JPH07306745A - Position detecting device - Google Patents

Abstract

PURPOSE:To provide a position detecting device which can be constituted only with a digital circuit without requiring an analog switch for switching loop coils, and is good in electric power availability. CONSTITUTION:Three-state drivers 5-1 to 5-3 are connected to one-terminal sides of the loop coils 2-1 to 2-3 respectively and a three-state driver 6 is connected to the other-terminal sides in common; while one of the three-state drivers 5-1-5-3 is connected to a NOR gate 4 and the remaining drivers are held in a high-impedance state, the three-state driver 6 is grounded to supply the signal from an oscillation circuit 3 to one loop coil and generates a radio wave. Further, the three-state driver 6 is placed in a high-impedance state to detect a voltage induced with the reflected radio wave from a position indicator 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a position detecting device for detecting a coordinate value of a position indicated by a position indicator having a resonance circuit.

[0002]

2. Description of the Prior Art Prior to this application,
No. 213970 (see Japanese Patent Application Laid-Open No. 63-70326) proposes a position detecting device that has only a resonance circuit and can detect the coordinate value of a position indicated by a position indicator that is not connected to anywhere.

To briefly explain the contents of the device, one loop coil is selected from a plurality of loop coils arranged in parallel in the position detection direction, and an alternating current signal of a predetermined frequency is supplied to this loop coil to transmit radio waves. Then, the radio wave is received by the resonance circuit provided in the position indicator. At this time, the one loop coil receives the radio wave generated from the resonance circuit receiving the energy of the radio wave, and the induced voltage is generated. This is repeated for a plurality of loop coils and repeated, and the position of the resonance circuit, that is, the coordinate value of the indicated position is obtained based on the magnitude of the induced voltage generated in each loop coil.

[0004]

By the way, in the conventional position detecting device of this type, the larger the number of turns of each loop coil, the more efficiently the radio waves can be transmitted and received, but from the viewpoint of accuracy improvement, cost reduction, etc. In many cases, the above-mentioned loop coil is configured by the conductor pattern formed on the printed circuit board, and in that case, all the loop coils must be arranged in close contact with or superposed on one printed circuit board. Actually, each loop coil was limited to about 2 turns, and its impedance was about several Ω.

On the other hand, in this type of conventional position detecting device,
An analog switch was used to switch each loop coil, but the impedance when the analog switch was on was 20Ω or more even though it was low, so most of the electric power when transmitting radio waves was consumed by the analog switch There was a problem of poor efficiency.

Further, when the power supply voltage of such an analog switch is lowered, the impedance at the time of turning on is further increased and the efficiency is further deteriorated, which is an obstacle to lowering the power supply voltage of the device. Further, since such an analog switch usually requires a negative power source as well as a positive power source, there is a problem that the configuration of the power source circuit becomes complicated and its scale becomes large.

Furthermore, in this type of position detecting device,
In order to downsize the entire device and rationalize the manufacturing process, there is a demand to integrate parts other than the loop coil into a dedicated IC, but it is difficult to integrate the analog switch part with other circuits. .

It is an object of the present invention that an analog switch is not required for switching the loop coil, and it can be configured by only a digital circuit, which makes it possible to use power efficiently and lower the power supply voltage of the device. The purpose of the present invention is to provide a position detection device that can be driven only by a single-polarity power supply and that can be easily integrated.

[0009]

In the present invention, in order to achieve the above object, a radio wave is transmitted and received between a position indicator having a resonance circuit and a plurality of loop coils arranged in parallel in a position detection direction. In a position detection device that obtains the coordinate value of the position indicated by the position indicator, it outputs a unipolar pulse signal with a frequency almost the same as the resonance frequency of the resonance circuit of the position indicator when transmitting a radio wave, and outputs a signal when receiving a radio wave. A transmission circuit that outputs a ground and one ends of a plurality of loop coils, respectively, and a plurality of first switches that can arbitrarily switch whether each one end is connected to the transmission circuit or opened. A second circuit that is commonly connected to the switching circuit and the other ends of the plurality of loop coils, and is capable of arbitrarily switching whether the other end is commonly connected to the signal ground or is in an open state. When transmitting a radio wave to the replacement circuit and the position indicator, the first switching circuit corresponding to the loop coil to transmit the radio wave among the plurality of first switching circuits is connected to the transmission circuit and the remaining first switching circuit is connected. The switching circuit of No. 1 is opened and the second switching circuit is controlled to be connected to the signal ground, and when the radio wave generated from the position indicator is received, The first switching circuit corresponding to the loop coil that should receive the radio wave is connected to the transmission circuit, the remaining first switching circuit is opened, and the second switching circuit is opened. A switching control means, a receiving circuit that is commonly connected to the other ends of the plurality of loop coils and detects an induced voltage generated in the loop coils, and the position based on the induced voltages generated in the plurality of loop coils. Suggest position detecting device and a coordinate calculation means for calculating the coordinate values of the position indicated by 示器.

[0010]

According to the present invention, at the time of transmitting radio waves, one end of the plurality of loop coils is connected to the transmitting circuit by the corresponding first switching circuit, and the other end is connected to the signal ground by the second switching circuit. A current based on a unipolar pulse signal from the transmission circuit flows between the connected one loop coil and the signal ground, and a radio wave having the same frequency as the resonance frequency of the resonance circuit of the position indicator is transmitted from the one loop coil. Occurs. At this time, one of the remaining loop coils of the plurality of loop coils is opened by the corresponding first switching circuit, and the other end is connected to the signal ground by the first switching circuit. No current flows and no radio waves are generated. That is, radio waves can be generated only from the loop coils selected by the plurality of first switching circuits. Further, the receiving circuit commonly connected to the other ends of the plurality of loop coils is also in a state in which the other ends are all connected to the signal ground, and therefore the above-mentioned unipolar pulse signal is not detected.

On the other hand, at the time of receiving a radio wave, one end of the plurality of loop coils is connected to the signal ground by the corresponding first switching circuit and the other end is opened by the second switching circuit. An induced voltage based on the radio wave reflected from the resonance circuit of the position indicator is generated between the loop coil and the signal ground and is detected by the reception circuit. At this time, one of the remaining loop coils of the plurality of loop coils is opened by the corresponding first switching circuit and the other end is opened by the second switching circuit. No voltage is generated. That is,
The induced voltage generated only in the loop coil selected by the plurality of first switching circuits can be detected.

The selection switching of a plurality of loop coils at the time of transmitting and receiving radio waves and the calculation of the coordinate value of the indicated position based on the induced voltage detected at the time of reception are the same as in the above-mentioned prior application or its related application. Is.

[0013]

1 shows a first embodiment of the position detecting device of the present invention, in which 1 is a position indicator, 2-1 and 2-
2, 2-3 are loop coils, 3 is an oscillation circuit, 4 is NOR
Gates, 5-1, 5-2, 5-3, 6, 7 are 3-state drivers, 8 is an amplifier, 9 is a detector, 10 is a peak hold circuit, 11 is an analog / digital (A / D) conversion circuit, 12 is a processing unit (CPU), R1 and R2 are resistors,
L is a coil and C is a capacitor.

The position indicator 1 is composed of a known resonance circuit having a resonance frequency of a predetermined frequency including a coil and a capacitor, for example, fo, and can be moved to an arbitrary position according to an operation of an operator. .

The loop coils 2-1 to 2-3 are juxtaposed substantially parallel to each other in the position detecting direction, and one end of each loop coil is 3
The output terminals of the state drivers 5-1 to 5-3 are respectively connected, and the other ends thereof are commonly connected to the output terminals of the 3-state driver 6 via the resistor R1, the coil L and the capacitor C, and the resistors are also connected. Amplifier 8 via R2
Are commonly connected to.

The oscillating circuit 3 generates the unipolar pulse signal having the above-mentioned predetermined frequency fo and sends it to one input terminal of the NOR gate 4. The other input terminal of the NOR gate 4 is added with a transmission / reception switching signal SR indicating a transmission period and a reception period of the radio wave, and during the transmission period of the radio wave, the unipolar pulse signal is transmitted to the output terminal to receive the radio wave. During the period, a low level signal is transmitted, that is, the output terminal is set to the signal ground state.

The input terminals of the three-state drivers 5-1 to 5-3 are commonly connected to the output terminal of the NOR gate 4, and the respective control (input) terminals have loop coil selection signals S1 and S.
2 and S3 are input. Further, the input terminal of the three-state driver 6 is grounded, and the transmission / reception switching signal SR is input to its control (input) terminal. Also, 3
The input terminal of the state driver 7 is grounded, the transmission / reception switching signal SR is input to its control (input) terminal, and the output terminal is between the other end of the loop coils 2-1 to 2-3 and the amplifier 8. (Strictly speaking, between the resistor R2 and the amplifier 8).

The 3-state driver is a well-known digital circuit that can output a normal high-level or low-level signal to the output terminal, and can also hold the output terminal in a high (high) impedance state, that is, an open state. When a low-level signal is input to the control terminal, the input signal is output as it is to the output terminal, and when a high-level signal is input to the control terminal, the output terminal is kept in a high impedance state. The detailed relationship between the input and output is shown in FIG.

The amplifier 8 is a well-known summing amplifier including an operational amplifier and a resistor, which amplifies an induction voltage generated in one of the loop coils 2-1 to 2-3 selected as described later, This is sent to the wave detector 9. The detector 9 is composed of a well-known diode and detects and rectifies the induced voltage and sends it to the peak hold circuit 10. The peak hold circuit 10 is a known capacitor and holds the peak value of the detected and rectified induced voltage. The A / D conversion circuit 11 converts the output of the peak hold circuit 10 from analog to digital and sends it to the processing device 12.

The processing unit 12 generates the transmission / reception switching signal SR and the coil selection signals S1 to S3, supplies them to the respective parts, and guides the loop coils 2-1 to 2-3 converted into the digital values. The coordinate value of the position indicated by the resonance circuit of the position indicator 1 is calculated based on the voltage value of the voltage.

The resistor R1 is a resistor for limiting the current, and is for preventing an excessive current from flowing through the three-state drivers 5-1 to 5-3 during transmission of radio waves. Also, the resistor 2
Is for reducing the current flowing to the side of the 3-state driver 7 and the amplifier 8 as much as possible during the transmission of radio waves,
It is set to R2 >> R1. The three-state driver 7 is provided so as to prevent current from flowing directly to the amplifier 8 during radio wave transmission, and is not always necessary.

Further, the coil L and the capacitor C blunt the waveform of the unipolar pulse signal generated in the oscillation circuit 3 at the time of transmitting the radio wave, generate the radio wave having a waveform as close to a sine wave as possible, and the unipolar pulse signal is At a low level (ground level), the stored energy causes a reverse current to flow in the loop coil, and the value is a unipolar pulse signal in which the resonance frequency of the loop including the coil L and the capacitor C during transmission is a unipolar pulse signal. Is set to match the frequency of.

The above-mentioned oscillation circuit 3 and NOR gate 4 constitute the transmission circuit described in claim 1, and the three-state drivers 5-1 to 5-3 are the plurality of first switching circuits described in claim 1. A circuit, the three-state driver 6 constitutes the second switching circuit in claim 1, the three-state driver 7 constitutes the third switching circuit in claim 5, and an amplifier. 8, detector 9, peak hold circuit 1
0 and the A / D conversion circuit 11 constitute the receiving circuit according to claim 1, the processing device 12 constitutes the switching control means and the coordinate calculating means according to claim 1, and the coil L and the capacitor C are included. An LC circuit according to claims 3 and 4 is configured.

FIG. 3 shows an example of the signal waveform of each part in this embodiment, and here shows an example in which the position indicator 1 is near the loop coil 2-2. In the figure, SR is a transmission / reception switching signal, S1, S2 and S3 are coil selection signals,
(A), (b) and (c) are loop coils 2-1 and 2-
Radio waves transmitted from 2, 2-3, (d) is position indicator 1
Induced voltage generated in the resonance circuit of, (e) is the received signal,
(F) is the peak hold waveform of the received signal. Less than,
The operation of this embodiment will be described in accordance with this.

First, when the transmission / reception switching signal SR is in a low-level radio wave transmission period, the coil selection signal S1 is at a low level and S2 and S3 are at a high level, the NOR gate 4
Open, the three-state drivers 5-1 and 6, 7 output the input signals as they are, and the three-state drivers 5-2 and 5-3
Sets the output terminal to a high impedance state, that is, an open state.

At this time, the unipolar pulse signal from the oscillation circuit 3 is supplied to the loop coil 2-1 via the NOR gate 4 and the 3-state driver 5-1 and the current based on the unipolar pulse signal is in 3 states. Between the signal ground connected via the driver 6 (although a small amount,
A radio wave follows the frequency of the unipolar pulse signal, that is, a radio wave having a frequency fo equal to the resonance frequency of the resonance circuit of the position indicator 1 (i.e., a signal ground connected via the three-state driver 7). ) Occurs. The radio wave generated from the loop coil 2-1 is tuned to the resonance circuit of the position indicator 1 to generate an induced voltage (d).

On the other hand, in the other loop coils 2-2 and 2-3, since the corresponding 3-state drivers 5-2 and 5-3 are in the open state, the current from the loop coil 2-1 does not flow, Does not generate radio waves (b) and (c). Since the input side of the amplifier 8 is connected to the signal ground by the 3-state drivers 6 and 7, no induced voltage is detected at its output (e).

Next, when the transmission / reception switching signal SR enters the high-level radio wave reception period while the coil selection signals S1 to S3 remain unchanged, the NOR gate 4 is closed and the 3-state driver 5 is closed.
-1 outputs the input signal as it is, and the 3-state drivers 5-2, 5-3, 6, 7 open the output terminals.

At this time, one end of the loop coil 2-1 is connected via the three-state driver 5-1 to the output terminal of the closed NOR gate 4, that is, the signal ground, but the other loop coils 2-2 and 2-2. One end of -3 is opened by the three-state drivers 5-2 and 5-3, and the other ends are all opened by the three-state drivers 6 and 7. Therefore, the radio wave generated from the resonance circuit based on the induction voltage (d) generated in the resonance circuit of the position indicator 1, that is, the reflected radio wave is generated only in the loop coil 2-1 by the induced voltage (frequency) substantially equal to the resonance frequency fo. E) is generated.

The induced voltage (e) is amplified by the amplifier 8, detected and rectified by the detector 9, the peak value thereof is held by the peak hold circuit 10 (f), and the digital value is obtained by the A / D conversion circuit 11. And is sent to the processing device 12.

Next, when the transmission / reception switching signal SR is in a low-level radio wave transmission period, the coil selection signals S1, S
When S3 is at a high level and S2 is at a low level, a radio wave is generated only from the loop coil 2-2, and thereafter, the same transmission and reception of the radio wave is repeated with the switching of the transmission / reception switching signal SR and the coil selection signals S1 to S3. Each loop coil 2-
The voltage value of the induced voltage generated in 1-2 is the processing device 12
Sent to.

The voltage value of the induced voltage generated in the loop coils 2-1 to 2-3 depends on the distance between the resonance circuit of the position indicator 1 and each loop coil 2-1 to 2-3. The smaller is the larger. Therefore, the loop coil 2-1
The voltage value of the induced voltage extracted from ~ 2-3 becomes maximum with the induced voltage corresponding to the loop coil closest to the pointing position of the position indicator 1, and gradually decreases as the corresponding loop coil moves away from the pointing position. The voltage value of each of the induced voltages is arithmetically processed by the processing device 12 to find the position where the distribution of the voltage value is maximum, and from this, the coordinate value of the position pointed by the position pointing device 1 is found.

As described above, according to the first embodiment, one of the loop coils 2-1 to 2-3 is selected by using the three-state driver, and a unipolar pulse signal is added to this. Since radio waves can be transmitted and the induced voltage can be detected by receiving the radio waves reflected from the resonance circuit of the position indicator 1, power is wasted when transmitting radio waves as in the case of using a conventional analog switch. Power can be efficiently used, the power supply voltage of the device can be lowered, and a negative power supply is not required, and the power supply circuit can be simplified. Further, since the analog portion is eliminated, the portions other than the loop coil can be integrated, and the dedicated IC can be realized.
Further, by providing the LC circuit in series with the loop coil, it is possible to generate a radio wave having a waveform close to a sine wave, and it is possible to transmit and receive a radio wave with few harmonic components, that is, a good SN ratio. Further, since the 3-state driver 7 is provided, there is no direct current flowing through the amplifier 8 during transmission of radio waves, and the amplifier 8 does not consume extra power.

FIG. 4 shows another example of the signal waveform of each part in the first embodiment, in which a predetermined loop coil is used during transmission of radio waves, usually the loop coil closest to the resonance circuit 1 (here, the loop coil). An example is shown in which the loop coil 2-2) is selected and the loop coils are sequentially switched and selected only during reception. In the figure, SR is a transmission / reception switching signal, S1, S2
S3 is a coil selection signal, and (b) 'is a loop coil 2-2.
Radio wave transmitted from, (d) 'is an induced voltage generated in the resonance circuit of the position indicator 1, (e)' is a received signal, (f) '
Is the peak hold waveform of the received signal.

The transmission / reception switching signal SR is the same as in the example of FIG. 3, and the coil selection signals S1 to S3 are always S when the radio wave is transmitted.
It is the same as the example of FIG. 3 except that only 2 becomes low level. Further, the level of the induced voltage (d) 'is constant because the loop coil is fixed during transmission of radio waves. The received signal (e) 'and the peak hold waveform (f)' of the received signal are basically similar to those in the case of FIG. Note that the position indicator 1 is used to select the loop coil that transmits radio waves.
It is switched with the movement of.

Further, in the loop coil selection method shown in FIG. 4, since the position of the resonance circuit 1 must be known to some extent, it is not used alone, and the position of the resonance circuit 1 is changed immediately after the start of use. If you are totally unsure,
The selection method as shown in FIG. 3 is used, and thereafter, it is used. The essence of the present invention is to select one of the loop coils and in what order. Irrespective of how to select and drive one of the plurality of loop coils to drive or detect the induced voltage.

FIG. 5 shows a second embodiment of the position detecting apparatus of the present invention. Here, in the first embodiment, a predetermined operation state of the position indicator, for example, a position to be actually input is designated. An example in which the state (pen-down state) can be detected will be shown.

In FIG. 5, 13 is a position indicator,
It is composed of a resonance circuit in which one capacitor is directly connected to both ends of a coil and another capacitor is connected in parallel via a switch, and the resonance frequency is a predetermined frequency depending on whether the switch is turned on or off, for example, It changes slightly with respect to fo.

Reference numeral 14 is a phase detection circuit composed of a comparator (waveform shaping circuit), an EXOR gate, a resistor and a capacitor, and a reception signal and a unipolar pulse signal from the oscillation circuit 3 in accordance with a switch operation in the position indicator 13. If there is a phase difference with the (transmission signal), EXOR
A signal according to the phase difference is output from the gate, integrated by a resistor and a capacitor, and output as a DC signal.

Further, 15 is an analog / digital (A /
D) A conversion circuit, which converts the output of the phase detection circuit 14 into an analog-digital signal and sends it to the processing device 12.
Reference numeral 16 denotes a processing device, which has the same function as that of the processing device 12 in the first embodiment and is based on the phase difference between the reception signal and the transmission signal converted into digital values by the A / D conversion circuit 15. The pen-down state in the position indicator 13 is detected.

Reference numeral 17 is an amplification / detection / peak-hold circuit in which the amplifier 8, the detector 9 and the peak-hold circuit 10 in FIG. 1 are omitted, and other configurations and effects are the same as those of the first embodiment. Is the same as.

In the second embodiment, the resonance frequency of the resonance circuit is changed according to a predetermined operation state of the position indicator, and the change in the resonance frequency is detected as a change in the phase of the received signal to identify the operation state. However, it is also possible to change the loss inside the resonance circuit and detect the attenuation rate of the received signal to identify the state, and to detect the time change of the signal strength, phase and attenuation rate. Then, the state can be identified. In this case, a method of giving meaning to the amount of change and a method of sending digital data in time series are also included. Furthermore, it is also possible to change the frequency of the radio wave generated from the loop coil side so as to match with the change of the resonance frequency of the resonance circuit of the position indicator, and to identify the operation state from this change amount.

FIG. 6 shows a third embodiment of the position detecting apparatus of the present invention. Here, in the first embodiment, a phase inversion signal of a unipolar pulse signal is added to the other end side of the loop coil to positively. An example will be shown in which a current in the opposite direction is made to flow.

That is, in the figure, reference numeral 18 denotes an inverter, which receives the unipolar pulse signal from the oscillation circuit 3 as an input signal and outputs a phase inversion signal of the unipolar pulse signal. Also, 19
Is a NOR gate, the phase inversion signal is applied to one input terminal thereof, and the transmission / reception switching signal SR is applied to the other input terminal thereof, and the single input terminal is applied to the output terminal during a radio wave transmission period. A phase inversion signal of the polarity pulse signal is transmitted, and a low level signal is transmitted during the reception period of radio waves, that is, the output terminal is set to the signal ground state. Also, the N
The output terminal of the OR gate 19 is connected to the input terminal of the 3-state driver 6.

According to the above configuration, the first and the second points are that the other end of the loop coil for transmitting the radio wave is at the low level (ground level) when the unipolar pulse signal is at the high level during the transmission of the radio wave. The same as in the second embodiment, but when the unipolar pulse signal is at a low level (ground level), the other end of the loop coil that should transmit the radio wave becomes a high level, so that the amount of energy stored in the LC circuit increases. Regardless, it becomes possible to flow a sufficient current from the other end side of the loop coil to the one end side, and it is possible to perform efficient radio wave transmission. The other configurations and effects are similar to those of the first embodiment.

The above-mentioned implanter 18 and NOR gate 19
Constitutes the second transmission circuit in claim 6. Further, it goes without saying that this embodiment can also be configured to detect a predetermined operation state of the position indicator as in the second embodiment.

Further, in the above embodiments, the plurality of loop coils are arranged separately, but they may be arranged so as to overlap each other. Further, it goes without saying that the number of loop coils is an example and can be set to any number. In addition, although the embodiments described so far perform position detection in one direction, similar loop coils are arranged so as to be orthogonal to each other, a switching circuit similar to the above is provided, and other circuits are switched and used alternately. Needless to say, the pointed position in two orthogonal directions can be detected by performing the position detection.

[0048]

As described above, according to claim 1 of the present invention, when transmitting a radio wave, a unipolar pulse signal having a frequency substantially the same as the resonance frequency of the resonance circuit of the position indicator is output and the radio wave is received. In this case, a transmission circuit that outputs a signal ground and a plurality of loop coils are respectively connected to one ends of the loop coils, and a plurality of the plurality of loop coils that can be arbitrarily switched between the connected state and the open state are connected to the transmission circuit. The first switching circuit is commonly connected to the other ends of the plurality of loop coils,
A second switching circuit capable of arbitrarily switching whether the other end is commonly connected to the signal ground or opened is provided, and when a radio wave is transmitted to the position indicator, a plurality of second switches are provided. Of the first switching circuit, the first switching circuit corresponding to the loop coil to transmit the radio wave is connected to the transmission circuit, the remaining first switching circuit is opened, and the second switching circuit is opened.
The switching circuit of the first switching circuit is controlled to be connected to the signal ground, and when the radio wave generated from the position indicator is received, the first switching circuit corresponding to the loop coil that should receive the radio wave is selected from the plurality of first switching circuits. When the electric wave is transmitted, only one loop coil is controlled by controlling the switching circuit of the second connection circuit to be connected to the transmission circuit and leaving the remaining first switching circuit in the open state and the second switching circuit in the open state. A radio wave can be transmitted by adding a unipolar pulse signal to the antenna, and the induction voltage can be detected by receiving the radio wave reflected from the resonance circuit of the position indicator, which allows radio waves to be detected as in the case of using a conventional analog switch. Power is not wasted during transmission, and power can be used efficiently,
In addition, the power supply voltage of the device can be lowered, and a negative power supply is not needed, and the power supply circuit can be simplified.

According to the second aspect of the present invention, since the plurality of first switching circuits and the second switching circuits are constituted by the three-state driver, the analog circuit portion can be eliminated, and other than the loop coil. Can be integrated, and a dedicated IC can be realized. Further, according to the third aspect of the present invention, by inserting the LC circuit in series with the loop coil, it is possible to generate a radio wave having a waveform close to a sine wave, which has less harmonic components, that is, a good SN ratio. It becomes possible to send and receive radio waves.

According to the fourth aspect of the present invention, the value of the LC circuit is set so that the resonance frequency of the loop including the LC circuit at the time of transmission matches the frequency of the unipolar pulse signal. It becomes possible to send and receive good radio waves.

According to a fifth aspect of the present invention, the other ends of the plurality of loop coils are connected to the connection point with the receiving circuit,
Transmission of radio waves by providing a third switching circuit that can be arbitrarily switched between connecting and disconnecting the connection point to the signal ground and is switch-controlled in the same manner as the second switching circuit. At times, there is no direct current flowing through the receiving circuit, and the receiving circuit does not consume extra power.

According to claim 6 of the present invention, a second transmission circuit is provided which outputs a phase inversion signal of a unipolar pulse signal when transmitting a radio wave and outputs a signal ground when receiving a radio wave. By setting the switching by the second switching circuit to be in the connection state or the open state to the second transmission circuit, even when the unipolar pulse signal is at the ground level, the current in the reverse direction to the loop coil is increased. Can be transmitted, and efficient radio wave transmission can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a position detecting device of the present invention.

FIG. 2 is a diagram showing a relationship between inputs and outputs of a 3-state driver.

FIG. 3 is a diagram showing an example of a signal waveform of each part in the first embodiment.

FIG. 4 is a diagram showing another example of the signal waveform of each part in the first embodiment.

FIG. 5 is a configuration diagram showing a second embodiment of the position detecting device of the present invention.

FIG. 6 is a configuration diagram showing a third embodiment of the position detecting device of the invention.

[Explanation of symbols]

1, 13 ... Position indicator, 2-1 to 2-3 ... Loop coil, 3 ... Oscillation circuit, 4, 19 ... NOR gate, 5-1.
5-3, 6, 7 ... 3-state driver, 8 ... Amplifier, 9
... Detector, 10 ... Peak hold circuit, 11, 15 ... Analog / digital (A / D) conversion circuit, 12, 16 ...
Processor (CPU), 14 ... Phase detection circuit, 17 ... Amplification / detection / peak hold circuit, 18 ... Inverter, R
1, R2 ... Resistance, L ... Coil, C ... Capacitor.

Claims (6)

[Claims] 1. Position detection for obtaining coordinate values of a position pointed by the position indicator by transmitting and receiving radio waves between a position indicator having a resonance circuit and a plurality of loop coils arranged in parallel in the position detection direction. In the device, when transmitting radio waves, it outputs a unipolar pulse signal with a frequency almost the same as the resonance frequency of the resonance circuit of the pointing device, and when receiving radio waves, it outputs a signal ground and a transmission circuit, and one end of multiple loop coils. And a plurality of first switching circuits each of which is capable of arbitrarily switching whether each one end is connected to the transmission circuit or is in an open state, and is commonly connected to the other ends of the plurality of loop coils. A second switching circuit that is connected and can arbitrarily switch whether the other end is commonly connected to the signal ground or open, and when transmitting radio waves to the position indicator Of the plurality of first switching circuits, the first switching circuit corresponding to the loop coil to transmit the radio wave is connected to the transmission circuit, the remaining first switching circuits are opened, and the second switching circuit is opened. The first switching circuit corresponding to the loop coil that should receive the radio wave among the plurality of first switching circuits when the radio wave generated from the position indicator is received. Is connected to the transmission circuit and the remaining first switching circuit is opened, and switching control means for controlling the second switching circuit to be opened is commonly connected to the other ends of the plurality of loop coils. A receiving circuit for detecting the induced voltage generated in the loop coil, and a coordinate calculation for calculating the coordinate value of the position pointed by the position indicator based on the induced voltage generated in each of the plurality of loop coils. Position detecting device characterized by comprising a stage. 2. The plurality of first switching circuits are composed of a plurality of three-state drivers in which signal input terminals are commonly connected to a transmission circuit, and the second switching circuits are three-state drivers in which signal input terminals are grounded. The position detecting device according to claim 1, wherein 3. The position detecting device according to claim 1, wherein an LC circuit is inserted in series between the other ends of the plurality of loop coils and the second switching circuit. 4. The L so that the resonance frequency of the loop including the LC circuit at the time of transmission matches the frequency of the unipolar pulse signal.
The position detecting device according to claim 3, wherein the value of the C circuit is set. 5. The second coil is connected to a connection point between the other ends of the plurality of loop coils and the receiving circuit, and can be arbitrarily switched between a connection state to the signal ground and an open state. The position detecting device according to any one of claims 1 to 4, further comprising a third switching circuit that is switched and controlled similarly to the switching circuit. 6. A second transmission circuit that outputs a phase-inverted signal of a unipolar pulse signal during transmission of radio waves and outputs a signal ground during reception of radio waves is provided, and switching by the second switching circuit is performed. The position detecting device according to any one of claims 1 to 5, wherein the second transmitting circuit is set to a connection state or an open state.