JP7207201B2 - magnetic sensor - Google Patents

Description

The present invention relates to magnetic sensors.

2. Description of the Related Art Conventionally, an output processing circuit for a magnetic sensor provided with a capacitor for AC coupling has been proposed, for example, in Japanese Unexamined Patent Application Publication No. 2002-200013. The capacitor forms part of the high pass filter. This removes the low-frequency component contained in the magnetic signal output from the magnetic sensor. Also. The effects of offset components such as temperature characteristic components and endurance fluctuations included in the magnetic signal are removed.

JP 2015-210537 A

However, in the above conventional technology, a capacitor with a very large capacity is required for the configuration of the high-pass filter. For this reason, conventionally, a high-pass filter could not be integrated on a semiconductor chip, and a capacitor was externally attached to the semiconductor chip. Using a capacitor as an external element is one of the factors that increase the cost of the magnetic sensor, complicate the sensor structure, and increase the size of the sensor.

Moreover, since a high-pass filter is used, the magnetic signal of low-speed rotation is attenuated. Therefore, the detection gap that defines the distance between the rotating body and the magnetic sensor is reduced. That is, the distance between the rotating body and the magnetic sensor must be shortened. In order to avoid this, it is necessary to further reduce the cutoff frequency of the high-pass filter, which in turn requires a capacitor with a larger capacity. In recent years, there are cases where rotation detection of 1 Hz or higher is required. In such a case, a capacitance on the order of μF is required, and a discrete capacitor must be externally attached to the semiconductor chip.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a magnetic sensor having a high-pass filter with a sufficiently low cutoff frequency using capacitors and resistors that can be realized with a semiconductor chip without using capacitors as external elements. .

In order to achieve the above object, according to the first aspect of the invention, the magnetic sensor includes a magnetic element (110) and a semiconductor chip (130). The magnetic element is arranged with a predetermined gap with respect to the outer circumference of a rotating body (200) on which rotational position information is periodically provided at regular intervals on the outer circumference (201). The magnetic element detects a magnetic change received from the outer peripheral portion as the rotational position of the rotating body changes due to the rotation of the rotating body, and outputs a detection signal. The semiconductor chip receives a detection signal from the magnetic element and performs signal processing.

The semiconductor chip also has a semiconductor substrate (131) and a high-pass filter (133). The high-pass filter is formed on a semiconductor substrate by a semiconductor process, receives a detection signal from a magnetic element, and removes an offset component and a low-frequency component contained in the detection signal. The high-pass filter comprises a capacitor (136) , a filter resistor (137), and a capacitance amplifier circuit (138) connected between the capacitor and the filter resistor and amplifying the capacitance of the capacitor.
The capacity amplifier circuit section has an operational amplifier (139), a first resistor (140), a second resistor (141), and a third resistor (142). and a non-inverting input terminal of the operational amplifier, a third resistor is connected to the inverting input terminal of the operational amplifier, and a connection point between the first resistor and the second resistor is connected to This is a configuration in which a filter resistor is connected.

According to this, since the capacitance amplifier circuit section is formed on the semiconductor chip by a semiconductor process, a capacitor as an external element is not required. Therefore, a magnetic sensor having a high-pass filter with a sufficiently low cutoff frequency can be configured with resistors and capacitors that can be realized with a semiconductor chip.

It should be noted that the reference numerals in parentheses of each means described in this column and claims indicate the correspondence with specific means described in the embodiments described later.

It is the figure which showed the arrangement|positioning relationship and each signal of the magnetic sensor and gear which concern on one Embodiment. It is the figure which showed the circuit structure of the magnetic sensor. It is the figure which showed the detection signal before and behind a high-pass filter. FIG. 4 is a diagram showing the relationship between signal frequency and gain characteristics;

An embodiment will be described below with reference to the drawings. As shown in FIG. 1 , magnetic sensor 100 is arranged to face outer peripheral portion 201 of gear 200 . Gear 200 is a gear-shaped rotating body incorporated in a vehicle transmission.

Protrusions 202 and recesses 203 are alternately provided on an outer peripheral portion 201 of the gear 200 in the rotational direction. The protrusions 202 are teeth. A convex portion 202 and a concave portion 203 indicate rotational position information of the gear 200 in the rotational direction. The convex portion 202 and the concave portion 203 have a constant width in the direction of rotation. The protrusions 202 and the recesses 203 are periodically provided at regular intervals in the rotation direction. The gear 200 is provided with a toothless portion 204 in which the convex portion 202 is not provided. A toothless portion 204 indicates the rotation reference position of the gear 200 . Note that FIG. 1 shows a part of the outer peripheral portion 201 of the gear 200 developed linearly.

As shown in FIG. 2, the magnetic sensor 100 has a magnetic element 110 and a semiconductor chip 130. As shown in FIG. As shown in FIG. 1 , the magnetic element 110 is configured as a detection chip 111 separate from the semiconductor chip 130 .

The magnetic element 110 is arranged with a predetermined gap with respect to the outer peripheral portion of the gear 200 in the gap direction. The gap direction is the radial direction of gear 200 . The magnetic element 110 includes a magnetoresistive element whose resistance value changes when affected by a magnetic field from the object to be measured. Magnetoresistive elements are, for example, AMR (Anisotropic Magneto Resistance), GMR (Giant Magneto Resistance), and TMR (Tunneling Magneto Resistance). The detection chip 111 and the semiconductor chip 130 are electrically connected via a plurality of wires.

The magnetic element 110 employs a magnetic detection method using a magnetoresistive element. Therefore, the magnetic element 110 detects a magnetic change received from the outer peripheral portion of the gear 200 as the rotational position of the gear 200 changes due to the rotation of the gear 200 . Specifically, the magnetic element 110 is configured by electrically connecting a plurality of magnetoresistive elements (not shown) so as to form a bridge circuit. As the gear 200 rotates, the magnetic element 110 outputs the midpoint potential of the bridge circuit as a detection signal corresponding to the uneven position.

As shown in FIG. 1, magnetic sensor 100 has bias magnet 150 . By applying a bias magnetic field to the magnetoresistive element, the bias magnet 150 increases the magnetic field detection sensitivity of the magnetoresistive element by a certain amount.

A semiconductor chip 130 shown in FIG. 2 is an electronic component that processes a detection signal input from the magnetic element 110 . The semiconductor chip 130 is configured as, for example, an ASIC (Application Specific Integrated Circuit). The semiconductor chip 130 has a semiconductor substrate 131 , a first amplifier section 132 , a high-pass filter 133 , a second amplifier section 134 and a signal processing section 135 .

The semiconductor substrate 131 is, for example, an SOI substrate having a first conductive layer, an insulating layer and a second conductive layer. A first amplifier 132, a high-pass filter 133, a second amplifier 134, and a signal processor 135 are formed on the second conductive layer of the semiconductor substrate 131 by a semiconductor process. Here, the semiconductor process is a manufacturing method for forming semiconductor structures and circuit elements by repeating microfabrication on SOI wafers.

Note that the semiconductor substrate 131 is not limited to the SOI substrate. The semiconductor substrate 131 may be a single layer substrate or a multilayer substrate as long as it can be processed by a semiconductor process.

The first amplification section 132 is a circuit section that differentially amplifies the detection signal of the magnetic element 110 . The first amplifier section 132 is a differential amplifier circuit configured by an operational amplifier, resistors, and the like (not shown).

The high-pass filter 133 is a circuit unit that receives the detection signal amplified by the first amplification unit 132 and removes the offset component and the low-frequency component contained in the detection signal. The offset component is a DC component such as temperature characteristics and endurance fluctuation.

The high-pass filter 133 includes a capacitor 136 , a resistor 137 , and a capacity amplifier circuit section 138 that amplifies the capacity of the capacitor 136 . These are formed on the semiconductor substrate 131 .

The capacitor 136 has one electrode connected to the first amplification section 132 and the other electrode connected to the capacity amplification circuit section 138 . The capacitor 136 is, for example, a capacitor formed by a depletion layer generated by applying a reverse bias to a base region and an emitter region that constitute a transistor. That is, capacitor 136 is equivalent to a diode formed by the PN junction of transistors.

As shown in FIG. 3, the detection signal containing the offset component and the low frequency component is processed by the high-pass filter 133 to remove the offset component and the low frequency component. As a result, the threshold is positioned at the center of the amplitude of the detection signal.

The capacity amplifier circuit section 138 has an operational amplifier 139 and resistors 140 , 141 and 142 . The other electrode of the capacitor 136 is connected to the non-inverting input terminal of the operational amplifier 139 . The output of the operational amplifier 139 is fed back to the non-inverting input terminal via a resistor 140 having a resistance value of R2 and a resistor 141 having a resistance value of R3. Also, the output terminal of the operational amplifier 139 is connected to the inverting input terminal through a resistor 142 having a resistance value of R3.

A resistor 137 is connected to the connection point between the resistors 140 and 141 . Resistor 137 is connected to the reference voltage section. A CR circuit of a high-pass filter is composed of the capacitor 136 , the capacitance amplifier circuit section 138 and the resistor 137 .

The second amplifier 134 is a circuit that differentially amplifies the detection signal that has been signal-processed by the high-pass filter 133 . The second amplifying section 134 is a differential amplifying circuit composed of operational amplifiers, resistors, and the like (not shown).

The signal processing unit 135 is a circuit unit that processes the detection signal processed by the second amplification unit 134 as a digital signal. The signal processing unit 135 compares the detection signal with the threshold value, binarizes it, and outputs the binarized signal to the outside. When the signal value indicated by the detection signal exceeds the threshold, the signal processing unit 135 outputs, for example, a Hi binarized signal to the outside, and when the signal value indicated by the detection signal is below the threshold, the signal processing unit 135 outputs, for example, a Lo binarized signal. output the conversion signal to the outside. Note that the threshold may have hysteresis.

The above is the overall configuration of the magnetic sensor 100 . The magnetic element 110 and the semiconductor chip 130 are mounted on a lead frame or the like, and sealed with a mold resin together with leads (not shown).

Next, operation of the magnetic sensor 100 will be described. First, as shown in FIG. 1, the magnetic sensor 100 is arranged at a position facing the ridges and valleys of the gear 200 . When the gear 200 starts rotating, the magnetoresistive element of the magnetic sensor 100 is affected by the external magnetic field and changes its resistance value. As a result, the magnetic element 110 outputs the midpoint potential of the bridge circuit as a detection signal. The first amplifier 132 differentially amplifies the detection signal and outputs it to the high-pass filter 133 .

The high-pass filter 133 amplifies the capacity of the capacity amplifier circuit section 138 . Specifically, the input voltage of the high-pass filter 133 is input to the non-inverting input terminal of the operational amplifier 139 of the capacity amplification circuit section 138 . As a result, the input voltage of the operational amplifier 139 works so that both ends have the same potential. Therefore, the resistor 140 having a resistance value of R2 and the resistor 141 having a resistance value of R3 divide the output current by the ratio of these resistors, so that the charge/discharge of the capacitor 136 is apparently large. It is amplified by the operational amplifier 139 as follows. That is, assuming that the capacitance of the capacitor 136 is C1, the capacitance amplifier circuit section 138 amplifies C1 as C=C1×(R3/R2).

For the resistor 137, current operation with a large time constant is performed. In other words, the capacitance C amplified by the capacitance amplification circuit section 138 and the resistor 137 form a CR circuit having a large time constant. The cut-off frequency fc is given by fc=1/(2π×C1×R1×(R3/R2)) where R1 is the resistance value of the resistor 137 . Therefore, the high-pass filter 133 functions as a filter that cuts low frequency components.

A high-pass filter 133 processes the detection signal according to the cutoff frequency fc. This removes the offset component and low frequency component contained in the detection signal. That is, since temperature characteristics, endurance fluctuations, etc. are eliminated, there is no need for processes, circuits, etc. for adjusting these. Due to the high-pass filter 133, the center of the detected signal amplitude is located at the threshold.

The detection signal has the maximum amplitude when the convex portion 202 of the gear 200 rises, and the minimum amplitude when the convex portion 202 of the gear 200 falls. When the detection gap between the magnetic element 110 and the gear 200 is small, the detection signal has a large-amplitude waveform indicated by the solid line. When the detection gap between the magnetic element 110 and the gear 200 is large, the detection signal has a small amplitude waveform indicated by the dashed line. In the toothless portion 204 of the gear 200, there is no change in the magnetic field received by the magnetic element 110 from the gear 200, so the amplitude of the detection signal is reduced.

The detection signal that has passed through the high-pass filter 133 is input to the signal processing section 135 . The signal processing unit 135 compares the signal value of the detection signal with a threshold value, binarizes the detection signal, and outputs the binarized signal to the outside. When the detection gap is small, the binarized signal rises faster than when the detection gap is large. Note that the binarized signal corresponding to the toothless portion 204 is Lo.

The inventors investigated the constants of the resistors 140 to 142 of the capacitor 136, the resistor 137, and the capacitance amplifier circuit section 138 for detecting rotations of 1 Hz or higher in the high-pass filter 133 described above.

As a result, if C1 = 560 pF for the capacitor 136, R1 = 10 kΩ for the resistor 137, R2 = 0.1 kΩ for the resistor 140 in the capacitance amplifying circuit section 138, and R3 = 3500 kΩ for the resistors 141 and 142, rotation detection of 1 Hz or more is possible. It turned out to be possible. Note that the constant of each element is an example, and other constants are of course possible.

Furthermore, the inventors investigated the relationship between the signal frequency of the detection signal and the gain specification by simulation for the constants of the respective elements. The results are shown in FIG. As shown in FIG. 4, a gain characteristic of -3 dB or more was obtained in the signal frequency range of 1 Hz to 12 kHz, which is the detection frequency target. This result also shows that even if the capacitor 136 is formed on the semiconductor chip 130, rotation detection of 1 Hz or more is possible.

As described above, since the capacitance amplifier circuit section 138 is formed on the semiconductor chip 130 by a semiconductor process, the capacitor 136 need not be an external element. Therefore, the resistor 137 and the capacitor 136 that can be realized by the semiconductor chip 130 can realize the high-pass filter 133 with a sufficiently low cutoff frequency fc. In recent years, miniaturization and cost reduction of the magnetic sensor 100 have been demanded, and since the external capacitor 136 is not used, there are merits such as a reduction in the number of parts and a reduction in mounting size.

Alternatively, the magnetic element 110 may be configured as a Hall element. In this case, the magnetic element 110 may be formed as a detection chip 111 separate from the semiconductor chip 130 or may be formed on the semiconductor chip 130 .

Regarding the correspondence relationship between the description of this embodiment and the description of the claims, the gear 200 corresponds to the "rotating body" of the claims. Also, the resistor 137 corresponds to the "filter resistor" in the claims, and the resistors 140, 141 and 142 correspond to the "first resistor", "second resistor" and "third resistor" in the claims. corresponds to

(Other embodiments)
The configuration of the magnetic sensor 100 shown in each of the above embodiments is an example, and the configuration is not limited to the configuration shown above, and other configurations that can realize the present invention are also possible. For example, the rotating body is not limited to the gear 200, and may be a magnetized rotor. The magnetized rotor is a disc-shaped rotating body in which first magnetic poles, which are N poles, and second magnetic poles, which are S poles, are alternately magnetized in the circumferential direction of the outer peripheral portion. In the case of a magnetized rotor, for example, the amplitude of the detection signal becomes the maximum or minimum signal at the boundary of each magnetic pole.

Moreover, the magnetic sensor 100 is not limited to gears and magnetized rotors incorporated in a vehicle transmission, and may be used to detect the rotation of other parts of the vehicle or rotating bodies other than the vehicle.

110 magnetic element 111 detection chip 130 semiconductor chip 131 semiconductor substrate 133 high-pass filter 136 capacitor 137 resistor 138 capacity amplification circuit

Claims (2)

Rotating body (200) having rotation position information provided periodically at regular intervals on the outer peripheral part (201) is arranged with a predetermined gap with respect to the outer peripheral part of the rotating body. a magnetic element (110) that detects a magnetic change received from the outer peripheral portion as the rotational position changes and outputs a detection signal;
a semiconductor chip (130) that receives the detection signal from the magnetic element and performs signal processing;
including
The semiconductor chip has a semiconductor substrate (131) and a high-pass filter (133) that is formed on the semiconductor substrate by a semiconductor process and removes an offset component and a low frequency component included in the detection signal,
The high-pass filter includes a capacitor (136) , a filter resistor (137), and a capacitance amplifier circuit (138) connected between the capacitor and the filter resistor and amplifying the capacitance of the capacitor. , and
The capacity amplifier circuit section has an operational amplifier (139), a first resistor (140), a second resistor (141), and a third resistor (142), and the capacitor is connected to a non-inverting input terminal of the operational amplifier, A series connection of the first resistor and the second resistor is connected between the output of the operational amplifier and the non-inverting input terminal of the operational amplifier, the third resistor is connected to the inverting input terminal of the operational amplifier, and the first A magnetic sensor in which the filter resistor is connected to a connection point between the resistor and the second resistor . 2. The magnetic sensor according to claim 1, wherein the magnetic element is configured as a detection chip (111) separate from the semiconductor chip.

Images