JP7082590B2 - Magnetic field measuring device, magnetic field measuring method, and magnetic field measuring program - Google Patents

Description

The present invention relates to a magnetic field measuring device, a magnetic field measuring method, and a magnetic field measuring program.

A bridge circuit is constructed using one TMR element and three fixed resistors, power is generated to pass a current through the magnetic field generation coil based on the output voltage of the bridge circuit, and a magnetic field is applied to the TMR module by the magnetic field generation coil. Magnetic sensors are known. (See, for example, Patent Document 1). Further, there is known a magnetic sensor that constitutes a bridge circuit by using one TMR element and three fixed resistors and controls a voltage applied to the bridge circuit based on the output voltage of the bridge circuit. (See, for example, Patent Document 2).
Patent Document 1 Japanese Patent Application Laid-Open No. 2017-0817373 Patent Document 2 Japanese Patent Application Laid-Open No. 2017-09626

In the conventional magnetic sensor, the magnetic operating point of the TMR element may come to the magnetic saturation region where the magnetic resolution is lowered, depending on the balance of each resistance value constituting the bridge circuit. However, in biomagnetic field measurement such as magnetic field measurement, it is desired to realize a magnetic field measuring device capable of measuring a weaker magnetic field.

In order to solve the above problems, in the first aspect of the present invention, a magnetic field measuring device is provided. The magnetic field measuring device may include a sensor unit having at least one magnetoresistive element. The magnetic field measuring device may include a reference voltage generating unit that outputs a reference voltage. The magnetic field measuring device may include a magnetic field generating unit that generates a magnetic field applied to the sensor unit. The magnetic field measuring device may include a feedback current generating unit that supplies a feedback current that generates a feedback magnetic field that reduces the input magnetic field to the sensor unit to the magnetic field generating unit according to the difference between the output voltage and the reference voltage of the sensor unit. .. The magnetic field measuring device may include a magnetic field measuring unit that outputs a measured value according to the feedback current. The magnetic field measuring device may include an adjusting unit that adjusts the reference voltage using the output voltage of the sensor unit.

The adjusting unit may adjust the reference voltage in the adjusting phase, and the magnetic field measuring unit may output a measured value according to the feedback current generated for the magnetic field to be measured in the measuring phase.

The reference voltage generating unit has at least one variable resistance, and the adjusting unit may adjust the reference voltage by changing the resistance value of the variable resistance.

The adjusting unit may adjust the reference voltage based on the feedback current.

The adjusting unit may adjust the reference voltage so that the measured value is within a predetermined range according to the adjusting magnetic field in response to the input of the adjusting magnetic field to the sensor unit.

The adjusting unit may adjust the reference voltage so as to reduce the dispersion value of the feedback current.

It also has a switching unit that switches whether to supply the feedback current to the magnetic field generation unit, and the adjustment unit adjusts the reference voltage using the output voltage of the sensor unit when the feedback current is not supplied to the magnetic field generation unit. It's okay.

In the state where the feedback current is not supplied to the magnetic field generation unit, the adjustment unit responds that the adjustment magnetic field is input to the sensor unit, and the difference between the output voltage and the reference voltage of the sensor unit depends on the adjustment magnetic field. The reference voltage may be adjusted so as to be within a predetermined range.

It further includes an adjustment current generator that generates an adjustment current, and the switching unit supplies the adjustment current to the magnetic field generator when the feedback current is not supplied to the magnetic field generator, and the adjustment unit adjusts to the magnetic field generator. The reference voltage may be adjusted using the output voltage of the sensor unit while the current is being supplied.

The adjusting unit may adjust the reference voltage based on the characteristics of the difference between the output voltage and the reference voltage of the sensor unit with respect to the adjusting current.

The magnetic field measuring unit may integrate and output the measured values in a predetermined period.

Before the measurement of the magnetic field to be measured by the magnetic field measuring unit, the adjusting unit may generate a reference voltage by the reference voltage generating unit to generate a reset magnetic field that magnetically saturates the magnetic resistance element by the feedback current generating unit.

Before the measurement of the magnetic field to be measured by the magnetic field measuring unit, the adjusting unit changes the resistance value of the variable resistance of the reference voltage generating unit to generate the reset magnetic field generating voltage to generate the reset magnetic field by the reference voltage generating unit. The reference voltage may be adjusted based on the resistance value of the variable resistance that generates the reset magnetic field generated voltage.

The adjusting unit adjusts the reference voltage by setting the resistance value of the variable resistance as a resistance value of 1/2 to 1/4 of the range of the upper reset magnetic field generation resistance value and the lower magnetic field generation resistance value that generate the reset magnetic field generation voltage, respectively. You can do it.

The range of the output voltage of the reference voltage generating unit may be larger than the range of the output voltage of the sensor unit.

Prior to the measurement of the magnetic field to be measured by the magnetic field measuring unit, the magnetic field generating unit may further be provided with a reset current generating unit that supplies a reset current that generates a reset magnetic field that magnetically saturates the magnetic resistance element.

A high-pass filter for passing a high-frequency component of the measured value output by the magnetic field measuring unit may be further provided.

The feedback current generating unit may be configured by using two or more operational amplifiers.

The sensor unit includes a magnetic convergence unit arranged adjacent to the magnetoresistive element, and the feedback current generation unit may be formed so as to surround the magnetoresistive element and the magnetic convergence unit.

In the magnetoresistive element, a magnetization free layer, a non-magnetic layer, and a magnetization fixing layer are laminated in this order on a substrate, and the area of the magnetization fixing layer is smaller than the area of the magnetization free layer in the top view, and the magnetization is fixed. The magnetizing area may be determined based on the area of the layer.

The sensor unit has a first magnetoresistive element and a second magnetoresistive element connected in series and having opposite polarities to each other, and may output a voltage between the first magnetoresistive element and the second magnetoresistive element.

In the second aspect of the present invention, a magnetic field measuring device provides a magnetic field measuring method for measuring a magnetic field. In the magnetic field measuring method, the magnetic field measuring device reduces the input magnetic field to the sensor unit according to the difference between the output voltage of the sensor unit having at least one magnetic resistance element and the reference voltage output by the reference voltage generating unit. The feedback current that generates the above may be provided to supply the magnetic field generating unit that generates the magnetic field applied to the sensor unit. The magnetic field measuring method may include the magnetic field measuring device to output a measured value according to the feedback current. The magnetic field measuring method may include the magnetic field measuring device adjusting the reference voltage based on the output voltage of the sensor unit.

In the third aspect of the present invention, a magnetic field measurement program is provided. The magnetic field measurement program may be executed by a computer. The magnetic field measurement program causes the computer to generate a feedback magnetic field that reduces the input magnetic field to the sensor unit according to the difference between the output voltage of the sensor unit having at least one magnetic resistance element and the reference voltage output by the reference voltage generator unit. The feedback current to be generated may function as a feedback current generating unit that supplies the magnetic field generating unit that generates the magnetic field applied to the sensor unit. The magnetic field measurement program may allow the computer to function as a magnetic field measurement unit that outputs a measured value according to the feedback current. The magnetic field measurement program may allow the computer to function as a regulator that adjusts the reference voltage using the output voltage of the sensor.

The outline of the above invention does not list all the necessary features of the present invention. A subcombination of these feature groups can also be an invention.

The configuration of the magnetic field measuring device 10 according to this embodiment is shown. In the magnetic field measuring device 10 according to the present embodiment, an example in which the reference voltage generating unit 120 has at least one variable resistor is shown. The flow of the first example of the magnetic operating point adjustment by the magnetic field measuring apparatus 10 which concerns on this embodiment is shown. The characteristics of the voltage Vopen with respect to the input magnetic field Bin before and after the magnetic operating point adjustment based on the flow of FIG. 3 by the magnetic field measuring device 10 according to the present embodiment are shown. The flow of the second example of the magnetic operating point adjustment by the magnetic field measuring apparatus 10 which concerns on this embodiment is shown. The characteristics of the voltage Vopen with respect to the input magnetic field Bin before and after the magnetic operating point adjustment based on the flow of FIG. 5 by the magnetic field measuring device 10 according to the present embodiment are shown. The configuration of the magnetic field measuring device 10 provided with the switching unit 710 according to the modification of the magnetic field measuring device 10 of the present embodiment is shown. The flow of the third example of the magnetic operating point adjustment by the magnetic field measuring apparatus 10 of FIG. 7 is shown. The characteristics of the voltage Vopen with respect to the input magnetic field Bin before and after the magnetic operating point adjustment based on the flow of FIG. 8 by the magnetic field measuring device 10 of FIG. 7 are shown. The configuration of the magnetic field measuring device 10 including the switching unit 710 and the adjusting current generating unit 1010 according to the modified example of the magnetic field measuring device 10 of the present embodiment is shown. The flow of the 4th example of the magnetic operating point adjustment by the magnetic field measuring apparatus 10 of FIG. 10 is shown. The characteristics of the voltage Vopen with respect to the input magnetic field Bin before and after the magnetic operating point adjustment based on the flow of FIG. 11 by the magnetic field measuring device 10 of FIG. 10 are shown. The adjusting unit 170 in the magnetic field measuring device 10 of FIG. 10 shows the characteristics of the voltage Vopen with respect to the adjusting current Iadjust used for calculating the voltage Vopen_adjust. The adjusting unit 170 in the magnetic field measuring device 10 of FIG. 10 shows the dVopen / dIadjust characteristic used for calculating the voltage Vopen_adjust. The flow for measuring the magnetic field by the magnetic field measuring apparatus 10 which concerns on this embodiment is shown. The configuration of the magnetic field measuring device 10 including the switching unit 710 and the reset current generating unit 1610 according to the modified example of the magnetic field measuring device 10 of the present embodiment is shown. In the magnetic field measuring device 10 according to the present embodiment, the state of the change of the voltage Vclosed when the resistance value of the variable resistance 224 is changed is shown. The configuration of the magnetic field measuring device 10 provided with the switch 1710 and the high-pass filter 1720 according to the modified example of the magnetic field measuring device 10 of the present embodiment is shown. The configuration of the magnetic field measuring device 10 provided with the third arithmetic amplifier 1910 according to the modification of the magnetic field measuring device 10 of this embodiment is shown. A specific example of the sensor unit 110 according to this embodiment is shown. The magnetic flux distribution when the feedback magnetic field is generated in the sensor unit 110 according to this specific example is shown. An example of the configuration of the sensor unit 110 according to this specific example is shown. An example of a computer 2200 in which a plurality of aspects of the present invention may be embodied in whole or in part is shown.

Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention within the scope of the claims. Also, not all combinations of features described in the embodiments are essential to the means of solving the invention.

FIG. 1 shows the configuration of the magnetic field measuring device 10 according to the present embodiment. The magnetic field measuring device 10 includes a sensor unit 110, a reference voltage generating unit 120, a feedback current generating unit 130, a magnetic field generating unit 140, and a calculation unit 150.

The sensor unit 110 has at least one magnetoresistive element. In the present embodiment, as an example, the sensor unit 110 has a first magnetic resistance element 112 and a second magnetic resistance element 114 connected in series between the power supply voltage Vcc and the ground GND, and has a first magnetic resistance. An example of outputting a voltage between the element 112 and the second magnetic resistance element 114 is shown. Instead, in the sensor unit 110, for example, one of the first magnetic resistance element 112 and the second magnetic resistance element 114 is fixed. It may be composed of resistors, and includes various aspects of outputting a voltage corresponding to a magnetic field input to at least one magnetic resistance element.

However, the sensor unit 110 has a first magnetoresistive element 112 and a second magnetoresistive element 114 of opposite polarities connected in series, and the voltage between the first magnetoresistive element 112 and the second magnetoresistive element 114. Is more preferable because it is possible to obtain the effect of reducing characteristic fluctuations such as offset and sensitivity due to temperature. Here, the reverse polarity means that the increasing / decreasing direction of the resistance of the magnetoresistive element is opposite to the input magnetic field in the same direction.

The first magnetoresistive element 112 and the second magnetoresistive element 114 may be, for example, a tunnel magnetoresistive (TMR) element or a giant magnetoresistive (GMR) element.

The reference voltage generation unit 120 outputs a reference voltage. The reference voltage generation unit 120 is configured so that the output reference voltage can be adjusted. The reference voltage generation unit 120 supplies the adjusted reference voltage to the feedback current generation unit 130.

The feedback current generation unit 130 generates a feedback current that generates a feedback magnetic field that reduces the input magnetic field to the sensor unit 110 according to the difference between the output voltage of the sensor unit 110 and the reference voltage output by the reference voltage generation unit 120. Supply to unit 140. In the present embodiment, as an example, the feedback current generation unit 130 has a first operational amplifier 132, and the output voltage and reference voltage generation unit of the sensor unit 110 are connected to the two differential input terminals of the first operational amplifier 132. Each of the 120 outputs (ie, reference voltage) is connected. Then, the first operational amplifier 132 generates a feedback current according to the difference between the output voltage and the reference voltage of the sensor unit 110, and supplies this to the magnetic field generation unit 140. Here, the difference between the output voltage and the reference voltage of the sensor unit 110 is defined as Vopen.

The magnetic field generation unit 140 generates a feedback magnetic field applied to the sensor unit 110. In the present embodiment, as an example, the magnetic field generating unit 140 has a coil 142. When the feedback current is supplied from the feedback current generation unit 130, the coil 142 generates a feedback magnetic field applied to the first magnetic resistance element 112 and the second magnetic resistance element 114 of the sensor unit 110 based on the supplied feedback current. do. Here, the sensor unit 110 (and the reference voltage generation unit 120) may be positioned so as to be included in the coil 142.

The calculation unit 150 includes a current-voltage conversion resistor 152, a second calculation amplifier 154, an AD converter 156, a magnetic field measurement unit 160, and an adjustment unit 170, and performs various calculations related to the magnetic field measurement device 10.

One end of the current-voltage conversion resistance 152 is connected to the magnetic field generator 140 and the other end is connected to the fixed voltage 1. The resistance value of the voltage conversion resistor 152) is generated. Here, the voltage based on the feedback current generated by the current-voltage conversion resistance 152 is defined as Vclosed.

The second operational amplifier 154 connects both ends of the current-voltage conversion resistor 152 to the differential input terminal, and outputs the voltage across the current-voltage conversion resistor 152, that is, the voltage VAMP corresponding to the voltage Vclosed.

The AD converter 156 is connected to the second operational amplifier 154 and converts the analog voltage value VAMP corresponding to the voltage Vclosed output by the second operational amplifier 154 into the digital value VADC.

The magnetic field measurement unit 160 outputs a measured value according to the feedback current in the measurement phase. In the present embodiment, as an example, the magnetic field measuring unit 160 is connected to the AD converter 156 and outputs a measured value based on the digital value VADC corresponding to the voltage Vclosed converted by the AD converter 156.

In the adjustment phase, the adjustment unit 170 adjusts the reference voltage output by the reference voltage generation unit 120 using the output voltage of the sensor unit 110. This will be described later. In the above description, the case where the magnetic field measuring unit 160 and the adjusting unit 170 are configured as separate functional units is shown as an example, but the magnetic field measuring unit 160 and the adjusting unit 170 are configured as an integrated functional unit. You may.

According to the magnetic field measuring device 10 according to the present embodiment, when the magnetic field to be measured is input to the sensor unit 110, it corresponds to the difference between the output voltage and the reference voltage of the sensor unit 110 according to the magnetic field to be measured (that is, voltage Vopen). Then, the feedback current generation unit 130 generates a feedback current and supplies it to the magnetic field generation unit 140. Then, the magnetic field generation unit 140 generates a feedback magnetic field that cancels the measurement target magnetic field input to the sensor unit 110 according to the supplied feedback current. Then, in the measurement phase, the magnetic field measuring unit 160 outputs a measured value corresponding to the feedback current generated with respect to the magnetic field to be measured, specifically, a digital value VADC corresponding to the voltage Vclosed. Here, this series of controls is defined as closed-loop control. Under closed-loop control, the value of the voltage Vopen is controlled to be 0, that is, a feedback magnetic field that cancels the input magnetic field is generated.

FIG. 2 shows an example in which the reference voltage generating unit 120 has at least one variable resistor in the magnetic field measuring device 10 according to the present embodiment. As shown in this figure, the reference voltage generator 120 has at least one variable resistor. As an example, the reference voltage generator 120 has a fixed resistance 222 and a variable resistance 224 connected in series between the power supply voltage Vcc and the ground GND, and the voltage between the fixed resistance 222 and the variable resistance 224 is used as a reference voltage. It may be configured to output as. Further, as shown in this figure, the bridge circuit 210 is composed of the first magnetoresistive element 112 of the sensor unit 110, the second magnetoresistive element 114, the fixed resistance 222 of the reference voltage generating unit 120, and the variable resistance 224. You can do it. In addition, in the reference voltage generation unit 120, the fixed resistance 222 is a magnetic resistance element having the same polarity as the second magnetic resistance element 114 (opposite to the first magnetic resistance element 112), and the variable resistance 224 is a first magnetic resistance element. A magnetic resistance element having the same polarity as 112 (opposite to the second magnetic resistance element 114) and a variable resistor may be connected in series. When the reference voltage generating unit 120 has a variable resistance, the adjusting unit 170 changes the resistance value of the variable resistance to adjust the reference voltage (reference voltage as the resistance dividing voltage) output by the reference voltage generating unit 120.

FIG. 3 shows a flow of a first example of magnetic operating point adjustment by the magnetic field measuring device 10 according to the present embodiment. The magnetic operating point is defined as the sum of the magnetic fields input to the magnetoresistive element constituting the magnetic field measuring device 10 according to the present embodiment. In step 310, for example, the measurer sets the input magnetic field input to the sensor unit 110 to an adjustment magnetic field which is a predetermined value for adjusting the magnetic operating point. Here, the adjusting magnetic field may have an arbitrary value within the magnetic field range in which the sensor unit 110 can magnetically detect. In the following, a case where the adjusting magnetic field is 0 will be described. When the adjustment magnetic field is 0, for example, the measurer shields the environmental magnetic field such as geomagnetism by placing the magnetic field measuring device 10 according to the present embodiment in a magnetic shield room or a portable magnetic shield box. The input magnetic field input to the sensor unit 110 is set to 0.

Next, in step 320, the adjusting unit 170 acquires a digital value VADC based on the voltage Vclosed in a state where the adjusting magnetic field, which is a predetermined value, is input to the sensor unit 110.

Then, in step 330, the adjusting unit 170 adjusts the reference voltage output by the reference voltage generating unit 120 based on the feedback current. In this flow, in the adjusting unit 170, the measured value, for example, the digital value VADC based on the voltage Vclosed, is set to a predetermined value according to the adjusting magnetic field in response to the input of the adjusting magnetic field to the sensor unit 110. The reference voltage output by the reference voltage generation unit 120 is adjusted so as to be within the range of, and the process is terminated. As an example, the adjusting unit 170 sets the voltage Vclosed to 0 when the adjusting magnetic field input to the sensor unit 110 is 0, for example, setting the digital value VADC based on the voltage Vclosed to be equal to or less than a predetermined threshold value. The reference voltage output by the reference voltage generation unit 120 is adjusted so as to be. When the adjusting magnetic field is not 0, the adjusting unit 170 adjusts the reference voltage output by the reference voltage generating unit 120 so that the voltage Vclosed becomes a value corresponding to the strength of the adjusting magnetic field. In the closed loop, the voltage Vclosed and the voltage VAMP uniquely correspond to each other and may be treated as equivalent physical quantities.

FIG. 4 shows the characteristics of the voltage Vopen with respect to the input magnetic field Bin before and after the magnetic operating point adjustment based on the flow of FIG. 3 by the magnetic field measuring device 10 according to the present embodiment. The curve 410 shows the characteristics of the voltage Vopen with respect to the input magnetic field Bin to the sensor unit 110 before the magnetic operating point adjustment based on the flow of FIG. For example, when the input magnetic field Bin to the sensor unit 110 is 0, the value of Vopen should be 0 if the output voltage and the reference voltage of the sensor unit 110 are ideally the same value. However, the output voltage of the sensor unit 110 and the reference voltage output by the reference voltage generation unit 120 are fixed, for example, of the first magnetic resistance element 112 and the second magnetic resistance element 114 of the sensor unit 110 and the reference voltage generation unit 120. The values of the resistors 222 and the variable resistors 224 are not necessarily the same ideally due to variations in the element forming process and the like. As a result, even if the input magnetic field Bin is 0, the value of the voltage Vopen does not become 0, and can take a finite value (referred to as “Vitial”) as shown at point 420, for example. The magnetic operating point at this time is point 420.

In this state, when the closed loop control is performed, the feedback current generation unit 130 generates a feedback current Ifedback_initial corresponding to the voltage Vinyl, and supplies this to the magnetic field generation unit 140. Then, the magnetic field generation unit 140 generates a feedback magnetic field Bfeedback_initial so that the voltage Vopen becomes 0 based on this feedback current Ifedback_initial. That is, due to the feedback magnetic field Bfeedback_initial, the voltage Vopen becomes 0, and the magnetic operating point transitions from the point 420 to the point 430. In this state, when the magnetic field measuring device 10 measures the magnetic field to be measured, the first magnetic resistance element 112 and the second magnetic resistance element 114 measure the magnetic field with the point 430 as the magnetic operating point.

However, the characteristics of the voltage Vopen with respect to the input magnetic field Bin have a magnetic saturation region as shown in FIG. 4, according to the magnetic saturation characteristics of the first magnetoresistive element 112 and the second magnetoresistive element 114 possessed by the sensor unit 110. When the first magnetoresistive element 112 and the second magnetoresistive element 114 are operated in the magnetic saturation region or a region close to the magnetic saturation region, high magnetic sensitivity (rate of change of voltage Vopen with respect to the magnetic field Bin) cannot be obtained and is weak. It becomes impossible to detect the magnetic field to be measured. Therefore, the magnetic field measuring device 10 in the present embodiment adjusts the magnetic operating points of the first magnetic resistance element 112 and the second magnetic resistance element 114 in the adjustment phase before the measurement phase, thereby adjusting the first magnetic resistance element 112. And the second magnetic resistance element 114 can be operated at a point having a relatively high magnetic sensitivity, that is, a high magnetic resolution.

Curve 440 shows the characteristics of the voltage Vopen with respect to the input magnetic field Bin to the sensor unit 110 after the magnetic operating point adjustment based on the flow of FIG. According to the magnetic field measuring device 10 according to the present embodiment, the operating points of the first magnetoresistive element 112 and the second magnetoresistive element 114 are changed from the point 430 to the point 450 by adjusting the magnetic operating points based on the flow of FIG. be able to. This point 450 is a point where the voltage Vclosed is 0, that is, the feedback current is 0 when the input magnetic field Bin is 0, and when the first magnetoresistive element 112 and the second magnetoresistive element 114 are operated at this point, The highest magnetic sensitivity can be obtained.

In the conventional magnetic sensor using a bridge circuit composed of one TMR element and three fixed resistors, the magnetic sensitivity of the magnetic operating point of the TMR element is lowered due to variations in the element forming process of the TMR element and the fixed resistance. It was sometimes located within the magnetic saturation region. On the other hand, according to the magnetic field measuring device 10 of the present embodiment, the magnetic operating points of the first magnetoresistive element 112 and the second magnetoresistive element 114 can be transitioned to points having relatively high magnetic sensitivity. It is possible to detect a weak magnetic field to be measured as a signal.

FIG. 5 shows a flow of a second example of magnetic operating point adjustment by the magnetic field measuring device 10 according to the present embodiment. The magnetic operating point adjustment by this flow is different from the magnetic operating point adjustment by the flow of FIG. 3, and it is not necessary to set the input magnetic field Bin input to the sensor unit 110 to the adjustment magnetic field which is a predetermined value. That is, for example, it is not necessary for the measurer to place the magnetic field measuring device 10 in a shield room or a portable shield box and set the input magnetic field input to the sensor unit 110 to zero. In step 510, the adjusting unit 170 acquires a digital value VADC based on the voltage Vclosed. The input magnetic field input to the sensor unit 110 at this point is not a predetermined known value as described above, but an unknown value.

Next, in step 520, the adjusting unit 170 calculates the dispersion value of the voltage Vclosed acquired in step 510. Here, the dispersion value is the magnitude of variation in the value that the voltage Vclosed can take in a predetermined period. For example, the adjusting unit 170 acquires the value of the voltage Vclosed in a predetermined period, calculates the average value thereof, squares the difference between the value of each Vclosed and the average value, and takes the average to distribute the voltage Vclosed. You may calculate the value.

Then, in step 530, the adjusting unit 170 adjusts the reference voltage output by the reference voltage generating unit 120 so as to reduce the dispersion value of the voltage Vclosed, and ends the process. As an example, the adjusting unit 170 adjusts the reference voltage output by the reference voltage generating unit 120 so that the dispersion value of the voltage Vclosed calculated in step 520 is minimized. Since the voltage Vclosed is the one in which the feedback current is converted into a voltage via the current-voltage conversion resistance 152, minimizing the dispersion value of the voltage Vclosed means minimizing the dispersion value of the feedback current. It corresponds.

FIG. 6 shows the characteristics of the voltage Vopen with respect to the input magnetic field Bin before and after the magnetic operating point adjustment based on the flow of FIG. 5 by the magnetic field measuring device 10 according to the present embodiment. The parts with the same reference numerals as those in FIG. 4 are the same as those in FIG. 4, and the description thereof will be omitted. The difference from FIG. 4 is that the input magnetic field Bin input to the sensor unit 110 has a certain finite unknown value (referred to as “Bsignal”) instead of a known value.

In this state, when the closed loop control is performed, the feedback current generation unit 130 generates a feedback current Ifedback for canceling the magnetic field Bsignal in addition to the feedback current Ifedback_initial according to the voltage Vinyl, and these are generated by the magnetic field generation unit. Supply to 140. Then, based on these feedback currents, the magnetic field generation unit 140 generates a feedback magnetic field Bfeedback_initial so as to make the voltage Vopen 0, and also generates a feedback magnetic field Bfeedback so as to cancel the magnetic field Bsignal. Also in this case, the magnetic operating points of the first magnetoresistive element 112 and the second magnetoresistive element 114 are the points 430, as in FIG. Here, the adjusting unit 170 adjusts the reference voltage output by the reference voltage generating unit 120 in order to adjust the magnetic operating points of the first magnetic resistance element 112 and the second magnetic resistance element 114 based on the feedback current. However, the adjusting unit 170 cannot distinguish the feedback current into Ifedback_initial and Ifedback.

Therefore, in the present embodiment, the adjusting unit 170 adjusts the reference voltage based on the dispersion value of the voltage Vclosed. In general, the magnetic sensitivity of a magnetoresistive element decreases as it approaches the magnetic saturation point, so that the ratio of output fluctuation (output uncertainty) to magnetic sensitivity increases (that is, the signal noise ratio in magnetic detection decreases. ) Has characteristics. Further, in the present embodiment, the feedback current generated by the feedback current generation unit 130 is based on the output voltage of the sensor unit 110 having the first magnetic resistance element 112 and the second magnetic resistance element 114, and therefore the first magnetism. It reflects the signal noise ratio in the magnetic detection of the resistance element 112 and the second magnetic resistance element 114. For example, as the first magnetoresistive element 112 and the second magnetoresistive element 114 approach the magnetic saturation point, the signal noise ratio decreases, so that the fluctuation of the feedback current also increases accordingly. Therefore, if the reference voltage is adjusted so as to reduce the fluctuation of the feedback current, the magnetic operating points of the first magnetoresistive element 112 and the second magnetoresistive element 114 are located farthest from the magnetic saturation point, that is, the highest magnetism. It is possible to make a transition to a point having sensitivity. Using this principle, the adjusting unit 170 adjusts the reference voltage output by the reference voltage generating unit 120 so as to reduce the distributed value of the voltage Vclosed that reflects the dispersion value of the feedback current, and the first magnetic resistance element 112. And the magnetic operating point of the second magnetoresistive element 114 is transitioned to a point having a relatively high magnetic sensitivity.

Curve 640 shows the characteristics of the voltage Vopen with respect to the input magnetic field Bin to the sensor unit 110 after the magnetic operating point adjustment based on the flow of FIG. According to the magnetic field measuring device 10 according to the present embodiment, the magnetic operating points of the first magnetoresistive element 112 and the second magnetoresistive element 114 are changed from the points 430 to the points 650 by adjusting the magnetic operating points based on the flow of FIG. Can be made to. At this point 650, the dispersion value of the voltage Vclosed is minimized, that is, the dispersion value of the feedback current is minimized, and the first magnetoresistive element 112 and the second magnetoresistive element 114 are operated at this point. And the highest magnetic sensitivity can be obtained.

In the above description, a method of reducing the dispersion value of the voltage Vclosed that reflects the dispersion value of the feedback current has been described as an example, but the present invention is not limited to this. The magnetic field measuring device 10 may adjust the reference voltage so as to reduce the peak-to-peak value of the signal amplitude of the voltage Vclosed, for example, instead of the dispersion value of the voltage Vclosed. Alternatively, the magnetic field measuring device 10 uses, for example, a signal analyzer (or FFT analyzer, etc.) to measure the measurement data of the voltage Vclosed on the time axis, and the signal intensity frequency dependence of the voltage Vclosed (for example, the frequency dependence of the power density, etc.). .) May be monitored. Since the signal intensity frequency dependence of this voltage Vclosed represents the signal intensity frequency dependence of the output fluctuation of the magnetic resistance element, the magnetic field measuring device 10 reduces the level of the signal intensity frequency dependence of the fluctuation. The reference voltage may be adjusted so as to cause. Note that this method for analyzing frequency dependence can be implemented with a processor such as a microcomputer without using a signal analyzer.

FIG. 7 shows the configuration of the magnetic field measuring device 10 provided with the switching unit 710 according to the modified example of the magnetic field measuring device 10 of the present embodiment. The magnetic field measuring device 10 in this figure further includes a switching unit 710 in addition to the magnetic field measuring device 10 in FIG. The switching unit 710 is provided between the feedback current generation unit 130 and the magnetic field generation unit 140, and can switch whether or not to supply the feedback current generated by the feedback current generation unit 130 to the magnetic field generation unit 140. Further, the switching unit 710 can supply the output of the feedback current generation unit 130 to the AD converter 156 when the feedback current is not supplied to the magnetic field generation unit 140. In this case, the adjusting unit 170 adjusts the reference voltage output by the reference voltage generating unit 120 by using the output voltage of the sensor unit 110 in a state where the feedback current is not supplied to the magnetic field generating unit 140.

FIG. 8 shows a flow of a third example of magnetic operating point adjustment by the magnetic field measuring device 10 of FIG. 7. Here, the state in which closed loop control is not performed is defined as an open loop. In step 810, the switching unit 710 switches from the closed loop control to a state in which the feedback current is not supplied to the magnetic field generating unit 140, that is, to an open loop. Further, the switching unit 710 supplies the output of the feedback current generation unit 130 to the AD converter 156.

In step 820, as in step 310 of FIG. 3, for example, the measurer sets the input magnetic field input to the sensor unit 110 to an adjustment magnetic field which is a predetermined value for adjusting the magnetic operating point. Also here, the adjustment magnetic field is preferably 0. In the following, a case where the adjusting magnetic field is 0 will be described.

Next, in step 830, the adjusting unit 170 acquires the value of the voltage Vopen in a state where the adjusting magnetic field, which is a predetermined value, is input to the sensor unit 110. As an example, the adjusting unit 170 acquires a digital value VADC based on the voltage Vopen by converting the output of the feedback current generating unit 130 into digital by the AD converter 156. In the open loop, the voltage Vopen and the digital value VADC uniquely correspond to each other and may be treated as equivalent physical quantities.

Then, in step 840, the adjusting unit 170 receives the adjustment magnetic field input to the sensor unit 110 in a state where the feedback current is not supplied to the magnetic field generating unit 140, and the output voltage and reference of the sensor unit 110. The process is terminated by adjusting the reference voltage output by the reference voltage generation unit 120 so that the voltage Vopen, which is the difference between the reference voltages output by the voltage generation unit 120, is within a range determined according to the adjustment magnetic field. As an example, the adjusting unit 170 sets the voltage Vopen to 0 when the adjusting magnetic field input to the sensor unit 110 is 0, for example, so that the absolute value of the voltage Vopen is equal to or less than a predetermined threshold value. In addition, the reference voltage output by the reference voltage generation unit 120 is adjusted.

FIG. 9 shows the characteristics of the voltage Vopen with respect to the input magnetic field Bin before and after the magnetic operating point adjustment based on the flow of FIG. 8 by the magnetic field measuring device 10 of FIG. The parts with the same reference numerals as those in FIG. 4 are the same as those in FIG. 4, and the description thereof will be omitted. The difference from FIG. 4 is that the magnetic field measuring device 10 adjusts the magnetic operating point under an open loop.

When the switching unit 710 switches from the closed loop control to the open loop, the feedback magnetic field Bfeedback_initial does not occur, so that the magnetic operating points of the first magnetoresistive element 112 and the second magnetoresistive element 114 shift from the point 430 to the point 420. do. In this state, for example, when the input magnetic field input to the sensor unit 110 is 0, the adjusting unit 170 adjusts the reference voltage output by the reference voltage generating unit 120 in order to set the voltage Vopen to 0. Curve 940 shows the characteristics of the voltage Vopen with respect to the input magnetic field Bin to the sensor unit 110 after the magnetic operating point adjustment based on the flow of FIG. According to the magnetic field measuring device 10 of FIG. 7, the magnetic operating points of the first magnetoresistive element 112 and the second magnetoresistive element 114 are changed from the points 420 to the points 950 by adjusting the magnetic operating points based on the flow of FIG. Can be done. This point 950 is a point where the voltage Vopen becomes 0 when the input magnetic field Bin is 0, and the magnetic field measuring device 10 of FIG. 7 switches from the open loop to the closed loop in this state and switches to the first magnetic resistance element 112 and The highest magnetic sensitivity can be obtained by operating the second magnetoresistive element 114.

FIG. 10 shows the configuration of the magnetic field measuring device 10 including the switching unit 710 and the adjusting current generating unit 1010 according to the modified example of the magnetic field measuring device 10 of the present embodiment. The magnetic field measuring device 10 in this figure further includes an adjusting current generating unit 1010 in addition to the magnetic field measuring device 10 in FIG. 7. The adjusting current generation unit 1010 generates the adjusting current Iadjust. Further, when the switching unit 710 of the magnetic field measuring device 10 in this figure does not supply the feedback current to the magnetic field generating unit 140, the output of the feedback current generating unit 130 is supplied to the AD converter 156 and the magnetic field generating unit 140 is supplied. The adjustment current can be supplied to the magnetic field generation unit 140 by connecting to the adjustment current generation unit 1010. In this case, the adjusting unit 170 adjusts the reference voltage output by the reference voltage generating unit 120 by using the output voltage of the sensor unit 110 in a state where the adjusting current is supplied to the magnetic field generating unit 140.

FIG. 11 shows a flow of a fourth example of magnetic operating point adjustment by the magnetic field measuring device 10 of FIG. In step 1110, the switching unit 710 switches from the closed loop control to the open loop in the same manner as in step 810. Further, the switching unit 710 supplies the output of the feedback current generation unit 130 to the AD converter 156, connects the magnetic field generation unit 140 to the adjustment current generation unit 1010, and supplies the adjustment current to the magnetic field generation unit 140. do.

In step 1120, the adjusting unit 170 acquires the value of the voltage Vopen while changing the magnitude of the adjusting current Iadjust generated by the adjusting current generating unit 1010, and the characteristic of the voltage Vopen with respect to the adjusting current Iadjust (Vopen). (Vs. Iadjust characteristic) is acquired.

In step 1130, the adjusting unit 170 calculates the voltage Vopen_adjust from the characteristics of the voltage Vopen with respect to the adjusting current acquired in step 1120. The calculation method of the voltage Vopen_adjust will be described later.

In step 1140, the adjusting unit 170 adjusts the reference voltage output by the reference voltage generating unit 120 based on the characteristics of the voltage Vopen, which is the difference between the output voltage of the sensor unit 110 and the reference voltage with respect to the adjusting current, and ends the process. do. As an example, the adjusting unit 170 adjusts the reference voltage output by the reference voltage generating unit 120 so that the voltage Vopen becomes the voltage Vopen_adjust calculated in step 1130. Alternatively, the adjusting unit 170 may adjust the reference voltage output by the reference voltage generating unit 120 so that the voltage Vopen_adjust becomes 0.

FIG. 12 shows the characteristics of the voltage Vopen with respect to the input magnetic field Bin before and after the magnetic operating point adjustment based on the flow of FIG. 11 by the magnetic field measuring device 10 of FIG. The parts with the same reference numerals as those in FIG. 9 are the same as those in FIG. 9, and the description thereof will be omitted. The difference from FIG. 9 is that the input magnetic field Bin is not 0 but has a certain finite value (referred to as “Bsignal”).

The switching unit 710 switches from the closed loop control to the open loop in a state where the magnetic field generating unit 140 generates the feedback magnetic fields Bfeedback_initial and Bfeedback based on the feedback current. Then, since the feedback magnetic fields Bfeedback_initial and Bfeedback do not occur, the magnetic operating points of the first magnetoresistive element 112 and the second magnetoresistive element 114 transition to the point 1210 based on the magnetic field Bsignal. In this state, the adjusting unit 170 adjusts the reference voltage output by the reference voltage generating unit 120 by adjusting the magnetic operating point based on the flow of FIG. Curve 1220 shows the characteristics of the voltage Vopen with respect to the input magnetic field Bin to the sensor unit 110 after the magnetic operating point adjustment based on the flow of FIG. 11 by the magnetic field measuring device 10 of FIG. According to the magnetic field measuring device 10 of FIG. 10, the magnetic operating points of the first magnetoresistive element 112 and the second magnetoresistive element 114 are changed from the points 1210 to the points 1230 by adjusting the magnetic operating points based on the flow of FIG. Can be done. This point 1230 is a point where the voltage Vopen = Vopen_adjust, and the magnetic field measuring device 10 in FIG. 10 switches from the open loop to the closed loop to operate the first magnetoresistive element 112 and the second magnetoresistive element 114 in this state. The highest magnetic sensitivity can be obtained.

FIG. 13 shows the characteristics of the voltage Vopen with respect to the adjusting current Iadjust used by the adjusting unit 170 in the magnetic field measuring device 10 of FIG. 10 to calculate the voltage Vopen_adjust. The adjusting unit 170 acquires the voltage Vopen characteristic with respect to the adjusting current Iadjust as shown in, for example, the curve 1320 by step 1120 of FIG. Then, the adjusting unit 170 calculates the voltage Vopen_adjust based on the curve 1320. As an example, the adjusting unit 170 acquires the voltage Vopen_max at which the voltage Vopen is maximum and the voltage Vopen_min at which the voltage Vopen is minimum from the curve 1320, and calculates the average value of the voltage Vopen_max and Vopen_min as the voltage Vopen_adjust.

FIG. 14 shows the characteristics of dVopen / dIadjust used by the adjusting unit 170 in the magnetic field measuring device 10 of FIG. 10 to calculate the voltage Vopen_adjust. The adjusting unit 170 differentiates the curve 1320 by the adjusting current Iadjust to obtain the characteristics of dVopen / dIadjust with respect to the adjusting current Iadjust, for example, as shown in the curve 1410. Then, the adjusting unit calculates the voltage Vopen at the point 1420 where dVopen / dIadjust is maximized as the voltage Vopen_adjust.

FIG. 15 shows a flow for measuring a magnetic field by the magnetic field measuring device 10 according to the present embodiment. In step 1510, the magnetic field measuring device 10 magnetically resets the first magnetoresistive element 112 and the second magnetoresistive element 114. As an example, a reference in which the adjusting unit 170 generates a reset magnetic field that magnetically saturates the first magnetic resistance element 112 and the second magnetic resistance element 114 by the feedback current generation unit 130 before the measurement target magnetic field is measured by the magnetic field measurement unit 160. The voltage is generated by the reference voltage generation unit 120, and then the reference voltage is adjusted to the original value to stop the generation of the reset magnetic field by the magnetic field generation unit 140. A series of operations for applying a magnetically saturated reset magnetic field to the first magnetoresistive element 112 and the second magnetoresistive element 114 and then removing the magnetic field is defined as magnetic reset.

In general, in a magnetic resistance element, the magnetization in the magnetic domain can be oriented in various directions depending on the history of the input magnetism, but by performing a magnetic reset, the magnetization in the magnetic domain can be once aligned. Therefore, when the magnetic field measuring device 10 measures the magnetic field, the direction of magnetization in the magnetic domain can be measured under the same conditions each time, whereby the measurement error can be reduced. The above-mentioned magnetic reset operation is performed, for example, when the power of the magnetic field measuring device 10 is turned on, when the magnetic field measuring device 10 detects an unintended magnetic field, or when a predetermined period has elapsed since the previous magnetic reset was performed. , And when the magnetic field is measured a predetermined number of times since the last magnetic reset, etc., it can be executed.

Next, in step 1520, the adjusting unit 170 magnetically operates the first magnetoresistive element 112 and the second magnetoresistive element 114 based on at least one of the flows of FIGS. 3, 5, 8, and 11. Adjust the points.

Next, in step 1530, the magnetic field measuring unit 160 measures the magnetic field to be measured. Then, in step 1540, the magnetic field measuring device 10 determines whether or not the number of times the magnetic field is measured has become a predetermined number of times n (where n is an integer of 1 or more). As a result of the determination, when the number of times the magnetic field is measured is less than the predetermined number of times n, the magnetic field measuring device 10 returns the process to step 1530 and continues the process. On the other hand, as a result of the determination, when the number of measurements of the magnetic field is n or more, the magnetic field measuring device 10 advances the process to step 1550, and in step 1550, the magnetic field measuring unit 160 measures n times. The measured values in a predetermined period are integrated and output by accumulating the values, and the process is terminated. According to the present embodiment, the magnetic field measuring unit 160 can obtain a more accurate output by integrating and outputting the measured values n times.

In the above description, the magnetic field measuring device 10 has described an example in which the process is returned to step 1530 when the number of measurements is less than the predetermined number of times n in step 1540. The process may be returned to step 1520, as indicated by the dotted line 15. That is, the magnetic field measuring device 10 may adjust the magnetic operating points of the first magnetic resistance element 112 and the second magnetic resistance element 114 each time by the adjusting unit 170 each time the magnetic field measuring unit 160 measures the magnetic field. By adjusting the magnetic operating point each time by the adjusting unit 170, the first magnetoresistive element 112 and the second magnetoresistive element 114 can be operated at the magnetic operating point having higher magnetic sensitivity.

FIG. 16 shows the configuration of the magnetic field measuring device 10 including the switching unit 710 and the reset current generating unit 1610 according to the modified example of the magnetic field measuring device 10 of the present embodiment. The magnetic field measuring device 10 in this figure further includes a reset current generating unit 1610 in addition to the magnetic field measuring device 10 in FIG. 7. The reset current generation unit 1610 generates a reset current that magnetically saturates the first magnetic resistance element 112 and the second magnetic resistance element 114 in the magnetic field generation unit 140 before the magnetic field measurement unit 160 measures the measurement target magnetic field. Supply. In step 1510 in the flow of FIG. 15, an example of magnetically resetting the first magnetic resistance element 112 and the second magnetic resistance element 114 by the adjusting unit 170 has been shown, but as shown in this figure, the reset current generating unit 1610 is further added. The first magnetic resistance element 112 and the second magnetic resistance element 114 may be magnetically reset by generating a reset magnetic field based on the reset current supplied by the reset current generation unit 1610. Further, as shown in FIG. 10, when the magnetic field measuring device 10 has the adjusting current generating unit 1010, the function of the reset current generating unit 1610 may be realized by the adjusting current generating unit 1010. Further, the reset magnetic field can also be generated by changing the resistance value of the variable resistance 224 when the magnetic field measuring device 10 has the variable resistance 224 in the reference voltage generating unit 120. For example, as in the embodiment of FIG. 2, when the reference voltage generating unit 120 has a fixed resistance 222 and a variable resistance 224 and the resistance value of the variable resistance 224 is adjusted to generate a reset magnetic field, a reset current is generated. Since it is not necessary to use the part 1610, the system can be simplified. Here, in order to use the reference voltage for generating the reset magnetic field, it is preferable that the range of the output voltage of the reference voltage generating unit 120 is larger than the range of the output voltage of the sensor unit 110. The range of the output voltage is defined by the difference between the maximum value that the output voltage can take and the minimum value that the output voltage can take.

FIG. 17 is a diagram showing a state of change in voltage Vclosed when the resistance value of the variable resistor 224 is changed in the embodiment of FIG. 2. The voltage Vclosed has a small change when the variable resistance value is between Rsat, lo and Rsat, up, but becomes very large or small when the variable resistance value is Rsat, lo or less or Rsat, up or more. The output value of 160 (AD value of voltage Vclosed) causes an overflow (sticks to the upper or lower limit of the output). That is, when the variable resistance value is between Rsat, lo and Rsat, up, the closed loop of the magnetic field measuring device 10 operates normally, but when the variable resistance value is Rsat, lo or less or Rsat, up or more, it is magnetic. The magnetic field measuring device 10 does not operate as a closed loop because the resistance element is magnetically saturated and the input magnetic field to the sensor unit 110 cannot be normally canceled by the feedback magnetic field. Therefore, the magnetic reset of the magnetoresistive element can be performed by setting the variable resistance value to Rsat, lo or less or Rsat, up or more. Here, Rsat and up are defined as the upward reset magnetic field generation resistance value, and the output voltage of the reference voltage generating unit 120 at this time is defined as the upward reset magnetic field generation voltage. Further, Rsat and lo are set to the downward reset magnetic field generation resistance value, and the output voltage of the reference voltage generating unit 120 at this time is set to the downward reset magnetic field generating voltage.

The magnetic field measuring device 10 changes the variable resistance 224 of the reference voltage generating unit 120 when the output range of the voltage Vclosed operating as a closed loop (closed loop operation output range) is set from Vclosed, sat_up to Vclosed, sat_lo. The voltage Vclosed may be measured while allowing the voltage Vclosed to be measured, and the resistance values exceeding this output range may be detected as Rsat, up and Rsat, lo, respectively. Then, the adjusting unit 170 may adjust the magnetic operating point of the magnetoresistive element based on the upper reset magnetic field generation resistance value Rsat, up or the lower reset magnetic field generation resistance value Rsat, lo. The adjusting unit 170 may adjust the variable resistance 224 so that the magnetoresistive element becomes a magnetic operating point having theoretically high magnetic resolution, for example. The magnetic resolution of the magnetoresistive element is high in that the magnetic field input to the magnetoresistive element is zero. The resistance of such a magnetoresistive element (1 element) is a resistance value moved by about 1/2 to 1/4 from the low resistance side of the resistance change range with respect to the magnetic field. Therefore, the resistance value of the variable resistance 224 is ½ to 1/4 of the range of the upper reset magnetic field generation resistance values Rsat, up and the lower reset magnetic field generation resistance values Rsat, lo that generate the reset magnetic field generation voltage, respectively (for example,). The resistance value may be 1/4 or more and 1/2 or less). For example, when there are two magnetic resistance elements, the resistance value of the variable resistance 224 is set to the upper reset magnetic field generation resistance value Rsat, up and the lower reset magnetic field generation resistance value Rsat, lo in order to superimpose the symmetric resistance change curve with respect to the magnetic field. It may be an intermediate value (1/2) of. Further, for example, when there is one magnetic resistance element, the resistance value of the variable resistance 224 is set to 1/2 to 1/4 of the range of the upper reset magnetic field generation resistance value Rsat, up and the lower reset magnetic field generation resistance value Rsat, lo ( For example, the resistance value may be 1/4 or more and 1/2 or less). Since the magnetic field measuring device 10 can adjust the magnetic operating point of the magnetoresistive element by changing the variable resistance 224 in this way, the magnetoresistive element can be operated at a point having high magnetic resolution. In other words, the adjusting unit 170 changes the resistance value of the variable resistance 224 of the reference voltage generating unit 120 before measuring the measurement target magnetic field by the magnetic field measuring unit 160 to generate a reset magnetic field generation voltage ( The upper reset magnetic field generation voltage and the lower reset magnetic field generation voltage) are generated in the reference voltage generation unit 120, and the reference voltage is adjusted based on the resistance value of the variable resistance 224 that generates the reset magnetic field generation voltage. That is, the magnetic field measuring device 10 changes and detects the resistance value of the variable resistance 224 while measuring the voltage Vclosed so as to detect the upper reset magnetic field generation resistance value Rsat, up and the lower reset magnetic field generation resistance value Rsat, lo. The generated voltage of the reference voltage generation unit 120 is adjusted based on the upward reset magnetic field generation resistance values Rsat, up and the downward reset magnetic field generation resistance values Rsat, lo. At this time, the magnetic field measuring device 10 may first change the resistance value of the variable resistance 224 so as to detect the upper reset magnetic field generation resistance values Rsat, up, and first detect the lower reset magnetic field generation resistance values Rsat, lo. The resistance value of the variable resistance 224 may be changed so as to be used. When the MR ratio (MR ratio = Rsat, up / Rsat, lo) of the magnetic resistance element is known in advance, the magnetic field measuring device 10 has an upper reset magnetic field generation resistance value Rsat, up and a lower reset magnetic field generation resistance. After detecting either one of the values Rsat and lo, the generated voltage of the reference voltage generating unit 120 may be adjusted based on the known MR ratio.

FIG. 18 shows the configuration of the magnetic field measuring device 10 including the switch 1810 and the high-pass filter 1820 according to the modified example of the magnetic field measuring device 10 of the present embodiment. The magnetic field measuring device 10 in this figure includes a switch 1810 and a high-pass filter 1820 in addition to the magnetic field measuring device 10 of FIG. The switch 1810 is provided between the second operational amplifier 154 and the AD converter 156, and either directly supplies the output voltage VAMP of the second operational amplifier 154 to the AD converter 156, or outputs the output of the second operational amplifier as a high-pass filter. It switches whether to supply to the AD converter 156 via 1820. The high-pass filter 1820 passes the high-frequency component of the output voltage VAMP of the second operational amplifier 154 and supplies it to the AD converter 156.

By switching the switch 1810, the magnetic field measuring device 10 in the figure directly supplies the output voltage VAMP of the second operational amplifier 154 to the AD converter 156 without going through the high-pass filter 1820 in the adjustment phase, and in the measurement phase, The output voltage VAMP of the second operational amplifier 154 is supplied to the AD converter 156 via the high-pass filter 1820. As a result, when the magnetic field to be measured in the measurement phase is an AC component, unnecessary DC components can be blocked, and the magnetic field measuring unit 160 can measure the magnetic field to be measured with higher accuracy. ..

FIG. 19 shows a configuration of a magnetic field measuring device 10 provided with a third arithmetic amplifier 1910 according to a modified example of the magnetic field measuring device 10 of the present embodiment. The magnetic field measuring device 10 in this figure further includes a third arithmetic amplifier 1910 in addition to the magnetic field measuring apparatus 10 of FIG. 1, and the feedback current generating unit 130 is configured by using two or more arithmetic amplifiers. In the third operational amplifier 1910, one of the differential input terminals is connected to the output of the first operational amplifier 132, and the other is connected to the fixed voltage source 1920. The feedback current generation unit 130 in this figure outputs a voltage Vopen which is a difference between the output voltage and the reference voltage of the sensor unit 110 by the first operational amplifier 132, and the voltage Vopen and the fixed voltage 2 by the third operational amplifier 1910. A feedback current may be generated based on the difference between. Here, the fixed voltage 1 and the fixed voltage 2 may be set at the same voltage.

FIG. 20 shows a specific example of the sensor unit 110 according to the present embodiment. The sensor unit 110 includes a magnetoresistive element 2010, and magnetic convergent plates 2020 and 2030 arranged at both ends of the magnetoresistive element 2010 (the magnetic convergent plate 2020 and the magnetic convergent plate 2030 are collectively referred to as a “magnetic convergent unit”). Has. Here, the magnetoresistive element 2010 may be, for example, at least one of the first magnetoresistive element 112 and the second magnetoresistive element 114. The magnetic focusing plates 2020 and 2030 are arranged at both ends of the magnetoresistive element 2010 so as to sandwich the magnetoresistive element 2010 in between. That is, the sensor unit 110 includes a magnetic convergence unit arranged adjacent to the magnetoresistive element 2010. In this figure, the magnetic focusing plate 2020 is provided on the negative side of the magnetoresistive element 2010 along the magnetic sensing axis, and the magnetic focusing plate 2030 is provided on the positive side of the magnetoresistive element 2010 along the magnetic sensing axis. There is. Here, the magnetically sensitive axis may be along the direction of magnetization fixed by the magnetization fixing layer forming the magnetoresistive element 2010. Further, when a magnetic field is input from the negative side of the magnetic sensing shaft toward the positive side, the resistance of the magnetoresistive element 2010 may increase or decrease. The magnetic focusing plates 2020 and 2030 are formed of a material having a high magnetic permeability such as permalloy. When the sensor unit 110 is configured as shown in this specific example, the coil 142 surrounds the cross section of the magnetoresistive element 2010 and the magnetic focusing plates 2020 and 2030 arranged at both ends of the magnetoresistive element 2010. It is wrapped in. That is, the feedback current generation unit 130 is formed so as to surround the magnetoresistive element 2010 and the magnetic convergence unit. When the sensor unit 110 has a plurality of magnetoresistive elements 2010, the sensor unit 110 may have a plurality of sets including the magnetoresistive element and the magnetic focusing plates arranged at both ends thereof. In that case, the coil 142 may be wound so as to surround the set including the magnetoresistive element and the magnetic focusing plates arranged at both ends thereof with one coil.

In such a sensor unit 110, when a magnetic field is input from the negative side to the positive side of the magnetic field axis, the magnetic focusing plates 2020 and 2030 made of a material having a high magnetic permeability are magnetized, whereby in this figure, A magnetic flux distribution as shown by the broken line occurs. Then, the magnetic flux generated by magnetizing the magnetic focusing plates 2020 and 2030 passes through the position of the magnetoresistive element 2010 sandwiched between the two magnetic focusing plates 2020 and 2030. Therefore, the magnetic flux density at the position of the magnetoresistive element 2010 can be significantly increased by arranging the magnetic focusing plates 2020 and 2030. Further, as in this specific example, the sampling point in space is clarified by sampling the spatial distribution of the magnetic field using the magnetoresistive element 2010 arranged at a narrow position sandwiched between the magnetic focusing plates 2020 and 2030. be able to.

FIG. 21 shows the magnetic flux distribution when a feedback magnetic field is generated in the sensor unit 110 according to this specific example. In FIG. 21, members having the same functions and configurations as those in FIG. 20 are designated by the same reference numerals, and the description thereof will be omitted except for the following differences. In the sensor unit 110 according to this specific example, when a feedback current is supplied to the coil 142, the coil 142 generates a feedback magnetic field, so that a magnetic flux distribution as shown by the alternate long and short dash line in this figure is generated. The magnetic flux generated by this feedback magnetic field is spatially distributed so as to cancel the spatial distribution of the magnetic field that is input to the magnetoresistive element 2010 and magnetically amplified by the magnetic focusing plates 2020 and 2030. Therefore, when the magnetic focusing plates 2020 and 2030 are arranged at both ends of the magnetic resistance element 2010 as shown in this specific example, the sensor unit 110 uses a feedback magnetic field to change the magnetic field distribution at the position of the magnetic resistance element 2010. Since it can be canceled accurately, it is possible to realize a sensor having high linearity between the input magnetic field and the output voltage.

FIG. 22 shows an example of the configuration of the sensor unit 110 according to this specific example. In FIG. 22, members having the same functions and configurations as those in FIG. 20 are designated by the same reference numerals, and the description thereof will be omitted except for the following differences. In this figure, the magnetoresistive element 2010 has a magnetization free layer 2110 and a magnetization fixed layer 2120. Generally, the magnetoresistive element 2010 has a structure in which a thin film layer of an insulator is sandwiched between two ferromagnetic layers. The magnetization free layer 2110 is a layer in which the magnetization direction changes according to an external magnetic field among the two ferromagnetic layers. Further, the magnetization fixed layer 2120 is a layer among the two ferromagnetic layers whose magnetization direction does not change with respect to an external magnetic field. As an example, in the magnetoresistive element 2010, a magnetization free layer 2110, a non-magnetic layer, and a magnetization fixed layer 2120 are laminated in this order on a substrate.

In this specific example, in the magnetoresistive element 2010, the magnetization free layer 2110 is arranged at the lower part, and the magnetization fixed layer 2120 is arranged at the upper part of the magnetization free layer 2110 via a thin film layer (not shown) of an insulator. It is a so-called bottom-free structure magnetoresistive element. In the magnetoresistive element having a bottom-free structure, the magnetization free layer 2110 can be formed in a relatively wide area, so that high magnetic sensitivity can be obtained. In the magnetoresistive element 2010, the area of the magnetized fixed layer 2120 is smaller than the area of the magnetized free layer 2110 in the top view, and the magnetic sensing area is determined based on the area of the magnetized fixed layer 2120.

Further, in this specific example, in the sensor unit 110, the magnetic focusing plates 2020 and 2030 are placed on both ends of the magnetoresistive element 2010 via an insulating layer (not shown) so as to sandwich the magnetoresistive element 2010 in the center. Have been placed. As a result, the magnetoresistive element 2010 is arranged in a narrow space sandwiched between the magnetic focusing plates 2020 and 2030.

Here, in this figure, the length of the magnetized free layer 2110 along the magnetic field axis direction is defined as the magnetized free layer length L_Free. Further, the length along the axis perpendicular to the magnetic field axis direction in the top view of the magnetization free layer 2110 is defined as the magnetization free layer width W_Free. Further, the length of the magnetized fixed layer 2120 along the magnetic field axis direction is defined as the magnetized fixed layer length L_Pin. Further, the length of the magnetization fixed layer 2120 along the axis perpendicular to the magnetic field axis direction in the top view is defined as the magnetization fixed layer width W_Pin. Further, the length along the magnetic field axis direction from the outer end of the magnetic convergence plate to the outer end of the magnetization free layer (in this figure, along the magnetic axis direction from the left end to the right end of the magnetic convergence plate 2020). The length and the length along the magnetic field axis direction from the right end to the left end of the magnetic convergence plate 2030) are defined as the magnetic convergence plate length L_FC. Further, the length along the axis perpendicular to the magnetic sensing axis direction in the top view of the magnetic focusing plate is defined as the magnetic focusing plate width W_FC. Further, the length of the magnetic converging plate along the axis perpendicular to the magnetic field axis direction in the side view is defined as the magnetic converging plate thickness T_FC. Further, the distance between the two magnetic convergence plates 2020 and 2030 along the magnetic axis direction (the length along the magnetic axis direction from the right end of the magnetic convergence plate 2020 to the left end of the magnetic convergence plate 2030 in this figure) is set. It is defined as the magnetic converging plate spacing G_FC. Further, the distance along the axis perpendicular to the magnetic sensing axis direction in the side view from the center of the magnetization free layer 2110 in the thickness direction to the bottom surface of the magnetic convergence plate is defined as the magnetic convergence plate height H_FC.

Various embodiments of the present invention may be described with reference to flowcharts and block diagrams, wherein the block is (1) a stage of the process in which the operation is performed or (2) a device having a role of performing the operation. May represent a section of. Specific stages and sections are implemented by dedicated circuits, programmable circuits supplied with computer-readable instructions stored on computer-readable media, and / or processors supplied with computer-readable instructions stored on computer-readable media. It's okay. Dedicated circuits may include digital and / or analog hardware circuits, and may include integrated circuits (ICs) and / or discrete circuits. Programmable circuits are memory elements such as logical AND, logical OR, logical XOR, logical NAND, logical NOR, and other logical operations, flip-flops, registers, field programmable gate arrays (FPGAs), programmable logic arrays (PLAs), and the like. May include reconfigurable hardware circuits, including, etc.

The computer readable medium may include any tangible device capable of storing instructions executed by the appropriate device, so that the computer readable medium having the instructions stored therein is specified in a flow chart or block diagram. It will be equipped with a product that contains instructions that can be executed to create means for performing the operation. Examples of computer-readable media may include electronic storage media, magnetic storage media, optical storage media, electromagnetic storage media, semiconductor storage media, and the like. More specific examples of computer-readable media include floppy (registered trademark) disks, diskettes, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), Electrically erasable programmable read-only memory (EEPROM), static random access memory (SRAM), compact disc read-only memory (CD-ROM), digital versatile disc (DVD), Blu-ray (RTM) disc, memory stick, integrated A circuit card or the like may be included.

Computer-readable instructions are assembler instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state-setting data, or object-oriented programming such as Smalltalk, JAVA®, C ++, etc. Includes either source code or object code written in any combination of one or more programming languages, including languages, and traditional procedural programming languages such as the "C" programming language or similar programming languages. good.

Computer-readable instructions are used locally or to a local area network (LAN), wide area network (WAN) such as the Internet, to a general purpose computer, a special purpose computer, or the processor or programmable circuit of another programmable data processing device. ) May execute computer-readable instructions to create means for performing the operations specified in the flowchart or block diagram. Examples of processors include computer processors, processing units, microprocessors, digital signal processors, controllers, microcontrollers, and the like.

FIG. 23 shows an example of a computer 2200 in which a plurality of embodiments of the present invention may be embodied in whole or in part. The program installed on the computer 2200 can cause the computer 2200 to function as an operation associated with the device according to an embodiment of the present invention or as one or more sections of the device, or the operation or the one or more. Sections can be run and / or the computer 2200 can be run a process according to an embodiment of the invention or a stage of such process. Such a program may be run by the CPU 2212 to cause the computer 2200 to perform certain operations associated with some or all of the blocks of the flowcharts and block diagrams described herein.

The computer 2200 according to this embodiment includes a CPU 2212, a RAM 2214, a graphic controller 2216, and a display device 2218, which are interconnected by a host controller 2210. The computer 2200 also includes input / output units such as a communication interface 2222, a hard disk drive 2224, a DVD-ROM drive 2226, and an IC card drive, which are connected to the host controller 2210 via the input / output controller 2220. There is. The computer also includes legacy input / output units such as the ROM 2230 and keyboard 2242, which are connected to the input / output controller 2220 via an input / output chip 2240.

The CPU 2212 operates according to a program stored in the ROM 2230 and the RAM 2214, thereby controlling each unit. The graphic controller 2216 acquires the image data generated by the CPU 2212 in a frame buffer or the like provided in the RAM 2214 or itself so that the image data is displayed on the display device 2218.

The communication interface 2222 communicates with other electronic devices via the network. The hard disk drive 2224 stores programs and data used by the CPU 2212 in the computer 2200. The DVD-ROM drive 2226 reads the program or data from the DVD-ROM 2201 and provides the program or data to the hard disk drive 2224 via the RAM 2214. The IC card drive reads programs and data from the IC card and / or writes programs and data to the IC card.

The ROM 2230 contains a boot program or the like executed by the computer 2200 at the time of activation, and / or a program depending on the hardware of the computer 2200. The input / output chip 2240 may also connect various input / output units to the input / output controller 2220 via a parallel port, serial port, keyboard port, mouse port, and the like.

The program is provided by a computer-readable medium such as a DVD-ROM 2201 or an IC card. The program is read from a computer-readable medium, installed on a hard disk drive 2224, RAM2214, or ROM2230, which is also an example of a computer-readable medium, and executed by the CPU 2212. The information processing described in these programs is read by the computer 2200 and provides a link between the program and the various types of hardware resources described above. The device or method may be configured to implement the manipulation or processing of information in accordance with the use of computer 2200.

For example, when communication is executed between the computer 2200 and an external device, the CPU 2212 executes a communication program loaded in the RAM 2214, and performs communication processing on the communication interface 2222 based on the processing described in the communication program. You may order. Under the control of the CPU 2212, the communication interface 2222 reads and reads transmission data stored in a transmission buffer processing area provided in a recording medium such as a RAM 2214, a hard disk drive 2224, a DVD-ROM 2201, or an IC card. The data is transmitted to the network, or the received data received from the network is written to the reception buffer processing area provided on the recording medium.

Further, the CPU 2212 makes the RAM 2214 read all or necessary parts of the file or the database stored in the external recording medium such as the hard disk drive 2224, the DVD-ROM drive 2226 (DVD-ROM2201), and the IC card. Various types of processing may be performed on the data on the RAM 2214. The CPU 2212 then writes back the processed data to an external recording medium.

Various types of information such as various types of programs, data, tables, and databases may be stored in recording media and processed. The CPU 2212 describes various types of operations, information processing, conditional judgment, conditional branching, unconditional branching, and information retrieval described in various parts of the present disclosure with respect to the data read from the RAM 2214. Various types of processing may be performed, including / replacement, etc., and the results are written back to RAM 2214. Further, the CPU 2212 may search for information in a file, a database, or the like in the recording medium. For example, when a plurality of entries each having an attribute value of the first attribute associated with the attribute value of the second attribute are stored in the recording medium, the CPU 2212 specifies the attribute value of the first attribute. Search for an entry that matches the condition from the plurality of entries, read the attribute value of the second attribute stored in the entry, and associate it with the first attribute that satisfies the predetermined condition. The attribute value of the second attribute obtained may be acquired.

The program or software module described above may be stored on or near a computer 2200 on a computer-readable medium. Also, a recording medium such as a hard disk or RAM provided within a dedicated communication network or a server system connected to the Internet can be used as a computer readable medium, thereby providing the program to the computer 2200 over the network. do.

Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various changes or improvements can be made to the above embodiments. It is clear from the description of the claims that the form with such changes or improvements may be included in the technical scope of the present invention.

The order of execution of each process such as operation, procedure, step, and step in the apparatus, system, program, and method shown in the claims, specification, and drawings is particularly "before" and "prior to". It should be noted that it can be realized in any order unless the output of the previous process is used in the subsequent process. Even if the scope of claims, the specification, and the operation flow in the drawings are explained using "first", "next", etc. for convenience, it means that it is essential to carry out in this order. It's not a thing.

10 Magnetic field measuring device 110 Sensor unit 112 First magnetic resistance element 114 Second magnetic resistance element 120 Reference voltage generation unit 130 Feedback current generation unit 132 First arithmetic amplifier 140 Magnetic field generator 142 Coil 150 Calculation unit 152 Current-voltage conversion resistance 154th 2 Arithmetic amplifier 156 AD converter 160 Magnetic field measurement unit 170 Adjustment unit 222 Fixed resistance 224 Variable resistance 710 Switching unit 1010 Adjustment current generation unit 1610 Reset current generation unit 1810 Switch 1820 High pass filter 1910 Third arithmetic amplifier 2010 Magnetic resistance element 2020, 2030 Magnetic Convergence Plate 2110 Magnetic Free Layer 2120 Magnetization Fixed Layer 2200 Computer 2201 DVD-ROM
2210 Host controller 2212 CPU
2214 RAM
2216 Graphic controller 2218 Display device 2220 I / O controller 2222 Communication interface 2224 Hard disk drive 2226 DVD-ROM drive 2230 ROM
2240 Input / Output Chip 2242 Keyboard

Claims (23)

A sensor unit having at least one magnetoresistive element,
The reference voltage generator that outputs the reference voltage and
A magnetic field generating unit that generates a magnetic field applied to the sensor unit,
A feedback current generating unit that supplies a feedback current that generates a feedback magnetic field that reduces an input magnetic field to the sensor unit to the magnetic field generating unit according to the difference between the output voltage of the sensor unit and the reference voltage.
A magnetic field measuring unit that outputs a measured value according to the feedback current, and
An adjusting unit that adjusts the reference voltage based on the feedback current ,
A magnetic field measuring device. The adjusting unit adjusts the reference voltage in the adjusting phase.
The magnetic field measuring device according to claim 1, wherein the magnetic field measuring unit outputs a measured value corresponding to the feedback current generated for the magnetic field to be measured in the measurement phase. The reference voltage generator has at least one variable resistor.
The magnetic field measuring device according to claim 1 or 2, wherein the adjusting unit adjusts the reference voltage by changing the resistance value of the variable resistance. Further equipped with a current-voltage conversion resistance having one end connected to the magnetic field generating portion,
The magnetic field measuring device according to any one of claims 1 to 3, wherein the adjusting unit adjusts the reference voltage using a value obtained by converting the feedback current into a voltage by the current-voltage conversion resistance. The adjusting unit adjusts the reference voltage so that the measured value is within a predetermined range according to the adjusting magnetic field in response to the input of the adjusting magnetic field to the sensor unit. The magnetic field measuring device according to any one of 1 to 4. The magnetic field measuring device according to any one of claims 1 to 4, wherein the adjusting unit adjusts the reference voltage so as to reduce the dispersion value of the feedback current. Further, a switching unit for switching whether or not to supply the feedback current to the magnetic field generation unit is provided.
The one according to any one of claims 1 to 6 , wherein the adjusting unit can adjust the reference voltage by using the output voltage of the sensor unit in a state where the feedback current is not supplied to the magnetic field generating unit. Magnetic field measuring device. In the state where the feedback current is not supplied to the magnetic field generating unit, the adjusting unit has a difference between the output voltage of the sensor unit and the reference voltage according to the input of the adjusting magnetic field to the sensor unit. The magnetic field measuring device according to claim 7, wherein the reference voltage can be adjusted so as to be within a predetermined range according to the adjusting magnetic field. Further equipped with an adjustment current generator that generates an adjustment current,
When the feedback current is not supplied to the magnetic field generation unit, the switching unit supplies the adjustment current to the magnetic field generation unit.
The magnetic field measuring device according to claim 7, wherein the adjusting unit can adjust the reference voltage by using the output voltage of the sensor unit in a state where the adjusting current is supplied to the magnetic field generating unit. The magnetic field measuring device according to claim 9, wherein the adjusting unit can adjust the reference voltage based on the characteristics of the difference between the output voltage of the sensor unit and the reference voltage with respect to the adjusting current. The magnetic field measuring device according to any one of claims 1 to 10, wherein the magnetic field measuring unit integrates and outputs measured values in a predetermined period. The adjusting unit generates the reference voltage by the reference voltage generating unit to generate a reset magnetic field that magnetically saturates the magnetic resistance element by the feedback current generating unit before the measurement of the magnetic field to be measured by the magnetic field measuring unit. Item 12. The magnetic field measuring device according to any one of Items 1 to 11. Before the measurement of the measurement target magnetic field by the magnetic field measuring unit, the adjusting unit changes the resistance value of the variable resistance of the reference voltage generating unit to generate the reset magnetic field generating voltage for generating the reset magnetic field. The magnetic field measuring device according to claim 12, wherein the reference voltage is adjusted based on the resistance value of the variable resistance that is generated by the unit and generates the reset magnetic field generation voltage. The adjusting unit sets the resistance value of the variable resistance as a resistance value of 1/2 to 1/4 of the range of the upper reset magnetic field generation resistance value and the lower magnetic field generation resistance value that generate the reset magnetic field generation voltage, respectively. The magnetic field measuring device according to claim 13, wherein the reference voltage is adjusted. The magnetic field measuring device according to any one of claims 12 to 14, wherein the range of the output voltage of the reference voltage generating unit is larger than the range of the output voltage of the sensor unit. Any of claims 1 to 15, further comprising a reset current generating unit that supplies a reset current that generates a reset magnetic field that magnetically saturates the magnetic resistance element to the magnetic field generating unit before the measurement of the magnetic field to be measured by the magnetic field measuring unit. The magnetic field measuring device according to item 1. The magnetic field measuring device according to any one of claims 1 to 16, further comprising a high-pass filter for passing a high-frequency component of a measured value output by the magnetic field measuring unit. The magnetic field measuring device according to any one of claims 1 to 17, wherein the feedback current generating unit is configured by using two or more operational amplifiers. The sensor unit includes a magnetic convergence unit arranged adjacent to the magnetoresistive element, and the feedback current generation unit is formed so as to surround the magnetoresistive element and the magnetic convergence unit, according to claim 1. 18. The magnetic field measuring device according to any one of 18. In the magnetic resistance element, a magnetized free layer, a non-magnetic layer, and a magnetized fixed layer are laminated in this order on a substrate, and the area of the magnetized fixed layer is smaller than the area of the magnetized free layer in top view. The magnetic field measuring device according to any one of claims 1 to 19, wherein the magnetically sensitive area is determined based on the area of the magnetized fixed layer. The sensor unit has a first magnetoresistive element and a second magnetoresistive element having opposite polarities connected in series.
The magnetic field measuring device according to any one of claims 1 to 20, which outputs a voltage between the first magnetoresistive element and the second magnetoresistive element. A magnetic field measuring device is a magnetic field measuring method that measures a magnetic field.
The magnetic field measuring device generates a feedback magnetic field that reduces the input magnetic field to the sensor unit according to the difference between the output voltage of the sensor unit having at least one magnetic resistance element and the reference voltage output by the reference voltage generating unit. Supplying the feedback current to the magnetic field generating section that generates the magnetic field applied to the sensor section,
The magnetic field measuring device outputs a measured value according to the feedback current, and
The magnetic field measuring device adjusts the reference voltage based on the feedback current .
A magnetic field measurement method. Performed by a computer, said computer,
The sensor uses a feedback current that generates a feedback magnetic field that reduces the input magnetic field to the sensor unit according to the difference between the output voltage of the sensor unit having at least one magnetic resistance element and the reference voltage output by the reference voltage generating unit. A feedback current generator that supplies the magnetic field that is applied to the unit, and a feedback current generator that generates the magnetic field.
A magnetic field measuring unit that outputs a measured value according to the feedback current, and
An adjusting unit that adjusts the reference voltage based on the feedback current ,
A magnetic field measurement program that works.

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