JP2000338207A - Driving circuit of magnetic impedance effect element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce consumption power, eliminate difference of detection sensitivity which is due to the direction of an external magnetic field, and simplify structure. SOLUTION: This driving circuit is provided with a magnetic impedance effect element 5, an element driving circuit 3 applying a driving pulse to the element 5, a detection coil 10 wound around the element 5, a first sample-hold circuit 11 and a second sample-hold circuit 12 which hold a voltage detected by the detection coil 10, and a differential amplifier 9 outputting a voltage of difference between a voltage held by a first sample-hold circuit and a voltage held by the second sample-hold circuit 12. The detection coil 10 detects a voltage whose polarity is reverse at the rise time and the fall time of the driving pulse. A voltage of one polarity is held by the first sample-hold circuit 11, and a voltage of the other polarity is held by the second sample-hold circuit 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for a magneto-impedance effect element (hereinafter, referred to as an MI element) used as a magnetic sensor of, for example, a biological signal detecting device.

[0002]

2. Description of the Related Art The magnetic impedance effect is a phenomenon in which when a high-frequency current flows through a magnetic material having a high magnetic permeability, the impedance of the magnetic material changes due to an external magnetic field. This magnetic material is called an MI element. I have. Magnetic sensors and the like utilizing this phenomenon have been put to practical use.

FIG. 3 is a block diagram of a conventional MI element driving circuit. A continuous pulse output from a pulse generator 31 is input to an element driving circuit 32 and a sampling pulse generating circuit 33. The element drive circuit 32 continuously outputs the same timing square wave drive pulses from the two C-MOS inverters 32a and 32b. First C-MOS
The driving pulse output from the inverter 32a is applied to one end of the first MI element 35 via the first resistor 34 in series, and the driving pulse output from the second C-MOS inverter 32b is 36 in series through the second M
Applied to one end of the I element 37. Since the other ends of the two MI elements 35 and 37 are grounded, the MI element 3
A high-frequency current (pulse current) flows through each of 5 and 37.

Here, the MI elements 35 and 37 are formed in a linear shape and are arranged so as to be parallel to each other.
Then, the magnetic flux of the first MI element 35 and the second MI element 37 changes due to the external magnetic field He, and the voltage appearing in the detection coils wound around the respective MI elements 35 and 37 changes accordingly.

The detecting section 40 comprises a first detecting circuit 41, a second detecting circuit 42 and a differential amplifier 43, and detects the voltage detected by the first detecting circuit 41 and the voltage detected by the second detecting circuit 42. The difference voltage from the voltage is amplified by the differential amplifier 43 and extracted.

[0006] The first detection circuit 41 includes a first MI element 3
5 and a first sample and hold circuit 45 for sampling and holding the voltage detected by the first detection coil 44. The first detection coil 44 The first sample and hold circuit 45 is connected in series. The first sample and hold circuit 45 includes a first switch 45 connected in series with each other.
a and a first charging circuit 45b. The first charging circuit 45b includes a resistor R and a capacitor C connected in parallel. The first detection coil 44 is wound around the first MI element 35.

The second detection circuit 42 is provided with a second MI
A second detection coil 46 for detecting a voltage appearing at the element 37;
And a second sample and hold circuit 47 that samples and holds the voltage detected by the second detection coil 46.
And the second detection coil 46 and the second sample and hold circuit 47 are connected in series. The second sample and hold circuit 47 includes a second switch 47a and a second charging circuit 47b connected in series with each other, and the second charging circuit 47b includes a resistor R and a capacitor C connected in parallel. The second detection coil 46 is a second MI element 37
Wound around. A resistor R for dividing the DC voltage B
A bias voltage is applied to the first detection circuit 41 and the second detection circuit 42 by 1 and R2.

On the other hand, the pulse output from the pulse generator 31 is also input to a sampling pulse generating circuit 33, and the sampling pulse generating circuit 33 outputs, for example, a rising edge of the driving pulse output from the element driving circuit 32. A sampling pulse is output at the time. This sampling pulse is applied to the first switch 45a and the second switch 47a.

When the driving pulse output from the element driving circuit 32 is applied to the MI elements 35 and 37, voltages that are opposite to each other are generated in the detection coils 44 and 46 at the rising time of the driving pulse. Voltage is detected by the first and second detection coils 44, 46, respectively. The directions of the detected voltages are also opposite to each other. That is, in the first coil 44, if the polarity of the voltage on the side where the first switch 45a is connected becomes positive, the second detection coil 46 detects the voltage on the side where the second switch 47a is connected. The polarity becomes negative.

Then, a sampling pulse is applied to the first switch 45a and the second switch 47a at the rising time of the drive pulse, and the first and second switches
5a and 47a are closed, and the first and second charging circuits 45 are closed.
The sampled voltage is held in each of b and 47b.

The two held voltages are differentially amplified by a differential amplifier 43. The output voltage output from the differential amplifier 43 has a positive or negative value depending on the direction of the external magnetic field, for example, as shown in FIG.

[0012]

As described above, the conventional circuit for driving a magneto-impedance effect element has two MI elements, and accordingly, two detection coils must be provided. The structure was complicated.
In addition, since a drive pulse is applied to the two MI elements, power consumption is increased. Further, when there is a difference between the characteristics of the two MI elements, there is a problem that the voltages detected by the two detection coils are different from each other, and the detection sensitivity changes due to a change in the direction of the external magnetic field.

In view of the above, it is an object of the present invention to reduce the power consumption, eliminate the difference in detection sensitivity depending on the direction of the external magnetic field, and simplify the structure of the driving circuit for the magneto-impedance effect element of the present invention.

[0014]

In order to solve the above-mentioned problems, a detection circuit for a magneto-impedance effect element according to the present invention comprises a magneto-impedance element, an element driving circuit for applying a drive pulse to the magneto-impedance element, A detection coil wound around the magneto-impedance effect element, a first sample and hold circuit and a second sample and hold circuit that hold a voltage detected by the detection coil, and a detection coil that is held by the first sample and hold circuit. A differential amplifier that outputs a voltage that is a difference between a voltage and a voltage held in the second sample-and-hold circuit, wherein the detection coil has opposite polarities at rising and falling times of the drive pulse. , The voltage of one polarity is held by the first sample and hold circuit, and the voltage of the other polarity is The serial was held in the second sample-and-hold circuit.

The detection circuit of the magneto-impedance effect element according to the present invention may be arranged such that the pulse width of the drive pulse is longer than the time from the rising time of the voltage output from the detection coil to the time when the voltage reaches the peak value. Set.

In the detection circuit for a magneto-impedance effect element according to the present invention, the pulse width of the drive pulse may be adjusted from a rising time of a voltage output from the detection coil to a time when the ringing of the detected voltage substantially converges. Was set to be the time.

[0017]

FIG. 1 is a block diagram showing a driving circuit of a magneto-impedance effect element (hereinafter, referred to as MI element) according to the present invention. A pulse continuously output from a pulse generator 1 is an element driving circuit. 2 and the sampling pulse generation circuit 3. The element driving circuit 2 includes an input buffer 2a composed of a two-stage inverter, a time constant circuit 2b, and an output buffer 2c composed of an inverter. The output buffer 3c continuously outputs square-wave driving pulses. The pulse width of the driving pulse is changed by the time constant circuit 2b, and the so-called duty ratio changes. The driving pulse is
The voltage is applied to one end of the MI element 5 via the resistor 4 in series.
The other end of the MI element 5 is grounded, and a high-frequency current (pulse current) flows.

Here, the MI element 5 is formed in a linear shape, the impedance of which is changed by the external magnetic field He, and the voltage appearing at the MI element 5 changes accordingly.

The detecting section 7 comprises a detecting circuit 8 and a differential amplifier 9. Further, the detection circuit 8 has a detection coil 10 wound around the MI element 5, a first sample and hold circuit 11, and a second sample and hold circuit 12, and the voltage held by the two sample and hold circuits 11, 12 Is amplified by the differential amplifier 9. The first sample and hold circuit 11 and the second sample and hold circuit 12 are both connected to the detection coil 10 in parallel.

The first sample and hold circuit 11 comprises a first switch 11a and a first charging circuit 11b connected in series to each other, and the first charging circuit 11b comprises a resistor R and a capacitor C connected in parallel to each other. Having. The second sample-and-hold circuit 12 includes a second switch 12a and a second charging circuit 12b connected in series to each other. The second charging circuit 12b includes a resistor R and a capacitor C connected in parallel to each other. Have. Then, a bias voltage is applied to the detection circuit 8 by voltage dividing resistors R1 and R2 that divide the DC voltage B.

On the other hand, the pulse output from the pulse generator 1 is also input to the sampling pulse generation circuit 3.
The sampling pulse generation circuit 3 has two systems, has output buffers 3a and 3b each composed of an inverter, and has a time constant circuit 3c between the output buffers 3a and 3b and the pulse generator 1. .

Then, from one output buffer 3a,
For example, of the drive pulse output from the element drive circuit 2,
A sampling pulse P1 synchronized with the rising time is output, and a sampling pulse P2 synchronized with the falling time of the driving pulse is output from the other output buffer 3b. One sampling pulse P1 is applied to the first switch 11a of the first sample and hold circuit 11, and the other sampling pulse P2 is applied to the second switch 12a of the second sample and hold circuit 12.
The pulse width of the sampling pulse P1P2 is determined by the time constant circuit 3
It can be adjusted by c.

When a square wave drive pulse as shown in FIG. 2A is applied from the element drive circuit 2 to the MI element 5, the detection coil 10 reverses the drive pulse at the rising time and the falling time. The direction voltage is generated. The magnitude of the voltage appearing in the detection coil 10 is proportional to the external magnetic field He. That is, as shown in FIG. 2B, a voltage having a positive polarity is detected at the rise of the drive pulse. Here, the voltage having a positive polarity is, for example, the switch 11 of the coil 10.
It is assumed that the side to which a and 12a are connected has a positive voltage. The detected voltage then oscillates, so-called ringing occurs. Ringing converges after a predetermined period determined by circuit constants.

On the other hand, when the square wave falls, a voltage having a negative polarity is detected. The negative voltage also causes ringing and converges after a predetermined period determined by the circuit constant. The positive voltage and the negative voltage detected by the detection coil 10 are also proportional to the external magnetic field He.

Here, in order to reduce the power consumption by the drive pulse under the condition that the repetition period of the drive pulse is determined, it is desirable that the duty ratio is 50% or less. Also, the power consumption can be reduced by narrowing the width of the drive pulse. However, if the width is too narrow, accurate drive can be achieved if the drive pulse falls before the positive voltage detected by the detection coil 10 reaches the peak value. Voltage cannot be obtained. Therefore, the pulse width must be at least longer than the time from when the positive voltage rises to when it reaches the peak value. If the drive pulse falls near the time at which the ringing of the positive voltage detected at the rising time of the drive pulse converges, the negative voltage will not be affected by the ringing of the positive voltage, so that it is accurate. Value.

Then, as shown in FIG. 2C, a sampling pulse P1 is applied to the first switch 11a at the rising time of the drive pulse, and as shown in FIG. 2D, the second switch 12a , A sampling pulse P2 is applied at the falling time of the drive pulse. Here, the pulse width of the sampling pulse P1 is set by the time constant circuit 3c so as to be the time width from the rise of the positive voltage detected by the detection coil 10 to the peak value. Similarly, the pulse width of the sampling pulse P2 is set by the time constant circuit 3c so as to be the time width from the rise of the negative voltage detected by the detection coil 10 to the peak value.

Then, at the rise of the drive pulse, the first switch 11a is closed by the sampling pulse P1, and the positive voltage detected by the detection coil 10 is sampled and charged to the charging circuit 11b. In the falling, the second switch 12a is closed by the sampling pulse P2, the negative voltage detected by the detection coil 10 is sampled, and the charging circuit 12b is charged. Then, by continuously applying the driving pulse to the MI element 5, the voltage charged in the charging circuits 11b and 12b is maintained as a substantially constant voltage as shown in E and F in FIG. You.

Although the voltage charged in the charging circuits 11b and 12b is discharged by the resistor R, the time constant of the charging circuits 11b and 12b is set so that the discharging during the repetition period of the driving pulse becomes negligible. Is set.

Since the two held voltages are opposite to each other with respect to the bias voltage, they are differentially amplified by the differential amplifier 9. The output voltage output from the differential amplifier 9 is proportional to the external magnetic field and changes its direction as shown in FIG. 3, for example.

[0030]

As described above, in the drive circuit for the magneto-impedance effect element according to the present invention, the detection coil detects the voltages whose polarities are opposite to each other at the rise time and the fall time of the drive pulse. Is held by the first sample and hold circuit, and the voltage of the other polarity is held by the second sample and hold circuit, so that a single magneto-impedance element can detect voltages with different polarities. Therefore, only one detection coil and one excitation coil are required, and the structure is simplified. Further, since only one magneto-impedance effect element is required, it is possible to eliminate a difference in detection sensitivity depending on the direction of the external magnetic field. Further, power consumption for driving can be reduced.

In the detection circuit of the magneto-impedance effect element according to the present invention, the pulse width of the driving pulse is set to be longer than the time from the rising time of the voltage output from the detection coil to the time when the voltage reaches the peak value. So
The detection coil can detect the maximum voltage.

Further, the detection circuit of the magneto-impedance effect element of the present invention sets the pulse width of the drive pulse to the time from the rising time of the voltage output from the detection coil to the time when the ringing of the detected voltage substantially converges. The voltage can be accurately detected by the detection coil.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a drive circuit of a magneto-impedance effect element according to the present invention.

FIG. 2 is a timing chart for explaining an operation in a drive circuit of the magneto-impedance effect element of the present invention.

FIG. 3 is a configuration diagram of a drive circuit of a conventional magneto-impedance effect element.

FIG. 4 is a characteristic diagram of an output voltage detected by a conventional driving circuit for a magneto-impedance effect element.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 pulse generator 2 element driving circuit 2 a input buffer 2 b time constant circuit 2 c output buffer 3 sampling pulse generation circuit 3 a, 3 b output buffer 3 c time constant circuit 4 resistor 5 magneto-impedance effect element 7 detection unit 8 detection circuit 9 differential amplifier 10 Detection coil 11 First sample and hold circuit 11a First switch 11b First time constant circuit 12 Second sample and hold circuit 12a Second switch 12b Second time constant circuit R resistance R1, R2 Voltage dividing resistance

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[Procedure amendment]

[Submission date] June 2, 1999 (1999.6.2)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

Claims (3)

[Claims] 1. A magneto-impedance effect element, an element driving circuit for applying a drive pulse to the magneto-impedance effect element, a detection coil wound around the magneto-impedance effect element, and holding a voltage detected by the detection coil. A first sample-and-hold circuit and a second sample-and-hold circuit, and a differential that outputs a difference voltage between the voltage held by the first sample-and-hold circuit and the voltage held by the second sample-and-hold circuit An amplifier, and the detection coil detects voltages whose polarities are opposite to each other at the rising time and the falling time of the drive pulse, and holds the voltage of one polarity by the first sample and hold circuit, and the other Characterized in that the voltage of the polarity is held by the second sample and hold circuit. Road. 2. The method according to claim 1, wherein a pulse width of the drive pulse is set to be longer than a time from a rising time of a voltage output from the detection coil to a time when the voltage reaches a peak value. Drive circuit for magneto-impedance effect element 3. The method according to claim 1, wherein a pulse width of the driving pulse is set to be a time from a rising time of a voltage output from the detection coil to a time when ringing of the detected voltage substantially converges. 3. The driving circuit for a magneto-impedance effect element according to claim 1, wherein