JP2008011057A - Antenna circuit and clock - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the accuracy of sideband detection by reducing the noise from a high-frequency signal generator, using a relatively simple circuit configuration. <P>SOLUTION: An antenna circuit 42 is provided with an MI magnetic sensor Z1 having electrical characteristics that vary with the change of magnetic field; a high-frequency signal generator S1 for applying a high-frequency signal to the MI magnetic sensor Z1; an inverter 92 for obtaining an inverted signal, by inverting the high-frequency signal; an adder for adding the inverted signal to a receiving signal, obtained from the MI magnetic sensor Z1 and the high-frequency signal generator S1, thereby reducing the high-frequency signal; and detector means D1, D2 for detecting the receiving signal, of which the high-frequency signal has been reduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an antenna circuit using a magnetic sensor and a timepiece including the antenna circuit.

  In recent years, a technique for forming an antenna using a magnetic sensor using a magneto-impedance effect element (MI element) has been proposed (for example, Patent Document 1). As described in Patent Document 1, when a minute high-frequency current is applied to a soft magnetic material formed in a wire shape or a ribbon shape, an output voltage due to impedance is generated at both ends of the soft magnetic material. The magneto-impedance effect refers to an effect that when an external magnetic field is applied to a soft magnetic material that is energized with a minute high-frequency current, the impedance of the soft magnetic material changes sensitively and the output voltage across the soft magnetic material changes.

  FIG. 18 shows an example of an antenna circuit configured to detect magnetism using a magnetic sensor using an MI element (hereinafter referred to as “MI magnetic sensor”), and a filter circuit following the antenna circuit. FIG. S1 is a high-frequency signal generator, R1 is a resistor, C1 is a capacitor, and Z1 is an MI magnetic sensor. In the magnetic detection circuit of FIG. 18, the high frequency signal from the high frequency signal generator S1 is divided by the resistor R1 and the MI magnetic sensor Z1, and is output through the capacitor C1. Here, when an alternating magnetic field as indicated by a broken arrow is applied to the MI magnetic sensor Z1, the signal of the high-frequency signal generator S1 is represented by the relationship between the magnetic field and impedance of the MI magnetic sensor Z1 as shown in FIG. Are divided to show a change in magnetic impedance due to an alternating magnetic field. Here, since the magnetic field changes positively or negatively, the output of the even function is a form in which the sine wave is folded back from the center, and a frequency component twice the change frequency is output.

  Further, when a fixed magnetic field (see reference numeral 1901) as shown in FIG. 19B is applied, a change in the external magnetic field is output at the center of the magnetic field. That is, in FIG. 19B, the line is almost linear in the vicinity of the fixed magnetic field, and changes in resistance according to the external magnetic field. That is, since the folding as described above does not occur, the magnetoresistance change occurs at the same frequency.

  In the antenna circuit of FIG. 18, the signal generated at point a is Asin ωt from S1, and the voltage at point a by the magnetic sensor subjected to the magnetic field change is Va = Asin ωt · Z1 / (R1 + Z1).

  Since the impedance of the MI magnetic sensor Z1 changes due to a change in the magnetic field, when Z1 = Z (1 + Bsinpt), Va is rewritten as follows from B << 1.

Va = Asinωt · Z1 (R1 + Z1)
= Asinωt · Z (1 + Bsinpt) / (R1 + Z (1 + Bsinpt))
≈ Asinωt · Z (1 + Bsinpt) / (R1 + Z) (1)
Equation (1) has the same format as amplitude modulation (AM) and indicates that the signal of the high-frequency signal generator S1 is subjected to amplitude modulation by the magnetic field frequency. On the other hand, the signal from the high-frequency signal generator S1 is a high-frequency signal for causing the skin effect of the magnetic sensor, and the impedance change of the magnetic sensor is in a state of modulating the signal from the high-frequency signal generator S1. As shown in FIG. 20A, the signal from the high-frequency signal generator S1 is changed as indicated by reference numeral 2002 due to the magnetic field change (see reference numeral 2000). Therefore, a waveform as shown in FIG. 10A is propagated from the point a or the capacitor C1. Therefore, the magnetic field change can be received by adopting a configuration in which this waveform is received by a circuit equivalent to the AM receiver. Here, since the changed signal is amplitude-modulated, sidebands 2011 and 2012 are generated with respect to the carrier signal 2010 as shown in FIG. Since the sideband fluctuates due to a magnetic change, it may be detected. However, as shown in the equation (1), since the value of B is sufficiently small (about several percent), the sideband is Remarkably small.
JP 2000-188558 A

Consider the reception sensitivity. For example, if the reception sensitivity of a general radio timepiece is 40 dBμ / m, the sensitivity is converted to a sensitivity of 10 ⁻⁸ (0e) (where 1 (0e) ≈79.6 A / m). In terms of vacuum permeability, 1 (0e) ≈1G can be considered, so that it is necessary to receive 10 ⁻⁸ G in order to be used for a radio timepiece.

However, the sensitivity of the current MI sensor is about 50 mV / G in the case of a normal sensor shape, and even if 1 μV signal detection is possible, the magnetic field detection is 1 / (5 * 10 ⁴ ). That is, while it is necessary to be able to receive 10 ⁻⁸ G, only about 2 * 10 ⁻⁵ G can be received. Therefore, for example, the sensitivity is insufficient for use in a radio timepiece.

In order to improve the sensitivity, the following means can be considered.
(1) The influence of the demagnetizing field is reduced by devising the shape of the MI sensor itself.
(2) Improve sideband detection accuracy.

  An object of the present invention is to provide a receiving device that can extract a desired signal from a received radio wave and a timepiece including the receiving device by improving the detection accuracy of sidebands.

For example, it is assumed that the C / N of the received signal (40 KHz) is 140 dB with respect to the 20 MHz signal from the high frequency signal generator S1, and the signal from S1 is applied to the resistor R1 at 3 Vrms. The impedance on the S1 side at the point (point a) between the resistor R1 and the MI magnetic sensor Z1 is preferably large in order to reduce power consumption. Therefore, considering R1 = Z1 = 1 MΩ, the noise from the high-frequency signal generator S1 is 0.949 μVrms. The impedance on the S1 side is 500 kΩ, and the thermal noise amount Vn is 10 Hz for the band B and 300 for the absolute temperature T.
Vn = 20 log√ (4 kBTR) = − 77.8 dBμ + 10 log (BR)
= -77.8 + 67.0 = -10.8 dBμ = 0, 29 μVrms
The total noise amount is 0.99 μVrms, and it can be seen that the applied signal noise is dominant.

  In order to reduce the thermal noise amount, it is known to take signal correlation. Therefore, instead of the envelope detection circuit using the diodes D1 and D2 shown in FIG. 18, a synchronous detection is performed using a phase comparator 81, a low-pass filter 82, an oscillator 83, and a mixer (mixer) 84 as shown in FIG. May be performed. However, the conventional synchronous detection as shown in FIG. 21 has a problem that it is difficult to achieve synchronization by the phase comparator 81 and the oscillator 83 due to the influence of noise under a weak electric field.

  The present invention provides an antenna circuit with improved sideband detection accuracy by reducing noise from a high-frequency signal generator with a relatively simple circuit configuration, and a watch equipped with the antenna circuit. Objective.

  An object of the present invention is to provide a magnetic field detecting means whose electrical characteristics change according to a change in a magnetic field, a high frequency signal generating means for applying a high frequency signal to the magnetic field detecting means, and the magnetic field detecting means and the high frequency signal generating means. It is achieved by an antenna device comprising: a signal reducing means for reducing at least a part of the high-frequency signal from the obtained received signal; and a detecting means for detecting the received signal with the reduced high-frequency signal. The

  According to the present invention, by canceling a high-frequency signal that is a carrier component included in a received signal by its inverted signal, the carrier component of the received signal can be reduced, and noise accompanying the carrier component can also be reduced. As a result, the sideband detection accuracy can be improved.

  In a preferred embodiment, the signal reducing means adds an inverter that inverts the high-frequency signal or the level-adjusted high-frequency signal, an adder that adds the received signal and the inverted high-frequency signal from the inverter. And having.

  In another preferred embodiment, the signal reducing means includes a differential amplifier that receives the received signal and the high-frequency signal or the level-adjusted high-frequency signal and outputs a difference between them. In the above embodiment, the carrier component is canceled using the differential amplifier.

  In a preferred embodiment, the detection means includes a synchronous detection circuit that receives a high-frequency signal or a high-frequency signal whose level is adjusted, and performs synchronous detection based on the received signal.

  In a preferred embodiment, the detection means includes a rectangular wave generation means for receiving a high-frequency signal or a level-adjusted high-frequency signal and generating a rectangular wave from the signal, and synchronous detection is realized by the rectangular wave. .

  In another preferred embodiment, the rising and falling detection means for detecting the rising and falling edges of the high-frequency signal and outputting the rising pulse and the falling pulse respectively indicating the rising and falling edges, and based on the falling pulse And clamping means for clamping the output of the differential amplifier to a predetermined reference voltage, and sampling and holding means for sampling and holding the clamped signal based on the falling pulse.

Another object of the present invention is to provide a magnetic field detecting means whose electrical characteristics change according to a change in the magnetic field,
A high-frequency signal generating means for applying a high-frequency signal to the magnetic field detecting means; and a detecting means for detecting a reception signal obtained by the magnetic field detecting means and the high-frequency signal generating means, wherein the detecting means is a high-frequency signal or level. This is achieved by an antenna device characterized by having a synchronous detection circuit that receives the adjusted high-frequency signal and performs synchronous detection based on the received signal.

  According to the present invention, the received signal can be synchronously detected using the high-frequency signal used for detecting the magnetic field.

  In a preferred embodiment, the detection means includes a rectangular wave generation means for receiving a high-frequency signal or a level-adjusted high-frequency signal and generating a rectangular wave from the signal, and synchronous detection is realized by the rectangular wave. .

In another embodiment, the antenna device includes: a magnetic field detection unit that changes electrical characteristics in response to a change in a magnetic field; a high-frequency signal generation unit that applies a high-frequency signal to the magnetic field detection unit;
Detection means for detecting a reception signal obtained by the magnetic field detection means and the high-frequency signal generation means, and the detection means accepts the reception signal and generates a rectangular wave from the signal; And a synchronous detection circuit for performing synchronous detection with the rectangular wave.

  In this embodiment, a synchronous signal component is extracted from a received signal, that is, a modulated signal, and synchronous detection is realized using the synchronous signal.

  Another object of the present invention is to detect the above-described antenna device, amplification means for amplifying a signal corresponding to a standard radio wave including time information obtained by the antenna device, and a signal output from the amplification means. Detecting means for outputting the demodulated signal, time information extracting means for extracting time information from the demodulated signal, time measuring means for measuring time, and time for displaying the time measured by the time measuring means It is also achieved by a timepiece characterized by comprising: a display means; and a time correction means for correcting the time measured by the time measurement means based on the time information extracted by the time information extraction means.

  According to the present invention, in the present invention, an antenna circuit with improved sideband detection accuracy by reducing noise from a high-frequency signal generator with a relatively simple circuit configuration and the antenna circuit are mounted. A clock can be provided.

[Watches]
Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 and 2 are a front view of a wristwatch including a receiving circuit according to an embodiment of the present invention, and a cross-sectional view taken along line AA ′ of FIG. 1 (a cross-sectional view at 12 o'clock to 6 o'clock), respectively. The wristwatch 1 includes a watch case 10 that houses a watch module and the like. A watch band 16 for the user to wear the wristwatch 1 on his / her wrist is attached to the outer peripheral portion of the watch case 10 at 6 o'clock and 12 o'clock. A switch 11 for executing various functions of the wristwatch 1 is provided.

  The watch case 10 is formed in an annular short column shape from a metal such as stainless steel or titanium. In addition, an extension part for attaching the watch band 16 is formed on the side part of each position of the watch case 10 at 6 o'clock and 12 o'clock, and the watch band 16 is attached to this extension part. A hole for passing a pin is formed.

  A watch glass 12 is fitted on the upper end portion of the watch case 10 via a seal member 13 so as to close the upper end portion, and a back cover is provided on the lower end portion of the watch case 10 so as to close the lower end portion. A (back) 14 is attached via an O-ring 15. The back cover 14 is formed in a substantially flat shape with a small thickness using a strong metal such as stainless steel or titanium.

  Inside the watch case 10, an upper housing 21 and a lower housing 22 are arranged with their peripheral portions attached to an inner frame provided on the inner peripheral surface of the watch case 10.

  A printed wiring board 30 made of a predetermined resin is disposed on the upper surface of the upper housing 21, and a dial 23 is further disposed on the upper surface, and a ring-shaped parting plate 24 is disposed on the upper surface of the dial 23. Are arranged in contact with the peripheral edge of the watch glass 12. A liquid crystal display panel 25 for displaying time and the like is supported by the upper housing 21 below an opening 23 a formed at a position near 6 o'clock on the dial 23. That is, when the wristwatch 1 is viewed from the front, the time displayed on the liquid crystal display panel 25 through the watch glass 12 can be visually recognized.

  Further, on the upper surface of the dial 23, twelve time letters 23b formed in a substantially rectangular shape in plan view are provided at equal intervals in the circumferential direction, and these time letters 23b are from 1 o'clock to 12 o'clock. It corresponds to each time. In the present embodiment, among these time characters 23b, an MI magnetic sensor 40 using a magnetoresistive effect element whose magnetic resistance changes according to an external magnetic field is formed in the time character 23b corresponding to 12:00. . The MI magnetic sensor 40 functions as an antenna that receives standard radio waves. The MI magnetic sensor 40 is made of a magnetic material patterned on the upper surface of the printed wiring board 30, and the upper surface of the MI magnetic sensor 40 is exposed from an opening formed at a corresponding position on the dial 23.

  In addition, the upper housing 21 includes an analog pointer mechanism 26 disposed in the vicinity of the center of the watch case 10. The analog pointer mechanism 26 includes a pointer shaft extending upward from a shaft hole formed in the central portion of the dial 23, and a pointer 26a such as an hour hand and a minute hand attached to the pointer shaft. Move the needle over the top.

  A battery 27 is incorporated in the lower housing 22. Further, between the upper housing 21 and the lower housing 22, an analog pointer mechanism 26 and a circuit board 28 connected to the antenna circuit 42 are disposed.

Various circuit elements are arranged on the circuit board 28. The circuit elements include a control IC such as a CPU, an oscillation circuit, a clock circuit that clocks the current time, an antenna circuit (in the antenna circuit, only the MI magnetic sensor 40 is formed in the time character 23b), an antenna circuit And a receiving circuit for amplifying and detecting the output signal of the antenna circuit to extract a time code signal included in the standard radio wave. The control IC corrects the current time by the clock circuit based on the time code in the signal extracted by the receiving circuit, and causes the liquid crystal display panel 25 to display the corrected current time. Alternatively, the analog pointer mechanism 26 is controlled to move the pointer 26a so as to indicate the current time.
[Circuit configuration]
FIG. 3 is a block diagram showing the internal configuration of the circuit of the wristwatch 1 according to the present embodiment. As shown in FIG. 3, the wristwatch 1 includes a CPU 50, an input unit 51, a display unit 52, a ROM 53, a RAM 54, a receiving circuit 44, a time measuring circuit unit 55, and an oscillation circuit unit 56.

  The CPU 50 reads out a program stored in the ROM 53 at a predetermined timing or in response to an operation signal input from the input unit 200, expands the program in the RAM 54, and based on the program to each unit constituting the wristwatch 1 Instructions and data transfer are executed. Specifically, for example, the reception circuit 44 is controlled every predetermined time so that the standard radio wave is received, and the current time data measured by the timing circuit unit 55 is corrected based on the time code signal from the reception circuit 44. Processing, processing for transferring the current time measured by the timing circuit unit 55 to the display unit 52, and the like are executed.

  The input unit 51 includes a switch 11 for instructing execution of various functions of the wristwatch 1, and outputs a corresponding operation signal to the CPU 50 when the switch 11 is operated. The display unit 52 includes the analog pointer mechanism 26 and the liquid crystal panel 25 controlled by the dial plate 23 and the CPU 50, and displays the current time measured by the time measuring circuit unit 55. The ROM 53 stores the system program, application program, data, etc. for operating the wristwatch 1 and realizing a predetermined function. The RAM 54 is used as a work area for the CPU 50, and temporarily stores programs and data read from the ROM 53, data processed by the CPU 50, and the like.

  As will be described in detail later, the receiving circuit 44 includes an antenna circuit 42, extracts a signal of a predetermined frequency from the signal received by the antenna circuit 42, and outputs the extracted signal to the CPU 50. The clock circuit unit 55 counts the signal input from the oscillation circuit unit 56, clocks the current time, and outputs the current time data to the CPU 50. The oscillation circuit unit 56 always outputs a clock signal having a constant frequency.

  FIG. 4 is a block diagram showing an outline of the receiving circuit 44. As illustrated in FIG. 4, the reception circuit 44 includes an antenna circuit 42, a filter circuit 70, an amplifier circuit 80, a bandpass filter (BPF) 90, and a detection circuit 100. The filter circuit 70 is illustratively a low-pass filter (see, for example, FIG. 5), but is not limited to this, and a band-pass filter (BPF) may be used.

  As will be described with reference to FIG. 5, the antenna circuit 42 includes a high-frequency signal generator S1, a resistor R1, an MI magnetic sensor Z1 (indicated by reference numeral 40 in FIG. 1), a capacitor C1, and diodes D1 and D2. including.

As described above, a signal corresponding to the standard radio wave is output from the antenna circuit 42, and is supplied to the detection circuit 100 through the filter circuit 70, the amplifier circuit 80, and the BPF 90. The detection circuit 100 demodulates a standard radio wave signal. The demodulated signal is given to the CPU 50, where it is decoded and the time information is extracted.
[First Embodiment]
Hereinafter, the antenna circuit according to the present embodiment will be described in more detail. FIG. 5 is a diagram illustrating the antenna circuit and the LPF subsequent to the antenna circuit according to the first embodiment of the present invention. As shown in FIG. 5, the antenna circuit 42 according to the first embodiment includes a high-frequency signal generator S1, a resistor R1, capacitors C1, C3, an MI magnetic sensor Z1, and the antenna circuit shown in FIG. , Diodes D1 and D2.

  The high frequency signal generator S1 generates a 20 MHz signal, for example. The high frequency signal generator S1 is connected to one end of the resistor R1. The other end of the resistor R1 is connected to one end of each of the MI magnetic sensor Z1 and the capacitor C1. The diodes D1 and D2 function as an envelope detection circuit.

  In the present embodiment, the antenna circuit 42 further receives a high frequency signal from the high frequency signal generator S1, inverts the input high frequency signal, and outputs an inverted signal, and the other end of the capacitor C1. And the envelope detection circuit, one input is connected to the other end of the capacitor C1, the other input is connected to the output of the inverter 92, and the output is connected to the clamping capacitor C3. And an adder 94 configured to be fed to the envelope detection circuit. The filter circuit 70 following the antenna circuit 42 is the same as that shown in FIG.

  The operation of the antenna circuit 42 thus configured will be described. As described above, the voltage Va at the point a of the antenna circuit 42 can be expressed as follows.

Va≈Asinωt · Z (1 + Bsinpt) / (R1 + Z) (1)
(Asinωt: signal of the high-frequency signal generator S1, Z (1 + Bsinpt): signal of the MI magnetic sensor Z1)
As shown in equation (1), the modulation signal has the same format as amplitude modulation (AM), and indicates that the signal of S1 is subjected to amplitude modulation by the magnetic field frequency. Accordingly, as shown in FIG. 6A, sidebands 602 and 603 due to magnetic field reception appear on both sides of the carrier signal 601 by the high-frequency signal generator S1. In FIG. 6A, reference numeral 600 denotes a standard radio wave reception signal. Since the applied signal noise (see reference numeral 604) is included in the carrier signal, it becomes difficult to detect the sideband due to the influence of this noise. Therefore, in the present embodiment, the carrier signal level is reduced as shown in FIG. 6B by adding the inverted signal of the carrier signal from the high frequency generator S1 to the modulation signal (FIG. 6B). b)). As the carrier signal level decreases, the noise component also decreases (see reference numeral 614). As a result, sideband detection becomes easy.

  It is desirable that the level of the inverted signal is determined so that the level of the carrier signal after the inverted signal is added is greater than twice the level of the sideband. Thereby, the modulation signal after the addition of the inverted signal is not over-modulated, and can be detected by the envelope detection circuit as shown in FIG.

According to the present embodiment, the MI magnetic sensor is driven by a high-frequency signal to generate a modulation signal corresponding to the change in the magnetic field, and the inverted signal obtained by inverting the high-frequency signal is synthesized with the modulation signal. Cancel the carrier signal, that is, the high-frequency signal. As a result, high-purity sidebands can be extracted, and the antenna circuit can be highly sensitive.
[Second Embodiment]
Next, a second embodiment of the present invention will be described. FIG. 7 is a diagram illustrating an antenna circuit according to a second embodiment of the present invention. Similar to the first embodiment, the antenna circuit 42 includes a high-frequency signal generator S1, a resistor R1, a capacitor C1, and an MI magnetic sensor Z1. Similarly to the first embodiment, the antenna circuit 42 according to the second embodiment includes an inverter 102 that inverts a high-frequency signal from the high-frequency signal generator S1 and outputs an inverted signal, An adder 104 having an input connected to the other end of the capacitor C1 and the other input connected to the output of the inverter 102 is provided. In the second embodiment, a mixer (mixer) 60 is provided in which one input is connected to the output of the adder 104 and the other input is connected to the output of the high-frequency generator S1. .

  Also in the antenna circuit 42 according to the second embodiment, since the inverted signal of the high frequency signal generator S1 is added to the modulation signal, the level of the carrier signal decreases. Here, particularly in the case where the level of the carrier signal in the adder 104 may be less than twice the level of the sideband, a mixer 60 is provided instead of the envelope detection circuit, Synchronous detection may be performed by multiplying the inverted signal.

  In the present invention, the high frequency signal output from the high frequency signal generator S1 is the carrier signal. Therefore, synchronous detection is realized by supplying the signal from the high-frequency signal generator S1 to the mixer 60 as it is (in the same phase). Of course, as in the first embodiment, since the level of the carrier signal can be reduced, the noise component is also reduced. Therefore, the sideband detection is facilitated.

According to the second embodiment, the modulation signal can be detected and the sidebands can be extracted regardless of the decrease level of the carrier signal, and the antenna circuit can be highly sensitive.
[Third Embodiment]
In the first embodiment and the second embodiment, an inverted signal of the carrier signal is given to cancel the carrier signal. In the third embodiment, a carrier signal is canceled using a differential amplifier. FIG. 8 is a diagram illustrating an antenna circuit according to the third embodiment.

  The antenna circuit 42 according to the third embodiment includes a high-frequency signal generator S1, a resistor R1, a capacitor C1, and an MI magnetic sensor Z1. In the third embodiment, the signal line output from the high-frequency signal generator S1 is connected to the resistor R3, and the resistor R3 is connected to the resistor R4.

  The signal line output from the capacitor C1 is connected to the + (plus) input of the differential amplifier 114, and the signal line extending from between the resistors R3 and R4 is − (minus) of the differential amplifier 114. ) Connected to the input. The signal line output from the differential amplifier 114 is connected to one input of the mixer 60, and the signal line extending from between the resistors R 3 and R 4 is also connected to the other input of the mixer 60.

  In the present embodiment, the impedance setting is not limited to this, but it is desirable that R1 = R3 = R4 = Z1. By setting in this way, the carrier component of the modulation signal applied to the + input of the differential amplifier 114 is canceled by the level-adjusted high frequency signal applied to the − input of the differential amplifier 114. That is, in the absence of a magnetic field, the signal applied to the + input of the differential amplifier 114 is almost canceled by the signal applied to the − input of the differential amplifier 114. Therefore, the signal output from the differential amplifier 114 is overmodulated, but the sideband can be extracted by using synchronous detection.

According to the third embodiment, in the differential amplifier, the sideband is extracted by removing the carrier component from the modulated signal and synchronously detecting the modulated signal from which a substantial part of the carrier component is removed. This makes it possible to increase the sensitivity of the antenna circuit.
[Fourth Embodiment]
As shown in FIG. 9, in the fourth embodiment, as in the antenna circuit shown in the third embodiment, a signal passing through a signal line from between the resistor R3 and the resistor R4 is sent to the mixer 60. Instead of applying, a pulse signal (rectangular wave) is applied via the comparator 126. Also in the antenna circuit according to the fourth embodiment, it is desirable that R1 = R3 = R4 = Z1 as in the third embodiment. With this setting, the carrier component of the modulation signal applied to the + input of the differential amplifier 124 is canceled by the high frequency signal applied to the − input of the differential amplifier 124.

  FIG. 10 is a diagram illustrating signals at points p, q, r, s, and t in FIG. As shown in FIG. 10, at the point p corresponding to the output of the differential amplifier 124, the signal is overmodulated. On the other hand, assuming that the signal of Asinωt is generated from the high-frequency signal generator S1, the signal of (A / 2) sinωt is input to the comparator 126 at the point q. Therefore, at the point r, a pulse signal (rectangular wave) synchronized with the signal input at the point q is output. By passing the signal that has been synchronously detected (see point s) by the mixer 60 through the filter circuit 70, a signal indicating the change in magnetic field (see point t) can be extracted.

In particular, in the fourth embodiment, the signal given to the mixer 60 by the comparator 126 is pulsed. As a result, the antenna circuit 42 can be integrated with a C-MOS or the like. In addition, the high-frequency signal is pulsed by the comparator 126, so that the power consumption of the antenna circuit 42 is reduced.
[Fifth Embodiment]
Next, a fifth embodiment of the present invention will be described. In the first to fourth embodiments, the sensitivity of the antenna circuit is increased by canceling the carrier signal in the modulated signal and appropriately extracting the sideband. In the fifth embodiment, in particular, an antenna circuit capable of reducing thermal noise is provided.

  FIG. 11 is a diagram illustrating an antenna circuit according to the fifth embodiment. As shown in FIG. 11, the antenna circuit 24 according to the fifth embodiment includes a high-frequency signal generator S1, a resistor R1, a bandpass filter (BPF) 130, an MI magnetic sensor Z1, and a mixer 60. In addition to the modulation signal, the mixer 60 is applied with a high-frequency signal from the high-frequency signal generator S1.

  For conventional synchronous detection, an LPF 82, a local oscillator 83, and a phase comparison circuit 84 are required to apply a signal having the same phase as the carrier signal of the modulation signal to the mixer 84, as shown in FIG. . However, in the antenna circuit 42 according to the present embodiment, it is desirable that the high-frequency signal generator S1 generates a high-frequency signal and removes the high-frequency signal from the modulation signal as a carrier signal. Therefore, by applying the signal from the high-frequency signal generator S1 to the mixer 60, it is possible to perform stable detection without any deviation.

This also makes it possible to compensate for the drawbacks of synchronous detection during weak electric fields, which has been a problem in conventional circuits. Therefore, high sensitivity of the antenna circuit can be realized.
[Sixth Embodiment]
FIG. 12 is a diagram illustrating an antenna circuit according to the sixth embodiment. As shown in FIG. 12, in the sixth embodiment, the signal from the high-frequency signal generator S1 is not applied to the mixer 60 as in the antenna circuit shown in the fifth embodiment, but the comparator 136 is used. A pulse signal (rectangular wave) is applied via The relationship between the sixth embodiment and the fifth embodiment substantially corresponds to the relationship between the fourth embodiment and the third embodiment.

The operation of the antenna circuit 42 according to the sixth embodiment is the same as that of the fifth embodiment. In the sixth embodiment, the signal given to the mixer 60 by the comparator 136 is pulsed. As a result, the antenna circuit 42 can be easily integrated with a C-MOS or the like. In addition, the power consumption of the antenna circuit 42 is reduced by pulsing the high frequency signal by the comparator 136.
[Seventh Embodiment]
FIG. 13 is a diagram illustrating an antenna circuit according to a seventh embodiment. As shown in FIG. 13, in the seventh embodiment, as in the sixth embodiment, the signal of the high-frequency signal generator S1 is received by the comparator, and the pulse signal (rectangular wave) having the cycle of the high-frequency signal is received. Is not applied to the mixer 60, but the output of the BPF 130, that is, the modulation signal is received by the comparator 146, and the output of the comparator 146 is applied to the mixer 60 to realize synchronous detection. That is, as in the fifth embodiment (sixth embodiment), the high frequency signal (or the corresponding rectangular wave) is not supplied to the mixer as it is and multiplied, but from the modulation signal, the same period as the high frequency signal is obtained. In addition, by producing a pulse signal (rectangular wave) having a phase and applying it to the mixer 60, the same effects as those of the fifth and sixth embodiments are obtained.
[Eighth Embodiment]
Next, an eighth embodiment of the present invention will be described. FIG. 14 is a diagram illustrating an antenna circuit according to the eighth embodiment. As shown in FIG. 14, the antenna circuit 42 according to the eighth embodiment includes a high-frequency signal generator S1 ′, resistors R1, R3, R4, an MI magnetic sensor Z1, a capacitor C4, a differential amplifier 154, rising and rising edges. A down detection circuit 156, a switch SW1, a sample and hold circuit 158 having a capacitor C5 and a resistor R5, and a switch SW2 are provided.

  In the eighth embodiment, almost the same as in the third embodiment, the differential amplifier 154 is used, and the modulation signal is applied to the + input of the differential amplifier 154, while the high-frequency signal generator S1 ′. The high-frequency signal whose level is adjusted by the resistors R3 and R4 is applied to the negative input of the differential amplifier 154. The impedance setting is not limited to this, but it is desirable that R1 = R3 = R4 = Z1. With this setting, the carrier component of the modulation signal applied to the + input of the differential amplifier 154 is canceled by the level-adjusted harmonic signal applied to the − input of the differential amplifier 154.

  In the eighth embodiment, the harmonic signal generator S1 'outputs a rectangular wave instead of a sine wave. A square wave contains many harmonic components compared to a sine wave of the same wavelength. Therefore, it is advantageous because the skin effect of the MI magnetic sensor Z1 is likely to occur.

  The rising / falling detection circuit 156 detects both the rising and falling of the rectangular wave from the harmonic signal generator S1 ′, and the rising clock CLK1 that generates a pulse when the rectangular wave rises, and the rectangular wave A falling clock CLK2 is output so that a pulse appears at the falling edge. FIG. 15 is a diagram illustrating a configuration of the rising / falling detection circuit 156.

  As illustrated in FIG. 15, the rising / falling detection circuit 156 includes a capacitor C6, a resistor R6, a comparator 190, an inverter 191, a capacitor C7, a resistor R7, and a comparator 191. A differentiation circuit is formed by the capacitor C6 and the resistor R6, and its output is applied to the + input of the comparator 190. The reference voltage Vref is applied to the negative input of the comparator 190. The differentiation circuit is also formed by the capacitor C7 and the resistor R7, and a rectangular wave inverted by the inverter 191 is applied to the differentiation circuit. The output of the differentiation circuit is applied to the + input of the comparator 191. The reference voltage Vref is also applied to the negative input of the comparator 190.

  The rising clock CLK1 controls the switch SW1 of the sample and hold circuit 158, and closes the switch SW1 when the rising clock CLK1 is at a high level so that the signal on the capacitor C4 side flows to the sample and hold circuit 158 side. . The falling clock CLK2 controls the switch SW2, closes the switch SW2 when the falling clock CLK2 is at a high level, and charges the capacitor C4 with the reference potential Vref.

  Hereinafter, the operation of the eighth embodiment will be described in more detail with reference to FIG. 16 showing waveforms at respective points of the antenna circuit shown in FIG. As shown in FIG. 16, at the position A between the resistors R3 and R4, a waveform in which the level of the rectangular wave from the high-frequency signal generator S1 'is adjusted appears. Even at the point B, when there is no magnetic field, a waveform similar to the point A appears as shown by a broken line. On the other hand, when MI magnetic sensor Z1 detects a magnetic field, the waveform changes as shown by the solid line. The differential amplifier 154 can extract a change due to the detection of the magnetic field at point B (see point C in FIG. 16). The change in the edge portion is particularly noticeable because the MI magnetic sensor Z1 is operated by using the high frequency component of the rising and falling frequency components.

  At the timing when CLK2 becomes high level due to falling detection, the output of the differential amplifier 154 (see point C) is charged into the capacitor C2, and the signal centered on Vref is set to Vref reference, that is, Vref becomes the lowest level. (See point D). With this clamping, both the rising edge and falling edge changes of the output of the differential amplifier 154 can be taken out. For example, if the output of the differential amplifier 154 is simply integrated by half-wave rectification (or full-wave rectification), as shown in FIG. 17, only the change at the rising portion can be extracted. Decreases and the detection sensitivity decreases. On the other hand, according to the present embodiment, it is possible to extract changes in both the rising portion and the falling portion, and to increase the level of the detection output.

  When the switch SW1 is controlled by the rising clock CLK1, the peak value of the waveform clamped by the sample and hold circuit 158 is detected, thereby realizing detection. The detected output is represented as a waveform at point E.

  According to the eighth embodiment, the falling edge of the high-frequency signal output from the high-frequency signal generator is detected, and the output of the differential amplifier, that is, the signal corresponding to the change due to the magnetic field detection is clamped at that timing. As a result, the level of the detection output can be increased.

  The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the invention described in the claims, and these are also included in the scope of the present invention. Needless to say.

  For example, in the first embodiment and the second embodiment, the level of the inverted signal of the high frequency signal applied to the adder may be adjusted using a resistor or the like.

  In the first to seventh embodiments, instead of the high-frequency signal generator S1 that outputs a high-frequency signal of a sine wave, a high-frequency signal generator S1 that generates a rectangular wave as in the eighth embodiment. 'May be used.

FIG. 1 is a front view of a wristwatch including a receiving circuit according to an embodiment of the present invention. 2 is a cross-sectional view taken along the line A-A ′ of FIG. 1 (a cross-sectional view at 12 o'clock to 6 o'clock). FIG. 3 is a block diagram showing the internal configuration of the circuit of the wristwatch 1 according to the present embodiment. FIG. 4 is a block diagram showing an outline of the receiving circuit 44 according to the present embodiment. FIG. 5 is a diagram illustrating the antenna circuit and the LPF subsequent to the antenna circuit according to the first embodiment of the present invention. 6A and 6B are diagrams for explaining the frequency components of the modulation signal. FIG. 7 is a diagram showing an antenna circuit according to the second embodiment of the present invention. FIG. 8 is a diagram illustrating an antenna circuit according to a third embodiment of the present invention. FIG. 9 is a diagram illustrating an antenna circuit and an LPF following the antenna circuit according to the fourth embodiment of the present invention. FIG. 10 is a diagram illustrating signals at points p, q, r, s, and t in FIG. FIG. 11 is a diagram illustrating an antenna circuit according to a fifth embodiment of the present invention. FIG. 12 is a diagram illustrating an antenna circuit according to a sixth embodiment of the present invention. FIG. 13 is a diagram illustrating an antenna circuit according to a seventh embodiment of the present invention. FIG. 14 is a diagram illustrating an antenna circuit according to an eighth embodiment of the present invention. FIG. 15 is a diagram illustrating a configuration of a rising / falling detection circuit according to the eighth embodiment. FIG. 16 is a diagram illustrating signals at respective points in the antenna circuit according to the eighth embodiment. FIG. 17 is a diagram illustrating an example of a signal in a conventional antenna circuit. FIG. 18 is a diagram illustrating an example of an antenna circuit configured to detect magnetism using an MI magnetic sensor, and a filter circuit subsequent to the antenna circuit. FIG. 19 is a diagram illustrating a relationship between a magnetic field and impedance. FIG. 20A is a diagram illustrating an example of a high-frequency signal subjected to a magnetic field change, and FIG. 20B is a diagram illustrating the frequency component. FIG. 21 is a diagram illustrating an example of a conventional antenna circuit and a filter circuit subsequent to the antenna circuit.

Explanation of symbols

42 Antenna circuit 44 Receiving circuit 50 CPU
51 Input Unit 52 Display Unit 55 Timekeeping Circuit Unit 56 Oscillation Circuit Unit 70 Filter Circuit 80 Amplification Circuit 90 BPF
DESCRIPTION OF SYMBOLS 100 Detection circuit S1 High frequency signal generator R1 Resistance Z1 MI magnetic sensor C1, C3 Capacitor D1, D2 Diode 92 Inverter 94 Adder

Claims (10)

Magnetic field detecting means whose electrical characteristics change in response to changes in the magnetic field;
High-frequency signal generating means for applying a high-frequency signal to the magnetic field detecting means;
Signal reduction means for reducing at least a part of the high-frequency signal from the reception signals obtained by the magnetic field detection means and the high-frequency signal generation means;
An antenna device comprising: detection means for detecting a reception signal in which the high-frequency signal is reduced.   The signal reducing means includes an inverter that inverts the high-frequency signal or the level-adjusted high-frequency signal, an adder that adds the received signal and the inverted high-frequency signal from the inverter. The antenna device according to claim 1.   The signal reducing means includes a differential amplifier that receives the received signal and the high-frequency signal or the level-adjusted high-frequency signal and outputs a difference between them. Antenna device.   The antenna according to any one of claims 1 to 3, wherein the detection means includes a synchronous detection circuit that receives a high-frequency signal or a high-frequency signal whose level is adjusted, and performs synchronous detection based on the received signal. apparatus.   The detection unit includes a rectangular wave generation unit that receives a high-frequency signal or a level-adjusted high-frequency signal and generates a rectangular wave from the signal, and synchronous detection is realized by the rectangular wave. Item 5. The antenna device according to Item 4. Further, rising and falling detection means for detecting rising and falling of the high-frequency signal and outputting a rising pulse and a falling pulse, respectively,
Clamping means for clamping the output of the differential amplifier to a predetermined reference voltage based on the falling pulse;
The antenna apparatus according to claim 3, further comprising sample-and-hold means for sampling and holding the clamped signal based on the falling pulse. Magnetic field detecting means whose electrical characteristics change in response to changes in the magnetic field;
High-frequency signal generating means for applying a high-frequency signal to the magnetic field detecting means;
Detecting means for detecting the received signal obtained by the magnetic field detecting means and the high-frequency signal generating means,
An antenna device, wherein the detection means includes a synchronous detection circuit that receives a high-frequency signal or a level-adjusted high-frequency signal and performs synchronous detection based on the received signal.   The detection unit includes a rectangular wave generation unit that receives a high-frequency signal or a level-adjusted high-frequency signal and generates a rectangular wave from the signal, and synchronous detection is realized by the rectangular wave. Item 8. The antenna device according to Item 7. Magnetic field detecting means whose electrical characteristics change in response to changes in the magnetic field;
High-frequency signal generating means for applying a high-frequency signal to the magnetic field detecting means;
Detecting means for detecting the received signal obtained by the magnetic field detecting means and the high-frequency signal generating means,
An antenna device, wherein the detection unit includes a rectangular wave generation unit that receives the reception signal and generates a rectangular wave from the signal, and a synchronous detection circuit that performs synchronous detection using the rectangular wave. An antenna device according to any one of claims 1 to 9,
Amplifying means for amplifying a signal corresponding to a standard radio wave including time information obtained by the antenna device;
A detection means for detecting a signal output from the amplification means and outputting a demodulated signal;
Time information extraction means for extracting time information from the demodulated signal;
A time measuring means for measuring time;
Time display means for displaying the time measured by the time measuring means;
A timepiece comprising: time correction means for correcting the time counted by the timekeeping means based on the time information extracted by the time information extraction means.