Magnetic sensor device

Abstract

A magnetic sensor device (1), (2), (3), (4) is provided with an energizing circuit (30) that periodically excites a magnetosensitive body (11) of a magnetic detecting element (10), the energizing circuit (30) comprising: a p-channel type first switching element (31) that is disposed between a power supply (20) and one end (11a) of the magnetosensitive body (11), and that is configured to be capable of switching between an ON state and an OFF state; a second switching element (32) that is disposed between the first switching element (31) and the one end (11a) of the magnetosensitive body (11), and to which a second control signal is input so as to maintain an ON state; and a capacitor (35) that is connected in parallel with a control signal line of the second switching element (32), and that is configured to have a capacitance Ca greater than a parasitic capacitance Cc.

Description

magnetic sensor device

[0001] The present disclosure relates to a magnetic sensor device.

[0002] Patent Document 1 discloses a magnetic sensor device that uses a magnetic detection element that includes a magnetosensitive body and a detection coil wound around the magnetosensitive body. Periodic excitation of the magnetosensitive body that constitutes the magnetic detection element generates an induced voltage in the detection coil. Since the magnitude of this induced voltage varies depending on the magnetism, the magnitude of the magnetism can be detected by detecting the induced voltage in the detection coil.

[0003] Japanese Patent Application Laid-Open No. 2006-184121

[0004] The current-carrying circuit for periodically exciting the magnetosensitive body includes, for example, a p-channel switching element between the magnetosensitive body and a power source. The magnetosensitive body can be excited by switching the switching element between an on state and an off state. When an excitation current is supplied to the magnetosensitive body, an induced voltage is generated in the detection coil.

[0005] However, there is a risk that fluctuations in the induced electromotive force generated in the detection coil will propagate back to the magnetosensitive body, causing fluctuations in the voltage of the magnetosensitive body. The voltage fluctuations in the magnetosensitive body are transmitted to a switching element in a current-carrying circuit connected to the magnetosensitive body. This may result in an unstable operating current for the switching element. If the operating current of the switching element becomes unstable, the excitation current supplied from the switching element to the magnetosensitive body may also become unstable, making it impossible to stably detect the induced electromotive force in the detection coil. In other words, there is a risk that the magnitude of the magnetic field may not be detected with high accuracy. Therefore, in order to detect the magnitude of the magnetic field with high accuracy, it is necessary to suppress the transmission of fluctuations in the induced electromotive force in the detection coil to the switching element.

[0006] The present disclosure has been made in view of the above background, and aims to provide a magnetic sensor device that can detect the magnitude of magnetism with high accuracy.

[0007] One aspect of the present disclosure is a magnetic sensor device comprising: a magnetic detection element including a magnetosensitive body and a detection coil wound around the magnetosensitive body; an energization circuit that periodically excites the magnetosensitive body of the magnetic detection element; and a detection circuit connected to the detection coil and detecting a voltage signal generated in the detection coil, wherein the energization circuit comprises: a first switching element that is arranged between a power source and one end of the magnetosensitive body and is configured to be switchable between an ON state in which an excitation current is supplied to the magnetosensitive body and an OFF state in which the supply of excitation current to the magnetosensitive body is stopped based on the input of a first control signal that is an ON / OFF signal, and is of a p-channel type; a second switching element that is arranged between the first switching element and one end of the magnetosensitive body and receives an input of a second control signal so as to maintain the ON state; and a capacitor that is connected in parallel to a control signal line of the second switching element and has a capacitance larger than a parasitic capacitance between a control signal terminal of the second switching element and a magnetosensitive body side terminal of the second switching element that is connected to one end of the magnetosensitive body, and is configured to maintain the ON state of the second switching element.

[0008] According to one aspect of the present disclosure, an energization circuit that periodically excites a magnetosensitive body includes a first switching element configured as a p-channel type between a power source and the magnetosensitive body. The first switching element is configured as a p-channel type and is configured to be switchable between an on state and an off state based on the input of a first control signal that is an on / off signal. In other words, the first switching element switches between the supply and stop of excitation current to the magnetosensitive body by switching between the on state and the off state. Note that the on / off signal refers to a signal selected from an on signal and an off signal.

[0009] Here, if only the first switching element is disposed between the power supply and the magnetosensitive body, as described above, fluctuations in the induced electromotive force generated in the detection coil may be propagated back to the magnetosensitive body, causing the operating current of the first switching element to become unstable. If the operating current of the first switching element becomes unstable, the excitation current supplied to the magnetosensitive body may become unstable, and as a result, the induced electromotive force of the detection coil may not be stably detected.

[0010] Therefore, the current-carrying circuit includes a second switching element and a capacitor. The second switching element is disposed between the first switching element and the magnetic sensitive body, and a second control signal is input to the second switching element so as to maintain the on state. The capacitor is connected in parallel to the control signal line of the second switching element, i.e., the wiring through which the second control signal is transmitted. Furthermore, the capacitance of the capacitor is set to be larger than the parasitic capacitance between the control signal terminal of the second switching element and the magnetic sensitive body side terminal of the second switching element connected to the magnetic sensitive body.

[0011] When the second switching element is maintained in the on state, the first switching element and the magnetosensitive element are always in a conductive state, and therefore, by switching the first switching element between the on state and the off state, the supply and stop of the excitation current to the magnetosensitive element is switched.

[0012] Here, the fluctuation of the induced voltage generated in the detection coil is propagated back to the magnetosensitive element, causing the voltage of the magnetosensitive element to fluctuate, which may affect the second control signal of the second switching element.

[0013] However, the capacitor connected in parallel to the control signal line of the second switching element has a capacitance larger than the parasitic capacitance between the control signal terminal of the second switching element and the magnetic body-side terminal of the second switching element located on the magnetic body side. Therefore, the parasitic capacitance between the control signal terminal of the second switching element and the magnetic body-side terminal of the second switching element has almost no effect on the second control signal in the control signal line of the second switching element. Therefore, even if fluctuations in the induced electromotive force generated in the detection coil are propagated back to the magnetic body, the second switching element can stably maintain its on state.

[0014] When the second switching element is in the on state, the second switching element has a predetermined electrical resistance between the power supply side terminal (positive terminal) of the second switching element and the terminal on the magnetic sensitive body side. Due to the influence of the electrical resistance of the second switching element, voltage fluctuations of the magnetic sensitive body are reduced by the time they reach the power supply side terminal (positive terminal) of the second switching element. Therefore, voltage fluctuations at the magnetic sensitive body side terminal (second switching element side terminal) of the first switching element are smaller than voltage fluctuations occurring at the magnetic sensitive body. As a result, the influence on the control signal terminal of the first switching element is reduced. Therefore, voltage fluctuations at the control signal terminal of the first switching element can be suppressed.

[0015] Furthermore, the electrical resistance of the second switching element may change depending on the voltage at the control signal terminal of the second switching element. If fluctuations in the induced voltage generated in the detection coil are propagated back to the magnetosensitive element, causing fluctuations in the voltage at the magnetosensitive element, the voltage at the control signal terminal of the second switching element may change.

[0016] However, as described above, due to the function of the capacitor, there is almost no effect on the second control signal in the control signal line of the second switching element through the parasitic capacitance between the control signal terminal of the second switching element and the magnetic sensor side terminal of the second switching element. Therefore, the voltage of the control signal terminal of the second switching element can be maintained in a stable state. As a result, the electrical resistance of the second switching element is stabilized at a predetermined value.

[0017] Therefore, even if fluctuations in the induced electromotive force generated in the detection coil are propagated back to the magnetosensitive body, the influence on the control signal terminal of the first switching element and the control signal terminal of the second switching element can be suppressed. As a result, the excitation current supplied to the magnetosensitive body from the first switching element via the second switching element is stabilized. In this state, the magnitude of the magnetic field can be detected with high accuracy by detecting the induced electromotive force generated in the detection coil.

[0018] FIG. 1 is a basic configuration diagram of a magnetic sensor device according to embodiment 1. FIG. 2 is a detailed configuration diagram of the magnetic sensor device according to embodiment 1. FIG. 3 is a timing chart of voltages at various parts of the magnetic sensor device according to embodiment 1. FIG. 4 is a detailed configuration diagram of a magnetic sensor device according to embodiment 2. FIG. 5 is a detailed configuration diagram of a magnetic sensor device according to embodiment 3. FIG. 6 is a detailed configuration diagram of a magnetic sensor device according to embodiment 4.

[0019] Each embodiment will be specifically described below with reference to the drawings.

[0020] It should be noted that each of the embodiments described below is a comprehensive or specific example, and the forms shown in the embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, any component that is not described in an independent claim that indicates a superordinate concept will be described as an optional component.

[0021] Furthermore, the magnetic sensor device according to the present disclosure is not limited to the following embodiments, and the present disclosure also includes the following embodiments, modifications obtained by applying various modifications to the following embodiments that would occur to those skilled in the art without departing from the spirit of the present disclosure, and various devices incorporating the magnetic sensor device according to the present disclosure.

[0022] First Embodiment FIG. 1 is a plan view showing a configuration example of a magnetic sensor device 1 according to a first embodiment.

[0023] 1. Basic Configuration of Magnetic Sensor Device 1 The basic configuration of the magnetic sensor device 1 according to the first embodiment will be described with reference to Fig. 1. As shown in Fig. 1, the magnetic sensor device 1 of this embodiment includes a magnetic detection element 10, a power supply 20, a current supply circuit 30, a detection circuit 40, and a control device 50.

[0024] The magnetic detection element 10 is configured to output a voltage corresponding to the strength of a magnetic field when excited. The magnetic detection element 10 includes, for example, a magnetosensitive body 11 and a detection coil 12 wound around the magnetosensitive body 11. The magnetic detection element 10 can be a magneto-impedance (MI) element including the magnetosensitive body 11 and the detection coil 12.

[0025] When an excitation current is supplied to the magnetic detection element 10, a magnetization change occurs in response to the strength of the magnetic field acting on the magnetic sensitive body 11. More specifically, when a pulse current or a high-frequency current is supplied as the excitation current, the magnetic permeability of the magnetic sensitive body 11 changes in response to the strength of the acting magnetic field, thereby changing the impedance. In other words, when an excitation current is supplied to the magnetic sensitive body 11 while a magnetic field is acting on the magnetic sensitive body 11, a magnetization change occurs in the magnetic sensitive body 11. The magnetic sensitive body 11 can be, for example, a magnetic wire, particularly an amorphous magnetic wire.

[0026] The detection coil 12 is wound around the magnetosensitive body 11. More specifically, the detection coil 12 is wound around the magnetosensitive body 11 with an insulating layer interposed therebetween. A magnetic field acts on the magnetosensitive body 11, and when an excitation current is supplied to the magnetosensitive body 11, an induced voltage is generated in the detection coil 12 due to a change in magnetization of the magnetosensitive body 11. Therefore, the detection coil 12 outputs the induced voltage generated by the change in magnetization of the magnetosensitive body 11 as a voltage signal.

[0027] The power supply 20 supplies power to the magnetic detection element 10. Although not shown, the power supply 20 also supplies power to other components, such as a current supply circuit 30, a detection circuit 40, and a control device 50.

[0028] The current supply circuit 30 periodically excites the magnetic sensitive body 11 of the magnetic detection element 10. The excitation current is a pulse current or a high-frequency current. The current supply circuit 30 is connected to the power supply 20 and the magnetic sensitive body 11, and supplies the excitation current to the magnetic sensitive body 11.

[0029] The detection circuit 40 is connected to the detection coil 12 of the magnetic detection element 10. The detection circuit 40 detects a voltage signal generated in the detection coil 12 when the magnetic sensitive body 11 is excited. The detection circuit 40 includes a sample-and-hold circuit 41 (indicated as "S / H" in FIG. 1), an amplifier 42, an analog-to-digital converter 43 (indicated as "A / D converter" in FIG. 1), and a signal processing unit 44.

[0030] The sample-and-hold circuit 41 is connected to the detection coil 12 and holds the voltage signal output by the detection coil 12 at the timing when an excitation current is supplied to the magnetosensitive body 11. The sample-and-hold circuit 41 is configured to include, for example, a sampling switch and a hold capacitor.

[0031] The amplifier 42 amplifies the output voltage of the sample-and-hold circuit 41. However, the detection circuit 40 may be configured without the amplifier 42. The analog-to-digital converter 43 converts the analog voltage signal output by the amplifier 42 into a digital signal. In a configuration in which the detection circuit 40 does not include the amplifier 42, the analog-to-digital converter 43 converts the analog voltage signal output by the sample-and-hold circuit 41 into a digital signal. The signal processing unit 44 performs predetermined processing on the digital signal output by the analog-to-digital converter 43 to generate a desired signal. The signal processing unit 44, for example, averages multiple digital signals or performs correction processing on the acquired digital signal.

[0032] The control device 50 outputs a control signal to the energization circuit 30 to cause the energization circuit 30 to perform a predetermined operation. For example, the control device 50 outputs a control signal to cause the energization circuit 30 to supply a pulse current or a high-frequency current to the magnetically sensitive body 11 of the magnetic detection element 10. Furthermore, the control device 50 outputs a sampling signal to the sample-and-hold circuit 41 in synchronization with the control signal to the energization circuit 30. That is, the control device 50 outputs control signals to the energization circuit 30 and the sample-and-hold circuit 41 to supply an excitation current to the magnetically sensitive body 11 of the magnetic detection element 10 and to enable detection of a voltage signal output by the detection coil 12 of the magnetic detection element 10. The control device 50 also outputs control signals to the other components of the detection circuit 40, namely, the amplifier 42, the analog-to-digital converter 43, and the signal processing unit 44.

[0033] 2, the detailed configuration of the energization circuit 30 constituting the magnetic sensor device 1 will be described. As described above, the energization circuit 30 periodically excites the magnetic sensitive body 11 of the magnetic detection element 10 based on the control signal output from the control device 50.

[0034] 2, the energization circuit 30 includes a first switching element 31, a second switching element 32, and a third switching element 33. The energization circuit 30 further includes a variable resistor 34, a first capacitor 35, and a second capacitor 36.

[0035] Here, the first switching element 31, the second switching element 32, and the third switching element 33 can be made of either a normal semiconductor or a power semiconductor. Each of the switching elements 31, 32, and 33 can be made of a bipolar transistor (BJT), a field-effect transistor (FET), an insulated gate transistor (IGBT), or the like. Furthermore, the field-effect transistor can be made of a metal-oxide semiconductor field-effect transistor (MOSFET), a junction field-effect transistor (JFET), or the like. In this embodiment, each of the switching elements 31, 32, and 33 will be described using a MOSFET as an example.

[0036] The first switching element 31 is disposed between the power supply 20 and one end 11a of the magnetosensitive element 11. The first switching element 31 is configured as a p-channel type. Therefore, the first switching element 31 has a source terminal connected to the power supply 20, a drain terminal connected to one end 11a of the magnetosensitive element 11, and a gate terminal serving as a control signal terminal connected to the control device 50. A first control signal S1 serving as an on / off signal is output from the control device 50 to a control signal line connecting the gate terminal of the first switching element 31 and the control device 50.

[0037] The first switching element 31 is configured to be able to switch, based on the input of the first control signal S1, between an ON state in which an excitation current is supplied to the magnetosensitive body 11 and an OFF state in which the supply of the excitation current to the magnetosensitive body 11 is stopped. In other words, when the first control signal S1 is an ON signal, the first switching element 31 is in the ON state, and when the first control signal S1 is an OFF signal, the first switching element 31 is in the OFF state.

[0038] The second switching element 32 is disposed between the first switching element 31 and one end 11a of the magnetosensitive element 11. The second switching element 32 is configured as a p-channel type. Therefore, the source terminal of the second switching element 32 is connected to the drain terminal of the first switching element 31, the drain terminal is connected to one end 11a of the magnetosensitive element 11, and the gate terminal, which is a control signal terminal, is connected to the control device 50. A second control signal S2, which is an on / off signal, is output from the control device 50 to a control signal line connecting the gate terminal of the second switching element 32 and the control device 50.

[0039] The second switching element 32 is configured to be able to switch between an ON state and an OFF state based on the input of the second control signal S2. In this embodiment, the second switching element 32 is configured to maintain the ON state by continuously inputting the second control signal S2, which has a constant value, from the control device 50.

[0040] The third switching element 33 is disposed between the other end 11b of the magnetosensitive element 11 and ground potential. The third switching element 33 is configured as an n-channel type. Therefore, the source terminal of the third switching element 33 is connected to ground potential, the drain terminal is connected to the other end 11b of the magnetosensitive element 11, and the gate terminal, which is a control signal terminal, is connected to the control device 50. A third control signal S3, which is an on / off signal, is output from the control device 50 to a control signal line connecting the gate terminal of the third switching element 33 and the control device 50.

[0041] Therefore, the third switching element 33 operates between an ON state and an OFF state in synchronization with the first switching element 31. When the first switching element 31 is in the ON state, the third switching element 33 is also in the ON state, and when the first switching element 31 is in the OFF state, the third switching element 33 is also in the OFF state. In this way, the third switching element 33 is configured to be switchable between an ON state in which an excitation current is supplied to the magnetosensitive element 11 and an OFF state in which the supply of the excitation current to the magnetosensitive element 11 is stopped, based on the input of the third control signal S3.

[0042] The variable resistor 34 is disposed between the other end 11b of the magnetic sensitive body 11 and the third switching element 33. The variable resistor 34 is configured so that its resistance value can be changed in accordance with the sensitivity of the magnetic detection element 10. For example, when the induced electromotive force generated in the detection coil 12 of the magnetic detection element 10 is large, i.e., when the sensitivity of the magnetic detection element 10 is high, the resistance value of the variable resistor 34 is increased. On the other hand, when the induced electromotive force generated in the detection coil 12 of the magnetic detection element 10 is small, i.e., when the sensitivity of the magnetic detection element 10 is low, the resistance value of the variable resistor 34 is decreased.

[0043] The first capacitor 35 is connected in parallel to the control signal line of the second switching element 32. In this embodiment, one end of the first capacitor 35 is connected to the control signal line of the second switching element 32, and the other end is connected to the ground potential.

[0044] The first capacitor 35 is configured to maintain the on state of the second switching element 32 even when fluctuations in the induced electromotive force generated in the detection coil 12 are propagated back to the magnetosensitive element 11. The first capacitor 35 has a capacitance Ca. The capacitance Ca of the first capacitor 35 is set to be larger than a parasitic capacitance Cc. The parasitic capacitance Cc is a parasitic capacitance between a control signal terminal (gate terminal) of the second switching element 32 and a magnetosensitive element side terminal (source terminal) of the second switching element 32 connected to one end 11a of the magnetosensitive element 11. For example, the capacitance Ca of the first capacitor 35 is set to be 10 times or more, preferably 100 times or more, the parasitic capacitance Cc.

[0045] Even if fluctuations in the induced electromotive force generated in the detection coil 12 are propagated back to the magnetosensitive body 11, causing fluctuations in the voltage of the magnetosensitive body 11, the presence of the first capacitor 35 results in almost no effect on the second control signal S2 in the control signal line of the second switching element 32 through the parasitic capacitance Cc. In other words, the first capacitor 35 acts to maintain the on state of the second switching element 32 even if fluctuations in the induced electromotive force generated in the detection coil 12 are propagated back to the magnetosensitive body 11.

[0046] The second capacitor 36 is connected in parallel to a current supply line connecting the second switching element 32 and one end 11 a of the magnetosensitive body 11. In this embodiment, the second capacitor 36 is connected in parallel to a current supply line connecting the drain terminal of the second switching element 32 and one end 11 a of the magnetosensitive body 11. Specifically, one end of the second capacitor 36 is connected to the current supply line located between the second switching element 32 and one end 11 a of the magnetosensitive body 11, and the other end is connected to ground potential. The capacitance Cb of the second capacitor 36 is set to be larger than the parasitic capacitance Cc. For example, the capacitance Cb of the second capacitor 36 is set to be 10 times or more, preferably 100 times or more, the parasitic capacitance Cc.

[0047] Like the first capacitor 35, the second capacitor 36 is configured to suppress the transmission of fluctuations in the voltage of the detection coil 12 to the second switching element 32 when the fluctuations in the induced voltage generated in the detection coil 12 are propagated back to the magnetic sensitive body 11.

[0048] 3. Basic Operation of Magnetic Sensor Device 1 The operation of the magnetic sensor device 1 will be described with reference to FIG. 3. At time T1, the control device 50 outputs OFF signals for the first control signal S1 and the third control signal S3. The first control signal S1 has a potential equal to or greater than the voltage of the power supply 20. The third control signal S3 has a potential equal to or less than the ground potential. Therefore, the first switching element 31 and the third switching element 33 are in the OFF state.

[0049] At time T1, the control device 50 outputs the second control signal S2 having a constant potential. The potential of the second control signal S2 is preferably equal to or lower than ground potential (including 0 V), but may be higher than ground potential. The first capacitor 35 is maintained in a state in which a charge corresponding to the potential of the second control signal S2 is stored. Therefore, the second switching element 32 is maintained in the ON state.

[0050] Thus, at time T1, the second switching element 32 is in the ON state, but the first switching element 31 and the third switching element 33 are in the OFF state, so the voltage S4 at the one end 11 a of the magnetosensitive body 11 is zero. In other words, no excitation current flows through the magnetosensitive body 11 of the magnetic detection element 10.

[0051] Between times T2 and T3, the control device 50 switches the first control signal S1 and the third control signal S3 to ON signals. Therefore, at time T3, the first control signal S1 falls below the ON threshold of the first switching element 31, switching it to the ON state. Also, at time T3, the third control signal S3 exceeds the ON threshold of the third switching element 33, switching it to the ON state.

[0052] Even after time T2, the control device 50 outputs the second control signal S2 having a constant potential, for example, equal to or lower than ground potential. Therefore, the second switching element 32 maintains the ON state. Therefore, at time T3, the first switching element 31 and the third switching element 33 are switched to the ON state, and the second switching element 32 maintains the ON state, so that the voltage S4 at the one end 11a of the magnetosensitive element 11 becomes a positive potential.

[0053] This state is maintained until time T4. Therefore, from time T3 to time T4, an excitation current flows through the magnetosensitive element 11. Therefore, an induced voltage is generated in the detection coil 12, and the detection coil 12 outputs a voltage signal corresponding to the magnitude of the magnetic field.

[0054] Between times T4 and T5, the control device 50 switches the first control signal S1 and the third control signal S3 to OFF signals. Therefore, at time T5, the first control signal S1 exceeds the ON threshold of the first switching element 31, switching it to the OFF state. Also, at time T5, the third control signal S3 falls below the ON threshold of the third switching element 33, switching it to the OFF state.

[0055] Therefore, at time T5, the second switching element 32 is in the ON state, but the first switching element 31 and the third switching element 33 are in the OFF state, so the voltage S4 at one end 11a of the magnetosensitive element 11 drops. In other words, no excitation current flows through the magnetosensitive element 11 of the magnetic detection element 10. In this way, a pulse current is supplied to the magnetosensitive element 11, and the detection coil 12 outputs a voltage signal corresponding to the magnitude of the magnetic field.

[0056] 4. Function of the Second Switching Element 32 and the First Capacitor 35 Next, the functions of the second switching element 32 and the first capacitor 35 will be described. If only the first switching element 31 were disposed between the power supply 20 and the magnetosensitive body 11, fluctuations in the induced electromotive force generated in the detection coil 12 would be propagated back to the magnetosensitive body 11, which could destabilize the operating current of the first switching element 31. If the operating current of the first switching element 31 becomes unstable, the excitation current supplied to the magnetosensitive body 11 would become unstable, and as a result, the induced electromotive force of the detection coil 12 could not be stably detected.

[0057] Therefore, the energization circuit 30 includes a second switching element 32 and a first capacitor 35. The second switching element 32 is disposed between the first switching element 31 and the magnetosensitive element 11, and a second control signal S2 is input to the second switching element 32 so as to maintain the second switching element 32 in an on state. The first capacitor 35 is connected in parallel to the control signal line of the second switching element 32, i.e., the wiring through which the second control signal S2 is transmitted. Furthermore, the capacitance Ca of the first capacitor 35 is set to be larger than the parasitic capacitance Cc between the control signal terminal (gate terminal) of the second switching element 32 and the magnetosensitive element-side terminal (drain terminal) of the second switching element 32 connected to the magnetosensitive element 11.

[0058] When the second switching element 32 maintains the on state, the first switching element 31 and the magnetosensitive element 11 are always in a conductive state. Therefore, by switching the first switching element 31 between the on state and the off state, the supply and stop of the excitation current to the magnetosensitive element 11 is switched, as described above.

[0059] Here, the fluctuations in the induced voltage generated in the detection coil 12 are propagated back to the magnetic sensitive body 11, causing the voltage of the magnetic sensitive body 11 to fluctuate, which may affect the second control signal S2 of the second switching element 32.

[0060] However, the first capacitor 35 connected in parallel to the control signal line of the second switching element 32 has a capacitance Ca larger than the parasitic capacitance Cc between the control signal terminal (gate terminal) of the second switching element 32 and the magnetosensitive body side terminal (drain terminal) of the second switching element 32 located on the magnetosensitive body 11 side. Therefore, there is almost no effect on the second control signal S2 in the control signal line of the second switching element 32 through the parasitic capacitance Cc between the control signal terminal of the second switching element 32 and the magnetosensitive body side terminal of the second switching element 32. Therefore, even if fluctuations in the induced electromotive force generated in the detection coil 12 are propagated back to the magnetosensitive body 11, the second switching element 32 can stably maintain an on state.

[0061] When the second switching element 32 is in the on state, the second switching element 32 has a predetermined electrical resistance between the terminal (source terminal) of the second switching element 32 on the power source 20 side and the terminal (drain terminal) on the magnetosensitive element 11 side. Due to the influence of the electrical resistance of the second switching element 32, the voltage fluctuation of the magnetosensitive element 11 is reduced by the time it reaches the terminal (source terminal) of the second switching element 32 on the power source 20 side. Therefore, the voltage fluctuation at the terminal (drain terminal) of the first switching element 31 on the magnetosensitive element 11 side is smaller than the voltage fluctuation occurring in the magnetosensitive element 11. As a result, the influence on the control signal terminal (gate terminal) of the first switching element 31 is reduced. Therefore, the voltage fluctuation at the control signal terminal (gate terminal) of the first switching element 31 can be suppressed.

[0062] Furthermore, the electrical resistance of the second switching element 32 may change depending on the voltage at the control signal terminal (gate terminal) of the second switching element 32. If fluctuations in the induced voltage generated in the detection coil 12 are propagated back to the magnetosensitive body 11, causing fluctuations in the voltage of the magnetosensitive body 11, the voltage at the control signal terminal (gate terminal) of the second switching element 32 may change.

[0063] However, as described above, due to the action of the first capacitor 35, there is almost no effect on the second control signal S2 in the control signal line of the second switching element 32 through the parasitic capacitance Cc between the control signal terminal (gate terminal) of the second switching element 32 and the magnetically sensitive body side terminal (drain terminal) of the second switching element 32. Therefore, the voltage of the control signal terminal (gate terminal) of the second switching element 32 can be maintained in a stable state. As a result, the electrical resistance of the second switching element 32 is stabilized at a predetermined value.

[0064] Therefore, even if fluctuations in the induced electromotive force generated in the detection coil 12 are propagated back to the magnetosensitive body 11, it is possible to suppress the influence on the control signal terminal of the first switching element 31 and the control signal terminal of the second switching element 32. As a result, the excitation current supplied to the magnetosensitive body 11 from the first switching element 31 via the second switching element 32 is stabilized. In this state, by detecting the induced electromotive force generated in the detection coil 12, the magnitude of the magnetism can be detected with high accuracy.

[0065] In particular, by setting the capacitance Ca of the first capacitor 35 to be 10 or more times, or even 100 or more times, the parasitic capacitance Cc, the influence of the parasitic capacitance Cc on the second control signal S2 in the control signal line of the second switching element 32 is extremely small, thereby making it possible to more reliably achieve the above-described operation.

[0066] 5. Function of the Second Capacitor 36 Next, we will explain the function of the second capacitor 36. One end of the second capacitor 36 is connected to the current supply line located between the second switching element 32 and one end 11 a of the magnetosensitive body 11, and the other end is connected to the ground potential.

[0067] When the fluctuations in the induced electromotive force generated in the detection coil 12 are propagated back to the magnetosensitive body 11, causing fluctuations in the voltage of the magnetosensitive body 11, the second capacitor 36 acts to suppress voltage changes at one end 11a of the magnetosensitive body 11. Therefore, when the fluctuations in the induced electromotive force generated in the detection coil 12 are propagated back to the magnetosensitive body 11, the second capacitor 36 acts to suppress transmission of the fluctuations in the voltage of the detection coil 12 to the second switching element 32 side.

[0068] 6. Function of the Variable Resistor 34 Next, a description will be given of the function of the variable resistor 34. The variable resistor 34 is configured so that its resistance value can be changed in accordance with the sensitivity of the magnetic detection element 10.

[0069] First, a case will be described in which a large induced voltage is generated in the detection coil 12 when an excitation current is supplied to the magnetosensitive body 11, i.e., a case in which the sensitivity of the magnetic detection element 10 is high. In such a case, by increasing the resistance value of the variable resistor 34, the current flowing through the magnetosensitive body 11 can be reduced, and as a result, the induced voltage generated across the detection coil 12 can be reduced.

[0070] Here, if the sensitivity of the magnetic detection element 10 is above a certain level, this can cause ringing, etc. In other words, there is a risk that the output voltage of the detection coil 12 will fluctuate, i.e., noise will occur.

[0071] In particular, in this embodiment, an insulating layer is formed between the magnetosensitive element 11 and the detection coil 12. This means that there is a capacitance between the magnetosensitive element 11 and the detection coil 12. Then, depending on the amount of energy of the induced electromotive force, coupling occurs from the detection coil 12 to the magnetosensitive element 11, and a signal called a reflection phenomenon is generated in the magnetosensitive element 11. In order to reduce the amount of this reflection, it is effective to increase the film thickness of the insulating layer or suppress the current in the magnetosensitive element 11. In other words, by increasing the resistance value of the variable resistor 34, the current in the magnetosensitive element 11 can be suppressed. As a result, ringing can be suppressed.

[0072] Furthermore, the induced electromotive force generated in the detection coil 12 affects the input range of the detection circuit 40. Here, a withstand voltage standard that the detection circuit 40 can withstand is set. In order to satisfy this withstand voltage standard, it is necessary to suppress the induced electromotive force generated in the detection coil 12. By increasing the resistance value of the variable resistor 34, it is possible to make the induced electromotive force generated in the detection coil 12 satisfy the withstand voltage standard of the detection circuit 40.

[0073] On the other hand, a case will be described in which the induced voltage generated in the detection coil 12 when an excitation current is supplied to the magnetosensitive body 11 is small, i.e., the sensitivity of the magnetic detection element 10 is low. In such a case, if the output signal of the detection coil 12 is smaller than the noise, the output signal will be significantly affected by the noise. Therefore, by reducing the resistance value of the variable resistor 34, the current flowing through the magnetosensitive body 11 can be increased, and the induced voltage generated in the detection coil 12 can be made larger than the noise.

[0074] (Embodiment 2) A magnetic sensor device 2 according to embodiment 2 will be described with reference to Fig. 4. Note that, among the symbols used in embodiment 2, those that are the same as those used in the previous embodiments represent the same components as those in the previous embodiments, unless otherwise specified.

[0075] In the first embodiment, the first capacitor 35 is connected between the control signal line of the second switching element 32 and the ground potential. In the present embodiment, one end of the first capacitor 35 is connected to the control signal line of the second switching element 32, and the other end is connected to the power supply 20. In this case, the same effects as in the first embodiment are achieved.

[0076] Third Embodiment A magnetic sensor device 3 according to a third embodiment will be described with reference to Fig. 5. In the first and second embodiments, the second switching element 32 is configured as a p-channel element.

[0077] In this embodiment, the second switching element 32 is configured as an n-channel type. Therefore, the source terminal of the second switching element 32 is connected to one end 11a of the magnetosensitive body 11, and the drain terminal is connected to the drain terminal of the first switching element 31. In this case, the second control signal S2 of the second switching element 32 has a positive constant potential, so that the second switching element 32 is maintained in the on state.

[0078] Furthermore, the capacitance Ca of the first capacitor 35 is set to be larger than the parasitic capacitance Cc between the gate and source of the second switching element 32 .

[0079] This embodiment also provides the same effects as those of the first and second embodiments. In this embodiment, the first capacitor 35 may be connected to the power supply 20 as in the second embodiment.

[0080] (Fourth Embodiment) A magnetic sensor device 1 according to a fourth embodiment will be described with reference to Fig. 6. In the first to third embodiments, one second switching element 32 is disposed between the first switching element 31 and one end 11a of the magnetosensitive body 11. In this embodiment, a plurality of second switching elements 32a, 32b are disposed in parallel between the first switching element 31 and one end 11a of the magnetosensitive body 11.

[0081] Specifically, the energization circuit 30 includes a second p-type switching element 32a and a second n-type switching element 32b as the second switching element 32. The second p-type switching element 32a is a p-channel type. The source terminal of the second p-type switching element 32a is connected to the drain terminal of the first switching element 31, and the drain terminal is connected to one end 11a of the magnetosensitive element 11.

[0082] The second p-type switching element 32a receives a second p-side control signal S2a, which has a potential equal to or lower than the ground potential, so that the second p-type switching element 32a is maintained in the ON state.

[0083] The second n-type switching element 32b is an n-channel type and is connected in parallel to the second p-type switching element 32a. The second n-type switching element 32b has a source terminal connected to one end 11a of the magnetosensitive element 11 and a drain terminal connected to the drain terminal of the first switching element 31.

[0084] The second n-type switching element 32b receives the second n-side control signal S2b, which is the inverse of the second p-side control signal S2a. That is, the second n-side control signal S2b has a positive potential. Therefore, the second n-type switching element 32b is maintained in the on state.

[0085] Furthermore, the energization circuit 30 includes a first p-side capacitor 35a and a first n-side capacitor 35b as the first capacitor 35. The first p-side capacitor 35a is connected in parallel to the control signal line of the second p-type switching element 32a. One end of the first p-side capacitor 35a is connected to the control signal line of the second p-type switching element 32a, and the other end is connected to ground potential. However, as in the second embodiment, the other end of the first p-side capacitor 35a may be connected to the power supply 20. The capacitance Ca1 of the first p-side capacitor 35a is set to be larger than the parasitic capacitance Cc1 between the gate and drain of the second p-type switching element 32a.

[0086] The first n-side capacitor 35b is connected in parallel to the control signal line of the second n-type switching element 32b. One end of the first n-side capacitor 35b is connected to the control signal line of the second n-type switching element 32b, and the other end is connected to ground potential. However, as in the second embodiment, the other end of the first n-side capacitor 35b may be connected to the power supply 20. The capacitance Ca2 of the first n-side capacitor 35b is set to be larger than the parasitic capacitance Cc2 between the gate and source of the second n-type switching element 32b.

[0087] This embodiment also provides the same effects as the first to third embodiments.

Claims

1. A magnetic sensor device comprising: a magnetic detection element having a magnetosensitive body and a detection coil wound around the magnetosensitive body; an energization circuit that periodically excites the magnetosensitive body of the magnetic detection element; and a detection circuit connected to the detection coil and detecting a voltage signal generated in the detection coil, wherein the energization circuit comprises: a first switching element of a p-channel type that is arranged between a power source and one end of the magnetosensitive body and is configured to be able to switch between an on state in which an excitation current is supplied to the magnetosensitive body and an off state in which the supply of excitation current to the magnetosensitive body is stopped based on the input of a first control signal that is an on / off signal; a second switching element that is arranged between the first switching element and one end of the magnetosensitive body and receives an input of a second control signal so as to maintain the on state; and a capacitor that is connected in parallel to the control signal line of the second switching element and has a capacitance larger than the parasitic capacitance between the control signal terminal of the second switching element and the magnetosensitive body side terminal of the second switching element that is connected to one end of the magnetosensitive body, and is configured to maintain the on state of the second switching element.

2. The magnetic sensor device according to claim 1, wherein one end of the capacitor is connected to the control signal line and the other end is connected to a ground potential.

3. The magnetic sensor device according to claim 1, wherein one end of the capacitor is connected to the control signal line and the other end is connected to the power supply.

4. A magnetic sensor device as described in any one of claims 1 to 3, wherein the current-carrying circuit further includes a second capacitor having one end connected to a current supply line located between the second switching element and one end of the magnetic sensitive body and the other end connected to ground potential.

5. The magnetic sensor device according to any one of claims 1 to 3, wherein the second switching element is of a p-channel type.

6. The magnetic sensor device according to any one of claims 1 to 3, wherein the second switching element is an n-channel type.

7. A magnetic sensor device according to any one of claims 1 to 3, wherein the second switching element comprises: a second p-type switching element configured as a p-channel type, to which a second p-side control signal is input as the second control signal; and a second n-type switching element connected in parallel to the second p-type switching element, to which a second n-side control signal, which is the inverse of the second p-side control signal, is input as the second control signal, to which a second n-side control signal, which is the inverse of the second p-side control signal, is input as the second control signal.

8. A magnetic sensor device as described in any one of claims 1 to 3, wherein the current-carrying circuit further comprises a third switching element of an n-channel type, arranged between the other end of the magnetic sensitive body and ground potential, and configured to be switchable between an on state in which an excitation current is supplied to the magnetic sensitive body and an off state in which the supply of excitation current to the magnetic sensitive body is stopped based on the input of a third control signal which is an on / off signal that is the inverse of the first control signal.

9. The magnetic sensor device according to claim 8, wherein the current-carrying circuit further comprises a variable resistor disposed between the other end of the magnetic sensitive body and the third switching element.

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