JP3078391B2 - Position detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

Prior to this application, the applicant filed Japanese Patent Application No. Sho 61
No. 213970 (see Japanese Patent Application Laid-Open No. 63-70326) has proposed a position detecting device which has only a resonance circuit and can detect a pointing position of a position pointing device which is not connected anywhere.

[0003] In brief, the contents of the above-mentioned apparatus are described below. One loop coil is selected from a plurality of loop coils arranged side by side in a position detection direction, and an alternating-current signal of a predetermined frequency is supplied to this to transmit a radio wave. Then, the radio wave is received by a resonance circuit provided in the position indicator. At this time, the one loop coil receives a radio wave generated from a resonance circuit that has received energy from the radio wave, and generates an induced voltage. This is repeated by sequentially switching the plurality of loop coils, and the position of the resonance circuit, that is, the coordinate value of the designated position is obtained based on the magnitude of the induced voltage generated in each loop coil.

[0004]

However, in the above device, the resonance circuit of the position pointer generates energy by generating energy from only the radio wave transmitted from the loop coil side. In order to obtain a strong reception signal (induction voltage), the resonance frequency of the resonance circuit must exactly match the frequency of the radio wave transmitted from the loop coil side, that is, the predetermined frequency,
There was a problem that the adjustment took time. Further, in the device, in order to identify the pen-down state of the position indicator, etc., the resonance frequency of the resonance circuit is slightly changed in accordance with the operation of a switch or the like, and the slight change in the resonance frequency is detected from the received signal. As described above, the pen-down state and the like are identified.Specifically, since the phase change of the received signal based on the predetermined frequency is detected and identified, the resonance frequency is determined. There has been a problem that the frequency must be more accurately matched with the predetermined frequency, and the adjustment takes more time and effort. Furthermore, the frequency of the radio wave exchanged between the loop coil and the resonance circuit is switched to a plurality of different frequencies, and a plurality of resonances respectively provided on the plurality of position indicators or operating according to the state of the position indicators are operated. Although it has been proposed to identify the circuit, also in this case, the resonance frequency of each resonance circuit must be exactly the same as the frequency of each radio wave transmitted from the loop coil side, as described above. There was a problem that the adjustment took a lot of time.

The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide a position detecting device capable of eliminating the need for accurate adjustment of a resonance frequency in a resonance circuit.

[0006]

According to the present invention, in order to achieve the above object, a position detecting device for detecting a position indicated by a position indicator having a resonance circuit generates a radio wave for exciting the resonance circuit of the position indicator. Radio wave generating means, a radio wave receiving means for receiving a radio wave generated from the resonance circuit of the position indicator, and a position for detecting a phase difference between the radio wave generated from the radio wave generating means and the radio wave received by the radio wave receiving means. There is proposed a position detecting device comprising: a phase difference detecting unit; and a phase difference controlling unit that controls a frequency and a phase of a radio wave generated from the radio wave generating unit so that the phase difference has a predetermined value.

[0007]

According to the present invention, the phase difference between the radio wave generated by the radio wave generation means and the radio wave received by the radio wave reception means is detected by the phase difference detection means, and the radio wave generation is performed so that the phase difference becomes a predetermined value. The frequency and phase of the radio wave generated by the means are controlled by the phase difference control means, so that the resonance frequency of the resonance circuit and the frequency of the radio wave transmitted to the resonance circuit have a fixed relationship, for example, a state of coincidence.

[0008]

FIG. 1 shows a first embodiment of a position detecting device according to the present invention. In the drawing, reference numeral 1 denotes a resonance circuit;
... 2-8 are loop coils, 3 is a selection circuit, 4 is a voltage controlled oscillator, 5 is a current driver, 6 is a transmission / reception switching circuit, 7 is a reception amplifier, 8 is a detector, 9 is a phase comparator, and 10 is a switch. , 11 and 12 are low-pass filters (LPF), 13 is a sample and hold circuit (S / H), 14 and 15 are analog / digital (A / D) conversion circuits, and 16 is a processing unit (C
PU).

The resonance circuit 1 includes a coil, a capacitor, and a switch. When the switch is turned off, a predetermined frequency, for example, fo is set as a resonance frequency, and when the switch is turned on, a frequency slightly lower than the frequency fo is set. , For example, f1 to constitute a position indicator which can be moved to an arbitrary position in accordance with the operation of the operator.

The loop coils 2-1 to 2-8 are arranged side by side substantially parallel to each other in a position detection direction, for example, the x direction. One end of each is connected to the selection circuit 3, and the other end is commonly used. Grounded. The selection circuit 3 is a processing device 1
6, one loop coil is sequentially selected from the loop coils 2-1 to 2-8 in accordance with a predetermined selection signal added from 6. The voltage-controlled oscillator 4 uses the above-mentioned predetermined frequency fo as a free-running frequency and generates a predetermined control signal, in this case, an AC signal having a frequency and a phase corresponding to the output voltage of the low-pass filter 12, and outputs this signal to a current driver 5. And to the phase comparator 9. The current driver 5 converts the AC signal into a current and sends it to the transmission / reception switching circuit 6. The transmission / reception switching circuit 6 alternately switches and connects the current driver 5 and the reception amplifier 7 to one loop coil selected by the selection circuit 3 according to a predetermined transmission / reception switching signal applied from the processing device 16.

The receiving amplifier 7 amplifies the induced voltage generated in the selected one loop coil and transmitted through the selection circuit 3 and the transmission / reception switching circuit 6, and amplifies the induced voltage by the detector 8 and the phase comparator 9. Send to The detector 8 detects and rectifies the induced voltage, that is, the received signal, and sends it to the low-pass filter 11, and the phase comparator 9 compares the phase with the signal from the voltage controlled oscillator 4 to obtain a phase difference signal. And sends it out to the low-pass filter 12 via the switch 10. The switch 10 is turned on when a loop coil other than immediately below the resonance circuit 1 is selected from among the loop coils 2-1 to 2-8 according to a control signal from the control device 16, that is, when an AC signal from the voltage controlled oscillator 4 is output. This is to prevent the output signal of the phase comparator 9 from being sent to the low-pass filter 12 when the phase of the received signal and the phase of the received signal are inverted and when the transmission / reception switching circuit 6 is on the transmission side. is there.

The low-pass filter 11 has a cut-off frequency sufficiently lower than the frequency fo described above, converts the output signal of the detector 8 into a DC signal, and sends the DC signal to the A / D conversion circuit 14 via the sample-and-hold circuit 13. Send out. The low-pass filter 12 also has a cutoff frequency sufficiently lower than the frequency fo described above, converts the output signal of the phase comparator 9 into a DC signal, and sends it to the voltage controlled oscillator 4 and the A / D conversion circuit 15. . The A / D conversion circuits 14 and 15 convert the outputs of the low-pass filters 12 and 13 from analog to digital, and send them to the processing unit 16. The processing device 16 calculates the position of the resonance circuit 1 based on the voltage values of the reception signals corresponding to the loop coils 2-1 to 2-8 output from the sample and hold circuit 13 and converted into digital values, The state of the switch in the resonance circuit 1 is identified based on the voltage value output from the low-pass filter 12, that is, the control signal of the voltage-controlled oscillator 4.

Next, the operation of the device will be described.

First, one of the loop coils 2-1 to 2-8 selected by the selection circuit 3 is connected to the current driver 5 via the transmission / reception switching circuit 6, and the predetermined voltage by the voltage controlled oscillator 4 When an alternating current having a frequency fo is supplied, a radio wave having a predetermined frequency fo is generated from the one loop coil. The radio wave excites the resonance circuit 1 and gives it electromagnetic energy. Thereafter, when the one loop coil is connected to the receiving amplifier 7 via the transmission / reception switching circuit 6, the generation of radio waves from the one loop coil stops.

At this time, the resonance circuit 1 generates a radio wave having substantially the same frequency as the predetermined frequency fo based on the given electromagnetic energy. Since the radio wave excites the one loop coil in reverse, an induced voltage having substantially the same frequency as the predetermined frequency fo is generated in the one loop coil.
The induced voltage is amplified by the receiving amplifier 7, and the detector 8,
Low-pass filter 11, sample and hold circuit 13 and A /
The signal is sent to the processing device 16 via the D conversion circuit 14 as a voltage value. Thereafter, one loop coil selected by the selection circuit 3 is sequentially switched and the same operation is repeated, and the voltage value of the induced voltage generated in each of the loop coils 2-1 to 2-8 is transmitted to the processing device 16. Is done.

The voltage value of the induced voltage extracted from each of the loop coils 2-1 to 2-8 depends on the distance between each loop coil and the resonance circuit 1. The smaller the distance, the larger the value. Therefore, the voltage value of the induced voltage taken out from each of the loop coils 2-1 to 2-8 is set such that the induced voltage corresponding to the position of the resonance circuit 1, that is, the loop coil closest to the position indicated by the position indicator is maximized. As the loop coil moves away from the indicated position, it gradually decreases. The voltage value of each of the induced voltages is subjected to arithmetic processing by the processing device 16, and the position where the distribution of the voltage value is maximum, that is, the coordinate value of the designated position is obtained.

On the other hand, the induced voltage amplified by the receiving amplifier 7 is also sent to the phase comparator 9 where the phase is compared with the AC signal from the voltage controlled oscillator 4. At this time, the resonance frequency of the resonance circuit 1 exactly matches the predetermined frequency fo,
If the phase of the induced voltage matches the phase of the AC signal, the output voltage of the phase comparator 9 becomes zero. Therefore, the output of the low-pass filter 12 also becomes 0, and the voltage controlled oscillator 4 continues to oscillate at the free-running frequency, that is, the frequency fo.

If the resonance frequency of the resonance circuit 1 is a frequency slightly different from the frequency fo, for example, fo ', the phase of the induced voltage and the phase of the AC signal become inconsistent. A voltage having a sign and a value corresponding to the phase difference is output. Therefore, low-pass filter 1
2 also has a sign and a value corresponding to the phase difference, whereby the voltage controlled oscillator 4 is controlled to oscillate at the frequency fo '. At this time, the output of the low-pass filter 12 is converted into a digital value in the A / D conversion circuit 15 as described above, and the value is stored as a value representing the reference frequency corrected in the processing device 16.

On the other hand, when the switch is turned on in the resonance circuit 1 and the resonance frequency becomes a frequency f1 slightly lower than the predetermined frequency fo, the phase of the induced voltage and the phase of the AC signal become inconsistent. , Phase comparator 9
A voltage having a sign and a value corresponding to the phase difference is output. Therefore, the output of the low-pass filter 12 also has a sign and a value corresponding to the phase difference, whereby the voltage controlled oscillator 4 is controlled to oscillate at the frequency f1. As described above, the output of the low-pass filter 12 is A /
It is converted to a digital value in the D conversion circuit 15,
The digital value is compared with a digital value stored as a value representing the reference frequency in the processing device 16, and the state of the switch in the resonance circuit 1 is identified from the difference.

In this embodiment, the position is detected in one direction, but a plurality of loop coils similar to the loop coils 2-1 to 2-8 are arranged so as to be orthogonal thereto, and the same selection as described above is performed. Needless to say, by providing a circuit and alternately detecting the position by switching and using another circuit, the designated position in two orthogonal directions can be detected.

FIG. 2 shows a second embodiment of the position detecting device according to the present invention. In this embodiment, the loop coils are divided into those for transmitting radio waves and those for receiving radio waves in the first embodiment, and these are orthogonal to each other. An example is shown. That is, in the figure,
Reference numerals 17-1, 17-2,..., 17-5 denote loop coils, which are arranged in parallel with each other in a direction orthogonal to the loop coils 2-1 to 2-8, that is, in the y direction. One end of each of the loop coils 17-1 to 17-5 is connected to a selection circuit 1
8 and the other ends thereof are commonly grounded. The selection circuit 18 sequentially selects one loop coil from the loop coils 17-1 to 17-5 according to a predetermined selection signal applied from the processing device 16.
Is connected only to the current driver 5, and the loop coils 17-1 to 17-5 constitute a loop coil for transmitting radio waves. The selection circuit 3 is connected only to the reception amplifier 7, and the loop coils 2-1 to 2-8 constitute a loop coil for radio wave reception. Reference numeral 19 denotes a synchronous detection circuit, which synchronously detects the reception signal amplified by the reception amplifier 7 using the AC signal from the voltage control transmitter 4 as a detection signal.

In the above configuration, the loop coil 17-1
17-5, one of the loop coils is selected by the selection circuit 18 and connected to the current driver 5 to generate a radio wave of the frequency fo. The radio wave excites the resonance circuit 1 as in the first embodiment, gives electromagnetic energy to the resonance circuit 1, and generates a radio wave having the same frequency fo from the resonance circuit 1. The radio wave reversely excites one of the loop coils 2-1 to 2-8 selected by the selection circuit 3, so that the one loop coil has the predetermined frequency f.
An induced voltage with almost the same frequency as o is generated.

Here, the sequential selection of the loop coils 2-1 to 2-8 is performed every period when one of the loop coils 17-1 to 17-5 is selected.
According to the sequential selection of the loop coils 2-1 to 2-8, the first
As in the case of the embodiment, the voltage value of the induced voltage corresponding to the position of the resonance circuit 1 in the x direction is obtained. At this time,
Although the induced voltage is synchronously detected by the synchronous detection circuit 19, when the loop coil immediately below the resonance circuit 1 is selected among the loop coils 17-1 to 17-5, the other loop coils are selected. Since the phase of the induced voltage is inverted from the time when the current is present, the voltage value of the induced voltage corresponding to the position of the resonance circuit 1 in the y direction is obtained according to the sequential selection of the loop coils 17-1 to 17-5.

The voltage values of the induced voltages obtained in accordance with the sequential selection of the loop coils 2-1 to 2-8 and the loop coils 17-1 to 17-5 are processed by the processing unit 16 so that the distribution of the voltage values is maximized. , Ie, x of the designated position
The coordinate values in the direction and the y direction are obtained. The correction of the reference frequency to the resonance frequency of the resonance circuit 1 and the discrimination of the switch state are performed in the same manner as in the first embodiment. Further, in this embodiment, the switch 10 is used only for inhibiting the input of the phase inversion signal except under the position indicator.

FIG. 3 shows a third embodiment of the position detecting device of the present invention. In the drawing, the same components as those in the first or second embodiment are denoted by the same reference numerals. That is, 1 is a resonance circuit,
4 is a voltage controlled oscillator, 5 is a current driver, 7 and 20 are receiving amplifiers, 9 is a phase comparator, 10 is a switch, and 11 and 1
2 is a low-pass filter (LPF), 19 is a synchronous detection circuit, 2
.., 21-12 are conductors, 22 is a selection circuit, 23 is a loop coil, 24 and 25 are transmission / reception switching circuits, 26 is a zero-cross detector, 27 is a timer, 28 is a timing generation circuit, 29 is a frequency discrimination circuit.

The conductors 21-1 to 21-12 are arranged side by side substantially parallel to each other in a position detection direction, for example, the x direction.
One end is connected to the selection circuit 22, and the other end is commonly grounded. The selection circuit 22 sequentially selects one conductor from the conductors 21-1 to 21-12 according to a predetermined sampling signal applied from the timing generation circuit 28. The loop coil 23 includes a plurality of conductors 21-1 and 21-2.
One end is connected to the transmission / reception switching circuit 24, and the other end is grounded. The transmission / reception switching circuit 24 controls the loop coil 23
Is connected to the current driver 5 or the receiving amplifier 20. The transmission / reception switching circuit 25 connects the selected one conductor to the reception amplifier 7 or grounds it according to a transmission / reception switching signal applied from the timing generation circuit 28.

The zero-cross detector 26 outputs a stop pulse when the input voltage changes from plus to minus (or minus to plus). The timer 27 has a specific signal among the sampling signals, for example, the conductor 21-
The time from when the start pulse synchronized with the signal for selecting 1 is applied to when the stop pulse is applied is measured. The timing generation circuit 28 includes a transmission / reception switching signal, a sampling signal for sequentially selecting one conductor from the conductors 21-1 to 21-12, and a specific signal among the sampling signals, for example, a signal for selecting the conductor 21-1. Generates a start pulse synchronized with. The frequency discrimination circuit 29 discriminates the resonance frequency of the resonance circuit 1 from the sign and value of the output voltage of the low-pass filter 12 and discriminates the on / off state of the switch of the resonance circuit 1.

Hereinafter, the operation of the above device will be described.

First, the loop coil 23 is connected to the transmission / reception switching circuit 2
4 and is supplied to a current driver 5 via an AC power supply 4. When an AC current having a predetermined frequency fo is supplied by the voltage controlled oscillator 4,
A radio wave of a predetermined frequency fo is generated from the loop coil 23. The radio wave excites the resonance circuit 1 and gives it electromagnetic energy. On the other hand, the selection circuit 22 outputs a signal from the conductor 21-1 based on the sampling signal from the timing generation circuit 28.
21-12, the transmission / reception switching circuit 25 grounds the input terminal of the reception amplifier 7 during the transmission period of the radio wave, so that the signal generated on the one conductor is transmitted to the reception amplifier 7. Is not transmitted.

Thereafter, when the loop coil 23 is connected to the receiving amplifier 20 via the transmission / reception switching circuit 24, the generation of radio waves from the loop coil 23 stops. On this occasion,
The resonance circuit 1 generates a radio wave having substantially the same frequency as the predetermined frequency fo based on the given electromagnetic energy. Since the radio wave excites the loop coil 23 together with the selected one conductor, an induced voltage having substantially the same frequency as the predetermined frequency fo is generated in the one conductor and the loop coil 23. Thereafter, one of the conductors selected by the selection circuit 22 is sequentially switched and the same operation is repeated to obtain an induced voltage having substantially the same frequency as the predetermined frequency fo corresponding to the conductors 21-1 to 21-12. . The induced voltage is amplified by the receiving amplifier 7, synchronously detected by the synchronous detection circuit 19 using the AC signal from the voltage control transmitter 4 as a detection signal, and further integrated by the low-pass filter 11.

Here, the direction of the radio wave with respect to each conductor is reversed with respect to the center position (designated position) of the coil of the resonance circuit 1, and the phase of the induced voltage is also reversed with the designated position as a boundary. The 19 output signal is also a signal of the opposite polarity with respect to the designated position. Therefore, the output signal of the low-pass filter 11 crosses 0 [V] corresponding to the designated position, the zero-cross point is detected by the zero-cross detector 26, and a stop pulse is generated. On the other hand, timer 2
7 is the time when the start pulse is input, that is, the conductor 21-
Since the measurement of time is started from the time point when 1 is selected, and the measurement is stopped by the stop pulse from the zero-cross detector 26, the measured time is measured from the conductor 21-1 to the position indicated by the resonance circuit 1. The coordinate value corresponds to the distance, that is, the coordinate value in the x direction.

The induced voltage generated in the loop coil 23 is amplified by the receiving amplifier 20, sent to the phase comparator 9 and compared in phase with the AC signal from the voltage controlled oscillator 4, and the sign and the sign corresponding to the phase difference are output. As in the case of the first or second embodiment, the correction of the reference frequency to the resonance frequency of the resonance circuit 1 and the identification of the switch state are performed by the voltage having the value. Further, in this embodiment, the switch 10 is for preventing the output signal of the phase comparator 9 from being output to the low-pass filter 12 when the transmission / reception switching circuit 24 is on the transmission side.

In this embodiment, the position is detected in one direction. However, a plurality of conductors similar to the conductors 21-1 to 21-12 are arranged so as to be orthogonal thereto, and a selection circuit similar to the above is provided. It is needless to say that the designated positions in the two orthogonal directions can be detected by providing and alternately detecting the position by using another circuit.

In the embodiments described above, an antenna other than the loop coil may be provided to receive the radio wave generated from the resonance circuit 1 and transmit the radio wave to the phase comparator 9.

In the above description, a resonance circuit whose resonance frequency is changed by connecting and disconnecting a capacitor by a switch is used. However, a coil may be used instead of the capacitor. In addition, a capacitor whose capacitance value continuously changes by pressure or a coil whose inductance continuously changes may be connected without a switch.In this case, continuous state change information such as writing pressure is used. Can be entered. Also, an offset signal divided into several stages is added to the control signal of the voltage control transmitter,
By detecting a signal for each frequency range corresponding to each offset signal, a plurality of position indicators each having a plurality of resonance circuits having different resonance frequency ranges can be identified. This can also be achieved with a plurality of voltage controlled oscillators having different frequency ranges.

As the phase comparator, an exclusive OR circuit, a leading edge judgment circuit, or the like can be used. Further, in the above embodiment, the output signal of the voltage control transmitter is directly
Although input to the phase comparator and the synchronous detection circuit, a circuit that shifts the phase in accordance with the phase characteristics of each circuit may be required.

[0037]

As described above, according to the present invention, the phase difference between the radio wave generated from the radio wave generating means and the radio wave received by the radio wave receiving means is detected by the phase difference detecting means, and the phase difference is determined by a predetermined value. By controlling the frequency and phase of the radio wave generated from the radio wave generating means to be a value by the phase difference control means,
Since the resonance frequency in the resonance circuit and the frequency of the radio wave transmitted to the resonance circuit are in a constant relationship, for example, in a state of being in agreement, there is no need to exactly match the resonance frequency of the resonance circuit with the constant frequency, The labor required for the adjustment is eliminated, and the cost can be reduced accordingly.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram showing a second embodiment of the position detection device of the present invention.

FIG. 3 is a configuration diagram showing a third embodiment of the position detection device of the present invention.

[Explanation of symbols]

1. Resonant circuit, 2-1 to 2-8, 17-1 to 17-5,
23 ... loop coil, 3, 18, 22 ... selection circuit, 4 ...
Voltage-controlled oscillator, 9: phase comparator, 12: low-pass filter, 16: processing device, 29: frequency discriminating circuit.

Claims (11)

(57) [Claims] 1. A position detecting device for detecting an indicated position of a position indicator having a resonance circuit, comprising: a radio wave generator for generating a radio wave for exciting the resonance circuit of the position indicator; Radio wave receiving means for receiving the generated radio wave; phase difference detecting means for detecting a phase difference between the radio wave generated from the radio wave generating means and the radio wave received by the radio wave receiving means; the phase difference being a predetermined value And a phase difference control means for controlling the frequency and phase of the radio wave generated from the radio wave generation means. 2. A position indicator having a resonance circuit, a plurality of first loop coils juxtaposed in a position detection direction, and a selection means for sequentially selecting one loop coil from the plurality of first loop coils. And at least one second loop coil provided in the vicinity of the first loop coil; and an AC signal for generating a radio wave for exciting a resonance circuit of the position indicator to the second loop coil. An AC signal supply unit for supplying; a position determination unit for determining an indicated position of the position indicator based on a magnitude of each induced voltage generated in the selected first loop coil; An antenna provided in the vicinity, phase difference detection means for detecting a phase difference between an induced voltage generated in the antenna and the AC signal, and the AC signal supply means such that the phase difference becomes a predetermined value. Position detecting device characterized by comprising a phase difference control unit for controlling the frequency and phase of the supplying alternating current signal. 3. The apparatus according to claim 2, wherein the second loop coil comprises a plurality of loop coils arranged in parallel in the position detection direction, and a second selecting means for selecting one loop coil from the plurality of second loop coils. 3. The position detecting device according to claim 2, wherein: 4. A plurality of first loop coils and a plurality of second loop coils.
4. The position detection device according to claim 3, wherein the loop coil is shared. 5. A second loop coil comprising a plurality of loop coils arranged side by side in a direction orthogonal to a position detection direction.
3. The position detecting device according to claim 2, further comprising a second selecting unit that selects one loop coil from the plurality of second loop coils. 6. The position detecting device according to claim 2, wherein the antenna is shared with the first loop coil or the second loop coil. 7. A position indicator having a resonance circuit, a plurality of conductors juxtaposed in a position detection direction, a selecting means for sequentially selecting one conductor from the plurality of conductors, At least one loop coil provided; AC signal supply means for supplying an AC signal for generating a radio wave for exciting a resonance circuit of the position indicator to the loop coil; and induction generated on the selected conductor. Synchronous detection means for synchronously detecting a voltage with a detection signal synchronized with the AC signal; integration means for integrating an output signal of the synchronous detection means; zero-cross detection means for detecting a change in polarity of an output signal of the integration means; Position determining means for measuring a time difference between a selection timing of a specific conductor among the plurality of conductors and a detection timing of the polarity change to obtain an indication position of the position indicator; An antenna provided in the vicinity of the conductor; a phase difference detecting means for detecting a phase difference between an induced voltage generated in the antenna and the AC signal; and the AC signal supplying means such that the phase difference has a predetermined value. And a phase difference control means for controlling a frequency and a phase of an AC signal supplied from the apparatus. 8. The position detecting device according to claim 7, wherein the loop coil and the antenna are shared. 9. The position according to claim 1, further comprising phase difference control means for controlling the frequency and phase of the AC signal supplied from the AC signal supply means so that the phase difference becomes zero. Detection device. 10. A position indicator that uses a plurality of position indicators each having a resonance circuit having a different resonance frequency, and identifies which one of the plurality of position indicators is being used based on an output of the phase difference control means. 10. The position detecting device according to claim 1, further comprising an identification unit. 11. A position indicator having a resonance circuit whose resonance frequency changes in accordance with a state, and state identification means for identifying the state of the position indicator from the output of the phase difference control means is provided. The position detecting device according to claim 1.