JP7108508B2 - Electronic circuit of electronic pen and electronic pen - Google Patents

Description

The present invention relates to an electronic circuit suitable for use in, for example, an electromagnetic induction type electronic pen. The present invention also relates to an electronic pen provided with this electronic circuit.

An electromagnetic induction type coordinate input device comprises a large number of loop coils arranged in the X-axis direction and the Y-axis direction of the coordinate axes, as disclosed in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2002-244806), for example. It is composed of a position detection device having a position detection sensor and an electronic pen having a resonance circuit composed of a coil wound around a magnetic core and a capacitor.

The position detection device supplies a transmission signal of a predetermined frequency to the loop coil of the position detection sensor, and the loop coil transmits electromagnetic energy to the electronic pen. The resonance circuit of the electronic pen is configured to have a resonance frequency f0 corresponding to the frequency of the transmission signal, and stores electromagnetic energy based on electromagnetic induction with the loop coil of the position detection sensor. Then, the electronic pen returns the electromagnetic energy stored in the resonance circuit to the loop coil of the position detection sensor of the position detection device.

A position detection sensor loop coil detects electromagnetic energy from the electronic pen. The position detection device detects the position of the loop coil that supplied the transmission signal and the position of the loop coil that detected the electromagnetic energy from the resonance circuit of the electronic pen, and detects the X-axis direction and the Y-axis direction on the sensor indicated by the electronic pen. Find the coordinate value of the direction.

The electronic pen also has a pen pressure detection unit for detecting the pressure (pen pressure) applied to the pen tip. is transmitted to the position detection device. As one of the methods of transmitting this writing pressure information to the position detecting device, a method of transmitting it in the form of a digital signal is known. is generally mounted (see, for example, Patent Document 2 (Japanese Patent No. 6008393)).

FIG. 6 is a diagram showing an example of an electronic circuit 200 provided in this type of electromagnetic induction type electronic pen. An electronic circuit 200 of the electronic pen of this example includes a resonance circuit 203 configured by connecting a coil 201 wound around a magnetic core and a capacitor 202 in parallel, and an IC 230 . IC 230 has the function of a control circuit.

In this example, the resonance circuit 203 has a coil 201 and a capacitor 202 connected in parallel with a variable capacitance capacitor (trimmer capacitor) 204 for adjusting the resonance frequency f0. An adjuster adjusts the capacitance of the variable capacitor 204, thereby adjusting the resonance frequency f0 of the resonance circuit 203 to be optimum.

In this example, a rectifier circuit 205 is provided that rectifies an induced current that flows by electromagnetic induction from the outside in the resonance circuit 203 and generates a power supply voltage Vcc for the IC 230 . Rectifier circuit 205 includes capacitors 206 and 209 and diodes 207 and 208 .

One end of the parallel circuit including the coil 201 , the capacitor 202 and the variable capacitor 204 of the resonance circuit 203 is grounded, and the other end is connected to one end of the capacitor 206 . The other end of capacitor 206 is connected to the connection point between the cathode of diode 207 and the anode of diode 208 . The anode side of diode 207 is grounded. The cathode of diode 208 is grounded via capacitor 209 . A connection point between the cathode of the diode 208 and the capacitor 209 is the output terminal of the rectifier circuit 205, and the power supply voltage Vcc is output. The output terminal of this rectifier circuit 205 is connected to the connection pin 230 a of the IC 230 .

In the electronic circuit 200 of FIG. 6, the connection point P0 between the other end of the resonance circuit 203 and one end of the capacitor 206 is connected through the capacitor 210 to the clock generation circuit formed inside the IC 230. It is connected to pin 230b. The connection point P 0 is also grounded through a series circuit of a capacitor 211 and a switch circuit 212 . The switch circuit 212 is connected to the connection pin 230c of the IC 230 to which the switching control signal SW is output. The switch circuit 212 is ON/OFF-controlled by the control signal SW from the IC 230 , thereby ON/OFF-controlling the connection of the capacitor 211 to the resonance circuit 203 . When the capacitor 211 is not connected, the resonance circuit 203 resonates at the above-described resonance frequency f0 and the predetermined phase. is in a different phase.

In the example of FIG. 6, the pen pressure detection unit detects the pen pressure as a change in capacitance. 220 to ground. A resistor 221 is connected in parallel with the variable capacitor 220 .

When the writing pressure value detected by the writing pressure detection unit is detected, the IC 230 fully charges the variable capacitor 220 and then stops charging the variable capacitor 220 via the resistor 221 . to discharge. Then, IC 230 measures the time required for the capacitance of variable capacitor 220 at that time to discharge to a predetermined charging potential, and detects the capacitance of variable capacitor 220 from the length of that time. , acquires information on pen pressure corresponding to the detected capacitance. The IC 230 acquires the writing pressure information as multi-bit digital information in this example, and transmits it to the position detection device.

In the electronic pen electronic circuit 200 , the resonance circuit 203 receives the signal sent from the position detection sensor by electromagnetic induction, and the rectifier circuit 205 rectifies the signal to generate the power supply voltage Vcc for driving the IC 230 . This drives the IC 230 . IC 230 takes in the received signal through capacitor 210 and generates a clock signal. Then, the IC 230 generates the control signal SW based on the generated clock signal and supplies the generated control signal SW to the switch circuit 212 .

The control signal SW is at a low level during the position detection period, the switch circuit 212 is turned off, and the capacitor 211 is disconnected from the resonance circuit 203 . As a result, in the electronic circuit 200, the resonance circuit 203 in the electronic circuit 200 transmits the signal received from the position detection sensor to the position detection sensor with the same frequency and phase.

In addition, the control signal SW corresponds to the detected pen pressure value digital information during the additional information period. 0", it becomes high level. As a result, a signal modulated according to the digital information is transmitted to the position detection sensor during the additional information period.

In the position detection device, in the position detection period, the pointed position is detected by the electronic pen depending on which position of the loop coil of the position detection sensor receives the signal from the electronic pen. Further, in the position detection device, the writing pressure value of the electronic pen is detected by demodulating the modulated signal during the additional information period.

JP-A-2002-244806 Japanese Patent No. 6008393

As described above, the electromagnetic induction type electronic pen includes the resonance circuit 203, and the resonance circuit 203 electromagnetically couples with the position detection sensor of the position detection device to transmit and receive signals. The resonance frequency of must be optimized to match the frequency of the AC signal transmitted from the position detection sensor. Therefore, in the electronic circuit of the conventional electronic pen, the resonance frequency of the resonance circuit 203 is optimized by connecting the trimmer capacitor 204 to the resonance circuit 203 and adjusting the trimmer capacitor 204 . rice field.

Therefore, in the electronic circuit 200 of the conventional electronic pen, there is a problem that adjustment of the trimmer capacitor 204 is troublesome.

It should be noted that electronic circuits including resonant circuits have similar problems, not limited to electronic pens.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to enable adjustment of the resonance frequency of a resonance circuit of an electronic circuit without using the trimmer capacitor 204 .

In order to solve the above problems,
An electronic circuit comprising an IC (Integrated Circuit) and a resonance circuit external to the IC, comprising a parallel circuit of a coil and a first capacitor,
The IC includes a variable capacitor for adjusting the frequency of the resonant circuit, and has a connection pin for connecting the variable capacitor to the outside,
one end of the parallel circuit is grounded and the other end of the parallel circuit is connected to one end of a second capacitor external to the IC;
The other end of the second capacitor is connected to the connection pin of the IC and connected to a diode for clamping the potential of the other end of the second capacitor to a predetermined value. to provide an electronic circuit characterized by

In the electronic circuit configured as described above, since the variable capacitor for adjusting the frequency of the resonant circuit is included in the IC, there is no need to connect a trimmer capacitor to the resonant circuit.

1 is a diagram showing a circuit configuration example of an electronic circuit of a first embodiment of an electronic pen according to the present invention; FIG. 1 is a longitudinal sectional view for explaining a configuration example of a first embodiment of an electronic pen according to the present invention; FIG. 1 is a diagram for explaining an electronic circuit of a first embodiment of an electronic pen according to the invention; FIG. 1 is a diagram showing a configuration example of part of an electronic circuit of a first embodiment of an electronic pen according to the present invention; FIG. 1 is a diagram showing a circuit configuration example of an electronic circuit of a first embodiment of an electronic pen according to the present invention; FIG. and FIG. 10 is a diagram showing a circuit example of an electronic circuit of a conventional electronic pen.

Embodiments of an electronic circuit according to the present invention will be described below with reference to the drawings, together with embodiments of an electromagnetic induction type electronic pen in which the electronic circuit is mounted.

FIG. 1 is a circuit diagram for explaining a configuration example of an electronic circuit 10 applied to an electronic pen 1 of the embodiment. Moreover, FIG. 2 is a longitudinal sectional view for explaining a hardware configuration example of the electronic pen 1 of the embodiment. First, a configuration example of the electronic pen 1 in FIG. 2 will be described.

As shown in FIG. 2, the electronic pen 1 includes a cylindrical housing (case) 2, a core body 3, a coil 5 wound around a cylindrical ferrite core 4, a printed circuit board 6, It is composed of a capacitor 7 and an IC 100 arranged on the printed circuit board 6, and a writing pressure detection section 8. FIG.

The cylindrical housing 2 has an opening 2a at one end in the axial direction and is closed at the other end in the axial direction. A printed circuit board 6 on which electronic components are mounted is fixedly disposed near the other end in the axial direction in the cylindrical hollow portion of the housing 2 . A ferrite core 4 is accommodated near one end of the housing 2 where the opening 2a is formed.

As shown in FIG. 2, the ferrite core 4 has a through hole 4a extending in the axial direction, and a coil 5 forming a resonance circuit is wound around the outer periphery of the through hole 4a. A capacitor 7 provided on a printed circuit board 6 is connected in parallel to both ends (not shown) of the coil 5 . The core 3 is inserted through the through hole 4 a of the ferrite core 4 .

The core 3 is made of a non-conductive material. One end of the core 3 in the axial direction serves as a tip portion 3a that functions as a pen tip. It protrudes so as to be exposed to the outside from the portion 2a. The other end 3b of the core 3 in the axial direction is connected to the pen pressure detecting section 8. As shown in FIG.

The writing pressure detection unit 8 uses a mechanism that changes the capacitance of the variable capacitor according to the pressure (writing pressure) applied to the core 3 (for example, Patent Document (Japanese Patent Application Laid-Open No. 2011-186803) ). Note that the writing pressure detection unit 8 can also use a variable capacitor configured by a semiconductor chip composed of a MEMS (Micro Electro Mechanical Systems) element (for example, see Patent Document (Japanese Patent Application Laid-Open No. 2013-161307)). The configuration of the writing pressure detection unit 8 is not limited to these configuration examples, and may detect writing pressure as a change in inductance.

An electronic circuit 10 of the electronic pen 1 is constructed as shown in FIG. That is, in this example, a resonance circuit 11 is formed by a parallel circuit of a coil 5 wound around a ferrite core 4 and a capacitor 7 arranged on a printed circuit board 6 .

In this example, a rectifier circuit 12 is provided that rectifies an induced current that flows by electromagnetic induction from the outside in a resonance circuit 11 to generate a power supply voltage Vcc for the IC 100 . The rectifier circuit 12 includes capacitors 13 and 16 and diodes 14 and 15, and in this example, is configured as a half-wave voltage doubler type rectifier circuit.

One end of the resonance circuit 11 is grounded, and the other end is connected to one end of the capacitor 13 . The other end of capacitor 13 is connected to the connection point between the cathode of diode 14 and the anode of diode 15 . The anode side of diode 14 is grounded. The cathode of diode 15 is grounded via capacitor 16 . A connection point between the cathode of the diode 15 and the capacitor 16 is the output terminal of the rectifier circuit 12, and the power supply voltage Vcc is output. The output terminal of this rectifier circuit 12 is connected to the connection pin 100a of the IC100. Here, the power supply voltage +Vcc is set to 5 volts in this example.

In the electronic circuit 10 of this embodiment, the connection point P1 between the other end of the capacitor 13 and the cathode of the diode 14 and the anode of the diode 15 is connected to the connection pin 100b of the IC100.

An induced voltage is generated by electromagnetic induction at the connection point P0 between one end of the capacitor 13 and the resonance circuit 11 . As shown in FIG. 3A, the induced voltage obtained at this connection point P0 has a positive peak value of Vcc/2+VF and a negative peak value of −(Vcc/2+VF) centering on zero potential. becomes an alternating voltage that oscillates as VF is the voltage drop when the diode 14 is conducting.

When the connection point P0 is connected to the IC 100, the peak value on the negative side becomes -Vcc/2-VF. In the IC100, when the voltage on the negative side is smaller than -VF volts, the diode 101 inside the IC100 becomes conductive and the voltage cannot be taken into the IC100. Therefore, the connection point P0 cannot be used by connecting it to the connection pin 100b of the IC 100 as it is.

On the other hand, at the connection point P1 between the other end of the capacitor 13 and the cathode of the diode 14 and the anode of the diode 15, the induced voltage obtained in the resonance circuit 11 is clamped by the diode 14. ), the positive side peak value is (Vcc+VF) volts, and the negative side peak value is -VF volts.

Therefore, even if the connection point P1 is connected to the connection pin 100b of the IC100, the voltage that can be taken in by the IC100 falls within the range of Vcc+VF to -VF, and the voltage can be taken into the IC100. That is, by connecting the connection point P1 between the other end of the capacitor 13 and the diode 14 to the connection pin 100b of the IC 100, the IC 100 can handle the induced voltage generated in the resonance circuit 11 without any trouble. Therefore, in this embodiment, a circuit for adjusting the resonance frequency of the resonance circuit 11 can be provided within the IC 100 .

That is, in the IC 100, an adjustment circuit 110 for adjusting the resonance frequency of the resonance circuit 11 is provided for the connection pin 100b. In this example, the resonance frequency adjustment circuit 110 includes a capacitance variable circuit 111, a capacitance setting signal generation circuit 112, a DC blocking capacitor 113, and a peak detection circuit 114, as shown in FIG. It is configured.

The peak detection circuit 114 has a circuit configuration including diodes 1141 and 1142 and a resistor 1143, as shown in FIG. be done.

In this example, the resonance frequency adjustment circuit 110 provided in the IC 100 cooperates with the resonance frequency setting device 120 provided outside the IC 100 to adjust the resonance frequency of the resonance circuit 11 to that of the position detection sensor. It is configured to be optimal in relation to The resonance frequency setting device 120 may be configured by a dedicated device, or may be configured by a general-purpose device such as a computer.

The variable capacitance circuit 111 is configured by connecting a plurality of series circuits each including a capacitor 111C and a switch circuit 111S in parallel. A capacitance setting signal generation circuit 112 generates a switching control signal for controlling the on/off state of each of the plurality of switch circuits 111S of the capacitance variable circuit 111. FIG. The capacitance of the variable capacitance circuit 111 is equal to that of a parallel circuit of one or a plurality of capacitors 111C connected in series to the switch circuit 111S turned on by a plurality of switching control signals from the capacitance setting signal generation circuit 112. combined capacity.

Then, the induced voltage (see FIG. 3B) applied to the connection pin 100b is supplied to the peak detection circuit 114 through the capacitor 113, and the peak value is detected. A peak value detection output detected by the peak detection circuit 114 is supplied to a resonance frequency setting device 120 outside the IC 100 through a connection pin 100d.

When optimizing the resonance frequency of the resonance circuit 11, the electronic pen 1 is set to receive an AC signal from the position detection sensor. Then, a search control signal is generated for searching the plurality of switch circuits 111S of the variable capacitance circuit 111 so that the variable capacitance circuit 111 sequentially presents a plurality of combined capacitances that can appear.

Then, the resonance frequency setting device 120 receives the peak value detection output of the peak detection circuit 114 during the search through the connection pin 100d and detects the maximum peak value. Resonance frequency setting device 120 stops the search control signal to capacitance setting signal generating circuit 112 after detecting the maximum peak value.

Then, the resonance frequency setting device 120 instructs the capacitance setting signal generation circuit 112 to maintain the state in which the plurality of switch circuits 111S of the capacitance variable circuit 111 were controlled when the maximum peak value was detected. A control signal is provided through connection pin 100e. The capacitance setting signal generation circuit 112 receives this control signal and maintains the state of supplying the switching control signal to the plurality of switch circuits 111S of the capacitance variable circuit 111 when the maximum peak value is detected. After this optimization process is finished, the connection between the resonance frequency setting device 120 and the connection pins 100d and 100e of the IC 100 is released.

Thereby, the resonance circuit 11 of the electronic pen 1 is controlled to have an optimum resonance frequency for the position detection sensor.

6, the electronic circuit 10 of the electronic pen 1 of this embodiment also includes a circuit for generating a clock signal from an AC signal obtained by electromagnetic induction from a position detection sensor, writing pressure information, and the like. is provided with a modulation circuit for transmitting the additional information to the position detection sensor side.

In this case, as described above, in the first embodiment, the induced voltage from the position detection sensor obtained in the resonance circuit 11 can be handled by the IC 100. Therefore, the IC 100 includes a clock generation circuit and a modulation circuit. and configure those circuits to connect to connection pin 100b.

That is, in this embodiment, in the IC 100, the connection pin 100b is connected to the input terminal of the clock generation circuit 104 via the capacitor 103 for blocking direct current. The clock generation circuit 104 generates a clock signal from an AC signal (induced voltage obtained by the resonance circuit 11 ) input through the connection pin 100 b and supplies the clock signal to the control circuit 107 .

The control circuit 107 is also grounded through a variable capacitor 8C constituted by the writing pressure detection unit 8 externally attached to the IC 100 through a connection pin 100c. A resistor 17 is connected in parallel with the variable capacitor 8C. The control circuit 107 detects the electrostatic capacitance of the variable capacitor 8C by detecting the discharge time of the variable capacitor 8C in the same manner as described for the electronic circuit 200 of FIG. Digital information of the pen pressure value is generated based on the capacitance.

Also, the connection pin 100b is grounded via a series circuit of a capacitor 105 and a switch circuit 106 inside the IC 100. FIG. The switch circuit 106 is turned on/off by a control signal SW from the control circuit 107. Similar to FIG. Modulation is performed to change the frequency of the frequency or change the phase. As a result, in the same manner as described with reference to FIG. 6, the digital pen pressure information is sent from the electronic pen 1 during the additional information period under the control of the control signal from the control circuit 107 .

In this example, the connection pin 100b is grounded through a protective diode 101 and connected through a diode 102 to the connection pin 100a from which the power supply voltage Vcc is obtained.

As described above, according to the electronic circuit 10 of the electronic pen 1 of the first embodiment, the trimmer capacitor for adjusting the resonance frequency of the resonance circuit 11 is not required, resulting in cost reduction. Further, since the resonance frequency of the resonance circuit 11 can be automatically adjusted by the resonance frequency setting device 120, the adjustment work of the resonance frequency becomes simpler than the case of adjusting the trimmer capacitor.

According to the first embodiment described above, a capacitor for connecting to the clock generation circuit 104 in the IC 100 can also be provided in the IC 100 by connecting to the connection pin 100b. 210 becomes unnecessary, and the connection pin 230b becomes unnecessary.

Further, since a modulation circuit for generating additional information can be provided in the IC 100 by connecting to the connection pin 100b, the capacitor 211 and switch circuit 212 shown in FIG. 230c is also unnecessary.

In the above example, the resonance frequency setting device 120 is externally attached to the IC 100, but the function of this resonance frequency setting device 120 is provided as a resonance frequency setting circuit inside the IC 100, and the resonance frequency setting circuit is externally connected. It may be configured to be able to control start and stop.

[Second embodiment]
In the electronic circuit 10 of the electronic pen 1 of the first embodiment described above, the writing pressure information detected by the writing pressure detection unit 8 is converted into digital information by modulating the resonance frequency signal of the resonance circuit 11 for position detection. I made it to send to the device. However, it is also known to transmit the writing pressure information detected by the writing pressure detection unit 8 from the electronic pen to the position detection device as a frequency shift or a phase shift of the resonance frequency signal of the resonance circuit 11. , can also be applied in this case. The electronic circuit of the second embodiment is configured in this way.

FIG. 5 is a diagram showing a configuration example of an electronic circuit 10A of an electronic pen 1A according to the second embodiment, and components similar to those in FIG. 1 are given the same reference numerals. It should be noted that the IC 100A of the second embodiment differs from the IC 100 of the first embodiment in its internal circuit configuration, and the hardware configuration of the electronic pen is a variable capacitor composed of the writing pressure detection unit 8. 8C is connected in parallel to the resonant circuit 11 and configured as a part of the resonant circuit 11, the configuration is exactly the same as that shown in FIG.

As shown in FIG. 5, a variable capacitor 8C constituted by the writing pressure detection unit 8 is connected in parallel between one end and the other end P0 of the resonance circuit 11, and the other end P0 of the resonance circuit 11 is connected to a capacitor. 13A. The other end P1A of the capacitor 13A is connected to the connection pin 100Ab of the IC 100A. Also, in this example, a battery 19 is provided, and the power supply voltage Vcc is supplied from the battery 19 to the connection pin 100Aa of the IC 100A.

In the IC 100A of the electronic circuit 10A of the second embodiment, the connection pin 100Ab is grounded via a diode 101 and connected to the connection pin 100Aa to which the power supply voltage Vcc is supplied via a diode 102. It is connected. In the electronic circuit 10A of the second embodiment, the diode 101 is essential, so that in the second embodiment, as in the first embodiment, the capacitor 13A is connected to the other end P1A side of the capacitor 13A. The resulting induced voltage is clamped to be as shown in FIG. 3(B).

In the second embodiment, a resonance frequency adjustment circuit 110A is connected to the connection pin 100Ab of the IC 100A. However, unlike the first embodiment, the IC 100A of the electronic circuit 10A of the second embodiment is not provided with a clock generation circuit and a modulation circuit.

In this example, as shown in FIG. 5, the resonant frequency adjustment circuit 110A of the IC 100A includes a variable capacitance circuit 111, a capacitance setting signal generation circuit 112, a DC blocking capacitor 113, a peak detection circuit 114, and a resonance frequency. It is configured including a frequency setting circuit 120A. The resonance frequency setting circuit 120A is a circuit having the same function as the resonance frequency setting device 120 externally attached to the IC 100 in the first embodiment. The resonance frequency setting circuit 120A is connected to the connection pin 100f of the IC 100A, and is configured to receive start-up control supplied from the outside through the connection pin 100f so that its start-up is controlled.

In this embodiment, adjustment and setting of the resonance frequency of the resonance circuit 11 are performed as follows. That is, the electronic pen 1A receives an AC signal from the position detection sensor of the position detection device in a state in which writing pressure is not applied. provides a control signal to activate the

Then, the resonance frequency setting circuit 120A supplies the search control signal to the capacitance setting signal generation circuit 112 in the same manner as the resonance frequency setting device 120 of the first embodiment. Resonance frequency setting device 120 stops the search control signal to capacitance setting signal generating circuit 112 after detecting the maximum peak value.

Then, the resonance frequency setting circuit 120A instructs the capacitance setting signal generation circuit 112 to maintain the state in which the plurality of switch circuits 111S of the capacitance variable circuit 111 were controlled when the maximum peak value was detected. Provides a control signal to The capacitance setting signal generation circuit 112 receives this control signal and maintains the state of supplying the switching control signal to the plurality of switch circuits 111S of the capacitance variable circuit 111 when the maximum peak value is detected.

Thus, also in the electronic circuit 100A of the electronic pen 1A of the second embodiment, the resonance frequency of the resonance circuit 11 can be optimally set by the IC 100A. In the case of this example, since the resonance frequency setting circuit 120A is incorporated in the IC 100A, the external resonance frequency setting device 120 as in the first embodiment is not required, which is convenient.

The IC 100A of the electronic circuit 100A of the second embodiment may also be configured to use the external resonance frequency setting device 120 as in the first embodiment.

Further, in the second embodiment, the battery 19 is provided, but as in the first embodiment, the power supply voltage Vcc is reduced by rectifying the induced voltage generated in the resonance circuit 11 by the rectifying circuit 12. may be generated.

[Other embodiments or modifications]
Although the case of the electronic circuit of the electronic pen has been described above, the present invention is applicable to any electronic circuit that includes a resonant circuit and an IC and needs to adjust the resonant frequency of the resonant circuit.

Further, as a method of optimizing the resonance frequency of the resonance circuit, the peak value of the induced voltage of the resonance circuit is detected and the peak value is maximized, but it goes without saying that the method is not limited to this method. stomach.

Note that the resonance circuit of the electronic pen may be used only for receiving signals from the position detection sensor, and signal transmission from the electronic pen to the position detection sensor does not necessarily have to be by electromagnetic induction using the resonance circuit. It is not limited. For example, magnetic field energy is received by a resonance circuit from a position detection sensor, and the received magnetic field energy is used as a drive voltage for the electronic pen, or used as a trigger signal from the position detection sensor, and the signal from the electronic pen is The present invention is also applicable to an electronic pen that uses an electric field to transmit data to a position detection sensor.

1, 1A... Electronic pen, 5... Coil, 7... Capacitor, 8... Writing pressure detection section, 8C... Variable capacitor composed of writing pressure detection section 8, 10, 10A... Electronic circuit, 11... Resonance circuit, 12 Rectifier circuit 13 Capacitor 14, 15 Diode 100, 100A IC 101, 102 Diode 110, 110A Resonance frequency adjustment circuit 111 Capacity variable circuit 112 Capacity setting signal generation circuit 114... Peak detection circuit 120... Resonance frequency setting device 120A... Resonance frequency setting circuit

Claims (10)

An electronic circuit of an electronic pen comprising an IC and a resonance circuit external to the IC, the resonance circuit being composed of a parallel circuit of a coil and a first capacitor,
The IC includes a variable capacitance circuit for adjusting the frequency of the resonant circuit, and has a connection pin for connecting the variable capacitance circuit to the outside,
one end of the parallel circuit is grounded and the other end of the parallel circuit is connected to one end of a second capacitor external to the IC;
The other end of the second capacitor is connected to the connection pin of the IC and connected to a diode for clamping the potential of the other end of the second capacitor to a predetermined value. An electronic circuit of an electronic pen characterized by: The electronic circuit of the electronic pen according to claim 1, wherein the diode has an anode grounded and a cathode connected to the other end of the second capacitor. The electronic circuit of the electronic pen according to claim 1, wherein the diode is attached externally to the IC. The electronic circuit of the electronic pen according to claim 1, wherein the diode is built in the IC. a circuit for generating a power supply voltage for the IC by rectifying an induced current generated in the resonance circuit by electromagnetic induction from the outside;
The electronic circuit of the electronic pen according to claim 2, wherein the diode forms part of a circuit that generates a power supply voltage for the IC. a clock circuit that generates a clock from an electromagnetic induction signal sent from a position detection sensor and received by the resonance circuit;
a modulation circuit for controlling the operation of the resonance circuit on and off to modulate a signal fed back to the position detection sensor;
is built in the IC,
The electronic circuit of the electronic pen according to any one of claims 1 to 5, wherein the clock circuit and the modulation circuit are connected to the connection pin. An electronic pen comprising the electronic circuit according to any one of claims 1 to 6. a resonant circuit including a coil and a first capacitor;
a rectifier circuit including a second capacitor having one end connected to the resonance circuit;
A variable capacitance circuit for frequency adjustment of the resonance circuit is provided, and a plurality of connection pins are provided, a first connection pin is connected to the rectifier circuit, and a second connection pin is connected to the other end of the second capacitor. a connected IC;
An electronic pen with The rectifier circuit includes a diode for clamping the potential of the other end of the second capacitor to a predetermined value,
The electronic pen according to claim 8.

The diode and the second capacitor constitute a half-wave voltage doubler type rectifier circuit as the rectifier circuit,
The electronic pen according to claim 9.

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