Magnetic sensor device

Abstract

The present invention provides a magnetic sensor device that can improve detection accuracy by reducing ground noise in the detection signal of a magnetic detection element. [Solution] The magnetic sensor device 1 comprises a magnetic detection element 2 having a magnetosensitive element 21 and a detection coil 22, an energizing circuit 3 that periodically energizes the magnetosensitive element 21, an on / off switch SW1 inserted between the other terminal 202 of the magnetosensitive element 21, one of which terminals 201 is connected to the energizing circuit 3, and ground GND, an on / off switch control unit 5, and a magnetic detection circuit 4 to which a detection signal S1 generated in the detection coil 22 is input. The on / off switch control unit 5 opens the on / off switch SW1 during the off period of periodic energizing of the magnetosensitive element 21, thereby electrically disconnecting the magnetosensitive element 21 from ground GND.

Description

Technical Field

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

Background Art

[0002] A magnetic sensor device using a magnetic detection element generally includes a current-carrying circuit that excites a magnetoresistive element of the magnetic detection element, and a magnetic detection circuit to which a detection signal generated in a detection coil of the magnetic detection element is input along with the excitation. The magnetic detection circuit has a sample-and-hold circuit that periodically samples at a predetermined timing synchronized with the current-carrying timing to the magnetic detection element, and is configured to detect the strength of an external magnetic field to be measured. At this time, when the detection signal changes due to an external factor, it affects the detection accuracy, and thus various proposals have been made to improve the detection accuracy by the magnetic sensor device.

[0003] For example, the magnetic sensor circuit disclosed in Patent Document 1 includes a pulse current supply circuit and a sample-and-hold circuit, and also includes a temperature detection circuit and a temperature compensation circuit for temperature compensation of the magnetic sensor circuit. The pulse current supply circuit supplies a pulsed excitation current to the magnetic detection element, and the sample-and-hold circuit is configured to hold and output the substantially peak value of the detection signal. The temperature detection circuit utilizes, for example, the temperature characteristics of a PN junction such as a diode, and the temperature compensation circuit performs correction based on the detected temperature signal on the hold signal held by the sample-and-hold circuit. Thereby, even in an environment where a temperature change occurs, for example, fluctuations in the hold signal due to the temperature characteristics of the sample-and-hold circuit can be compensated.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in the magnetic sensor circuit disclosed in Patent Document 1, one end of the magnetic detection element's magnetometer is connected to a pulse current supply circuit, and the other end is grounded. In this configuration, when no excitation current is supplied to the magnetometer, the node on the current supply side of the magnetometer becomes floating. If fluctuations occur in the ground potential in this state, the fluctuations propagate from the grounded side of the magnetometer to the floating node, and current flows bidirectionally through the magnetometer according to the potential difference that occurs on both sides of the magnetometer. Therefore, the magnetization vector of the magnetometer may change slightly prior to detection, potentially affecting the detection signal, and it is desirable to reduce noise caused by ground fluctuations.

[0006] This invention has been made in view of the above problems, and aims to provide a magnetic sensor device that can improve detection accuracy by reducing ground noise in the detection signal of a magnetic detection element. [Means for solving the problem]

[0007] To solve the above problems, a magnetic sensor device according to one aspect of this disclosure is provided. A magnetic detection element having a magnetosensitive element and a detection coil, A current-carrying circuit that periodically energizes the magnetic sensor, An on / off switch is inserted between the other terminal of the magnetic sensor, which is connected to the current circuit, and ground, and one terminal of the switch is connected to the current circuit. A switch control unit that controls the operation of the switch, It comprises a magnetic detection circuit to which a detection signal generated in the detection coil in accordance with periodic excitation is input, The on / off switch control unit is located in a magnetic sensor device that opens the on / off switch during the off-period of periodic excitation of the magnetic sensor, thereby electrically isolating the magnetic sensor from the ground.

[0008] Furthermore, magnetic sensor devices relating to other aspects of this disclosure are: A magnetic detection element having a magnetosensitive element and a detection coil, A current-carrying circuit that periodically energizes the magnetic sensor, A short-circuit switch is inserted between one terminal of the magnetosensitive element connected to the current-carrying circuit and the other terminal of the magnetosensitive element connected to ground. A short-circuit switch control unit that controls the driving of the short-circuit switch, It comprises a magnetic detection circuit to which a detection signal generated in the detection coil in accordance with periodic excitation is input, The short-circuit switch control unit is located in a magnetic sensor device that closes the short-circuit switch during the on-period of periodic excitation of the magnetic sensor, thereby short-circuiting the terminals of the magnetic sensor. [Effects of the Invention]

[0009] In the magnetic sensor device according to the above embodiment, one terminal of the magnetic sensing element is connected to an energizing circuit, and the other terminal is connected to ground via an on / off switch. The on / off switch is controlled by the on / off switch control unit to be open during the off period of periodic excitation of the magnetic sensing element, electrically isolating the magnetic sensing element from ground. Therefore, even when one terminal of the magnetic sensing element is a floating node, ground fluctuations do not propagate from the other terminal, preventing a potential difference from occurring on both sides of the magnetic sensing element and suppressing changes in the magnetization vector. In this state, when the on / off switch is closed by the on / off switch control unit during the on period of periodic excitation of the magnetic sensing element, the magnetic sensing element and ground are electrically connected, and the detection signal generated in the detection coil of the magnetic sensing element is input to the magnetic detection circuit. This reduces the influence of ground fluctuations on magnetic detection, enabling accurate detection.

[0010] In the magnetic sensor device of the other embodiment described above, a short-circuit switch is provided between one terminal of the magnetic detection element connected to the current circuit and the other terminal connected to the ground. The short-circuit switch is controlled by a short-circuit switch control unit so that it is open during the on-period of periodic excitation of the magnetic sensor. Therefore, even if ground fluctuations can propagate from the other terminal to one terminal of the magnetic sensor, the potential difference is eliminated when both terminals are short-circuited during the on-period. As a result, changes in the magnetization vector caused by the potential difference are suppressed, the influence of ground fluctuations on magnetic detection is reduced, and accurate detection becomes possible.

[0011] As described above, according to the above embodiment, it is possible to provide a magnetic sensor device that can reduce ground noise in the detection signal of a magnetic detection element and improve detection accuracy. [Brief explanation of the drawing]

[0012] [Figure 1] This is a circuit diagram showing an example of the configuration of a magnetic sensor device in Embodiment 1. [Figure 2] This figure shows an example of the configuration of the main parts of the magnetic sensor device in Embodiment 1. [Figure 3] This is a timing chart showing the operation of the magnetic sensor device in Embodiment 1. [Figure 4] This figure illustrates the effects of the magnetic sensor device in Embodiment 1. [Figure 5] This is a schematic diagram illustrating the effect of ground noise acting on a magnetic sensor element in Embodiment 1. [Figure 6] This figure shows an example of the main components of the switch control unit of the magnetic sensor device in Embodiment 1. [Figure 7] This figure shows an example of the main components of the switch control unit of the magnetic sensor device in Embodiment 1. [Figure 8] This is a circuit diagram showing an example configuration of the magnetic sensor device in Embodiment 2. [Figure 9]It is a diagram showing a configuration example of an open / close switch used in the magnetic sensor device in Embodiment 2. [Figure 10] It is a circuit diagram showing a configuration example of the magnetic sensor device in Embodiment 3. [Figure 11] It is a circuit diagram showing a configuration example of the magnetic sensor device in Embodiment 4. [Figure 12] It is a circuit diagram showing a modified example of the magnetic sensor device in Embodiment 4. [Figure 13] It is a schematic diagram showing a main part configuration example of the magnetic sensor element in Embodiment 4.

Embodiments for Carrying out the Invention

[0013] Hereinafter, each embodiment will be specifically described with reference to the drawings.

[0014] In addition, each of the embodiments described below shows comprehensive or specific examples. Numerical values, shapes, components, arrangement positions of components, connection forms, etc. shown in the embodiments are just examples and are not intended to limit the present disclosure. Among the components in the following embodiments, components not described in the independent claims indicating the most general concept shall be described as optional components.

[0015] Also, the magnetic sensor device of the present disclosure will be described based on the embodiments, but the magnetic sensor device according to the present disclosure is not limited to the following embodiments. Modifications obtained by those skilled in the art by making various modifications to the following embodiments without departing from the gist of the present disclosure, and various devices incorporating the magnetic sensor device according to the present disclosure are also included in the present disclosure.

[0016] (Embodiment 1) FIG. 1 is a circuit diagram showing a configuration example of the magnetic sensor device 1 according to Embodiment 1. FIGS. 2 to 7 are diagrams for explaining a configuration example or operation of the main part of the magnetic sensor device 1.

[0017] [Basic configuration of magnetic sensor device 1] In Figure 1, the magnetic sensor device 1 comprises a magnetic detection element 2 having a magnetosensitive element 21 and a detection coil 22, an energizing circuit 3 that periodically energizes the magnetosensitive element 21, and a magnetic detection circuit 4 to which a detection signal S1 generated in the detection coil 22 due to the periodic energizing is input. The magnetic sensor device 1 also includes an on / off switch SW1 and an on / off switch control unit 5.

[0018] One terminal of the magnetic sensor 21 is connected to the power supply circuit 3, and an on / off switch SW1 is inserted between the other terminal of the magnetic sensor 21 and the ground GND. In other words, the other terminal of the magnetic sensor 21 is electrically connected in series with the ground GND via the on / off switch SW1, and the on / off switch SW1 can switch between conduction and disconnection with the ground GND. The on / off switch control unit 5 controls the driving of the on / off switch SW1.

[0019] Specifically, the on / off switch control unit 5 opens the on / off switch SW1 during the off-period of periodic excitation to the magnetic sensor 21 (see Figures 2 and 3), thereby electrically disconnecting the magnetic sensor 21 from the ground GND. The off-period and on-period of excitation can be set as appropriate according to the waveform of the detection signal S1, the detection timing, etc.

[0020] As a result, even when the ground GND fluctuates relative to the reference voltage (see Figure 4), the fluctuations in the ground GND are not propagated to the magnetosensitive element 21 during the excitation off period, making it possible to perform magnetic detection in a stable state.

[0021] The switching switch SW1 can be, for example, a voltage-driven switching element (see Figure 2). In that case, the switching switch control unit 5 can control the magnitude of the voltage applied to the control electrode of the switching element SW1 during the off-period of periodic excitation of the magnetic sensor 21. Specifically, it is desirable that the control voltage applied to the control electrode during the off-period of excitation does not exceed the threshold voltage required to turn on the switching element.

[0022] The switching control unit 5 includes, for example, a drive voltage generation unit 50 for driving the switching element on and off. The drive voltage generation unit 50 can generate a positive on-drive voltage applied to the control electrode during the on-period of the switching element, and can also generate an off-drive voltage applied to the control electrode during the off-period of the switching element that is lower than the ground reference voltage (see Figure 4).

[0023] With this configuration, during the off-period of excitation to the magnetic sensor 21, the switching element remains in an undriven state, and the on / off switch SW1 remains open. This reliably disconnects the electrical connection between the magnetic sensor 21 and the ground GND, suppressing the propagation of ground fluctuations and reducing the influence of ground noise on the detection signal S1.

[0024] [Components of Magnetic Sensor Device 1] Next, we will specifically describe each component of the magnetic sensor device 1 in this embodiment. In Figure 1, the magnetic sensor device 1 comprises, as described above, a magnetic detection element 2, a power supply circuit 3, a magnetic detection circuit 4, an on / off switch SW1, and an on / off switch control unit 5. The magnetic sensor device 1 may also include a detection clock generation unit 30 and a signal processing unit 60.

[0025] The detection clock generation unit 30 generates a detection clock SMPL that corresponds to the peak value of the detection signal S1 in the magnetic detection circuit 4. The signal processing unit 60 can perform processing on the output signal from the magnetic detection circuit 4, such as analog-to-digital conversion or temperature compensation based on temperature characteristics.

[0026] The magnetic detection element 2 is, for example, a magneto impedance (MI) element comprising a magnetosensitive element 21 and a detection coil 22 (hereinafter referred to as the "MI element"). The magnetosensitive element 21 is, for example, made of amorphous wire, and the detection coil 22 is wound around the magnetosensitive element 21 with an insulating layer in between. The MI element 2 outputs an induced electromotive force Vi generated across the detection coil 22 when an excitation current is supplied to the magnetosensitive element 21 as a detection signal S1.

[0027] The MI element 2 is arranged, for example, on an element substrate 20, and a pair of terminals provided on the element substrate 20 are electrically connected to both ends of the magnetic sensor 21. One terminal of the magnetic sensor 21, the first terminal 201, is connected to the output terminal of the driver 32 of the energizing circuit 3, and the other terminal, the second terminal 202, is connected to the on / off switch SW1. One end of the detection coil 22 of the MI element 2 is connected to the magnetic detection circuit 4 via a signal line 71, and the other end is grounded.

[0028] A reference voltage source VREF is connected to signal line 71 via a resistor. Furthermore, the magnetic detection element 2 can be any element capable of detecting magnetism; in addition to the MI element 2, for example, a Hall element, MR element (magnetoresistive element), GMR element (giant magnetoresistive element), or TMR element (tunnel junction magnetoresistive element) can be used.

[0029] The energizing circuit 3 periodically supplies an excitation current to the MI element 2. Here, the energizing circuit 3 is configured as a pulse energizing circuit that can supply a pulse current to the magnetosensitive element 21, as an example. The excitation current can be any periodic current; in addition to a pulse current, a high-frequency current can also be used, for example.

[0030] The power supply circuit 3 generates a pulsed excitation clock MSI to supply excitation current to the MI element 2, for example, in synchronization with an external clock CLK. The power supply circuit 3 includes a clock generation unit 31 and a driver 32. The clock generation unit 31 receives a pulsed detection clock SMPL from a detection clock generation unit 30. As a result, the clock generation unit 31 generates a clock signal based on the rising edge of the external clock CLK and the falling edge of the detection clock SMPL, which drives the driver 32 and outputs the excitation clock MSI.

[0031] The magnetic detection circuit 4 includes, for example, a sample-and-hold circuit 41 and an amplification circuit 42 located thereafter. The sample-and-hold circuit 41 has a switch 401 for opening and closing a signal line 71 and a capacitor 402 for sampling the detection signal S1. One end of the capacitor 402 is connected between the switch 401 and the amplification circuit 42, and the other end is grounded. A detection clock generation unit 30 is connected to the sample-and-hold circuit 41 via the signal line 72, and the switch 401 is driven on and off by the detection clock SMPL.

[0032] The detection clock generation unit 30 is configured, for example, using a delay circuit including multiple delay elements, and can generate a pulsed detection clock SMPL having a predetermined delay amount based on an external clock CLK. The predetermined delay amount is set in advance, for example, so that the falling edge of the detection clock SMPL corresponds to the peak value of the detection signal S1.

[0033] The switching control unit 5 controls the connection between the MI element 2 and ground GND by switching the switching switch SW1 in response to the periodic excitation of the MI element 2 by the energizing circuit 3. As shown in Figure 2, a voltage-driven transistor can be used as the switching element for the switching switch SW1, and here, as an example, an n-type MOS transistor is used.

[0034] An n-type MOS transistor can switch between conduction and disconnection between the drain electrode D and the source electrode S by switching the control voltage of the gate electrode G, which is the control electrode, to a high level or a low level. In other words, when the switching element is turned on (or turned off), the on / off switch SW1 becomes closed (or open), and the magnetic detection element 2 and ground GND are electrically connected (or disconnected).

[0035] In Figure 1, the switching control unit 5 includes a control signal generation unit 501 that generates a switching control signal MISW, and a drive voltage generation unit 50 that generates an on-drive voltage and an off-drive voltage based on the switching control signal MISW. The drive voltage generation unit 50 includes an off-voltage generation circuit 51, a level shift circuit 52, and a driver circuit 53, and generates an on-drive voltage (>threshold voltage) output from the driver circuit 53 during the on period of the switching element, and also generates an off-drive voltage output during the off period of the switching element.

[0036] Specifically, the switching control unit 5 controls the switching element so that the magnitude of the control voltage does not exceed the threshold voltage for ON drive during the off period of the switching element, in other words, so that the switching element remains in the OFF state. To this end, the drive voltage generation unit 50 uses the off voltage generation circuit 51 and the level shift circuit 52 to adjust the voltage of the power supply line for OFF drive so that the OFF drive voltage is lower than the reference voltage of ground GND. A detailed example of the configuration of the drive voltage generation unit 50 will be described later.

[0037] In an n-type MOS transistor, the drain electrode D is connected to the magnetic detection element 2, and the source electrode S is connected to ground GND. Current flows from the drain electrode D to the source electrode S when the gate voltage > source voltage. Furthermore, the n-type MOS transistor is mounted on a p-type substrate B, and the gate electrode G is electrically insulated from the other electrodes.

[0038] In an n-type MOS transistor, the substrate B is usually connected to ground (GND) along with the source electrode S. However, in this configuration, it can be connected to the power supply line for off-drive operation. This allows the potential of the substrate B to be lower than that of the source electrode S, electrically isolating it and stabilizing the switching operation.

[0039] [Basic operation of magnetic sensor device 1] In Figure 2, when an external magnetic field H is applied to the MI element 2, the magnetization vector of the magnetosensitive element 21 changes in the Z-axis direction (the longitudinal direction of the magnetosensitive element 21). The amount of change (θ) at this time depends on the strength of the external magnetic field H. Furthermore, when current Ia flows through the magnetosensitive element 21 due to the energizing circuit 3, the magnetization vector changes due to the impedance effect, and an induced electromotive force Vi is generated across the detection coil 22. At this time, the on / off switch SW1 is assumed to be in the closed state.

[0040] As shown in Figure 3, when the excitation clock MSI rises in synchronization with the external clock CLK, a current Ia flows through the MI element 2 and rises to a predetermined current value. Consequently, the induced electromotive force Vi, which is the detection signal S1, gradually increases and reaches its peak value with a predetermined delay time relative to the rising edge of the external clock CLK. At this timing, the detection clock SMPL falls, and simultaneously, the excitation clock MSI falls, stopping the current Ia flowing through the MI element 2. After reaching its peak value, the induced electromotive force Vi gradually decreases.

[0041] The detection clock SMPL rises prior to the output of the induced electromotive force Vi, closing the switch 401 of the sample-and-hold circuit 41 and allowing charge to be stored in the capacitor 402. Subsequently, when the detection clock SMPL falls at the timing when the induced electromotive force Vi reaches its peak, the switch 401 opens, and the charge is retained in the capacitor 402. By retaining the charge at the peak timing in this way, highly sensitive detection becomes possible.

[0042] [Operation of MI Element 2] On the other hand, in Figure 2, when the supply of excitation current to the MI element 2 is interrupted, node N1 on the first terminal 201 side of the magnetosensitive element 21 becomes floating. In a conventional configuration without an on / off switch SW1, as shown in Figure 4, if fluctuations occur in the ground GND (GND floating or GND sinking), the fluctuations propagate from the ground GND through the magnetosensitive element 21 to the floating node N1. At this time, as shown in Figure 5, the propagation of fluctuations requires a time difference determined by the time constant (RC) of the magnetosensitive element 21, causing a small change in the magnetization vector.

[0043] In Figure 5, if state A is floating to GND and state B is submerged to GND, then a potential difference (±α) is generated across the magnetic sensor 21. As a result, a current Ib flows in both directions along the Z axis, causing a small change in the direction in which the magnetization vector increases (+θ1) or decreases (-θ2) relative to the initial change (θ).

[0044] Thus, when the magnetization vector of the magnetosensitive element 21 is affected by fluctuations in the ground (GND), the detection accuracy of the external magnetic field H decreases because ground noise is included in the detection signal S1. For example, in a configuration where the ground of the MI element 2 and the surrounding circuitry are shared, the effect of ground noise becomes larger and cannot be ignored. Therefore, in this embodiment, an on / off switch SW1 is placed between the MI element 2 and the ground (GND), isolating the MI element 2 from the ground (GND) during the excitation off period. This reduces the effect of ground noise on the detection signal S1 output during the on period.

[0045] [Configuration of the on / off switch control unit 5] Furthermore, in this embodiment, a switching control unit 5 is provided to control the switching switch SW1, and as shown in Figure 4, the off-drive voltage generated by the drive voltage generation unit 50 is adjusted to be lower than the reference voltage of the ground GND.

[0046] Preferably, taking into account fluctuations in the ground (GND), it is desirable to set the offset amount of the off-drive voltage to be larger on the negative side than the magnitude of the fluctuation (GND floating or GND sinking) relative to the reference voltage (e.g., 0V). This maintains a state in which the gate voltage applied to the n-type MOS transistor constituting the switching switch SW1 is less than or equal to the ground (GND) voltage, thereby suppressing the flow of current to the MI element 2 during the excitation off period.

[0047] The drive voltage generation unit 50 uses the off voltage generation circuit 51 to generate a low voltage for off-drive by stepping down the reference voltage of the ground GND, and supplies it to the level shift circuit 52 and the driver circuit 53. The level shift circuit 52 generates a signal by level-shifting the switching control signal MISW, drives the driver circuit 53, and can output a signal to turn on or off the switching switch SW1.

[0048] As shown in Figure 6 as an example, the off-voltage generation circuit 51 takes the ground reference voltage (e.g., 0V) as the input voltage Vin, steps it down to a desired voltage for off-drive (e.g., -0.5V), and outputs it from the output terminal 511. The off-voltage generation circuit 51 steps down the input voltage Vin using the first capacitor C1 and the second capacitor C2, and maintains the voltage of the step-down voltage line 512 connected to the output terminal 511 at a desired output voltage Vout using an LDO (Low Drop Out) type regulator R. A p-type MOS transistor T1 is inserted in the step-down voltage line 512, and its on-resistance is controlled according to the output of the regulator R.

[0049] Between the p-type MOS transistor T1 and the input terminal 513, a first capacitor C1 and a second capacitor C2 are connected in parallel to each other between the step-down voltage line 512 and the reference voltage line 514 connected to ground GND. On the step-down voltage line 512, a first diode D1 and a second diode D2 are inserted between the connection point of the first capacitor C1 and the input terminal 513, and between the two connection points of the first capacitor C1 and the second capacitor C2, with the input terminal 513 side as the cathode. A third capacitor C3 is placed between the output terminal 511 and the reference voltage line 514.

[0050] Here, input terminal 513 is connected to reference voltage line 514, and the input voltage Vin is the reference voltage (e.g., 0V). In addition, a driver circuit 515 that outputs a pulsed voltage signal (e.g., 1V) based on an external clock or the like is connected between the first capacitor C1 and the step-down voltage line 512.

[0051] At this time, as shown in the figure as (1) and (2), first, charge is accumulated in the first capacitor C1 by pulse current, and then discharged to the reference voltage line 514 via the first diode D1. Consequently, charge moves from the second capacitor C2 side to the first capacitor C1 via the second diode D2, and the potential across the first capacitor C1 and the second capacitor C2 drops relative to the reference voltage. Here, the potential on the driver circuit 515 side becomes 0.5V from 0V, and the potential on the step-down voltage line 512 becomes -0.5V from 1V.

[0052] In this way, the stepped-down voltage is output from the output terminal 511 to the level shift circuit 52. The regulator R compares the voltage of the step-down voltage line 512 and the voltage of the reference voltage Vref to generate the output voltage Vmon and control the on-resistance of the p-type MOS transistor T1. For example, if the voltage at the output terminal 511 is -0.6V, the on-resistance of the p-type MOS transistor T1 increases, and the supply to the output terminal 511 stops. Also, if the voltage at the output terminal 511 is -0.4V, the on-resistance of the p-type MOS transistor T1 decreases, and the driver circuit 515 lowers (supplies) the voltage at the output terminal 511 to -0.5V while it is operating. The off-voltage generation circuit 51 constantly monitors the voltage at the output terminal 511 and, by repeatedly operating, maintains a constant voltage on the step-down voltage line 512, enabling the supply of a stable output voltage Vout to the level shift circuit 52 and the driver circuit 53.

[0053] As shown in Figure 7 as an example, the level shift circuit 52 is a switch circuit using multiple stages of CMOS transistors, and it shifts the L-level voltage of the switching control signal MISW, which is the off-drive voltage of the switching switch SW1. The level shift circuit 52 is composed of CMOS transistors, specifically the first CMOS 521 to the fourth CMOS 524, which are p-type MOS transistors (hereinafter referred to as pMOS) and n-type MOS transistors (hereinafter referred to as nMOS) connected in series, and the switching control signal MISW is input to the input terminal of the first CMOS 521.

[0054] As a result, a signal obtained by inverting the opening / closing control signal MISW is output from the first CMOS 521. The output of the first CMOS 521 is input to the pMOS and nMOS of the second CMOS 522 and also input to the nMOS of the fourth CMOS 524. The output of the second CMOS 522 is input to the nMOS of the third CMOS 523, and the output of the third CMOS 523 is input to the pMOS of the fourth CMOS 524. Further, the output of the fourth CMOS 524 is input to the pMOS of the third CMOS 523 and output to the driver circuit 53.

[0055] The high-potential power supply line 502 of the level shift circuit 52 and the driver circuit 53 is connected to the power supply VDD (for example, 3.3V). The low-potential power supply line has a first line 503 connected to the ground GND (for example, 0V) and a second line 504 (<GND; for example, -0.5V) connected to the output terminal 511 from the step-down voltage line 512. The low-potential sides of the first CMOS 521 and the second CMOS 522 of the level shift circuit 52 are connected to the first line, and the low-potential sides of the third CMOS 523 and the fourth CMOS 524 of the level shift circuit 52 and the driver circuit 53 are connected to the second line 504.

[0056] Also, the driver circuit 53 has a two-stage structure of the fifth CMOS 525 and the sixth CMOS 526. The input signal to the driver circuit 53 is inverted by the fifth CMOS 525 and input to the sixth CMOS 526, and is configured to output an on-drive voltage or an off-drive voltage.

[0057] As a result, when the H level of the opening / closing control signal MISW is input (true value 1), an on-drive voltage of H level (3.3V) is output from the driver circuit 53 (true value 1). Also, when the L level of the opening / closing control signal MISW is input (false value 0), an off-drive voltage of L level (-0.5V) is output from the driver circuit 53 (false value 0).

[0058] By using the opening / closing switch control unit 5 having such a configuration, the driving of the opening / closing switch SW1 can be stably controlled.

[0059] Therefore, according to this embodiment, the on / off switch SW1, which is placed between the MI element 2 and the ground GND, is controlled by the on / off switch control unit 5, and the MI element 2 can be isolated from the ground GND during the excitation off period. As a result, the influence of ground noise on the detection signal S1 detected by the magnetic detection circuit 4 is suppressed, and the detection accuracy can be improved.

[0060] (Embodiment 2) Figure 8 is a circuit diagram showing an example configuration of the magnetic sensor device 1 according to Embodiment 2, and Figure 9 is a diagram showing another example of the on / off switch SW1 that constitutes the magnetic sensor device 1. In this embodiment, the basic configuration and operation of the magnetic sensor device 1 are the same as in Embodiment 1 described above, but the configuration and operation of the on / off switch control unit 5 are slightly different. The main differences will be explained below.

[0061] In Figure 8, the magnetic sensor device 1 comprises a magnetic detection element (MI element) 2, a power supply circuit 3, a detection clock generation unit 30, a magnetic detection circuit 4, an on / off switch SW1, an on / off switch control unit 5, and a signal processing unit 60.

[0062] In this embodiment, the switch control unit 5 of the magnetic sensor device 1 includes a control signal generation unit 501 that generates a switch control signal MISW. In this embodiment, there is no drive voltage generation unit 50, and the H-level voltage and L-level voltage of the switch control signal MISW output from the control signal generation unit 501 are used as the on-drive voltage and off-drive voltage to drive the switch SW1.

[0063] In this configuration as well, the MI element 2 is periodically energized by the energizing circuit 3, a detection signal S1 is output and sampled by the sample-and-hold circuit 41 of the magnetic detection circuit 4. The switching control unit 5 uses the switching control signal MISW to turn on the switching switch SW1 during the energization ON period and to turn off the switching switch SW1 during the energization OFF period.

[0064] As a result, the MI element 2 and the ground GND are isolated during the excitation off period, thus suppressing the propagation of fluctuations in the ground GND. For example, in configurations where the ground GND of the MI element 2 is not shared with other circuits, and the ground noise propagated to the MI element 2 is relatively small and there is no need to adjust the off-drive voltage, the switching control signal MISW may be used to directly control the switching switch SW1.

[0065] As shown in Figure 9, the switching switch SW1 can use an n-type MOS transistor similar to that in Embodiment 1, or a transfer gate switch TGSW which combines a p-type MOS transistor T2 and an n-type MOS transistor T3. In the transfer gate switch TGSW, the gate electrode G of the p-type MOS transistor T2 is input to the switching control signal MISW, and the gate electrode G of the n-type MOS transistor T3 is input to the inverted signal of the switching control signal MISW via an inverter INV. The p-type MOS transistor T2 and the n-type MOS transistor T3 are connected in parallel to the drain electrode D and the source electrode S.

[0066] The transfer gate switch TGSW is turned off when the switching control signal MISW is at a high level and turned on when it is at a low level. Since the p-type MOS transistor T2 and the n-type MOS transistor T3 are connected in parallel, the transfer gate switch TGSW is turned on (or off) when either of them is turned on (or off). Therefore, when the switching switch SW1 is configured as a transfer gate switch TGSW, faster on / off operation becomes possible, and the connection and disconnection with ground GND can be switched quickly.

[0067] Even with this configuration, the on / off switch control unit 5 maintains the open state of the on / off switch SW1 during the excitation off period, suppressing the effects of ground noise and enabling accurate magnetic detection.

[0068] (Embodiment 3) Figure 10 is a circuit diagram showing an example configuration of the magnetic sensor device 1 according to Embodiment 3. In this embodiment, the basic configuration and operation of the magnetic sensor device 1 are the same as in Embodiment 1 described above, except that a short-circuit switch SW2 is inserted instead of the on / off switch SW1. The main differences will be explained below.

[0069] In Figure 10, the magnetic sensor device 1 comprises a magnetic detection element (MI element) 2, an energizing circuit 3, a detection clock generation unit 30, and a magnetic detection circuit 4. The magnetic sensor device 1 also comprises a short-circuit switch SW2 and a short-circuit switch control unit 5a.

[0070] In this embodiment, the short-circuit switch SW2 is electrically inserted in parallel with the MI element 2 so that both sides of the MI element 2 can be short-circuited. That is, one end of the short-circuit switch SW2 is connected between the energizing circuit 3 and the first terminal 201 of the MI element 2, and the other end is connected between the ground GND and the second terminal 202 of the MI element 2. The switching switch SW1 and switching switch control unit 5 used in the above embodiments are not arranged, and the second terminal 202 of the MI element 2 is directly electrically connected to the ground GND.

[0071] The short-circuit switch control unit 5a has the same configuration as the switching switch control unit 5 in the first embodiment described above, and includes a control signal generation unit 501a that generates a short-circuit control signal ASW, and a drive voltage generation unit 50a. The drive voltage generation unit 50a may include an off-voltage generation circuit 51a, a level shift circuit 52a, and a driver circuit 53a, and generates a positive on-drive voltage output from the driver circuit 53a during the on-period of the switching element, as well as an off-drive voltage output during the off-period of the switching element. The configuration of each part of the drive voltage generation unit 50a is the same as that of the drive voltage generation unit 50 in the first embodiment described above, and therefore no further explanation is provided.

[0072] Alternatively, the short-circuit switch control unit 5a may be configured without a drive voltage generation unit 50a, and the short-circuit switch SW2 may be driven by the H-level and L-level voltages of the short-circuit control signal ASW output from the control signal generation unit 501a.

[0073] In this configuration as well, the MI element 2 is periodically energized by the energizing circuit 3, a detection signal S1 is output and sampled by the sample-and-hold circuit 41 of the magnetic detection circuit 4. The short-circuit switch control unit 5a drives the on / off switch SW1 to the ON period of the excitation and drives the on / off switch SW1 to the OFF period of the excitation using the short-circuit control signal ASW.

[0074] In the short-circuit switch control unit 5a, the timing at which the short-circuit control signal ASW is output from the control signal generation unit 501 can be the same as, for example, the output timing of the open / close control signal MISW in each of the above embodiments. In this case, during the ON period of excitation of the MI element 2, an ON drive voltage is output that closes the short-circuit switch SW2, causing conduction between the first terminal 201 and the second terminal 202 of the MI element 2. During the OFF period of excitation, an OFF drive voltage is output that opens the short-circuit switch SW2, interrupting conduction between the first terminal 201 and the second terminal 202 of the MI element 2.

[0075] As a result, during the excitation ON period, the first terminal 201 and the second terminal 202 of the MI element 2 are short-circuited via the short-circuit switch SW2, causing both terminals 201 and 202 to be at the same potential. Therefore, even when fluctuations occur in the ground GND, the potentials of both terminals 201 and 202 fluctuate similarly, thereby suppressing the generation of a potential difference.

[0076] Furthermore, during the excitation off period, the short-circuit switch SW2 is opened, and the short circuit between both terminals 201 and 202 of the MI element 2 is resolved. In this case, the drive voltage generation unit 50a of the short-circuit switch control unit 5a applies an off-drive voltage lower than the reference voltage of the ground GND, maintaining the off state and enabling stable switching control.

[0077] Thus, in this embodiment, by connecting the short-circuit switch SW2 to both sides of the MI element 2 and controlling its control voltage with the short-circuit switch control unit 5a, the potential difference generated in the MI element 2 during the excitation ON period can be eliminated. This suppresses the effects of ground noise and enables accurate magnetic detection.

[0078] (Embodiment 4) Figure 11 is a circuit diagram showing an example configuration of the magnetic sensor device 1 according to Embodiment 4, and Figure 12 is a modified example thereof. Figure 13 is a schematic diagram showing the main parts of the magnetic sensor device 1. In this embodiment, the basic configuration and operation of the magnetic sensor device 1 are the same as in Embodiment 1 described above, except that in addition to the on / off switch SW1 and the on / off switch control unit 5, a short-circuit switch SW2 and a short-circuit switch control unit 5a, similar to those in Embodiment 3, are also provided. The main differences will be explained below.

[0079] In Figure 11, the magnetic sensor device 1 comprises a magnetic detection element (MI element) 2, an energizing circuit 3, a detection clock generation unit 30, a magnetic detection circuit 4, an on / off switch SW1, and an on / off switch control unit 5. The magnetic sensor device 1 also comprises a short-circuit switch SW2 and a short-circuit switch control unit 5a.

[0080] In this embodiment, the arrangement of the on / off switch SW1 and the configuration of the on / off switch control unit 5 are the same as in Embodiment 1 above, and will not be described. The arrangement of the short-circuit switch SW2 and the basic configuration of the short-circuit switch control unit 5a are the same as in Embodiment 3 above, with only a slight difference in the configuration of the short-circuit switch control unit 5a.

[0081] The short-circuit switch control unit 5a includes a control signal generation unit 501a that generates a short-circuit control signal ASW, and a drive voltage generation unit 50a. The drive voltage generation unit 50a includes a level shift circuit 52a and a driver circuit 53a, and the off-voltage generation circuit 51 of the drive voltage generation unit 50 can be used as the off-voltage generation circuit 51a. That is, the off-voltage generation circuit 51 is connected to the step-down voltage line 512 of the drive voltage generation unit 50, and also to step-down voltage lines 512a and 512b that branch off from the step-down voltage line 512. The step-down voltage lines 512a and 512b are connected to the low-potential power lines of the level shift circuit 52a and the driver circuit 53a of the drive voltage generation unit 50a, respectively.

[0082] As a result, the step-down voltage generated in the off-voltage generation circuit 51 is supplied from the step-down voltage line 512 to the level shift circuit 52 and driver circuit 53 of the drive voltage generation unit 50, and also to the level shift circuit 52 and driver circuit 53 of the drive voltage generation unit 50a. This configuration simplifies the circuit configuration for switch control. As shown in Figure 12, the low-potential power lines of the level shift circuit 52a and driver circuit 53a of the drive voltage generation unit 50a do not necessarily have to be connected to the step-down voltage line 512, and may be grounded.

[0083] Furthermore, as schematically shown in Figure 13, the cross-sectional configuration of the MI element 2 is provided, with an insulating film 23 interposed between the magnetosensitive element 21, which is placed on the element substrate 20, and the detection coil 22 surrounding it, and a parasitic capacitance 24 exists. In such a configuration, for example, if fluctuations occur in the reference voltage source VREF or the ground GND connected to the detection coil 22 in Figure 11, there is a risk that the fluctuations will propagate to the magnetosensitive element 21 via the parasitic capacitance 24.

[0084] In that case, the influence of noise propagated through parasitic capacitance 24 can be reduced by connecting both ends of the magnetic sensor 21 via a short-circuit switch SW2. Therefore, by opening the on / off switch SW1 during the excitation off period to block noise propagated from ground GND through the magnetic sensor 21, and by closing the short-circuit switch SW2 during the excitation on period to short-circuit both ends of the magnetic sensor 21, the influence of noise caused by parasitic capacitance can be reduced.

[0085] According to this embodiment, by inserting an on / off switch SW1 between the magnetic sensor 21 and the ground GND, and by inserting a short-circuit switch SW2 connecting both ends of the magnetic sensor 21, magnetic detection can be performed with greater accuracy.

[0086] (Other embodiments) In the configuration of Embodiment 1 described above, the transfer gate switch TGSW exemplified in Embodiment 2 can also be used as the on / off switch SW1. Furthermore, although the third and fourth embodiments described above show configurations in which the magnetic sensor device 1 does not have a signal processing unit 60, a configuration in which the signal processing unit 60 is included is also possible. In addition, the configurations described in each of the above embodiments may be combined.

[0087] The present invention is not limited to the embodiments described above, and can be applied to various embodiments without departing from its spirit. [Explanation of Symbols]

[0088] SW1 Open / Close Switch SW2 Short-circuit switch GND (Ground) S1 detection signal 1. Magnetic sensor device 2 Magnetic sensor element 21 Magnetically sensitive body 22 detection coils 201 First terminal (one of the terminals) 202 Second terminal (the other terminal) 3. Power supply circuit 30 Detection clock generation unit 4. Magnetic detection circuit 5. On / Off Switch Control Unit 5a Short-circuit switch control unit 50 Drive voltage generation unit 60 Signal Processing Unit

Claims

1. A magnetic detection element having a magnetosensitive element and a detection coil, A current-carrying circuit that periodically energizes the magnetic sensor, An on / off switch is inserted between the other terminal of the magnetic sensor, which is connected to the current circuit, and ground, and one terminal of the switch is connected to the current circuit. A switch control unit that controls the operation of the switch, It comprises a magnetic detection circuit to which a detection signal generated in the detection coil in accordance with periodic excitation is input, The on / off switch control unit sets the on / off switch to an open state during the off-period of periodic excitation of the magnetic sensor, thereby electrically isolating the magnetic sensor from the ground.

2. The aforementioned switching switch is a voltage-driven switching element, The magnetic sensor device according to claim 1, wherein the switching control unit controls the magnitude of the voltage applied to the control electrode of the switching element during the off period of the switching element so as not to exceed the threshold voltage for turning on the switching element.

3. The magnetic sensor device according to claim 2, wherein the switching control unit generates a positive on-drive voltage applied to the control electrode during the on-period of the switching element, and a drive voltage generation unit generates an off-drive voltage applied to the control electrode during the off-period of the switching element that is lower than the reference voltage of the ground.

4. The magnetic sensor device according to claim 3, wherein the switching element is an n-type MOS transistor or a transfer gate switch.

5. moreover, A short-circuit switch is inserted between one terminal and the other terminal of the magnetic sensor, The system includes a short-circuit switch control unit that controls the driving of the short-circuit switch, The magnetic sensor device according to any one of claims 1 to 4, wherein the short-circuit switch control unit closes the short-circuit switch during the on-period of periodic excitation of the magnetic sensor, thereby short-circuiting the terminals of the magnetic sensor.

6. The aforementioned short-circuit switch is a voltage-driven switching element, The magnetic sensor device according to claim 5, wherein the short-circuit switch control unit controls the magnitude of the voltage applied to the control electrode of the switching element during the off period of the switching element so as not to exceed a threshold voltage for turning on the switching element.

7. The magnetic sensor device according to claim 6, wherein the short-circuit switch control unit generates a positive on-drive voltage applied to the control electrode during the on-period of the switching element, and a drive voltage generation unit generates an off-drive voltage applied to the control electrode during the off-period of the switching element that is lower than the reference voltage of the ground.

8. The magnetic sensor device according to claim 7, wherein the switching element is an n-type MOS transistor or a transfer gate switch.

9. A magnetic detection element having a magnetosensitive element and a detection coil, A current-carrying circuit that periodically energizes the magnetic sensor, A short-circuit switch is inserted between one terminal of the magnetosensitive element connected to the current-carrying circuit and the other terminal of the magnetosensitive element connected to ground. A short-circuit switch control unit that controls the driving of the short-circuit switch, It comprises a magnetic detection circuit to which a detection signal generated in the detection coil in accordance with periodic excitation is input, The short-circuit switch control unit closes the short-circuit switch during the on-period of periodic excitation of the magnetic sensor, thereby short-circuiting the terminals of the magnetic sensor.

10. The aforementioned short-circuit switch is a voltage-driven switching element, The magnetic sensor device according to claim 9, wherein the short-circuit switch control unit controls the magnitude of the voltage applied to the control electrode of the switching element during the off period of the switching element so as not to exceed the threshold voltage for turning on the switching element.

11. The magnetic sensor device according to claim 10, wherein the short-circuit switch control unit has a drive voltage generation unit that generates a positive on-drive voltage applied to the control electrode during the on-period of the switching element, and a drive voltage generation unit that generates an off-drive voltage applied to the control electrode during the off-period of the switching element that is lower than the reference voltage of the ground.

12. The magnetic sensor device according to claim 11, wherein the switching element is an n-type MOS transistor or a transfer gate switch.

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