Electromagnetic induction pen and position detection device

Abstract

The invention provides an EMR-type electromagnetic induction pen capable of realizing multi-valued pen signals. An electromagnetic induction pen (2) is provided with: a resonance circuit (23) that transmits a pen signal (PS) using power obtained from an alternating magnetic field (AM) transmitted from a position detection device (3); and a control circuit (26) that, on the basis of information transmitted to the position detection device (3), temporarily changes the resonance frequency of the resonance circuit (23) from a first frequency to a second frequency different from the first frequency, and thereafter, restores the resonance frequency of the resonance circuit (23) to the first frequency, thereby causing the resonance circuit (23) to transmit a pen signal (PS) phase-modulated on the basis of the information.

Description

Technical Field

[0001] The present invention relates to an electromagnetic induction pen and a position detection device, and in particular to an electromagnetic induction pen and a position detection device supporting position detection based on an electromagnetic induction method. Background Art

[0002] As one of the methods for detecting the position of an electromagnetic induction pen within the panel surface of a tablet terminal, etc., an electromagnetic induction method (EMR method) is known. The electromagnetic induction pen based on the EMR method is configured to have a resonant circuit including a coil and a capacitor provided at the pen tip. On the other hand, a position detection device for detecting the position of the electromagnetic induction pen is provided in the tablet terminal based on the EMR method. The position detection device is configured to have a plurality of annular coils arranged within the panel surface and a sensor controller connected to the plurality of annular coils.

[0003] The position detection device has a function of sending an alternating magnetic field from the panel surface by passing an alternating current through one or more annular coils. If the coil in the electromagnetic induction pen enters the alternating magnetic field, an electromotive force is excited in the coil by electromagnetic induction. The electromagnetic induction pen is configured such that after the position detection device stops sending the alternating magnetic field, the electric power obtained from the electromotive force is used to control the resonant characteristics of the resonant circuit, thereby sending a signal (hereinafter referred to as a "pen signal") representing information (for example, a pen pressure value) to the position detection device. The position detection device is configured to obtain the information sent by the electromagnetic induction pen by demodulating the pen signal that appears in the form of an alternating current in each annular coil. Examples of electromagnetic induction pens that send pen signals are disclosed in Patent Documents 1 and 2.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 7-175572

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 7-182094 Summary of the invention

[0008] Problems to be solved by the invention

[0009] However, in the previous EMR method, the electromagnetic induction pen can only send one bit of information at a time using the pen signal, and it is not possible to simultaneously send multiple bits of information (i.e., to make the pen signal multi-valued) as QPSK (Quadrature Phase Shift Keying) and 16QAM (16 Quadrature Amplitude Modulation) used in mobile communications.

[0010] The reason for this is briefly explained. First, as a premise, when the electromagnetic induction pen is to transmit n bits of information at the same time in the EMR method, the electromagnetic induction pen changes the resonance frequency of the built-in resonance circuit to 2. n Since the electromagnetic induction pen transmits the pen signal in synchronization with the position detection device, the position detection device can demodulate the pen signal by detecting a change in the phase of the pen signal.

[0011] Here, the position detection device receives the pen signal by orthogonal detection (discrete Fourier transform) at a predetermined frequency, but in the orthogonal detection, there is a characteristic that the reception level decreases as the frequency of the received signal deviates from the predetermined frequency. As a result, in the conventional EMR method, the resonant frequency of the resonant circuit in the electromagnetic induction pen cannot be greatly changed from the predetermined frequency, which becomes an obstacle to the multi-valued pen signal.

[0012] Therefore, one of the objects of the present invention is to provide an electromagnetic induction pen and a position detection device of the EMR method that can realize multi-valued pen signals.

[0013] Means for solving problems

[0014] The electromagnetic induction pen of the present invention comprises: a resonant circuit (23) which transmits a pen signal (PS) using power obtained from an alternating magnetic field (AM) sent by a position detection device (3); and a control circuit (26) which temporarily changes the resonant frequency of the resonant circuit (23) from a first frequency to a second frequency different from the first frequency based on information sent to the position detection device (3), and then restores the resonant frequency of the resonant circuit (23) to the first frequency, thereby causing the resonant circuit (23) to transmit the pen signal (PS) obtained by phase modulation according to the information.

[0015] The position detection device of the present invention uses a coil (LC) to send out an alternating magnetic field (AM) of a first frequency, and after stopping the sending of the alternating magnetic field (AM), the information sent by the electromagnetic induction pen (2) is demodulated based on the phase of the signal of the first frequency detected during the detection period of the pen signal (PS).

[0016] Effects of the Invention

[0017] According to the present invention, the phase of the pen signal transmitted at the first frequency can be controlled by the information of the transmission target, so that the pen signal can be multi-valued without causing a decrease in the reception level in the orthogonal detection of the position detection device. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a diagram for explaining the principle of the present invention.

[0019] Figure 2 It is a diagram showing the configuration of a position detection system 1 according to the first embodiment of the present invention.

[0020] Figure 3 : is a diagram showing the timing of the alternating magnetic field AM and the pen signal PS.

[0021] Figure 4 It is shown Figure 2 FIG. 2 is a diagram showing the internal structure of the resonance circuit 23.

[0022] Figure 5 It is shown Figure 4 A diagram showing a specific configuration example of the modulation unit 25 is shown.

[0023] Figure 6 1 is a diagram showing simulation waveforms of the AC current v1, the voltage signal comp, the control signal din, and the control signal swc1 according to the first embodiment of the present invention.

[0024] Figure 7 1 is a diagram showing simulation waveforms of the AC current v1, the voltage signal comp, the control signal din, and the control signal swc1 according to the first embodiment of the present invention.

[0025] Figure 8 This is a graph in which the level of the AC current v1 and the amount of change in the phase of the AC current v1 are plotted for each capacitor Cx selected by the selector SEL.

[0026] Fig. 9 (a) to (c) are respectively about the electromagnetic induction pen 2 and the first to third modified examples of the first embodiment of the present invention. Figure 8 Similarly, the level of the AC current v1 and the amount of change in the phase of the AC current v1 are plotted.

[0027] Fig.10 1 is a diagram showing the internal structure of the resonance circuit 23 according to the second embodiment of the present invention.

[0028] Fig.11 It is shown Fig.10 A diagram showing a specific configuration example of the modulation unit 25 is shown.

[0029] Fig.12 1 is a diagram showing simulation waveforms of the AC current v2, the voltage signal comp, the control signal din, and the control signal swc2 according to the second embodiment of the present invention.

[0030] Fig.131 is a diagram showing simulation waveforms of the AC current v2, the voltage signal comp, the control signal din, and the control signal swc2 according to the second embodiment of the present invention.

[0031] Fig.14 1 is a diagram showing the internal structure of a resonance circuit 23 according to a third embodiment of the present invention.

[0032] Fig.15 1 is a diagram showing simulation waveforms of the AC current v1, the AC current v2, the current iL, and the control signal swc2 according to the third embodiment of the present invention.

[0033] Fig.16 1 is a diagram showing simulation waveforms of the AC current v1, the AC current v2, the current iL, and the control signal swc2 according to the third embodiment of the present invention.

[0034] Fig.17 1 is a diagram showing the internal structure of a resonance circuit 23 according to a fourth embodiment of the present invention.

[0035] Fig.18 1 is a diagram showing simulation waveforms of the AC current v1, the AC current v2, the current iL, and the control signal swc2 according to the fourth embodiment of the present invention.

[0036] Fig.19 1 is a diagram showing simulation waveforms of the AC current v1, the AC current v2, the current iL, and the control signal swc2 according to the fourth embodiment of the present invention.

[0037] Fig. 20 1 is a diagram showing simulation waveforms of current iC23 and current iR5 according to the fourth embodiment of the present invention.

[0038] Fig.21 1 is a diagram showing simulation waveforms of the AC current v1, the AC current v2, the current iL, and the control signal swc2 according to another example of the fourth embodiment of the present invention.

[0039] Fig. 22 1 is a diagram showing simulation waveforms of the AC current v1, the AC current v2, the current iL, and the control signal swc2 according to another example of the fourth embodiment of the present invention.

[0040] Fig.23 1 is a diagram showing the internal structure of a resonance circuit 23 according to a fifth embodiment of the present invention.

[0041] Fig.24 1 is a diagram showing simulation waveforms of the AC current v1, the control signal swc3, the control signal swc4, and the voltage signal cap according to the fifth embodiment of the present invention.

[0042] Fig.251 is a diagram showing simulation waveforms of the AC current v1, the control signal swc3, the control signal swc4, and the voltage signal cap according to the fifth embodiment of the present invention. DETAILED DESCRIPTION

[0043] First, refer to the attached Figure 1 The principle of the present invention will be described below.

[0044] Figure 1 It is a diagram for explaining the principle of the present invention. Figure 1 (a) shows the waveform of the pen signal of the present invention, Figure 1 (b) shows the waveform of a pen signal of an example of the background technology of the present invention. Figure 1 (c) shows the waveform of the pen signal of another example of the background art of the present invention. Time t0 in each figure indicates the timing when the position detection device ends sending the alternating magnetic field.

[0045] In the case of modulating the pen signal using the information sent to the position detection device, it has been performed so far. Figure 1 (b) Figure 1 If we briefly explain each of them, first Figure 1 (b) is an example of using on-off modulation. In this example, a switch element is provided in parallel with the capacitor of the resonant circuit in the electromagnetic induction pen. When the switch element is turned on, the capacitor is short-circuited and the resonant circuit is no longer formed, and the transmission of the pen signal stops. The position detection device sets the state where the pen signal is detected by the above-mentioned orthogonal detection to "1" and the state where the pen signal is not detected to "0" to demodulate the pen signal.

[0046] Figure 1 (c) is an example of using analog phase modulation. In this example, as part of the capacitor of the resonant circuit in the electromagnetic induction pen, a variable capacitance capacitor whose capacitance changes according to the pen pressure value is used. If the capacitance of the variable capacitance capacitor changes, the resonant frequency of the resonant circuit changes, so Figure 1 As shown in the example of the solid line in (c), a pen signal vibrating at a second frequency different from the first frequency equal to the frequency of the alternating magnetic field AM is sent. The position detection device is configured to derive the phase θ of the pen signal based on the value of the pen signal at time t2 after a predetermined time from time t0, and obtain the pen pressure value sent by the electromagnetic induction pen based on the derived phase θ. This example is sometimes referred to as "phase modulation" in the past because the phase θ is derived in the position detection device, but the actual modulation is the resonant frequency, not the phase modulation in the original sense.

[0047] exist Figure 1In the on-off modulation shown in (b), there is a problem that the more information is sent, the longer it takes to send. Figure 1 Although not shown in (b), the actual pen signal gradually decays after time t0. Therefore, it is impossible to send it over time in reality. Figure 1 In the on-off modulation shown in (b), the amount of information transmitted is limited. Figure 1 In the analog phase modulation shown in (c), there is a problem that the resonant frequency of the resonant circuit in the electromagnetic induction pen cannot be significantly changed due to the above-mentioned orthogonal detection characteristics (the characteristic that the reception level decreases as the frequency of the received signal deviates from the specified frequency), which will hinder the multi-valued nature of the pen signal.

[0048] In contrast, Figure 1 As shown in (a) of the present invention, the electromagnetic induction pen of the present invention performs the following processing: based on the information of the transmitting object, the resonant frequency of the resonant circuit is temporarily changed from the first frequency (the frequency of the alternating magnetic field = the center frequency of the orthogonal detection performed by the position detection device) to the second frequency (≠ the first frequency) (at Figure 1 In the example of the transmission object, the resonant frequency of the resonance circuit is restored to the first frequency during the period from time t0 to time t1, and then the resonance frequency of the resonance circuit is restored to the first frequency. Specifically, the value of the capacitance of the capacitor constituting the resonance circuit can be changed based on the information of the transmission object, the length of the period during which the state in which the capacitance of the capacitor constituting the resonance circuit is changed is maintained can be changed based on the information of the transmission object, and other methods can be used to change the capacitance of the capacitor constituting the resonance circuit. In addition, the inductance of the coil constituting the resonance circuit can also be changed based on the information of the transmission object. Regardless of which processing is used, after the resonance frequency is restored to the first frequency, a pen signal can be obtained that vibrates at the first frequency and is phase-modulated with the original meaning based on the information of the transmission object. Therefore, according to the present invention, the multi-valued pen signal can be achieved without causing a decrease in the reception level in the orthogonal detection of the position detection device.

[0049] Below, while referring to Figure 2 to Figure 25 Hereinafter, taking the case where the capacitance of a capacitor constituting a resonant circuit is changed in order to change the resonant frequency of the resonant circuit as an example, first to fifth embodiments in which the specific changing methods are different are described.

[0050] Figure 21 is a diagram showing the structure of a position detection system 1 according to a first embodiment of the present invention. As shown in the figure, the position detection system 1 is configured to include an electromagnetic induction pen 2 and a position detection device 3 each supporting an EMR method. The electromagnetic induction pen 2 is a pen-shaped device including a core 20, a pressure sensor 21, a side switch 22, a resonant circuit 23, and a control circuit 26. Hereinafter, the alternating magnetic field sent by the position detection device 3 is referred to as an "alternating magnetic field AM", and the signal sent by the electromagnetic induction pen 2 to the position detection device 3 is referred to as a "pen signal PS".

[0051] The core 20 is a rod-shaped member constituting the pen tip of the electromagnetic induction pen 2, and is configured to be movable in the pen axis direction. The rear end of the core 20 abuts against the pressure sensor 21. The pressure sensor 21 is a sensor that detects the pressure applied to the pen tip by detecting the pressing force from the rear end of the core 20, and is configured to supply a value representing the detected pressure (pen pressure value) to the processing circuit 24.

[0052] The side switch 22 is an on-off switch provided on the surface of the electromagnetic induction pen 2, and is configured to supply information indicating its on-off state (on-off information) to the processing circuit 24. Figure 2 2 shows an example in which the electromagnetic induction pen 2 has one side switch 22, but the electromagnetic induction pen 2 may have a plurality of side switches 22. In addition, a similar switch may be provided on a surface other than the side surface of the electromagnetic induction pen 2 (for example, the tip).

[0053] The resonant circuit 23 is an integrated circuit including an LC resonant circuit composed of a coil L and a capacitor C connected in series. However, part or all of the components constituting the resonant circuit 23 may be constituted by elements outside the integrated circuit. This also applies to the processing circuit 24 and the modulation unit 25 described later.

[0054] The coil L is a component that is disposed near the pen tip and is magnetically coupled to the toroidal coil LC (described later) in the position detection device 3. When the coil L enters the alternating magnetic field AM, an electromotive force is excited in the coil L by electromagnetic induction, an alternating current is generated in the resonant circuit 23, and power is stored in the capacitor C. The resonant circuit 23 plays the following role: it supplies the generated alternating current to the processing circuit 24, and after the alternating magnetic field AM disappears, it uses the power stored in the capacitor C to send the pen signal PS as a reflection signal.

[0055] The control circuit 26 is a circuit that temporarily changes the resonance frequency of the resonance circuit 23 from the first frequency to the second frequency based on the information sent to the position detection device 3, and then restores the resonance frequency of the resonance circuit 23 to the first frequency, thereby causing the resonance circuit 23 to send the pen signal PS obtained by phase modulation based on the above information. Specifically, the following processing is performed: after the position detection device 3 ends sending the alternating magnetic field AM, the capacitance of the capacitor C is temporarily changed from the first capacitance to the second capacitance based on the above information, thereby changing the resonance frequency of the resonance circuit 23 from the first frequency to the second frequency based on the above information. The control circuit 26 includes a processing circuit 24 and a modulation unit 25, and is configured to perform this processing using them.

[0056] The processing circuit 24 is an integrated circuit that acquires the command sent by the position detection device 3 by demodulating the alternating current supplied from the resonance circuit 23, determines the content of information (digital information) to be sent to the position detection device 3, and controls the resonance circuit 23 and the modulation unit 25 so that the determined content information is sent through the pen signal PS. Specific examples of the information to be sent include data for response to the command, the pen pressure value supplied from the pressure sensor 21, and on / off information supplied from the side switch 22.

[0057] The modulation unit 25 is an integrated circuit that temporarily changes the capacitance of the capacitor C from the first capacitance to the second capacitance (≠ the first capacitance) after the transmission of the alternating magnetic field AM by the position detection device 3 is completed according to the control from the processing circuit 24, thereby controlling the phase of the pen signal PS remaining after the capacitance of the capacitor C is restored to the first capacitance. The resonant circuit 23 of this embodiment is configured to be able to select a second capacitor from a plurality of second capacitors that are different from each other, and the processing circuit 24 performs the selection (i.e., controls the value of the second capacitor) based on the information determined as the transmission object, thereby realizing the phase control of the pen signal PS based on the information of the transmission object. The details of this point will be described later.

[0058] The position detection device 3 is a device including a plurality of loop coils LC, a switch unit 30, a sensor controller 31, and a main processor 32. A typical example of the position detection device 3 is a tablet terminal or a laptop computer whose display surface also serves as a touch surface, but the position detection device 3 may also be configured using a digitizer or the like that does not have a display surface.

[0059] The plurality of loop coils LC are coils arranged in the touch surface, and are configured to include a plurality of loop coils LCx arranged side by side along the x direction and a plurality of loop coils LCy arranged side by side along the y direction. One end of each loop coil LC is connected to the switch unit 30, and the other end is grounded. The switch unit 30 is a circuit that functions to connect one or more of the plurality of loop coils LC to the sensor controller 31 under the control of the sensor controller 31.

[0060] The sensor controller 31 is an integrated circuit having the following functions: detecting the position of the electromagnetic induction pen 2 within the touch surface, obtaining the data sent by the electromagnetic induction pen 2 through the pen signal PS, and sequentially supplying the detected position and the obtained data to the main processor 32. In order to perform these processes, the sensor controller 31 is configured to send the alternating magnetic field AM and receive the pen signal PS via a plurality of loop coils LC. Among them, regarding the reception of the pen signal PS, the sensor controller 31 sets the prescribed period after stopping the sending of the alternating magnetic field AM as the detection period of the pen signal PS, and receives the pen signal PS by performing orthogonal detection (discrete Fourier transform) at a prescribed frequency on the voltage signal appearing in the loop coil LC during the detection period.

[0061] The sensor controller 31 is configured to perform different processing in the stage where the electromagnetic induction pen 2 has not been detected (global scanning) and the stage where the electromagnetic induction pen 2 has been detected (local scanning). In the global scanning, the sensor controller 31 performs the following processing: the alternating magnetic field AM is sent out from the plurality of loop coils LC in sequence, and each loop coil LC is scanned in sequence after the sending of the alternating magnetic field AM is completed. As a result, when the pen signal PS is detected at any loop coil LC, the position of the electromagnetic induction pen 2 is derived based on the receiving strength of the pen signal PS at each loop coil LC, and the process is switched to the local scanning.

[0062] The sensor controller 31 that has switched to the local scan performs the following processing: selects each of the multiple loop coils LCx and LCy located near the latest position of the electromagnetic induction pen 2, and sequentially sends out the alternating magnetic field AM from the selected multiple loop coils LCx, and scans the selected multiple loop coils LCy in sequence after the sending of the alternating magnetic field AM is completed each time. As a result, when the pen signal PS is detected at any loop coil LCy, the position of the electromagnetic induction pen 2 is derived based on the receiving strength of the pen signal PS at each loop coil LCy, and the information sent by the electromagnetic induction pen 2 is obtained by demodulating the pen signal PS received at the loop coil LCy with the strongest receiving strength. When the pen signal PS is not detected at all the loop coils LCy, the sensor controller 31 switches to the global scan and performs the above-mentioned global scan processing.

[0063] Regarding the demodulation of the pen signal PS, the sensor controller 31 pre-stores a table that establishes a correspondence between the phase of the pen signal PS and information of a predetermined number of bits. And, the sensor controller 31 is configured to detect the phase of the pen signal PS received by orthogonal detection, search the above table based on the detected phase, and thereby obtain the information sent by the electromagnetic induction pen 2.

[0064] Figure 3 1 is a diagram showing the timing of the alternating magnetic field AM and the pen signal PS. The diagram shows an example of a situation where the sensor controller 31 is performing a partial scan. As shown in the diagram, the sensor controller 31 is configured to send a command CMD at a period T. The alternating magnetic field AM used to send the command CMD is modulated by the command CMD and sent within a specified time T1.

[0065] The command CMD is used, for example, to inquire about the type of the electromagnetic induction pen 2. In the electromagnetic induction pen 2, in addition to Figure 2 In addition to the type of structure shown in the figure (hereinafter referred to as "professional model"), there may also be a type in which a variable capacitance capacitor for detecting the pen pressure value is installed in the resonance circuit so that the capacitance change of the variable capacitance capacitor is directly reflected in the change of the resonance frequency (hereinafter referred to as "entry-level model"). The electromagnetic induction pen 2 that receives the command CMD for inquiring about the type of the electromagnetic induction pen 2 sends a response signal ACK indicating which type it is using the pen signal PS as a reflection signal. Figure 3 The timing chart shown is an example of a case where the electromagnetic induction pen 2 is a professional model.

[0066] The sensor controller 31, which recognizes that the electromagnetic induction pen 2 is a professional model through the response signal ACK, sends out a burst Burst as an unmodulated alternating magnetic field AM within a specified time T2 that is longer than the specified time T1. While the alternating current based on the alternating magnetic field AM is supplied from the resonance circuit 23, the processing circuit 24 of the electromagnetic induction pen 2 operates using the power generated by the alternating current while generating information to be sent to the sensor controller 31. Specifically, the pen pressure value is obtained from the pressure sensor 21, and the on / off information is obtained from the side switch 22, and the information to be sent is constructed using these data. The processing circuit 24 monitors the amplitude of the alternating current supplied from the resonance circuit 23. If it is detected that the position detection device 3 has stopped sending the alternating magnetic field AM due to the decrease in the amplitude, the resonance circuit 23 is caused to send the first 4 bits of data DATA containing the generated information through the pen signal PS.

[0067] After that, the sensor controller 31 sends out the alternating magnetic field AM as a burst Burst 7 times. This sending is performed at a predetermined interval, and the sending of each burst Burst lasts for a predetermined time T3. The predetermined time T3 is a time shorter than the predetermined time T2, and can be the same as the predetermined time T1 or different from the predetermined time T1. The processing circuit 24 of the electromagnetic induction pen 2 obtains 4 bits of data DATA from the unsent part of the information of the sending object every time the supply of the alternating current based on the alternating magnetic field AM is newly started, and causes the resonant circuit 23 to send it through the pen signal PS. As a result, the processing circuit 24 can send a maximum of 32 bits of data during the period T.

[0068] return Figure 2 The main processor 32 receives the position and information from the sensor controller 31 and uses them to move the cursor displayed on the display surface, generate stroke data representing the trajectory of the electromagnetic induction pen 2 on the touch surface, and so on. Regarding the stroke data, the main processor 32 also renders and displays the generated stroke data, generates and records digital ink containing the generated stroke data, and sends the generated digital ink to an external device according to the user's instructions.

[0069] Next, regarding the structure and operation for temporarily changing the capacitance of the capacitor C in the resonance circuit 23 from the first capacitance to the second capacitance, referring to Figures 4 to 7 While explaining in detail.

[0070] Figure 4 2 is a diagram showing the internal structure of the resonance circuit 23 of the present embodiment. As shown in the figure, the resonance circuit 23 includes a coil L, capacitors C0 to C16, C20, diodes D1, D2, a switch element SW1, and a selector SEL.

[0071] Coil L and Figure 2 The coil L shown is the same as that shown in the figure, and is connected between the node n1 shown in the figure and the ground terminal. The capacitor C0 is composed of Figure 2 All or part of the capacitor C shown is connected between the node n1 and the ground terminal. Through these connections, the coil L and the capacitor C0 form an LC resonance circuit.

[0072] Capacitor C20 is a decoupling capacitor that adds a DC voltage to AC current v1 (voltage signal oscillating around 0 V) ​​appearing at node n1 to convert it into AC current v2 oscillating in a positive range, and is inserted in the middle of the wiring connecting node n1 and processing circuit 24.

[0073] The diode D1 is a Schottky barrier diode that has the function of preventing surge current from flowing into the processing circuit 24. The cathode of the diode D1 is connected to the electrode of the capacitor C20 on the processing circuit 24 side, and the anode is grounded. The diode D2 is a Schottky barrier diode that has the function of rectifying the current flowing into the processing circuit 24. The cathode of the diode D2 is connected to the electrode of the capacitor C20 on the processing circuit 24 side, and the anode is connected to the input terminal of the processing circuit 24. The current passing through the diode D2 is supplied to the processing circuit 24 as an alternating current AC.

[0074] The switch element SW1 is a single-pole single-throw analog switch that is turned on and off by a control signal swc1 supplied from the modulation unit 25. One end of the switch element SW1 is connected to the node n1, and the other end is connected to the common terminal of the selector SEL.

[0075] The selector SEL is a switching circuit with multiple contacts (specifically, 16 contacts in one circuit) that is switched and controlled by a selection signal dsel supplied from the processing circuit 24. One electrode of capacitors C1 to C16 is connected to each selection terminal of the selector SEL. The capacitors C1 to C16 have different capacitances, and the other electrodes of each are connected to the ground terminal in common.

[0076] The capacitor Cx (x is any one of 1 to 16) selected by the selector SEL is connected in parallel with the capacitor C0 when the switch element SW1 is turned on, and together with the capacitor C0, constitutes Figure 2 The second capacitance is the capacitance of the capacitor C configured in this way, specifically, the combined capacitance of the capacitor C0 and the capacitor Cx. On the other hand, when the switch element SW1 is turned off, the capacitor Cx is disconnected from the capacitor C0. Figure 2 The capacitor C shown is composed of only the capacitor C0. The first capacitance described above is the capacitance of the capacitor C thus constructed, and specifically, is the capacitance of the capacitor C0 alone.

[0077] Here, the processing circuit 24 stores in advance a table that associates 4-bit information with the capacitors C1 to C16. Figure 3 Each time the data DATA shown is transmitted, the capacitor Cx corresponding to the data DATA to be transmitted is determined by referring to the above table, and the selection signal dsel for selecting the determined capacitor Cx is supplied to the selector SEL. As a result, the selector SEL is in a state of selecting the capacitor Cx corresponding to the data DATA to be transmitted, and a second capacitor corresponding to the data DATA to be transmitted is realized.

[0078] The modulation unit 25 performs a process of temporarily changing the capacitance of the capacitor C from the first capacitance to the second capacitance by controlling the on / off state of the switch element SW1 using the control signal swc1. More specifically, the capacitance of the capacitor C is changed from the first capacitance to the second capacitance by turning on the switch element SW1, and the capacitance of the capacitor C is changed from the second capacitance to the first capacitance by turning off the switch element SW1. The timing of turning on and off the switch element SW1 by the modulation unit 25 is controlled by the above-mentioned alternating current v1 and the control signal din supplied from the processing circuit 24.

[0079] The control signal din is a signal indicating that the sending of the alternating magnetic field AM has ended. The processing circuit 24 is configured to activate the control signal din within a predetermined time if it is detected that the position detection device 3 has ended sending the alternating magnetic field AM by detecting the decrease in the amplitude of the alternating current AC. The modulation unit 25 controls the switch element SW1 to be turned on at the timing of the rise of the alternating current v1 during the activation of the control signal din, and after the control signal din is restored to inactivity, the switch element SW1 is restored to be turned off at the timing of the alternating current v1 rising again.

[0080] During the period until the modulation unit 25 controls the switch element SW1 to be turned on, the resonant frequency of the resonance circuit 23 becomes a value corresponding to the first capacitance (the above-mentioned first frequency). If the modulation unit 25 that detects the rise of the alternating current v1 controls the switch element SW1 to be turned on during the activation of the control signal din, the capacitance of the capacitor C becomes the second capacitance, so the resonant frequency of the resonance circuit 23 changes to a value corresponding to the second capacitance (the above-mentioned second frequency). Here, as described above, the second capacitance is the combined capacitance of the capacitor C0 and the capacitor Cx, so the specific value of the resonant frequency of the resonance circuit 23 after the change is different depending on the capacitance of the capacitor Cx. Therefore, the timing when the switch element SW1 is restored to be turned off also varies depending on the capacitance of the capacitor Cx. Therefore, in the electromagnetic induction pen 2 of this embodiment, the phase of the alternating current v1 restored to the first frequency can be controlled by the 4-bit information as the transmission object. In addition, the frequency of the resonance circuit 23 is changed from the first frequency to the second frequency in a very short time, and it is restored to the first frequency after the switch element SW1 is turned off, so there is almost no drop in the reception level in the orthogonal detection performed by the position detection device 3. Therefore, according to the electromagnetic induction pen of the present embodiment, it is possible to realize multi-valued (specifically, 4-bit phase modulation) the pen signal PS without causing a decrease in the reception level in the quadrature detection of the position detection device 3 .

[0081] It should be noted that the reason why the modulation unit 25 temporarily changes the capacitance of the capacitor C after the activation of the control signal din is that, in a situation where an electromotive force based on the alternating magnetic field AM is generated, even if the resonant frequency of the resonant circuit 23 changes due to the change in the capacitance of the capacitor C, the frequency of the alternating current v1 is determined by the frequency of the alternating magnetic field AM. By changing the capacitance of the capacitor C after the sending of the alternating magnetic field AM ends, the frequency of the alternating current v1 can be controlled to a value corresponding to the second capacitance.

[0082] Figure 5 2 is a diagram showing a specific configuration example of the modulation unit 25. As shown in the figure, the modulation unit 25 of this example is configured to include a comparator 11, a D-type flip-flop circuit 12, resistors R1 and R2, and a diode D3.

[0083] Resistors R1 and R2 are provided to divide the voltage of the AC current v1 and are connected in series between the node n1 and the ground terminal. The junction of the resistor R1 and the resistor R2 is connected to the non-inverting input terminal of the comparator 11. The diode D3 is a Schottky barrier diode connected in parallel with the resistor R2, and plays a role in preventing surge current from flowing into the comparator 11.

[0084] The comparator 11 is a circuit that compares the AC current vcomp obtained by dividing the AC current v1 by the resistors R1 and R2 with the ground potential supplied to the inverting input terminal, and outputs a voltage signal comp corresponding to the comparison result. Specifically, the comparator 11 is configured such that the voltage signal comp becomes high when the AC current vcomp is larger than the ground potential, and the voltage signal comp becomes low when the AC current vcomp is smaller than the ground potential.

[0085] The D-type flip-flop circuit 12 has a clock terminal CLK, a data terminal D, an output terminal Q, an inverting output terminal The circuit latches the value of the data terminal D and outputs it from the output terminal Q by the rising of the clock terminal CLK. The output signal of is a signal obtained by inverting the output signal from the output terminal Q, but it is not used in this embodiment. The voltage signal comp is supplied from the comparator 11 to the clock terminal CLK, and the low active pulse signal, i.e., the control signal din, is supplied from the processing circuit 24 to the data terminal D. The output of the output terminal Q is supplied to the switch element SW1 as the control signal swc1. Figure 5 The control signal swc1 of the example is a low active signal that turns off the switch element SW1 when it is high and turns on the switch element SW1 when it is low.

[0086] When the processing circuit 24 determines that the sending of the alternating magnetic field AM has ended, the control signal din is activated (made low) in a period slightly shorter than one cycle of the first frequency. If the voltage signal comp changes from low to high during the activation of the control signal din, the control signal swc1 is activated (becomes low) through the control of the D-type trigger circuit 12, and the switch element SW1 becomes turned on. Therefore, after the sending of the alternating magnetic field AM ends, at the timing when the alternating current v1 changes from negative to positive, the capacitance of the capacitor C changes from the first capacitance to the second capacitance.

[0087] After that, the control signal din returns to inactive state, and then, if the voltage signal comp changes from low to high again, the control signal swc1 returns to inactive state (becomes high) through the control of the D-type trigger circuit 12, and the switch element SW1 becomes disconnected. Therefore, after the switch element SW1 is turned on, at the timing when the AC current v1 changes from negative to positive again, the capacitance of the capacitor C returns from the second capacitance to the first capacitance.

[0088] As above, according to Figure 5 The structural example shown can realize the operation of the above-mentioned modulation unit 25. In addition, since the rise of the voltage signal comp and the timing when the AC current v1 becomes 0 are consistent, the switching element SW1 can be turned on and off when no power (charge) is stored in the capacitor Cx, thereby preventing the level of the AC current AC from decreasing due to the turning on and off of the switching element SW1.

[0089] Figure 6 and Figure 7 The following are diagrams showing the analog waveforms of the AC current v1, the voltage signal comp, the control signal din, and the control signal swc1. The horizontal axis of each diagram represents time, and the vertical axis represents voltage. The unit of the horizontal axis is μ seconds (indicated as "u" in the diagram). This is also the case for the other analog waveforms described later. Figure 6 At the left end time point (0 μs), the position detection layer 3 is sending out the alternating magnetic field AM. Figure 6 At the right end time point (120 μsec), the electromagnetic induction pen 2 is transmitting the pen signal PS as a reflection signal. Figure 7 Yes Figure 6 The waveform shown is a diagram obtained by enlarging the period between 37 μs and 49 μs.

[0090] exist Figure 6 and Figure 7 In the simulation, according to Figure 5The modulation unit 25 is constituted by the structural example shown in the figure. In addition, the first frequency is set to 666kHz (about 1.502μs in cycle), the inductance of the coil L is set to 37.5μH, the capacitance of the capacitor C0 is set to 1519.8pF, the capacitance of the capacitor C20 is set to 0.01μF, the resistance value of the resistor R1 is set to 82kΩ, and the resistance value of the resistor R2 is set to 1kΩ. The capacitances of the capacitors C1 to C16 are set to 1pF, 82pF, 167pF, 253pF, 342pF, 432pF, 525pF, 620pF, 718pF, 817pF, 919pF, 1022pF, 1128pF, 1236pF, 1347pF, and 1459pF, respectively. From the following description Figure 8 It can be understood that these values ​​are selected in such a way that the amplitude of the change in phase is constant.

[0091] However, in Figure 6 and Figure 7 In FIG. 1 , only four waveforms corresponding to the case where the selector SEL selects capacitors C1 (=1pF), C6 (=432pF), C11 (=919pF), and C16 (=1459pF). In fact, there are of course waveforms corresponding to capacitors C2, C3, C4, C5, C7, C8, C9, C10, C12, C13, C14, and C15, but if all of them are written, the drawing will become difficult to read, so Figure 6 and Figure 7 Omitted in .

[0092] First refer to Figure 6 At time t0 (≈40 μs) when the amplitude of the AC current v1 starts to decrease, the control signal din is activated to a low level. This is because the processing circuit 24 detects that the amplitude of the AC current AC starts to decrease.

[0093] Next refer to Figure 7 If the voltage signal comp changes from low to high (at time t1) during the period when the control signal din is activated to low, the control signal swc1 is activated to low at the timing when the voltage signal comp becomes high through the control of the D-type flip-flop circuit 12. As a result, the switch element SW1 is turned on and the capacitance of the capacitor C changes from the first capacitance to the second capacitance, but the second capacitance that becomes the target value of the change becomes a different value due to the capacitor Cx selected by the selector SEL. As a result, Figure 7 As shown, the frequency (second frequency) of the AC current v1 becomes a value that varies depending on the capacitor Cx.

[0094] After that, the control signal din returns to high. If the voltage signal comp changes from low to high again (time t2-t5), the control signal swc1 returns to an inactive state at the timing when the voltage signal comp becomes high through the control of the D-type trigger circuit 12, and the frequency of the AC current v1 returns to the first frequency. Here, the specific value of the frequency (second frequency) of the AC current v1 during the period when the switch element SW1 is turned on varies depending on the capacitor Cx, so the timing when the frequency of the AC current v1 returns to the first frequency also varies depending on the capacitor Cx. As a result, Figure 7 As shown in FIG. 1 , the phase of the AC current v1 after the vibration at the first frequency is changed by an amount corresponding to the capacitance of the capacitor Cx compared to before the switch element SW1 is turned on. Therefore, it can be said that: Figure 6 and Figure 7 In the simulation, it is achieved that the phase of the pen signal PS transmitted at the first frequency is changed by an amount corresponding to the information of the transmission object.

[0095] Figure 8 This is a graph obtained by plotting the level of the AC current v1 and the amount of change in the phase of the AC current v1 for each capacitor Cx selected by the selector SEL. The numbers 1 to 16 shown on the horizontal axis of the graph correspond to x of the capacitor Cx. In addition, the level of the AC current v1 represents the level just after the capacitance of the capacitor C is restored from the second capacitance to the first capacitance.

[0096] from Figure 8 As can be seen from the results, according to the electromagnetic induction pen 2 of this embodiment, by temporarily changing the capacitance of the capacitor C from the first capacitance to the second capacitance, the phase can be changed by a maximum of about 150° without almost decreasing the level of the AC current v1.

[0097] As described above, according to the electromagnetic induction pen 2 of this embodiment, the phase of the pen signal PS transmitted at the first frequency can be controlled based on the information of the transmission object, thereby realizing multi-valued pen signal PS without causing a decrease in the reception level in the orthogonal detection of the position detection device 3.

[0098] It should be noted that, in the above-mentioned embodiment, 4-bit phase modulation is realized using 16 capacitors C1 to C16, but the number of capacitors C connected to the selector SEL can be suppressed to 15 by also using a case where the capacitance of the capacitor C is not temporarily changed from the first capacitance to the second capacitance. In addition, multi-valued modulation other than 4-bit phase modulation such as 2-bit phase modulation and 8-bit phase modulation can be performed by appropriately adjusting the number of capacitors selected by the selector SEL.

[0099] Fig. 9 (a)~ Fig. 9(c) are respectively about the electromagnetic induction pen 2 and the first to third modified examples of the present embodiment. Figure 8 Similarly, the level of the AC current v1 and the amount of change in the phase of the AC current v1 are plotted.

[0100] Fig. 9 The first modified example shown in (a) is an example in which the selector SEL is not provided, only one capacitor with a capacitance of 200pF is provided in the rear section of the switch element SW1, and the phase of the AC current v1 is controlled by the length of time the switch element SW1 is turned on. However, the timing of turning on the switch element SW1 is the same as in the present embodiment, and is set to the timing when the voltage signal comp changes to high. In addition, the numbers 1 to 16 shown on the horizontal axis of the figure correspond to the cases where the length of time the switch element SW1 is turned on is 0.0μs, 1.5μs, 3.0μs, 4.5μs, 6.0μs, 7.5μs, 9.0μs, 10.5μs, 12.0μs, 13.5μs, 15.0μs, 16.5μs, 18.0μs, 19.5μs, 21.0μs, and 22.5μs, respectively.

[0101] like Fig. 9 As shown in (a), in the first variant, a phase change of more than 360° can be achieved. On the other hand, if the switching element SW1 is turned on for a longer time, the level of the AC current v1 will drop significantly. Therefore, the electromagnetic induction pen of the first variant needs to be used in a range where the level of the AC current v1 drops less.

[0102] Fig. 9 The second modification shown in (b) is that the capacitance of the capacitor provided at the rear stage of the switch element SW1 is 100 pF and the capacitance of the capacitor provided at the rear stage of the switch element SW1 is 100 pF. Fig. 9 The second modification example is not as good as the present embodiment, but the level drop of the AC current v1 is suppressed compared with the first modification example, so it is considered that multi-value phase modulation can be achieved compared with the first modification example.

[0103] Figure 8The third modification shown in (c) is an example of controlling the phase of the AC current v1 using the same structure as the present embodiment except that the switch element SW1 is turned on at the timing when the voltage signal comp becomes high, and the length of the period until the switch element SW1 becomes off is fixed to 1.5 μs, which is different from the present embodiment. However, the capacitances of the capacitors C1 to C16 are respectively 0 pF, 100 pF, 200 pF, 300 pF, 400 pF, 500 pF, 600 pF, 700 pF, 800 pF, 900 pF, 1000 pF, 1100 pF, 1200 pF, 1300 pF, 1400 pF, and 1500 pF.

[0104] In the third variation, if Fig. 9 As shown in (c), substantially the same result as that of the second modification example is obtained. Therefore, it is considered that the third modification example can also realize multi-value phase modulation compared with the first modification example.

[0105] Next, the position detection system 1 of the second embodiment of the present invention is described. The position detection system 1 of this embodiment is the same as the position detection system 1 of the first embodiment, except that the internal structure of the resonance circuit 23 and the operation of the modulation unit 25 are different from those of the position detection system 1 of the first embodiment. Therefore, the following description focuses on the differences from the position detection system 1 of the first embodiment.

[0106] Fig.10 23 is a diagram showing the internal structure of the resonance circuit 23 of this embodiment. Figure 4 By comparison, it can be understood that the resonant circuit 23 of the present embodiment is different from the resonant circuit 23 of the first embodiment in that the switching element SW1 is replaced by the switching element SW2 and the electrode on the processing circuit 24 side of the capacitor C20 (hereinafter referred to as "node n2") is connected to the common terminal of the selector SEL and the modulation unit 25 instead of the node n1.

[0107] The switch element SW2 is an N-channel MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). The drain of the switch element SW2 is commonly connected to the other electrode of the capacitors C1 to C16, and the source is connected to the ground. In addition, the control signal swc2 is supplied to the gate of the switch element SW2 from the modulation unit 25. The common terminal of the selector SEL is not connected via Figure 4 The switch element SW1 is shown to be directly connected to the node n2.

[0108] The modulation unit 25 of this embodiment controls the on / off state of the switch element SW2 using the control signal swc2. Figure 2 20 is a process of temporarily changing the capacitance of the capacitor C from the first capacitance to the second capacitance. In the present embodiment, the first capacitance is the capacitance of the capacitor C0 alone, and the second capacitance is the combined capacitance of the capacitors C0, C20, and Cx. More specifically, the modulation unit 25 is configured to change the capacitance of the capacitor C from the first capacitance to the second capacitance by turning on the switch element SW2, and to change the capacitance of the capacitor C from the second capacitance to the first capacitance by turning off the switch element SW2. The modulation unit 25 controls the timing of turning on and off the switch element SW2 by the alternating current v2 appearing at the node n2 and the control signal din supplied from the processing circuit 24.

[0109] Specifically, the modulation unit 25 controls the switch element SW2 to be turned on at the timing of the rise of the AC current v2 during the period when the control signal din is activated, and after the control signal din is restored to inactive, the switch element SW2 is restored to be turned off at the timing of the AC current v2 rising again. According to the operation of the modulation unit 25, as in the first embodiment, the resonance frequency of the resonance circuit 23 is temporarily changed from the first frequency to the frequency (second frequency) corresponding to the capacitance of the capacitor Cx, so that the phase of the AC current v1 restored to the first frequency can be controlled by the 4-bit information as the transmission object. In addition, the frequency of the resonance circuit 23 is changed from the first frequency to the second frequency in a very short time, and is restored to the first frequency after the switch element SW2 is turned off, so there is almost no drop in the reception level in the orthogonal detection performed by the position detection device 3. Therefore, by the electromagnetic induction pen of this embodiment, it is also possible to realize the multi-valued pen signal PS (specifically, 4-bit phase modulation) without causing a drop in the reception level in the orthogonal detection of the position detection device 3.

[0110] Fig.11 2 is a diagram showing a specific configuration example of the modulation unit 25 of this embodiment. As shown in the figure, the modulation unit 25 of this example is configured to include a D-type flip-flop circuit 12, a resistor R3, and a capacitor C21.

[0111] The resistor R3 and the capacitor C21 are connected in series between the node n2 and the ground terminal. The voltage signal comp appearing at the junction of the resistor R1 and the capacitor C21 is connected to the clock terminal of the D-type flip-flop circuit 12. The voltage signal comp of the first embodiment is a pulse signal, but the voltage signal comp of this embodiment becomes a substantially sinusoidal signal similar to the alternating current v2.

[0112] The structure and operation of the D-type trigger circuit 12 are similar to Figure 4The D-type flip-flop circuit 12 shown is the same. However, the control signal swc2 is not output from the output terminal Q but from the inverting output terminal The output is a high active signal.

[0113] If the voltage signal comp rises during the period when the control signal din is activated and low by the processing of the processing circuit 24, the control signal swc2 is activated (becomes high) by the control of the D-type flip-flop circuit 12, and the switch element SW2 becomes turned on. Therefore, after the transmission of the alternating magnetic field AM is completed, at the timing of the rise of the alternating current v2, the capacitance of the capacitor C changes from the first capacitance to the second capacitance.

[0114] After that, the control signal din returns to inactivity, and then, if the voltage signal comp rises again, the control signal swc2 returns to an inactive state (becomes low) through the control of the D-type trigger circuit 12, and the switch element SW2 becomes disconnected. Therefore, after the switch element SW2 is turned on, at the timing when the AC current v1 rises again, the capacitance of the capacitor C returns from the second capacitance to the first capacitance.

[0115] As above, according to Fig.11 The illustrated configuration example can realize the operation of the modulation unit 25 described above.

[0116] Fig.12 and Fig.13 2 is a diagram showing the simulated waveforms of the AC current v2, the voltage signal comp, the control signal din, and the control signal swc2 according to the present embodiment. Fig.12 At the left end time point (260 μs), the position detection layer 3 is sending out the alternating magnetic field AM. Figure 6 At the right end time point (340 μsec), the electromagnetic induction pen 2 is transmitting the pen signal PS as a reflection signal. Fig.13 Yes Fig.11 The waveform shown is a diagram obtained by enlarging the period between 307 μs and 317 μs.

[0117] exist Fig.12 and Fig.13 In the simulation, according to Fig.11 The modulation unit 25 is constructed by using the configuration example shown in the figure. In addition, the capacitance of the capacitor C21 is set to 1 pF, and the resistance of the resistor R3 is set to 10 kΩ. The other circuit constants are set to the same values ​​as Figure 6 The same value of the simulation.

[0118] exist Fig.12 and Fig.13 In, with Figure 6 and Figure 7Similarly, only four waveforms corresponding to the case where the capacitors C1 (=1pF), C6 (=432pF), C11 (=919pF), and C16 (=1459pF) are selected by the selector SEL are shown. In fact, of course, there are waveforms corresponding to the capacitors C2, C3, C4, C5, C7, C8, C9, C10, C12, C13, C14, and C15, but if all of them are written, the drawing will become difficult to read, so Fig.12 and Fig.13 Omitted in .

[0119] First refer to Fig.12 At time t0 (≈310 μs) when the amplitude of the AC current v2 starts to decrease, the control signal din is activated to a low value. This is because the processing circuit 24 detects that the amplitude of the AC current AC starts to decrease.

[0120] Next refer to Fig.13 If the voltage signal comp rises during the activation of the control signal din (times t1 and t2), the control signal swc2 is activated to high at the timing of the rise of the voltage signal comp by the control of the D-type flip-flop circuit 12. As a result, the switch element SW2 is turned on and the capacitance of the capacitor C changes from the first capacitance to the second capacitance. However, the second capacitance that becomes the target value of the change is the same as the first embodiment, and becomes a different value depending on the capacitor Cx selected by the selector SEL. As a result, Fig.13 As shown, the frequency (second frequency) of the AC current v2 becomes a different value depending on the capacitor Cx.

[0121] Here, in this embodiment, if Fig.13 As shown in FIG. 1 , in the stage before the switch element SW2 is turned on, the waveform also differs due to the capacitor Cx selected by the selector SEL. This is because, due to the presence of the parasitic capacitance of the switch element SW2, even if the switch element SW2 is turned off, the capacitor Cx selected by the selector SEL will not be completely disconnected from the circuit. Therefore, in this embodiment, the first frequency also differs slightly due to the capacitor Cx selected by the selector SEL.

[0122] After the capacitance of capacitor C changes to the second capacitance, the control signal din returns to high. If the voltage signal comp rises again (time t3-t6), the control signal swc2 returns to an inactive state at the timing of the rise of the voltage signal comp through the control of the D-type trigger circuit 12, and the frequency of the AC current v1 returns to the first frequency. Here, as in the first embodiment, the specific value of the frequency (second frequency) of the AC current v1 during the period when the switch element SW2 is turned on varies depending on the capacitor Cx, so the timing at which the frequency of the AC current v1 returns to the first frequency also varies depending on the capacitor Cx. As a result, Fig.13 As shown in FIG. 1 , the phase of the AC current v2 after the vibration at the first frequency is changed by an amount corresponding to the capacitance of the capacitor Cx compared to before the switch element SW1 is turned on. Fig.13 Although the AC current v1 is not shown in FIG, the phase of the AC current v1 also changes in the same way as the AC current v2. Therefore, it can be said that: Fig.12 and Fig.13 In the simulation, it is achieved that the phase of the pen signal PS transmitted at the first frequency is changed by an amount corresponding to the information of the transmission object.

[0123] As described above, the electromagnetic induction pen 2 of this embodiment can also control the phase of the pen signal PS transmitted at the first frequency based on the information of the transmitting object, thereby realizing multi-valued pen signal PS without causing a decrease in the receiving level in the orthogonal detection of the position detection device 3.

[0124] In addition, according to the electromagnetic induction pen 2 of this embodiment, since the AC current v2 is input to the common terminal of the selector SEL and the modulation unit 25 instead of the AC current v1, the comparator 11 is not required compared to the first embodiment, and the switching element SW3 which is a MOSFET can be used instead of the switching element SW1 which is an analog switch. Therefore, in the electromagnetic induction pen 2 of this embodiment, the circuit scale is reduced compared to the electromagnetic induction pen 2 of the first embodiment.

[0125] Next, the position detection system 1 of the third embodiment of the present invention is described. The position detection system 1 of this embodiment is the same as the position detection system 1 of the second embodiment, except that the internal structure of the resonance circuit 23 and the operations of the processing circuit 24 and the modulation unit 25 are different from those of the position detection system 1 of the second embodiment. Therefore, the following description focuses on the differences from the position detection system 1 of the second embodiment.

[0126] Fig.14 23 is a diagram showing the internal structure of the resonance circuit 23 of this embodiment. Fig.10 By comparison, it can be understood that the resonance circuit 23 of this embodiment is different from the resonance circuit 23 of the second embodiment in that it does not include the capacitor C0, does not include the selector SEL, and includes a capacitor C22 instead of the capacitors C0 to C16.

[0127] The capacitor C22 is connected between the node n2 and the drain of the switch element SW2. The selection signal dsel supplied to the selector SEL in the second embodiment is supplied to the modulation unit 25 in this embodiment. The selection signal dsel in this embodiment is not a signal for selecting one of the capacitors C1 to C16, but a signal for selecting the length of the period during which the modulation unit 25 maintains the capacitance of the capacitor C at the second capacitance.

[0128] The processing circuit 24 of this embodiment stores in advance a table of 4-bit information and the length of the period during which the modulation unit 25 maintains the capacitance of the capacitor C at the second capacitance. Figure 3 Each time the data DATA shown is transmitted, the length of the period corresponding to the data DATA to be transmitted is determined by referring to the above table, and a selection signal dsel indicating the determined length is supplied to the modulation unit 25.

[0129] The modulator 25 of this embodiment performs a process of temporarily changing the capacitance of the capacitor C from the first capacitance to the second capacitance by controlling the on / off state of the switch element SW2 using the control signal swc2, similarly to the modulator 25 of the second embodiment. However, the modulator 25 of this embodiment is configured such that, unlike the modulator 25 of the second embodiment, the switch element SW2 is controlled to be turned on (so-called normally on) in the initial state, the capacitance of the capacitor C is changed from the first capacitance to the second capacitance by turning off the switch element SW2, and the capacitance of the capacitor C is changed from the second capacitance to the first capacitance by turning on the switch element SW2.

[0130] In the initial state, the switch element SW2 is controlled to be turned on in order to use the capacitor C22 and the coil L to form a resonant circuit. By doing so, the capacitor C0 is not required in this embodiment. The first capacitance of this embodiment becomes the combined capacitance of the capacitors C20 and C22. Fig.14 In the circuit diagram, there is no capacitor connected to the coil L except the capacitor C20, but actually, since there is a parasitic capacitance in the switch element SW2, the coil L and the capacitor C22 are not completely disconnected, and therefore, a resonant circuit is formed even when the switch element SW2 is turned off. The second capacitance of this embodiment is a composite capacitance of the parasitic capacitance of the capacitors C20 and C22 and the switch element SW2.

[0131] The modulation unit 25 of this embodiment controls the timing of turning the switch element SW2 on and off by the AC current v2 appearing at the node n2 and the control signal din and the selection signal dsel supplied from the processing circuit 24. Specifically, the modulation unit 25 controls the switch element SW2 to be turned off at the timing when the current iL appearing in the coil L becomes 0 during the period when the control signal din is activated, and then returns the switch element SW2 to be turned on at the timing when the length of time indicated by the selection signal dsel has passed. The switch element SW2 is turned off at the timing when the current iL of the coil L becomes 0 in order to prevent the level of the AC current v1 from decreasing. According to the operation of the modulation unit 25, the resonant frequency of the resonance circuit 23 is changed to the second frequency within the length of time indicated by the selection signal dsel, so the phase of the AC current v1 restored to the first frequency can be controlled by the 4-bit information as the transmission object. In addition, the frequency of the resonance circuit 23 is changed from the first frequency to the second frequency in a very short time, and is restored to the first frequency after the switch element SW2 is turned on, so the reception level is almost not reduced in the orthogonal detection performed by the position detection device 3. Therefore, the electromagnetic induction pen of this embodiment can also realize multi-valued (specifically, 4-bit phase modulation) the pen signal PS without causing a decrease in the reception level in the quadrature detection of the position detection device 3 .

[0132] Fig.15 and Fig.16 1 is a diagram showing the simulated waveforms of the AC current v1, the AC current v2, the current iL, and the control signal swc2 according to the present embodiment. Fig.15 At the left end time point (250 μs), the position detection layer 3 is sending out the alternating magnetic field AM. Figure 6 At the right end time point (340 μsec), the electromagnetic induction pen 2 is transmitting the pen signal PS as a reflection signal. Fig.16 Yes Fig.15 The waveform shown is a diagram obtained by enlarging the period between 309 μs and 313 μs.

[0133] exist Fig.15 and Fig.16 In the simulation, the capacitance of capacitor C22 is set to 1755pF. The other circuit constants are set to Fig.12 The same value as the simulation. In addition, the length of the period during which the modulation unit 25 maintains the switch element SW2 in the off state is 0 μs, 0.5 μs, 1.0 μs, and 1.5 μs. In practice, if, for example, n-bit phase modulation is performed, 2 n However, if all the conditions are written, the drawings will become difficult to read, so Fig.15 and Fig.16 Omitted in .

[0134] The modulation unit 25 of this embodiment controls the signal din (in Fig.15 and Fig.16 (not shown) during the activation period, such as Fig.16 As shown in FIG. 1 , at the timing when the AC current v2 becomes zero, that is, the current iL becomes zero (time t0), the control signal swc2 is activated to low. Fig.15 and Fig.16 The control signal swc2 is restored to high at the timing of the length of time indicated by (not shown).

[0135] If the control signal swc2 changes to low, the capacitance of the capacitor C changes from the first capacitance to the second capacitance and the frequency of the AC current v1 increases. Fig.16 As shown in FIG. 1 , the frequency (second frequency) is maintained during the period when the control signal swc2 is low. Therefore, the timing at which the resonance frequency of the resonance circuit 23 returns to the first frequency varies depending on the length of time that the capacitance of the capacitor C is the second capacitance. As a result, Fig.16 As shown in FIG. 1 , the phase of the alternating current v2 after the vibration at the first frequency is changed by an amount corresponding to the length of time that the capacitance of the capacitor C is the second capacitance compared to before the capacitance of the capacitor C becomes the second capacitance. Therefore, it can be said that: Fig.15 and Fig.16 In the simulation, it is achieved that the phase of the pen signal PS transmitted at the first frequency is changed by an amount corresponding to the information of the transmission object.

[0136] As described above, the electromagnetic induction pen 2 of this embodiment can also control the phase of the pen signal PS transmitted at the first frequency based on the information of the transmitting object, thereby realizing multi-valued pen signal PS without causing a decrease in the receiving level in the orthogonal detection of the position detection device 3.

[0137] Next, the position detection system 1 of the fourth embodiment of the present invention is described. The position detection system 1 of this embodiment is the same as the position detection system 1 of the third embodiment, except that the internal structure of the resonance circuit 23 and the operation of the modulation unit 25 are different from those of the position detection system 1 of the third embodiment. Therefore, the following description focuses on the differences from the position detection system 1 of the third embodiment.

[0138] Fig.17 23 is a diagram showing the internal structure of the resonance circuit 23 of this embodiment. Fig.14 As can be understood from the comparison, the resonance circuit 23 of the present embodiment is different from the resonance circuit 23 of the third embodiment in that the capacitor C22 is replaced with a capacitor C23 and resistors R4 and R5.

[0139] The resistors R4 and R5 are connected in series between the node n2 and the switch element SW2. One electrode of the capacitor C23 is connected to the connection point between the resistors R4 and R5, and the other electrode is connected to the source of the switch element SW2.

[0140] The modulation unit 25 of this embodiment is different from the modulation unit 25 of the third embodiment. In the initial state, the switch element SW2 is controlled to be disconnected (so-called normally off). In this embodiment, when the switch element SW2 is disconnected, the capacitors C20, C23 and the coil L constitute a resonant circuit. The first capacitance of this embodiment becomes the composite capacitance of the capacitors C20 and C23. On the other hand, when the switch element SW2 is turned on, the capacitor C23 is short-circuited, so the resonant circuit is formed by the capacitor C20 and the coil L. The second capacitance of this embodiment becomes the capacitance of the capacitor C20 alone.

[0141] In addition, the modulation unit 25 of the present embodiment is configured to change the capacitance of the capacitor C from the first capacitance to the second capacitance by turning on the switch element SW2, and to change the capacitance of the capacitor C from the second capacitance to the first capacitance by turning off the switch element SW2. As in the third embodiment, the modulation unit 25 controls the timing of turning on and off the switch element SW2 by the alternating current v2 appearing at the node n2 and the control signal din and the selection signal dsel supplied from the processing circuit 24.

[0142] Specifically, the modulation unit 25 of the present embodiment controls the switch element SW2 to be turned on during the period when the control signal din is activated, and then returns the switch element SW2 to be turned off at the timing when the length of time indicated by the selection signal dsel has passed. According to the operation of the modulation unit 25, as in the third embodiment, the resonance frequency of the resonance circuit 23 is changed to the second frequency within the length of time indicated by the selection signal dsel, so that the phase of the AC current v1 restored to the first frequency can be controlled by the 4-bit information as the transmission object. In addition, the frequency of the resonance circuit 23 is changed from the first frequency to the second frequency in a very short time, and is restored to the first frequency after the switch element SW2 is turned off, so there is almost no drop in the reception level in the orthogonal detection performed by the position detection device 3. Therefore, the electromagnetic induction pen of the present embodiment can also realize the multi-valued pen signal PS (specifically, 4-bit phase modulation) without causing a drop in the reception level in the orthogonal detection of the position detection device 3.

[0143] Fig.18 and Fig.19 : is a diagram showing the simulated waveforms of the AC current v1, the AC current v2, the current iL, and the control signal swc2 according to the present embodiment. Fig. 202 is a diagram showing the simulated waveforms of the current iC23 flowing to the capacitor C23 and the current iR5 flowing to the resistor R5. Fig.18 and Fig. 20 At the time point (0 μs) on the left end of (a) and (b), the position detection layer 3 is sending out the alternating magnetic field AM. Fig.18 and Fig. 20 At the time point (100 μsec) on the right end of (a) and (b), the electromagnetic induction pen 2 is transmitting the pen signal PS as a reflection signal. Fig.19 Yes Fig.18 The waveform shown is a magnified image between 38μs and 42μs. Fig. 20 (c) and (d) are respectively Fig. 20 The waveforms shown in (a) and (b) are enlarged between 38 μs and 42 μs.

[0144] exist Figure 18 to Figure 20 In the simulation, the capacitance of capacitor C23 is set to 8481pF, the resistance value of resistor R4 is set to 1mΩ, and the resistance value of resistor R5 is set to 10Ω. The other circuit constants are set to the same Fig.15 The same value as the simulation. In addition, the modulation unit 25 maintains the switch element SW2 on for a period of 0 μs, 0.5 μs, 1.0 μs, and 1.5 μs. In practice, for example, if n-bit phase modulation is performed, 2 n However, if all the conditions are written, the drawings will become difficult to read, so Fig.18 , Fig.19 , Fig. 20 Omitted in .

[0145] The modulation unit 25 of this embodiment controls the signal din (in Figure 18 to Figure 20 (not shown) during the activation period, such as Fig.19 As shown, the control signal swc2 changes to high. And, after the selection signal dsel (in Figure 18 to Figure 20 The control signal swc2 is restored to low at the timing of the length of time indicated by (not shown).

[0146] If the control signal swc2 changes to high, the capacitance of the capacitor C changes from the first capacitance to the second capacitance and the frequency of the AC current v1 decreases. Fig.19 As shown in FIG. 1 , the frequency (second frequency) is maintained during the period when the control signal swc2 is high. Therefore, the timing at which the resonance frequency of the resonance circuit 23 returns to the first frequency varies depending on the length of time that the capacitance of the capacitor C is the second capacitance. As a result, Fig.19As shown in FIG. 1 , the phase of the alternating current v2 after the vibration at the first frequency is changed by an amount corresponding to the length of time that the capacitance of the capacitor C is the second capacitance compared to before the capacitance of the capacitor C becomes the second capacitance. Therefore, it can be said that: Figure 18 to Figure 20 In the simulation, it is achieved that the phase of the pen signal PS transmitted at the first frequency is changed by an amount corresponding to the information of the transmission object.

[0147] Fig.21 and Fig. 22 1 is a diagram showing simulation waveforms of the AC current v1, the AC current v2, the current iL, and the control signal swc2 according to another example of the present embodiment. Fig.21 and Fig. 22 The details of the simulation are similar to those of FIG. 1 except that the capacitance of capacitor C20 is 4nF and the capacitance of capacitor C23 is 2481p. Figure 18 to Figure 20 The simulation is the same.

[0148] If you observe Fig.21 and Fig. 22 It is understandable that Fig.18 and Fig.19 Compared with the example, the level of the AC current v1 rises after the control signal swc2 is restored to low. Fig.21 and Fig. 22 In the simulation, Fig.18 and Fig.19 Compared with the simulation, the phase variation range is reduced. From this result, it can be understood that in order to suppress the level drop of the AC current v1 while changing the phase as much as possible, it is necessary to appropriately determine the capacitance of the capacitors C20 and C23. For example, if the capacitance of the capacitor C20 is 4nF and the capacitance of the capacitor C23 is 2449p, it is possible to prevent the level drop of the AC current v1 after the control signal swc2 is restored to low while changing the phase from 0° to 220°.

[0149] As described above, the electromagnetic induction pen 2 of this embodiment can also control the phase of the pen signal PS transmitted at the first frequency based on the information of the transmitting object, thereby realizing multi-valued pen signal PS without causing a decrease in the receiving level in the orthogonal detection of the position detection device 3.

[0150] Furthermore, according to the electromagnetic induction pen 2 of this embodiment, since the initial state of the switch element SW2 can be set to OFF, the circuit can be realized more easily than the electromagnetic induction pen 2 of the third embodiment which requires the normally-on switch element SW2.

[0151] Next, the position detection system 1 of the fifth embodiment of the present invention is described. The position detection system 1 of this embodiment is the same as the position detection system 1 of the first embodiment, except that the internal structure of the resonance circuit 23 and the operations of the processing circuit 24 and the modulation unit 25 are different from those of the position detection system 1 of the first embodiment. Therefore, the following description focuses on the differences from the position detection system 1 of the first embodiment.

[0152] Fig.23 23 is a diagram showing the internal structure of the resonance circuit 23 of this embodiment. Figure 4 By comparison, it can be understood that the resonant circuit 23 of this embodiment is different from the resonant circuit 23 of the first embodiment in that it does not have the switching element SW1 and the selector SEL, has a capacitor C24 instead of the capacitors C0 to C16, has resistors R6 and R7, and has switching elements SW3 and SW4.

[0153] The switch elements SW3 and SW4 are P-channel MOSFETs. The drain of the switch element SW3 is connected to one electrode of the capacitor C24 via the resistor R6, and the source is connected to the node n3 formed by the cathode of the diode D2. The drain of the switch element SW4 is connected to the node n1, and the source is connected to one electrode of the capacitor C24 via the resistor R7. The other electrode of the capacitor C24 is connected to the ground.

[0154] The processing circuit 24 of this embodiment stores in advance a table that associates 4-bit information with the timing at which the modulation unit 25 changes the capacitance of the capacitor C from the first capacitance to the second capacitance. Figure 3 Each time the data DATA shown is transmitted, the timing corresponding to the data DATA to be transmitted is determined by referring to the above table, and the selection signal dsel indicating the determined timing is supplied to the modulation unit 25. It should be noted that the timing indicated by the selection signal dsel is specifically determined by the elapsed time from a predetermined timing (for example, the timing when the AC current v1 changes from negative to positive) that arrives during the period when the control signal din is activated.

[0155] The modulation unit 25 of the present embodiment performs the following processing: before the position detection device 3 ends sending out the alternating magnetic field AM, the capacitor C24 is charged by temporarily turning on the switch element SW3, and after the position detection device 3 ends sending out the alternating magnetic field AM, the capacitance of the capacitor C is temporarily changed from the first capacitance (the capacitance of the capacitor C0 alone) to the second capacitance (the combined capacitance of the capacitors C0 and C24) by temporarily turning on the switch element SW4. The modulation unit 25 determines the timing of turning on and off the switch element SW3 in such a way that the charging is completed before the control signal din is activated. Specifically, the modulation unit 25 is configured to turn on the switch element SW3 after a specified time from the generation of the alternating current v1, and further turn off the switch element SW3 after a specified time. On the other hand, the modulation unit 25 controls the timing of turning on and off the switch element SW4 by the control signal din and the selection signal dsel supplied from the processing circuit 24.

[0156] Specifically, if the modulation unit 25 of the present embodiment detects that the above-mentioned predetermined timing has arrived during the activation of the control signal din, it waits for the time indicated by the selection signal dsel to pass from this moment on, and controls the switch element SW4 to be turned on. In addition, when the predetermined time has passed since the switch element SW4 was controlled to be turned on, the switch element SW4 is controlled to be turned off. In the present embodiment, since the capacitor C24 is charged in the stage before the modulation unit 25 turns on the switch element SW4, the level of the alternating current v1 rises sharply after the switch element SW4 is turned on. The frequency of the alternating current v1 at this time is not constant, but at least becomes a value different from the first frequency (second frequency). If the switch element SW4 is restored to be turned off, the level of the alternating current v1 gradually stabilizes, but under the influence of the temporary rapid rise in the level, the phase changes compared to before the switch element SW4 is turned on. And the amount of change in the phase is different depending on the timing indicated by the selection signal dsel. Therefore, through the operation of the modulation unit 25 of the present embodiment, it is also possible to control the phase of the alternating current v1 restored to the first frequency through the 4-bit information as the transmission object. In addition, since the level of the AC current v1 temporarily changes for a very short time, it returns to the vibration at the first frequency soon after the switch element SW4 is turned off, and therefore there is almost no drop in the reception level in the orthogonal detection performed by the position detection device 3. Therefore, the electromagnetic induction pen of this embodiment can also realize multi-valued (specifically, 4-bit phase modulation) pen signal PS without causing a drop in the reception level in the orthogonal detection of the position detection device 3.

[0157] Fig.24 and Fig.251 is a diagram showing simulated waveforms of the AC current v1, the control signal swc3, the control signal swc4, and the voltage signal cap appearing at one electrode of the capacitor C24 according to the present embodiment. Fig.24 At the left end time point (0 μs), the position detection layer 3 is sending out the alternating magnetic field AM. Fig.24 At the right end time point (40 μsec), the electromagnetic induction pen 2 is transmitting the pen signal PS as a reflection signal. Fig.25 Yes Fig.24 The waveform shown is a diagram obtained by enlarging the period between 4 μs and 14 μs.

[0158] exist Fig.24 and Fig.25 In the simulation, the capacitance of capacitor C24 is set to 5nF, and the resistance values ​​of resistors R6 and R7 are set to 20Ω. The other circuit constants are set to Figure 6 The same value as the simulation. In addition, the length of the time from the predetermined timing that arrives during the activation of the control signal din to the time when the control signal swc4 changes to low is set to 0 μs, 0.5 μs, 1.0 μs, and 1.5 μs. In fact, if, for example, n-bit phase modulation is performed, 2 n However, if all the conditions are written, the drawings will become difficult to read, so Fig.24 and Fig.25 The length of time during which the control signal swc4 is maintained at the low level is set to 0.1 μsec.

[0159] First refer to Fig.24 The modulation unit 25 of this embodiment changes the control signal swc3 to low within a predetermined time at the time t0 before the reception of the alternating magnetic field AM is completed. As a result, the voltage signal cap rises and the capacitor C24 is charged. The specific length of time for which the control signal swc3 is maintained at low is a sufficient length required to complete the charging of the capacitor C24 before the reception of the alternating magnetic field AM is completed.

[0160] After that, the modulation unit 25 controls the signal din (in Fig.24 and Fig.25 During the period of activation of the control signal din (not shown in the figure), if the arrival of the specified timing (the timing when the control signal din is activated, the timing when the control signal din returns to inactivity, the timing when the AC current v1 changes from negative to positive, etc.) is detected at the time t1 shown in the figure, then from this moment on, the time indicated by the selection signal dsel is waited for to pass, and the switching element SW4 is controlled to be turned on within 0.1μ second.

[0161] After the modulation unit 25 controls the switch element SW4 to be turned on, Fig.25As shown in FIG. 1 , the level of the AC current v1 rises sharply. This is because the capacitor C24 is charged in the stage before the switch element SW4 is turned on. Afterwards, if the switch element SW4 is turned off again, the level of the AC current v1 gradually stabilizes and returns to the vibration at the first frequency. However, if Fig.25 As shown, the phase of the AC current v1 after returning to the first frequency is changed compared to before the switch element SW4 is controlled to be turned on due to the timing of the modulation unit 25 turning on the switch element SW4. Therefore, it can be said that: in this embodiment, the phase of the pen signal PS sent at the first frequency is changed by an amount corresponding to the information of the sending object.

[0162] As described above, the electromagnetic induction pen 2 of this embodiment can also control the phase of the pen signal PS transmitted at the first frequency based on the information of the transmission object, so that the pen signal PS can be multi-valued without causing a decrease in the reception level in the orthogonal detection of the position detection device 3. In addition, according to the electromagnetic induction pen 2 of this embodiment, the phase can be controlled 360 degrees without almost causing a decrease in the level of the AC current v1.

[0163] As mentioned above, although the preferred embodiment of the present invention has been described, the present invention is not limited to such embodiment at all, and the present invention can be implemented in various forms within the scope not departing from the gist of the present invention.

[0164] Description of symbols

[0165] 1 Position detection system

[0166] 2 Electromagnetic induction pen

[0167] 3 Position detection device

[0168] 11. Comparator

[0169] 12 D-type trigger circuit

[0170] 20 Core

[0171] 21. Pressure sensor

[0172] 22 Side switch

[0173] 23 Resonance Circuit

[0174] 24 Processing circuit

[0175] 25 Modulation Department

[0176] 26 Control circuit

[0177] 30 Switch

[0178] 31 Sensor Controller

[0179] 32 Main processor

[0180] C, C0~C16, C21~C24 capacitors

[0181] D1~D3 diodes

[0182] AM Alternating Magnetic Field

[0183] PS pen signal

[0184] L Coil

[0185] LC Toroidal Coil

[0186] R1~R7 resistors

[0187] SEL Selector

[0188] SW1~SW4 Switching elements

Claims

1. An electromagnetic induction pen, comprising: A resonant circuit (23) transmits a pen signal (PS) using power obtained from an alternating magnetic field (AM) sent by a position detection device (3); and A control circuit (26) temporarily changes the resonance frequency of the resonance circuit (23) from a first frequency to a second frequency different from the first frequency based on information sent to the position detection device (3), and then restores the resonance frequency of the resonance circuit (23) to the first frequency, so that the resonance circuit (23) sends the pen signal (PS) obtained by phase modulation according to the information.

2. The electromagnetic induction pen according to claim 1, wherein: The pen signal (PS) obtained by performing phase modulation according to the information is a signal vibrating at the first frequency.

3. The electromagnetic induction pen according to claim 1, wherein: The resonant circuit (23) comprises a capacitor (C), After the position detection device (3) completes sending out the alternating magnetic field (AM), the control circuit (26) temporarily changes the capacitance of the capacitor (C) from a first capacitance to a second capacitance different from the first capacitance based on the information, thereby changing the resonance frequency of the resonant circuit (23) from the first frequency to the second frequency based on the information.

4. The electromagnetic induction pen according to claim 3, wherein: The control circuit (26) includes a processing circuit (24) that controls the value of the second capacitance based on the information.

5. The electromagnetic induction pen according to claim 4, wherein: The resonant circuit (23) includes a coil (L) and a switch element (SW1). The capacitor (C) includes a first capacitor (C0) and a second capacitor (C1), the first capacitor (C0) being connected in series with the coil (L), and the second capacitor (C1) being connected in parallel with the first capacitor (C0) via the switch element (SW1). The control circuit (26) includes a modulation unit (25) which changes the capacitance of the capacitor (C) from the first capacitance to the second capacitance by turning on the switch element (SW1), and changes the capacitance of the capacitor (C) from the second capacitance to the first capacitance by turning off the switch element (SW1).

6. The electromagnetic induction pen according to claim 5, wherein: The modulation unit (25) performs on-off control of the switch element (SW1) at the timing when the pen signal (PS) becomes 0.

7. The electromagnetic induction pen according to claim 5 or 6, wherein: The capacitor (C) includes a plurality of second capacitors (C1 to C16) having different capacitances from each other, The resonant circuit (23) includes a selector (SEL) that selectively connects one of the plurality of second capacitors (C1 to C16) to the switch element (SW1). The processing circuit (24) controls the selector (SEL) based on the information, thereby controlling the value of the second capacitance based on the information.

8. The electromagnetic induction pen according to claim 4, wherein: The resonant circuit (23) comprises a coil (L), The capacitor (C) includes a decoupling capacitor (C20), a first capacitor (C0), and a second capacitor (C1), wherein the decoupling capacitor (C20) adds a DC component to the output of the resonant circuit (23) and supplies the DC component to the processing circuit (24), the first capacitor (C0) is connected in series with the coil (L), and the second capacitor (C1) is connected to an electrode of the decoupling capacitor (C20) on the processing circuit (24) side in parallel with the first capacitor (C0). The resonant circuit (23) further includes a switch element (SW2), wherein the switch element (SW2) is arranged between the second capacitor (C1) and a ground terminal. The control circuit (26) includes a modulation unit (25) which changes the capacitance of the capacitor (C) from the first capacitance to the second capacitance by turning on the switch element (SW2), and changes the capacitance of the capacitor (C) from the second capacitance to the first capacitance by turning off the switch element (SW2).

9. The electromagnetic induction pen according to claim 8, wherein: The capacitor (C) includes a plurality of second capacitors (C1 to C16) having different capacitances from each other, The resonant circuit (23) includes a selector (SEL) that selectively connects one of the plurality of second capacitors (C1 to C16) to an electrode of the decoupling capacitor (C20) on the processing circuit (24) side. The processing circuit (24) controls the selector (SEL) based on the information, thereby controlling the value of the second capacitance based on the information.

10. The electromagnetic induction pen according to claim 3, wherein: The control circuit (26) further includes a processing circuit (24) that controls the length of a period during which the capacitance of the capacitor (C) is maintained at the second capacitance based on the information.

11. The electromagnetic induction pen according to claim 10, wherein: The capacitor (C) includes a decoupling capacitor (C20) that adds a DC component to the output of the resonant circuit (23) and supplies the DC component to the processing circuit (24), and a first capacitor (C22) that is connected to an electrode of the decoupling capacitor (C20) on the processing circuit (24) side in series with the coil (L). The resonant circuit (23) includes a switch element (SW2), which is arranged between the first capacitor (C22) and the ground terminal. The control circuit (26) includes a modulation unit (25), which changes the capacitance of the capacitor (C) from the first capacitance to the second capacitance by setting the switch element (SW2) to be disconnected, and changes the capacitance of the capacitor (C) from the second capacitance to the first capacitance by setting the switch element (SW2) to be connected.

12. The electromagnetic induction pen according to claim 11, wherein: The processing circuit (24) controls the length of a period during which the modulation unit (25) maintains the switch element (SW2) in an off state based on the information, thereby controlling the length of a period during which the capacitance of the capacitor (C) is maintained at the second capacitance based on the information.

13. The electromagnetic induction pen according to claim 10, wherein: The capacitor (C) includes a decoupling capacitor (C20) that adds a DC component to the output of the resonant circuit (23) and supplies the DC component to the processing circuit (24), and a first capacitor (C23) that is connected in series with the coil (L) to an electrode of the decoupling capacitor (C20) on the processing circuit (24). The resonant circuit (23) includes a switch element (SW2) which is arranged in parallel with the first capacitor (C23). The control circuit (26) includes a modulation unit (25) which changes the capacitance of the capacitor (C) from the first capacitance to the second capacitance by turning on the switch element (SW2), and changes the capacitance of the capacitor (C) from the second capacitance to the first capacitance by turning off the switch element (SW2).

14. The electromagnetic induction pen according to claim 13, wherein: The processing circuit (24) controls the length of a period during which the modulation unit (25) maintains the switch element (SW2) on based on the information, thereby controlling the length of a period during which the capacitance of the capacitor (C) is maintained at the second capacitance based on the information.

15. The electromagnetic induction pen according to claim 3, wherein: The control circuit (26) comprises: a modulation unit (25) that, after changing the capacitance of the capacitor (C) to the second capacitance, restores the capacitance of the capacitor (C) to the first capacitance after a predetermined time; and The processing circuit (24) controls the timing at which the modulation unit (25) changes the capacitance of the capacitor (C) to the second capacitance based on the information.

16. The electromagnetic induction pen according to claim 15, wherein: The resonant circuit (23) includes a coil (L), a first switch element (SW3) and a second switch element (SW4). The capacitor (C) includes a first capacitor (C0) and a second capacitor (C24), the first capacitor (C0) being connected in series with the coil (L), and the second capacitor (C24) being connected in parallel with the first capacitor (C0) via the first switch element (SW3) and the second switch element (SW4), respectively. The modulation unit (25) charges the second capacitor (C24) by temporarily turning on the first switch element (SW3) before the position detection device (3) finishes sending out the alternating magnetic field (AM). After the position detection device (3) completes sending out the alternating magnetic field (AM), the modulation unit (25) temporarily changes the capacitance of the capacitor (C) from the first capacitance to the second capacitance by temporarily turning on the second switch element (SW4).

17. The electromagnetic induction pen according to claim 16, wherein: The processing circuit (24) controls the timing of the modulation unit (25) turning on the second switch element (SW4) based on the information, thereby controlling the timing of the modulation unit (25) changing the capacitance of the capacitor (C) to the second capacitance based on the information.

18. A position detection device, wherein: The coil (LC) is used to send out an alternating magnetic field (AM) of a first frequency. After stopping the sending of the alternating magnetic field (AM), the information sent by the electromagnetic induction pen (2) is demodulated based on the phase of the signal of the first frequency detected during the detection period of the pen signal (PS).

Images