JP2003121521A - Magnetism detecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetism detecting circuit that realizes the reduction of power consumption and the simplification of circuit configuration, without dropping detection sensitivity and uses for the magnetism detecting element of an orthogonal flux gate-type, suitable for turning into an IC. SOLUTION: The magnetism detecting circuit comprises a pulse-generating circuit 10 outputting a pulse signal for passing the excitation current of a pulse waveform through the magnetism detecting element, a detection circuit 11 for magnetic flux variation 11 has both integral characteristic and differential characteristic for regenerating the variation component of a magnetic field to be measured, based on a detection voltage detected from the magnetism detecting element, a sample-and-hold circuit (SH circuit) 12 for synchronous sampling of the output voltage of the magnetic variation detecting circuit 11, to then hold it to an output signal outputted by the pulse-generating circuit 10, and a smoothing circuit 13 for smoothing a voltage value held to output it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic flux detection circuit of the orthogonal flux gate type, which is capable of detecting the magnetism of a magnetic field to be measured.

[0002]

2. Description of the Related Art In recent years, PDA (Personal Digital Assis)
electronic compass used for tant), that is, a direction sensor, a direction sensor for complementing a GPS device used for an in-vehicle navigation system, a direction sensor for attitude control of a vehicle body used for an automatic traveling system of an automated guided vehicle, or a color shift correction of a high-precision TV. Demand for high-precision, small-sized, low-cost magnetic sensors that can detect the magnetism of the magnetic field to be measured (magnetic field strength and direction), such as geomagnetic sensors for active magnetic shields, is increasing. .

As conventional magnetic sensors of this type, Hall elements, MR elements, MI elements, quantum interference elements (SQUI) are used.
D), parallel or orthogonal fluxgate type elements are used. Among these, the Hall element has a low sensitivity, and the MR element, the MI element, and the like have the drawback that they cannot detect the direction of the magnetic field by themselves and require a plurality of them. Any of the orthogonal types has the advantage that the strength and direction of the magnetic field can be detected by itself. Moreover, the linearity of detection output, temperature characteristics, and resolution are also excellent, and in particular, in terms of detection accuracy, an orthogonal fluxgate type element that can perform detection with higher accuracy is drawing attention.

FIG. 8 is a perspective view showing the structure of a magnetic sensor (magnetic detecting element) of an orthogonal fluxgate type element.
In the figure, 1 is an inner conductor, 2 is a core, 3 is a detection coil, 4 is an outer conductor, and 100 is a high frequency power source. Inner conductor 1
Is made of metal or other conductive material and has a cylindrical shape. The outer conductor 4 is also made of metal or other conductive material, and has a cylindrical shape whose inner diameter is larger than the diameter of the inner conductor 1. The inner conductor 1 and the outer conductor 4 are coaxially arranged with the former inside and the latter outside with an insulating material interposed therebetween.
The one end portions on the same side in the magnetic detection direction indicated by the arrow in the figure are electrically connected by the end plate 4a.

The other end of the inner conductor 1 is positioned so as to project outward from the other end of the outer conductor 4 by a predetermined length. An insulating material is vapor-deposited or coated on the outer peripheral surface of the inner conductor 1, the outer peripheral surface of the outer conductor 4, and the inner peripheral surface of the end plate 4a. Then, for example, permalloy (Ni-Fe alloy), sendust (Fe-Al-Si) is provided in the cylindrical space formed between the inner conductor 1 and the outer conductor 4.
A core 2 formed in a cylindrical shape with a soft magnetic material such as an alloy) or soft ferrite is fitted and inserted.

One end of the core 2 is inserted to a position in contact with the inner peripheral surface of the end plate 4a, and the other end is projected from the other end of the outer conductor 4 by a predetermined length. The core 2 and the inner conductor 1 and the outer conductor 4 do not need to be in close contact with each other, but may be in a movable state with appropriate play. The detection coil 3 is wound around the outer conductor 4 in a predetermined direction a predetermined number of times.

In the magnetic sensor as described above, an exciting current is passed from the high frequency power source 100 between the other ends of the inner conductor 1 and the outer conductor 4 to excite the core 2 and the detection coil 3
The magnetism of the magnetic field to be measured is detected based on the output of.

FIG. 9 is a schematic diagram of a conventional magnetic detection circuit which is connected to the inner conductor 1 and the outer conductor 4 to allow a current to flow therethrough, and is also connected to the detection coil 3 to detect the magnetism of the magnetic field to be measured. FIG. 10 is a block diagram showing a configuration, and FIGS. 10 and 11 are circuit diagrams showing an example of the magnetic detection circuit.
Reference numeral 5 in the figure denotes an oscillation / frequency dividing circuit using a ceramic oscillator, a crystal oscillator, or the like. For example, two types of high-frequency power (rectangular wave) of 7 kHz and 14 kHz are output.
The high frequency (excitation signal: frequency f) of kHz is applied to the excitation circuit 6
Is input to. The excitation circuit 6 is composed of a charging / discharging circuit using a capacitor (C) and a resistance element (R) and the like, converts the input high frequency into a substantially sine wave, outputs it as an exciting current, and applies it to the inner conductor 1 and the outer conductor 4. It Further, of the high frequency power output from the oscillating / dividing circuit 5, a high frequency of 14 kHz (reference signal for detection: frequency 2f) is applied to the phase detector (synchronous rectifier: PSD) 8. .

Here, in the case of the magnetic detection circuits shown in FIGS. 9 to 11, the magnitude of the exciting current, that is, the current (peak current) Ip required to saturate the magnetization of the core 2 is the material of the core 2. Is uniquely determined by the magnetic characteristics (coercive force) and the shape of the core 2 (excitation magnetic path length), and the average excitation current is about 0.7 Ip.

On the other hand, the detection voltage of the detection coil 3 is input to a bandpass filter (hereinafter referred to as BPF) 7, noise is removed, and input to a phase detector 8 to be detected, and then C,
The data is input to the rectification / smoothing circuit 9 including R and operational amplifiers. The rectifying / smoothing circuit 9 full-wave rectifies and smoothes the input detection signal, and outputs a positive or negative detection signal corresponding to the direction of the magnetic field strength.

FIG. 12 shows the exciting current, the degree of magnetization in the detecting direction of the core 2, the output voltage of the detecting coil 3, and the rectifying / smoothing circuit 9 when the magnetism is detected by the orthogonal fluxgate type magnetic sensor. FIG. 7 is a waveform diagram of each of the detection signals that are full-wave rectified by the above method. Magnetic sensor with its inner conductor 1
When the axis of the core 2 is arranged to be parallel to the direction of the external magnetic field (magnetic field to be measured), the magnetic flux of the external magnetic field is attracted to the core 2 and a magnetic path passing through the core 2 is formed.

When a sinusoidal exciting current as shown in FIG. 12 is passed through the inner conductor 1, the peripheral surface of the core 2 is magnetized, and the exciting current increases from the state shown in FIG. 12 (a). When the maximum value is reached as shown in FIG. 12 (b), the magnetization of the core 2 becomes saturated, and the magnetic flux of the external magnetic field is separated from the core 2 and becomes parallel to the internal conductor.

During this time, the degree of magnetization of the core 2 in the detection direction decreases as shown in FIG. 12, and the output voltage of the detection coil 3 increases at a position where the rate of decrease of the degree of magnetization of the core 2 in the detection direction is large. , Becomes 0 when the degree of magnetization reaches the minimum value.

As the exciting current decreases from the maximum value and reaches the zero cross point, the magnetic flux of the external magnetic field again passes through the core 2 as shown in FIG. 12 (c). When the direction of the exciting current is reversed, the peripheral surface of the core 2 is magnetized in the opposite direction of the circumferential direction, and when the exciting current decreases and reaches the maximum negative value, the magnetization of the core 2 is saturated again. The magnetic flux of the external magnetic field becomes parallel to the axis of the core 2. During this time, the output of the detection coil 3 decreases at a position where the rate of increase in the degree of magnetization of the core 2 is large, and changes to 0 again when the degree of magnetization reaches the maximum value (FIG. 12 (c)- (See (e)). As a result, the output voltage of the detection coil 3 changes by two cycles corresponding to the change of the excitation current by one cycle. The signal obtained by detecting the output voltage of the detection coil 3 by the phase detector 8 and rectifying it by the rectifying / smoothing circuit 9 changes by four cycles as shown in FIG.

As described above, the inner conductor 1 and the outer conductor 4
By passing a sinusoidal excitation current between them and periodically exciting the core 2 in the circumferential direction, the magnetic flux of the external magnetic field passing through the core 2 changes, and as shown in FIG. It is possible to obtain an output voltage corresponding to that.

Incidentally, various effective measures have been taken to the magnetic detection circuit. For example, first, in the case of the excitation circuit 6, since the waveform of the electric power output from the oscillation / frequency division circuit 5 is a rectangular wave, it is necessary to make it a sine wave, and a low pass filter for extracting the fundamental wave component is used. However, the filter characteristic of the low-pass filter changes due to the temperature change based on the temperature coefficient of the low-pass filter, and the phase of the excitation signal changes depending on the temperature. By the way, since the magnetic detection circuit uses the phase detector 8, the phase change of the excitation signal and the detection reference signal has a relatively large influence on the sensitivity coefficient. That is, the sensitivity coefficient greatly changes as the phase of the excitation signal changes, and the temperature characteristics deteriorate. Therefore, the cutoff frequency of the low pass filter is set to the frequency f of the fundamental wave.
By setting a low-pass filter that is set in the middle of the range of 3 f and 3 f, and uses a low-pass filter that significantly cuts frequency components of 3 f and above, most of the fundamental wave is passed, and the influence of temperature change of the low-pass filter is avoided.

Secondly, the phase characteristic in the vicinity of 2f which is the frequency of the detection voltage is important for the filter provided in the BPF 7. That is, when the rate of change in the phase when the frequency changes near the frequency 2f is large, the phase of the detection voltage changes greatly according to the temperature change based on the temperature coefficient of the filter, and the temperature coefficient of detection sensitivity is It becomes large and the temperature characteristics deteriorate. Therefore, a filter having a relatively small phase change near the center frequency 2f is used as the filter. More specifically, a one-stage filter with a high Q is not used, but a filter with a low Q is used in two stages. Also, the same effect can be obtained by shifting the center frequencies of the filters in the first stage and the second stage. Furthermore, it is also effective to use a switched capacitor filter.

Thirdly, when a plurality of magnetic sensors are used for magnetic detection, the characteristics of the magnetic sensors are different from each other. Therefore, an IC and a switch are used in the oscillation / frequency dividing circuit 5,
The phase of the detection reference signal is optimized according to the characteristics of each magnetic sensor.

Fourthly, the detected signal input to the rectifying / smoothing circuit 9 is full-wave rectified, so that the frequency component is mainly 4f. Therefore, a filter that can significantly cut 4f when smoothing is used. Further, preferably, a filter having a transmission zero point at 4f is used.

[0020]

9 to 1 described above.
In the case of the magnetic detection circuit shown by 1, the magnetism of the magnetic field to be measured (the strength and direction of the magnetic field) can be detected, and the size and cost can be relatively reduced. But PDA
When it is mounted on a mobile terminal such as, it needs to be driven by electric power supplied from a battery or a rechargeable battery, and reduction of power consumption is an issue. That is, the main power consumption in the magnetic detection circuit is due to the exciting current. As described above, when the magnetic sensor is determined in the magnetic detecting circuit, the average exciting current is determined to be about 0.7 Ip. There is a problem that it is difficult to reduce power consumption.

When a charging / discharging circuit is used in the exciting circuit 6, the exciting current can be reduced by reducing the CR time constant of the charging / discharging circuit, and the power consumption can be reduced. However, along with this, the component of the frequency 2f included in the reference signal for detection decreases, resulting in a decrease in sensitivity.

Further, since the excitation signal and the detection reference signal have different frequencies, there is a problem that the oscillation / frequency dividing circuit is relatively complicated. Also, in the BPF 7, the center frequency 2
In order to stabilize in the vicinity of f, a large-capacity and high-accuracy capacitor and resistance element are required, and film capacitors, metal film resistance elements, etc. are used, but these electronic elements have a large volume and are especially magnetic. This is a major obstacle to realizing an IC detection circuit. Similarly, with respect to the capacitors and resistance elements used in the charge / discharge circuit, the size of the volume hinders their IC implementation.

The present invention has been made in view of the above-mentioned circumstances, and includes a pulse generation circuit in place of the oscillation / frequency dividing circuit 5 so that the current flowing to the magnetic sensor is a pulse waveform current. As a result, the excitation circuit 6 including a charge / discharge circuit is unnecessary, and it is not necessary to use a large-capacity capacitor and resistance element, and further miniaturization can be achieved, and an IC can be realized. It is an object to provide a magnetic detection circuit.

Further, instead of the BPF 7, a magnetic flux change detection circuit for detecting a change in magnetic flux in the magnetic field to be measured based on the output of the detection coil is provided, and the magnetic flux change detection circuit integrates with a time constant equal to or less than a first threshold value. By having the characteristic and having the differential characteristic with the time constant being equal to or larger than the second threshold different from the first threshold, the large-capacity capacitor and the resistance element used in the BPF 7 are not required, and the IC can be realized. , The offset can be removed by the differential characteristic and the zero point can be secured.The output of the magnetic flux change detection circuit changes at almost the same timing as the pulse waveform current generated by the pulse generation circuit, and a frequency divider circuit is required. The purpose is to provide a more inexpensive magnetic detection circuit.

A sampling hold for sampling the output value of the magnetic flux change detection circuit synchronously with the output time point of the pulse waveform current generated by the pulse generation circuit and holding the value obtained by sampling Even if the duty ratio (ON / ON + OFF time ratio) of the pulse waveform current is reduced by providing the circuit, the detection sensitivity will not be reduced and the duty ratio will be reduced to reduce power consumption. It is an object of the present invention to provide a magnetic detection circuit that can reduce the magnetic field and that is more versatile.

[0026]

A magnetic detection circuit according to a first aspect of the present invention provides an output of the detection coil when the magnetic flux of a magnetic field to be measured is changed by energizing a conductor around which the detection coil is wound. On the basis of the above, in the magnetic detection circuit for detecting the magnetism in the magnetic field to be measured, a pulse generation circuit for generating a pulse waveform current flowing to the conductor is provided.

A magnetic detection circuit according to a second aspect of the present invention is the magnetic detection circuit according to the first aspect, further comprising a magnetic flux change detection circuit for detecting a change in magnetic flux in the magnetic field to be measured based on the output of the detection coil. The change detection circuit is characterized in that it has an integration characteristic when the time constant is equal to or less than the first threshold value and has a differentiation characteristic when the time constant is equal to or more than a second threshold value different from the first threshold value.

A magnetic detection circuit according to a third aspect of the present invention is the magnetic detection circuit according to the second aspect, wherein the output value of the magnetic flux change detection circuit is synchronized with the output time point of the pulse waveform current generated by the pulse generation circuit. Is sampled and a sampling hold circuit for holding the value obtained by sampling is provided.

In the case of the magnetic detection circuit according to the first aspect of the present invention, since the pulse generation circuit is provided, an oscillation / frequency division circuit having a complicated structure is unnecessary, and a charging / discharging requiring a capacitor and a resistance element having a large volume. It is possible to realize a magnetic detection circuit that does not require an excitation circuit composed of a circuit and the like and can be made into an IC by further miniaturization.

In the case of the magnetic detection circuit according to the second invention, the magnetic detection circuit according to the first invention is provided with a magnetic flux change detection circuit having an integral characteristic and a differential characteristic according to a time constant, instead of the BPF. , The large-capacity capacitor and resistance element used in the BPF are not required, and miniaturization, that is, IC can be realized, and the offset can be removed by the differential characteristic, and the zero point can be secured.
Furthermore, since the output of the magnetic flux change detection circuit changes at substantially the same timing as the pulse waveform current output from the pulse generation circuit, the frequency division circuit is not required, and a magnetic detection circuit with a simple circuit configuration can be realized. .

In the case of the magnetic detection circuit according to the third invention, the magnetic detection circuit according to the second invention is provided with a sampling hold circuit so that the pulse waveform current
Even if the duty ratio is reduced, the detection sensitivity does not decrease, and by further reducing the duty ratio, it is possible to realize a magnetic detection circuit that can reduce power consumption.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the drawings showing the embodiments thereof. FIG. 1 is a schematic diagram showing a schematic configuration of a magnetic detection circuit according to the present invention, and FIG. 2 is a circuit diagram showing an example of the magnetic detection circuit. Reference numeral 10 in FIG. 1 denotes a pulse generation circuit, and the pulse signal generated by the pulse generation circuit 10 is used as an excitation current of a pulse waveform as shown in FIG.
The core 2 is excited by being applied to the inner conductor 1 and the outer conductor 4 as shown in FIG. Although the pulse generation circuit 10 is omitted in FIG. 2, it can be configured using a known circuit. In addition, in the present embodiment, the pulse generation circuit 10 sets the Duty as the on-time T1 and the off-time T2.
A pulse having a ratio of 1 to 2% is generated and output. In addition, Duty
The ratio is preferably at least 10% or less, and is preferably 1 to 2% or less for more complete reproduction of the magnetic flux change due to the restriction of the time constant setting of the magnetic flux change detection circuit 11 described later.

Reference numeral 14 in FIGS. 1 and 2 denotes a pulse generation circuit 1.
It is an excitation pulse current generation circuit for generating an excitation current having a peak current of Ip to excite the core 2 based on the pulse signal output from 0. The excitation pulse current generation circuit 14 includes a transistor 14 having a base terminal to which the pulse signal output from the pulse generation circuit 10 is input.
1, and the collector terminal of the transistor 141 is
A positive constant voltage source 142 is connected via the resistance element 143. A capacitor 145 is provided between the collector terminal and the common contact of the resistance element 143 and the negative constant voltage source 144.
The common contact of the negative constant voltage source 144 and the capacitor 145 and the emitter terminal of the transistor 141 via the resistance element 146 form the output terminal of the excitation pulse current generation circuit 14. .

On the other hand, the detection voltage of the detection coil 3 is input to the magnetic flux change detection circuit 11, the change of the magnetic field to be measured is reproduced and output as a voltage. Magnetic flux change detection circuit 11
One of the two input terminals to which the detection voltage is input is connected to the non-inverting input terminal of the operational amplifier 111, and the resistance element 112 is interposed between the other input terminal. A resistor element 113 and a capacitor 114, which are connected in parallel, are connected between the inverting input terminal and the output terminal of the operational amplifier 111 for negative feedback, and a series connection is made between the inverting input terminal and the other input terminal. The resistor element 115 and the capacitor 116 are interposed. The output terminal of the operational amplifier 111 forms one output terminal of the magnetic flux change detection circuit 11 via the resistance element 117, and the other input terminal forms the other output terminal of the magnetic flux change detection circuit 11 and detects the magnetic field. It constitutes one output terminal of the circuit. The magnetic flux change detection circuit 1
1, the resistance element 113 and the capacitor 114 are
A time constant of about 1/2 to 1 times the pulse width of the exciting current (first
Threshold value) or less, it is preset so as to have an integration characteristic, and the resistance element 115 and the capacitor 116 are
It is preset to have a differential characteristic at a time constant (second threshold value) of about 50 to 100 times the pulse width of the exciting current. In addition, it is preferable that the time constant is appropriately selected in consideration of the duty ratio of the pulse signal.

The pulse signal output from the pulse generating circuit 10 becomes an exciting current through the exciting pulse current generating circuit 14, and a sampling hold circuit (in the figure,
The voltage value corresponding to the change in the magnetic field reproduced by the magnetic flux change detection circuit 11 is sampled and held for a predetermined period. The sampling and holding circuit 12 includes a transistor 121 having a base terminal to which the pulse signal is input, and the collector terminal of the transistor 121 is connected to one output terminal of the magnetic flux change detection circuit 11. In addition, the transistor 121
The emitter terminal serves as one output terminal of the sampling and holding circuit 12, and a capacitor 122 is interposed between the emitter terminal and the other output terminal of the magnetic flux change detection circuit 11. The capacitor 122 and the magnetic flux change detection circuit 1
The common contact with the other output terminal of 1 constitutes the other output terminal of the sampling and holding circuit 12.

The voltage value held by the sampling and holding circuit 12 is smoothed by the smoothing circuit 13 to output a signal corresponding to the direction and strength of the magnetic field to be measured. The smoothing circuit 13 includes an operational amplifier 131 having a non-inverting input terminal connected to one output terminal of the sampling and holding circuit 12, and the operational amplifier 1
Variable resistance element 1 is provided between the inverting input terminal and the output terminal of 31.
32 is connected and negative feedback is applied. Further, the resistance elements 134, 13 connected in series to the variable resistance element 133
5, the common contact of the resistance elements 134 and 135 is connected to the inverting input terminal of the operational amplifier 131. Further, the other output terminal of the sampling and holding circuit 12 is connected to a terminal of the resistance element 135 opposite to the common contact, and forms one output terminal of the smoothing circuit 13. Further, the output terminal of the operational amplifier 131 serves as the other output terminal of the smoothing circuit 13 via the resistance element 136, and the capacitor 137 is interposed between both output terminals.

Next, a case will be described in which the magnetic field of the magnetic field to be measured is detected by using the magnetic field detection circuit having the above-described circuit configuration according to the present embodiment. FIG. 3 shows the excitation current, the magnetic flux of the magnetic field to be measured, the output voltage of the detection coil 3, the output voltage of the magnetic flux change detection circuit 11, and the sampling and holding circuit 12 when the orthogonal flux gate type magnetic sensor is used.
3 is a waveform diagram of each output voltage of FIG.

When an exciting current having a single-pole rectangular pulse waveform as shown in FIG. 3 is passed through the inner conductor 1, the peripheral surface of the core 2 is magnetized when the exciting current is on, and is saturated immediately after that. The magnetic flux of the measured magnetic field separates from the core 2, and the magnetic flux of the measured magnetic field passing through the core 2 becomes zero as shown in FIG. When the exciting current is turned off after the lapse of time T1, a magnetic flux due to the magnetic field to be measured is formed in the core 2, and this state is maintained from the turning off of the exciting current to the lapse of time T2. After that, subsequently, an exciting current having a pulse waveform, which is turned on at time T1 and turned off at time T2, is passed through, and along with this, the magnetic flux in the core 2 formed by the magnetic field to be measured is opposite to the exciting current. The change that forms the rectangular pulse waveform, which consists of turning off at time T1 and turning on at time T2, is repeated.

During this period, the output voltage of the detection coil 3 takes a maximum value when the rate of increase in the degree of magnetization of the core 2 is maximum, and a minimum value when the rate of decrease is maximum, and converges to a zero point during that time. The change of going is repeated.

Further, the output voltage of the magnetic flux change detection circuit 11 accumulates the output voltage value of the detection coil 3 due to its integral characteristic during the time T1 when the exciting current is in the ON state.
The waveform is as shown in. Also, during the time T2 when the exciting current is in the off state, the output voltage decreases due to its integral characteristic, and further falls below the zero point due to its differential characteristic and then converges to the zero point again (offset Removal,
, And ensuring the zero point), the waveform is as shown in FIG.

The sampling and holding circuit 12 samples the voltage value input from the magnetic flux change detection circuit 11 substantially in synchronization with the pulse signal input from the pulse generation circuit 10. Therefore, by sampling the voltage value output from the magnetic flux change detection circuit 11 during the time T1, and then holding the sampled voltage value during the time T2, the output voltage has a waveform as shown in FIG. Eggplant Therefore, even when the pulse signal is not output from the pulse generation circuit 10, the voltage value output from the detection coil 3 and reproduced by the magnetic flux change detection circuit 11 is held, so that the smoothing circuit 13 is operated. The sensitivity of the output signal does not decrease, the duty ratio of the pulse signal can be reduced, and the exciting current, that is, the power consumption can be reduced.

In the present embodiment, the pulse signal generated by the pulse generation circuit 10 has a constant cycle of T1 + T2, but the pulse signal is not limited to this and, for example, the magnetic field to be measured is measured. When a command to detect magnetism is generated, one or a predetermined number of pulse signals are generated, and the pulse signal is generated until the detection of magnetism based on the pulse signal is completed or another command is generated. You don't have to.

4 to 7 are graphs showing the results of experiments conducted using the magnetic detection circuit according to the present embodiment.
In Fig. 4, the pulse width of the pulse signal is 6μ as a parameter.
S, peak value Ip of exciting current is 450 mA, and power supply voltage is 6 V (± 3 V), 3 to 14 kH
z and the consumption current with respect to the changed frequency of the pulse signal,
3 is a logarithmic graph showing the detection sensitivity when the magnetic flux density of the measured magnetic field is 0.5 gauss. As shown in the figure, the consumption current (in the figure, the unit is mA) increases as the frequency increases, but it is about 10 to 40 mA, that is, 0.02I.
p-0.08 Ip, which is a conventional average excitation current of 0.
It can be seen that the current consumption is remarkably reduced as compared with 7 Ip. In addition, the detection sensitivity hardly depends on the change in frequency, and good results were obtained.

FIG. 5 shows the current consumption with respect to the frequency of the pulse signal when the pulse width, the frequency, the power supply voltage, and the parameters relating to the magnetic flux density of the magnetic field to be measured have the same conditions, and the peak value Ip of the exciting current is 250 mA. 2 is a logarithmic graph showing the detection sensitivity. As shown in the figure, similar to the experimental result shown in FIG. 4, the result that the detection sensitivity hardly depends on the frequency change was obtained. Moreover, the current consumption is further reduced from the experimental result shown in FIG.
An experimental result of about 20 mA is obtained, which shows that the magnetic detection circuit has excellent characteristics as compared with the conventional one.

In FIG. 6, the pulse width of the pulse signal is 6 μS and the peak value Ip of the exciting current is 450 m as parameters.
A, the frequency of the pulse signal is 13.8 kHz, the power supply voltage is 6 V (± 3 V), the current consumption of the entire magnetic detection circuit is 40 m.
6 is a logarithmic graph showing the relationship between the output voltage and the changed magnetic field to be measured when A is set. The solid line and the broken line in the figure show the characteristics of the N pole and the S pole, respectively, when the experiment was performed by reversing the direction (N pole, S pole) of the magnetic field to be measured, and the solid line shows the N pole and the broken line. Indicates the characteristics at the S pole. As shown in the figure, it can be seen that the output voltage from the magnetic detection circuit has excellent linearity with respect to changes in the magnetic field to be measured.

In FIG. 7, the parameters relating to the pulse width and the power supply voltage are the same, and the peak value Ip of the exciting current is 25.
6 is a logarithmic graph showing the relationship of the output voltage with respect to the changed magnetic field under measurement when 0 mA, the frequency of the pulse signal is 3 kHz, and the current consumption of the entire magnetic detection circuit is 8 mA. As shown in the figure, similar to the experimental result shown in FIG. 6, it can be seen that the output voltage from the magnetic detection circuit has characteristics of excellent linearity with respect to changes in the magnetic field to be measured. Also, in this experiment, the current consumption of the entire magnetic detection circuit was set to 8
Although the current is set to mA, the current consumption of the Hall element, which is said to have a particularly low current consumption among general magnetic sensors, is 10 mA.
It is about the same level, and it is clear that it is comparable to the Hall element.

According to the magnetic detection circuit of this embodiment, the pulse generation circuit 10 is provided in place of the oscillation / frequency dividing circuit so that the current flowing to the magnetic sensor is a pulse waveform current.
An excitation circuit such as a charging / discharging circuit is not required, there is no need to use a large-capacity capacitor and resistance element, further downsizing can be achieved, and an IC can be realized, and the production cost can be further reduced. You can

Further, instead of the BPF, a magnetic flux change detection circuit for detecting a change in magnetic flux in the magnetic field to be measured is provided based on the output of the detection coil, and the magnetic flux change detection circuit has a time constant of a predetermined first threshold value or less. By having the integral characteristic and the differential characteristic when the time constant is equal to or more than the predetermined second threshold value, the large-capacity capacitor and resistance element used in the BPF are not required, and it is possible to realize an IC, and the differential characteristic The offset can be removed and the zero point can be secured.
Further, the output of the magnetic flux change detection circuit changes at substantially the same timing as the pulse waveform current generated by the pulse generation circuit, which eliminates the need for a frequency dividing circuit and further reduces the production cost.

A sampling and holding circuit for sampling the output value of the magnetic flux change detection circuit in synchronism with the output timing of the pulse waveform current generated by the pulse generation circuit and holding the value obtained by sampling. By including, even when the duty ratio of the pulse waveform current is reduced, without lowering the detection sensitivity,
Further, the power consumption can be reduced and the versatility can be further enhanced by reducing the duty ratio.

[0050]

According to the magnetic detection circuit of the first invention,
It does not require an oscillation and frequency dividing circuit with a complicated configuration, and does not require an excitation circuit such as a charge and discharge circuit that requires a large volume capacitor and resistance element.
It is possible to realize a magnetic detection circuit that can achieve C conversion.

According to the magnetic detection circuit of the second aspect of the present invention, the large-capacity capacitor and resistance element used in the conventional BPF are not required, which enables miniaturization, that is, IC, and the offset characteristic due to the differential characteristic. It can be removed and the zero point can be secured. Furthermore, since the output of the magnetic flux change detection circuit changes at almost the same timing as the pulse waveform current output from the pulse generation circuit, a frequency divider circuit is not required and a simple circuit A magnetic detection circuit having the configuration can be realized.

According to the magnetic detection circuit of the third aspect of the present invention, even if the duty ratio of the pulse waveform current is reduced, the detection sensitivity does not decrease, and the duty ratio is further reduced to reduce power consumption. It is possible to realize a magnetic detection circuit capable of performing the above.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of a magnetic detection circuit according to the present invention.

FIG. 2 is a circuit diagram showing an example of a magnetic detection circuit shown in FIG.

FIG. 3 shows waveforms of an exciting current, a magnetic flux of a magnetic field to be measured, an output voltage of a detection coil, an output voltage of a magnetic flux change detection circuit, and an output voltage of a sampling hold circuit when an orthogonal fluxgate magnetic sensor is used. It is a figure.

FIG. 4 is a graph showing a result of an experiment performed using the magnetic detection circuit according to the present embodiment.

FIG. 5 is a graph showing a result of an experiment using the magnetic detection circuit according to the present embodiment.

FIG. 6 is a graph showing a result of an experiment using the magnetic detection circuit according to the present embodiment.

FIG. 7 is a graph showing a result of an experiment performed using the magnetic detection circuit according to the present embodiment.

FIG. 8 is a perspective view showing a configuration of a magnetic sensor (magnetic detection element) of an orthogonal fluxgate type element.

FIG. 9 is a block diagram showing a schematic configuration of a conventional magnetic detection circuit that is connected to an inner conductor and an outer conductor to allow a current to flow therethrough, and is also connected to a detection coil to detect the magnetism of a magnetic field to be measured. is there.

10 is a circuit diagram showing an example of the magnetic detection circuit shown in FIG.

11 is a circuit diagram showing an example of the magnetic detection circuit shown in FIG.

FIG. 12 is an excitation current, a degree of magnetization in a detection direction of a core, an output voltage of a detection coil, and full-wave rectification by a rectification / smoothing circuit when magnetism is detected by an orthogonal fluxgate magnetic sensor. It is a wave form diagram of each detection signal.

[Explanation of symbols]

10 pulse generation circuit 11 Magnetic flux change detection circuit 12 Sampling and holding circuit (SH circuit) 13 Smoothing circuit 14 Excitation pulse current generation circuit

Claims (3)

[Claims] 1. A magnetic field for detecting magnetism in the magnetic field to be measured based on the output of the detection coil when the magnetic flux of the magnetic field to be measured is changed by energizing a conductor around which the detection coil is wound. The magnetic detection circuit, wherein the detection circuit includes a pulse generation circuit that generates a pulse waveform current flowing to the conductor. 2. A magnetic flux change detection circuit for detecting a change in magnetic flux in a magnetic field to be measured based on the output of the detection coil, wherein the magnetic flux change detection circuit has an integral characteristic with a time constant equal to or less than a first threshold value. , A second whose time constant is different from the first threshold
A differential characteristic is provided at a threshold value or more.
Magnetic detection circuit according to. 3. A sampling hold for sampling the output value of the magnetic flux change detection circuit in synchronism with the output time point of the pulse waveform current generated by the pulse generation circuit and holding the value obtained by sampling. The magnetic detection circuit according to claim 2, further comprising a circuit.