminal T ₃₀₁ .
The connector terminal 17 is fixed by a resin connector housing 160.
In the present embodiment, the common voltage wiring portion 100 is provided adjacent to both the sensor current wiring end portion 111 and the monitor current wiring end portion 121 with a certain gap d1 therebetween, and a plurality of common voltages is provided. The wiring part 100 is formed as a single unit at the board terminal part TME to form a common voltage wiring end part 101 and surrounds the sensor current wiring front end part 111 and the monitor current wiring end part 121.

The connector housing 160 is configured to engage with a mating connector housing (not shown) so that the connector terminal 17 is electrically connected to the mating connector terminal (not shown).
Generally, the input / output terminals of the integrated circuit 2 are arranged at a predetermined terminal interval (for example, 0.5 mm pitch to 2.54 mm pitch).
On the other hand, in the board terminal portion TME, the distance between terminals (for example, from the 1.25 mm pitch to the distance of 6.25 mm) is longer than the distance between the terminals of the integrated circuit portion because of the necessity of fitting with the mating connector terminal. 25 mm pitch).
Therefore, the common voltage line 100, sensor current wiring portion 110, the monitor current wiring portion 120 running parallel and adjacent in the predetermined gap d ₁ from each other, the substrate terminal part TME, wire spacing to fit spreads terminal interval It will be.

Therefore, in the present embodiment, the area of the common voltage wiring end portion 101 is enlarged, the gap d1 between the common voltage wiring end portion 101 and the sensor current wiring end portion 111, and the monitor current wiring end portion 121 and the common voltage wiring end portion. The gap d1 with the part 101 is constant.
The connector housing 160 is made of a known insulating resin such as polyamide, polyimide, PBT, glass fiber-filled PBT, and has higher insulation between the terminals than the surface of the printed circuit board 10 and is unlikely to generate a leakage current. It has become.
Therefore, the sensor terminal _T111 and the monitor terminal _T121 are adjacent to each other, and either one of the common voltage terminal _{T101 and the} pump terminal _T131 is adjacent to the outside thereof, and the heater terminal _T301 or the battery terminal T141 is connected to the sensor terminal _T111 . It is made not to adjoin.

Since high insulation by the connector housing 160 is maintained, without providing a common voltage terminal T ₁₀₁ between the sensor terminal T ₁₁₁ and the monitor terminal T ₁₂₁ can be sufficiently suppressed leakage current.
Further, even if the common voltage terminal _T101 is not provided between the monitor terminal _T121 and the battery terminal _T141, and the pump terminal _T131 having a non-constant potential is disposed instead, the connector housing 160 provides high insulation. Since it is ensured, the leakage current between the monitor terminal T ₁₂₁ and the pump terminal T ₁₃₁ is sufficiently small.

As a result, the number of connector terminals 17 provided in the connector housing 160 can be minimized, and the physique can be reduced.
Even if the number of connector terminals 17 is reduced, in the substrate end terminal portion TME, the sensor current wiring end portion 111 and the monitor current wiring end portion 121 each have a constant gap d1 at the common voltage end portion 101 having the same reference potential. Since they are covered separately, the leakage currents I _L1 and I _L2 between them are not affected.

With reference to FIG. 4, the structure of the board | substrate terminal part TME and the connector 16 which aim at the connection of the micro electric current detection apparatus 5a and the exterior in the 2nd Embodiment of this invention is demonstrated.
In the present embodiment, the common voltage wiring unit 100 is not disposed between the sensor current wiring unit 110 and the monitor current wiring unit 120, and the sensor current wiring unit 110 and the monitor current wiring unit 120 are adjacent to each other. The common voltage wiring portion 100 and the common voltage wiring end portion 101a are disposed so as to surround the outside of the sensor current wiring end portion 111 and the monitor current wiring end portion 121 with a certain gap d1 therebetween.

The connector 16 has the same configuration as that of the above embodiment.
Also in the present embodiment, intrusion of leakage current from the outside is blocked by the common voltage wiring portion 100 and the common voltage wiring end portion 101 that are arranged at a fixed distance from the sensor current wiring portion 110 and the monitor current wiring portion 120. can do.
Moreover, at equal and leakage currents I _L1 and I _L2 between the common voltage line 100 and the common voltage line end 101a and the sensor current wiring portion 110 and the monitor current wiring portion 120 serving as a constant reference potential, the sensor By calculating the difference between the current Is and the monitor current Im, it is possible to realize a NOx sensor that accurately detects the NOx amount by offsetting the influence of the leakage current.

With reference to FIG. 5, the outline of the minute current detection device 5b according to the third embodiment of the present invention will be described.
In the embodiment, the common voltage wiring portion 100 serving as the reference potential is formed in the same layer as the sensor current wiring portion 110 and the monitor current wiring portion 120. However, in the present embodiment, the common voltage wiring portion 100 is formed of a multilayer substrate. In the printed board 10b, the common voltage wiring portion 100b serving as a reference potential is different from the layer where the sensor current wiring portion 110 and the monitor current wiring portion 120 are formed.
In this embodiment, the pump current wiring portion 130b close to the reference potential is formed in the same layer as the common voltage wiring portion 100b, and the battery voltage wiring portion 140b and the heater energization wiring portion 300b are disposed on the back side. Although shown, the present invention is not limited to this.

At least, the common voltage wiring portion 100b serving as a reference potential is arranged in a layer different from the sensor current wiring portion 110 and the monitor current wiring portion 120 with a certain gap, and is interposed between other wiring portions. A large leakage current I _LL from a wiring portion having a large potential difference is cut off by the common voltage wiring portion 100b, a leakage current _IL1 from the common voltage wiring portion 100b to the sensor current wiring portion 110, and a leakage current to the monitor current wiring portion 120. By making I _L2 equal, it is possible to cancel the influence of the leakage current when calculating the difference between the sensor current Is and the monitor current Im.
Further, since the insulating layer is interposed, the leakage currents I _L1 and I _L2 generated in the cross-sectional direction from the common voltage wiring unit 100 b to the sensor current wiring unit 110 and the monitor current wiring unit 120 are leakage currents on the surface of the printed circuit board 10. This can be made smaller than in the above-described embodiment.

The housing 15 is a known housing made up of the housing portion 150 and the lid portion 151 and is formed of resin or metal, and houses the printed circuit board 10b and holds the terminal fixing portion 16b. The housing 15 may be filled with an insulating resin 152 and sealed.
Moreover, in the said embodiment, although shown in the example which used the terminal part 17 accommodated in the connector housing 160 for the connection with the sensor part 4 provided outside, in this invention, the terminal part which aims at the connection with the outside Is not limited to a connector structure that mates with the other party.
In the present embodiment, a part of the flat terminal portion 17b is embedded and fixed in the resin terminal fixing portion 16b to ensure insulation between the terminal portions 17b.
The terminal portion 17b includes a heater terminal _T301 , a sensor terminal _T111 , a monitor terminal _T121 , a pump terminal _T131 , and a battery terminal _T141 .
One end of the terminal portion 17b is inserted into the through hole TH is formed in the printed circuit board 10b, are fixed through the connected land LND and solder portion SLD a wiring circuit portion P _CT, the other end Are directly connected to the wires (400 to 450) drawn from the sensor unit 4.
For connection between the terminal portion 17c and each wiring, a known connection method such as brazing, soldering, ultrasonic welding, resistance welding, laser welding, or connection via a crimp terminal can be appropriately employed.
In the embodiment, the same configuration can be adopted.

In general, it is known to form a ground plane to prevent noise from entering the circuit, but instead of the common voltage wiring portion 100b provided as the reference potential portion in the present embodiment. When the ground plane is provided, the sensor voltage Vs and the monitor voltage Vm become a potential difference, the leakage current from the sensor current wiring unit 110b and the monitor current wiring unit 120b to the ground plane increases, and it may be difficult to detect a minute current. .
In this embodiment, the common voltage wiring portion 100b is provided as the reference potential portion, and the potential difference between the common voltage Vcom, the sensor voltage Vs, and the monitor voltage Vm is smaller than the potential difference from the ground, and the common voltage wiring The sensor current Is and the monitor current Im are not reduced by the leakage currents IL1 and IL2 from the unit 100b.

With reference to FIG. 6, the minute electric current detection apparatus 5c in the 4th Embodiment of this invention is demonstrated.
In this embodiment, instead of the connector 16 in the first embodiment, a block-like terminal fixing portion 16c made of an insulating resin is provided, and instead of the connector terminal 17 fitted to the other party, a flat-plate-like terminal portion 17c is provided. The difference is that each wiring portion (400 to 450) embedded in the terminal fixing portion 16c and connected to the sensor portion 4 is directly connected to the terminal portion 17c.
However, the terminal portion 17c is, the heater terminal _{T 301,} the common voltage terminal _{T 101,} the sensor terminal _T11, the monitor terminal _{T 121,} pump terminal _{T 131,} that is constituted by the battery terminal _{T 141} is common.

In the first and second embodiments, the example in which the connector terminal 17 is embedded and fixed in the connector housing 160 has been described. However, in the present invention, a connector structure is not necessarily required for connection to the outside. There is no.
In this embodiment, buried terminal portion 17c to achieve the connection with the outside terminal fixing portion 16c made of insulating resin, a large potential difference between the sensor terminal T ₁₁₁ and the monitor terminal T ₁₂₁ flows low current, battery The terminal T ₁₄₁ and the heater energizing terminal T ₃₀₁ are not adjacent to each other, and the common voltage terminal T ₁₀₁ or the pump terminal T ₁₃₁ having a small potential difference between the sensor terminal T ₁₁₁ and the monitor terminal T ₁₂₁ are adjacent to each other, thereby preventing leakage current in the terminal portion 17c. Occurrence is suppressed.

Further, in the above-described embodiment, the configuration in which one end of the terminal portion 17b is inserted into the through hole TH provided in the printed circuit board 10 and fixed by soldering or the like is shown. However, as shown in FIG. One end of T ₃₀₁ , common voltage terminal T ₁₀₁ , sensor terminal _{T 111} , monitor terminal T ₁₂₁ , pump terminal T ₁₃₁ , battery terminal T ₁₄₁ , heater energization wiring end 301, common voltage wiring end 101, sensor current wiring The end 111, the monitor current wiring end 121, the pump current wiring end 131, and the battery voltage wiring end ₁₄₁ are connected via the bonding wires BD ₃₀₁ , BD ₁₀₁ , BD ₁₂₁ , BD ₁₃₁ , and BD _141. Also good.
Since the wires are three-dimensionally wired via the air or the filling resin 152, the insulation between the bonding wires is high, and no leakage current flows between the bonding wires.

Further, with respect to a method for fixing the terminal portion 17c to the terminal fixing portion 16c, the terminal portion 17c may be embedded in the terminal fixing portion 16c by known insert molding, or the terminal fixing portion 16c provided with a claw groove in advance is formed. And you may make it fix by the outsert molding which fits the terminal part 17c.
For connection between the terminal portion 17c and each wiring portion (400 to 450), similarly to the above-described embodiment, known methods such as brazing, soldering, ultrasonic welding, resistance welding, laser welding, and connection via a crimp terminal are used. A connection method can be appropriately employed.

The present invention is not limited to the above-described embodiment, and the parallel wiring lengths of a plurality of minute current wiring portions through which a minute current flows are made equal, and a common voltage wiring portion having a predetermined potential as a reference potential is fixed. Adjacent by distance, while eliminating leakage current from other wiring parts, the leakage current from the common voltage wiring part to each minute current outside line part is made equal, and the difference between multiple minute currents is calculated Thus, the present invention can be changed as appropriate as long as it does not violate the gist of the present invention to eliminate the influence of the leakage current and to perform highly accurate current detection.
For example, in the above embodiment, the wiring examples shown in FIGS. 2A and 2B are examples in which they are formed on the same plane. However, this is regarded as a wiring in a cross-sectional direction, and is applied to a circuit having a multilayer structure. You can also.

The present invention is a minute current detection device for accurately detecting a difference between a plurality of minute currents input from a sensor unit, and more particularly to a gas sensor for detecting a specific component in a gas under measurement from a change in the minute current. It can be used suitably.
In addition, the present invention can be applied not only to detection of a minute current from a sensor unit but also to a control circuit that controls an actuator using a difference between a plurality of minute currents flowing in a high impedance circuit.

DESCRIPTION OF SYMBOLS 1 Control circuit part 10 Printed circuit board 100 Common voltage wiring part 101 Common voltage wiring edge part 110 1st input wiring part (sensor current wiring part)
111 First input wiring end (sensor current end)
112 First feedback wiring section 120 Second input wiring section (monitor current wiring section)
121 Second input wiring end (monitor current wiring end)
122 Second feedback wiring section 130 Third input wiring section (pump current wiring section)
131 Third input wiring end (pump current wiring end)
132 third feedback wiring section 140 battery voltage wiring section 2 sensor control integrated circuit section 20 common voltage source section 201 common voltage output terminal 21 first minute current detection means (sensor current detection section)
211 First output terminal 212 First inverting input terminal (sensor current input terminal)
213 1st non-inverting input terminal 22 2nd minute electric current detection means (monitor current detection part)
221 Second output terminal 222 Second inverting input terminal (monitor current input terminal)
223 Second non-inverting input terminal 23 Third minute current detecting means (pump current detecting unit)
231 Third output terminal 232 Third inverting input terminal (pump current input terminal)
233 Third non-inverting input terminal 24 Difference calculation circuit (NOx calculation circuit)
3 Heater control unit 300 Heater current wiring unit 301 Heater current wiring end 4 Sensor unit (NOx sensor element)
400 Common voltage transmission line 41 First detection element (sensor cell)
410 first signal line (sensor current transmission line)
42 Second detection element (monitor cell)
420 Second signal line (monitor current transmission line)
43 Third sensing element (pump cell)
430 Common voltage supply line 44 Heater 440 Heater energization line 5 Minute current detection device (NOx sensor)
Is First minute current (sensor current)
Im Second minute current (monitor current)
Ip Third minute current (pump current)
_IL1 first leakage current (sensor current side leakage current)
_IL2 second leakage current (monitor current side leakage current)
Vs Second detection voltage (sensor voltage)
Vm Second detection voltage (monitor voltage)
Vcom common voltage Vp third detection voltage (pump voltage)
V _HTR heater voltage Vcc Control voltage + B Power supply voltage

Claims (6)

A plurality of minute current detection means used in a gas sensor for detecting a specific component in a gas to be measured, wherein a plurality of minute currents (Is, Im) input from the sensor unit (4) are arranged on the printed circuit board (10). (21, 22) and a minute current detecting device for detecting a difference between the first minute current (Is) and the second minute current (Im) detected by the minute current detecting means (21, 22). (5)
On the printed circuit board,
A first minute current wiring portion (110) through which a first minute current flows;
The second microcurrent wiring portion (120) through which the second microcurrent flows is provided and run in parallel, and these wiring lengths (L) are made equal.
And,
A common voltage wiring portion (100) for supplying a predetermined common voltage (Vcom) as a reference potential wiring portion having a predetermined reference potential;
The first micro-current wiring portion and the second at a gap (d1) equal for each of the micro-current wiring portion brought adjacent the common voltage line unit Rutotomoni, the first micro-current wiring portion And a difference in potential between each of the second minute current wiring portions and the common voltage wiring portion is smaller than a potential difference from the ground.   In the substrate terminal portion (TME) in which the first micro current wiring portion and the second micro current wiring portion are connected to the outside, the first micro current wiring portion is connected to the outside. The first microscopic current line part (121) and the second microcurrent current wiring part connected to the outside are covered with a predetermined gap (d1) so as to cover the end part (111) and the second microcurrent wiring part. 2. The minute current detection device according to claim 1, wherein the common voltage wiring part adjacent to the current wiring part and the common voltage wiring part adjacent to the second minute current wiring part are connected. In the substrate terminal portion, at least a first microcurrent terminal (T111) connected to the first microcurrent wiring end and a second microcurrent terminal (T111) connected to the second microcurrent wiring end ( T121) and a common voltage terminal (T101) connected to a common voltage wiring end (101) which is an end of the common voltage wiring,
The first minute current terminal and the second minute current terminal are adjacent to each other at a predetermined terminal interval, and either one of the first minute current terminal and the second minute current terminal has a predetermined value. The common voltage terminals are adjacent to each other with a terminal interval, and the other is a quasi-reference potential wiring portion having a potential close to the reference potential, which is another wiring portion formed on the common voltage terminal or the printed board. 3. A micro-current detection device according to claim 2 , wherein a quasi-reference potential terminal connected to the terminal is adjacently connected to the outside. The printed circuit board is a multilayer board, and the common voltage wiring portion is disposed in a separate layer adjacent to the first minute current wiring portion and the second minute current wiring portion and in the cross-sectional direction with an insulating layer therebetween. The minute current detection device according to claim 1.   5. The minute current detection device according to claim 1, wherein a potential of the first minute current wiring portion is equal to a potential of the second minute current wiring portion. The sensor unit comprises a plurality of detection cells configured by providing a pair of electrodes on a solid electrolyte body,
A sensor cell (41) having an electrode active with respect to NOx in the gas to be measured as a first detection cell,
A monitor cell (42) having an electrode inert to NOx in the gas to be measured as a second detection cell,
The sensor current (Is) flowing through the sensor cell when a predetermined voltage is applied to the sensor cell and the monitor cell is defined as the first minute current,
The monitor current (Im) flowing through the monitor cell is set as the second minute current,
6. The minute current detection device according to claim 1, wherein a difference between the sensor current and the monitor current is calculated to measure the amount of NOx in the gas to be measured.

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