JP2014006061A - Sensor driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress reduction of detection accuracy caused by variation between Hall sensors.SOLUTION: A constant current source 10 and a Hall sensor HE0 are connected in this order between a power source VDD and a ground GND, and similarly a constant current source 11, a Hall sensor HE1, a constant current source 12, and a Hall sensor HE2 are connected. Further, an input voltage Va to the Hall sensor HE0 is output to the input side of the Hall sensor HE1 by a voltage follower circuit 22. Similarly, an input voltage Va to the Hall sensor HE0 is output to the input side of the Hall sensor HE2 by a voltage follower circuit 24. Driving currents I1 and I2 to the Hall sensors HE1 and HE2 are adjusted so as to set the input voltages to the Hall sensors HE1 and HE2 to Va, and a sensor driving circuit is operated to cancel variation in resistance values among the Hall sensors HE0 to HE2. Thus, a detection error caused by the variation in resistance values among the Hall sensors is suppressed.

Description

  The present invention relates to a sensor drive circuit that drives a plurality of sensors.

Conventionally, as an example of a technique using a plurality of hall sensors, there is a position detection mechanism (for example, see Patent Document 1).
FIG. 2 is a schematic configuration diagram illustrating an example of a signal processing unit of the position detection mechanism.
The position detection mechanism 100 in FIG. 2 includes three hall sensors HE0 to HE2 having the same functional configuration, and these are housed in a semiconductor chip. For example, a hall sensor HE0 disposed in the center of the semiconductor chip, and hall sensors HE1 and HE2 disposed on the left and right sides of the semiconductor chip across the hall sensor HE0 are provided. As shown in FIG. 3, the Hall sensors HE <b> 0 to HE <b> 2 are arranged at equal intervals on the mounting substrate 1, and are arranged so that the magnetosensitive direction is perpendicular to the mounting substrate 1.

  As shown in FIG. 3, a rectangular parallelepiped magnet 2 as a measurement object has a configuration in which N and S poles are magnetized perpendicularly to a substrate 1 on which Hall sensors HE0 to HE2 are mounted. 1 is supported so as to be movable in a parallel direction with respect to a straight line connecting the centers of the magnetic sensing portions of the Hall sensors HE0 to HE2. Then, position detection is performed using the correlation of the output values of the three Hall sensors with respect to the moving distance of the rectangular parallelepiped magnet 2 when the rectangular parallelepiped magnet 2 is moved in parallel with the mounting substrate 1.

That is, a magnetic field corresponding to the positional relationship between the rectangular parallelepiped magnet 2 and the hall sensors HE0 to HE2 is applied to the hall sensors HE0 to HE2, and detection voltages such as VHE0, VHE1, and VHE2 are output.
And the output voltage of each Hall sensor HE0-HE2 is input into the signal processing part 50, and position detection is performed using a predetermined correlation.

  That is, as shown in FIG. 2, the output voltages of the hall sensors HE0 to HE2 are first input to the adder / subtractor circuit 51, and the difference between the output voltages of the two hall sensors HE1 and HE2 (VHE1−VHE2) and the three hall sensors. A sum of output voltages HE0 to HE2 (VHE0 + VHE1 + VHE2) is generated. The reference voltage Vr is generated by the reference voltage circuit 53. Further, based on the calculation result in the addition / subtraction circuit 51, the division circuit 52 performs the calculation represented by the following expression (1), and outputs this as the final output, that is, the position detection signal Vout.

Vout
= {(VHE1-VHE2) / (VHE0 + VHE1 + VHE2)} * Vr
...... (1)

JP 2010-107440 A

By the way, for example, when a magnetic field having the same intensity is applied to the hall sensors HE1 and HE2, a measurement object (rectangular magnet 2 in the case of FIG. 3) that applies the magnetic field is a magnetic sensing part of the hall sensors HE0 to HE2. Are located at the midpoint position of the straight line connecting the centers of the two (hereinafter referred to as the sensor midpoint position).
When the measurement object is present at the sensor midpoint position, the output voltages of the hall sensors HE1 and HE2 arranged on the left and right of the hall sensor HE0 are “VHE1−VHE2 = 0”, and the final output (position detection signal) Vout becomes “0”.

FIG. 4 is a schematic configuration diagram illustrating an example of the Hall sensor drive circuit 60 that drives the Hall sensors HE0 to HE2, and is a Hall sensor drive circuit to which a constant current drive system is applied.
As shown in FIG. 4, the hall sensor HE1 is connected between the power supply VDD and the ground GND, and the constant current source 11 is interposed between the hall sensor HE1 and the power supply VDD.
The voltage VHE1 between the output terminals Vp11 and Vn11 of the hall sensor HE1 is output as an output voltage.

Similarly, the hall sensor HE0 is connected between the power supply VDD and the ground GND, and the constant current source 10 is interposed between the hall sensor HE0 and the power supply VDD. A voltage VHE0 between the output terminals Vp10 and Vn10 of the hall sensor HE0 is output as an output voltage.
The hall sensor HE2 is connected between the power supply VDD and the ground GND, and a constant current source 12 is interposed between the hall sensor HE2 and the power supply VDD. A voltage VHE2 between the output terminals Vp12 and Vn12 of the hall sensor HE2 is output as an output voltage.
Here, the output voltage VHE of the Hall sensor can be expressed by the following equation (2).
VHE = G · (Rh / d) · Ic · B
= Α ・ R ・ Ic ・ B (2)

  In Equation (2), G is a shape factor such as the shape of the sensor or terminal electrode, Rh is the Hall coefficient, d is the thickness of the Hall sensor, Ic is the Hall sensor drive current, B is the applied magnetic field, and R is the Hall sensor. Resistance value. Α is a proportionality coefficient, and α = G · Rh / d.

In FIG. 4, the resistance values of the hall sensors HE0 to HE2 are R0, R1, and R2, and the output voltage VHE0 of the hall sensors HE0 to HE2 when the object to be measured (cuboid magnet 2) is present at the sensor midpoint position. Consider ~ VHE2.
When the measurement object (rectangular magnet 2) is present at the sensor midpoint, magnetic fields having the same strength are applied to the Hall sensors HE1 and HE2. If the magnetic field applied to the hall sensor HE0 is B0 and the magnetic field applied to the hall sensors HE1 and HE2 is B12, the output voltages VHE0 to VHE2 of the hall sensors HE0 to HE2 can be expressed by the following equation (3). .
VHE0 = α ・ R0 ・ Ic ・ B0
VHE1 = α ・ R1 ・ Ic ・ B12
VHE2 = α ・ R2 ・ Ic ・ B12 (3)
When the expression (3) is applied to the arithmetic expression in the addition / subtraction circuit 51 of the signal processing unit 50 of the position detection mechanism 100 of FIG. 2, it can be expressed by the following expressions (4) and (5).

VHE1-VHE2
= (Α · R1 · Ic · B12)-(α · R2 · Ic · B12)
= Α · (R1-R2) · Ic · B12 (4)
VHE0 + VHE1 + VHE2
= (Α · R0 · Ic · B0) + (α · R1 · Ic · B12)
+ (Α ・ R2 ・ Ic ・ B12) ...... (5)
Here, when the resistance values R1 and R2 of the Hall sensors HE1 and HE2 are equal, the equation (4) becomes VHE1-VHE2 = 0. Therefore, accurate detection without error can be performed.

However, when variations occur in the plurality of Hall sensors during the manufacturing process and the resistance values R1 and R2 of the Hall sensors HE1 and HE2 are different, R1−R2 ≠ 0. When R1-R2 = ΔR and VHE1-VHE2 = ΔV, the equation (4) becomes the following equation (6).
ΔV = VHE1-VHE2
= Α ・ ΔR ・ Ic ・ B12 (6)
That is, an error corresponding to “α · ΔR · Ic · B12” occurs in the detection voltages of the hall sensors HE1 and HE2.

As a result, the calculation represented by the equation (1) executed by the division circuit 52 at the subsequent stage of the signal processing unit 50 can be expressed by the following equation (7) from the equations (4) and (5). it can.
{(VHE1-VHE2) / (VHE0 + VHE1 + VHE2)} * Vr
= [{Α · (R1-R2) · Ic · B12} /
{(Α · R0 · Ic · B0) + α · (R1 + R2) · Ic · B12}] × Vr
= [(ΔR · B12) / {(R0 · B0) + (R1 + R2) · B12}] × Vr
...... (7)
From the equation (7), it can be seen that there is a problem that an error proportional to ΔR occurs in the final output Vout, and the final output Vout does not become “0” indicating the sensor middle point position.

  Therefore, the present invention has been made paying attention to the above-mentioned conventional unsolved problems, and provides a sensor drive circuit capable of performing magnetoelectric conversion with higher accuracy regardless of variations in Hall sensors and the like. The purpose is to do.

  To achieve the above object, a sensor driving circuit according to the present invention includes a plurality of sensors having the same functional configuration, a plurality of current sources that are provided for the respective sensors and that supply the same current to the sensors, A buffer circuit that buffers an output voltage of one of the current sources and outputs the output voltage to an output terminal of the other current source to the sensor.

According to the present invention, variation in characteristics between sensors can be suppressed. Therefore, it is possible to obtain a more accurate sensor output with reduced influence of characteristic variation.
Moreover, since it can implement | achieve, without providing the correction circuit etc. which correct | amend a sensor output, it can implement | achieve, without affecting the response speed of the circuit itself provided with these some sensors.

It is a schematic block diagram which shows an example of the Hall sensor drive circuit to which this invention is applied. It is a block diagram which shows an example of the signal processing part which comprises the position detection mechanism to which this invention is applied. It is a figure with which it uses for operation | movement description of a position detection mechanism. It is a schematic block diagram which shows an example of the conventional Hall sensor drive circuit.

Hereinafter, an embodiment of the Hall sensor drive circuit 20 of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing an example of a Hall sensor drive circuit 20 according to the present invention. The functional configuration of the signal processing unit 50 of the position detection mechanism 100 including the Hall sensor drive circuit 20 is the same as that shown in FIG.
The hall sensor drive circuit 20 in the present embodiment is applied to a position detection mechanism of a type having a plurality of hall sensors (three in the case of FIG. 1) inside the IC as shown in FIG. By controlling the drive current of the other hall sensors based on the input voltage of one hall sensor, variation in output voltage between the hall sensors is reduced.

That is, the hall sensor drive circuit 20 in the present embodiment includes three hall sensors HE0 to HE2 as shown in FIG.
The hall sensor HE1 is connected between the power supply VDD and the ground GND, and the constant current source 11 is interposed between the hall sensor HE1 and the power supply VDD. Further, a voltage follower circuit 22 including an operational amplifier 21 is connected between the constant current source 11 and the hall sensor HE1. That is, the output terminal of the operational amplifier 21 is connected between the constant current source 11 and the hall sensor HE1, and the inverting input terminal of the operational amplifier 21 is connected between the constant current source 11 and the hall sensor HE1, The non-inverting input terminal of the operational amplifier 21 is connected between a constant current source 10 (described later) and the hall sensor HE0.

The voltage VHE1 between the output terminals Vp11 and Vn11 of the hall sensor HE1 is output as an output voltage.
Similarly, the hall sensor HE0 is connected between the power supply VDD and the ground GND, and the constant current source 10 is interposed between the hall sensor HE0 and the power supply VDD. A voltage VHE0 between the output terminals Vp10 and Vn10 of the hall sensor HE0 is output as an output voltage.

  The hall sensor HE2 is connected between the power supply VDD and the ground GND, and the constant current source 12 is interposed between the hall sensor HE2 and the power supply VDD. Furthermore, a voltage follower circuit 24 including an operational amplifier 23 is connected between the constant current source 12 and the hall sensor HE2. That is, the output terminal of the operational amplifier 23 is connected between the constant current source 12 and the Hall sensor HE2, and the inverting input terminal of the operational amplifier 23 is connected between the constant current source 12 and the Hall sensor HE2. The non-inverting input terminal of the operational amplifier 23 is connected between the constant current source 10 and the Hall sensor HE0.

The voltage VHE2 between the output terminals Vp12 and Vn12 of the hall sensor HE2 is output as an output voltage.
The voltage follower circuit 22 receives a voltage Va (hereinafter referred to as an input voltage) Va between the Hall sensor HE0 disposed at the center and the constant current source 10, and the input voltage Va and an input voltage to the Hall sensor HE1 are obtained. It operates to supply or draw current to the current supply line to the hall sensor HE1 so as to match.

Similarly, the voltage follower circuit 24 inputs Va (referred to as an input voltage between the Hall sensor HE0 and the constant current source 10 disposed in the center), and the input voltage Va coincides with the input voltage to the Hall sensor HE2. As described above, the operation is performed so as to supply or draw a current to the current supply line to the hall sensor HE2.
In the hall sensor drive circuit 20, the hall sensors HE0 to HE2 have the same functional configuration. The constant current sources 10 to 12 hold the output current at the same constant current.

  Here, when the magnetic field applied to the hall sensor HE0 is B0 and the same intensity magnetic field is applied to the hall sensors HE1 and HE2, and this magnetic field is B12, the output voltages VHE0 of the three hall sensors HE0 to HE2 are output. -VHE2 can be represented by the following formula (8). In Equation (8), I1 and I2 are the drive currents of the Hall sensors HE1 and HE2, respectively, and Ic is the drive current of the Hall sensor HE0. R1 and R2 are resistance values of the hall sensors HE1 and HE2, respectively, and R0 is a resistance value of the hall sensor HE0.

VHE0 = α ・ R0 ・ Ic ・ B0
VHE1 = α ・ R1 ・ I1 ・ B12
VHE2 = α ・ R2 ・ I2 ・ B12 (8)
The input voltages of the hall sensors HE0 to HE2 are determined by the current (drive current) Ic flowing through the hall sensor HE0 and the resistance value R0 of the hall sensor HE0.

As described above, the voltage follower circuits 22 and 24 generate the drive current supplied to the hall sensors HE1 and HE2 so that the input voltage to the hall sensors HE1 and HE2 matches the input voltage Va to the hall sensor HE0. By adjusting, the operational amplifiers 21 and 23 operate so as to satisfy the following expression (9). At this time, the drive current is adjusted without changing the drive current Ic of the Hall sensor HE0.
Va = R0 · Ic = R1 · I1 = R2 · I2 (9)
That is, the drive currents I1 and I2 adjusted by the voltage follower circuits 22 and 24 change so as to cancel the variations in the resistance values R1 and R2 of the Hall sensors HE1 and HE2.

Here, in order to satisfy said (9), said Formula (8) can be represented as following Formula (10).
VHE0 = α ・ B0 ・ Va
VHE1 = α ・ B12 ・ Va
VHE2 = α · B12 · Va (10)
When the equation (10) is applied to the equation (4), the following equation (11) is obtained.
VHE1-VHE2
= Α · B12 · Va-α · B12 · Va
= 0 (11)
That is, as shown in the equation (11), even if the resistance values of the hall sensors HE0 to HE2 vary, the error included in the equation (4) can be canceled out.

  As a result, the final output Vout expressed by the equation (1) obtained by the Hall sensor drive circuit 20 shown in FIG. 1 can be expressed by the following equation (12). Therefore, it can be seen that by using the Hall sensor drive circuit 20 shown in FIG. 1, it is possible to obtain a true final output (position detection signal) Vout that does not include errors due to variations in the Hall sensors HE0 to HE2.

{(VHE1-VHE2) / (VHE0 + VHE1 + VHE2)} * Vr
= {(Α · B12 · Va−α · B12 · Va)
/ (Α · B0 · Va + α · B12 · Va + α · B12 · Va)} × Vr
= {0 / (α · B0 · Va + α · B12 · Va + α · B12 · Va)} × Vr
= 0
(12)
Thus, by using the Hall sensor drive circuit 20 having the configuration shown in FIG. 1, it is possible to mitigate the influence caused by the variation in resistance value between Hall sensors. Therefore, accurate magnetoelectric conversion can be performed without being affected by variations in Hall sensors.

Further, as shown in FIG. 1, by merely providing the voltage follower circuits 22 and 24, it is possible to alleviate the influence of variations in the resistance values of the Hall sensors, correct the output voltage of each Hall sensor, Since it is not necessary to separately provide a correction circuit or the like for adjusting the output current, it can be realized without affecting the response speed of the IC.
In addition, although FIG. 1 demonstrated the case where Hall sensors HE0-HE2 were driven by the source drive type constant current drive system, it is not restricted to this.

For example, the present invention can be applied even when the hall sensors HE0 to HE2 are driven by a sink driving type constant current driving method.
Further, the reference voltage Vr for determining the voltage of the final output Vout can be arbitrarily set, and may be set in advance at the time of shipment, or may be set at the time of incorporating the Hall sensor driving circuit 20 into the apparatus. It is.

  In FIG. 1, the case where the three hall sensors HE0 to HE2 are driven has been described. However, the present invention is not limited to this, and the present invention can be applied to the case where two or four or more hall sensors are driven. In this case as well, as in FIG. 1, any one of the hall sensors is used as a reference hall sensor, and a voltage follower circuit that inputs the input voltage Va of the reference hall sensor is provided corresponding to each hall sensor. The driving current supplied to each hall sensor is adjusted so that the input voltage of the sensor becomes the input voltage Va of the reference hall sensor.

By adopting such a configuration, the drive current is adjusted so as to cancel the variation in the resistance value of each Hall sensor by adjusting the drive current to each Hall sensor as described above. A highly accurate final output Vout can be obtained without being affected by variations in the resistance value of the sensor.
Further, in the above-described embodiment, among the three hall sensors HE0 to HE2, the input voltage Va of the center hall sensor HE0 is used as a reference so that the input voltages of the other hall sensors HE1 and H2 coincide with the input voltage Va. The case where the drive current to the hall sensors HE1 and HE2 is adjusted has been described. However, the present invention is not limited to this, and the drive current to other hall sensors is adjusted based on the input voltage of the hall sensor HE1 or HE2. You may comprise.

  Moreover, although the case where the drive current to the other two hall sensors HE is adjusted based on the input voltage to one hall sensor among the three hall sensors HE0 to HE2 has been described, the present invention is not limited to this. . For example, based on the input voltage of the hall sensor located at one end of the three hall sensors HE0 to HE2, for example, the hall sensor HE2, the drive current of the hall sensor HE0 located at the center arranged next to the hall sensor HE2 Adjust. Then, with reference to the input voltage of the hall sensor HE0 located at the center, the drive current of the hall sensor HE1 located at the other end arranged next to the hall sensor HE0 is adjusted in order, so that A configuration may be employed in which the drive current is adjusted.

  For example, when four or more hall sensors are provided, when the input voltage of the center hall sensor is used as a reference, it is necessary to adjust the driving current across the driving current supply lines of other hall sensors. However, by adopting a configuration in which the drive current of the adjacent hall sensor is sequentially adjusted, it can be realized without straddling the drive current supply lines of other hall sensors.

In the above-described embodiment, the case where the drive current supplied to each Hall sensor is adjusted using the voltage follower circuit has been described. However, the present invention is not limited to the voltage follower circuit, and may be applied to a buffer circuit. it can.
Moreover, although the said embodiment demonstrated the Hall sensor drive circuit which drives a Hall sensor, it is not restricted to this. For example, a 3-axis gyro sensor, a MEMS (Micro Electro Mechanical Systems) sensor, or the like can be applied. In short, any sensor having a plurality of bridge resistors can be applied.

HE0 to HE2 Hall sensors 10 to 12 Constant current sources 21 and 23 Operational amplifiers 22 and 24 Voltage follower circuit

Claims (1)

A plurality of sensors having the same functional configuration;
A plurality of current sources provided for each of the sensors and supplying the same current to the sensors;
And a buffer circuit for buffering an output voltage of one of the plurality of current sources and outputting the output voltage to an output terminal of the other current source to the sensor.

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