JP5557181B2 - Synchronous detection circuit, fluxgate sensor, and FM demodulator - Google Patents

Description

  The present invention relates to a synchronous detection circuit using a switched capacitor.

  As a basic configuration of the synchronous detection circuit, there is a configuration using several analog switches and an inverting amplifier. However, since the number of components required for the circuit configuration is large and a smoothing circuit is required, there is a problem in circuit integration. Although a synchronous detection circuit using a switched capacitor is widely known, several analog switches and operational amplifiers are required, so here too, the number of components necessary for the circuit configuration increases, and there is a problem in circuit integration. is there.

  On the other hand, it is possible to configure a synchronous detection circuit with a small number of parts using a high-accuracy balanced modulator, but the high-accuracy balanced modulator is expensive and consumes more power. There is.

  In relation to the above problem, a rectifying / smoothing circuit and a synchronous detector are disclosed. In the rectifying / smoothing circuit disclosed in Patent Document 1, at least one of the first and second switched capacitors that outputs a voltage corresponding to a rectified signal voltage, and a first period in which the rectified signal voltage is equal to or higher than a reference voltage And selecting the output voltage of the first switched capacitor and selecting the output voltage of the second switched capacitor in the second period other than the first period, and the output voltage of the selection means is supplied. It comprises an integrator having a third switched capacitor, and is configured so as to obtain a smoothed signal voltage by rectifying the rectified signal voltage.

  In the synchronous detection circuit shown in Patent Document 2, the single switched capacitor circuit is selectively connected to a positive-phase integrator and a single switched capacitor circuit by switching the supply form of the two-phase clock to the single switched capacitor circuit according to an input signal. It is configured to function as a negative phase integrator.

JP 62-92774 A JP 2005-20434 A

  However, the technique disclosed in Patent Document 1 samples an input signal at an arbitrary timing in a first period and repeatedly executes charging and discharging, and samples the input signal at an arbitrary timing also in a second period. Therefore, since the circuit configuration repeatedly executes charging and discharging, the switched capacitor cannot be charged during the discharging period, and there is a problem that sufficient charges cannot be output. In addition, two control systems, ie, control of the switch in the switched capacitor and control of the switch for selecting the first and second switched capacitors are required, and there is a problem that the configuration becomes complicated.

  Although the technique shown in Patent Document 2 is reduced in size by reducing the number of components of the circuit itself by using a single switched capacitor, it is necessary to generate and supply a two-phase clock. There is a problem that the configuration becomes large. In addition, the virtual grounding of the operational amplifier is required as a constituent element for charging and discharging, and there is a problem that the configuration becomes large.

  Therefore, the present invention has been made to solve the above-mentioned problems, and it is possible to make integration advantageous by reducing the number of parts constituting the circuit and reducing the size while securing a sufficient charge. An object of the present invention is to provide a synchronous detection circuit, a fluxgate sensor, and an FM demodulator that can be used.

  In the synchronous detection circuit using a switched capacitor, the synchronous detection circuit according to the present invention includes an input means for inputting an input signal having a predetermined period, and at least a high level state and a low level state in synchronization with the input signal. Reference signal input means for inputting a reference signal having two different states, a first switched capacitor that charges and discharges charge according to control of the switch, and the first switched capacitor according to control of the switch And a second switched capacitor that performs charge and discharge in a complementary manner, and when the reference signal input by the reference signal input means is at a high level, the first switched capacitor is charged with the charge of the input signal. , Discharging the electric charge charged in the second switched capacitor, and when the reference signal is at a low level, While discharging the electric charge charged in the first switched capacitor, and is characterized in that electric charge of the input signal to said second switched capacitor.

  As described above, the synchronous detection circuit according to the present invention controls charging / discharging using two switched capacitors in accordance with reference signals having two different states of a high level state and a low level state. There is no need for clock generation, virtual grounding of operational amplifiers, etc., and the number of components can be reduced to a simplified configuration, switch control can be simplified, and circuit integration is advantageous. There is an effect that can be. In addition, since the two switched capacitors perform complementary charging and discharging according to the reference signal synchronized with the input signal, it is possible to realize a high-performance synchronous detection circuit by charging the input signal to the maximum extent. There is an effect.

The synchronous detection circuit according to the present invention is characterized in that the input signal and the reference signal are signals generated by the same signal oscillator.
Thus, in the synchronous detection circuit according to the present invention, since the input signal and the reference signal are signals generated by the same signal oscillator, the positive and negative synchronization can be accurately and easily performed by matching the frequencies of the respective signals. There is an effect that it can be performed.

The synchronous detection circuit according to the present invention is characterized by comprising phase adjusting means for adjusting a phase difference between the reference signal and the input signal in accordance with a phase advance of the input signal.
As described above, the synchronous detection circuit according to the present invention adjusts the phase of the reference signal in accordance with the phase advance of the input signal, and thus obtains the maximum output in consideration of the phase advance of the input signal. In addition, by adjusting the phase, it is possible to detect an input signal having a specific phase difference with respect to the reference signal, and it is possible to realize a high-performance synchronous detection circuit.

  The synchronous detection circuit according to the present invention is characterized by comprising charging means for charging the charge discharged from the first switched capacitor and the second switched capacitor charged with the charge of the input signal. is there.

Thus, since the synchronous detection circuit according to the present invention includes the first switched capacitor charged with the charge of the input signal and the charging means for charging the charge discharged from the second switched capacitor, the input signal As a result, it is possible to realize a high-performance synchronous detection circuit by maximally charging the electric charge.
As the charging means, for example, a capacitor, a capacitor via an operational amplifier, a smoothing circuit, or the like can be used.

  The fluxgate sensor according to the present invention includes a sensor head that detects a change in magnetic flux in the fluxgate sensor having the synchronous detection circuit, and an oscillator that supplies an AC excitation current and a DC bias current to the sensor head, An oscillator supplies a reference signal synchronized with the AC excitation current to the synchronous detection circuit.

  As described above, since the fluxgate sensor according to the present invention includes the synchronous detection circuit, the fluxgate sensor can have a simplified small-scale configuration, and the oscillator generates a reference signal synchronized with the AC excitation current. Thus, each signal can be accurately synchronized, and there is an effect that a high-performance fluxgate sensor can be realized.

The fluxgate sensor according to the present invention is characterized in that the phase adjusting means adjusts a phase difference between an induced voltage generated in the sensor head and the reference signal.
Thus, in the fluxgate sensor according to the present invention, the phase adjustment means adjusts the phase difference between the induced voltage generated in the sensor head and the reference signal, so that a maximum output voltage is obtained and high performance is obtained. It is possible to function as a simple sensor.

  The fluxgate sensor according to the present invention is characterized in that the phase adjusting means is a capacitor connected in parallel to an inductance component constituting the sensor head.

  Thus, in the fluxgate sensor according to the present invention, since the phase adjusting means is a capacitor connected in parallel to the inductance component constituting the sensor head, the LC circuit formed by the sensor head and the capacitor, There is an effect that a maximum output voltage can be obtained by performing accurate phase adjustment with a simplified configuration.

  The FM demodulator according to the present invention is the FM demodulator having the synchronous detection circuit, wherein the input signal is an FM modulated signal, and the reference signal is a rectangular wave generated based on a zero cross of the FM modulated signal. It is characterized by.

  As described above, since the FM demodulator according to the present invention includes the synchronous detection circuit, the FM demodulator can have a simplified small-scale configuration, and can also perform FM modulation using a reference signal synchronized with the FM modulation signal. An output voltage that accurately corresponds to the signal can be obtained, and an effect is achieved that a high-performance FM demodulator can be realized.

It is a figure which shows the output signal of a common synchronous detection circuit. 1 is a circuit diagram of a synchronous detection circuit according to a first embodiment. FIG. It is a functional block diagram of the fluxgate sensor which concerns on 2nd Embodiment. It is a circuit diagram of the fluxgate sensor which concerns on 2nd Embodiment. It is a figure which shows the change of the output voltage of the FM demodulator which concerns on 3rd Embodiment. It is a figure which shows the experimental result of the input-output characteristic in the fluxgate sensor of this invention. It is a figure which shows the experimental result of the frequency characteristic in the fluxgate sensor of this invention. It is a figure which shows the experimental result of the resolution measurement in the fluxgate sensor of this invention.

(First embodiment of the present invention)
The synchronous detection circuit according to the present embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram illustrating an output signal of a general synchronous detection circuit, and FIG. 2 is a circuit diagram of the synchronous detection circuit according to the present embodiment.

  As shown in FIG. 1, the synchronous detection generally switches the sign of the input signal by adding a reference signal (rectangular wave) synchronized with the input signal (sine wave), and the product of the value of the input signal and the reference signal. The DC output is represented by the time average of. By shifting the phase of the input signal and the reference signal, the output value changes, and when the phases completely match, the maximum positive output is obtained. If the phase shifts by 90 °, the output is zero. Is obtained. FIG. 1A shows a waveform when the phases of the input signal and the output signal completely match, and FIG. 1B shows the values of the input signal and the reference signal in FIG. The output signal by the time average of the product of is shown.

In FIG. 2, in the synchronous detection circuit 1, input signal lines 2a and 2b, a reference signal line 3, an IC (here, LT1043 is used) 4, and output signal lines 5a and 5b are connected. External capacitors C1 and C2 are connected to the IC 4 to form switched capacitors 7a and 7b, respectively. The output signal lines 5a and 5b are connected to the capacitor C3. The resistor R1 is a resistor for adjusting the time constant, and the resistors R _on connected above and below the capacitors C1 and C2 indicate the on-resistance of the switch.

  The external capacitors C1 and C2 are switching-controlled by the IC 4, and the capacitor C1 is connected to the terminal 10 and the terminal 12 or the terminal 11 and the terminal 13 according to the reference signal. The capacitor C2 is connected to the terminal 14 and the terminal 16 or the terminal 15 and the terminal 17 according to the reference signal. The reference signal is a rectangular wave having two states of a high level state and a low level state based on the zero cross of the input signal, and switching control is performed in a complementary manner in accordance with each state.

  The IC 4 performs synchronous detection by switching the switch according to a rectangular wave reference signal synchronized with the positive and negative of the input signal, and controlling charging and discharging of the capacitors C1 and C2. When the positive / negative of the input signal is synchronized with the positive / negative of the reference signal, when the reference signal is at a high level, the capacitor C1 is connected to the terminal 10 and the terminal 12 by switching, so that the input signal line 2a is connected. The electrode on the capacitor C1 is charged with a positive charge. When the reference signal is at a low level, the capacitor C1 is connected to the terminal 11 and the terminal 13 by switching, so that the charge charged in the capacitor C1 is discharged to the capacitor C3 via the output signal line 5a.

Similarly, when the reference signal is at a low level, the capacitor C2 is connected to the terminals 14 and 16 by switching, so that a positive charge is charged to the electrode below the capacitor C2 via the input signal line 2b. Is done. When the reference signal is at a high level, the capacitor C2 is connected to the terminal 15 and the terminal 17 by switching, so that the charge charged in the capacitor C2 is discharged to the capacitor C3 via the output signal line 5b.

  The value of the DC signal can be obtained by transient phenomenon analysis. When the input signal is sin (ωt + Φ) and Φ is the phase difference between the input signal and the reference signal, the output voltage is a value represented by the following equation (1). It becomes.

上記式（１）から、本実施形態に係る同期検波回路では、

From the above equation (1), in the synchronous detection circuit according to this embodiment,

のときに最大の出力が得られることがわかる。

It can be seen that the maximum output can be obtained at.

  That is, unlike the conventional synchronous detection circuit that obtains the maximum output when the input signal is synchronized with the reference signal, by adjusting the phase difference between the input signal and the reference signal by shifting by the equation (2), The maximum possible output can be obtained.

  When the input signal is a modulated wave, the amplitude of the modulated input signal changes with time, so the charge amount of the capacitor C3 is not constant, and an envelope of the amplitude of the input signal is output. That is, the modulated wave is demodulated and a modulated signal is output.

  Note that the oscillator that oscillates the input signal and the reference signal may be generated by one oscillator or may be generated by different oscillators. In the case of being generated by one oscillator, the origin of each signal is the same, so that it is easy to achieve synchronization.

  Thus, according to the synchronous detection circuit according to the present embodiment, charge / discharge is controlled using two switched capacitors in accordance with reference signals having two different states of a high level state and a low level state. There is no need for two-phase clock generation, virtual grounding of operational amplifiers, etc., and the number of components can be reduced to a simplified configuration, switch control can be simplified, and circuit integration can be simplified. Can be an advantage. In addition, since charge and discharge are complementarily performed by two switched capacitors in accordance with a reference signal synchronized with the input signal, it is possible to realize a high-performance synchronous detection circuit by charging the charge of the input signal to the maximum.

Further, when the input signal and the reference signal are signals generated by the same signal oscillator, the positive and negative synchronization can be accurately and easily performed by matching the frequencies of the respective signals.
Furthermore, since the phase of the reference signal and the input signal is adjusted according to the phase advance of the input signal, the maximum output can be obtained in consideration of the phase advance of the input signal.

(Second embodiment of the present invention)
The fluxgate sensor according to this embodiment will be described with reference to FIGS. 3 and 4. FIG. 3 is a functional block diagram of the fluxgate sensor according to this embodiment, and FIG. 4 is a circuit diagram of the fluxgate sensor according to this embodiment.

  A fluxgate sensor, which is one of magnetic field sensors, is suitable for detecting a magnetic field of about 100 μT to 10 pT, and is used in various fields such as navigation systems for automobiles and airplanes, security, and geological surveys. Fluxgate sensors have a wide range of applications, and the recent main trends are downsizing, cost reduction, and power consumption. An AMR element is an excellent magnetic sensor in terms of small size, low cost, and low power consumption compared to the fluxgate sensor, but it is far from the fluxgate in terms of sensitivity and resolution. In the fluxgate sensor according to the present embodiment, the sensor is reduced in size, cost, and power consumption.

  The synchronous detection circuit that converts the induced voltage to the detection coil into a DC signal is an important functional block of the electronic circuit of the fluxgate sensor. In the present embodiment, a small-sized, low-cost, low-power-consumption fluxgate sensor is realized by using the synchronous detection circuit in the first embodiment.

  In FIG. 3, the fluxgate sensor 30 according to the first embodiment that detects an input signal and a reference signal, an oscillator 31 that detects a magnetic field, a sensor head 32 that detects a magnetic field, and a signal that the sensor head 32 detects synchronously. And a synchronous detection circuit 1. The sensor head 32 is composed of a stable magnetic wire having a high permeability and a detection coil having a large number of turns (see, for example, JP-A-2005-315812). The magnetic wire is magnetized by applying an external magnetic field, and an induction voltage is generated in the detection coil by changing the magnetization of the magnetic wire with an alternating current. The fluxgate sensor shown in FIG. 3 is a fundamental wave type orthogonal fluxgate sensor. By applying a DC bias current to an AC excitation current having a frequency of fHz, a voltage of fHz is induced in the detection coil by applying an external magnetic field. The induced voltage is detected by being converted into direct current by the synchronous detection circuit. These processes can be performed without using a double frequency generation circuit required for a normal fluxgate sensor.

  In the circuit diagram of FIG. 4, an AC excitation current is passed through the sensor head 32 by an oscillator 31 using a COMS Hex inverter, and a DC bias current is passed by a DC power supply 42. A reference signal synchronized with the AC excitation current is supplied from the oscillator 31 to the synchronous detection circuit 1. The sensor head 32 and the oscillator 31 are connected via a capacitor 41 in order to prevent a direct current from flowing from the sensor head 32 side to the oscillator 31 side.

  The phase between the induced voltage generated in the pickup coil of the sensor head 32 and the reference signal is deviated due to the advance of the capacitor. A capacitor 43 is connected in parallel on the secondary side of the sensor head 32 as an adjustment means for adjusting the phase shift. The capacitor 43 may be connected in series. The phase is adjusted based on the resonance frequency of the pickup coil and the capacitor 43. If the frequency is higher than the resonance frequency, the phase is adjusted using the advanced phase and the phase lower than the resonance frequency is a delayed phase. To do. Further, the capacitor 43 has a function of adjusting the phase as described above and reducing noise by removing harmonics.

The voltage induced by the sensor head 32 is amplified by the inverting amplifier 44. The amplified signal is rectified by the synchronous detection circuit 1 using a switched capacitor, and the output is taken out by the low-pass filter 45.
Instead of providing the low-pass filter 45, a resistor R2 may be provided between the IC 4 and the capacitor C2.

  The characteristics of the circuit shown in FIG. 4 will be described. Gained frequency characteristics can be obtained by circuit analysis. When the external magnetic field is alternating current, the induced voltage of the pickup coil becomes a modulated wave, so that the modulated wave signal is E, and the charge amounts of the capacitors C1, C2, and C3 in FIG. 4 are q1, q2, and q3, respectively. The differential equation of the following formula (3) is obtained by the state averaging method.

式（３）から、図４の回路の特性方程式を求めると、以下の式（４）となる。

When the characteristic equation of the circuit of FIG. 4 is obtained from the equation (3), the following equation (4) is obtained.

  As described above, according to the fluxgate sensor according to the present embodiment, since the synchronous detection circuit according to the first embodiment is included, a simplified small-scale configuration can be achieved, and the oscillator can be connected to an AC excitation current. By generating a reference signal in synchronization with each other, each signal can be accurately synchronized. Further, since the phase adjusting means adjusts the phase difference between the induced voltage generated in the sensor head and the reference signal, it is possible to obtain the maximum output voltage and to function as a high-performance sensor. Further, since the phase adjusting means is a capacitor connected in parallel with the inductance component constituting the sensor head, the LC circuit formed by the sensor head and the capacitor performs accurate phase adjustment with a simplified configuration. Thus, the maximum output voltage can be obtained.

(Third embodiment of the present invention)
The synchronous detection circuit 1 according to the first embodiment can be applied to an FM demodulator. In this case, the input signal is an FM modulated signal. In the relationship between the frequency and the output voltage, when the frequency of the FM modulated wave changes within the frequency range (proportional relationship, and the voltage change region) until the output voltage reaches a constant value from 0, the frequency The output voltage changes according to the change. That is, the FM modulation signal can be demodulated based on the output voltage.

FIG. 5 is a diagram showing a change in the output voltage of the FM demodulator according to the present embodiment. In FIG. 4, for example, resistance R1 = 500Ω, R _on = 300Ω, and C1 = C2 = C3 = 0.01 μF. Then, as shown in the figure, the voltage change region is 0 Hz to 2000 Hz, and it is desirable to perform the synchronous detection around the center value of 1000 Hz.

  As described above, according to the FM demodulator according to the present embodiment, the configuration including the synchronous detection circuit 1 can be achieved, so that a simplified small-scale configuration can be achieved, and a reference signal synchronized with the FM modulation signal can be obtained. By using this, an output voltage that accurately corresponds to the FM modulation signal can be obtained, and a high-performance FM demodulator can be realized.

  Although the present invention has been described with the above embodiments, the technical scope of the present invention is not limited to the scope described in the embodiments, and various modifications or improvements can be added to these embodiments. . And embodiment which added such a change or improvement is also contained in the technical scope of the present invention. This is apparent from the claims and the means for solving the problems.

The experimental result using the fluxgate sensor which concerns on the said 2nd Embodiment is shown.
(Condition) A sensor head having a core formed by bending an amorphous wire into a U shape and having the structure shown in Table 1 was used. Further, an oscillator having the driving conditions shown in Table 2 below was used.

The values of each element were R1 = 1 kΩ, R2 = 10 kΩ, C1 = C2 = C3 = 10 nF, and the amplification factor of the amplifier was 7.5 times.
(Input / output characteristics) Using a Helmholtz coil, a triangular wave current of 60 mHz was applied, the output of the sensor and the applied magnetic field were measured simultaneously with an oscilloscope, and the data was plotted in XY. The results are shown in FIG. The input / output characteristics showed almost linearity, and the sensitivity was 1.11 V / G.

  (Frequency characteristics) Using a Helmholtz coil, a sinusoidal current at 1 Hz to 10 kHz was applied, the amplitude of the output waveform was measured with an oscilloscope, and frequency and gain data were plotted. FIG. 7 shows a theoretical value and a measurement result according to the equation (4). The measured value showed a value following the theoretical value up to around 4 kHz.

  (Measurement of resolution) In order to measure the noise of the sensor, the sensor head was placed in a permalloy five-layer cylindrical shield so that the direction of the sensor head coincided with the radial direction of the cylinder. An FFT analyzer (Stanford Research Systems SR780) was used for noise spectrum measurement. Using a Blackman-Harris (BMH) window, the RMS value is averaged eight times. The band frequency was set to 100 Hz, the number of lines was set to 100, and a value of 1 / √Hz was measured. Measurement was performed by connecting an amplifier having a gain of 30 times to the output of the circuit of FIG. When the input conversion noise of the circuit of FIG. 4 is Vno1, the input conversion noise when the amplifier is connected to the circuit of FIG. 4 is Vno2, and the input conversion noise of only the amplifier is Vno3, Vno1 is expressed by the following equation (5). .

  FIG. 8 shows the result of input conversion of the circuit of FIG. 4 obtained by FFT analyzer data and Equation (5). The resolution was 327 pT / √Hz from the average value of 10 Hz to 100 Hz in FIG.

  (Measurement of power consumption) A multimeter was sandwiched between the plus terminal and minus terminal of the DC power supply and the circuit, the current supplied from the DC power supply was measured, and the power consumption of the entire circuit was obtained. Table 3 shows the measurement results. The reason why the supply current from the minus terminal is larger than the supply current from the plus terminal is that the DC bias current is supplied from the minus terminal to the amorphous wire. The overall power consumption was 99 mW, indicating that the power consumption was low.

  From the above, the fluxgate sensor according to the present invention uses only three ICs including the CMOS Hex inverter and the operational amplifier, including the LT1043, and can realize downsizing with few parts, and the power consumption of the entire sensor. Was reduced to 99 mW. As for the resolution, a result of 327 pT / √Hz was obtained, but a value capable of sufficiently functioning as a product could be obtained. This value can be further refined and improved.

  In addition, it is known from a separate experiment that there is a trade-off relationship between resolution and power consumption, and sensitivity and power consumption. That is, it is possible to properly use the sensor according to the intended use.

1 Synchronous detection circuit 2a, 2b Input signal line 3 Reference signal line 4 IC
5a, 5b Output signal line 10-17 Terminal 30 Flux gate sensor 31 Oscillator 32 Sensor head 41 LC resonator 42 DC power supply 43 Capacitor 44 Inverting amplifier 45 Low pass filter

Claims (8)

In a synchronous detection circuit using a switched capacitor,
Input means for inputting an input signal having a predetermined period;
Reference signal input means for inputting a reference signal having at least two different states of a high level state and a low level state in synchronization with the input signal;
According to the control of the switch, the first electrode which is one electrode is switched between the terminal on the input means side and the terminal on the discharge destination side, and the second electrode which is the other electrode is switched between the ground. A first switched capacitor for charging and discharging electric charges;
In accordance with the control of the switch, a charge / discharge operation complementary to the first switched capacitor is performed, and the third electrode as one electrode is switched between the terminal on the input means side and the ground, and the other The fourth electrode is grounded when the third electrode is connected to the terminal on the input means side, and is connected to the terminal on the discharge destination side when the third electrode is grounded. A second switched capacitor that performs charging and discharging by switching to
When the reference signal input by the reference signal input means is at a high level, the first electrode of the first switched capacitor is connected to a terminal on the input means side, and the second electrode is grounded, so that the input signal and electric charge, to discharge the charges said third electrode of said second switched capacitor is charged to the second switched capacitor and the fourth electrode is connected to the terminals of the discharge destination side is grounded ,
When the reference signal is at a low level, the first electrode of the first switched capacitor is connected to the terminal on the discharge destination side, and the second electrode is grounded to charge the first switched capacitor discharges, the synchronous detection circuit, wherein the fourth electrode is characterized in that electric charge of the input signal is grounded second of said third electrode of the switched capacitor connected to the input means of terminals.
In the synchronous detection circuit according to claim 1,
The synchronous detection circuit, wherein the input signal and the reference signal are signals generated by the same signal oscillator. In the synchronous detection circuit according to claim 1 or 2,
A synchronous detection circuit comprising phase adjusting means for adjusting a phase difference between the reference signal and the input signal according to a phase advance of the input signal. In the synchronous detection circuit according to any one of claims 1 to 3,
A synchronous detection circuit comprising: charging means for charging the first switched capacitor charged with the charge of the input signal and the charge discharged from the second switched capacitor. In the fluxgate sensor having the synchronous detection circuit according to any one of claims 1 to 4,
A sensor head for detecting magnetic flux changes;
An oscillator for supplying an AC excitation current and a DC bias current to the sensor head;
The flux gate sensor, wherein the oscillator supplies a reference signal synchronized with the AC excitation current to the synchronous detection circuit. The fluxgate sensor according to claim 5, wherein
The flux gate sensor, wherein the phase adjusting means adjusts a phase difference between an induced voltage generated in the sensor head and the reference signal. The fluxgate sensor according to claim 6, wherein
The flux gate sensor, wherein the phase adjusting means is a capacitor connected to an inductance component constituting the sensor head. The FM demodulator having the synchronous detection circuit according to any one of claims 1 to 4,
The FM demodulator characterized in that the input signal is an FM modulated signal and the reference signal is a rectangular wave generated based on a zero cross of the FM modulated signal.

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