JPH03137583A - magnetic field detection circuit - Google Patents

Abstract

PURPOSE:To obtain a detection circuit which is small, requires no high resistance, free from possible aging and resists strongly to extraneous noise by applying a hysteresis voltage to an input terminal of a comparator with an opening or closing of an output thereof. CONSTITUTION:A circuit is so arranged that a third resistor R3 is inserted between one power source terminal GND and a partial resistor R2 in series with the partial resistor R2 as an arm of a bridge 2, a switch SW is connected in parallel with the resistor R3 and the switch SW is opened or closed interlocking an output of a comparator 4. Then, an opening or a closing is made between a terminal 7 as connection point between the partial resistor R2 and the third resistor R3 and the negative terminal GND of a power source with the switch SW interlocking an output of the comparator 4. In this case, a feedback resistor of a high resistance is not required and can be replaced with a third resistance of a resistance value low relatively to apply a hysteresis voltage thereby permitting realization of magnetic field detection circuit with a low power consumption.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a magnetic field detection method that converts changes in the magnetic field of a magnet attached to a rotating shaft of a motor or a water meter impeller into an electric pulse signal. The present invention relates to circuits, and particularly to magnetic field detection circuits having hysteresis characteristics.

[Prior Art] The circuit shown in FIG. 7, which detects the rotation or change of a magnetic field using a magnetic sensor having a magnetoresistive effect, is well known. MRI
and MR2 are magnetic sensors consisting of a thin film in which a ferromagnetic magnetoresistive material is formed on an insulating substrate, and its resistance value changes depending on the direction (angle) of a magnetic field rotating within the plane of the insulating substrate. If the angle between the main current path of the magnetic sensor and the direction of the magnetic field is θ, and the resistance value of the magnetic sensor when no magnetic field is applied is Ro, then the resistance value of the magnetic sensor is equal to the angle θ
As a function of R-Ro(1+cr Co52θ). Since the strength of the magnetic field is used at a level above which the magnetic sensor is saturated, α is approximately 2%. And re-magnetic sensor MI? 1 and MR2 are formed so that their main current paths form a distance of 90'' from each other. R1 and R2
are voltage dividing resistors connected in series to form the reference voltage generating circuit 1, and as shown in the figure, the magnetic sensors MR1, M
It is connected to form a bridge 2 together with R2, and a voltage V is applied between the negative terminal GND and the positive terminal 3 of the power supply voltage. 4 is a comparator whose non-inverting input receives the voltage at the output terminal 6 of the bridge 2, ie, the reference voltage, and its inverting input receives the output terminal 5 of the bridge 2, ie, the output signal of the magnetic sensor. Also, comparator 4
There is a hysteresis voltage between the output terminal and the non-inverting input.
A feedback resistor Rf for applying □□ is connected.

The resistance values of magnetic sensors MRI and MR2 are respectively MHI.
.

Assuming that the resistance values of MR2 and voltage dividing resistors R1 and R2 are R1 and R2, and MR1=MR2, R1=R2=R, the hysteresis voltage ■□□ is the output voltage of the comparator 4 at V. , then Vlliss'i HR, vt 2 1R. The hysteresis is provided to prevent chattering of the output waveform of the comparator 4 due to external noise, etc. The hysteresis voltage to be applied is the output signal of the magnetic sensor ■=■+(1+α5in2θ
)/2 is used.
Therefore, the resistance value of the feedback resistor Rf is (50 to 250)
It was set to R.

[Problem to be solved by the invention]

In order to reduce the power consumption of the circuit with the above conventional technology, it is necessary to reduce the power consumption of the comparator 4 and the current flowing through the bridge 2. The current in the bridge 2 can be reduced by increasing the resistance value of the magnetic sensor or voltage dividing resistor. Normally, the resistance value of the magnetic sensor is the same as that of the voltage dividing resistor. In order to reduce power consumption, the resistance value of the magnetic sensor is set to several hundred Ω, the α is 2%, and the hysteresis voltage is set to 0.1 to 0.5 times the output voltage of the magnetic sensor. , the feedback resistance Rf requires a resistance value of several hundred to several hundred times the resistance value of the magnetic sensor, which is several MΩ to several hundred MΩ.

Resistors with such high resistance values are not available as small chip resistors. Even if a structure other than a chip resistor is used, there are problems in that the change over time is large, which not only makes the circuit unstable, but also tends to pick up external noise.

It is an object of the present invention to solve these problems and to propose a magnetic field detection circuit that is small, does not require high resistance, is free from aging, and is resistant to external noise.

[Means to solve the problem]

In order to achieve the above object, the magnetic field detection circuit of the present invention uses a magnetic sensor having a magnetoresistive effect (MRI).
(MR2) and a voltage dividing resistor (MR2) for generating the reference voltage (
R1) (R2) and the magnetic sensor (MHI) (M
A bridge (2) consisting of a voltage dividing resistor (R2) and a voltage dividing resistor (R1) (R2), and an output terminal (5) of the bridge (2) (
Comparator (4) that inputs the voltage of 6) and shapes the waveform.
and a third resistor (R3) inserted in series with the magnetic sensor or voltage dividing resistor, and a switch (Pongee) connected in parallel with the third resistor, and the switch (SW) is connected to the comparator. Claim (1) characterized in that the device is opened and closed depending on the output of (4).

Further, in the invention of claim 2, a magnetic sensor (MRI) (MR2) having a magnetoresistive effect, a reference voltage generation circuit (1) for generating a reference voltage, and a reference voltage generation circuit (1). It has a comparator (4) that compares the output of the magnetic sensor with a reference voltage and converts the signal of the magnetic sensor into a pulse, and a switch (SW) that is opened and closed in conjunction with the output of the comparator (4). Between the terminal (7) provided in the magnetic sensor or reference voltage generation circuit (1) so that the voltage corresponds to the hysteresis voltage applied to the comparator (4) and the power supply terminal (3, GND) or the terminal (
It is characterized in that hysteresis is applied by opening and closing the switch (SW) between 7) and the terminal (7').

The voltage dividing resistors (R1) (R2) may be magnetoresistive elements.

Further, the third resistor (R3) may be a magnetoresistive element.

Also, the switch (SW) is an enhancement MOSFET.
, analog switches or bipolar transistors can be used.

Furthermore, it is effective to insert an amplifier (10) between the comparator (4) and the switch (SW) to amplify the output of the comparator and drive the switch.

[Effect]

The switch (or) is opened or closed according to the output of the comparator (4), and a hysteresis voltage is applied to the input of the comparator, so it operates as a magnetic field detection circuit having hysteresis characteristics.

〔Example〕

In the embodiment shown in FIG. 1(a), a third resistor R3 is inserted in series with the voltage dividing resistor R2, which is one side of the bridge 2, between one power supply terminal GND and the voltage dividing resistor R2. A switch SW was connected in parallel with R3, and the switch S- was configured to open and close in conjunction with the output of the comparator 4.

And between this switch, the output of comparator 4 is LO.
It turns ON and closes when it is W, and turns OFF when it is HIGH.
It opens.

The hysteresis voltage of this circuit is VN! is is R1+R
3Rz ■M”'= (R1+R1+R3±RL+R1)” ”
becomes. In the conventional circuit shown in FIG. 7 in which the third resistor R3 is not inserted, the re-input voltages of the comparator 4 are equal when no magnetic field is applied.

And suppose R2 is 2%X(0.1~0.5) than R1
If it is larger by X2, the voltage at the non-inverting input will be larger by 0.1 to 0.5 times the output (2% x 2) of the magnetic sensor, and if it is smaller, the voltage at the non-inverting input will be that much smaller.

Therefore, the value of the voltage dividing resistor R2 in FIG. 1(a) is set to be 2%×(0.1 to 0.5)×2 times smaller than R1 in the case of FIG. 7. That is (0,004~0.0
2) Decrease only R1, and connect the third resistor R3, which has a resistance value 2 (0,004 to 0.02) R1, which is twice this value, in series with the voltage dividing resistor R2 as described above. . Then, the switch S- connects the terminal 7, which is the connection point between the voltage dividing resistor R2 and the third resistor R3, and the negative terminal GN of the power supply.
It opens and closes between the DOs in conjunction with the output of the comparator 4.

The voltage between power supply terminal GND and terminal 7 is detected by comparator 4.
Corresponds to the hysteresis voltage applied to

Further, as shown in FIG. 1(0)), even when the third resistor R3 is located between the resistors R1 and R2, the same operation as in the embodiment shown in FIG. 1(a) can be performed. In this case, the voltage between the terminals (7) and (7') provided at both ends of the third resistor R3 corresponds to the hysteresis voltage applied to the comparator 4.

Note that in FIGS. 1(a) and 1(b), the reference voltage generating circuit 1 is configured by the voltage dividing resistors R1 and R2 and the third resistor R3;
Voltage dividing resistors R1 and R2 are configured with magnetoresistive elements, and each magnetic sensor and magnetic Elements MR1 and MR determine the relative orientation of the main current paths of the resistive elements and constitute the four sides of the bridge 2.
2, R1, and R2 are all magnetically sensitive, the signal corresponding to the change in the magnetic field input to the comparator 4 will be twice as large. In this case, the decrease in voltage dividing resistor R2 with respect to R1 is 2%X (0,1 to 0.
5) X 4 XRI, and the resistance value of the third resistor R3 is also doubled to 4 (0,004 to 0.02)·R1.

This third resistor R3 is also composed of a magnetoresistive element,
Moreover, it is preferable to configure the structure so that the change in resistance depending on the angle of the magnetic field is in phase with the voltage dividing resistor R2 formed by a magnetoresistive element.

In the embodiment shown in FIG. 2, magnetic sensors MRI and MR2 are formed so as to exhibit resistance changes in opposite phases to each other in response to changes in the angle θ of the magnetic field, and both sensors are connected in series, and at the connection point. The output signal from a certain output terminal 6 is sent to the comparator 4.
The resistance values of the remagnetic sensor are equal and the sum is 650Ω. And 50
[Exhibits a main resistance change of 1°5% in response to a magnetic field with a strength of Oel. Each reference voltage generation circuit 1 has a voltage of 620 K.
A voltage dividing resistor R1゜R2 of Ω, a third resistor R3 of 4Ω, and a volume VR of 50Ω are connected in series as shown in the figure, and both ends of the series connection are connected to the negative terminal GND and positive terminal of the power supply. 3
and are connected to each other, and voltage ■ is applied.
The intermediate terminal of the volume VR is connected to the non-inverting input of the comparator 4. 8 is a rotating shaft with a permanent magnet 8a attached to its tip, and magnetic sensors MR1, ! :
MR2 senses the rotating magnetic field generated by the permanent magnet 8a.

The voltage V at the output terminal 6 is expressed as ■=■・(1+0.
015 cos 2θ)/2. The reference voltage for this is the power supply voltage (1), which is in the range of 1.48 to 0.52, and is adjusted by the volume VR. This adjustment deals with variations in the resistance value of the magnetic sensor, variations in the voltage dividing resistors R1 and R2, and the third resistor R3, and adjusts the non-inverting input of the comparator 4 to adjust the duty ratio of the output pulse of the comparator 4. Make it 50%. Comparator 4 is a low power consumption operational amplifier whose power supply voltage is 3 (V
The resistor Rs is set so that the power consumption is 2 μA when the voltage is 1. Reference numeral 10 denotes an inverter serving as an amplifier, which amplifies the output of the comparator 4 and applies it to the gate of the enhancement MOSFET forming the switch sh.
The drain and source of this MOSFET are connected between the terminal 7 and one power supply terminal GND to be used as a switch.

Since the amplifier 10 sends a pulse signal to an external device,
If necessary, it is converted into an open collector by the illustrated output circuit 9. It may be converted into an open drain signal instead of an open collector signal.

The operational amplifier that constitutes the comparator 4 has a main output voltage of 0°6 (V) when the output voltage range is ±1.5 [Vl of the power supply voltage. In other words, cso+o, 5rv) ~ v −
o, a[Vl, so the power supply voltage is 3[V
], the FET constituting the switch S-
I can't say it's enough to drive. Therefore, it is amplified by an amplifier 10 using a C-MOS inverter and converted into a pulse signal that turns 0N-OFF within the power supply voltage range.
This is to drive the gate of the switch S-.

In the embodiment shown in FIG. 2, the resistance value of the second resistor R3 was selected so as to add a hysteresis of 10% of the peak value of the output signal of the magnetic sensor.

The method for calculating the resistance value of the third resistor R3 necessary to apply the desired hysteresis voltage is as follows.

(1) First, decide what ratio of hysteresis voltage you want to apply to the peak value of the output signal of the magnetic sensor. If this ratio is k, then as mentioned above, the resistance change of the magnetic sensor due to the magnetic field is mainly 1°5%, that is, mainly 0°0%.
15, the peak value of the output signal of the magnetic sensor is (V/2) x o.

15, the hysteresis voltage Vllist (one side) is V
H4fil (one side) = (V /2) x O,0
It can be expressed as 15.

Assuming that k is set to 10%, or 0.1, as in the previous example, Vntss (one side) - (Vl/2) X 1.5X1
0-'(2) The reference voltage is R1=R2, R3=0 (7
), then v/2, so when the voltage dividing resistor R2 becomes smaller than R1 by α, the reference voltage becomes smaller by ΔV in the following equation.

8V = R2 (1-s), ■12 R
1 order R1 (1-s) Here, by rearranging the above equation by setting R1=R2, we obtain ΔVζ-xv''.

(3) VNiss (one side) obtained in (1) and (2
) are equal, then (V”/2) x 1.5xlO-3= (V/4
) ・α, and if we calculate α from this, we get α=3X10-3. Circuit constants R1, R2 = 620Ω in Figure 2
, considering Ω in VR=50 and including the resistance value of volume VR in the sum of voltage dividing resistors R1 and R2, R1+
R2=(620x2+50) KΩ= 1290 KΩ
Then, Ω is obtained as RIX(2-α)=1290.

Substituting α=3X10-” to find R1, R1=6
Obtain Ω at 46. Also, R2 is Ω-R to R2=1290
1 = 644Ω.

Therefore, R3=(R1-R2)X2=4KΩ.

(4) When calculating the hysteresis angle, use 5in2θ
By finding θ from −K and finding 2θ, the hysteresis angle can be obtained. In this case, it is 5.7@.

FIG. 3 shows the voltage waveform of the main part of FIG. 2 under this condition. The figure (a) shows the output signal of the magnetic sensor, that is, the non-inverting input voltage of the comparator 4, and the figure (b) compares the output waveform of the amplifier 10 (inverter) when the magnet 8a rotates in the forward direction and in the reverse direction. This is an indication.

As an example of a circuit constant for applying a hysteresis voltage that is 0.5 times the P-P value of the output voltage of the magnetic sensor, consider that the resistance bone of the volume VR is included in the voltage dividing resistors R1 and R2, and R1 = 650. Ω to R2 = 640Ω.

R3=20KΩ can be adopted.

Incidentally, as mentioned above, in order to obtain a hysteresis voltage of 10%, the third resistor R3 was set to 4Ω, but in order to obtain the same hysteresis voltage with the prior art shown in FIG.
has a large value of 103 MΩ, which causes various problems such as the size of the feedback resistor becoming thicker, the insulation of the circuit board needing to be improved, and the resistance to noise.

In the above embodiment, the magnetic sensors MRI and MR2 have the same resistance value, and the voltage dividing resistors R1 and R2 have almost the same resistance value, but they do not necessarily have to be the same. A resistance R3 can be defined.

The embodiment shown in FIG. 4 is different from the embodiment shown in FIG.
are composed of magnetoresistive elements MR3, MR4, and MR5, respectively, and these magnetoresistive elements are used as a magnetic sensor MRI.

Together with MR2, it is formed of a thin film ferromagnetic resistor on a single insulating substrate. In this case, the magnetic field detection sensitivity can be doubled compared to the case shown in FIG.

Note that the switch S- is preferably a voltage-controlled type with low power consumption, and is an enhancement MOSF like the one in the above embodiment.
Although it is preferable to use an ET or an analog switch, the present invention is not necessarily limited to these, and a bipolar transistor may also be used.

In FIG. 5, a third resistor R3 for applying a hysteresis voltage is inserted between the voltage dividing resistor R1 and the positive terminal 3 of the power supply, and the output terminal 5 of the bridge 2 (i.e., the output of the reference voltage generating circuit l) Terminals ) and 6 are connected to the inverting and non-inverting inputs of the comparator 4, respectively, and operate similarly to the previous embodiment.

In the embodiment shown in FIG. 6, the third resistor for applying a hysteresis voltage is composed of a magnetoresistive element MR5,
Together with R1 and MR2, it is formed as a thin film ferromagnetic resistor on a single insulating substrate.

In both FIGS. 5 and 6, the switch needle is turned ON when the output of the amplifier 10 is LOW.

〔Effect of the invention〕

Since the present invention is configured as described above, a high-resistance feedback resistor as in the prior art is unnecessary, and can be replaced with a third resistor with a relatively low resistance value that applies a hysteresis voltage. Even if the resistance value of the magnetic sensor is increased,
The resistance value of the third resistor can be much lower than the resistance value of the feedback resistor Rf of the prior art. Therefore, a magnetic field detection circuit with low power consumption can be realized by increasing the resistance values of the magnetic sensor and the reference voltage generation circuit. Furthermore, the amount of hysteresis can also be maintained stably. And since high resistance is not used in the circuit, it is resistant to noise. In addition, there is no need to improve the insulation of the circuit board that much, and the circuit can be made smaller in terms of both insulation and the fact that large high resistances are not used.

Moreover, in the invention of claim 9, the output of the comparator is amplified and the switch S! Since A is driven, even when used at a low power supply voltage, there is almost no change in the hysteresis voltage due to fluctuations in the power supply voltage, and a stable hysteresis width can be obtained.

[Brief explanation of the drawing]

1(a), (b), FIG. 2, FIG. 4, FIG. 5, and FIG. 6 are circuit diagrams of different embodiments of the present invention, and FIG.
The figure shows the voltage waveform of FIG. 2, and FIG. 7 shows the circuit of the prior art. 1... Reference voltage generation circuit, 2... Bridge, 3...
・Power terminal (positive terminal), 4... Comparator, 5.6
...Output terminal, 7.7"...terminal, lO...amplifier, R1, R2...divider resistor, R3...third resistor, or...switch, MH1, M) !2...Magnetic sensor (magnetoresistive element), MR3, MR4, MR5...
Magnetoresistive element, GND...power terminal (negative terminal)

Claims (1)

[Claims] 1. Magnetic sensor (MR1) having magnetoresistive effect (MR
2) and a voltage dividing resistor (R1) for generating a reference voltage
(R2), a bridge (2) composed of the magnetic sensors (MR1) (MR2), voltage dividing resistors (R1) (R2), and the voltage at the output terminals (5) and (6) of the bridge (2). a comparator (4) that inputs and shapes the waveform, and a third resistor (R3) inserted in series with the magnetic sensor or voltage dividing resistor.
) and a switch (SW
), and the switch (SW) is connected to the comparator (
4) A magnetic field detection circuit that is opened and closed according to the output of item 4). 2. Magnetic sensor (MR1) with magnetoresistive effect (MR
2), a reference voltage generation circuit (1) for generating a reference voltage, and a reference voltage of the reference voltage generation circuit (1);
A comparator (4) that compares the output of the magnetic sensor and converts the magnetic sensor signal into a pulse;
a switch (SW) that opens and closes in conjunction with the output of the magnetic sensor or the reference voltage generating circuit (1), and is provided in the magnetic sensor or the reference voltage generating circuit (1) so that the voltage corresponds to the hysteresis voltage applied to the comparator (4). Terminal (7) and power terminal (3, G
A magnetic field detection circuit characterized in that hysteresis is applied by opening and closing the switch (SW) between the terminal (ND) or between the terminal (7) and the terminal (7'). 3. The voltage dividing resistors (R1) (R2) are magnetoresistive elements (M
The magnetic field detection circuit according to claim 1, wherein the magnetic field detection circuit is R3) (MR4). 4. The third resistor (R3) is a magnetoresistive element (MR5)
The magnetic field detection circuit according to claim 1 or 3. 5. Both the magnetic sensors (MR1) (MR2) and the reference voltage generation circuit (1) are magnetoresistive elements (MR1, MR2,
3. The magnetic field detection circuit according to claim 2, wherein the magnetic field detection circuit comprises MR3, MR4, MR5), which are bridge-connected. 6. The switch (SW) is an enhancement MOSF
The magnetic field detection circuit according to claim 1, 2, 3, 4 or 5, which is an ET. 7. The magnetic field detection circuit according to claim 1, 2, 3, 4 or 5, wherein the switch (SW) is an analog switch. 8. The magnetic field detection circuit according to claim 1, 2, 3, 4 or 5, wherein the switch (SW) is a bipolar transistor. 9. Claims 1, 2, 3, 4, 5, 6, wherein an amplifier (10) is inserted between the comparator (4) and the switch (SW).
, 7 or 8. The magnetic field detection circuit according to .