JPH02210217A - Driving circuit for magnetism sensing element - Google Patents

Abstract

PURPOSE:To enable temperature compensation with high accuracy by controlling a current which flows through a magnetism sensing element and compensating variation in the detection sensitivity of the magnetism sensing element with temperature when the magnetism sensing element is driven with a constant current. CONSTITUTION:The magnetism sensing element 10 has one driving terminal connected to the output terminal of an operational amplifier 11 and the other driving terminal connected to the negative input terminal of the amplifier 11. The other driving terminal of the element 10 is grounded through a current detection resistance 12. Further, the positive input terminal of the amplifier 11 is connected to a reference voltage source 14 through an input resistance 13 and its output terminal and positive input terminal are connected through a feedback resistance 15. Thus, the output voltage of the amplifier 11 is fed back to the input side of the amplifier 11 through the resistance 15 to perform the compensation so that variation in the internal resistance of the element 10 with temperature and variation in the detection sensitivity of the element 10 with temperature when the element 10 is driven with the constant current cancel each other.

Description

Detailed Description of the Invention A6 Industrial Application Field The present invention relates to a drive circuit for a magnetically sensitive element such as a ferromagnetic magnetoresistive element or a GaAs Hall element. It is applied to a drive circuit for a magnetically sensitive element for tension detection.

B. Prior Art Conventionally, tape running systems in video tape recorders and the like employ a bank tension servo mechanism configured as shown in Figure 1, for example, in order to apply a constant back tension to the running magnetic tape. has been done.

This bank tension servo mechanism includes a tension arm 1 having a tension detection pin 2 planted at one end. This tension arm 1 is rotatably attached via a support shaft 9 so as to be rotatably displaced in response to the back tension of the magnetic tape 8 that is wound around the tension detection pin 2 and runs. In addition, the above tension arm 1
is biased to rotate in one direction by a spring 7 so as to balance the back tension of the magnetic tape 8.

Further, a magnetic body 3 facing the magnetically sensitive element 4 is attached to the other end of the tension arm 1 .

The magnetically sensitive element 4 detects the magnetic flux from the magnetizing body 3. In the back tension servo mechanism configured as described above, when the tension arm 1 is rotated and displaced in response to changes in the running magnetic tape 80, the magnetic flux from the magnetizing body 3 detected by the magnetically sensitive element 4 changes.

The amount of change in this magnetic flux is outputted from the magnetically sensitive element 4 as a detection voltage (2) proportional to the amount of rotational change of the tension arm 1. This detection voltage ■ is compared with the reference voltage E□2, and a current corresponding to the difference is supplied from the error amplifier 5 to the supply side reel motor 6 to apply back tension to the magnetic tape 8. A tension servo is applied so that the balance point of the spring force applied by the spring 7 to the tension arm 1 is always constant, thereby obtaining a constant back tension.

By the way, as the magnetically sensitive element 4 for detecting the amount of rotational displacement of the tension arm l used in the back tension servo mechanism, a magnetically sensitive element such as a ferromagnetic magnetoresistive element or a Hall element is used.

These magnetically sensitive elements generally have a temperature characteristic in their detection sensitivity, and the detection output changes due to changes in ambient temperature or the effects of accidental heat generation due to the drive current, so it is known that detection errors due to the above temperature characteristics occur. ing.

Conventionally, when detecting the amount of rotational displacement of the tension arm 1 etc. with high accuracy using a magnetically sensitive element having the above-mentioned temperature characteristics, in order to improve the above-mentioned temperature characteristics, the driving of the magnetically sensitive element is A constant voltage driving method or a constant current driving method is adopted as a method. Then, if we adopt the constant current drive method,
Compared to constant voltage driving, the temperature characteristics can be improved to about 1/7 for the ferromagnetic magnetoresistive element, and about 3/1 for the G, A, and Hall elements. For example, in a magnetically sensitive element, as shown in Figure 2, which shows an example of temperature characteristics, the detection output when driven at a constant current is β, = -3,5XIO-''%
The temperature coefficient β9 is about /C'', whereas the detection output when driven with a constant current has a temperature coefficient β of about 5XIO-'%/C''.

In addition, as shown in FIG. 2, it is known that the temperature coefficient α of the resistance between the drive terminals of the magnetically sensitive element, that is, the internal resistance, is about 3×10 −3%/C°. In general, the temperature characteristics of magnetically sensitive elements are approximately constant for each product in the case of commercially available devices, and the temperature coefficients α, βV, and βC are usually published as catalog data.

The temperature characteristics of the magnetically sensitive element are determined by the temperature coefficient β when driven at a constant voltage. In order to further improve the above-described temperature characteristics, the temperature coefficient of the detected output voltage of the magnetically sensitive element can be set to zero by using the conventional temperature-sensitive element. Methods such as compensation are being adopted.

C1 Problems to be Solved by the Present Invention However, the above-mentioned method of performing temperature compensation using a temperature-sensitive element requires a temperature-sensitive element in addition to the magnetically-sensitive element, and if there is a difference in the heat capacity of each element, transient It is not possible to compensate for temperature changes. Furthermore, not only is it impossible to compensate for accidental heat generation of the magnetically sensitive elements, but there is also the problem that compensation errors occur due to differences in environmental conditions due to differences in the installation locations of each element.

Therefore, in view of the problems in temperature compensation of a magnetically sensitive element using a temperature sensitive element as described above, the present invention focuses on the temperature characteristics of the internal resistance of the magnetically sensitive element itself and the dependence of detection sensitivity on the drive current, This was proposed for the purpose of providing a drive circuit for a magnetically sensitive element that can perform temperature compensation with high precision even against transient temperature changes, self-heating, and the like.

09 Means for Solving the Problems The present invention aims to solve the problems of the conventional circuits as described above, and in order to achieve the above object, the present invention provides a circuit that is connected in series to a magnetically sensitive element and connected to the magnetically sensitive element. A drive circuit for a magnetically sensitive element, comprising a current detection resistor that obtains a detection voltage according to a flowing drive current, and an operational amplifier that compares the detected voltage with a reference voltage and drives the magnetically sensitive element at a constant current, A feedback resistor that feeds back changes in the output voltage of the operational amplifier due to changes in the internal resistance of the magnetically sensitive element to the input side of the operational amplifier is connected between the output terminal and the input terminal of the operational amplifier, and By detecting the change in internal resistance due to temperature as a change in the output voltage of the operational amplifier,
The current flowing through the magnetically sensitive element is controlled to compensate for changes in detection sensitivity of the magnetically sensitive element due to temperature when the magnetically sensitive element is driven with a constant current.

Accordingly, the magnetically sensitive element drive circuit according to the present invention feeds back the output voltage of the operational amplifier to the input side of the operational amplifier through the feedback resistor, thereby reducing the temperature-induced change in the internal resistance of the magnetically sensitive element. , compensation is made so that a change in detection sensitivity due to temperature of the magnetically sensitive element when the magnetically sensitive element is driven with a constant current is offset.

F. Examples Specific examples of the present invention will be described below with reference to the drawings.

FIG. 3 is a circuit diagram showing the basic configuration of a drive circuit for a magnetically sensitive element according to the present invention.

In the drive circuit shown in FIG. 3, the magnetically sensitive element 10 is arranged such that one drive terminal is connected to the output terminal of the operational amplifier 11 and the other drive terminal is connected to the negative input terminal of the operational amplifier 11. has been done. The other drive terminal of this magnetically sensitive element 10 is grounded via a current detection resistor 12.

Further, the operational amplifier 11 has its positive input terminal connected to a reference voltage source 14 via an input resistor 13, and its output terminal and the positive input terminal connected via a feedback resistor 15. .

The drive circuit having the circuit configuration as described above includes the magnetically sensitive element 10.
r, the resistance value of the input resistor 13 is Ro, the resistance value of the feedback resistor 15 is Rz, the resistance value of the current detection resistor 12 is R1, and the reference voltage given from the reference voltage source 14 is is E, and the output voltage of operational amplifier 11 is R6.
, if the drive current flowing through the magnetically sensitive element 10 is i, then
Perform the following actions.

That is, a drive current i determined from the following equation 1 flows through the magnetically sensitive element 10 and the current detection resistor 12 that are connected in series between the output terminal of the operational amplifier 11 and the ground.

R.

i= . . . 1st equation. Then, at the negative input terminal of the operational amplifier 11, there is a detection voltage (2) determined from the following 2nd equation depending on the drive current i obtained from the current detection resistor 12. is applied.

RtsVD=Vo... 2nd formula also,
A reference voltage source 1 is connected to the positive input terminal of the operational amplifier 11.
4 is applied to the reference voltage E, and a part of the output voltage vo of the operational amplifier 11 determined by the resistance ratio of the feedback resistor 15 and the input resistor 13 is fed back, as shown below. The comparison reference voltage 1F obtained from the second equation is applied.

17+ 'J*ty -(Vo E) 10B...
3rd Equation Then, the operational amplifier 11 compares the detection voltage v0 applied to each input terminal with the comparison reference voltage VltEF to obtain an output voltage (VD-REF) expressed by the following 4th equation. will be output.

RZR3-Rlr Therefore, the drive current i of the electromagnetic element 10 shown in the above first equation can be shown as i=E...Fifth equation % equation %, and the inside of the above magnetic element lO If the resistance r does not change, it will be a constant value. That is, the magnetically sensitive element 10 is driven with a constant current in principle by this drive circuit.

Here, α is the temperature coefficient of the internal resistance r of the magnetically sensitive element IO, and based on temperature change, the internal resistance r is calculated as r=ro(1+αL)... Equation 6
The drive current i in the equation is: 8th equation % equation % And the temperature coefficient α of the internal resistance r of the magnetically sensitive element 10
The temperature coefficient βゎ of the detection output of the magnetically sensitive element during constant voltage driving can generally be determined in advance from catalog data, etc. as described above, so the temperature of the drive current i of the magnetically sensitive element 10 in the above equation 8 is Coefficient RtR3RIr.

■ R□Rs　-RIr6 and 1-　　　　　　　・at RtR3RIr.

By determining R+, Rz, and Rz, it is possible to prevent the detected output voltage of the magnetically sensitive element 10 from having temperature characteristics.

In the drive circuit shown in FIG. 3, for example, when the resistance value R1 of the human resistor 13 and the resistance value R1 of the current detection resistor 12 are determined in advance, Lr. (α+β,) The resistance value R2 of the feedback resistor 15 can be determined from the 10th equation.

・In addition, in the drive circuit shown in FIG. Although it may be calculated as a negative value from formula 10,
In this case, the output voltage of the operational amplifier 11 is ■. A method of inverting the polarity and feeding it back to the positive input terminal via the feedback resistor 15, or the above output voltage (2). What is necessary is to adopt a method such as feeding back the signal to the negative input terminal.

By the way, FIG. 4 shows the operating principle of a three-terminal type magnetically sensitive element, in which two magnetically sensitive elements r.

rt are connected in series, and these two magnetically sensitive elements r+, rz are configured such that the change in resistance when the applied magnetic field changes has opposite polarity. Then, a predetermined voltage E is applied across these two magnetically sensitive elements rl, r, and the two magnetically sensitive elements rl+r! By changing the magnetic field applied to the two magnetically sensitive elements r1*rz, the output is obtained from the connection point of the two magnetically sensitive elements r1, r! The resistance is changed, and the detection voltage v0 is changed.

Next, FIG. 5 shows a circuit configuration of a specific embodiment in which a magnetically sensitive element is driven at a constant current according to the operating principle of the three-terminal type magnetically sensitive element shown in FIG. 4 described above.

In FIG. 5, the positive input terminal of the first operational amplifier 11 is grounded via a first resistor 13A and connected to the drive power input terminal 20 via a second resistor 13B. A reference voltage E is provided by dividing the power supply voltage VCC supplied to the drive power input terminal 20 by the resistance ratio R+A:R+* of each of the resistors 13A and 13B.

The circuit shown in FIG. 5 combines two three-terminal type magnetically sensitive elements 18 and 19, and uses the difference between the detection voltages (1) and (2) of the two three-terminal type magnetically sensitive elements as an output voltage.

Here, the resistance of the three-terminal type magnetically sensitive element 18 and 19 is:
rl and r4+r! and r have the same polarity, and when the magnetic field applied to the three-terminal magnetically sensitive element 18 and 19 changes and the resistances of r and r increase, r2
When the resistances of r and r decrease, and the resistances of rl and r4 decrease, the resistances of r2 and r increase. Therefore, since two three-terminal type magnetically sensitive elements 18, 19 are used, the difference between the detection voltage ■^ and V++ is doubled, and 1
The first operational amplifier 11 constitutes the drive circuit according to the present invention, and the second operational amplifier 21 constitutes the drive circuit according to the present invention.
constitutes an operational amplifier circuit that amplifies the detection output output from the magnetically sensitive element 10.

G1 Effects of the Invention As is clear from the above description, in the drive circuit for the magnetically sensitive element according to the present invention, the output voltage of the operational amplifier is fed back to the input side of the operational amplifier through the feedback resistor, thereby reducing the magnetically sensitive element. Since the change in internal resistance of the element due to temperature is compensated for and the change in detection sensitivity due to temperature of the magnetically sensitive element when the magnetically sensitive element is driven with a constant current are compensated for, Temperature compensation can be performed with high precision even against excessive temperature changes, accidental heat generation, etc., and the magnetically sensitive element can be operated extremely stably.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a general mechanism of a back tension servo mechanism using a magnetically sensitive element to which the present invention is applied. FIG. 2 is a characteristic diagram showing an example of the temperature characteristics of a ferromagnetic magnetoresistive element. FIG. 3 is a circuit diagram showing the basic circuit configuration of a drive circuit for a magnetically sensitive element according to the present invention. FIG. 4 is a principle diagram showing the operating principle of a three-terminal type magnetically sensitive element, and FIG. 5 is a circuit diagram showing a magnetically sensitive drive circuit configured according to the operating principle of the three-terminal type magnetically sensitive element shown in FIG. 4 above. It is. 10... Magnetically sensitive element 11... Operational amplifier 12... Current detection resistor 14... Reference voltage source 15... Feedback resistor

Claims (1)

[Claims] A current detection resistor that is connected in series with the magnetically sensitive element and obtains a detection voltage corresponding to the drive current flowing through the magnetically sensitive element, and a current detection resistor that compares the detected voltage with a reference voltage to detect the magnetically sensitive element. In a drive circuit for a magnetically sensitive element comprising an operational amplifier that drives a constant current, the feedback resistor is configured to feed back changes in the output voltage of the operational amplifier due to changes in internal resistance of the magnetically sensitive element to the input side of the operational amplifier. It is connected between the output terminal and the input terminal of the operational amplifier, and controls the current flowing through the magnetically sensitive element by detecting a change in the internal resistance of the magnetically sensitive element due to temperature as a change in the output voltage of the operational amplifier. A driving circuit for a magnetically sensitive element, characterized in that the magnetically sensitive element is configured to compensate for changes in detection sensitivity of the magnetically sensitive element due to temperature when the magnetically sensitive element is driven with a constant current.