JP2002107346A - Magnetic body detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic body detector that can be used over a wide temperature range by using first and second resistance blocks, having a resistance temperature coefficient and making the resistance temperature coefficient correspond to the temperature coefficient of the operating voltage of an amplifying transistor. SOLUTION: The magnetic body detector 10 includes an amplifying transistor 12. A first resistance block 14, including a semiconductor magnetic resistance element, is connected between the base and emitter of the amplification transistor 12, and a series circuit of a constant-current circuit 16 and a resistor 18 for preventing chattering is connected between the collector and the base. The constant-current circuit 16 comprises an FET 20 and a second resistance block 22. As the first resistance block 14 and a second resistance block 22, ones having resistance temperature coefficient are used, and the temperature characteristics of a voltage that is applied between the base and emitter of the amplifying transistor 12 are made to correspond to the operating voltage of the amplifying transistor 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic detector, and more particularly to a magnetic detector used for detecting a steel ball such as a pachinko ball using a semiconductor magnetoresistive element.

[0002]

2. Description of the Related Art FIG. 10 is a circuit diagram showing an example of a conventional magnetic detector. The magnetic detector 1 includes a resistor 2 and a semiconductor magnetoresistive element 3 connected in series. Further, the magnetic detector 1 includes an NPN-type amplifying transistor 4. The collector of the amplifying transistor 4 is connected to the resistor 2 and the power supply voltage Vin. The emitter of the amplifying transistor 4 is connected to the semiconductor magnetoresistive element 3 and grounded via the output resistor 5. Further, the connection between the resistor 2 and the semiconductor magnetoresistive element 3 is connected to the base of the amplifying transistor 4. In the magnetic detector 1, a bias magnetic field is applied to the semiconductor magnetoresistive element 3 by a magnet or the like.

In the magnetic detector 1, when a magnetic body approaches the semiconductor magnetoresistive element 3, a magnetic field concentrates on the semiconductor magnetoresistive element disposed between the magnet and the magnetic body, and the magnetic field of the semiconductor magnetoresistive element 3 The resistance value changes. When the resistance value of the semiconductor magnetoresistive element 3 increases, the voltage applied to the base of the amplifying transistor 4 increases, the current flowing through the amplifying transistor 4 increases, and the output voltage from the resistor 5 increases. Therefore, the magnetic substance can be detected by measuring the output voltage of the resistor 5.

As the semiconductor magnetoresistive element 3 used here, for example, as shown in FIG. 11, a semiconductor magnetoresistive pattern 7 is formed on a substrate 6 so as to meander. The semiconductor magnetoresistive pattern 7 is, for example, InS
A thin film of a compound semiconductor such as b, InAs, or GaAs is formed by vapor deposition, sputtering, or the like, and short bar electrodes 8 of Al or the like are formed on the surface thereof at predetermined intervals. In such a semiconductor magnetoresistive pattern 7, the resistance value increases as the applied magnetic field increases.

However, in the magnetic detector 1 as shown in FIG. 10, when the power supply voltage Vin fluctuates, the voltage between the base and the emitter of the amplifying transistor 4 changes and malfunctions. As described above, the magnetic detector 1 using the constant current circuit 8 composed of the FET and the resistor
Has been proposed. In the magnetic detector 1, a constant current can be obtained by the constant current circuit 9 regardless of the fluctuation of the power supply voltage Vin, and the base-emitter voltage of the amplifying transistor 4 can be stabilized.

[0006]

However, FIG.
As shown in (1), the semiconductor magnetoresistive element has a large negative resistance-temperature characteristic, and has a property that the resistance value increases as the temperature decreases. In FIG. 13, the vertical axis represents
The ratio between the resistance value R (T) of the semiconductor magnetoresistive element at each temperature and the resistance value R (25) at 25 ° C. is shown. With such characteristics, when the power supply voltage Vin is constant,
When examining the voltage V _MR across the semiconductor magnetoresistive element, as shown in FIG. 14, the V _MR at the time of detection of the magnetic substance and at the time of non-detection show a negative temperature characteristic. here,
The operating voltage of the amplifying transistor, that is, the base-emitter voltage V _BE also shows a negative temperature characteristic, but its slope is smaller than the voltage V _MR across the semiconductor magnetoresistive element. Therefore, the operating range of the magnetic detector becomes a detection time and V _MR and operating voltage V _BE is intersected portion of the amplifying transistor during the non-detection of a semiconductor magnetoresistive element, that only works in a narrow temperature range Understand.

[0007] Therefore, a main object of the present invention is to provide a magnetic detector which can be used in a wide temperature range.

[0008]

According to the present invention, there is provided a first resistance block including at least one semiconductor magnetoresistive element,
A second resistance block, which is composed of an FET and one of the first resistance block or the second resistance block, and one of the first resistance block or the second resistance block is connected between the gate and the source of the FET. A constant current circuit, and an amplifying transistor in which the other of the first resistor block or the second resistor block is connected between the base and the emitter, and the constant current circuit is connected between the base and the collector. The first resistor block and the second resistor block have a temperature coefficient of resistance, and the temperature characteristic of the base-emitter voltage of the transistor for amplification corresponds to the temperature characteristic of the operating voltage of the transistor for amplification by the temperature coefficient of resistance. And a magnetic detector. In such a magnetic detector, the temperature characteristics of the base-emitter voltage of the amplifying transistor and the temperature of the amplifying transistor when detecting the magnetic material are determined by the temperature coefficient of resistance of the first resistor block and the second resistor block. It is preferable to match the characteristics. Further, by associating the temperature coefficient of resistance of the first resistor block and the temperature coefficient of resistance of the second resistor block with the temperature characteristic of the operating voltage of the amplifying transistor, the voltage between the base and the emitter of the amplifying transistor when the magnetic substance is not detected. Is preferably lower than the operating voltage of the amplifying transistor, and the voltage between the base and the emitter of the amplifying transistor is higher than the operating voltage of the amplifying transistor when the magnetic substance is detected. Further, each of the resistance temperature coefficients of the first resistance block and the second resistance block is determined by the temperature characteristic of the operating voltage of the amplifying transistor,
It is preferable to correspond to the resistance of the semiconductor magnetoresistive element and the temperature coefficient of sensitivity. Such a magnetic detector includes a means for applying a bias magnetic field to the semiconductor magnetoresistive element. Further, at least one resistance element constituting the second resistance block can be formed of the same material as the semiconductor magnetoresistance element. Further, at least one resistance element and the semiconductor magneto-resistance element constituting the first resistance block may be formed on a single substrate.

By using the first and second resistance blocks having a temperature coefficient of resistance and making these resistance temperature coefficients correspond to the temperature coefficient of the operating voltage of the amplifying transistor, the resistance blocks of these resistance blocks can be used over a wide temperature range. The temperature coefficient of resistance and the temperature coefficient of the operating voltage of the amplifying transistor can be substantially matched. At this time, when the magnetic substance is not detected, the base-emitter voltage of the amplifying transistor is lower than the operating voltage of the amplifying transistor,
In addition, when the magnetic substance is detected, by setting the base-emitter voltage of the amplifying transistor higher than the operating voltage of the amplifying transistor, the amplifying transistor can be operated according to the presence or absence of the magnetic substance. . In order to operate the amplifying transistor in this manner, each of the resistance temperature coefficients of the first resistor block and the second resistor block is changed according to the temperature characteristic of the operating voltage of the amplifying transistor, the resistance and sensitivity of the semiconductor magnetoresistive element. And the temperature coefficient of Further, in order to change the strength of the magnetic field applied to the semiconductor magnetoresistive element as the magnetic body approaches, a bias magnetic field is applied to the semiconductor magnetoresistive element in advance. By forming at least one resistive element of the second resistive block from the same material as the semiconductor magnetoresistive element, the resistance temperature coefficient of the second resistive block can be adjusted. Furthermore, in the first resistance block, by forming one resistance element and the semiconductor magnetoresistance element on a single substrate, it is possible to reduce the component space.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments of the present invention with reference to the accompanying drawings.

[0011]

FIG. 1 is a circuit diagram showing an example of a magnetic detector according to the present invention. The magnetic detector 10 includes, for example, an NPN-type amplifying transistor 12. Between the base and the emitter of the amplifying transistor 12, a first
Are connected. Further, a series circuit of a constant current circuit 16 and a resistance 18 for preventing chattering is connected between the collector and the base of the transistor 12 for amplification. The constant current circuit 16 includes, for example, an N-channel F
ET 20 and second resistance block 22. One end of the second resistance block 22 is connected to the source of the FET 20, and the other end of the second resistance block 22 is connected to the gate of the FET 20. Further, the second resistance block 22
Is connected to a resistance 18 for preventing chattering. The collector of the amplifying transistor 12 and the drain of the FET 20 are connected to the power supply voltage Vin. The emitter of the amplifying transistor 12 is connected to the first
, And grounded via an output resistor 24.

In the magnetic detector 10, the first resistance block 14 includes at least one semiconductor magnetoresistive element. The first resistance block 14 may be a semiconductor magnetoresistive element alone, or may be a combination with another resistance element. When the first resistance block 14 is a combination of a semiconductor magnetoresistive element and another resistance element, a semiconductor magnetoresistive pattern 32 and a resistance pattern 34 are formed on one substrate 30 as shown in FIG. 2, for example. Is done. The semiconductor ceramic resistance pattern 32 is made of, for example, InS
Compound semiconductors such as b, InAs, and GaAs are formed in a meandering manner by vapor deposition, sputtering, or the like, and short bar electrodes 36 of Al or the like are formed at predetermined intervals. As described above, by forming the semiconductor magnetoresistive element and the other resistive element on one substrate 30, the number of parts can be reduced, and the magnetic substance detector 10
Can be reduced in size.

The second resistance block 22 is formed of, for example, an element formed of the same material as the semiconductor magnetoresistive element or an element having resistance temperature characteristics such as a thermistor. Further, the second resistance block 22 may be configured by a combination of an element formed of the same material as the semiconductor magnetoresistive element and a resistance, or a combination of a thermistor and a resistance.

The magnetic detector 10 is used, for example, as a steel ball detector. As shown in FIG. 3, the steel ball detection device 40 includes a substrate 44 in which a through hole 42 is formed, and a case 46 is formed adjacent to the through hole 42.
The first resistance block 14 is disposed in the case portion 46 at a portion facing the through hole 42. Further, a magnet 48 is arranged so as to be in contact with the first resistance block 14, and a DC magnetic field is applied to the semiconductor magnetoresistive element in the first resistance block 14. Therefore, when the steel ball 50 passes through the through hole 42, the magnetic field concentrates in the first resistance block portion, and the resistance value of the semiconductor magnetoresistive element changes.

In the magnetic detector 10, the constant current circuit 1
6, a constant current can be obtained even when the power supply voltage Vin fluctuates. That is, when the power supply voltage Vin increases, the current flowing through the second resistance block 22 increases, and the voltage input to the gate of the FET 20 increases.
Therefore, the resistance value between the drain and the source of the FET 20 increases, and the current flowing therethrough is suppressed. Conversely, when the power supply voltage Vin decreases, the resistance value between the drain and the source of the FET 20 decreases, and the current flowing therethrough increases. Thus, a constant current is supplied from the constant current circuit 16 irrespective of the fluctuation of the power supply voltage Vin. Therefore, a constant voltage is applied between the base and the emitter of the amplifying transistor 12 irrespective of the fluctuation of the power supply voltage.

In this state, when the steel ball 50 passes through the through-hole 42, the steel ball 50 approaches the semiconductor magnetoresistive element of the first resistance block 14, and the bias magnetic field concentrates on the semiconductor magnetoresistive element and the resistance is concentrated. The value increases. Therefore, the resistance value of the first resistance block 14 increases, the voltage applied between the base and the emitter of the amplification transistor 12 increases, and the output resistance 2
4 is increased. Therefore, the output voltage obtained from the resistor 24 increases, and the passage of the steel ball 50 can be detected. If the gate of the FET 20 and the base of the amplification transistor 12 are short-circuited, the switching operation of the amplification transistor 12 becomes too fast,
The output voltage also chatters according to the chattering of the resistance value of the first resistor block 14. Therefore, by using the resistor 18 for preventing chattering, the switching operation of the amplifying transistor 12 is set to an appropriate speed.

In the magnetic detector 10, a semiconductor magnetoresistive element is used for the first resistance block 14, and an element or thermistor made of the same material as the semiconductor magnetoresistive element is also used for the second resistance block 22. Used. Therefore, the first resistance block 14 and the second resistance block 22 have resistance temperature characteristics. When a thermistor is used, a semiconductor magnetoresistive element or an amplifying transistor 1
A thermistor having a negative resistance temperature characteristic is used in accordance with the temperature characteristic of the operating voltage of No. 2. When an element made of the same material as the semiconductor magnetoresistive element is used for the second resistance block 22, a plurality of short bar electrodes on the semiconductor magnetoresistive pattern are not formed so that the resistance value does not change due to a magnetic change.

In the magnetic detector 10, the first resistance is changed so that the voltage applied between the base and the emitter of the amplification transistor 12 changes according to the temperature characteristic of the operating voltage of the amplification transistor 12. Block 14 and second
The temperature coefficient of the resistance block 22 is adjusted.

That is, the characteristics of the amplification transistor 12
Is the voltage V between the base and the emitter as shown in FIG._BE
Is turned on when is higher than a predetermined value Va,
It turns off when not in use. This operating voltage changes with temperature
And has a negative temperature characteristic. Therefore, the amplification
Base-emitter voltage V applied to transistor 12
_BEIs the temperature characteristic of the operating voltage of the transistor 12 for amplification.
If correspondingly changed, the magnetic detector 10 can be used over a wide temperature range.
Can be used.

In order to obtain such characteristics, the second resistance block 22 for adjusting the current of the constant current circuit 16 has a temperature characteristic. As shown in FIG. 5, between the resistance value of the current adjusting resistor connected to the constant current circuit 16 and the current value,
There is a relationship that the current value decreases as the resistance value of the current adjusting resistor increases. Utilizing this property, the voltage of the second resistance block 22 and the amplification transistor 12
The operating temperature range of the magnetic detector 10 can be expanded by matching the operating voltage temperature characteristics.

That is, at a low temperature, the first resistance block 14
When the resistance value of the second resistor block 22 increases, the current value is decreased by increasing the resistance value of the second
When the resistance value of the resistance block 14 decreases, the resistance temperature coefficient of the first resistance block 14 and the second resistance block 22 increases so that the current value increases by reducing the resistance value of the second resistance block 22. Can be adjusted. As described above, by adjusting the resistance temperature coefficients of the first resistor block 14 and the second resistor block 22, the voltage applied between the base and the emitter of the transistor 12 for amplification is changed to the operating voltage of the transistor 12 for amplification. Can correspond. Therefore, as shown in FIG. 6, in a wide temperature range, the voltage V _MR of the first resistor block 14 at the time of detecting the magnetic material is set higher than the operating voltage of the amplifying transistor 12, and the first voltage at the time of detecting no magnetic material is detected. The voltage _VMR of the resistor block 14 can be made lower than the operating voltage of the amplifying transistor 12.

Actually, characteristics were examined using a conventional magnetic detector and the magnetic detector 10 of the present invention. In a conventional magnetic detector, a semiconductor magnetoresistive element is used as the first resistance block, and a fixed resistance is used as the second resistance block connected to the FET. Further, as one of the magnetic detectors 10 of the present invention, a resistance element formed of the same material as the semiconductor magnetoresistance element is used for the second resistance block 22. Note that the resistance value of this resistance element does not change due to a change in the magnetic field. Further, as another magnetic substance detector 10 of the present invention, the second resistance block 2
No. 2 was used by forming a composite resistor with a resistor element formed of the same material as the semiconductor magnetoresistive element and another resistor element.

The characteristics of these magnetic detectors were examined and are shown in Tables 1, 2 and 3, respectively. In these tables, MR indicates the first resistive block and MR
During standby, the resistance value when there is no magnetic material, MR K = 1.1
And K = 1.3 indicate the sensitivity of the MR at which the magnetic detector operates. The current value indicates a current value of the constant current circuit determined by the value of the second resistance block. Further, the MR voltage indicates a product of a resistance value of the first resistance block and a current value. The amplification transistor operating voltage V _BE indicates a voltage at which the amplification transistor is turned on. In addition, V _BE /
V _MR is _calculated as (operating voltage of amplifying transistor / M during standby)
R voltage), which is 1.1 in the operating temperature range.
It is desirable that

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

The characteristics of Table 1, Table 2, and Table 3 are shown in FIGS. 7, 8, and 9, respectively. From these results, the conventional magnetic detector operates normally around 25 ° C., but becomes unstable in other temperature ranges. On the other hand, in the magnetic detector 10 using a resistance element formed of the same material as the semiconductor magneto-resistance element for the second resistance block 22, the voltage (MR voltage) of the first resistance block 14 and the amplification transistor Twelve operating voltages (V _BE ) show temperature characteristics substantially parallel to each other, indicating that the device operates normally in the entire temperature range in which the measurement was performed. Further, it is understood that almost ideal characteristics can be obtained by adjusting the second resistance block 22 with the composite resistance.

As described above, by providing the second resistor block 22 used in the constant current circuit 16 with the resistance temperature characteristic, the temperature characteristic of the voltage obtained from the first resistance block 14 and the operating voltage of the amplifying transistor 12 is obtained. And the operating temperature range of the magnetic detector 10 can be expanded. That is, the first resistance block 1
4 increases, the resistance value of the second resistance block 22 used in the constant current circuit 16 is increased, and the current value is decreased, so that the voltage applied between the base and the emitter of the amplifying transistor 12 is reduced. Amplifying transistor 1
2 can be matched with the operating voltage. When the resistance value of the first resistance block 14 decreases at a high temperature, the resistance value of the second resistance block 22 used in the constant current circuit 16 is reduced, and the current value is increased. The voltage applied between the base and the emitter and the operating voltage of the amplifying transistor 12 can be matched. Therefore, the magnetic detector 10 can be used in a wide temperature range.

In the magnetic detector 10 shown in FIG.
NPN amplifying transistor 12 and N-channel FE
Although an example using T20 has been described, similar effects can be obtained by using a PNP-type amplifying transistor and a P-channel FET. Further, the first resistance block 14 including the semiconductor magnetoresistive element is used for the constant current circuit 16,
The second resistor block 22 may be connected between the base and the emitter of the transistor 12 for amplification. In this case, the magnetic material approaches and the resistance of the semiconductor magnetoresistive element increases,
As the resistance value of the first resistance block 14 increases accordingly, the current flowing through the second resistance block 22 decreases. Therefore, the voltage applied between the base and the emitter of the amplifying transistor 12 decreases, and the current flowing from the amplifying transistor 12 to the output resistor 24 decreases. Therefore, in such a magnetic detector 10, the output voltage becomes low when a magnetic substance is detected, and the output waveform is inverted from that of the magnetic detector described above. Also in such a magnetic detector 10, by providing the first resistance block 14 and the second resistance block 22 with a resistance temperature coefficient, the magnetic detector can be used in a wide temperature range.

[0030]

According to the present invention, the second resistance block used in the constant current circuit is provided with a temperature coefficient of resistance, whereby the temperature coefficient of resistance of the semiconductor magnetoresistive element included in the first resistance block and the amplification of the temperature coefficient are increased. A magnetic detector capable of adjusting to the temperature characteristics of the operating voltage of the transistor and capable of accurately detecting a magnetic substance over a wide temperature range can be obtained. Further, by providing a means for applying a bias magnetic field to the semiconductor magnetoresistive element, when the magnetic body approaches, the magnetic field can be concentrated on the semiconductor magnetoresistive element, and the detection sensitivity of the magnetic body can be increased. . Further, by forming the resistance element constituting the first resistance block and the semiconductor magnetoresistance element on the same substrate, the element can be reduced in size, thereby reducing the size of the magnetic detector. Can be.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a magnetic detector according to the present invention.

FIG. 2 is an illustrative plan view showing one example of a first resistance block used in the magnetic detector shown in FIG. 1;

FIG. 3 is an illustrative view showing an example in which the magnetic detector of the present invention is applied to a steel ball detector.

FIG. 4 is a graph showing operating characteristics of an amplifying transistor.

FIG. 5 is a graph showing a relationship between a resistor connected to a constant current circuit and a current.

FIG. 6 is a characteristic diagram showing the temperature characteristics of the operating voltage of the amplifying transistor and the voltage obtained from the first resistor block in the magnetic detector of the present invention.

FIG. 7 is a graph showing characteristics shown in Table 1.

FIG. 8 is a graph showing characteristics shown in Table 2.

FIG. 9 is a graph showing characteristics shown in Table 3.

FIG. 10 is a circuit diagram showing an example of a conventional magnetic detector.

11 is an illustrative plan view showing one example of a semiconductor magnetoresistive element used in the magnetic detector shown in FIG. 10;

FIG. 12 is a circuit diagram of a magnetic detector proposed to solve the problem of the magnetic detector shown in FIG.

FIG. 13 is a graph showing resistance temperature characteristics of a semiconductor magnetoresistive element.

14 is a graph showing an operating temperature range of the magnetic detector shown in FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 magnetic detector 12 amplifying transistor 14 first resistor block 16 constant current circuit 18 chattering prevention resistor 20 FET 22 second resistor block 24 output resistor 48 magnet

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H01L 43/08 G01R 33/06 R F-term (Reference) 2G005 BA03 2G017 AA01 AB05 AC09 AD55 AD63 AD65 2G053 AA21 AB22 BA02 BA11 CA06 CB01 CB08

Claims (7)

[Claims] A first resistor block including at least one semiconductor magnetoresistive element, a second resistor block, an FET, and one of the first resistor block or the second resistor block; One of the first resistance block and the second resistance block is a constant current circuit connected between the gate and the source of the FET, and the other of the first resistance block and the second resistance block is connected to the base. The constant current circuit includes an amplifying transistor connected between the base and the collector, and the first resistance block and the second resistance block have a temperature coefficient of resistance. The temperature characteristic of the base-emitter voltage of the amplifying transistor and the temperature characteristic of the operating voltage of the amplifying transistor depend on the temperature coefficient of resistance. A magnetic detector that responds. 2. The first resistance block and the second resistance block.
2. The temperature characteristic of a voltage between a base and an emitter of the amplifying transistor and a temperature characteristic of the amplifying transistor at the time of detection of a magnetic material according to the temperature coefficient of resistance of the resistor block. Magnetic detector. 3. The first resistance block and the second resistance block.
The resistance temperature coefficient of the resistor block corresponds to the temperature characteristic of the operating voltage of the amplifying transistor, so that the voltage between the base and the emitter of the amplifying transistor is reduced when the magnetic substance is not detected. 3. The magnetic detector according to claim 1, wherein the voltage is lower and a base-emitter voltage of the amplifying transistor is higher than an operating voltage of the amplifying transistor when a magnetic material is detected. . 4. A temperature coefficient of resistance of each of the first resistance block and the second resistance block,
4. The magnetic detector according to claim 3, wherein a temperature characteristic of an operating voltage of the amplification transistor and a temperature coefficient of resistance and sensitivity of the semiconductor magnetoresistive element correspond to each other. 5. The semiconductor device according to claim 1, further comprising means for applying a bias magnetic field to said semiconductor magnetoresistive element.
The magnetic detector according to any one of the above. 6. The magnetic detector according to claim 1, wherein at least one resistance element constituting the second resistance block is made of the same material as the semiconductor magnetoresistance element. 7. The magnetic body according to claim 1, wherein at least one resistance element constituting said first resistance block and said semiconductor magnetoresistance element are formed on a single substrate. Detector.