JPH03257387A - Driving circuit of magnetoresistance element - Google Patents

Abstract

PURPOSE:To lessen a consumed current and also to obtain an output having a high midpoint fluctuation potential by a method wherein a magnetoresistance element is driven by a rectangular wave voltage and an output signal of the magnetoresistance element is subjected to wave-shaping by an integrating circuit and taken out. CONSTITUTION:A driving circuit of a magnetoresistance element is constructed of a power source Vcc 1 for IC, a semiconductor circuit component, etc., a comparator 2, a reference signal 3 of a triangular wave or a sine wave and a resistor 4 formed of the magnetoresistance element (MR element) made of a thin film. Integrating circuits 5 and 6 are composed of a resistor R1 and a capacitor C1 and a resistor R2 and a capacitor C2 respectively. An amplifier 7 receives outputs of the circuits 5 and 6 as inputs and is provided with resistors R5 to R7. Resistors R3 and R4 and a capacitor C3 are connected to the comparator 2. Construction is made so that a rectangular wave voltage is impressed on the MR element and that an output signal of the MR element is subjected to wave-shaping by the circuits 5 and 6 and taken out. According to this constitution, a consumed current can be lessened even when the MR element of low resistance is employed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a drive circuit for a thin film type magnetoresistive element (hereinafter referred to as an MR element).

2. Prior Art In order to enable driving by a hunter, water meters, gas flow meters, etc. using this type of MR element are required.
It is necessary to reduce the current supplied to the element to a minute current, but for this purpose, the DC supply voltage must be lowered or the MR
Connect a resistor in series with the element j7 to limit the current to a low level, or
Alternatively, the resistance value of the MR element itself may be set high and the current may be limited to a low level by direct current driving using a DC voltage.

Problems to be Solved by the Invention However, when the resistance value of the MR element itself is low, characteristics change due to self-heating, and to avoid this, the supply D
It is necessary to set the C voltage low.

For this reason, there is a drawback that the same supply voltage cannot be used for semiconductor elements (ICs) and semiconductor circuit components.

Furthermore, if the supply voltage applied to the MR element itself is lowered by inserting a series resistor, there is a drawback that the output of the MR element decreases. Furthermore, in order to set the resistance value of the MR element itself high, it is necessary to increase the area of the MR film, and with the trend toward smaller external dimensions by reducing the film thickness and film 111. There was a drawback due to problems with the construction method.

In view of these problems, it is an object of the present invention to reduce the power loss of the MR element drive section and improve the output characteristics of the MR element, especially for low resistance values.

Means for Solving the Problem In order to solve this problem, the present invention drives the MR element with a rectangular wave current, and by appropriately setting the ON-FF time, an arbitrary minute current can be caused to flow. This is what I did.

Duty D=Ton/(Ton-+-Tof f)
If this is the case, the smaller D is shifted, the more it becomes possible to drive with a minute current.

Effect: With this configuration, the low resistance MR element can be driven with a voltage approximately equal to the driving voltage of the IC1 semiconductor circuit components, etc., thereby expanding the selectable range of the resistance value of the MR element. Furthermore, the size of the film pattern of the Mrl element itself is reduced, and it acts effectively on the applied magnetic field.

Examples Examples of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 is a diagram showing a drive circuit for a magnetoresistive element according to an embodiment of the present invention. In FIG. or a sine wave reference signal, 4 is M
A resistor composed of an R element constitutes a Brinon circuit.

5 and 6 are integration circuits (low-pass filter 1) consisting of resistor R1, contin + JC1, resistor R2 and capacitor C2, 7
is an integrator 11 to which the outputs of the integrating circuits 5 and 6 are input. Also, R3, R4, R5, R6 and R7 are resistors, and C3
is a capacitor.

FIG. 2 shows one input signal of the comparator 2 and the voltage waveform supplied to the MR element, and a rectangular wave voltage of PWM waveform is applied to the MR element.

Duty D connects the input voltage of comparator 2 to resistor R3,
You can change the ratio of R4 from here.

FIG. 3 shows a midpoint potential waveform 9 when an external magnetic field is applied to the MR element. Further, FIG. 4 shows an output waveform IO amplified by the amplifier 7.

In this way, a rectangular wave voltage is applied to the MR element, and the MR
The output signal of the element is waveform-shaped by integrating circuits 5 and 6,
Even if a low-resistance MR element is used, current consumption can be reduced and the midpoint fluctuation potential can be increased.

Effects of the Invention As described above, according to the present invention, even if the MR element has a low resistance, by applying a rectangular wave supply voltage to the MR element, current consumption can be reduced, and an output with a high midpoint fluctuation potential can be achieved. is obtained. Further, in a high-resistance MR element, even lower current consumption is possible. By reducing the current consumption in this way, the heat generation of the resistor is suppressed and a good M
R characteristics can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of a drive circuit for a magnetoresistive element according to an embodiment of the present invention, FIG. 2 is a waveform diagram of the driving voltage of the MR element, FIG. 3 is a waveform diagram of the midpoint voltage of the MR element, and FIG. Figure 4 is the first
FIG. 3 is an output waveform diagram of the circuit configuration shown in the figure. 2...Comparator, 4...Resistor of MR element, 5.6...Integrator circuit.

Claims (1)

[Claims] 1. A drive circuit for a magnetoresistive element, characterized in that the magnetoresistive element is driven by a rectangular wave voltage, and the output signal of the magnetoresistive element is waveform-shaped and extracted by an integrating circuit.