JP2018105818A - Magnetic body detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic body detector which can detect a magnetic body highly accurately and highly sensitively.SOLUTION: A magnetic body detector includes: a Hall sensor 20 having a detection surface for detecting a magnetic body; an applied magnetic field generation circuit 30 for generating an applied magnetic field in a direction along the detection surface to be applied to the detection surface, based on a magnetic field generation signal; a sensor driving circuit 40 for driving the Hall sensor based on a sensor driving signal; a signal processing circuit 50 for performing signal processing on a voltage detection signal from the Hall sensor based on the magnetic field generation signal and the sensor driving signal and generating the processing signal; and a determination circuit 60 for determining the presence or absence of the magnetic body based on the processing signal.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a magnetic body detection device that includes a Hall sensor using a Hall element and detects a magnetic body.

  Conventionally, a Hall element is known as an element for detecting magnetism. The Hall element uses the Hall effect and detects magnetism as a voltage. For example, the Hall element has a pair of terminals for applying a driving current to the element and a pair of terminals for detecting a Hall voltage generated in the element due to the Hall effect. Various Hall sensors have been studied for the purpose of improving the detection accuracy of the Hall voltage.

  For example, in Patent Document 1, a pair of first and second Hall elements, and a drive current supply terminal and a Hall voltage detection terminal are alternately provided for each terminal of the first and second Hall elements. A Hall voltage detection device for driving an element so as to switch to is disclosed.

Japanese Patent No.5512561

  As a use of the Hall sensor, a magnetic body detection device that detects an object attached on the Hall sensor using a particulate magnetic body as a marker has been studied. More specifically, for example, an immunosensor using an antigen-antibody reaction in which an antibody binds to an antigen has been studied. The immunosensor is, for example, a biosensor that detects biometric information by binding a magnetic substance to an antigen or antibody and detecting magnetism generated by the magnetic substance. In such a magnetic body detection apparatus, it is preferable that the presence or absence of a magnetic body can be reliably detected.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a magnetic body detection device capable of detecting a magnetic body with high accuracy and high sensitivity.

  The invention according to claim 1 is a Hall sensor having a detection surface for detecting a magnetic material, and an applied magnetic field generation circuit for generating an applied magnetic field in a direction along the detection surface applied to the detection surface based on a magnetic field generation signal. A sensor drive circuit that drives the Hall sensor based on the sensor drive signal, and a signal processing circuit that performs signal processing of the voltage detection signal from the Hall sensor based on the magnetic field generation signal and the sensor drive signal and generates a processing signal And a determination circuit for determining the presence or absence of a magnetic substance based on the processing signal.

It is a block diagram which shows the structure of the magnetic body detection apparatus which concerns on Example 1. FIG. 1 is a circuit diagram illustrating a configuration example of a magnetic body detection device according to Embodiment 1. FIG. It is a block diagram which shows typically the structure of the Hall sensor of the magnetic body detection apparatus based on Example 1. FIG. (A) And (b) is a figure which shows typically the operation principle of the magnetic body detection apparatus based on Example 1. FIG. It is a circuit diagram which shows the structural example of the Hall sensor of the magnetic body detection apparatus based on Example 1. FIG. (A) And (b) is a figure which shows the drive structural example of the Hall sensor of the magnetic body detection apparatus based on Example 1. FIG. (A) And (b) is a figure which shows typically the example of a drive of a Hall sensor of the magnetic body detection apparatus based on Example 1, and the example of a calculation. (A) And (b) is a figure which shows typically the example of a drive of a Hall sensor of the magnetic body detection apparatus based on Example 1, and the example of a calculation. (A) And (b) is a timing chart which shows the signal processing example by the signal processing circuit of the magnetic body detection apparatus based on Example 1. FIG. It is a timing chart which shows transition of an applied magnetic field generated from a magnetic field generation signal to an applied magnetic field generation circuit and an applied magnetic field generation circuit.

  Examples of the present invention will be described in detail below.

  FIG. 1 is a block diagram illustrating the configuration of the magnetic body detection device 10 according to the first embodiment. The magnetic body detection device 10 is based on a Hall sensor 20, an applied magnetic field generation circuit 30 that generates an applied magnetic field SM applied to the Hall sensor 20 in order to generate a magnetic field to be detected in the magnetic body, and a sensor drive signal CL. And a sensor drive circuit 40 that generates a drive current (sensor drive current) SD for driving the hall sensor 20.

  The magnetic body detection device 10 includes a signal processing circuit 50 that performs various signal processing on the voltage detection signal SS indicating the electromotive force generated in the Hall sensor 20 based on the applied magnetic field SM and the sensor drive signal CL. And a determination circuit 60 that determines whether or not a magnetic material is present based on the processing signal SO processed by the signal processing circuit 50. In addition, the magnetic body detection device 10 includes a central control circuit 70 that functions as a control unit for the entire device, and a display unit 80 that displays various output results of the device.

  FIG. 2 is a block diagram illustrating a detailed configuration example of the magnetic body detection device 10. In this embodiment, the applied magnetic field generation circuit 30 includes an applied magnetic field generation unit 31 and a drive signal application circuit 32 that applies a drive signal for driving the applied magnetic field generation unit 31 to the applied magnetic field generation unit 31 as an application signal BD. Have.

  The applied magnetic field generation unit 31 includes, for example, an electromagnet made of an iron core CO including a coil L, and a capacitor C connected to the coil L of the electromagnet. In the present embodiment, the applied magnetic field generation unit 31 constitutes a resonance circuit, for example, an LC resonance circuit.

  Further, the applied magnetic field generation unit 31 has a magnetic field generation region 31A. For example, the iron core CO has a C-shaped shape, and the magnetic field generation region 31A is a region between end faces of the C-shaped iron core CO. The magnetic body detection device 10 performs a magnetic body detection operation by arranging (inserting) the Hall sensor 20 in the magnetic field generation region 31A of the magnetic field generation unit 31.

  The applied magnetic field generation circuit 30 includes a drive signal generation circuit 33 that generates a magnetic field generation signal MD that serves as a reference signal for the applied signal BD that the drive signal application circuit 32 applies to the applied magnetic field generation unit 31. The drive signal generation circuit 33 is a clock generation circuit that generates a clock signal as the magnetic field generation signal MD, for example. The drive signal application circuit 32 generates an application signal BD based on the magnetic field generation signal MD and supplies it to the application magnetic field generation unit 31. In the present embodiment, the magnetic field generation signal MD is generated as an AC signal having the first frequency f1, and the applied signal BD is generated as an AC voltage based on the first frequency f1. As a result, a current flows through the coil L of the applied magnetic field generation unit 31, and a magnetic field is generated in the magnetic field generation region 31A.

  The applied magnetic field generation circuit 30 includes an applied magnetic field detection circuit 34 that detects the applied magnetic field SM generated (actually generated) by the applied magnetic field generation unit 31 and generates an applied magnetic field detection signal BM. For example, the applied magnetic field detection circuit 34 includes a Hall element.

  The applied magnetic field generation circuit 30 includes an amplitude detection circuit 35 that detects the amplitude of the applied magnetic field detection signal BM detected by the applied magnetic field detection circuit 34. Further, the applied magnetic field generation circuit 30 includes a phase comparison circuit 36 that performs a phase comparison between the magnetic field generation signal MD generated by the drive signal generation circuit 33 and the applied magnetic field detection signal BM detected by the applied magnetic field detection circuit 34. Have.

  The sensor drive circuit 40 applies a drive signal (sensor drive current) for driving the Hall sensor 20 as an application signal SD, and a drive signal for generating a sensor drive signal CL that serves as a reference signal for the application signal SD. And a generation circuit 42. The drive signal generation circuit 42 is a clock generation circuit that generates a clock signal as the sensor drive signal CL, for example. In the present embodiment, the drive signal generation circuit 42 generates the sensor drive signal CL as an AC signal having the second frequency f2. The drive current application circuit 41 generates the application signal SD as an alternating current having the second frequency f2.

  The signal processing circuit 50 includes a first filter circuit 51 that performs filtering on the voltage detection signal SS from the hall sensor 20, and the voltage detection signal SS that has been filtered by the first filter circuit 51. 2 has a first demodulation circuit 52 that demodulates according to the frequency f2), and an amplification circuit 53 that amplifies the voltage detection signal SS demodulated by the first demodulation circuit 52. The first filter circuit 51 is a high-pass filter (HPF) in this embodiment.

  The signal processing circuit 50 also demodulates the voltage detection signal SS amplified by the amplification circuit 53 in accordance with the magnetic field generation signal MD (first frequency f1), and the second demodulation circuit 54. The second filter circuit 55 that performs filtering on the voltage detection signal SS demodulated by the second filtering circuit 55 and the conversion circuit 56 that performs AD conversion on the voltage detection signal SS filtered by the second filter circuit 55. In the present embodiment, the second filter circuit 55 is a low-pass filter (LPF). Further, the signal obtained by AD conversion by the conversion circuit 56 becomes the processing signal SO of the signal processing circuit 50.

  The determination circuit 60 determines the presence or absence of a magnetic material on the hall sensor 20 based on the signal level of the processing signal SO from the signal processing circuit 50. In this embodiment, the case where the signal processing circuit 50 includes the conversion circuit 56 has been described. However, the conversion circuit 56 may be included in the determination circuit 60 instead of the signal processing circuit 50. That is, the determination circuit 60 may determine the presence or absence of a magnetic substance after receiving the voltage detection signal SS filtered by the second filter circuit 55 and performing AD conversion.

  FIG. 3 is a block diagram schematically showing the configuration of the hall sensor 20. The configuration of the hall sensor 20 will be described with reference to FIG. In the present embodiment, the Hall sensor 20 includes a sensor circuit 21 including a pair of Hall elements 22 and 23. FIG. 1 schematically shows the upper surfaces of the Hall elements 22 and 23.

  In the present embodiment, a case where the sensor circuit 21 includes a pair, that is, two Hall elements 22 and 23 has been described. However, the sensor circuit 21 may include a plurality of pairs of Hall elements. And two or more Hall elements including 23 may be included.

  The Hall element 22 includes, for example, a semiconductor element (not shown) provided on a semiconductor substrate. For example, the Hall element 22 includes a CMOS element. The Hall element 22 has four terminals T1, T2, T3, and T4 that function as a drive terminal for driving the Hall element 22 or a detection terminal for detecting an electromotive force generated in the Hall element 22. In the terminals T1 to T4, the terminals T1 and T2 operate as a pair (terminal pair), and the terminals T3 and T4 operate as a terminal pair. That is, the Hall element 22 has two terminal pairs.

  Specifically, for example, when the terminals T1 and T2 which are one terminal pair function as a driving terminal pair for supplying a driving current (applied signal SD) to the Hall element 22, the terminal T3 which is the other terminal pair. T4 function as a detection terminal pair for detecting an electromotive force (detection voltage or output voltage) generated in the Hall element 22 during driving. Further, when the terminals T3 and T4 function as a drive terminal pair, the terminals T1 and T2 function as a detection terminal pair.

  In the present embodiment, the upper surface of the Hall element 22 functions as a detection surface 22A for detecting a magnetic material existing on the upper surface. The Hall element 22 has a rectangular (in the present embodiment, square) detection surface shape, and terminals T1 to T4 are arranged at corner portions thereof. Further, the terminals T1 and T2 are arranged to face each other with the center of the Hall element 22 in between. Further, the terminals T3 and T4 are arranged to face each other with the center of the Hall element 22 in between.

  Accordingly, the hall elements 22 are supplied with drive currents diagonally to each other on the rectangular detection surface 22A of the hall element 22. The Hall element 22 detects (outputs) an electromotive force generated in the diagonal direction of the detection surface 22A.

  The Hall element 23 has four terminals T5, T6, T7, and T8 that constitute two terminal pairs. Further, in the terminals T5 to T8, similarly to the terminals T1 to T4 of the Hall element 22, the terminals T5 and T6 operate as a terminal pair, and the terminals T7 and T8 operate as a terminal pair.

  Further, the upper surface of the Hall element 23 functions as a detection surface 23A for detecting a magnetic material. As shown in FIG. 3, in the present embodiment, the Hall element 23 has a detection surface 23A having the same shape as the Hall element 22, for example, a square, and the terminals T5 to T8 are respectively arranged at the corners. Similarly to the Hall element 22, the Hall element 23 performs a detection operation of the Hall voltage generated in the Hall element 23 while each terminal pair functions as a drive terminal pair or a detection terminal pair. The Hall elements 22 and 23 are arranged so that the side portions of the square detection surfaces 22A and 23A face each other.

  The Hall sensor 20 also includes a switching circuit 24 that performs connection switching for causing the Hall elements 22 and 23 to function as two drive terminal pairs or detection terminal pairs. The switching circuit 24 is provided between the power supplies VS1 and VS2 and the terminals T1 to T8, and switches the connection state between the power supplies VS1 and VS2 and the terminals T1 to T8.

  For example, the switching circuit 24 supplies the power supply potential on the high potential side from the first power supply VS1 to the sensor circuit 21 via the terminal pair serving as the drive terminal pair, and the power supply potential on the low potential side from the second power supply VS2. Is supplied to the sensor circuit 21. As a result, a drive current is applied to the Hall elements 22 and 23 of the sensor circuit 21.

  In the present embodiment, a power supply potential is applied to the switching circuit 24 as a potential from the first power supply VS1, and a ground potential GND is applied as a potential from the second power supply VS2. For example, the switching circuit 24 switches whether each of the terminals T1 to T8 is supplied with a power supply potential, a ground potential GND, or connected to an arithmetic circuit 24 described later. Note that the terminal pair connected to the arithmetic circuit 25 by the switching circuit 24 functions as a detection terminal pair.

  The sensor drive circuit 40 supplies a drive current SD to the switching circuit 24 to control terminal switching by the switching circuit 24 and drive the sensor circuit 21. In the present embodiment, the sensor drive circuit 40 generates a control signal for performing switching control of the switching circuit 24 and supplies the control signal to the switching circuit 24. Further, the sensor drive circuit 40 supplies a drive current to the Hall elements 22 and 23 through the terminal pair that is a drive terminal pair.

  The hall sensor 20 includes an arithmetic circuit 25 that performs arithmetic processing on the detected voltage from the sensor circuit 21. The arithmetic circuit 25 performs arithmetic processing on the electromotive force generated in the detection terminal pair of the sensor circuit 21 to generate a voltage detection signal SS and outputs the voltage detection signal SS to the signal processing circuit 50.

  Next, the magnetic substance detected by the magnetic substance detection device 10 and the magnetic field to be detected applied to the Hall sensor 20 by this will be described with reference to FIGS. In the present embodiment, the magnetic body detection device 10 is an immunosensor that detects the antigen AG bound to the magnetic bead BZ by detecting the magnetic bead BZ as the magnetic body attached on the Hall sensor 20. The sensor circuit 21 of the hall sensor 20 has a detection surface 21A for detecting the magnetic beads BZ.

  FIG. 4A is a diagram schematically showing a specimen SP including the magnetic beads BZ to be detected by the magnetic substance detection device 10 and an antigen-antibody reaction on the Hall sensor 20 by the specimen SP. As shown in FIG. 4A, first, the sensor circuit 21 of the hall sensor 20 is configured as an integrated circuit CP in which the sensor circuit 20 is integrated with the switching circuit 24 and the arithmetic circuit 25, and the integrated circuit CP is mounted. It is mounted on the board. The magnetic substance detection device 10 inserts the integrated circuit CP into the applied magnetic field generation unit 31A (FIG. 2) of the applied magnetic field generation circuit 30 and drives the Hall sensor 20 to detect the magnetic beads BZ.

  A plurality of antibodies AB1 are fixed on the detection surface 21A of the sensor circuit 21. On the other hand, the specimen SP to be detected is a solution containing the magnetic beads BZ bound to the antibody AB2 and the antigen AG. For example, the specimen SP is a solution collected from human blood or mucous membranes.

  The specimen SP is dropped on the detection surface 21A of the sensor circuit 21. When the specimen SP is dropped onto the detection surface 21A of the sensor circuit 21, the antibody AB1 on the sensor circuit 21, the antigen AG and the antibody AB2 in the specimen SP undergo an antigen-antibody reaction and bind to each other. As a result, the magnetic beads BZ adhere to the detection surface 21A of the sensor circuit 21. The magnetic beads BZ are, for example, nano-sized magnetic particles in which a specific functional group is chemically decorated on a magnetic core material.

  FIG. 4B is a diagram illustrating the applied magnetic field SM applied by the applied magnetic field generation circuit 30. The applied magnetic field generation circuit 30 applies the applied magnetic field SM in a direction parallel to the detection surface 21A of the sensor circuit 21 (sometimes referred to as a horizontal direction). When the magnetic beads BZ adhere to the sensor circuit 21, the applied magnetic field SM is applied to the magnetic beads BZ. As shown in FIG. 4B, the magnetic beads BZ generate a magnetic field MF in a direction different from the direction of the applied magnetic field SM by causing the magnetic field direction to be changed by the applied magnetic field SM. This magnetic field MF includes a magnetic field (vertical magnetic field) to be detected by the sensor circuit 21.

  The detection surface 21A of the sensor circuit 21 includes the detection surface 22A of the Hall element 22, the detection surface 23A of the Hall element 23, and the surface area of the sensor circuit 21 between the detection surfaces 22A and 23A. For example, the detection surface 21A of the sensor circuit 21 is a surface of a wiring layer, a protective film, or a sealing film (not shown) on the semiconductor substrate on which the Hall elements 22 and 23 are formed.

  As shown in FIG. 4B, for example, when the magnetic beads BZ are attached between the Hall elements 22 and 23 on the detection surface 21A of the sensor circuit 21, the direction of the magnetic field MF generated by the magnetic beads BZ is the Hall element. 22 includes a component in a direction toward the detection surface 22A and a component in a direction away from the detection surface 23A of the Hall element 23. That is, magnetic fields in opposite directions are applied to the Hall elements 22 and 23 of the sensor circuit 21.

  In most cases, even when the magnetic beads BZ adhere to any position on the detection surface 21A of the sensor circuit 21, a magnetic field MF including components in opposite directions is input to the Hall elements 22 and 23. .

  Thus, the applied magnetic field generation circuit 30 generates the applied magnetic field SM in the direction along the detection surface 21A on the detection surface 21A (detection surfaces 22A and 23A) of the Hall sensor 20, and excites the magnetic beads BZ. Thereby, the magnetic field MF to be detected by the Hall sensor 20 is generated for the magnetic beads BZ to which the applied magnetic field SM is applied.

  In the present embodiment, in the magnetic substance detection device 10, the first antibody AB1 is fixed to the detection surface 21A of the Hall sensor 20, and the magnetic beads BZ are bound to the second antibody AB2. Then, the determination circuit 60 determines the presence or absence of the magnetic beads BZ attached to the detection surface 21A of the Hall sensor 20 by binding the first and second antibodies AB1 and AB2 to the antigen AG. Then, the determination circuit 60 detects the presence of the magnetic beads BZ and detects (determines) the presence or absence of the antigen AG. The magnetic body detection device 10 as an immunosensor can determine whether or not the human body has a virus that is the antigen AG by detecting a specific antigen AG, for example.

  FIG. 5 is a schematic circuit diagram illustrating a configuration example of the hall sensor 20. A configuration example of the switching circuit 24 and the arithmetic circuit 25 will be described with reference to FIG. First, the switching circuit 24 selects whether to apply a power supply potential, a ground potential GND, or a connection to the arithmetic circuit 25 for each of the terminals T1, T2, T3, and T4 of the Hall element 22. Switching elements S1, S2, S3, and S4 are provided for switching. Similarly, the switching circuit 24 includes switching elements S5, S6, S7, and S8 that switch the connection states of the terminals T5, T6, T7, and T8 of the Hall element 23, respectively.

  Specifically, the switching element S1 selectively switches between applying the ground potential GND to the terminal T1 of the Hall element 22 or connecting the terminal T1 to the arithmetic circuit 25. The switching element S2 selectively switches between applying a power supply potential to the terminal T2 and connecting the terminal T2 to the arithmetic circuit 25. The switching element S3 selectively switches between applying the ground potential GND to the terminal T3 or connecting the terminal T3 to the arithmetic circuit 25. The switching element S4 switches whether to apply a power supply potential to the terminal T4 or to connect the terminal T4 to the arithmetic circuit 25.

  The switching element S5 selectively switches whether to apply the power supply potential to the terminal T5 of the Hall element 23 or to connect the terminal T5 to the arithmetic circuit 25. The switching element S6 selectively switches between applying the ground potential GND to the terminal T6 or connecting the terminal T6 to the arithmetic circuit 25. The switching element S7 selectively switches between applying a power supply potential to the terminal T7 or connecting the terminal T7 to the arithmetic circuit 25. The switching element S8 selectively switches between applying the ground potential GND to the terminal T8 or connecting the terminal T8 to the arithmetic circuit 25.

  The sensor drive circuit 40 generates a control signal for controlling the switching state of each of the switching elements S1 to S8 as the application signal SD and supplies the control signal to each switching element S1 to S8.

  Next, in the present embodiment, the arithmetic circuit 25 includes a first differential amplifier A1 connected to the detection terminal pair of the terminals T1 to T4 of the Hall element 22 via the switching circuit 24, and the switching circuit 24. Through the second differential amplifier A2 connected to the detection terminal pair of the terminals T5 to T8 of the Hall element 23 and the third difference connected to the first and second differential amplifiers A1 and A2. And a dynamic amplifier A3.

  The first differential amplifier A1 has its non-inverting input terminal connected to terminals T1 and T3 of the Hall element 22 via switching elements S1 and S3, respectively, and its inverting input terminal via switching elements S2 and S4, respectively. Terminals T2 and T4 are connected. The output terminal of the first differential amplifier A1 is connected to the non-inverting input terminal of the third differential amplifier A3.

  The second differential amplifier A2 has its non-inverting input terminal connected to terminals T6 and T8 of the Hall element 23 via switching elements S6 and S8, respectively, and its inverting input terminal via switching elements S5 and S7, respectively. Terminals T5 and T7 are connected. The output terminal of the second differential amplifier A2 is connected to the inverting input terminal of the third differential amplifier A3.

  In the present embodiment, the sensor circuit 21, the switching circuit 24, and the arithmetic circuit 25 are integrated in one IC chip as the integrated circuit CP.

  Next, the drive configuration of the hall sensor 20 will be described with reference to FIGS. In the present embodiment, the Hall sensor 20 is controlled by the switching circuit 24 by the sensor drive circuit 40, so that the phase shown in FIG. 6A (first phase) and the phase shown in FIG. 6B (second phase). Are alternately switched based on the second frequency f2 to perform the Hall voltage detection operation.

  For example, as shown in FIG. 6A, the sensor drive circuit 40 has drive currents (drive currents D1 and D2) in directions opposite to each other with respect to the Hall elements 22 and 23 via a terminal pair that is a drive terminal pair. The switching circuit 24 is controlled to supply.

  For example, as shown in FIGS. 6A and 6B, the sensor drive circuit 40 supplies a drive current (eg, drive current D1) in the first direction to each of the Hall elements 22 and 23. (First phase) and a period (second phase) in which a driving current (for example, driving current D3) is supplied in a second direction orthogonal to the first direction are repeated to drive each of the Hall elements 22 and 23. Supply.

  More specifically, in the first phase shown in FIG. 6A, the power supply potential is applied to the terminals T4 and T7, and the ground potential is applied to the terminals T3 and T8. Accordingly, in the Hall element 22, the terminals T3 and T4 function as a drive terminal pair, and a drive current (element drive current) D1 from the terminal T4 to the terminal T3 is supplied. At this time, in the Hall element 23, the terminals T7 and T8 function as a drive terminal pair, and the drive current D2 from the terminal T7 toward the terminal T8 is supplied. The directions of the drive currents D1 and D2 are opposite to each other.

  In the first phase, the terminals T1 and T2 function as a detection terminal pair in the Hall element 22 and the terminals T5 and T6 function in the Hall element 23, and the terminals T1, T2, T5, and T6 function as the arithmetic circuit 25. Connected to.

  In the second phase shown in FIG. 6B, the power supply potential is applied to the terminals T2 and T5, and the ground potential is applied to the terminals T1 and T6. Accordingly, the terminals T1 and T2 function as a drive terminal pair in the Hall element 22 and the terminals T5 and T6 function in the Hall element 23, respectively. The hall element 22 is supplied with a drive current D3 from the terminal T2 toward the terminal T1, and the hall element 23 is supplied with a drive current D4 from the terminal T5 in the direction opposite to the drive current D3 toward the terminal T6.

  As described above, in the hall sensor 20, the sensor drive circuit 40 controls the switching circuit 24 so as to supply drive currents in opposite directions to the hall elements 22 and 23. In other words, the sensor drive circuit 40 supplies drive currents in opposite directions to the Hall elements 22 and 23 via the terminal pair that is the drive terminal pair.

  In addition, between the first phase and the second phase, the sensor driving circuit 40 drives the Hall elements 22 and 23 in the directions orthogonal to each other (for example, the driving currents D1 and D3 or the driving currents D2 and D4). The switching circuit 24 is controlled so as to be alternately supplied. Such a driving configuration for supplying a driving current to the Hall elements 22 and 23 in different directions periodically may be referred to as a spinning current method.

  Next, referring to FIGS. 7A and 7B and FIGS. 8A and 8B, the voltage detection operation by the Hall elements 22 and 23 in the first phase and the second phase, and the arithmetic processing by the arithmetic circuit 25 The operation will be described. 7A and 7B and FIGS. 8A and 8B, the directions of the drive currents D1 to D4 to the hall elements 22 and 23 are indicated by broken lines.

  First, FIGS. 7A and 7B are schematic operation descriptions when magnetic fields M1 and M2 in opposite directions are generated with respect to the Hall elements 22 and 23 in the first phase and the second phase, respectively. FIG. This corresponds to the operation when the magnetic beads BZ are attached on the detection surface 21A of the sensor circuit 21.

  First, in the first phase shown in FIG. 7A, a magnetic field M1 is generated in a direction (depth direction in the drawing) toward the detection surface 22A in a direction perpendicular to the detection surface 22A (paper surface in the drawing) of the Hall element 22. . Therefore, between the terminals T1 and T2 which are the detection terminal pair of the Hall element 22, an electromotive force having the terminal T1 side as a high potential and the terminal T2 side as a low potential is generated as the detection voltage V1. On the other hand, in the Hall element 23, a magnetic field M2 is generated in a direction (front side in the drawing) away from the detection surface 23A in a direction perpendicular to the detection surface 23A (paper surface in the drawing) of the Hall element 23. Therefore, an electromotive force is generated between the terminals T5 and T6, which is the detection terminal pair of the Hall element 23, as the detection voltage V2 with the terminal T5 at a high potential and the terminal T6 side at a low potential.

  In the first phase, the first differential amplifier A1 of the arithmetic circuit 25 is connected to the non-inverting input terminal of the high-potential side terminal T1 of the detection terminal pair in the Hall element 22 and connected to the inverting input terminal. Is connected to a terminal T2 on the low potential side. Therefore, the first differential amplifier A1 outputs the positive amplification voltage AV1 (+ AV1). On the other hand, the non-inverting input terminal of the second differential amplifier A2 is connected to the low potential side terminal T6 of the detection terminal pair in the Hall element 23, and the high potential side terminal T5 is connected to the inverting input terminal. Is done. Therefore, the second differential amplifier A2 outputs the negative amplification voltage AV2 (−AV2).

  The third differential amplifier A3 receives a positive amplification voltage AV1 at its non-inverting input terminal and a negative amplification voltage AV2 at its inverting input terminal. Therefore, the third differential amplifier A3 has a positive polarity, and is a voltage (AV1 + AV2) obtained by adding the amplified voltage AV1 from the first differential amplifier A1 and the amplified voltage AV2 from the second differential amplifier A2. ) Is output as the voltage detection signal SS.

  On the other hand, in the second phase shown in FIG. 7B, an electromotive force between the terminals T3 and T4, which are the detection terminal pair of the Hall element 22, has a high potential on the terminal T4 side and a low potential on the terminal T3 side. It occurs as a detection voltage V3. Further, between the terminals T7 and T8, which is the detection terminal pair of the Hall element 23, an electromotive force having the terminal T8 side as a high potential and the terminal T7 side as a low potential is generated as a detection voltage V4.

  In the second phase, the first differential amplifier A1 of the arithmetic circuit 25 is connected to the non-inverting input terminal of the low potential side terminal T3 of the detection terminal pair in the Hall element 22 and connected to the inverting input terminal. Is connected to a terminal T4 on the high potential side. Therefore, the first differential amplifier A1 outputs the negative amplification voltage AV1 (−AV1). On the other hand, the non-inverting input terminal of the second differential amplifier A2 is connected to the high potential side terminal T8 of the detection terminal pair in the Hall element 23, and the low potential side terminal T7 is connected to the inverting input terminal. Is done. Therefore, the second differential amplifier A2 outputs a positive amplification voltage AV2 (+ AV2).

  The third differential amplifier A3 receives a negative amplification voltage AV1 at its non-inverting input terminal and a positive amplification voltage AV2 at its inverting input terminal. Therefore, the third differential amplifier A3 has a negative polarity, and is a voltage (−−) obtained by adding the amplified voltage AV1 from the first differential amplifier A1 and the amplified voltage AV2 from the second differential amplifier A2. AV1-AV2) is output as the voltage detection signal SS.

  As described above, the arithmetic circuit 25 applies the components perpendicular to the drive currents D1 to D4 of the magnetic field (magnetic field to be detected) applied to the Hall elements 22 and 23 in opposite directions (for example, the magnetic fields M1 and M2 are applied). The detection voltages detected by the detection terminal pairs of the Hall elements 22 and 23 are added (intensify). That is, when the direction of the applied vertical magnetic field is opposite between the elements, the differential amplifier A3 of the arithmetic circuit 25 functions as an adder circuit.

  Next, FIGS. 8A and 8B are schematic operation explanatory diagrams in the case where magnetic fields M3 and M4 in the same direction are generated in the Hall elements 22 and 23 in the first phase and the second phase, respectively. It is. This is an operation explanatory diagram when the magnetic bead BZ is not attached to the detection surface 21 of the sensor circuit 21, for example, when the magnetic bead BZ is attached to a surface region other than the detection surface 21A, for example. Alternatively, it corresponds to the case where the magnetic beads BZ are not attached to either of them.

  First, in the first phase shown in FIG. 8A, in the Hall element 22, an electromotive force having a high potential on the terminal T1 side and a low potential on the terminal T2 side is generated as the detection voltage V5. In the Hall element 23, an electromotive force having a high potential on the terminal T6 side and a low potential on the terminal T5 side is generated as the detection voltage V6. Accordingly, the first and second differential amplifiers A1 and A2 both output positive voltages as amplified voltages AV1 and AV2 (+ AV1 and + AV2). Accordingly, the third differential amplifier A3 outputs the voltage difference (+ AV1-AV2) between the amplified voltages AV1 and AV2 as the voltage detection signal SS.

  On the other hand, in the second phase shown in FIG. 8B, in the Hall element 22, an electromotive force having a high potential on the terminal T4 side and a low potential on the terminal T3 side is generated as the detection voltage V7. In the Hall element 23, an electromotive force having a high potential on the terminal T7 side and a low potential on the terminal T8 side is generated as the detection voltage V8. Therefore, the first and second differential amplifiers A1 and A2 both output negative voltages as amplified voltages AV1 and AV2 (-AV1 and -AV2). Accordingly, the third differential amplifier A3 outputs the voltage difference (−AV1 + AV2) between the amplified voltages AV1 and AV2 as the voltage detection signal SS.

  As described above, the arithmetic circuit 50 is configured so that the components perpendicular to the drive currents D1 to D4 of the magnetic field applied to the Hall elements 22 and 23 are in the same direction (for example, when the magnetic fields M3 and M4 are applied). An operation of subtracting (weakening) the detection voltages detected by the detection terminal pairs of the elements 22 and 23 is performed. That is, when a vertical magnetic field in the same direction is applied between the elements, the differential amplifier A3 of the arithmetic circuit 50 functions as a subtraction circuit.

  Here, detection voltages V1 to V8 from the Hall elements 22 and 23 and calculation processing by the calculation circuit 25 of the detection voltages V1 to V8 will be described. The detection voltages V <b> 1 to V <b> 8 include a Hall voltage generated by the Hall effect due to the application of a magnetic field and an offset voltage generated by the influence of the shape error, manufacturing error, and stress of the Hall elements 22 and 23. In order to accurately detect the Hall voltage, it is preferable to distinguish (separate) the offset voltage from the Hall voltage.

  In the present embodiment, the Hall sensor 20 supplies the drive current in the opposite direction by the spinning current method, and calculates the detection voltages V1 to V4 or the detection voltages V5 to V8, thereby converting the voltage detection signal SS into an AC signal. Output as (AC component). On the other hand, the polarity of the offset voltage unique to the element changes depending on the direction of the current. Therefore, it appears as a DC component in the voltage detection signal SS from the arithmetic circuit 25.

  Therefore, for example, the offset voltage component can be separated (removed) by performing a filtering process on the voltage detection signal SS. Even when a magnetic field in the same direction is applied to the Hall elements 22 and 23, the offset voltage component can be removed using this principle, and the Hall voltage can be detected accurately.

  In the present embodiment, the hall sensor 20 is configured to supply drive current in directions orthogonal to each other between the first and second phases. For example, a first period (first phase) in which the first drive current D1 (FIG. 4A or 5A) is supplied in the first direction to the Hall element 22; The second period (second phase) in which the second drive current D3 (FIG. 4 (b) or 5 (b)) is supplied in a second direction orthogonal to the direction is alternately repeated, and the Hall element 22 is repeated. Is supplied with a drive current.

  By performing driving using this spinning current method, the Hall voltage becomes an AC component in the amplified voltages AV1 and AV2 by the differential amplifiers A1 and A2 even if the Hall elements 22 and 23 are considered alone, and the offset voltage Becomes a DC component.

  In other words, it is possible to separate and remove the offset voltage in the Hall elements 22 and 23 by supplying drive currents to the Hall elements 22 and 23 in directions orthogonal to each other between phases. Furthermore, by supplying a drive current between the Hall elements 22 and 23 in the opposite direction, the offset voltage generated in the entire Hall elements 22 and 23 can be separated and removed.

  The Hall elements 22 and 23 have a square detection surface shape, and two terminal pairs (terminal pairs T1 and T2 and terminal pairs T3 and T4) are diagonal portions of the detection surfaces 22A and 23A of the Hall elements 22 and 23. With the simple configuration, it is possible to supply drive currents in opposite directions within the same phase and drive currents in directions orthogonal to each other between the two phases.

  For example, when the detection surface 22A or 23A of the Hall element 22 or 23 is rectangular, even if a terminal pair is arranged at each diagonal portion, the drive current in the opposite direction or the drive current in the orthogonal direction between the phases Supply may not be possible. Therefore, it is necessary to devise terminal positioning. On the other hand, the terminals are arranged on the diagonal portions of the square detection surfaces 22A and 23A like the Hall elements 22 and 23, so that they are orthogonal to each other in the opposite direction and between the phases without an accurate examination of the terminal positions. The driving current can be supplied in the direction in which the current flows.

  Further, since the arithmetic circuit 25 includes the first to third differential amplifiers A1 to A3, the detection voltage can be easily added or subtracted without using, for example, an addition circuit and a subtraction circuit.

  The shape of the detection surface of the Hall elements 22 and 23 is only an example. Moreover, although the case where the arithmetic circuit 25 adds and subtracts the detection voltage from a detection terminal pair was demonstrated, the arithmetic circuit 25 should just have the structure which adds the said detection voltage.

  Further, the case where the sensor drive circuit 40 supplies drive currents orthogonal to each other in the Hall element 22 or 23 between phases has been described. Further, the case where the sensor drive circuit 40 supplies drive currents in opposite directions to the Hall elements 22 and 23 has been described. However, the switching circuit 24 may perform connection switching so that the two terminals alternately function as a pair of driving terminals or a pair of detection terminals, and the sensor driving circuit 40 is connected to the Hall elements 22 and 23 via the pair of driving terminals. What is necessary is just to supply a drive current to a different direction alternately.

  In the present embodiment, the case where the sensor circuit 21 of the Hall sensor 20 has two Hall elements 22 and 23 has been described. However, the sensor circuit 21 is configured by one Hall element (for example, only the Hall element 22). May be. The Hall sensor 20 only needs to include at least one Hall element (for example, the Hall element 22) having a detection surface (for example, the detection surface 22A) for detecting a magnetic material (magnetic bead BZ). In this case, for example, the switching circuit 24 may perform connection switching that causes the two terminal pairs T1 and T2 and the terminals T3 and T4 of one Hall element 22 to function alternately as a drive terminal pair or a detection terminal pair. 40 may supply a drive current to the Hall element 22 through a terminal pair which is a drive terminal pair.

  FIGS. 9A and 9B schematically show the voltage detection signal SS and its respective processing results when the magnetic beads BZ are present on the sensor circuit 21 of the Hall sensor 20 and when they are not present. FIG.

  First, as illustrated in FIG. 9A, when the magnetic beads BZ are attached to the detection surface 21 </ b> A of the sensor circuit 21, the Hall sensor 20 sends a sensor drive signal CL of the second frequency f <b> 2 of the Hall sensor 20. The voltage detection signal SS modulated based on the magnetic field generation signal MD of the first frequency f1 is output.

  The demodulation circuit 52 performs demodulation (synchronous detection based on the sensor drive signal CL) based on the second frequency f2 with respect to the voltage detection signal SS. As a result, the voltage detection signal SS is restored as a sine wave. Thereafter, the voltage detection signal SS is demodulated by the demodulation circuit 54 based on the first frequency f1. Then, the demodulated voltage detection signal SS is filtered by the low-pass filter 55, and the voltage detection signal SS is smoothed. In this way, the signal processing circuit 50 extracts the Hall voltage component from the voltage detection signal SS and outputs it to the determination circuit 60 as the processing signal SO.

  In other words, the signal processing circuit 60 performs synchronous detection of the voltage detection signal SS from the hall sensor 20 based on the magnetic field generation signal MD and the sensor drive signal CL.

  On the other hand, FIG. 9B is a diagram illustrating the voltage detection signal SS and the processing result when the magnetic beads BZ are not attached to the detection surface 21A of the sensor circuit 21. When the magnetic bead BZ is not present, the voltage detection signal SS is ideally output as no signal, but an offset voltage component is actually output.

  Here, since the offset voltage is generated only in accordance with the applied signal (element drive current) SD of the Hall sensor 20, the voltage detection signal SS is a rectangular wave having the second frequency f2 similar to the sensor drive signal CL. . Therefore, it becomes a direct current component after demodulation by the demodulation circuit 52 and is removed after filtering by the low-pass filter 55. Therefore, it can be determined (detected) that the magnetic beads BZ do not exist. Since the offset voltage processing is performed even when the magnetic beads BZ are present, only the Hall voltage generated by the magnetic beads BZ can be extracted with high accuracy (high sensitivity).

  Next, the applied magnetic field SM generated by the applied magnetic field generation circuit 30 will be described with reference to FIG. In the present embodiment, the drive signal generation circuit 33 of the applied magnetic field generation circuit 30 generates a magnetic field generation signal so that the first frequency f1 of the magnetic field generation signal MD becomes the resonance frequency f0 of the resonance circuit in the applied magnetic field generation unit 31. Generate MD. Therefore, the applied signal BD is applied to the applied magnetic field generating unit 31 under the condition that the resonant circuit including the coil L (electromagnet) and the capacitor C resonates.

  As a result, the applied magnetic field SM has the same phase as the magnetic field generation signal MD and the applied magnetic field detection signal BM from the applied magnetic field detection circuit 34 (the applied magnetic field SM that is actually generated). Specifically, when the first frequency f1 of the magnetic field generation signal MD is equal to the resonance frequency f0 of the applied magnetic field generation unit 31, the coil voltage V (L) generated in the coil L is 90 ° with respect to the applied signal BD. Make progress. The coil current I (L) generated in the coil L causes a phase delay of 90 ° from the coil voltage V (L) due to its impedance characteristics.

  Therefore, the applied magnetic field SM (applied magnetic field detection signal BM) generated by the coil current I (L) has the same phase as the magnetic field generation signal MD. Therefore, the demodulation circuit 54 of the signal processing circuit 50 demodulates the voltage detection signal SS based on the magnetic field generation signal MD, so that a decrease in detection sensitivity can be suppressed. Therefore, it is possible to detect a highly sensitive magnetic material.

  In addition, although the case where the magnetic field generation signal MD is generated at the frequency f1 that matches the resonance frequency f0 of the applied magnetic field generation unit 31 has been described, the configuration of the magnetic field generation signal MD is not limited to this. The applied magnetic field generation circuit 30 includes a phase comparison circuit 36, and the drive signal generation circuit 33 may generate the magnetic field generation signal MD so that the magnetic field generation signal MD and the applied magnetic field detection signal BM have the same phase.

  As described above, the magnetic body detection device 10 is applied to the detection surface 21A of the Hall sensor 20 based on the magnetic field generation signal MD and the Hall sensor 20 having the detection surface 21A for detecting the magnetic body (magnetic beads BZ). An applied magnetic field generation circuit 30 that applies an applied magnetic field SM in a direction along the detection surface 21A, a sensor drive circuit 40 that drives the Hall sensor 20 based on the sensor drive signal CL, a magnetic field generation signal MD, and a sensor drive signal signal CL. The signal processing of the voltage detection signal SS from the hall sensor is performed based on the signal processing circuit 50 to generate a processing signal, and the presence or absence of the magnetic material (magnetic bead BZ) is determined based on the processing signal SO from the signal processing circuit 50. And a determination circuit 60 for determination. Therefore, it is possible to provide the magnetic body detection device 10 capable of detecting a magnetic body with high accuracy and high sensitivity.

DESCRIPTION OF SYMBOLS 10 Magnetic body detection apparatus 20 Hall sensor 21 Sensor circuit 21
22, 23 A pair of Hall elements 21A, 22A, 23A Detection surfaces T1 to T8 Terminals (terminal pairs)
30 Applied Magnetic Field Generation Circuit 31 Applied Magnetic Field Generation Unit 32 Drive Signal Application Circuit 33 Drive Signal Generation Circuit 34 Applied Magnetic Field Detection Circuit 36 Phase Comparison Circuit

Claims (6)

A hall sensor having a detection surface for detecting a magnetic material;
An applied magnetic field generation circuit that generates an applied magnetic field in a direction along the detection surface applied to the detection surface based on a magnetic field generation signal;
A sensor drive circuit for driving the Hall sensor based on a sensor drive signal;
A signal processing circuit that performs signal processing of a voltage detection signal from the Hall sensor based on the magnetic field generation signal and the sensor driving signal, and generates a processing signal;
And a determination circuit for determining the presence or absence of the magnetic material based on the processing signal. The applied magnetic field generation circuit includes an applied magnetic field generation unit that generates the applied magnetic field based on the magnetic field generation signal, a drive signal generation circuit that generates the magnetic field generation signal, and the application generated by the applied magnetic field generation unit. An applied magnetic field detection circuit that detects a magnetic field, and a phase comparison circuit that performs a phase comparison between the applied magnetic field detection signal from the applied magnetic field detection circuit and the magnetic field generation signal,
2. The magnetic body detection device according to claim 1, wherein the drive signal generation circuit generates the magnetic field generation signal so that the magnetic field generation signal and the applied magnetic field detection signal have the same phase. The applied magnetic field generation unit includes an electromagnet and a capacitor constituting a resonance circuit,
The magnetic body detection device according to claim 2, wherein the drive signal generation circuit generates the magnetic field generation signal so that a frequency of the magnetic field generation signal becomes a resonance frequency of the applied magnetic field generation unit.   The said signal processing circuit performs synchronous detection of the said voltage detection signal from the said Hall sensor based on the said sensor drive signal and the said magnetic field generation signal, The Claim 1 characterized by the above-mentioned. Magnetic body detection device.   The Hall sensor includes a pair of Hall elements each having two terminal pairs, and each of the two terminal pairs as a drive terminal pair or a detection terminal pair with respect to the pair of Hall elements based on the sensor drive signal. When the components perpendicular to the detection surface of the magnetic field applied to each of the pair of Hall elements are in opposite directions to each other, the detection voltage from each of the detection terminal pairs is added. The magnetic body detection device according to claim 1, further comprising an arithmetic circuit that performs an arithmetic operation. A first antibody is fixed to the detection surface of the Hall sensor,
The magnetic substance is bound to a second antibody;
6. The determination circuit according to claim 1, wherein the determination circuit determines the presence or absence of the magnetic substance attached to the detection surface of the Hall sensor by binding the first and second antibodies to an antigen. The magnetic body detection apparatus as described in any one.

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