JP4514104B2 - Magnetic detector - Google Patents

Description

  The present invention relates to a magnetic detection device having a Hall element.

  In a magnetic detection device employing a Hall element, since the Hall element has an offset voltage, the offset voltage is removed. As an example, the spinning current principle described in Non-Patent Document 1 is used. Are known.

  This spinning current principle will be described with reference to FIG. 6 for a four-terminal hole plate. Between the two terminals of the four terminals of the four-terminal hall plate, a current is caused to flow by rotating the direction by 90 ° counterclockwise, and the remaining two terminals of the four terminals are As shown in FIGS. 6A to 6D, the polarity of the output of the differential amplifier connected to the inverting terminal and the non-inverting terminal of the differential amplifier is changed by a switch, as shown in FIGS. Switching shall be made as shown in FIG. At this time, the differential amplifier output voltage in the state shown in FIG. 6A (hereinafter, this state is referred to as “0 ° state” and represented by (0 °)) is defined as V1 (0 °) = Vh + Oh + Oe. Then, the output of the switch is V2 (0 °) = Vh + Oh + Oe. In the state shown in FIG. 6B (hereinafter, this state is referred to as “90 ° state” and is represented by (90 °)), the output of the switch can be expressed as V2 (90 °) = Vh−Oh + Oe. In the state shown in FIG. 6C (hereinafter, this state is referred to as “180 ° state” and is represented by (180 °)), the output V2 of the switch can be expressed as V2 (180 °) = Vh + Oh−Oe. In the state shown in FIG. 6D (hereinafter, this state is referred to as “270 ° state” and represented by (270 °)), the output of the switch can be expressed as V2 (270 °) = Vh−Oh−Oe. . However, the direction of the magnetic field is the direction from the paper surface to the paper back and there is no change from FIG. 6 (a) to FIG. 6 (d), Vh is the Hall voltage, Oh is the offset voltage of this 4-terminal Hall plate, and Oe is the difference. This is an offset voltage unique to the dynamic amplifier.

And when adding the output voltage of the switch in each of the above states,
V2 (0 °) + V2 (90 °) + V2 (180 °) + V2 (270 °)
= (Vh + Oh + Oe) + (Vh-Oh + Oe)
+ (Vh + Oh-Oe) + (Vh-Oh-Oe)
= 4 x Vh
Thus, an expression irrelevant to the offset voltage (Oh) of the four-terminal Hall plate and the offset voltage (Oe) unique to the differential amplifier is obtained, which is related only to Vh. FIG. 7 shows the relationship between the output V1 of the differential amplifier and the output V2 of the switch in each of the above states. Here, since Oh >> Vh and Oh >> Oe, V1≈Oh. Also, if the offset voltage of the Hall element is much larger than the Hall voltage when a very small magnetic force such as geomagnetism is measured, it is effective to integrate the output of the Hall element.

  As shown in FIG. 8, a magnetic detection device that implements this spinning current principle includes a hall element 81, a switch 82, a differential amplifier 83, a switch 84, and switches 82 and 84 that are appropriately used in the above states. A switching control unit 85 for switching and an integrator 86 for integrating the output of the switch 84 can be considered.

JP 2002-303661 A Japanese Patent Laid-Open No. 9-329460 A. Bakker, AA Bellekom, S. Middelhoek and JH Huijsing “Low-Offset Low-Noise 3.5mW CMOS Spinning-Current Hall Effect Sensor With Integrated Chopper Amplifier” The 13th European Conference on Solid-State Transducers September 12-15, 1999, The Hague, The Netherlands, pp.1045-1048

  However, in this magnetic detection device, the settling time of the differential amplifier when the polarity of the input voltage of the differential amplifier 83 differs by switching the switch 82 is finite, and the settling time (Tr ) And the settling time (Tf) at the time of falling, and this affects the voltage waveforms of the output voltage V1 of the differential amplifier 83 and the output voltage V2 of the switch 84. These voltage waveforms are, for example, as shown in FIGS. Since the voltage waveform of the output voltage V2 of the switch 84 is thus different, even if the output voltage V2 of the switch 84 is integrated by the integrator 86, the offset voltage of the Hall element 81 and the inherent offset voltage of the differential amplifier 83 are different. The magnetic detection device could not measure a very small magnetic force such as geomagnetism.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve such problems and to provide a magnetic detection device capable of removing the offset voltage of the Hall element and the offset voltage inherent to the amplifier that amplifies the output of the Hall element. And

  The invention of claim 1 is unique to the 4-terminal Hall element having a cross-shaped Hall plate and four terminals arranged at each end of the Hall plate, current supply means, and the 4-terminal Hall element. Four times in each cycle, the polarity of the Hall offset voltage alternates four times in each cycle, from the current supply means to two opposing terminals of the four terminals of the four-terminal Hall element. Switching means for switching the direction of the current and taking out the voltage from two opposing terminals in a direction orthogonal to the direction of the current, amplifying means for amplifying the voltage taken out by switching by the switching means, and the switching means Among the four current direction switchings in each cycle according to the above, when there is a switching that is opposite to the previous current direction, By inverting the polarity of the voltage from the amplifying means, and in synchronization with the switching of the direction of the immediately following current, characterized in that a reversing means for reversing the polarity of the voltage from the amplifying means.

  In the first aspect of the present invention, the switching means includes a current from the current supply means from a first terminal of the four terminals of the Hall element toward a second terminal opposite to the first terminal. So that the current supply means is connected to the first and second terminals, and the third terminal and the fourth terminal facing the third terminal are connected to the first terminal of the amplifier. A first switching unit connected to each of the terminal and the second terminal, and the current supply unit so that current from the current supply unit flows from the third terminal toward the fourth terminal; A second switch connecting a third and a fourth terminal, and connecting the first terminal and the second terminal to the second terminal and the first terminal of the amplifier, respectively; From the second terminal toward the first terminal, the front The current supply means is connected to the first and second terminals so that a current from the current supply means flows, and the third terminal and the fourth terminal are connected to the first of the amplifier. A third switch connected to each of the second terminal and the second terminal, and the current supply means so that a current from the current supply means flows from the fourth terminal toward the third terminal. A fourth switch connecting the third and fourth terminals and connecting the first terminal and the second terminal to the second terminal and the first terminal of the amplifier; In each cycle, the first switching, the second switching, the fourth switching, and the third switching can be performed in this order, and the inversion means can perform the fourth switching and the second switching. Synchronously with the switching of 3 It is possible to reverse the polarity of the voltage from the amplifying means.

  In the invention of claim 1, the switching means is arranged in the order of the first switching, the third switching, the fourth switching, and the second switching according to claim 2 for each cycle. Switching can be performed, and the inverting means can invert the polarity of the voltage from the amplifying means in synchronization with the third switching and the fourth switching.

  In the invention of claim 1, the switching means is arranged in the order of the first switching, the second switching, the fourth switching, and the third switching, according to claim 2, every two cycles. 3. Two cycles including a first cycle to be performed and a second cycle to be performed in the order of the first switching, the third switching, the fourth switching, and the second switching according to claim 2 are repeated. The inversion means inverts the polarity of the voltage from the amplification means in synchronization with the fourth switching and the third switching in the first cycle, and the second cycle Can be reversed in synchronism with the third switching and the fourth switching.

  According to the present invention, since it is configured as described above, it is possible to remove the offset voltage of the Hall element and the offset voltage specific to the amplifier that amplifies the output of the Hall element.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
<First Embodiment>
FIG. 1 shows a first embodiment of the present invention. This is an example of a magnetic detection device. In FIG. 1, reference numeral 1 denotes a Hall element, which has a cross-shaped Hall plate and four terminals, and these four terminals are for supplying current, and voltages appearing on the Hall plate. It is for taking out. Among these four terminals, in FIG. 1, the upper terminal is called “terminal 1”, the lower terminal facing this terminal 1 is called “terminal 2”, and the left terminal is called “terminal 3”. The terminal facing the terminal 3 is referred to as “terminal 4”. Reference numeral 2 denotes a switch for switching the connection between each terminal of the terminal pair in which the Hall voltage appears and the inverting terminal and the non-inverting terminal of the differential amplifier 3 provided in the subsequent stage of the switch 2. The differential amplifier 3 inverts and amplifies the output voltage of the switch 2. Reference numeral 4 denotes a switch for switching the polarity of the output voltage of the differential amplifier 3. A switching control unit 5 controls switching of internal connections of the switches 2 and 4. Reference numeral 6 denotes an integrator that integrates the output of the switch 4. An analog-to-digital converter (ADC) 7 converts an analog signal from the integrator 6 into a digital signal.

  The states illustrated in FIGS. 2A to 2D are states corresponding to the 0 ° state, the 90 ° state, the 180 ° state, and the 270 ° state, respectively, which have already been described with reference to FIG. However, similarly, they are referred to as 0 ° state, 90 ° state, 180 ° state, and 270 ° state, respectively, and are represented as (0 °), (90 °), (180 °), and (270 °), respectively. To do.

  Here, the state in which the internal connection of the switch 2 and the switch 4 is switched to the connection shown in FIG. 1 is the 0 ° state. However, in FIG. The 90 ° state, 180 ° state, and 270 ° state are not shown.

  In the 0 ° state, the switching control unit 5 controls the switch 2 to connect the terminal 1 to the power supply Vdd, the terminal 2 to the ground, and the terminal 3 to the differential amplifier 3 among the four terminals of the Hall element 1. The terminal 4 is connected to the non-inverting terminal of the differential amplifier 3, and the switch 4 is controlled so that the polarity of the output of the differential amplifier 3 is not inverted. In this 0 ° state, the output voltage of the differential amplifier 3 is V1 = Vh + Oh + Oe, and the output voltage of the switch 4 is V2 = Vh + Oh + Oe.

  In the 90 ° state, the switching control unit 5 controls the switch 2 to connect the terminal 3 to the power source Vdd and the terminal 4 to the ground among the four terminals of the Hall element 1 and connect the terminal 2 to the differential amplifier 3. The terminal 1 is connected to the non-inverting terminal of the differential amplifier 3 and the switch 4 is controlled so that the polarity of the output of the differential amplifier 3 is not inverted. In this 90 ° state, the output voltage of the differential amplifier 3 is V1 = Vh−Oh + Oe, and the output voltage of the switch 4 is V2 = Vh−Oh + Oe.

  In the 180 ° state, the switching control unit 5 controls the switch 2 to connect the terminal 2 to the power source Vdd and the terminal 1 to the ground among the four terminals of the Hall element 1 and connect the terminal 3 to the differential amplifier 3. The terminal 4 is connected to the non-inverting terminal of the differential amplifier 3, and the switch 4 is controlled so that the polarity of the output of the differential amplifier 3 is reversed. In this 180 ° state, the output voltage of the differential amplifier 3 is V1 = −Vh−Oh + Oe, and the output voltage of the switch 4 is V2 = − (− Vh−Oh + Oe).

  In the 270 ° state, the switching control unit 5 controls the switch 2 to connect the terminal 4 to the power supply Vdd, the terminal 3 to the ground, and the terminal 2 to the differential amplifier 3. The terminal 1 is connected to the non-inverting terminal of the differential amplifier 3 and the switch 4 is controlled so that the polarity of the output of the differential amplifier 3 is reversed. In this 270 ° state, the output voltage of the differential amplifier 3 is V1 = −Vh + Oh + Oe, and the output voltage of the switch 4 is V2 = − (− Vh + Oh + Oe).

  Next, switching control of the switches 2 and 4 by the switching control unit 5 of FIG. 1 will be described with reference to FIG. The switching control unit 5 switches the switch 2 so that the polarity of the offset voltage of the Hall element 1 supplied to the inverting terminal and the non-inverting terminal of the differential amplifier 3 changes alternately. Here, as the state transition in which the polarity of the offset voltage of the Hall element 1 changes alternately, the state transition (hereinafter referred to as “first”) that transitions from (0 °) → (90 °) → (270 °) → (180 °). "State transition") and (0 °) → (180 °) → (270 °) → (90 °) state transition (hereinafter referred to as “second state transition”). The unit 5 controls the switches 2 and 4 by setting either the first state transition or the second state transition as one cycle.

  First, an example in which the switching control unit 5 controls the switches 2 and 4 with the first state transition as one cycle will be described. When the switch 2 is controlled by the switching control unit 5 with the first state transition as one cycle, the waveform of the output voltage of the differential amplifier 3 corresponds to the state transition as shown in FIG. When the output voltage rises and falls, it is affected by the settling of the differential amplifier 3 and at the same time there is a switching in which the direction of the current is reversed (ie (270 °)). Thus, the polarity of the output voltage of the differential amplifier 3 is inverted, and the polarity of the output voltage of the switch 4 is inverted in synchronization with the switching of the current direction (that is, (180 °)) immediately after this. When controlled in this way, the waveform of the output voltage of the switch 4 is as shown in FIG.

  As can be seen from FIG. 3B, the voltage obtained by inverting the voltage waveform appearing in the half cycle (that is, (0 °) and (90 °)) before the first cycle of the first state transition with respect to the voltage axis. Waveforms appear in the latter half cycle ((270 °) and (180 °)).

  Next, an example in which the switching control unit 5 controls the switches 2 and 4 with the second state transition as one cycle will be described. When the switch 2 is controlled by the switching control unit 5 with the second state transition as one cycle, the waveform of the output voltage of the differential amplifier 3 is as shown in FIG. At the time of falling, in response to the settling of the differential amplifier 3 according to the state transition, and at the same time, the switching of the current direction is reversed (ie, (180 °)), it is synchronized with this. Thus, the polarity of the output voltage of the differential amplifier 3 is inverted, and the polarity of the output voltage of the switch 4 is inverted in synchronization with the switching of the current direction (that is, (270 °)) immediately after this. When controlled in this way, the waveform of the output voltage of the switch 4 is as shown in FIG.

  As can be seen from FIG. 4B, the voltage obtained by inverting the voltage waveform appearing in the half cycle (that is, (0 °) and (180 °)) before one cycle of the second state transition with respect to the voltage axis. Waveforms appear in the latter half cycle ((270 °) and (90 °)).

  When the voltage appearing at the output terminal of the switch 4 is integrated by the integrator 6, the offset voltage of the Hall element 1 and the offset voltage inherent to the differential amplifier 3 are thereby removed, and only the Hall voltage is obtained. Is output to the ADC 7.

  The example of the magnetic detection device using the four-terminal Hall element as the Hall element has been described above, but the present invention can be applied to a magnetic detection device having an eight-terminal Hall element as shown in FIG. In FIG. 5, the direction of current flow is indicated by arrows, and only the external terminals for taking out the Hall voltage are shown. 5, such a state changes as shown in FIG. 5 (a) → FIG. 5 (c) → FIG. 5 (e) → FIG. 5 (g), and FIG. 5 (b) → FIG. d) → FIG. 5 (f) → FIG. 5 (h) is regarded as a four-terminal Hall element, and it is effective to apply and combine the present invention independently for each. is there.

<Second Embodiment>
This embodiment is different from the first embodiment in the state transition of one cycle that the switching control unit 5 generates by controlling the switch 2. That is, in the first embodiment, the first state transition of (0 °) → (90 °) → (270 °) → (180 °) or (0 °) → (180 °) → (270 ° ) → (90 °), the second state transition is created. On the other hand, in the present embodiment, one cycle of state conversion is performed by the first state transition → the second state transition, that is, (0 ° ) → (90 °) → (270 °) → (180 °) → (0 °) → (180 °) → (270 °) → (90 °) or second state transition → first state transition, (0 °) → (180 °) → (270 °) → (90 °) → (0 °) → (90 °) → (270 °) → (180 °).

  In the present embodiment, switch 2 is controlled by switching control unit 5 based on the first and second state transitions, and switch 4 is controlled at (180 °) and (270 °). Since the voltage appearing at the output terminal is integrated by the integrator 6, the offset voltage of the Hall element 1 and the offset voltage specific to the differential amplifier 3 are removed.

It is a block diagram which shows the 1st Embodiment of this invention. It is explanatory drawing for demonstrating the state which the switching control part 5 produces by controlling the switch 2. FIG. It is a wave form diagram which shows the waveform of the output voltage of the differential amplifier 3 when the 1st state transition is produced, and the waveform of the output voltage of the switch 4. FIG. It is a wave form diagram which shows the waveform of the output voltage of the differential amplifier 3 when the 2nd state transition is produced, and the waveform of the output voltage of the switch 4. FIG. It is explanatory drawing for demonstrating the direction of the electric current sent with respect to an 8-terminal Hall element, and how to take out Hall voltage. It is explanatory drawing for demonstrating the state produced in a prior art example. It is a wave form diagram which shows the relationship between the output V1 of a differential amplifier, and the output V2 of a switch in each state. It is a block diagram which shows an example of a structure of the conventional magnetic detection apparatus. FIG. 9 is a waveform diagram showing a waveform of an output voltage of the differential amplifier 83 of FIG. 8 and a waveform of an output voltage of the switch 84;

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hall element 2, 4 Switch 3 Differential amplifier 5 Switching control part 6 Integrator 7 ADC

Claims (4)

A four-terminal Hall element having a cross-shaped Hall plate and four terminals arranged at each end of the Hall plate;
Current supply means;
Four times in each cycle, the opposite two terminals of the four terminals of the four-terminal Hall element are connected so that the polarity of the Hall offset voltage inherent to the four-terminal Hall element alternates four times in each cycle. On the other hand, switching means for switching the direction of the current from the current supply means, and taking out the voltage from two terminals facing each other in a direction orthogonal to the direction of the current;
Amplifying means for amplifying the voltage extracted by switching by the switching means;
Of the four current direction switchings in each cycle by the switching means, when there is a switching that is opposite to the previous current direction, the voltage from the amplifying means is synchronized with this switching. And a reversing means for reversing the polarity of the voltage from the amplifying means in synchronization with the switching of the current direction immediately thereafter. In Claim 1, the switching means comprises:
The current supply means, so that the current from the current supply means flows from a first terminal of the four terminals of the Hall element toward a second terminal facing the first terminal; A first terminal that connects the first terminal and the second terminal, and that connects the third terminal and the fourth terminal opposite to the third terminal to the first terminal and the second terminal of the amplifier, respectively. Switching between
The current supply means and the third and fourth terminals are connected such that the current from the current supply means flows from the third terminal toward the fourth terminal, and the first terminal A second switch connecting the first terminal and the second terminal to the second terminal and the first terminal of the amplifier, respectively;
The current supply means is connected to the first and second terminals so that a current from the current supply means flows from the second terminal toward the first terminal, and the third terminal A third switch connecting the first terminal and the fourth terminal to the first terminal and the second terminal of the amplifier, respectively,
The current supply means and the third and fourth terminals are connected so that the current from the current supply means flows from the fourth terminal toward the third terminal, and the first terminal And a fourth switching for connecting the second terminal and the second terminal to the second terminal and the first terminal of the amplifier, in each cycle, the first switching and the second switching , Performing the fourth switching and the third switching in this order,
The inversion means inverts the polarity of the voltage from the amplifying means in synchronization with the fourth switching and the third switching. The switching means according to claim 1, for each cycle, performs switching in the order of the first switching, the third switching, the fourth switching, and the second switching according to claim 2. Done
The inversion means inverts the polarity of the voltage from the amplifying means in synchronization with the third switching and the fourth switching. The switching means according to claim 1, wherein the switching means performs the first switching, the second switching, the fourth switching, and the third switching in order of every two cycles. The switching of repeating two cycles including one cycle and the second cycle performed in the order of the first switching, the third switching, the fourth switching, and the second switching according to claim 2. Done
The inverting means inverts the polarity of the voltage from the amplifying means in synchronization with the fourth switching and the third switching in the first cycle, and the third switching in the second cycle. A magnetic detection device that reverses in synchronization with the fourth switching.

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