JPH06250773A - Coordinate detecting device - Google Patents

Abstract

PURPOSE:To improve S/N and perform highly precise position detection and to eliminate malfunction even when a conductive body like a ring is close to a tablet by reducing signal attenuation due to floating capacity by a coil which has a resistance component and is connected to a level detecting circuit in parallel. CONSTITUTION:The tip conductor 8 of a detection pen and tablet electrode lines are connected by small electrostatic capacitors, the impedance viewed from a voltage driving side to a load side varies, and the current of a resistance Rs3 also varies and appears as variation in voltage level at the connection point between the resistance Rs3 and an analog switch SW4, so the load state can be known by detecting the voltage level at the connection point. The floating capacitors Cs1, Cs21-Cs2n have gentle parallel resonance characteristics as well as the circuit of a coil Lp12 and a resistance RD13 put in parallel to a level detection circuit 9. Consequently, the floating load impedance becomes large and an unnecessary load is reduced, so that a large detection level can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coordinate detecting device for outputting, as a digital value, contact position information of a detection pen without a cable contacted on a doublet with a tablet.

[0002]

2. Description of the Related Art As a conventional tablet detecting means using a detecting pen without a cable connected to a main body of a device, there is a detecting pen having an active circuit including a battery built therein.
It is also known that a detection pen is provided with only a resonance circuit which is a passive circuit by using an electromagnetic coupling method as an adjacent technology of the capacitive coupling type coordinate detecting device.

[0003]

The former one using the above-mentioned conventional technique is heavy because it has a built-in battery, and requires replacement of the battery due to exhaustion of the battery.
Further, in the latter electromagnetic coupling type, placing a metal ring such as a finger ring of the operator on the tablet causes a malfunction. The stray capacitance of the circuit is more or less present, and the signal is greatly attenuated by the stray capacitance.

[0004]

Means for Solving the Problems The present invention has been made in view of the above-mentioned conventional problems, and a tablet having a plurality of electrode lines arranged along a coordinate axis and each electrode line of the tablet are sequentially arranged. A frequency sweep voltage driving unit to drive, a detection pen having a parallel resonance circuit internally connected to an end and one end connected to the electrode wire and capacitively coupled to the electrode wire, and the electrode The present invention proposes a coordinate detection device having a level detection circuit connected to a signal line for applying a frequency sweep voltage to a line, and a coil having a resistance component connected in parallel with the level detection circuit.

[0005]

[Function] In a parallel resonant circuit with small capacitance coupling, impedance dip points and peak points exist continuously in the vicinity of the resonance frequency. The level difference between the dip point and the peak point is obtained for each electrode line, and the maximum level difference is obtained. It is detected that the detection pen is in contact with the vicinity of the electrode wire of the above, but the signal attenuation due to the stray capacitance is reduced by the coil having the resistance component connected in parallel with the level detection circuit.

[0006]

The details of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall configuration diagram of the device of the present invention. The tablet electrode wires 1, 1, ... Are actually arranged in both the X-axis direction and the Y-axis direction, but only one direction is shown for convenience of explanation. The voltage driving unit Vs2 is a frequency sweep voltage source, and sequentially drives the electrode lines 1, 1, ... Of the tablet through a resistor Rs3 and an analog switch SW4. The circuit of the detection pen 5 is composed of a parallel resonant circuit including passive elements such as a coil L6 and a capacitor C7, and the tip conductor 8 of the detection pen 5 is connected to one end of a parallel resonant circuit including the coil L6 and the capacitor C7. The other end of the parallel resonant circuit including L6 and the capacitor C7 is electrically connected to the housing of the detection pen 5.

The tip conductor 8 of the detection pen 5 and the doublet electrode wires 1, 1, ... Are coupled with a small capacitance. Further, the casing of the detection pen 5 becomes a pseudo signal return due to the electrostatic capacitance with the tablet casing ground through the human body, and further due to the effect of the electromagnetic wave radiation impedance to the space, and is shown as Zp in FIG. In this state, the impedance of the voltage viewed from the driving side changes depending on the frequency, and the current of the resistor Rs3 also changes accordingly, resulting in a change in the voltage level at the connection point between the resistor Rs3 and the analog switch SW4. . The state of the load can be known by detecting the voltage level at this connection point. Stray capacitance Cs1 (11) related to signal attenuation,
Although Cs21 (11), ..., Cs2n (11) constitute unnecessary stray load impedance, they have a gentle parallel resonance characteristic together with the circuit of the coil Lp12 and the resistor RD13 which are in parallel with the level detection circuit 9.

FIG. 2 is an equivalent drawing of only the electric circuit. Here, the resistor Rsp14 is an analog switch SW.
4 and the tablet electrode wires 1, 1, ... Combined resistance, and Cc15 is the coupling capacitance between the tip conductor 8 of the detection pen 5 and the tablet electrode wires 1, 1 ,. L16,
C17 and RQ18 are internal circuits of the detection pen 5, and are effective resistance components that determine Q of the coil 6, the capacitor 7, and the resonance circuit, respectively. RM and CM are the resistance component and the capacitance component of the pseudo return Zp. Cs1 and Cs2 are equivalent capacitances of stray capacitances. As can be seen from this, the resonance characteristic itself of the resonance circuit of the detection pen 5 can be seen as a level change from the output end of the resistor Rs3 connected to the voltage driving unit Vs2 by sweeping the signal frequency. Due to the small capacitance coupling of several picofarads or less, the dip point and the peak point continuously appear in the vicinity of the resonance point of only the circuit of the detection pen 5 as shown in FIG. Coil Lp1
2. The level curve shown in the lower part of FIG. 3 is the conventional level curve without the resistor RD13, which is the detection level accompanied by signal attenuation due to unnecessary stray load impedance due to stray capacitance. This circuit, which has a coil Lp12 and a resistor Rd13 that cause a gentle resonance with the stray capacitance in the sweep frequency band, has a large stray load impedance due to its resonance characteristic, and therefore an unnecessary load is lightened. A large detection level can be obtained as shown in. Further, even when a conductive material other than the resonance circuit approaches the tablet, such a dip point A and a peak point B do not continue, so that malfunction due to this can be prevented.

The analog switch SW4 sequentially switches the tablet electrode lines 1, 1, ...
For 0, the dip point A and the peak point B are searched for, but 3 from the one with the largest level difference between the dip point A and the peak point B.
One electrode line is selected, and from the positions of the three electrode lines, the control unit 10 interpolates the lines by a table or calculation to determine the precise position of the detection pen 5. The coordinates of the detection pen 5 are obtained by the same means in both the X-axis direction and the Y-axis direction and are output as digital values.

To explain the actual operation, a signal voltage is applied from the voltage driver Vs2 to the resistor Rs3 and the analog switch SW4, and the analog switch SW4 receives the resistor Rs.
3 and the electrode wire 1 are sequentially switched and electrically connected. Here, the dip point A and the peak point B are measured and detected by the level detection circuit 9 for each electrode wire 1, 1, ..., And the result is applied to the control unit 10. When analyzing the signal level to the level detection circuit 9, the coil Lp1
2. If there is no resistor RD13, the load is heavy and the detection level is small due to the effect of the floating load impedance of the stray capacitances Cs1 and Cs2 in FIG. 2, but the coil Lp12 and the resistor RD13 are provided. In this circuit, this shows parallel resonance characteristics with the stray capacitances CS1 and CS2, and since the parallel resonance causes the circuit impedance to increase at the time of resonance, the unnecessary load impedance including the stray capacitances Cs1 and Cs2 also increases ( (Because the unnecessary load becomes lighter) The unnecessary attenuation of the signal is reduced and the detection level is increased. The resistor RD13 is a damping resistor, and has the effect of smoothing its resonance characteristic and not having peaking at only one point of the sweep frequency. From the above analysis, the coil Lp12 acts as a stray capacitance compensation coil, and the resistor Rd13 acts as a stray capacitance compensation resistor. The control unit 10 measures the level difference between the detected dip point A and the peak point B of each electrode wire 1, 1, ...
The electrode line of the book is extracted, and the control unit 10 uses the conversion table based on the actually measured data or interpolates the line by calculation, and the precision of the tablet with which the tip conductor 8 of the detection pen 5 is abutted. Position coordinates are determined and output. still,
Needless to say, the same result can be obtained even if the tablet electrode wire is made of a resistive material such as an ITO film.

[0011]

As described above, according to the present invention, the coordinates can be detected more efficiently and the S / N ratio can be improved by using the pen without the cable and the battery-less detection pen, and the conductive material other than the resonance circuit can be used as the tablet. Highly reliable coordinate detection that does not malfunction even when approaching is possible, and even if the operator loses or damages the detection pen because the detection pen part does not have a cable, the detection pen can be purchased at low cost, so replacement of the detection pen by the operator It can also reduce the economic burden of.

[Brief description of drawings]

FIG. 1 Overall configuration diagram of the apparatus

FIG. 2 Electrically equivalent circuit

[Fig. 3] Level detection characteristic diagram

[Explanation of symbols]

 1 electrode wire 2 frequency sweep voltage source 3 resistance 4 analog switch 5 detection pen 6 coil 7 capacitor 8 tip conductor 9 level detection circuit 10 control unit 11 stray capacitance 12 stray capacitance compensation coil 13 stray capacitance compensation resistor 14 combined resistance 15 coupling capacitance 16 Coil 17 Capacitor 18 Effective resistance

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[Procedure amendment]

[Submission date] January 6, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

The analog switch SW4 sequentially switches the tablet electrode lines 1, 1, ...
For 0, the dip point A and the peak point B are searched for, but 3 from the one with the largest level difference between the dip point A and the peak point B.
One of the electrode lines is selected, and the control unit 10 interpolates between the lines based on the positions of the three electrode lines to determine the precise position of the detection pen 5. The coordinates of the detection pen 5 are obtained by the same means in both the X-axis direction and the Y-axis direction and are output as digital values.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

To explain the actual operation, a signal voltage is applied from the voltage driver Vs2 to the resistor Rs3 and the analog switch SW4, and the analog switch SW4 receives the resistor Rs.
3 and the electrode wire 1 are sequentially switched and electrically connected. Here, the dip point A and the peak point B are measured and detected by the level detection circuit 9 for each electrode wire 1, 1, ..., And the result is applied to the control unit 10. When analyzing the signal level to the level detection circuit 9, the coil Lp1
2. If the resistor RD13 is not provided, the load is heavy and the detection level is small due to the effect of the floating load impedance of the stray capacitances Cs1 and Cs2 in FIG. 2, but the coil Lp12 and the resistor RD13 are provided. In this circuit, this exhibits parallel resonance characteristics with the stray capacitances CS1 and CS2, and since the parallel resonance causes the circuit impedance to increase at the time of resonance, the unnecessary load impedance including the stray capacitances Cs1 and Cs2 also increases ( (Because the unnecessary load becomes lighter) The unnecessary attenuation of the signal is reduced and the detection level is increased. The resistor RD13 is a damping resistor and has the effect of smoothing its resonance characteristic and not having peaking at only one point of the sweep frequency. From the above analysis, the coil Lp12 acts as a stray capacitance compensation coil, and the resistor Rd13 acts as a stray capacitance compensation resistor. The control unit 10 measures the level difference between the detected dip point A and the peak point B of each electrode wire 1, 1, ...
The electrode line of the book is extracted, and the control unit 10 uses a conversion table based on the actually measured data or interpolates between lines by calculation, and the precision of the tablet to which the tip conductor 8 of the detection pen 5 is abutted. Position coordinates are determined and output. still,
Needless to say, the same result can be obtained even if the tablet electrode wire is made of a resistive material such as an ITO film.

Claims (1)

[Claims] 1. A tablet having a plurality of electrode lines arranged along a coordinate axis, a frequency sweep voltage driving unit for sequentially driving each electrode line of the tablet, and a tip end portion for capacitively coupling with the electrode line. And a level detection circuit connected to a signal line for applying a frequency sweep voltage to the electrode line, A coordinate detection device, comprising: a level detection circuit; and a coil having a resistance component connected in parallel.