JP2019174436A - Magnetic sensor - Google Patents

Abstract

To provide a magnetic sensor capable of suppressing noise.SOLUTION: A magnetic sensor comprises: a magnetic detection part that includes first to fourth magnetoresistance effect elements (10, 20, 30, and 40) to which a first magnetic field as a detection object is applied; a magnetic field generating conductor 70 that generates a second magnetic field for making the magnetic detection part kept in magnetic equilibrium; and a current supplying circuit 50 to which an output voltage of the magnetic detection part is input and which supplies a current for generating the second magnetic field to the magnetic field generating conductor 70. The current supplying circuit 50 supplies the current of a predetermined value except zero to the magnetic field generating conductor 70 when the first magnetic field does not exist.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a magnetic sensor having a configuration in which a current corresponding to a detection target magnetic field applied to a magnetic detection unit is passed through a magnetic field generating conductor.

  Patent Document 1 below discloses a magnetic field detection sensor capable of detecting a minute magnetic field. This magnetic field detection sensor includes four magnetoresistive elements forming a bridge circuit and a magnetic body. The fixed magnetization directions of the four magnetoresistive elements are the same. The magnetic body collects the magnetic field to be detected in the vertical direction as viewed from the bridge circuit, and the collected magnetic field is approximately parallel to the fixed magnetization direction of the four magnetoresistive elements constituting the bridge circuit. Change the direction. The differential output from the bridge circuit is input to a differential arithmetic circuit, and the differential arithmetic circuit passes a feedback current through the magnetic field generating conductor. The magnetic field generating conductor through which the feedback current flows causes the four magnetoresistive elements to generate a magnetic field in a direction opposite to the direction of the detection target magnetic field. The magnetic field to be detected is measured by measuring the feedback current.

Japanese Patent Laid-Open No. 2015-219061

  In the magnetic sensor of Patent Document 1, the differential output from the bridge circuit composed of four magnetoresistive effect elements is substantially zero (the magnetic field parallel to the magnetosensitive surface at the position of each magnetoresistive effect element is substantially zero. A feedback current is passed through the magnetic field generating conductor. For this reason, the free layer magnetization direction of the magnetoresistive effect element is unstable and easily fluctuates, and noise appearing in the sensor output increases. When the noise increases, the S / N (SN ratio) decreases and the resolution of the magnetic sensor decreases.

  The present invention has been made in recognition of such a situation, and an object thereof is to provide a magnetic sensor capable of suppressing noise.

One embodiment of the present invention is a magnetic sensor. This magnetic sensor
A magnetic detection unit including at least one magnetoresistance effect element to which a first magnetic field to be detected is applied;
A magnetic field generating conductor for generating a second magnetic field for bringing the magnetic detection unit into a magnetic equilibrium state;
A current supply circuit that receives an output voltage of the magnetic detection unit and supplies a current for generating the second magnetic field to the magnetic field generating conductor;
The current supply circuit supplies a non-zero current of a predetermined value to the magnetic field generating conductor when the first magnetic field does not exist.

The current supply circuit includes:
A first differential amplifier to which an output voltage of the magnetic detection unit is input;
An output voltage of the first differential amplifier is input to one input terminal, a bias voltage is input to the other input terminal, and a second differential amplifier that supplies current from the output terminal to the magnetic field generating conductor is provided. May be.

The current supply circuit includes a differential amplifier to which an output voltage of the magnetic detection unit is input,
The differential amplifier may have an offset adjustment function and may be adjusted so as to output a current of a predetermined value that is not zero when the input voltage to the differential amplifier is zero.

  The magnetic detection unit may include a plurality of magnetoresistive elements that are bridge-connected.

  The magnetic detection unit may be configured to output a voltage having a predetermined value that is not zero when there is no magnetic field.

The magnetic detection unit includes a plurality of magnetoresistive elements that are bridge-connected,
At least one magnetoresistive effect element of the plurality of magnetoresistive effect elements may be different in resistance value in the absence of a magnetic field from other magnetoresistive effect elements of the plurality of magnetoresistive effect elements.

  The magnetic detector may have a configuration in which resistance is added to a plurality of bridge-connected magnetoresistive elements having the same resistance value when there is no magnetic field.

  The magnetoresistive effect element may include a fixed layer having a constant magnetization direction regardless of an external magnetic field, and a free layer whose magnetization direction is changed by an external magnetic field.

  It should be noted that any combination of the above-described constituent elements, and those obtained by converting the expression of the present invention between methods and systems are also effective as aspects of the present invention.

  According to the present invention, a magnetic sensor capable of suppressing noise can be provided.

1 is a schematic circuit diagram of a bridge circuit constituting a magnetic detection unit of a magnetic sensor according to a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a magnetic detection unit and its vicinity in the magnetic sensor. FIG. The wiring pattern explanatory drawing of the magnetic field generation | occurrence | production conductor in the said magnetic sensor. The schematic diagram which shows the direction of the detection object magnetic field in the position of each magnetoresistive effect element of the bridge circuit shown in FIG. 1, and the resistance value change of each magnetoresistive effect element by it. The schematic diagram which shows the modification of FIG. 1 is a schematic circuit diagram of a magnetic sensor according to a first embodiment. The graph which shows the relationship between the bias magnetic field applied to the magnetic detection part of the said magnetic sensor, and the magnetic resolution of the said magnetic sensor. The graph which shows the ideal characteristic of the sensor output with respect to a detection target magnetic field, and an actual characteristic. The schematic circuit diagram of the magnetic sensor which concerns on a comparative example. The schematic graph which shows the characteristic of resistance with respect to the magnetic field (magnetic-sensitive direction component) of a magnetoresistive effect element, and the operating point of the magnetoresistive effect element in each of Embodiment 1 and a comparative example on the said characteristic. The schematic circuit diagram of the magnetic sensor which concerns on Embodiment 2 of this invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or equivalent component, member, etc. which are shown by each drawing, and the overlapping description is abbreviate | omitted suitably. In addition, the embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

(Embodiment 1)
FIG. 1 is a schematic circuit diagram of a bridge circuit constituting the magnetic detection unit of the magnetic sensor according to the first embodiment of the present invention. The bridge circuit includes a first magnetoresistive effect element 10, a second magnetoresistive effect element 20, a third magnetoresistive effect element 30, and a fourth magnetoresistive effect element 40. The first to fourth magnetoresistance effect elements (10, 20, 30, 40) include a fixed layer having a constant magnetization direction regardless of an external magnetic field, and a free layer whose magnetization direction is changed by an external magnetic field, and is fixed. The layer magnetization directions are the same. One end of the first magnetoresistance effect element 10 and one end of the second magnetoresistance effect element 20 are connected to a first power supply line to which a first power supply voltage Vcc is supplied. The other end of the first magnetoresistance effect element 10 is connected to one end of the fourth magnetoresistance effect element 40. The other end of the second magnetoresistive element 20 is connected to one end of the third magnetoresistive element 30. The other end of the third magnetoresistance effect element 30 and the other end of the fourth magnetoresistance effect element 40 are connected to a second power supply line to which a second power supply voltage −Vcc is supplied. The voltage output to the interconnection point between the first magnetoresistance effect element 10 and the fourth magnetoresistance effect element 40 is output to Va, and the voltage output to the interconnection point between the second magnetoresistance effect element 20 and the third magnetoresistance effect element 30. The voltage is Vb.

  FIG. 2 is a schematic cross-sectional view of a magnetic detection unit and the vicinity thereof in the magnetic sensor according to the first embodiment. FIG. 3 is a schematic plan view of the same. 2 and 3, the XYZ axes that are orthogonal three axes are defined. 2 and 3 also show the lines of magnetic force of the magnetic field to be detected. In the magnetic sensor of the present embodiment, the first to fourth magnetoresistive elements (10, 20, 30, 40) are provided in the multilayer body 5 together with the magnetic field generating conductor 70, and on the surface of the multilayer body 5 A magnetic body 80 is provided. As shown in FIG. 3, the first magnetoresistive element 10 and the third magnetoresistive element 30 have the same position in the X direction. Similarly, the second magnetoresistive element 20 and the fourth magnetoresistive element 40 have the same position in the X direction. Further, the first magnetoresistive element 10 and the second magnetoresistive element 20 have the same position in the Y direction. Similarly, the third magnetoresistive element 30 and the fourth magnetoresistive element 40 have the same position in the Y direction.

  In FIG. 3, the arrangement of the first magnetoresistive effect element 10 and the third magnetoresistive effect element 30 and the arrangement of the second magnetoresistive effect element 20 and the fourth magnetoresistive effect element 40 are axisymmetric in the X direction. Let A be the center line. A center line in the Y direction in which the arrangement of the first magnetoresistive effect element 10 and the second magnetoresistive effect element 20 and the arrangement of the third magnetoresistive effect element 30 and the fourth magnetoresistive effect element 40 are axisymmetric. Is B. The magnetic body 80 is preferably disposed at a position where the center line in the X direction and the center line in the Y direction of the magnetic body 80 match A and B, respectively. Further, the magnetic body 80 extends to the Y direction side of the first magnetoresistive effect element 10 and the second magnetoresistive effect element 20, and − of the third magnetoresistive effect element 30 and the fourth magnetoresistive effect element 40. It is preferable to extend in the Y direction side. Furthermore, the magnetic body 80 is arranged such that the end face on the laminated body 5 side is closest to the first to fourth magnetoresistive elements (10, 20, 30, 40) in the Z direction, that is, the end face on the laminated body 5 side is laminated. It is preferable to be in contact with the surface of the body 5. By arranging in this way, the resistance change of the first to fourth magnetoresistance effect elements (10, 20, 30, 40) according to the change of the magnetic field to be detected is efficiently and evenly generated. Become. The layer forming the magnetic field generating conductor 70 in the multilayer body 5 is lower than the layer where the first to fourth magnetoresistance effect elements (10, 20, 30, 40) are formed (on the −Z direction side). Layer). By disposing the magnetic field generating conductor 70 below the layer where the first to fourth magnetoresistive elements (10, 20, 30, 40) are formed, the magnetic body 80 and the first to fourth magnetoresistive elements ( 10, 20, 30, 40) can be made closer to each other in the Z direction, so that the first to fourth magnetoresistive elements (10, 20, 30, 40) can respond efficiently to changes in the detection target magnetic field. become. The magnetic body 80 may be a soft magnetic body. The magnetic body 80 collects the magnetic field to be detected in the Z direction, and the magnetic field to be detected is approximately the same as the fixed layer magnetization direction of the first to fourth magnetoresistive elements (10, 20, 30, 40). Change to parallel direction.

  FIG. 4 is an explanatory diagram of a wiring pattern of the magnetic field generating conductor 70 in the magnetic sensor according to the first embodiment. In this figure, the wiring pattern of the magnetic field generating conductor 70 in the multilayer body 5 is indicated by a solid line. The magnetic field generating conductor 70 is preferably formed in a single layer in the same laminate 5 as the first to fourth magnetoresistive elements (10, 20, 30, 40). In the example of FIG. 4, the magnetic field generating conductor 70 is a U-shaped planar coil that is less than one turn, but may be a planar coil that circulates a plurality of turns in a spiral shape. Both ends of the magnetic field generating conductor 70 are electrically connected to terminal portions (terminals) 71 and 72 such as through holes, respectively. As will be described later with reference to FIG. 7, the magnetic field generating conductor 70 generates a second magnetic field that brings the magnetic detection unit into a magnetic equilibrium state.

  FIG. 5 is a schematic diagram showing the direction of the magnetic field to be detected at the position of each magnetoresistive element in the bridge circuit shown in FIG. 1 and the change in resistance value of each magnetoresistive element due to this. In FIGS. 5 and 6, a bias magnetic field which will be described later is ignored. In FIG. 5, the magnetic field to be detected is a magnetic field that is entirely parallel to the −Z direction when the magnetic body 80 is not present, and is partially bent due to the presence of the magnetic body 80, so that the first to fourth magnetoresistances At the position of the effect element (10, 20, 30, 40), it has a component in the direction shown in FIG. In the first magnetoresistance effect element 10, the direction of the magnetic field to be detected has a component that is the same as the magnetization direction of the fixed layer. Therefore, the magnetization direction of the free layer coincides with the magnetization direction of the fixed layer. The resistance value changes by −ΔR from the resistance value R0 in the absence of a magnetic field. On the other hand, in the second magnetoresistance effect element 20, since the direction of the magnetic field to be detected has a component opposite to the fixed layer magnetization direction, the free layer magnetization direction is opposite to the fixed layer magnetization direction. The resistance value of the effect element 20 changes by + ΔR from the resistance value R0 when there is no magnetic field. Similarly, the resistance value of the third magnetoresistive effect element 30 changes by −ΔR as compared to when there is no magnetic field, and the resistance value of the fourth magnetoresistive effect element 40 changes by + ΔR as compared with when there is no magnetic field. Due to the resistance change of the first to fourth magnetoresistive elements (10, 20, 30, 40), the voltage Va becomes higher than that in the absence of a magnetic field, and the voltage Vb becomes lower than that in the absence of a magnetic field. Become. Therefore, the bridge circuit of the first to fourth magnetoresistive elements (10, 20, 30, 40) has a differential output, that is, a voltage Va and a voltage Vb that change in opposite directions according to the change in the detection target magnetic field. Output is possible. In addition, even if the wiring of the bridge circuit is changed as shown in FIG. 6 and the fixed layer magnetization directions of the third magnetoresistive effect element 30 and the fourth magnetoresistive effect element 40 are changed, the differential output can be similarly performed. is there.

  FIG. 7 is a schematic circuit diagram of the magnetic sensor according to the first embodiment. The first to fourth magnetoresistance effect elements (10, 20, 30, 40) connected in a bridge form a magnetic detection unit to which a first magnetic field to be detected is applied. The first differential amplifier 51 has an inverting input terminal connected to the interconnection point of the first magnetoresistive effect element 10 and the fourth magnetoresistive effect element 40, and a non-inverting input terminal connected to the second magnetoresistive effect element 20 and the third magnetoresistive effect element 20. The magnetoresistive effect element 30 is connected to the interconnection point, and the output terminal is connected to the inverting input terminal of the second differential amplifier 52. A resistor for surely determining the voltage of the output terminal of the first differential amplifier 51 may be provided between the output terminal of the first differential amplifier 51 and the ground, if necessary. Each of the first differential amplifier 51 and the second differential amplifier 52 may be a single operational amplifier or a combination of an operational amplifier and a plurality of resistors. The non-inverting input terminal of the second differential amplifier 52 is connected to the plus terminal of the bias voltage source 53. The negative terminal of the bias voltage source 53 is connected to the ground as a fixed voltage terminal.

  The bias voltage source 53 can be composed of, for example, two resistors that divide the voltage of the first power supply voltage Vcc at a predetermined voltage dividing ratio. In this case, an arbitrary voltage dividing ratio can be set by making at least one of the resistors trimmable. The output terminal of the second differential amplifier 52 is connected to one end of the magnetic field generating conductor 70. A detection resistor Rs is provided between the other end of the magnetic field generating conductor 70 and the ground. Both the first differential amplifier 51 and the second differential amplifier 52 are driven by both power sources, and the first power source line to which the first power source voltage Vcc is supplied and the second power source to which the second power source voltage -Vcc is supplied. Connected to the line respectively.

  The first differential amplifier 51 receives the output voltages (voltages Va and Vb) of the magnetic detection unit. In the second differential amplifier 52, the output voltage of the first differential amplifier 51 is input to the inverting input terminal, the output voltage (bias voltage) of the bias voltage source 53 is input to the non-inverting input terminal, and a magnetic field is generated from the output terminal. A negative feedback current is supplied to the conductor 70. The magnetic field generating conductor 70 generates a second magnetic field that brings the magnetic detection unit into a magnetic equilibrium state when a negative feedback current output from the second differential amplifier 52 flows. The first differential amplifier 51, the second differential amplifier 52, and the bias voltage source 53 constitute a current supply circuit 50. The second differential amplifier 52 and the bias voltage source 53 constitute a bias circuit. The current supply circuit 50 receives the output voltage of the magnetic detection unit and supplies a current (negative feedback current) for generating the second magnetic field to the magnetic field generating conductor 70.

  The current supply circuit 50 has a configuration in which the operation is stabilized when the output voltage of the first differential amplifier 51 and the output voltage of the bias voltage source 53 substantially match. The second differential amplifier 52 is configured so that the output voltage of the first differential amplifier 51 substantially matches the output voltage of the bias voltage source 53, that is, the difference between the voltages Va and Vb input to the first differential amplifier 51. A negative feedback current is supplied to the magnetic field generating conductor 70 so that the predetermined value is not zero. For this reason, in the magnetic sensor of the present embodiment, the state in which the magnetic field applied to the magnetic detection unit sets the difference between the voltages Va and Vb to the predetermined value is the magnetic equilibrium state (closed loop feedback point) of the magnetic detection unit. It becomes.

  The negative feedback current flowing through the magnetic field generating conductor 70 also flows through the resistor Rs connected in series with the magnetic field generating conductor 70. The voltage across the detection resistor Rs becomes the output voltage Vout as a magnetic sensor. As shown in FIG. 7, when the negative feedback current is I, the output voltage Vout is Vout = Rs × I. Since the negative feedback current has a one-to-one correspondence with the magnitude of the detection target magnetic field (first magnetic field), the detection target magnetic field can be detected by the output voltage Vout. Since the current supply circuit 50 supplies a non-zero current (bias current) to the magnetic field generating conductor 70 when the detection target magnetic field does not exist, the output voltage Vout does not include the detection target magnetic field. But it will not be zero. Therefore, the voltage resulting from the detection target magnetic field is the voltage obtained by subtracting the output voltage Vout (predetermined value) when there is no detection target magnetic field from the output voltage Vout when the detection target magnetic field exists.

  FIG. 8 is a graph showing the relationship between the bias magnetic field applied to the magnetic detection unit of the magnetic sensor according to the first embodiment and the magnetic resolution of the magnetic sensor. The bias magnetic field on the horizontal axis in FIG. 8 is a magnetic field applied to the magnetic detection unit when there is no detection target magnetic field, and is proportional to the output current (bias current) of the second differential amplifier 52 in that case. It is proportional to the output voltage (bias voltage) of the bias voltage source 53. As is apparent from FIG. 8, the magnetic resolution can be improved by increasing the bias magnetic field applied to the magnetic detection unit from zero. This is because noise is suppressed by restraining the free layer magnetization direction of the first to fourth magnetoresistive elements (10, 20, 30, 40). However, if the bias magnetic field is increased to some extent, the magnetic resolution is deteriorated due to the effect of the sensitivity of the first to fourth magnetoresistive elements (10, 20, 30, 40) being lowered. In the present embodiment, the bias magnetic field is set so that the magnetic resolution is better than when the bias magnetic field is zero.

  FIG. 9 is a graph showing ideal characteristics and actual characteristics of the sensor output with respect to the detection target magnetic field. The ideal characteristic shown in FIG. 9 is an output characteristic of a magnetic sensor that can detect a slight magnetic field change with a minimum magnetic resolution, and the sensor output is a completely linear characteristic with respect to the detection target magnetic field. On the other hand, the actual characteristic shown in FIG. 9 is an output characteristic of a magnetic sensor having an arbitrary magnetic resolution, and the sensor output has a step-like characteristic with respect to the detection target magnetic field. In actual characteristics, the smallest step (magnetic field change) that can be identified includes a noise component, and thus has a certain width.

  FIG. 10 is a schematic circuit diagram of a magnetic sensor according to a comparative example. Compared to the magnetic sensor of the first embodiment shown in FIG. 7, the magnetic sensor of the comparative example shown in FIG. 10 eliminates the second differential amplifier 52 and the bias voltage source 53, and the output terminal of the first differential amplifier 51. Are different from each other in that they are connected to one end of the magnetic field generating conductor 70, and are the same in other points. In the magnetic sensor of the comparative example, a state where the magnetic field of the magnetic detection unit makes the difference between the voltages Va and Vb substantially zero is a magnetic equilibrium state (closed loop feedback point).

  FIG. 11 is a schematic graph showing the resistance characteristic of the magnetoresistive element with respect to the magnetic field (magnetically sensitive direction component) and the operating point of the magnetoresistive element in each of the first embodiment and the comparative example on the characteristic. The operating point of each magnetoresistive element of the magnetic sensor of the comparative example is a zero magnetic field point, whereas the operating point of each magnetoresistive element of the magnetic sensor of the first embodiment is shifted by a predetermined amount from the zero magnetic field point. Has been.

  According to the present embodiment, the following effects can be achieved.

(1) The first to fourth magnetoresistive elements are used to shift the magnetic equilibrium state (the feedback point of the closed loop of the magnetic sensor) from the zero magnetic field point by the second differential amplifier 52 and the bias voltage source 53. The free layer magnetization direction of (10, 20, 30, 40) is restricted to some extent, and fluctuations in the free layer magnetization direction are suppressed. For this reason, the noise which appears in a sensor output can be suppressed, S / N (SN ratio) can be raised, and the resolution of a magnetic sensor can be made favorable.

(2) Since the magnetic field generating conductor 70 that generates a magnetic field for bringing the magnetic detection unit into a magnetic equilibrium state is used for generating a bias magnetic field, a separate permanent magnet or There is no need to provide a magnetic field generating conductor, and an increase in the number of parts and cost can be suppressed.

(3) Since the first to fourth magnetoresistive elements (10, 20, 30, 40) connected in a bridge are used as the magnetic detection unit, the resolution of the magnetic field detection can be increased.

(4) By holding the magnetic balance in the magnetic detection unit by the negative feedback current, the change in the resistance change rate due to the environmental temperature in the first to fourth magnetoresistance effect elements (10, 20, 30, 40) is suppressed and detected. Accuracy can be maintained.

(5) Since the magnetic field generating conductor 70 is formed in the same laminate 5 as the first to fourth magnetoresistive elements (10, 20, 30, 40), the product is more than the case where a separate solenoid coil is used. In addition to being advantageous for downsizing, it is possible to suppress variations in positional accuracy during manufacturing.

(Embodiment 2)
FIG. 12 is a schematic circuit diagram of the magnetic sensor according to the second embodiment of the present invention. The magnetic sensor according to the present embodiment is different from the magnetic sensor of the comparative example shown in FIG. 10 in that a resistance Ra is added to the magnetic detection unit, and is identical in other points. One end of the resistor Ra is connected to a first power supply line to which the first power supply voltage Vcc is supplied. The other end of the resistor Ra is connected to an interconnection point between the first magnetoresistance effect element 10 and the fourth magnetoresistance effect element 40.

  Since the resistance values R0 of the first to fourth magnetoresistive elements (10, 20, 30, 40) in the absence of a magnetic field are equal to each other, the presence of the resistance Ra causes a resistance in the absence of a magnetic field compared to the absence of the resistance Ra. The voltage Va output to the interconnection point between the first magnetoresistance effect element 10 and the fourth magnetoresistance effect element 40 is output to the interconnection point between the second magnetoresistance effect element 20 and the third magnetoresistance effect element 30. Higher than the voltage Vb. That is, the magnetic detection unit is configured to output a voltage (Va−Vb) of a predetermined value that is not zero when there is no magnetic field. Since the first differential amplifier 51 supplies a current to the magnetic field generating conductor 70 so that the voltage Va matches the voltage Vb, the magnetic equilibrium state of the magnetic detection unit (the closed loop feedback point of the magnetic sensor) starts from the zero magnetic field point. shift. According to the present embodiment, although the addition of the resistor Ra is required, the magnetic balance state of the magnetic detection unit (with the second differential amplifier 52 and the bias voltage source 53 omitted from the current supply circuit 50 of the first embodiment ( The feedback point of the closed loop of the magnetic sensor) is shifted from the zero magnetic field point, the S / N can be increased, and the resolution of the magnetic sensor can be improved.

  In the present embodiment, the connection destination of one end of the resistor Ra is not limited to the first power supply line as long as it is a fixed voltage terminal that is a voltage other than the ground. The connection destination of one end of the resistor Ra may be a second power supply line to which the second power supply voltage −Vcc is supplied. The connection destination of the other end of the resistor Ra may be an interconnection point between the second magnetoresistance effect element 20 and the third magnetoresistance effect element 30. The resistor Ra is an arbitrary position where the resistance balance of the bridge circuit composed of the first to fourth magnetoresistive effect elements (10, 20, 30, 40) can be biased, that is, the output voltage of the bridge circuit in the absence of a magnetic field. What is necessary is just to connect to the arbitrary positions which can be shifted to the predetermined value which is not zero.

(Embodiment 3)
Compared with the magnetic sensor of the comparative example shown in FIG. 10, the magnetic sensor of the present embodiment has a resistance value of the first magnetoresistive element 10 in the absence of a magnetic field of the second to fourth magnetoresistive elements (20 , 30, 40) are different from the resistance value R0 in the absence of a magnetic field, and are different in other points. It is desirable that the rate of resistance change with respect to the applied magnetic field of the first magnetoresistive effect element 10 matches the rate of resistance change ΔR / R0 with respect to the applied magnetic field of the second to fourth magnetoresistive effect elements (20, 30, 40).

  In the present embodiment, the resistance balance of the bridge circuit including the first to fourth magnetoresistive elements (10, 20, 30, 40) is biased, and the output voltage of the bridge circuit when no magnetic field is set to a predetermined value that is not zero. shift. Since the first differential amplifier 51 supplies a current to the magnetic field generating conductor 70 so that the voltage Va matches the voltage Vb, the magnetic equilibrium state of the magnetic detection unit (the closed loop feedback point of the magnetic sensor) starts from the zero magnetic field point. shift. According to the present embodiment, the second differential amplifier 52 and the bias voltage source 53 are omitted from the current supply circuit 50 of the first embodiment, and the magnetic detection state of the magnetic detection unit (the closed loop feedback point of the magnetic sensor). Can be shifted from the zero magnetic field point, S / N can be increased, and the resolution of the magnetic sensor can be improved.

  In the present embodiment, instead of or in addition to changing the resistance value of the first magnetoresistance effect element 10 in the absence of a magnetic field, the resistance value of the third magnetoresistance effect element 30 in the absence of a magnetic field is changed. Also good. Alternatively, the resistance value of the first magnetoresistive effect element 10 and the third magnetoresistive effect element 30 when there is no magnetic field is not changed, and at least one of the second magnetoresistive effect element 20 and the fourth magnetoresistive effect element 40 is free of magnetic field. The resistance value at the time may be changed. The resistance balance of the bridge circuit composed of the first to fourth magnetoresistive elements (10, 20, 30, 40) is biased, that is, the output voltage of the bridge circuit when no magnetic field is set to a predetermined value that is not zero. The resistance value in the absence of a magnetic field of at least one magnetoresistive element may be changed.

(Embodiment 4)
In the magnetic sensor of the present embodiment, the first differential amplifier 51 has an offset adjustment function and the input voltage to itself is zero as compared with the magnetic sensor of the comparative example shown in FIG. However, it is different in that it is adjusted so as to output a current of a predetermined value that is not zero, and is identical in other points. As is well known, the offset adjustment function of the first differential amplifier 51 is a function of adjusting the output voltage of the first differential amplifier 51 to zero when the input voltage to the first differential amplifier 51 is zero. is there. In the present embodiment, by using this offset adjustment function, the output voltage of the first differential amplifier 51 when the input voltage to the first differential amplifier 51 is zero is set to a predetermined value that is not zero. Thus, the magnetic equilibrium state of the magnetic detector (the closed loop feedback point of the magnetic sensor) is shifted from the zero magnetic field point. According to the present embodiment, the second differential amplifier 52 and the bias voltage source 53 are omitted from the current supply circuit 50 of the first embodiment, and the magnetic equilibrium state of the magnetic detection unit (the closed loop feedback point of the magnetic sensor). Can be shifted from the zero magnetic field point, S / N can be increased, and the resolution of the magnetic sensor can be improved.

  The present invention has been described above by taking the embodiment as an example. However, it is understood by those skilled in the art that various modifications can be made to each component and each processing process of the embodiment within the scope of the claims. By the way. Hereinafter, modifications will be described.

  The number of magnetic detection elements is not limited to the four exemplified in the embodiment, and may be one or more arbitrary numbers. In the embodiment, a magnetic detection unit in which four magnetoresistive effect elements are connected in a full bridge has been described as an example. However, the magnetic detection unit may be a structure in which two magnetoresistive effect elements are connected in a half bridge. One magnetoresistive element and one fixed resistor may be half-bridge connected. The magnetic detection element and the magnetic field generating conductor are not limited to being configured in a common laminated body, and may be provided separately from each other. The magnetic detection unit, the first differential amplifier 51, and the second differential amplifier 52 are not limited to the dual power supply drive, but may be a single power supply drive.

5 Stack, 10 1st magnetoresistive effect element, 20 2nd magnetoresistive effect element, 30 3rd magnetoresistive effect element, 40 4th magnetoresistive effect element, 50 Current supply circuit, 51 1st differential amplifier, 52 1st 2 differential amplifiers, 53 bias voltage source, 70 magnetic field generating conductor, 80 magnetic material

Claims (8)

A magnetic detection unit including at least one magnetoresistance effect element to which a first magnetic field to be detected is applied;
A magnetic field generating conductor for generating a second magnetic field for bringing the magnetic detection unit into a magnetic equilibrium state;
A current supply circuit that receives an output voltage of the magnetic detection unit and supplies a current for generating the second magnetic field to the magnetic field generating conductor;
The magnetic sensor, wherein the current supply circuit supplies a non-zero current of a predetermined value to the magnetic field generating conductor when the first magnetic field does not exist. The current supply circuit includes:
A first differential amplifier to which an output voltage of the magnetic detection unit is input;
An output voltage of the first differential amplifier is input to one input terminal, a bias voltage is input to the other input terminal, and a second differential amplifier supplies current from the output terminal to the magnetic field generating conductor. The magnetic sensor according to claim 1. The current supply circuit includes a differential amplifier to which an output voltage of the magnetic detection unit is input,
The magnetic sensor according to claim 1, wherein the differential amplifier has an offset adjustment function and is adjusted so as to output a current of a predetermined value that is not zero when an input voltage to the differential amplifier is zero.   The magnetic sensor according to claim 1, wherein the magnetic detection unit includes a plurality of magnetoresistive elements that are bridge-connected.   The magnetic sensor according to claim 1, wherein the magnetic detection unit is configured to output a voltage of a predetermined value that is not zero when there is no magnetic field. The magnetic detection unit includes a plurality of magnetoresistive elements that are bridge-connected,
2. At least one magnetoresistive effect element of the plurality of magnetoresistive effect elements is different in resistance value in the absence of a magnetic field from other magnetoresistive effect elements of the plurality of magnetoresistive effect elements. To 5. The magnetic sensor according to any one of items 5 to 5.   6. The magnetic sensor according to claim 1, wherein the magnetic detection unit has a configuration in which resistance is added to a plurality of bridge-connected magnetoresistive effect elements having equal resistance values in the absence of a magnetic field. .   6. The magnetism according to claim 1, wherein the magnetoresistive element includes a fixed layer having a constant magnetization direction regardless of an external magnetic field, and a free layer whose magnetization direction is changed by an external magnetic field. Sensor.