JP2003185685A - Detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a detector by which an output nearly twice that in conventional cases can be obtained, by which a circuit consumption current can be reduced when the same maximum difference voltage as that in conventional cases is maintained or by which a space used to arrange a detecting element can be reduced, and which can be miniaturized by a method wherein a bridge circuit is not used and detecting elements having opposite characteristics are driven individually by a constant current. <P>SOLUTION: A resistance Ra and a resistance Rb whose resistance values are changed according to a change in an external magnetic field, and a resistance Rc and a resistance Rd whose characteristics are opposite to those of the resistances Ra, Rb, are connected in parallel with reference to a power- supply terminal (c). A constant-current source 20 and a constant-current source 21 are connected respectively to the resistances Ra, Rb and the resistances Rc, Rd. The respective resistances Ra to Rb are driven by the constant current. The middle point (a) of the source 21 and the respective resistances and the middle point (b) of the source 20 and the respective resistances are used respectively as output terminals for detection. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detection device equipped with a detection element whose resistance value changes according to changes in an external physical quantity.

[0002]

2. Description of the Related Art Conventionally, for example, a magnetoresistive element has been known as a detecting element whose resistance value changes in accordance with a change in an external physical quantity. A detection device is known in which the magnetoresistive element is connected to a Wheatstone bridge circuit (see FIG. 7) to detect a change in the magnetic field.

As shown in FIG. 7, in a Wheatstone bridge circuit, a magnetoresistive element R located on each side facing each other.
The a and Rb and the magnetoresistive elements Rc and Rd have the same characteristics, and the adjacent magnetoresistive elements have mutually opposite characteristics.

The magnetoresistive element is, for example, Fe,
In the case of being composed of a transition metal alloy such as Ni or Co, the anisotropic magnetoresistance which is different depending on whether the direction of the current flowing through the magnetoresistive element is parallel or perpendicular to the direction of the magnetic field (this is called AMR (Anisotropic) Magneto-Resistance))). In this case, the characteristics of the arrangement of the magnetoresistive elements are opposite to each other when the direction of the current is parallel to the direction of the magnetic field as described above. That is, when the external magnetic field changes and the resistance value of one magnetoresistive element increases, the resistance value of the other magnetoresistive element decreases. Conversely, when the external magnetic field changes and the resistance value of one magnetoresistive element decreases, the resistance value of the other magnetoresistive element increases.

As described above, when the resistance value of one (the other) detection element increases and the resistance value of the other (one) detection element decreases when the external physical quantity changes,
In this specification, it is said to have an inverse characteristic. In the above example, the external physical quantity is the external magnetic field.

The Wheatstone bridge circuit has a simple circuit structure, and an output determined by the electrical characteristics of the detection element and the applied voltage can be obtained.

[0007]

However, in the Wheatstone bridge circuit (hereinafter referred to as a bridge circuit), when the applied voltage is determined, the output is also determined, and no further output can be obtained.

The reason will be described below with reference to FIG. Hereinafter, the detection element will be simply referred to as resistors Ra to Rd. In the case where the resistors Ra to Rd have the anisotropic magnetoresistive property, the largest difference voltage (Va-Vb) is obtained if the opposing resistances have the same characteristics and the adjacent resistances have the opposite characteristics on each side. You can get a change.

[0009] where Ra = Rb = R ± α Rc = Rd = R And

As shown in FIG. 8, R and α are R: central value of change in resistance value when a sufficient magnetic field is applied α: amount of change in resistance value from R. Also, for discrimination, ± (plus / minus),
The same characteristics and the opposite characteristics are represented by "minus" and "plus" (hereinafter, common in this specification).

Then, the midpoint voltage V between the resistors Ra and Rd
b and the midpoint voltage Va between the resistors Rc and Rb are expressed by the following equations (1) and (2). Va = Rb · Vcc / (Ra + Rb) = (R ± α) · Vcc / (2R) (1) Vb = Rd · Vcc / (Ra + Rd) = (R + α) · Vcc / {(R ± α) + (R-α)} = (R-α) · Vcc / (2R) (2)

The maximum differential voltage (Va-Vb) is Va-Vb = ± (α / R) .Vcc = ± A.Vcc (3) A: Maximum resistance change rate (= α / R) Vcc : Power supply voltage (applied voltage) of bridge circuit Among Ra to Rd, Ra and Rb, Rc and Rd have the same characteristics, and Ra and Rc have the opposite characteristics.

From the above, in the bridge circuit, the maximum output (maximum difference voltage) is obtained at the maximum resistance change rate A and the power supply voltage Vcc.
Is decided. As described above, the conventional detection device including the bridge circuit has a problem that it is impossible to obtain a larger output.

The present invention has been made to solve the above problems. That is, according to the present invention, the detection elements having the reverse characteristics are individually driven at constant current without using the bridge circuit. Accordingly, it is an object of the present invention to provide a detection device that can obtain an output that is approximately twice that of the conventional one.

Further, in the case of maintaining the same maximum differential voltage as in the conventional case, the circuit consumption current can be reduced, or the space for arranging the detection element can be reduced, and the detection device can be downsized. Is intended to provide.

[0016]

In order to solve the above-mentioned problems, the invention according to claim 1 has a first detection element whose resistance value changes in accordance with a change in an external physical quantity, and the first detection element. A second detection element having a characteristic opposite to that of the element is connected in parallel to a power supply terminal, and a constant current source for supplying a drive current of the same magnitude is connected to each of the detection elements,
The gist of a detection device is characterized in that each detection element is driven with a constant current, and a middle point between the constant current source and each resistor is used as an output terminal for detection.

According to a second aspect of the present invention, in the first aspect, the constant current source is a current mirror circuit. According to a third aspect of the invention, in the first aspect, each of the current mirror circuits individually drives the first and second detection elements with a constant current.

According to a fourth aspect of the present invention, in the current mirror circuit according to the second aspect, the collectors are connected to the detection elements, the emitters are grounded, and the bases are connected to each other. And a third transistor whose base is connected to the collector of the first transistor and whose collector and emitter are connected to the high power source side and the bases of the first and second transistors, respectively. Characterize.

According to a fifth aspect of the invention, in the fourth aspect, when the output at the midpoint of the first detection element side is the reference voltage,
A level shift circuit is provided between the first detection element and the first transistor, and the level shift circuit raises the reference voltage.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) A first embodiment of the present invention will be described below with reference to FIG.

In the detection device 10, a pair of resistors Ra and Rb as a first detection element connected to the power supply terminal c and a constant current source 20 grounded are connected in series. In addition, a pair of resistors R as the second detection element connected to the power supply terminal c.
c and Rd and the grounded constant current source 21 are connected in series.

The resistors Ra to Rd are magnetoresistive elements and have anisotropic magnetoresistance, and the resistors Ra and Rb have the same characteristic, and the resistors Rc and Rd have the same characteristic. Further, the resistors Ra and Rb and the resistors Rc and Rd are arranged so as to have opposite characteristics.

That is, the resistors Ra and Rb (magnetoresistive element) and the resistors Rc and Rd (magnetoresistive element) are mutually different when the direction of the current is parallel to the direction of the magnetic field. They are arranged so that they have opposite characteristics. That is, when the resistance value of one of the resistors Ra and Rb (magneto-resistive element) increases due to the change of the external magnetic field, the other resistor R and Rb
The resistance values of c and Rd (magnetoresistive element) decrease.
Further, when the resistance value of one of the resistors Ra and Rb (magnetoresistive element) decreases due to the change of the external magnetic field, the other resistance Rc,
In Rd (magnetoresistive element), the resistance value increases.

The constant current sources 20 and 21 are each composed of a current mirror circuit, and the resistors Ra to Rd are
Constant current drive is performed by constant current sources 20 and 21. The current mirror circuit, which is the constant current sources 20 and 21 in the present embodiment, is provided with a known constant current drive circuit (not shown) so that the drive currents I of the same magnitude can be made to flow individually.

Reference numeral b is a midpoint between the resistor Ra and the constant current source 20, which serves as an output terminal for detection. Further, a is a midpoint between the resistor Rd and the constant current source 21, and serves as an output terminal for detection. Here, similarly to the conventional example, Ra = Rb = R ± α Rc = Rd = Rαα R: The central value of the resistance change when a sufficient magnetic field is applied.

In the detector 10 constructed as described above, the midpoint voltages Va and Vb of the midpoints a and b and the differential voltage (Va-Vb) between the midpoints a and b are as follows. become.

Va = Vcc− (Rc + Rd) · I = Vcc−2 (R + α) · I (4) Vb = Vcc− (Rb + Ra) · I = Vcc−2 (R ± α) · I (5) ) Va-Vb = {Vcc-2 (R-α) I}-{Vcc-2 (R ± α) · I} = ± 4α · I (6) In addition, α: amount of change in resistance value from R ( Hereinafter, simply referred to as resistance change amount) I: drive current flowing by the constant current sources 20 and 21, Vcc: power supply voltage (applied voltage).

From the equation (6), it is understood that the difference voltage (Va-Vb) increases as the drive current I increases. If the drive current I is too large, the power supply voltage Vcc and the resistance R
The difference voltage (Va-Vb) is limited by a to Rd.

Here, the range that the drive current I can take is as follows. Driving current I ≦ {Vcc- (constant current source voltage drop)} / 2 (R ± α) (7) Here, the constant current source voltage drop and the resistance value change amount α are the power supply voltage Vcc and the resistance value R. Is very small compared to
The maximum drive current is given by the following equation (8).

Maximum current I≈Vcc / (2R) (8) (Premise: power supply voltage Vcc >> constant current source voltage drop, R >>
α) Substituting the above equation (8) into the equation (6), the following (9)
It becomes an expression, and it can be seen that an output approximately doubled is obtained as compared with the expression (3) of the conventional example.

[0031] A: Maximum resistance change rate (= α / R) According to the present embodiment, the following operational effects are achieved.

(1) In this embodiment, the resistance Ra, whose resistance value changes according to the change of the external magnetic field (external physical quantity),
Rb (first detection element) and resistors Rc and Rd (second detection element) having reverse characteristics to the resistors Ra and Rb are connected to the power supply terminal c.
Connected in parallel to. Further, the constant current sources 20 and 21 are connected to the resistors Ra and Rb and the resistors Rc and Rd, respectively, and the resistors Ra to Rd are driven with constant current. The points a and b were used as output terminals for detection.

As a result, without using the bridge circuit,
By individually driving the detection elements having the reverse characteristics with a constant current, it is possible to obtain an output approximately twice that of the conventional one. (2) In the present embodiment, the conventional maximum differential voltage (Va-
In the case of maintaining Vb) = ± A · Vcc, it can be realized by the following configuration.

1) The drive current I of the constant current sources 20 and 21 is halved to I / 2. By doing so, the equation (9) is replaced with the following equation (9-1). That is, since the drive current I is halved to I / 2, the circuit consumption current (drive current I) of the detection device 10 can be reduced when maintaining the conventional maximum differential voltage.

2) Halve the resistance. For example, the resistance R
Omit d and Rb. By doing this, the midpoint voltages Va, V
b and the difference voltage (Va-Vb) are Becomes

In this case, the area for disposing the resistors as the first and second detecting elements can be reduced, and the size can be reduced. (3) In the present embodiment, the constant current sources 20 and 21 are current mirror circuits, so that the resistors Ra to Rd can be driven with a constant current.

(4) In this embodiment, the constant current sources 20 and 21 (current mirror circuits) are connected to resistors Ra and Rb.
The (first detection element) and the resistors Rc and Rd (second detection element) are individually driven with a constant current. As a result, the resistors Ra and Rb (first detection element) and the resistors Rc and
Rd (second detection element) can be driven with a constant current.

(Second Embodiment) Next, the second embodiment will be described with reference to FIG.
And FIG. 3 will be described. In the detection device 10, a resistor Ra connected to the power supply terminal c and a transistor TR1 whose collector is connected to the resistor Ra and whose emitter is grounded are connected in series. A resistor Rb connected to the power supply terminal c and a transistor TR2 having a collector connected to the resistor Rb and an emitter grounded are connected in series.

The bases of the transistors TR1 and TR2 are connected to each other. Power supply terminal d and transistor T
The transistor T is connected to the connection point of the bases of R1 and TR2.
The collector and emitter of R3 are connected together. The base of the transistor TR3 is connected to the connection point (middle point a) between the resistor Ra and the collector of the transistor TR1. The transistors TR1 and TR2 have the same electrical characteristics.

The transistor TR1 corresponds to the first transistor, and the transistor TR2 corresponds to the second transistor. Further, the transistors TR1 to TR3 form a current mirror circuit.

In the second embodiment, as shown in FIG.
The detection element is a resistor Ra, and the second detection element is a resistor Rb. The resistors Ra and Rb are magnetoresistive elements, have anisotropic magnetoresistance, and the resistors Ra and Rb are arranged so as to have opposite characteristics.

That is, the resistance Ra (magnetoresistive element),
The resistance Rb (magnetoresistive element) is arranged so as to have opposite characteristics when the direction of the current is parallel to the direction of the magnetic field and when it is perpendicular to the direction of the magnetic field. That is, when the resistance value of one resistance Ra (magnetoresistance element) increases due to the change of the external magnetic field, the resistance value of the other resistance Rb (magnetoresistance element) decreases. Further, when the resistance value of one of the resistors Ra (magnetoresistive element) decreases due to the change of the external magnetic field,
The resistance value of the other resistor Rb (magnetoresistive element) increases.

Due to the action of the transistor TR3, the transistors TR1 and TR2 are constant current sources of the resistor Ra and the resistor Rb, respectively, and the base current is corrected by the transistor TR3 for high current ratio accuracy.

That is, when the transistor TR3 is turned on, the transistors TR1 and TR2 are turned on.
At this time, the emitter current 2Ib flowing from the transistor TR3 is shunted as the base current Ib of both the transistors TR1 and TR2. At this time, the transistors TR1,
Since it has the same electrical characteristics as TR2, the transistor TR
The emitter currents (driving currents I) of 1 and TR2 are constant currents of the same value.

The transistor TR3 corrects the base current correction current so that the base current 2Ib / β of the transistor TR3 is current-amplified to flow 2Ib. Note that β is the current amplification factor of the transistor TR3.

The drive current I flowing through the transistor TR1 is Ii, and the drive current I flowing through the transistor TR2 is Ii.
Is I0, the following equation is established in the current mirror circuit of the second embodiment.

I0≈Ii−2Ib / β≈Ii (1-2Ib / (β ^ 2)) (Note that ^ indicates a power, that is, ^ 2 indicates a square.) As a result, the current amplification factor β is small. The closer I0 is to Ii.

In this way, the transistor TR3 is
The current used as the base current of the transistors TR1 and TR2 is covered by current amplification. The transistor TR3 has a circuit configuration that corrects the drive current I (= Ii) on the transistor TR1 side that is reduced by the base current of the transistor TR3.

Next, the operation of the detection device 10 of the second embodiment will be described. In the second embodiment, the resistance Ra is used as the first detection element and the resistance Rd is used as the second detection element.

In order to compare the first embodiment with the second embodiment, if the formulas (4) to (7) described in the first embodiment are changed according to the configuration of the second embodiment, The following equations (4a) to (7a) are obtained.

[0051]   Va = Vcc-Ra · I       = Vcc- (R dried α) I (4a)   Vb = Vcc-Rb · I       = Vcc- (R ± α) · I (5a)   Difference voltage Va−Vb = {Vcc− (Rαα) I} − {Vcc− (R ± α) · I}         = ± 2α · I (6a) In the second embodiment, Ra = R dried α Rb = R ± α R: central value of resistance change when a sufficient magnetic field is applied And

The range that the drive current I can take is as follows: drive current I≤ {Vcc- (constant current source voltage drop)} / (R ± α) (7a) (4)-(1) of the first embodiment. Each equation of 7) is as described above, but in the first embodiment, the constant current source voltage drop and the resistance value change amount α are very small as compared with the power supply voltage Vcc and the resistance value R. I ignored it.

In the second embodiment, the constant current source voltage drop and the resistance change amount α are not ignored.
That is, although the constant current source voltage drop and the resistance value change amount α are smaller than the power supply voltage Vcc and the resistance value R,
Not 0.

Assuming that the constant current source voltage drop and the resistance value variation α are 0, I ≦ Vcc / R and the difference voltage (Va-Vb) becomes Va−Vb ≦ 2A · Vcc.

Here, when the drive current I is set including not only the initial resistance variation of the resistors Ra and Rb but also the temperature change, it is necessary to do the following. I ≦ {Vcc (MIN)-(constant current source voltage drop (MAX))} / {R
(MAX) ± α (MAX)} MAX indicates the maximum value and MIN indicates the minimum value.

In the first embodiment, conversely, Vcc (MA
X), constant current source voltage drop (MIN), R (MIN), α (MIN)
Even in this case, since the drive is performed by the minimum drive current I set as described above, there is a problem that the difference voltage (Va-Vb) becomes small.

On the other hand, in the second embodiment, the midpoint voltage Va, the drive current I, the midpoint voltage Vb, and the difference voltage (Vb
-Va) is as follows. Va = 2Vbe ... (13) I = (Vcc-Va) / Ra = (Vcc-Va) / (R-alpha) ... (14) Vb = Vcc-Rb.multidot.I = Vcc- (R ± .alpha.). Multidot.I = Vcc · {(dried 2α) / (R dried α)} + Va {(R ± α) / (R dried α)} (15) Differential voltage Vb−Va = ± 2A · {Vcc−Va} (16) Note that Vbe is a base-emitter voltage required for operating the transistors TR1 to TR3.

In the second embodiment, the midpoint voltage Va is a fixed voltage, as shown in equation (13). Therefore, (1
As shown in FIG. 3, the midpoint voltage Vb represented by the equation (5) changes around the midpoint voltage Va as the center of amplitude. In FIG. 3, the vertical axis represents the output and the horizontal axis represents the external magnetic field (input signal) as an external physical quantity.

From the equation (14) of the driving current I, Vcc> Va
In that case, since the drive current I can be determined, it is not necessary to consider initial resistance variations and temperature changes. And
If the resistance value of the resistor Ra increases and the resistance value of the resistor Rb decreases, in the constant current drive of the first embodiment, the voltage drop caused by the resistance change changes Va and Vb, which is about 2 times smaller than the conventional one. Get twice the output.

On the other hand, in the second embodiment, the resistance R
When the resistance value of a increases and the resistance value of the resistor Rb decreases, the midpoint voltage Va is a fixed voltage. Therefore, when the drive current I on the resistor Ra side decreases, the drive current I on the resistor Rb side similarly. Decrease. For this reason, the output voltage at the midpoint b (midpoint voltage Vb) overlaps with the decrease in the resistance value of the resistor Rb, and the output is approximately doubled.

In the second embodiment, when the resistance value of the resistor Ra decreases and the resistance value of the resistor Rb increases, the drive current I on the resistor Ra side increases because the midpoint voltage Va is a fixed voltage. However, the drive current I on the resistance Rb side also increases. For this reason, the output voltage at the midpoint b (midpoint voltage Vb) overlaps with the increase in the resistance value of the resistor Rb, and the output is approximately doubled.

From the above, in the second embodiment, the drive current I can always be set optimally and a large sensor output can be obtained. According to the second embodiment, the following operational effects are obtained in addition to the operational effects (1) to (4) of the first embodiment.

(1) In the second embodiment, the transistors TR1 to TR3 form a current mirror circuit. That is, the collectors are resistors Ra and R, respectively.
A transistor TR1 (first transistor) and a transistor TR2 (second transistor), which are connected to b, the emitters of which are grounded, and the bases of which are connected to each other, are provided. The collector and the emitter of the transistor TR3 are connected to the high power source side (Vcc) and the transistor T, respectively.
The bases of R1 and TR2 were connected to each other, and the base of the transistor TR3 was connected to the collector of the transistor TR1.

As a result, in the second embodiment, the drive current I
Can always be set optimally and a large sensor output can be obtained. Further, in the first embodiment, the constant current sources 20 and 21 as the current mirror circuit are provided with a known constant current drive circuit (not shown) so that the drive currents I having the same magnitude can be separately supplied. It was

On the other hand, in the second embodiment, since the transistors TR1 to TR3 are configured as the current mirror circuit connected as described above, a separate constant current drive circuit is not necessary. From this, even when the power supply voltage range or the detection element is changed, other circuit configurations can be used as they are.

Further, since the drive current I can be always optimized as compared with the first embodiment, it is not necessary to consider the initial resistance variation and temperature change. (Third Embodiment) Next, a third embodiment will be described with reference to FIGS.

The same components as those of the second embodiment will be designated by the same reference numerals, and the description thereof will be omitted. Differences will be mainly described. The present embodiment is different from the second embodiment in that a diode D is connected between the resistor Ra and the collector of the transistor TR1. That is, the diode D
Is connected to the resistor Ra, and the cathode is connected to the collector of the transistor TR1.

When the resistance value of the diode D is Rf,
Due to the drive current I flowing through the diode D, the diode D
Then, a voltage drop corresponding to the voltage Vd = Rf · I occurs. In the present embodiment, the midpoint voltage Vd is equal to the voltage Vd.
The amplitude center of b is set to be higher than that of the second embodiment. Further, the rise of the amplitude center prevents the lower limit of amplitude, which will be described later, of the midpoint voltage Vb from being clamped. The conditions for not being clamped will be described later.

Now, the detecting device 1 constructed as described above
The action of 0 will be described. In the third embodiment, the midpoint voltage Va
Unlike the second embodiment, only the drive current I, the midpoint voltage Vb, and the difference voltage (Vb−Va) are different from those in the second embodiment as in the equation (13a).
Is the same formula as in the second embodiment.

Va = 2Vbe + Vd (13a) Vd: shift voltage (in this embodiment, the voltage of the resistance of the diode) I = (Vcc−Va) / Ra = (Vcc−Va) / (R α) ... ( 14) Vb = Vcc−Rb · I = Vcc− (R ± α) · I = Vcc · {(dried 2α) / (R dried α)} + Va {(R ± α) / (R dried α)} ... ( 15) Differential voltage Vb−Va = ± 2A · {Vcc−Va} (16) = ± 2A · {Vcc− (2Vbe + Vd)} (16a) (13a) is equivalent to the shift voltage (correction amount), and FIG. As shown in, the amplitude center of the midpoint voltage Vb rises as compared with the second embodiment. On the other hand, from the output amplitude of the second embodiment, the third
The output amplitude (difference voltage (Vb-Va)) of the embodiment is (± 2
A ・ Vd) decrease. In this case, the maximum resistance change rate A
Since A << 1, the rise of the amplitude center is larger than the decrease of the output amplitude.

In the second embodiment, there is no problem if the resistance value changes of the resistors Ra and Rb are small and the amplitude of the midpoint voltage Vb is small as shown in FIG. For example, this may be the case when a change near the center of the amplitude is required instead of the magnitude of the amplitude.

However, when Vcc increases, the midpoint voltage V
Although a does not change, the amplitude of the midpoint voltage Vb increases.
At this time, the lower limit of the amplitude approaches the GND side as shown in FIG. Further, when the change in the midpoint voltage Vb is so large that the current mirror circuit cannot drive the output, the output is clamped (V
a-Vce), and there is a possibility that it will not operate normally. Vce is the minimum collector-emitter voltage (minimum operating voltage) required for the operation of the transistor TR2.

The conditions under which this is not clamped are as follows. 2A · {Vcc-Va} <Va-Vce (17) In the third embodiment, the condition that satisfies the above formula (17) is set so as to be satisfied under all operating conditions of the detection device 10.

As a result, the output of the midpoint voltage Vb is not distorted. According to the third embodiment, in addition to the operational effects (1) to (4) of the first embodiment, the following operational effects are exhibited.

(1) In the third embodiment, when the output of the middle point a on the resistance Ra (first detection element) side is used as the reference voltage,
Resistor Ra and transistor TR1 (first transistor)
A diode D (level shift circuit) is provided between and.
Then, the voltage (reference voltage) that is the center of the amplitude is increased by the diode D.

As a result, the lower limit of the amplitude of the midpoint voltage Vb is not clamped, and the output on the midpoint b side can be an output without distortion. Further, since the output is determined with respect to the input signal, the undistorted output does not make the input signal undetectable.

The embodiment of the present invention can be modified as follows in addition to the above embodiment. (1) In the third embodiment, the diode D is a level shift circuit, but the resistor may be a level shift circuit.

(2) In the second embodiment, the transistors TR1 to TR3 form a high-precision current mirror circuit, but other current mirror circuits may be used. For example, a current mirror circuit such as a Wilson mirror circuit may be used.

(3) In each of the above embodiments, the magnetoresistive element is used as the first detecting element and the second detecting element. However, it is of course possible to replace the magnetoresistive element of the present embodiment with a detection element other than the magnetoresistive element that has conventionally constituted the detection unit in the Wheatstone bridge circuit.

[0080]

As described above in detail, according to the first to fifth aspects of the invention, the detection elements having the reverse characteristics are individually driven by the constant current without using the bridge circuit. Also, it is possible to obtain almost double the output.

Further, in the case of maintaining the same maximum voltage difference as in the conventional case, the circuit consumption current can be reduced, or the space for disposing the detection element can be reduced, and the size can be reduced.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of a detection device according to a first embodiment.

FIG. 2 is an electric circuit diagram of a detection device according to a second embodiment.

FIG. 3 is an output characteristic diagram of the detection device according to the second embodiment.

FIG. 4 is an electric circuit diagram of a detection device according to a third embodiment.

FIG. 5 is an output characteristic diagram of the detection device.

FIG. 6 is an output characteristic diagram of the detection device according to the third embodiment.

FIG. 7 is an electric circuit diagram of a conventional detection device.

FIG. 8 is a characteristic diagram showing the relationship between the resistance value of anisotropic magnetoresistance and the magnetic field direction.

[Explanation of symbols]

10 ... Detection device 20, 21 ... Constant current source (current mirror circuit) Ra ... Magnetoresistive element (first detection element) Rb ... Magnetoresistive element (first detection element, second detection element) Rc ... Magnetoresistive element (second detection element) Rd ... Magnetoresistive element (second detection element) TR1 ... Transistor (first transistor) TR2 ... transistor (second transistor) TR3 ... Transistor (third transistor) D: Diode (level shift circuit)

Claims (5)

[Claims] 1. A first detection element whose resistance value changes according to a change in an external physical quantity, and a second detection element having a characteristic opposite to that of the first detection element are connected in parallel to a power supply terminal. ,
A constant current source for supplying a drive current of the same magnitude is connected to each of the detection elements to drive each detection element with a constant current, and a middle point between the constant current source and each resistor is used for detection. A detection device characterized by being used as an output terminal of. 2. The detection device according to claim 1, wherein the constant current source is a current mirror circuit. 3. The detection device according to claim 1, wherein each of the current mirror circuits individually drives the first and second detection elements with a constant current. 4. A first mirror in which each collector is connected to each detection element, each emitter is grounded, and each base is connected to each other in the current mirror circuit.
And a third transistor whose base is connected to the collector of the first transistor and whose collector and emitter are connected to the high power source side and the bases of the first and second transistors, respectively. The detection device according to claim 2, which is characterized in that. 5. A level shift circuit is provided between the first detection element and the first transistor when an output at the midpoint of the first detection element side is used as a reference voltage, and the level shift circuit comprises: The detection device according to claim 4, wherein the reference voltage is increased.