JP4232280B2 - Magnetic impedance sensor circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic impedance sensor circuit including a high frequency drive and detection circuit for using a small and highly sensitive magnetic impedance element.
[0002]
[Prior art]
Conventionally, a magneto-impedance sensor circuit using a magneto-impedance element is disclosed in Japanese Patent Laid-Open No. 9-318719.
[0003]
FIG. 10 shows the structure of a conventional magnetic impedance sensor circuit. In FIG. 10, reference numeral 1 denotes a Colpitts oscillator, which includes a magnetic impedance element 2 as a part of an inductance element. A reference signal generator 3 can output a signal having a constant frequency without being affected by an external magnetic field. Reference numeral 4 denotes a comparator which is configured to output a signal corresponding to a frequency difference between the Colpitts oscillator 1 and the reference signal generator 3.
[0004]
The operation of the magnetic impedance sensor circuit configured as described above will be described. The Colpitts oscillator 1 oscillates at a frequency corresponding to the circuit constant and outputs a sine wave of that frequency. At this time, when an external magnetic field is applied to the magnetic impedance element 2 included in the Colpitts oscillator 1, the impedance of the magnetic impedance element 2 changes and the oscillation frequency of the Colpitts oscillator 1 changes. Since the reference signal generator 3 always oscillates at a constant frequency without being affected by an external magnetic field, the magnitude of the external magnetic field applied to the magneto-impedance element 2 can be known by comparing these frequencies. Can do.
[0005]
[Problems to be solved by the invention]
In such a magneto-impedance sensor circuit, when the temperature changes and the characteristics of the magneto-impedance element 2 change, the change appears as an output of the magneto-impedance sensor circuit, resulting in a temperature drift. .
[0006]
In magneto-impedance sensor circuits, the effects of temperature drift due to high sensitivity and drift due to instability of circuit characteristics are regarded as problems, and stable drive / detection circuits including temperature factors are required. Yes.
[0007]
It is an object of the present invention to provide a magneto-impedance sensor circuit that reduces the temperature drift of the magneto-impedance element and its drive / detection circuit.
[0008]
[Means for Solving the Problems]
In order to solve this problem, the present invention cancels the characteristic change of the magneto-impedance element due to temperature by applying a reverse bias magnetic field to each of the two magneto-impedance elements and performing synchronous detection at the oscillation frequency. It is configured to be able to.
[0009]
Thereby, a stable output can be obtained without being influenced by the temperature characteristics of the magnetic impedance element and the circuit element.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
According to the first aspect of the present invention, a pair of magneto-impedance elements arranged in parallel and close to each other, a bias winding and a feedback winding wound around each of the magneto-impedance elements, and the bias winding A connected current source, a two-phase high-frequency oscillator connected so that a portion where one end of each of the pair of magneto-impedance elements is connected becomes a midpoint, and a comparator that generates a square wave from the output of the two-phase high-frequency oscillator And a synchronous detection circuit that synchronously detects the output voltage of the portion where each one end of the pair of magneto-impedance elements is connected by the output of the comparator, and the high frequency component of the output of the synchronous detection circuit is cut and converted to a direct current component. Consists of a DC amplifier that amplifies, and the feedback winding adjusts the magnitude of the output of the DC amplifier to feed back Are those were, canceling the temperature characteristics of the magneto-impedance element, such an action can provide less magnetic impedance sensor circuit of temperature drift by further reducing the circuit specific temperature drift.
[0011]
According to a second aspect of the present invention, in the first aspect of the present invention, the two-phase high-frequency oscillator is constituted by one high-frequency oscillator and an inverting amplifier that inverts the output thereof, so that a two-phase signal can be easily generated. It has the effect that it can be generated.
[0012]
According to a third aspect of the present invention, there is provided a magneto-impedance element, a bias winding and a feedback winding wound around the magneto-impedance element, a high-frequency oscillator that drives both ends of the magneto-impedance element, and the high-frequency oscillator A comparator that generates a square wave from the output of the comparator, a multiplier circuit that generates a multiplied signal of the output of the comparator, a synchronous detector circuit that synchronously detects the voltage of the magneto-impedance element by the output of the comparator, and the synchronous detector circuit A secondary synchronous detection circuit that synchronously detects the output by the output of the multiplier circuit, and a DC amplifier that cuts a high frequency component of the output of the synchronous detection circuit, converts it to a direct current component, and amplifies it, A current is supplied by adjusting the output of the multiplication circuit, and the feedback winding By adjusting the magnitude of the output of the amplifier is obtained by a configuration in which feedback has the effect of reducing the temperature drift without also affecting the individual variation of the magneto-impedance element.
[0013]
The invention according to claim 4 of the present invention is configured by replacing the synchronous detection circuit with a diode detection circuit in the invention according to claim 3, and realizes a circuit having excellent temperature characteristics without the need for performing high-speed synchronous detection. Has the effect of being able to.
[0014]
The invention described in claim 5 of the present invention is configured by using a low frequency square wave oscillator instead of the multiplier circuit in the invention described in claim 3, and when the frequency of the external magnetic field to be detected is low, By making the frequency of the low-frequency square wave oscillator sufficiently lower than the frequency of the high-frequency oscillator, it is possible to obtain a frequency-stable signal output.
[0015]
The invention according to claim 6 of the present invention is configured by using a low-frequency square wave oscillator in place of the comparator and the multiplier circuit in the invention according to claim 4, and does not require a high-speed comparator or circuit processing for synchronous detection. Therefore, it is not necessary to use an electronic component that can operate at high speed, and a circuit having excellent temperature characteristics can be realized.
[0016]
Hereinafter, embodiments of the present invention will be described with reference to FIGS.
[0017]
(Embodiment 1)
FIG. 1 shows a magneto-impedance sensor circuit according to a first embodiment of the present invention. In FIG. 1, reference numerals 1a and 1b denote magneto-impedance elements, which are arranged close to each other and detect magnetic fields in parallel. Reference numerals 2a and 2b denote bias windings which are wound around the magnetic impedance elements 1a and 1b in the same shape and the same number of turns. Reference numerals 3a and 3b denote feedback windings which are wound around the magnetic impedance elements 1a and 1b in the same shape and the same number of turns. A constant current source 4 supplies a constant current in series to the bias windings 2a and 2b.
[0018]
In the sensitivity characteristic of the magneto-impedance element shown in FIG. 2, this current is set to a value that generates a magnetic field sufficient to bias the point A near the center of the sensitivity curve, and the direction of the current is the magneto-impedance elements 1a and 1b. The direction in which a magnetic field in the opposite direction is generated is used. Reference numeral 5 denotes a two-phase high-frequency oscillator, which is wired so that the connecting portion between the magnetic impedance elements 1a and 1b becomes a middle point, and supplies a high-frequency current to the magnetic impedance elements 1a and 1b. A comparator 6 converts the sine wave signal of the two-phase high-frequency oscillator 5 into a square wave with a duty of 50%.
[0019]
Reference numeral 7 denotes a synchronous detection circuit that synchronously detects a signal at the midpoint of the connecting portion of the magnetic impedance elements 1 a and 1 b with a signal from the comparator 6. A direct-current amplifier 8 includes a low-pass filter that can sufficiently smooth the frequency of the two-phase high-frequency oscillator 5 and an amplifier that amplifies the smoothed direct-current signal to a desired voltage level. The output of the DC amplifier 8 becomes a sensor output and is supplied in series to the feedback windings 3a and 3b. The direction of the current is a direction in which a magnetic field having the same direction is generated in each of the magnetic impedance elements 1a and 1b.
[0020]
The operation of the magnetic impedance sensor circuit configured as described above will be described. A high-frequency current is supplied from the two-phase high-frequency oscillator 5 to the magnetic impedance elements 1a and 1b, and a bias magnetic field Hb is applied by the bias windings 2a and 2b. Thereby, the magneto-impedance element 1a is at the operating point A shown in FIG.
[0021]
In this state, when an external magnetic field Hex is applied to the magnetic impedance elements 1a and 1b, the impedance of the magnetic impedance elements 1a and 1b changes due to the magnetic impedance effect, and the operating point changes. Since a reverse bias magnetic field is applied to the magneto-impedance elements 1a and 1b, the moving direction of the operating point is reverse, and the external magnetic field Hex can be detected as the difference between them. More specifically, the external magnetic field Hex is converted into a DC voltage value by synchronously detecting the amplitude values of the magnetic impedance elements 1a and 1b as positive and negative with the synchronous detection circuit 7 and smoothing and amplifying with the DC amplifier 8. These signal processing waveforms are shown in FIG. In addition, the circuit operation can be stabilized by supplying the output of the DC amplifier 8 to the feedback windings 3a and 3b, and the sensitivity can be determined by the feedback amount.
[0022]
As described above, when the magnetic impedance elements 1a and 1b change their characteristics due to temperature change by applying reverse bias magnetic fields to the two magnetoimpedance elements 1a and 1b, respectively, and obtaining output by synchronous detection, they are the same. Since the operating point moves in the direction, it does not appear as sensor output. Further, when compared with an envelope detection circuit such as a diode, the use of the synchronous detection circuit 7 can greatly improve the temperature characteristics of the detection circuit. Moreover, since the influence of the output characteristics of the constant current source 4 and the two-phase high-frequency oscillator 5 can be canceled out by the synchronous detection processing, the offset voltage characteristics can provide a magnetic impedance sensor circuit with extremely excellent temperature. .
[0023]
(Embodiment 2)
Since the magneto-impedance sensor circuit according to the second embodiment of the present invention has many parts in common with those shown in the first embodiment of the present invention, only the part of the two-phase high-frequency oscillator is different. Only that will be described. FIG. 4 shows the configuration of the two-phase high-frequency oscillator. In FIG. 4, 9 is a high frequency oscillator. An inverting amplifier 12 is connected to the output of the high frequency oscillator 9. The output of the high frequency oscillator 9 and the output of the inverting amplifier 12 are connected to both ends of the magnetic impedance elements 1a and 1b in FIG.
[0024]
The magneto-impedance sensor circuit configured as described above performs the same operation as that shown in the first embodiment of the present invention. That is, by inverting the output of the high-frequency oscillator 9 by the inverting amplifier 12, an output equivalent to the output of the two-phase high-frequency oscillator 5 shown in FIG.
[0025]
By configuring as described above, a two-phase high-frequency signal having a phase difference can be easily obtained.
[0026]
In order to compensate for the phase lag and temperature characteristics of the inverting amplifier 12, it is also effective to connect the output of the high-frequency oscillator 9 via a non-inverting amplifier instead of being directly connected to the magnetic impedance elements 1a and 1b. .
[0027]
(Embodiment 3)
FIG. 5 shows a magneto-impedance sensor circuit according to a third embodiment of the present invention. In FIG. 5, reference numeral 1 denotes a magneto-impedance element, which is arranged in a portion for detecting a magnetic field. A bias winding 2 is wound around the magnetic impedance element 1. A feedback winding 3 is wound around the magnetic impedance element 1. A high frequency oscillator 9 supplies a high frequency current to the magnetic impedance element 1. A comparator 6 converts the sine wave signal of the high-frequency oscillator 9 into a square wave with a duty of 50%. A multiplication circuit 11 multiplies the square wave output of the comparator 6. In this case, an appropriate value such as 2 or 4 is possible. The output of the multiplier circuit 11 supplies a current to the bias winding 2. At this time, positive and negative symmetric bias magnetic fields are alternately applied to the magneto-impedance element 1, and the current values are such that the operating points thereof are A and B in FIG.
[0028]
Reference numeral 7 denotes a synchronous detection circuit, which synchronously detects the output signal of the magnetic impedance element 1 using the signal of the comparator 6. Reference numeral 10 denotes a secondary synchronous detection circuit that synchronously detects the output of the synchronous detection circuit 7 with the signal of the multiplier circuit 11. A direct-current amplifier 8 includes a low-pass filter that can sufficiently smooth the frequency of the high-frequency oscillator 9 and an amplifier that amplifies the smoothed direct-current signal to a desired voltage level. The output of the DC amplifier 8 becomes a sensor output and is supplied to the feedback winding 3 at the same time.
[0029]
The operation of the magnetic impedance sensor circuit configured as described above will be described. A high-frequency current is supplied from the high-frequency oscillator 9 to the magneto-impedance element 1, and a positive and negative symmetric bias magnetic field Hb is applied by the bias winding 2 at a period determined by the multiplier circuit 11. Thus, the magneto-impedance element 1 is at the operating point A shown in FIG. 2 when the bias is positive, and is at the operating point B when the bias is negative. In this state, when an external magnetic field Hex is applied in parallel to the magnetic impedance element 1, the impedance of the magnetic impedance element 1 changes due to the magnetic impedance effect, and the operating point changes. Since a reverse bias magnetic field is periodically applied to the magneto-impedance element 1, the movement directions of the positive and negative operating points are opposite, and the external magnetic field Hex can be detected as the difference between them.
[0030]
Specifically, first, the amplitude value of the magneto-impedance element 1 is synchronously detected by the synchronous detection circuit 7 using the fundamental frequency, and then the output in the positive and negative bias magnetic fields is positive and negative, respectively, and is synchronized by the secondary synchronous detection circuit 10. Detect. By smoothing and amplifying this with the DC amplifier 8, the external magnetic field Hex is converted into a DC voltage value. These signal processing waveforms are shown in FIG. Further, the circuit operation can be stabilized by supplying the output of the DC amplifier 8 to the feedback winding 3, and the sensitivity can be determined by the feedback amount.
[0031]
As described above, when the magnetic impedance element 1 is periodically subjected to positive and negative bias magnetic fields and the output is obtained by synchronous detection, the operating point is changed in the same direction when the characteristic of the magnetoimpedance element changes due to temperature change. Because it moves, it does not appear as a sensor output. Since the magneto-impedance element 1 can be composed of a single element, there is no need to consider variations between elements when a plurality of magneto-impedance elements are used. Further, when compared with an envelope detection circuit such as a diode, the temperature characteristic of the detection circuit can be greatly improved by using the synchronous detection circuit 7. Further, in terms of circuit characteristics, the output characteristics of the constant current source 4 and the high frequency oscillator 9 can be canceled by the synchronous detection process, so that a magnetic impedance sensor circuit having very excellent temperature characteristics can be provided.
[0032]
(Embodiment 4)
FIG. 7 shows a magneto-impedance sensor circuit according to a fourth embodiment of the present invention. Many parts in FIG. 7 are the same as those shown in the third embodiment of the present invention. Only a certain diode detection circuit will be described.
[0033]
Reference numeral 13 denotes a diode detection circuit, which detects the output signal of the magneto-impedance element 1 by passing only a positive voltage. The output of the diode detection circuit 13 is connected to the secondary synchronous detection circuit 10.
[0034]
The operation of this configuration is basically the same as that described in the third embodiment of the present invention shown in FIG. 6, but the output of the diode detection circuit 13 is generally half-wave rectification.
[0035]
With the configuration described above, it is conceivable that the diode detection circuit 13 has temperature characteristics. However, the offset drift due to the temperature characteristics of the diode detection circuit 13 is canceled out by the secondary synchronous detection circuit 10 in the subsequent stage. Is stable. In general, the magneto-impedance effect requires a frequency of several MHz or more, but the diode detection circuit 13 can operate at a higher speed than the synchronous detection circuit 7, so that the third embodiment of the present invention is used. In comparison, the circuit configuration is facilitated.
[0036]
(Embodiment 5)
FIG. 8 shows a magneto-impedance sensor circuit according to a fifth embodiment of the present invention. Many parts in FIG. 8 are the same as those shown in the third embodiment of the present invention. Only the part of a certain low frequency square wave oscillator will be described.
[0037]
Reference numeral 14 denotes a low frequency square wave oscillator connected to the bias winding 2 and the secondary synchronous detection circuit 10. This corresponds to the multiplier circuit 11 shown in the third embodiment of the present invention, but the frequency can be arbitrarily set under the condition that the frequency is sufficiently lower than that of the high-frequency oscillator 9.
[0038]
The operation of this configuration is basically the same as that described in the third embodiment of the present invention shown in FIG. 6, but the frequency of the low-frequency square wave oscillator 14 corresponding to the output of the multiplier circuit 11 is It can be made low enough. For example, the oscillation frequency of the high frequency oscillator 9 can be set to 10 MHz, and the oscillation frequency of the low frequency square wave oscillator 14 can be set to 1 kHz. Here, the oscillation frequency of the low-frequency square wave oscillator 14 needs to be a value sufficiently higher than the cutoff frequency of the magnetic impedance sensor circuit.
[0039]
By configuring as described above, the oscillation frequency of the low-frequency square wave oscillator 14 is set to an intermediate frequency between the high frequency necessary for obtaining the magnetoimpedance effect and the cutoff frequency necessary for the response of the magnetic impedance sensor circuit. It becomes easy to select, and the degree of freedom in circuit design can be increased.
[0040]
(Embodiment 6)
FIG. 9 shows a magneto-impedance sensor circuit according to a sixth embodiment of the present invention. In FIG. 9, the respective parts are the same as those shown in the fourth and fifth embodiments of the present invention. The configuration will be briefly described.
[0041]
Reference numeral 1 denotes a magnetic impedance element, and reference numerals 2 and 3 denote a bias winding and a feedback winding wound around the magnetic impedance element 1, respectively. The magneto-impedance element 1 is driven by a high-frequency oscillator 9 and subjected to detection processing by a diode detection circuit 13 and a secondary synchronous detection circuit 10. Then, the output is smoothed and amplified by the DC amplifier 8 and output as an output signal, and the output is fed back to the feedback winding 3. The output of the low-frequency square wave oscillator 14 is supplied to the bias winding 2 and used as a detection timing signal of the secondary synchronous detection circuit 10.
[0042]
The operation of this configuration is basically the same as that described in the third embodiment of the present invention shown in FIG. 6, but the output of the diode detection circuit 13 is generally a half-wave rectification and is a low-frequency square. The oscillation frequency of the wave oscillator 14 is characterized by being sufficiently lower than the oscillation frequency of the high-frequency oscillator 9.
[0043]
With the configuration described above, only the high-frequency oscillator 9, the magnetic impedance element 1, and the diode detection circuit 13 are operating at a frequency of several MHz or more necessary for the magneto-impedance effect. Compared to a circuit or the like, it can be easily operated at high speed. Therefore, the oscillation frequency of the high-frequency oscillator 9 can be set to an optimum frequency as the magneto-impedance effect without being limited by the circuit operation frequency. Thereby, the characteristic as a magnetic impedance sensor circuit can be improved.
[0044]
【The invention's effect】
As described above, according to the present invention, the temperature stability of the magnetic impedance sensor is improved without being affected by the temperature characteristics of the magneto-impedance element and hardly affected by the temperature characteristics of circuit components such as diodes and transistors. The advantageous effect that it can be made is obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a magneto-impedance sensor circuit according to a first embodiment of the present invention. FIG. 2 is a diagram showing sensitivity characteristics of a magneto-impedance element. FIG. 3 is a magneto-impedance according to the first embodiment of the invention. FIG. 4 is a diagram showing an operation waveform of a sensor circuit. FIG. 4 is a diagram showing an oscillation circuit according to a second embodiment of the invention. FIG. 5 is a diagram showing a magneto-impedance sensor circuit according to a third embodiment of the invention. 6 is a diagram showing an operation waveform of the magneto-impedance sensor circuit according to the third embodiment of the present invention. FIG. 7 is a diagram showing a magneto-impedance sensor circuit according to the fourth embodiment of the present invention. FIG. 9 is a diagram showing a magnetic impedance sensor circuit according to a fifth embodiment. FIG. 9 is a diagram showing a magnetic impedance sensor circuit according to a sixth embodiment of the present invention. It shows a dance sensor circuit EXPLANATION OF REFERENCE NUMERALS
1, 1a, 1b Magnetic impedance elements 2, 2a, 2b Bias winding 3, 3a, 3b Feedback winding 4 Constant current source 5 Two-phase high frequency oscillator 6 Comparator 7 Synchronous detection circuit 8 DC amplifier 9 High frequency oscillator 10 Secondary synchronous detection Circuit 11 Multiplication circuit 12 Inverting amplifier 13 Diode detection circuit 14 Low frequency square wave oscillator

Claims (6)

A pair of magneto-impedance elements arranged close to each other in parallel, a bias winding and a feedback winding wound around each of the magneto-impedance elements, a current source connected to the bias winding, and the pair of magneto-impedance elements A two-phase high-frequency oscillator connected so that a portion where each one end of the element is connected becomes a middle point, a comparator that generates a square wave by the output of the two-phase high-frequency oscillator, and each one end of the pair of magnetic impedance elements It consists of a synchronous detection circuit that synchronously detects the output voltage of the connected part by the output of the comparator, and a direct current amplifier that cuts the high frequency component of the output of the synchronous detection circuit, converts it to a direct current component, and amplifies it. Is a magnetic impedance sensor circuit configured to feed back by adjusting the output level of the DC amplifier. . 2. The magneto-impedance sensor circuit according to claim 1, wherein the two-phase high-frequency oscillator includes one high-frequency oscillator and an inverting amplifier that inverts and amplifies the output thereof. A magneto-impedance element; a bias winding and a feedback winding wound around the magneto-impedance element; a high-frequency oscillator that drives both ends of the magneto-impedance element; a comparator that generates a square wave from the output of the high-frequency oscillator; A multiplier circuit for generating a multiplier signal of the output of the comparator; a synchronous detector circuit for synchronously detecting the voltage of the magneto-impedance element by the output of the comparator; And a DC amplifier that cuts a high frequency component of the output of the synchronous detection circuit, converts it to a DC component, and amplifies it. The bias winding adjusts the output of the multiplier circuit to adjust the current. And adjust the magnitude of the output of the DC amplifier to the feedback winding. Configuration and the magnetic impedance sensor circuit fed back. 4. The magnetic impedance sensor circuit according to claim 3, wherein a diode detection circuit is used instead of the synchronous detection circuit. 4. The magnetic impedance sensor circuit according to claim 3, wherein a low frequency square wave oscillator is used in place of the multiplier circuit. 5. The magnetic impedance sensor circuit according to claim 4, wherein a low frequency square wave oscillator is used in place of the comparator and the multiplier circuit.

Images