JP2010223862A - Magnetic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic sensor that eliminates the need for setting correction of an offset voltage in accordance with a state during a use, and obtains a detecting signal of a sufficient voltage level. <P>SOLUTION: A magnetic field change detection unit 10 includes a series circuit having a magnetic resistant element MR1 and a resistant element R1 to output a magnetic field change detecting signal Voutψ meeting the change of the passing magnetic flux density of the magnetic resistant element MR1 by carrying a body to be detected. An integrating unit 20 generates an integrating signal VoutI obtained by integrating the magnetic field change detecting signal Voutψ. The magnetic field change detecting signal Voutψ includes an offset component as a constant voltage and an effective variation component meeting the change of a magnetic field. The effective variation component is generated during an extremely short period, so that the integrating signal VoutI corresponds to the offset component of the magnetic field change detecting signal Voutψ. A differential amplification unit 30 differentially amplifies the magnetic change detecting signal Voutψ and the integrating signal VoutI to output a sensor detecting signal Vout with the offset component removed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a magnetic sensor for detecting a magnetic pattern and magnetic information of a detection object.

  Currently, various magnetic sensors for detecting a magnetic pattern and magnetic information of an object to be detected are used. As shown in FIG. 13 of Patent Document 1, the conventional magnetic sensor includes a magnetic field change detection unit that detects a change in magnetic field using a magnetoresistive element, and an amplification unit that amplifies a detection signal. The magnetic field change detection unit is composed of a circuit in which a first magnetoresistive element that is highly sensitive to changes in the magnetic field and a second magnetoresistive element that is sensitive to changes in the magnetic field are connected in series. A detection voltage is applied to one end, and the other end is connected to the ground. Then, the magnetic field change detection unit uses a connection point between the first magnetoresistive element and the second magnetoresistive element as an output end of the detection signal, and detects a voltage level due to voltage division between the first magnetoresistive element and the second magnetoresistive element. A detection signal is output. As a result, the detection signal becomes a predetermined voltage level in a state where the magnetic field is not changed, and becomes a signal whose voltage level changes in accordance with a change in the magnetic field due to passage of the detection object.

  Such a detection signal has a low amplitude level (voltage level), and it is better to amplify the amplitude level as much as possible in order to use it for the detection of the above-described magnetic pattern and magnetic information. For this reason, the amplifying unit comprises two stages of differential amplifiers, and amplifies the detection signal. At this time, since the detection signal is a signal using the divided voltage as described above, the detection signal includes an offset voltage corresponding to the voltage level in a state where the magnetic field is not changed. However, when amplifying the detection signal, if the offset voltage is amplified, there is a possibility that it may lead to erroneous detection or destruction of the circuit that detects the magnetic pattern and magnetic information in the subsequent stage. It should be removed.

  For this reason, in Patent Document 1, an offset removal voltage generated by resistance voltage division of an individually provided resistor series circuit is applied to a differential amplifier, and the offset removal voltage is differenced (offset correction) with respect to a detection signal. Amplification processing is performed.

JP 2005-56950 A

  However, the magnetoresistive element and the resistance element of the resistor series circuit that generates the offset removal voltage have different temperature characteristics, so even if the difference between the offset voltage and the offset removal voltage is about 0 V at the beginning of manufacture. Even if it can be set, the offset voltage and the offset removal voltage may fluctuate during actual use, and there may be a difference between the offset voltage and the offset removal voltage in the input stage of the differential amplifier. For example, if this difference is 0.1 V, and the detection signal is amplified 10,000 times with a two-stage differential amplifier circuit, the final offset voltage is 1000 V, which can be used practically. It is no longer a thing.

  As described above, in the conventional configuration as described above, a signal level for detection cannot be gained unless amplification is performed, and it becomes difficult to detect a magnetic pattern or magnetic information. Although it can earn, it has the subject that offset voltage correction is not easy.

  Accordingly, an object of the present invention is to realize a magnetic sensor that does not require the offset voltage correction to be set according to the situation during use and can obtain a detection signal having a sufficient voltage level.

  The magnetic sensor of the present invention includes a magnetic field change detector, an integrator, and a differential amplifier. The magnetic field change detection unit uses at least one set of magnetoresistive elements having different resistance value change characteristics caused by a change in magnetic flux density, and outputs a magnetic field change detection signal based on the difference in the characteristics. The integration unit outputs an offset component signal by integrating the magnetic field change detection signal. The differential amplifying unit differentially amplifies the magnetic field change detection signal and the offset component signal.

  In this configuration, the effective variation component does not appear by utilizing the fact that the magnetic field change detection signal is composed of an effective variation component and an offset component that vary in accordance with the change in the passing magnetic flux due to the magnetic pattern or magnetic information of the detected object. A signal corresponding to the offset component is generated by the integration unit. Here, the detected object detects a magnetic pattern by being conveyed at a predetermined speed in the vicinity of the magnetic sensor (on the top surface where the magnetoresistive element is installed on the top surface of the housing). The effective fluctuations of are for extremely short times. For this reason, when the time constant is appropriately set and the magnetic field change detection signal is integrated, a signal having only an offset component that is hardly affected by the effective variation is output from the integrating unit. Since the differential amplification section differentially amplifies the magnetic field change detection signal and the offset component signal generated based on the magnetic field change detection signal, only the offset component of the magnetic field change detection signal is removed and only the effective fluctuation component is present. Amplified and output.

  The magnetic sensor of the present invention further includes a second integration unit and a second differential amplification unit. The second integration unit outputs a second offset component signal by integrating the detection signal output from the differential amplification unit. The second differential amplification unit performs differential amplification processing on the detection signal and the second offset component signal.

  In this configuration, the detection signal can be output with a larger amplitude (voltage) level. At this time, since the second integration unit is arranged before the second differential amplification unit, offset correction is performed at the input stage of the second differential amplification unit. As a result, even if the two-stage amplification is performed, the offset voltage is hardly amplified, and only the effective fluctuation component of the detection signal can be effectively amplified.

  In the magnetic sensor of the present invention, the second integration unit and the second differential amplification unit are connected in multiple stages.

  In these configurations, the detection signal can be output with a larger amplitude (voltage) level. At this time, since the second integration unit is disposed in front of each second differential amplification unit, offset correction is always performed at the input stage of each second differential amplification unit. Thereby, only the effective fluctuation component of the detection signal can be amplified more effectively.

  The magnetic field change detection unit of the magnetic sensor according to the present invention includes a magnetoresistive element having different characteristics or a magnetoresistive element and a resistive element connected in series between the voltage input terminal and the ground terminal, and the magnetoresistive element having the different characteristics. The voltage level at the connection position between them is output as a magnetic field change detection signal.

  This configuration shows a specific configuration of the magnetic field change detection unit that outputs the above-described magnetic field change detection signal. With such a configuration, a magnetic field change detection signal can be obtained if there is a series circuit of at least two magnetoresistive elements having different characteristics or a series circuit of a magnetoresistive element and a resistive element. That is, the magnetic field change detection unit can be configured with a simple structure.

  The magnetic field change detection unit of the magnetic sensor according to the present invention includes a first series circuit, a constant voltage output circuit, and a previous-stage differential amplifier circuit. In the first series circuit, a magnetoresistive element having different characteristics or a magnetoresistive element and a resistive element are connected in series between a voltage input terminal and a ground terminal, and a connection position between magnetoresistive elements having different characteristics or a magnetoresistive element is connected. The voltage level at the connection position between the element and the resistance element is output as the first magnetic field change detection signal. The constant voltage output circuit is composed of a set of resistance elements having a constant resistance value regardless of a change in magnetic flux density, and the first magnetic field of the first series circuit in a state where the resistance value of the magnetoresistive element of the first series circuit is stable. A constant voltage signal having a voltage level substantially the same as the change detection signal level is output. The pre-stage differential amplifier circuit outputs a magnetic field change detection signal as a magnetic change detector by differentially amplifying the first magnetic field change detection signal and the constant voltage signal.

  In this configuration, the first magnetic field change detection signal including the effective variation component is output from the first series circuit, and the constant voltage signal corresponding to the offset component of the magnetic field change detection signal is output from the constant voltage output circuit. In the pre-stage differential amplifier circuit, these signals are differentially amplified, so that they are amplified after removing the offset component of the first magnetic field change detection signal by the constant voltage signal. For this reason, the magnetic field change detection signal as the magnetic field change detection unit is obtained as a signal with a small offset component and a large effective fluctuation component. Then, by performing integration processing and differential amplification processing based on the magnetic field change detection signal with a small offset component, the gain of the differential amplification section can be set to a large value, and more effective fluctuation components can be obtained while removing the offset components. Can be effectively amplified to a high level.

  The magnetic field change detection unit of the magnetic sensor according to the present invention includes a first series circuit, a second series circuit, and a previous differential amplifier circuit. In the first series circuit, a magnetoresistive element having different characteristics or a magnetoresistive element and a resistance element are connected in series between a voltage input terminal and a ground terminal, and a connection position or a magnetoresistance of magnetoresistive elements having different characteristics is connected. The voltage level at the connection position between the element and the resistance element is output as the first magnetic field change detection signal. In the second series circuit, magnetoresistive elements having different characteristics or magnetoresistive elements and resistance elements are connected in series so as to produce a characteristic that is inverted with respect to the first series circuit, and the connection positions of the magnetoresistive elements having different characteristics are connected. Alternatively, the voltage level at the connection position between the magnetoresistive element and the resistive element is output as the second magnetic field change detection signal. The pre-stage differential amplifier circuit outputs a magnetic field change detection signal as a magnetic change detector by differentially amplifying the first magnetic field change detection signal and the second magnetic field change detection signal.

  In this configuration, the first magnetic field change detection signal and the second magnetic field change detection signal whose characteristics are inverted between the first series circuit and the second series circuit are output. In the pre-stage differential amplifier circuit, differential amplification of the first magnetic field change detection signal and the second magnetic field change detection signal is performed. For this reason, the magnetic field change detection signal as the magnetic field change detection unit is a signal with a small offset component and a larger effective fluctuation component. Then, integration processing and differential amplification processing are performed based on the magnetic field change detection signal with a small offset component and a large effective variation component, thereby effectively removing only the effective variation component at a high level while removing the offset component. Can be amplified.

  According to the present invention, based on the magnetic field change detection signal from the magnetic field change detection unit, an offset component signal corresponding to the offset component of the magnetic field change detection signal is generated and amplified by being differentially amplified from the magnetic field change detection signal. Only the effective variation component can be effectively amplified without being affected by the offset component. As a result, it is not necessary to perform an offset adjustment process or the like, and it is possible to obtain a detection signal at a high level according to the magnetic pattern and magnetic information of the detection target without being affected by the fluctuation of the offset. Accurate magnetic patterns and magnetic information can be detected.

It is a figure for demonstrating the equivalent circuit and operation | movement description of the magnetic sensor which concerns on 1st Embodiment. It is a top view which shows the structure of the magnetic field change detection part of 1st Embodiment. It is a figure for demonstrating the equivalent circuit and operation | movement description of the magnetic sensor which concerns on 2nd Embodiment. It is a top view which shows the structure of the magnetic field change detection part of 2nd Embodiment. It is a graph which shows the offset experiment result at the time of using the structure of 2nd Embodiment. It is a top view which shows the structure of the magnetic field change detection part of 3rd Embodiment. It is a graph which shows the offset experiment result at the time of using the structure of 3rd Embodiment. It is a figure for demonstrating the equivalent circuit and operation | movement description of a magnetic sensor by a two-stage connection.

  A magnetic sensor according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining an equivalent circuit and operation of the magnetic sensor according to the present embodiment.

The magnetic sensor of this embodiment includes a magnetic field change detection unit 10, an integration unit 20, and a differential amplification unit 30.
The magnetic field change detection unit 10 includes a series circuit of a resistance element R1 and a magnetoresistance element MR1. The end of the series circuit on the side of the resistance element R1 is an input terminal for the applied voltage Vin, and the end of the series circuit on the side of the magnetoresistive element MR1 is connected to the ground GND. The connection point between the resistance element R1 and the magnetoresistance element MR1 is an output terminal of the magnetic field change detection signal Voutψ.

  The magnetoresistive element MR1 is an element whose resistance value changes in response to a change in magnetic field. For example, a semiconductor film made of InSb is formed on a Si substrate with a long pattern whose length is larger than the width. And it implement | achieves by forming the short circuit electrode which consists of a conductor at predetermined intervals along the elongate direction on the said semiconductor film. At this time, the magnetoresistive element MR1 is set to have high sensitivity to the magnetic field due to the formation pattern of the short-circuit electrode. That is, the magnetoresistive element MR1 is set such that the resistance value changes greatly when the density of the passing magnetic flux changes by a predetermined amount.

  The resistance element R1 is an element having a constant resistance value without corresponding to a change in the magnetic field. For example, a semiconductor film made of InSb in a long pattern whose length is larger than the width is formed on a Si substrate. Realized by forming. That is, the magnetic resistance element MR1 is formed in a shape having no short-circuit electrode. Thereby, the resistance element R1 can be set to a very low sensitivity to the magnetic field, and the resistance value remains constant even when the density of the passing magnetic flux changes.

  More specifically, the magnetic field change detection unit 10 has a structure as shown in FIG. FIG. 2 is a plan view showing the configuration of the magnetic field change detection unit 10 of the present embodiment.

In the magnetic field change detection unit 10, a semiconductor film (magnetic sensing unit) and electrodes that form the magnetoresistive element MR 1 and the resistive element R 1 are formed on the Si substrate 11. As the substrate, a semi-insulating substrate such as GaAs: SiO ₂ can be used in addition to an insulating substrate such as a Si substrate. At one end along the first direction (vertical direction in FIG. 2) of the region where the magnetic field change detection unit 10 is formed on the substrate 11, a voltage input electrode 191 for applying the applied voltage Vin, and a ground connection electrode for ground connection 192 is formed. At the other end, a voltage output electrode 193 that outputs a magnetic field change detection signal Voutψ is formed. The voltage input electrode 191, the ground connection electrode 192, and the voltage output electrode 193 are made of a conductive material.

  In a region between the voltage input electrode 191 and the ground connection electrode 192 and the voltage output electrode 193 on the substrate 11, the magnetic sensing parts 121 to 124 and the connection line electrodes 141 to 145 constituting the magnetoresistive element MR 1 are provided. Magnetic sensing portions 131 to 134 and connection line electrodes 151 to 155 constituting the resistance element R1 are formed. Short-circuit electrodes are formed on the magnetic sensing parts 121 to 124 constituting the magnetoresistive element MR1, and no short-circuit electrodes are formed on the magnetic sensing parts 131 to 134 constituting the resistance element R1.

  The magnetic sensing parts 121 to 124 constituting the magnetoresistive element MR1 are arranged so that the longitudinal direction is parallel to the second direction, and the connection line electrodes 141 to 145 extending along the first direction They are connected in series. The magnetoresistive element MR1 has a structure in which the ground connection electrode 192 and the voltage output electrode 193 are connected to each other by the series connection portion including the magnetic sensing portions 121 to 124 and the connection line electrodes 141 to 145.

  Similarly to the magnetic sensing parts 121 to 124 constituting the magnetoresistive element MR1, the magnetic sensing parts 131 to 134 constituting the resistance element R1 are also arranged so that the longitudinal direction is parallel to the second direction, The connection line electrodes 151 to 155 extending along the first direction are connected in series. The resistance element R1 is connected between the voltage input electrode 191 and the voltage output electrode 193 by a series connection portion including the magnetic sensing portions 131 to 134 and the connection line electrodes 151 to 155. .

  Thus, the magnetoresistive element MR1 and the resistive element R1 are formed in a so-called meander shape, and the magnetic sensitive parts 121 to 124 that constitute the magnetoresistive element MR1 and the magnetic sensitive parts 131 to 134 that constitute the resistive element R1. Is a state in which the longitudinal direction is all along the second direction, which is the conveyance direction of the detection target, and is arranged in order along the first direction.

As shown in FIG. 1B, the magnetic field change detection signal Voutψ output from the magnetic field change detection unit 10 having such a structure is
Voutψ = Vin * MR1 / (MR1 + R1)
And is composed of a divided voltage of the magnetoresistive element MR1 and the resistive element R1.

  Therefore, the magnetic field change detection signal Voutψ includes an offset voltage Vdo corresponding to the resistance value of the magnetoresistive element MR1 in a state where the detection target does not pass as shown in FIG. The waveform includes an effective fluctuation component Vef that increases and decreases at a voltage level higher than the offset voltage Vdo due to the passage of the body.

  The integration unit 20 includes a resistance element Rcr connected to the output terminal of the magnetic field change detection unit 10. The end of the resistance element Rcr opposite to the connection end to the magnetic field change detection unit 10 is connected to the ground via the capacitor element Ccr. With such a circuit configuration, the parallel circuit of the resistance element Rcr and the capacitor element Ccr functions as an integration circuit, and a magnetic field change detection signal is output from an output terminal that is a connection end of the resistance element Rcr and the capacitor element Ccr. An integrated signal VoutI obtained by integrating Voutψ is output.

  Here, since the effective variation component Vef of the magnetic field change detection signal Voutψ is generated by the magnetic pattern of the detected object to be conveyed, it is extremely short on the time axis. Therefore, if the element constants of the resistance element Rcr and the capacitor element Ccr constituting the product portion 20 are set to a predetermined value and the time constant is set large, the integration corresponding to the appearance of the effective variation component Vef of the magnetic field change detection signal Voutψ. The rising edge of the signal VoutI is delayed, and as shown by the broken line in FIG. 1C, an integrated signal VoutI whose voltage level does not change can be generated from the offset voltage Vdo. This integrated signal VoutI corresponds to the “offset component signal” of the present invention.

  The differential amplifying unit 30 includes a differential amplifying circuit including an operational amplifier OP and resistance elements Ra, Rb, Rc, and Rd.

  Specifically, the output terminal of the magnetic field change detection unit 10 is connected to the non-inverting input terminal of the operational amplifier OP through the resistance element Ra, and the magnetic field change detection signal Voutψ is input. The non-inverting input terminal is connected to the ground GND through the resistance element Rc. The output terminal of the integrating unit 20 is connected to the inverting input terminal of the operational amplifier OP through the resistance element Rb, and the integration signal VoutI is input thereto. The output terminal of the operational amplifier OP is connected to the inverting input terminal via the resistance element Rd. By adopting such a configuration and appropriately setting the resistance ratio of the resistance elements Rb and Rd, a differential amplifier circuit is constructed that amplifies the signal with a predetermined gain K by subtracting the integral signal VoutI from the magnetic field change detection signal Voutψ. . Note that the output terminal of the operational amplifier OP serves as an output terminal as the differential amplifier 20 and the magnetic sensor, and the sensor detection signal Vout is output.

  As described above, in the differential amplifier 30, the integrated signal VoutI is amplified after being subtracted from the magnetic field change detection signal Voutψ, and therefore the offset voltage Vdo of the magnetic field change detection signal Voutψ is removed by the integrated signal VoutI. As a result, only the effective fluctuation component Vef of the magnetic field change detection signal Voutψ is the same as that amplified by the gain K, and as shown in FIG. 1D, only the effective fluctuation component having almost no offset component is at a high level. Can be obtained.

  As described above, by using the configuration of the present embodiment, the effective variation component Vef is detected at a high level without being affected by the inevitably generated offset voltage and its variation due to the configuration of the magnetic field change detection unit. be able to. Thereby, the magnetic pattern and magnetic information of a to-be-detected body can be detected reliably and with high precision. Further, the configuration of the present embodiment is a simple configuration in which the configuration of the magnetic field change detection unit includes the magnetoresistive element MR1 and the resistive element R1 as compared with the configurations of the respective embodiments described later. A magnetic sensor having a detection capability can be realized with a simple structure.

  Furthermore, as described above, the magnetoresistive element MR1 and the resistive element R1 are arranged in a meander shape and alternately arranged with the magnetic sensitive portions orthogonal to the transport direction of the detection target, particularly along the first direction. Since a plurality of pairs of arrays in which the magnetosensitive part of the magnetoresistive element MR1 and the magnetosensitive part of the resistive element R1 are adjacent to each other are formed, the temperature between the magnetoresistive element MR1 and the resistive element R1 Differences and time differences can be eliminated. Thereby, the magnetic field change detection signal Voutψ based on the absolute magnetic quantity is obtained, and a more accurate sensor detection signal Vout can be obtained.

Next, a magnetic sensor according to a second embodiment will be described with reference to the drawings. FIG. 3 is a diagram for explaining an equivalent circuit and operation of the magnetic sensor according to the present embodiment.
The magnetic sensor of the present embodiment has the same configuration and basic signal processing of the integrating unit 20 and the differential amplifying unit 30, and the configuration before the integrating unit 20 is the same as that of the magnetic sensor of the first embodiment. Different.

  The magnetic sensor of the present embodiment includes a magnetic field change detection unit 10 ′, a previous-stage differential amplification unit 40, an integration unit 20, and a differential amplification unit 30.

  The magnetic field change detection unit 10 'includes a first series circuit including a resistance element R1 and a magnetoresistance element MR1, and a constant voltage circuit in which the resistance element R3 and the resistance element R4 are connected in series. The end of the first series circuit on the side of the resistance element R1 is an input terminal for the applied voltage Vin, and the end of the series circuit on the side of the magnetoresistive element MR1 is connected to the ground GND. A connection point between the resistor element R1 and the magnetoresistive element MR1 is an output terminal of the magnetic field change detection signal Voutψ.

  Further, the end of the constant voltage circuit composed of a series circuit of the two resistance elements R3 and R4 is connected to the input terminal of the applied voltage Vin, and the end of the constant voltage circuit on the side of the resistance element R4 is connected to the ground GND. It is connected to the. A connection point between the two resistance elements R3 and R4 is an output terminal of the constant voltage signal VoutR.

  As shown in the first embodiment, the magnetoresistive element MR1 is an element whose resistance value changes with high sensitivity in accordance with a change in magnetic field. The resistance element R1, the resistance element R3, and the resistance element R4 are elements that have constant resistance values without corresponding to changes in the magnetic field. At this time, the resistance value of the resistance element R1 is set so as to substantially match the resistance value in a state where the magnetoresistance element MR1 is not subjected to the change of the passing magnetic flux by the detection target. For example, as shown in FIG. 4 described later, this is realized by forming the resistance element R1 to be 2/3 thinner and 2/3 shorter than the magnetoresistive element MR1. Similarly, the resistance values of the resistance elements R3 and R4 can be made substantially equal by forming the resistance element R4 to be 2/3 thinner and 2/3 shorter than the resistance element R3. .

  More specifically, the magnetic field change detection unit 10 'has a structure as shown in FIG. FIG. 4 is a plan view showing the configuration of the magnetic field change detection unit 10 ′ of this embodiment.

  Similarly to the magnetic field change detection unit 10 of the first embodiment, the magnetic field change detection unit 10 ′ is a semiconductor film (magnetic sensing unit) that forms the magnetoresistive element MR1 and the resistance elements R1, R3, and R4 on the Si substrate 31. ) And electrodes are formed. At one end along the second direction (lateral direction in FIG. 4) of the formation region of the magnetic field change detection unit 10 ′ on the substrate 31, there are ground connection electrodes 3921 and 3922 for ground connection, and the constant voltage signal VoutR. A voltage output electrode 3932 as an output terminal is formed. At the other end, a voltage output electrode 3931 for outputting a magnetic field change detection signal Voutψ and voltage input electrodes 3911 and 3912 for providing an applied voltage Vin are formed. These voltage input electrodes 3911 and 3912, ground connection electrodes 3921 and 3922, and voltage output electrodes 3931 and 3932 are made of a conductive material.

  In a region between one end and the other end of the substrate 31 in the second direction, the magnetosensitive elements 3211, 3221, 3231 and the connection line electrodes 3411, 3421, 3431, 3441 constituting the magnetoresistive element MR1, and the resistive element Magnetic sensing parts 3311, 3321 and connection line electrodes 3511, 3521, 3441 constituting R1, magnetic sensing parts 3312, 3322, 3332 and connection line electrodes 3512, 3522, 3532, 3542 constituting one resistance element R3, Magnetic sensing portions 3212 and 3222 and connection line electrodes 3412, 3422, and 3542 constituting the other resistance element R4 are formed. Short-circuit electrodes are formed on the magnetic sensing portions 3211, 3221, and 3231 constituting the magnetoresistive element MR1, and no short-circuit electrodes are formed on the other magnetic sensitive portions constituting the resistive elements R1, R3, and R4.

  The magnetic sensitive parts 3211, 3221, 3231 constituting the magnetoresistive element MR1 are connected in series by connection line electrodes 3411, 3421, 3431, 3441. The magnetoresistive element MR1 is connected between the ground connection electrode 3921 and the voltage output electrode 3931 by the series connection portion including the magnetic sensing portion and the connection line electrode.

  The magnetic sensing parts 3311 and 3321 constituting the resistance element R1 are connected in series by connection line electrodes 3511, 3521 and 3441. The resistance element R1 is connected between the voltage input electrode 3911 and the voltage output electrode 3931 by the series connection portion including the magnetic sensing portion and the connection line electrode.

  The magnetic sensing parts 3312, 3322, 3332 constituting one resistance element R3 are connected in series by connection line electrodes 3512, 3522, 3532, 3542. One resistance element R3 is connected between the voltage input electrode 3912 and the voltage output electrode 3932 by the series connection portion including the magnetic sensing portion and the connection line electrode.

  The magnetic sensing parts 3212 and 3222 constituting the other resistance element R4 are connected in series by connection line electrodes 3412, 3422, and 3542. The other resistance element R4 is connected between the ground connection electrode 3922 and the voltage output electrode 3932 by the series connection portion including the magnetic sensing portion and the connection line electrode.

  As described above, the magnetoresistive element MR1 and the resistive elements R1, R3, and R4 are formed in a so-called meander shape, and constitute all the magnetosensitive parts and the resistive elements R1, R3, and R4 that constitute the magnetoresistive element MR1. All the magnetic sensing parts to be configured have a configuration in which the longitudinal direction is along the second direction, which is the conveyance direction of the detection target, and is sequentially arranged along the first direction.

As shown in FIG. 3B, the magnetic field change detection signal Voutψ output from the magnetic field change detection unit 10 ′ having such a structure is
Voutψ = Vin * MR1 / (MR1 + R1)
And is composed of a divided voltage of the magnetoresistive element MR1 and the resistive element R1.

  Therefore, as shown in FIG. 3B, the magnetic field change detection signal Voutψ includes an offset voltage corresponding to the resistance value of the magnetoresistive element MR1 in a state where the detection target does not pass, and the detection target. As a result, the waveform includes an effective fluctuation component that increases and decreases at a voltage level higher than the offset voltage. Since the offset voltage is set so that the resistance value of the magnetoresistive element MR1 at the time of non-detection and the resistance value of the resistance element R1 substantially coincide with each other as described above, the offset voltage is intermediate between Vin and the ground level. The value is close to the voltage.

On the other hand, the constant voltage signal VoutR is set so that the resistance values of the resistance element R3 and the resistance element R4 match.
VoutR = Vin / 2
And a constant voltage corresponding to an intermediate voltage between Vin and the ground level.

  The pre-stage differential amplification unit 40 includes a differential amplification circuit including an operational amplifier OPf and resistance elements Rfa, Rfb, Rfc, and Rfd.

  Specifically, the output terminal of the magnetic field change detection signal Voutψ of the magnetic field change detection unit 10 ′ is connected to the non-inverting input terminal of the operational amplifier OPf through the resistance element Rfa, and the magnetic field change detection signal Voutψ is input. Is done. The non-inverting input terminal is connected to the ground via the resistance element Rfc.

  The output terminal of the constant voltage signal VoutR of the magnetic field change detection unit 10 ′ is connected to the inverting input terminal of the operational amplifier OPf through the resistance element Rfb, and the constant voltage signal VoutR is input thereto. The output terminal of the operational amplifier OPf is connected to the inverting input terminal via the resistance element Rfd. By adopting such a configuration and appropriately setting the resistance ratio of the resistance elements Rfb and Rfd, a differential amplifier circuit is configured that subtracts the constant voltage signal VoutR from the magnetic field change detection signal Voutψ and amplifies it with a predetermined gain Kf. The

  In this way, in the previous-stage differential amplifying unit 40, the constant voltage signal VoutR substantially corresponding to the offset is amplified from the magnetic field change detection signal Voutψ and then amplified, so that the offset voltage of the magnetic field change detection signal Voutψ is almost equal. Removed. As a result, only the effective variation component of the magnetic field change detection signal Voutψ is the same as that amplified by the gain Kf, and the offset component is reduced and the effective variation component is amplified as shown in FIG. A post-detection signal Voutψ ′ can be obtained.

  The correction detection signal Voutψ ′ thus generated is input to the integration unit 20 and the non-inversion of the operational amplifier OP via the resistance element Ra of the differential amplification unit 30 as in the first embodiment. It is given to the input terminal.

  The integrator 20 integrates the correction detection signal Voutψ ′ to generate an integration signal VoutI ′ as shown in FIG. The integration signal VoutI ′ is given to the inverting input terminal of the operational amplifier OP via the resistance element Rb of the differential amplifier 30.

  The differential amplifying unit 30 performs amplification processing in a state where the integral signal VoutI ′ is subtracted from the correction detection signal Voutψ ′, so that the offset voltage of the correction detection signal Voutψ ′ is also removed, and the correction detection signal Voutψ ′ is effective. Only the fluctuation component is amplified by the gain K ′. Thereby, as shown in FIG. 3E, it is possible to obtain the sensor detection signal Vout in which the offset component is further removed and the level of the effective variation component is higher.

  In such a configuration, since the offset component is suppressed by the upstream differential amplifier circuit 40, the differential amplifier 30 which is the final stage can take a very large value of the gain K ′. . Therefore, by using the configuration of the present embodiment, a gain larger than that of the configuration of the first embodiment can be set, and the level of the effective variation component of the sensor detection signal Vout can be made extremely high. Thereby, the magnetic sensor which can be detected more reliably and with high accuracy can be realized.

  FIG. 5 is a graph showing an offset experiment result when the configuration of the present embodiment is used. As shown in FIG. 5, by using the configuration of this embodiment, even if the difference between the magnetic field change detection signal Voutψ and the constant voltage signal VoutR is about ± 0.5 V, the offset voltage of the sensor detection signal Vout is ± 1. It can be suppressed to less than 0.0V. Thereby, the sensor detection signal Vout having almost no offset voltage can be obtained. Further, the offset voltage transition characteristic resulting from the potential difference between the signals can be applied to the fluctuation of the offset voltage due to the temperature characteristic of the magnetoresistive element or the resistive element. Therefore, by using the configuration of the present embodiment, it is possible to realize a magnetic sensor that can perform magnetic detection reliably and highly accurately without being affected by the magnetoresistive element or the temperature characteristics of the resistive element.

  As described above, even if there is a certain difference between the offset component of the magnetic field change detection signal Voutψ and the constant voltage signal VoutR in the front-stage differential amplification unit 40, the integration unit 20 and the differential amplification unit 30 Since the resulting offset is removed, the accuracy and temperature characteristics required for the magnetoresistive element MR1 and the resistive elements R1, R3, and R4 do not need to be extremely excellent. As a result, the design is facilitated, and even an inexpensive element whose accuracy and temperature characteristics are slightly lowered can be used.

  Further, by forming the magnetoresistive element MR1 and the resistive elements R1, R3, and R4 in a meander shape as described above, it is possible to obtain a magnetic field change detection signal made up of an absolute magnetic quantity as in the first embodiment.

  Next, a magnetic sensor according to a third embodiment will be described with reference to the drawings. FIG. 6 is a diagram for explaining an equivalent circuit and operation of the magnetic sensor according to the present embodiment.

  The magnetic sensor of the present embodiment is the same as the magnetic sensor of the second embodiment except that the configuration of the magnetic field change detection unit 10 ″ and the resistance value of each resistance element of the previous-stage differential amplification unit 40 ′ are different. It is.

  The magnetic field change detection unit 10 ″ includes a first series circuit including a resistor element R1 and a magnetoresistive element MR1, and a second series circuit in which the magnetoresistive element MR2 and the resistor element R2 are connected in series. The end portion on the resistance element R1 side is an input terminal for the applied voltage Vin, and the end portion on the magnetoresistive element MR1 side of the series circuit is connected to the ground, and the connection point between the resistance element R1 and the magnetoresistive element MR1 is This is an output terminal for the first magnetic field change detection signal Voutψ (+).

  The end of the second series circuit on the side of the magnetoresistive element MR2 is an input terminal for the applied voltage Vin, and the end of the second series circuit on the side of the resistor R2 is connected to the ground. A connection point between the magnetoresistive element MR2 and the resistive element R2 is an output terminal of the second magnetic field change detection signal Voutψ (−).

  As shown in the first embodiment, the magnetoresistive elements MR1 and MR2 are elements whose resistance values change with high sensitivity in accordance with changes in the magnetic field. The resistance elements R1 and R2 are elements that have a constant resistance value without corresponding to a change in the magnetic field. At this time, the voltage dividing ratio between the resistance element R1 and the magnetoresistive element MR1 in a state where the magnetic field of the detection object is not received, and the division ratio of the magnetoresistance element MR2 and the resistance element R2 in the state where the magnetic field of the detection object is not received The pressure ratio is set to be substantially the same.

  More specifically, the magnetic field change detection unit 10 ″ has a structure as shown in FIG. 7. FIG. 7 is a plan view showing the configuration of the magnetic field change detection unit 10 ″ of the present embodiment.

  The magnetic field change detection unit 10 ″ has a structure similar to that of the magnetic field change detection unit 10 ′ of the second embodiment, and a semiconductor film constituting the magnetoresistive elements MR1 and MR2 and the resistance elements R1 and R2 on the Si substrate 41. (Magnetic sensing portion) and electrodes are formed. A ground connection for ground connection is provided at one end along the second direction (lateral direction in FIG. 7) of the formation region of the magnetic field change detection portion 10 ″ in the substrate 41. Electrodes 4921 and 4922 and a voltage output electrode 4932 which is an output terminal of the second magnetic field change detection signal Voutψ (−) are formed. At the other end, a voltage output electrode 4931 for outputting the first magnetic field change detection signal Voutψ (+) and voltage input electrodes 4911 and 4912 for applying the applied voltage Vin are formed. These voltage input electrodes 4911 and 4912, ground connection electrodes 4921 and 4922, and voltage output electrodes 4931 and 4932 are made of a conductive material.

  In a region between one end and the other end of the substrate 41 in the second direction, magnetic sensitive portions 4211, 4221, 4231 and connection line electrodes 4411, 4421, 4431, 4441 constituting the magnetoresistive element MR1, and a resistive element Magnetic sensing parts 4311, 4321 and connection line electrodes 4511, 4521, 4441 constituting R1, magnetic sensing parts 4312, 4322, 4332 and connection line electrodes 4512, 4522, 4532, 4542 constituting a magnetoresistive element MR2, resistance Magnetic sensing portions 4212 and 4222 and connection line electrodes 4412, 4422, and 4542 constituting the element R2 are formed. Short-circuit electrodes are formed on the magnetic sensing parts 4211, 4221, 4231 constituting the magnetoresistive element MR1 and the magnetic sensing parts 4312, 4322, 4332 constituting the magnetoresistive element MR2, and other sensing elements constituting the resistive elements R1, R2. No short-circuit electrode is formed on the magnetic part.

  The magnetic sensing parts 4211, 4221, 4231 constituting the magnetoresistive element MR1 are connected in series by connection line electrodes 4411, 4421, 4431, 4441. The magnetoresistive element MR1 is connected between the ground connection electrode 4921 and the voltage output electrode 4931 by the series connection portion including the magnetic sensing portion and the connection line electrode.

  The magnetic sensing parts 4311 and 3321 constituting the resistance element R1 are connected in series by connection line electrodes 4511, 4521 and 4441. The resistance element R1 is connected between the voltage input electrode 4911 and the voltage output electrode 4931 by the series connection portion including the magnetic sensing portion and the connection line electrode.

  The magnetic sensing parts 4312, 4322, 4332 constituting the magnetoresistive element MR2 are connected in series by connection line electrodes 4512, 4522, 4532, 4542. The magnetoresistive element MR <b> 2 is connected between the voltage input electrode 4912 and the voltage output electrode 4932 by the series connection portion including the magnetic sensing portion and the connection line electrode.

  The magnetic sensing parts 4212 and 4222 constituting the resistance element R2 are connected in series by connection line electrodes 4412, 4422, and 4542. The resistance element R2 is connected between the ground connection electrode 4922 and the voltage output electrode 4932 by the series connection portion including the magnetic sensing portion and the connection line electrode.

  As described above, the magnetoresistive elements MR1 and MR2 and the resistive elements R1 and R2 are formed in a so-called meander shape, and constitute all the magnetosensitive parts and the resistive elements R1 and R2 constituting the magnetoresistive elements MR1 and MR2. All the magnetic sensing parts to be configured have a configuration in which the longitudinal direction is along the second direction, which is the conveyance direction of the detection target, and is sequentially arranged along the first direction.

The first magnetic field change detection signal Voutψ (+) output from the magnetic field change detection unit 10 ″ having such a structure is shown in FIG. 6B because the magnetoresistive element MR1 is on the ground side with respect to the voltage output terminal. like,
Voutψ (+) = Vin * MR1 / (MR1 + R1)
It is represented by

  As a result, as shown in FIG. 6B, an offset voltage corresponding to the resistance value of the magnetoresistive element MR1 in a state in which the detection target does not pass is higher than the offset voltage due to the passage of the detection target. The waveform includes an effective fluctuation component (+) in which the voltage increases and decreases with the level.

On the other hand, since the magnetoresistive element MR2 is closer to the voltage input terminal than the voltage output terminal, the second magnetic field change detection signal Voutψ (−) is as shown in FIG.
Voutψ (−) = Vin * R2 / (MR2 + R2)
It is represented by

  As a result, as shown in FIG. 6B, the voltage is composed of an offset voltage corresponding to the resistance value of the resistance element R2 in a state in which the detection target is not passing, and is lower than the offset voltage due to the passage of the detection target. The waveform includes an effective fluctuation component (−) in which the voltage decreases and increases with the level.

  At this time, as described above, the magnetic sensing portions of the magnetoresistive elements MR1 and MR2 and the sensitive elements of the resistive elements R1 and R2 along the direction (first direction in FIG. 7) orthogonal to the transport direction of the detection target. By arranging a plurality of pairs of arrays arranged so that the magnetic parts are adjacent to each other, the maximum timing of the effective variation component (+) and the minimum timing of the effective variation component (-) can be made substantially the same. .

  The front-stage differential amplifying unit 40 ′ includes a differential amplifying circuit including an operational amplifier OPf and resistance elements Rfa ′, Rfb ′, Rfc ′, and Rfd ′, and has the same configuration as that of the front-stage differential amplifying unit 40 of the second embodiment. Consists of. The second magnetic field change detection signal Voutψ (−) is input to the inverting input terminal of the operational amplifier OPf, and the first magnetic field change detection signal Voutψ (+) is input to the non-inverting input terminal. As a result, the previous-stage differential amplification unit 40 ′ differentially amplifies the second magnetic field change detection signal Voutψ (−) with respect to the first magnetic field change detection signal Voutψ (+), that is, as shown in FIG. Is added to the first magnetic field change detection signal Voutψ (+) and the inverted second magnetic field change detection signal Voutψ (−), and a combined detection signal Voutψ ″ amplified by the gain Kf ′ is output. Since the offset voltage of the magnetic field change detection signal Voutψ (+) and the offset voltage of the second magnetic field change detection signal Voutψ (−) are set to be approximately the same, they are canceled out by differential amplification and combined after differential amplification. The offset voltage included in the detection signal Voutψ ″ is reduced as compared with each signal before differential amplification.

  The integration unit 20 integrates the combined detection signal Voutψ ′ to generate an integration signal VoutI ″ as shown in FIG. 6D. The integration signal VoutI ″ generates the resistance element Rb of the differential amplification unit 30. Through the inverting input terminal of the operational amplifier OP.

  Since the differential amplifier 30 performs the amplification process with the integrated signal VoutI ″ being different from the combined detection signal Voutψ ″, the offset voltage of the combined detection signal Voutψ ″ is also removed, and the combined detection signal Voutψ ″ is effective. Only the fluctuation component is amplified with the gain K ″. As a result, as shown in FIG. 6E, the offset detection component is further removed and the sensor detection signal Vout having a higher effective fluctuation component level can be obtained. .

  In such a configuration, since the offset component is suppressed by the upstream differential amplifier circuit 40 ′, the differential amplifier 30 which is the final stage can take a very large value of the gain K ″. Therefore, by using the configuration of the present embodiment, a gain larger than that of the configuration of the first embodiment can be set, and the level of the effective variation component of the sensor detection signal Vout can be made extremely high. Furthermore, in the configuration of the present embodiment, since the two signals whose effective variation components are inverted with respect to the offset voltage are differentially amplified, the effective variation component of the combined detection signal Voutψ ″ is originally large. Become. Therefore, the level of the effective variation component can be further increased by using the configuration of the present embodiment. Thereby, the magnetic sensor which can be detected more reliably and with high accuracy can be realized.

  Further, by using the configuration of the present embodiment, the first magnetic field change detection signal Voutψ (+) obtained from the magnetoresistive element MR1 and the resistor element R1, and the second magnetic field change detection obtained from the resistor element R2 and the magnetoresistive element MR2. Even if the offset of the signal Vout (−) is not adjusted with high accuracy, the offset is removed by the differential amplifier 40, the integrator 20, and the differential amplifier 30, so that the magnetoresistive elements MR1, MR2, resistance It is not necessary to set the elements R1 and R2 strictly. As a result, design becomes easy and inexpensive elements can be used.

  Further, as described above, the magnetoresistive elements MR1 and MR2 and the resistive elements R1 and R2 are formed in a meander shape, and the magnetosensitive parts of the magnetoresistive elements MR1 and MR2 and the magnetosensitive parts of the resistive elements R1 and R2 are provided. By providing a plurality of adjacent arrays arranged in the direction perpendicular to the longitudinal direction of the magnetic sensing part, a magnetic field change detection signal composed of an absolute magnetic quantity as in the first and second embodiments. Can be obtained.

  In each of the above-described embodiments, an example in which only one set of the integrating unit 20 and the differential amplifying unit 30 is used has been described. However, as illustrated in FIG. Two sets may be used, and a multi-stage connection of three or more stages may be used. FIG. 8 is a diagram for explaining an equivalent circuit and operation of a magnetic sensor by two-stage connection.

  When two-stage connection or multi-stage connection as shown in FIG. 8 is performed, by providing the integration unit 20 in front of each differential amplification unit 30, each integration unit 20 corresponds to an offset of the input detection signal. An integrated signal can be generated. Thereby, since the offset is removed in each differential amplifier, multistage amplification can be performed without being affected by the offset voltage in each stage. Thereby, even if the level of the effective variation component detected by the magnetoresistive element of the magnetic field change detection unit is low, a detection signal with a very high signal level can be output without being affected by the offset.

  10, 10 ', 10 "-magnetic field change detector, 20-integrator, 30-differential amplifier, 40, 40'-previous differential amplifier

Claims (6)

Magnetic field change that outputs a magnetic field change detection signal based on a difference in the characteristics of at least one set of magnetoresistive elements or magnetoresistive elements and resistance elements that have different resistance value change characteristics caused by changes in magnetic flux density A detection unit;
An integration unit that outputs an offset component signal by integrating the magnetic field change detection signal;
A magnetic sensor comprising: a differential amplifying unit that differentially amplifies the magnetic field change detection signal and the offset component signal. A second integrator that outputs a second offset component signal by integrating the detection signal output from the differential amplifier;
The magnetic sensor according to claim 1, further comprising: a second differential amplification unit that performs differential amplification processing on the detection signal and the second offset component signal.   The magnetic sensor according to claim 2, wherein the second integration unit and the second differential amplification unit are connected in multiple stages.   The magnetic field change detection unit connects the magnetoresistive elements having different characteristics or the magnetoresistive elements and the resistive elements in series between a voltage input terminal and a ground terminal, and the connection positions of the magnetoresistive elements having different characteristics or The magnetic sensor according to claim 1, wherein a voltage level at a connection position between the magnetoresistive element and the resistive element is output as the magnetic field change detection signal. The magnetic field change detection unit
A magnetoresistive element having different characteristics or a magnetoresistive element and a resistive element are connected in series between a voltage input terminal and a ground terminal, and a connection position between magnetoresistive elements having different characteristics or the magnetoresistive element and the resistive element. A first series circuit that outputs a voltage level at a connection position with the first magnetic field change detection signal;
The first magnetic field change detection signal of the first series circuit in a state in which the resistance value of the magnetoresistive element of the first series circuit is stable, the resistance value of the magnetoresistive element of the first series circuit being stable without changing the magnetic flux density. And a constant voltage output circuit that outputs a constant voltage signal having a voltage level substantially the same as the level,
2. A pre-stage differential amplification circuit that outputs the magnetic field change detection signal as the magnetic change detection unit by differentially amplifying the first magnetic field change detection signal and the constant voltage signal. The magnetic sensor according to claim 3. The magnetic field change detection unit
A magnetoresistive element having different characteristics or a magnetoresistive element and a resistive element are connected in series between a voltage input terminal and a ground terminal, and a connection position between magnetoresistive elements having different characteristics or the magnetoresistive element and the resistive element. A first series circuit that outputs a voltage level at a connection position with the first magnetic field change detection signal;
The magnetoresistive elements having different characteristics or the magnetoresistive elements and the resistor elements are connected in series so as to produce a characteristic that is inverted with respect to the first series circuit, and the connection positions of the magnetoresistive elements having different characteristics or the magnetic field A second series circuit that outputs a voltage level at a connection position between the resistance elements as a second magnetic field change detection signal;
A pre-stage differential amplification circuit that outputs the magnetic field change detection signal as the magnetic change detection unit by differentially amplifying the first magnetic field change detection signal and the second magnetic field change detection signal; The magnetic sensor in any one of Claims 1-3.

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