JP2803832B2 - Coordinate input device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a coordinate input device, and more particularly to a coordinate input device that prevents a malfunction caused by noise generated from an inverter circuit for lighting an illuminator such as a backlight. .

(Prior Art) Conventionally, an input display unit including a sense unit, a display arranged so as to overlap with the sense unit, and a backlight arranged below the sense unit and illuminating a display screen of the display unit;
An inverter circuit for turning on the backlight; a position detection circuit for detecting a position indicated by a position indicator (hereinafter referred to as an input pen) via the sense; and a first signal for generating a clock signal for operating the position detection circuit. And a second clock signal generation circuit for generating a clock signal for operating the inverter circuit.

The input pen includes a coil, a capacitor, and the like, and includes a tuning circuit that can change a tuning frequency with a predetermined frequency f01 as a center tuning frequency.

The sensor section is configured by arranging a number of loop coils at predetermined positions on a transparent substrate.

The backlight is composed of a cold cathode tube or the like, is connected to the inverter circuit operated by a clock signal CK02 having a predetermined frequency f02, and is turned on by applying a high voltage, for example, an AC voltage of 300V.

The position detecting circuit and the sensing unit constitute the tablet, the position detecting circuit includes a signal generating unit that outputs an AC signal having a frequency f01 to a loop coil of the sensing unit, and a frequency induced in the loop coil of the sensing unit. Signal detection means for detecting a frequency AC signal within a predetermined frequency band with f01 as a center frequency, and coordinate detection means for obtaining a coordinate value of a designated position by an input pen based on the AC signal detected by the signal detection means. Have. Further, the position detection circuit operates by the reference clock signal CK01 having the frequency f01.

The first clock signal generation circuit includes a clock signal CK
01, and the second clock signal generation circuit generates the clock signal CK02. Further, there is no electrical connection between the first and second clock signal generation circuits.

The position detection circuit having the above-described configuration detects a position indicated by the input pen on the input display unit using radio waves. That is, the position detection unit operates by the reference clock signal CK01 having the predetermined frequency f01, and transmits a radio wave having the frequency f01 from the loop coil provided in the sensing unit to the input pen during the transmission period. The coil of the tuning circuit of the input pen is excited by the radio wave transmitted from the loop coil of the sensing unit, and an induced voltage synchronized with the radio wave is generated in the tuning circuit.

Thereafter, the position detection circuit enters a reception period. At this time,
The radio wave transmitted from the loop coil of the sense unit disappears immediately. On the other hand, the induced voltage generated in the tuning circuit of the input pen gradually attenuates according to the loss of the tuning circuit. In the course of this attenuation, the coil of the tuning circuit
The induced voltage generates a radio wave corresponding to the tuning frequency of the tuning circuit. The position detection circuit detects a radio wave generated from a tuning circuit of the input pen by a loop coil of a sensor unit, and obtains an indicated position of the input pen. By alternately repeating the transmission and the reception in this manner, the pointing position of the input pen is obtained.

Further, in order to reduce the influence of external noise, the position detection circuit tunes the input pen through a band-pass filter that passes a signal having a frequency within a predetermined frequency band around a frequency f01. Radio waves generated from the circuit are received.

(Problems to be Solved by the Invention) However, in the conventional coordinate input device, it is generated as harmonic noise of the clock signal CK02 of the inverter circuit. Further, when the frequency of the harmonic of the clock signal CK02 matches the frequency 01 of the reference clock signal CK01 of the position detection circuit or exists in a predetermined frequency band around the frequency f01 of the reference clock signal CK01. However, when receiving a radio wave transmitted from the tuning circuit of the input pen, the harmonics are superimposed on the received signal, so that there is a problem that the coordinate detection accuracy of the position indicated by the input pen is reduced.

In view of the above problems, an object of the present invention is to provide a coordinate input device capable of preventing an influence of noise due to a harmonic of a clock signal of an inverter circuit for lighting an illuminator such as a backlight.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a tablet using radio waves of a first frequency as a signal of coordinate detection, and an illuminator driven by a signal of a second frequency. In the coordinate input device, the first frequency is different from the second frequency, and a harmonic of the second frequency is outside a predetermined frequency band centered on the first frequency. A coordinate input device in which the first and second frequencies are set such that

(Operation) According to the present invention, a radio wave of the first frequency is used as a coordinate detection signal, and the illuminator is driven by the signal of the second frequency. In addition, since the first frequency does not match the second frequency, and a harmonic of the second frequency does not exist within a predetermined frequency band centered on the first frequency, the coordinates are Upon detection, no harmonic of the second frequency generated from the illuminator is detected.

FIG. 1 shows an outline of a coordinate input device according to the present invention.
In the drawing, 1 is an input display unit for inputting coordinates, 2 is a position indicator for designating a position, for example, a stylus pen (hereinafter simply referred to as a pen), 3 is a control device, and 4 is a power supply device. is there.

FIG. 2 is a sectional view showing the configuration of the input display unit 1.
According to FIG. 2, the input display unit 1 has a transparent substrate, which will be described in detail later, has a sensing unit 10 for detecting designated position coordinates in the X and Y directions by the pen 2, and is mounted on the sensing unit 10. A flat coordinate display panel 50, for example, a liquid crystal display panel on which a hard core acrylic plate (not shown) is disposed on the upper surface, and a light emitted by the light emission disposed on the lower part of the sense unit 10 and the upper liquid crystal display. A backlight 60 provided with a reflection plate (not shown) for reflecting light toward the panel 50; and a backlight 60 and the sensing unit 10 for illuminating the entire liquid crystal display panel 50 with uniform brightness.
Light guide plate 70 disposed between, for example, a milky white acrylic plate,
An opening 81 is formed at the center of the upper surface, and is constituted by a non-metal case 80 in which the sensing unit 10, the liquid crystal display panel 50, the backlight 60, and the light guide plate 70 can be integrally housed.

The backlight 60 includes the liquid crystal display panel.
For improving the contrast of 50 and displaying brightly, for example, a cold cathode tube is used. By using a cold cathode tube as the backlight 60 in this manner, for example, EL
The liquid crystal display panel 50 can be illuminated from below with three times or more the brightness as when the element is used as a backlight.

FIG. 3A is a schematic diagram showing a transparent substrate 11 constituting the sensing unit 10 of the input display unit 1, and FIG.
It is a partially omitted enlarged sectional view of FIG. In FIG. 3, 12, 13,
14, 15 are transparent films made of polyester, polyvinyl chloride, vinyl chloride or the like; 16 is a large number of, for example, 96, copper wires (actually, annealed tin-plated wires are used) along the Y direction; Reference numeral 17 denotes 96 copper wires arranged in the X direction. First, copper wires 17 are arranged in parallel between the transparent film 12 and the transparent film 13, and these are bonded with, for example, a polyethylene-based transparent adhesive. Similarly, the copper wire 16 is juxtaposed between the transparent film 14 and the transparent film 15 and adhered by the transparent adhesive, and the transparent film 13 and the transparent film 14 are further formed by the copper wire 16 and the copper wire 17. The transparent substrate 11 is formed by bonding so as to be orthogonal to each other.For example, when the transparent film 15 side is irradiated from the transparent film 12 side using the backlight 60, the liquid crystal display panel 50 is formed on the transparent film 15 side. As described above, it is possible to obtain an amount of light sufficient to illuminate brightly.

Also, in FIG. 3 (b), the surface of the transparent substrate 11 is shown to have considerable irregularities, but in practice, the thickness of the transparent film and the diameter of the copper wire are in one direction (X direction or Y direction). ) Even if they are combined, they are less than 0.2mm and can be almost ignored.

Further, in order to configure the sensing portion 10 using the transparent substrate 11, a transparent substrate 11 is provided at the center of a frame-shaped substrate (not shown), and the copper wires 16 and 17 and the pattern of the frame-shaped substrate are soldered, for example. Connected to form a number of loop coils for detecting coordinate values in the X and Y directions. The copper wires 16 and 17 exposed from the transparent substrate 11 may be covered with an insulator except for the soldered portions.

FIG. 4 shows details of a loop coil group 160 for detecting a coordinate value in the X direction and a loop coil group 170 for detecting a coordinate value in the Y direction. The X-direction loop coil group 160 includes a large number of, for example, 48 loop coils 160-1, 160-2,..., 160 arranged in parallel with each other along the Y direction.
−48, and the loop coil group 170 in the Y direction is X
There are a large number of 48 loop coils 170-1, 170-2, ..., 170-48 arranged in parallel to each other along the direction,
As shown in FIG. 3 (a), the loop coil group 16 in the X direction
The loop coil group 170 in the 0 direction and the Y direction are closely overlapped with each other via the transparent film 13 and the transparent film 14 (however, they are drawn apart in the drawings for easy understanding). Here, each loop coil is constituted by one turn, but may be constituted by a plurality of turns as necessary.

FIG. 5 is a cross-sectional view showing a detailed structure of the pen 2. A pen 22 made of a non-metallic material such as a synthetic resin is inserted into a pen shaft 21 from the tip thereof, and a core 22 such as a ball-point pen is slid. A ferrite core 23 having a through hole that can be movably accommodated, a coil spring 24, and a tuning circuit 25 including a switch 251, a coil 252 wound around the ferrite core 23, and capacitors 253 and 254 are integrally formed. They are combined and built in, and a cap 26 is attached to the rear end.

The coil 252 and the capacitor 253 are connected in series with each other as shown in FIG. 7 which will be described in detail later, and constitute a well-known resonance circuit.
The numerical value of 53 is set to a value at which the phase of the voltage and the current resonate (tune) at the predetermined frequency f1. Also,
The capacitor 254 is connected in parallel to both ends of the capacitor 253 via the switch 251.When the switch 251 is turned on, the phase of the current in the above-described resonance circuit is delayed, and the phase of a received signal described later is delayed by a predetermined angle. Perform the action. The switch 251 holds the pen shaft 21 by hand or the like, and pushes the tip of the core body 22 into the pen shaft 21 by, for example, pressing the tip of the core 22 on the upper surface of the input display unit 1. To be turned on.

As shown in FIG. 6, the control device 3 includes a position detection circuit 300 for controlling the sensing unit 10, a display control circuit 500 for controlling the liquid crystal display panel 50, an electronic computer 900 for controlling these components, and an inverter circuit 600. And a clock signal generation circuit 700 that outputs the clock signal CK1 of the frequency f1 to the position detection circuit 300 and the clock signal CK2 of the frequency f2 to the inverter circuit 600, respectively. The inverter circuit 600 uses the clock signal CK2 to drive the position detection circuit 30
0 operates according to the clock signal CK1. Further, the sensing section 10 and the position detection circuit 300 constitute the tablet.

The power supply device 4 includes a well-known rectifier, transformer, DC-DC converter, and the like, and supplies power to each circuit in the control device 3.

FIG. 7 is a block diagram showing details of the tuning circuit 25, the position detection circuit 300, the inverter circuit 600, and the clock signal generation circuit 700. In the figure, 301 is a control circuit, 302 is a signal generation circuit, and 303x and 303y are selection circuits in the X and Y directions. 304x and 304y are transmission / reception switching circuits, 305 is an XY switching circuit, and 306 is a reception timing switching circuit. Also, 3
07 is a bandpass filter (BPF), 308 is a detector, 309 is a low-pass filter (LPF), 310 and 311 are phase detectors (PSD), 312,313
Is a low pass filter (LPF). Further, 314x and 314y are drive circuits, and 315x and 315y are amplifiers.

The inverter circuit 600 includes a driver circuit 6 operated by an AC output circuit 601 and a clock signal CK2 having a frequency f2 described later.
02, which converts a DC voltage into an AC voltage of 300 V having a frequency f2 and outputs the AC voltage. The AC output circuit 601 includes two switching transistors, a transformer, and the like. The driver circuit 602 controls the AC output circuit 60 based on the clock signal CK2.
Alternately drive one switch transistor.

The clock signal generating circuit 700 includes an original oscillation circuit 701, a first frequency dividing circuit 702, and a second frequency dividing circuit 703. The original oscillation circuit 701 generates a clock signal CK having a frequency f0, for example, 1000 KHz.
Generates 0. The first frequency dividing circuit 702 outputs the clock signal CK0
To output a clock signal CK1 having a frequency f1 of f0 / 2, that is, 500 KHz. Further, the second frequency dividing circuit 703 receives the clock signal CK0 and outputs a clock signal CK2 having a frequency f2 of f0 / 25, that is, 40 KHz.

Next, the operation of the position detection circuit 300 will be described together with its configuration. First, the radio wave for position detection is transmitted and received between the sensing unit 10 and the pen 2 and the signals obtained at this time are described below. This will be described with reference to FIG.

The control circuit 301 includes a well-known microprocessor or the like, controls the signal generation circuit 302,
Selection circuits 303x and 303y according to the flowchart shown in FIG.
Control the switching of each loop coil of the sensing unit 10 via
In addition, the XY switching circuit 305 and the reception timing switching circuit 306 control switching of the coordinate detection direction, and furthermore, output values from the low-pass filters 309, 312, and 313 are converted from analog to digital (A / D), and arithmetic operations described later are performed. By executing the processing, the coordinate value of the position specified by the pen 2 is calculated, the state of the switch is identified, and these are sent to the computer 900.

The selection circuit 303x sequentially selects one loop coil from the X-direction loop coil group 160, and the selection circuit 303y sequentially selects one loop coil from the Y-direction loop coil group 170. And operates based on information from the control circuit 301.

The transmission / reception switching circuit 304x alternately connects the selected one loop coil in the X direction to the driving circuit 314x and the amplifier 315x, and the transmission / reception switching circuit 304y includes the selected one loop coil in the Y direction. Are alternately connected to a drive circuit 314y and an amplifier 315y, which operate according to a transmission / reception switching signal described later.

The signal generating circuit 302 has a predetermined frequency f1, for example, a rectangular wave signal A of 500 kHz, a signal A '(not shown) obtained by delaying the phase of the rectangular wave signal A by a predetermined angle, a predetermined frequency fk, for example, 15.
A 625 kHz transmission / reception switching signal B and a reception timing signal C are generated. The rectangular wave signal A is sent to the phase detector 310 and is converted into a sine wave signal by a low-pass filter (not shown).
Or 314y, the square wave signal A 'is sent to the phase detector 311, the transmission / reception switching signal B is sent to the transmission / reception switching circuits 304x and 304y, and the reception timing signal C is a reception timing switching circuit 30
Sent to 6.

Now, assuming that information for selecting the X direction from the control circuit 301 has been input to the XY switching circuit 305 and the reception timing switching circuit 306, the sine wave signal is converted into a balanced signal sent to the driving circuit 314x. Although transmitted to the transmission / reception switching circuit 304x, the transmission / reception switching circuit 304x switches and connects one of the driving circuit 314x and the amplifier 315x based on the transmission / reception switching signal B, and is output from the transmission / reception switching circuit 304x to the selection circuit 303x. Signal is time T (= 1 / 2fk) where every 32 μsec
The signal D is a signal D that outputs or does not output a signal of 500 kHz.

The signal D is sent to one loop coil 160-i (i = 1, 2,..., 48) in the X direction of the sensing unit 10 via the selection circuit 303x. A radio wave based on D is generated.

At this time, when the pen 2 is held substantially upright, that is, in a use state on the input display unit 1, the radio wave based on the signal D excites the coil 252 of the pen 2 and the tuning circuit 25 sends the signal D to the tuning circuit 25. To generate an induced voltage E synchronized with

Thereafter, when the signal D enters a period of no signal, that is, a reception period, and the loop coil 160-i is switched to the amplifier 315x side, the radio wave from the loop coil 160-i immediately disappears, but the induced voltage E becomes less. It gradually attenuates according to the loss in the tuning circuit 25.

On the other hand, the current flowing through the tuning circuit 25 based on the induced voltage E causes the coil 252 to emit radio waves. Since the radio wave excites the loop coil 160-i connected to the multiplexing amplifier 315x in reverse, an induced voltage due to the radio wave from the coil 252 is generated in the loop coil 160-i. The induced voltage is transmitted from the transmission / reception switching circuit 340x to the amplifier 315x, amplified and becomes the reception signal F only during the reception period, and further transmitted to the reception timing switching circuit 306.

Either the selection information in the X direction or the Y direction, here, the selection information in the X direction and the reception timing signal C, which is substantially the inverted signal of the transmission / reception switching signal B, are input to the reception timing switching circuit 306. When the signal C is at the high (H) level, the reception signal F is output, and during the low (L) level, nothing is output. Therefore, the signal G is output at the output (substantially the same as the reception signal F). Is obtained.

The signal G is transmitted to the band filter 307. The band filter 307 is a ceramic filter that allows a signal in a frequency band of ± 10 kHz around the frequency f1 to pass therethrough. The signal H having the amplitude h according to the energy of the signal (strictly speaking, when several signals G are input to the bandpass filter 307 and converged) is sent to the detector 308 and the phase detectors 310 and 311.

The signal H input to the detector 308 is detected and converted into a signal I, and then a low-pass filter 309 having a sufficiently low cut-off frequency.
A voltage value corresponding to approximately half of the amplitude h, for example, Vx
And transmitted to the control circuit 301.

The voltage value Vx of the signal J is the pen 2 and the loop coil 160−
The value indicates a value dependent on the distance to i, here a value inversely proportional to the fourth power of the distance, and changes when the loop coil 160-i is switched, so that the control circuit 301 obtains the value for each loop coil. By converting the voltage value Vx into a digital value and performing an arithmetic process described later on these,
The coordinate value of the designated position in the X direction by the pen 2 is calculated.
Note that the coordinate value of the designated position in the Y direction by the pen 2 is calculated in the same manner.

On the other hand, the rectangular wave signal A is input to the phase detector 310 as a detection signal. At this time, the switch 251 is off and the phase of the signal H substantially matches the phase of the rectangular wave signal A. In this case, a signal (in substantially the same as the signal I) obtained by inverting the signal H to the positive side is output. This signal is converted into a DC signal (substantially the same as the signal J) having a voltage value corresponding to almost half of the amplitude h by the low-pass filter 312 as described above, and sent to the control circuit 301.

The rectangular wave signal A 'is input to the phase detector 311 as a detection signal.
Is off and the phase of the signal H is advanced by a predetermined angle with respect to the phase of the rectangular wave signal A ', a signal having components on the positive side and the negative side is output. This signal is sent to the control circuit 301 converted into a DC signal by the low-pass filter 313 as described above. However, since the output signal of the phase detector 311 has components on the positive side and the negative side, the low-pass filter 313 Output voltage value is considerably smaller than the output voltage value of the low-pass filter 312.

Here, when the switch 251 of the pen 2 is turned on, the phase of the current flowing through the tuning circuit 25 is delayed with respect to the induced voltage E,
The phase of the received signal F is also delayed by a predetermined angle, that is, almost coincides with the phase of the rectangular wave signal A '. Accordingly, the output H of the bandpass filter 307 at this time is converted into a signal having components on the positive side and the negative side by the phase detector 310, and the lowpass filter 31
The output of 2 has substantially the same voltage value as the output of the low-pass filter 313 when the switch 251 is off, but the phase detector 3
The signal is inverted to the positive side by 11 and the low-pass filter 31
The output of 3 is a DC signal having a predetermined voltage value corresponding to approximately 1/2 of the amplitude h, as described above.

Thus, when the switch 251 is off, the low-pass filter 3
A predetermined voltage value is obtained at the output of 12 and the switch 251
Is ON, a predetermined voltage value is obtained at the output of the low-pass filter 313.
By monitoring the output values of 12 and 313, switch 251
Can be identified as being off or on.

The information indicating the on (or off) state of the switch 251 identified here is used as information for specifying a value to be actually input among the coordinate values of the position specified by the pen 2.

Next, a description will be given of the operation of the entire apparatus together with the details of the coordinate detection operation in the position detection circuit 300 and the state of the pen 2 (in this case, the ON / OFF state of the switch 251), with reference to FIGS.

First, when the power of the entire apparatus is turned on and the measurement is started, the control circuit 301 sends information for selecting the X direction to the XY switching circuit 305 and the reception timing switching circuit 306, and the loop of the sensing unit 10 in the X direction. Coil 160-1 to 160-
Of the 48, the information for selecting the first loop coil 160-1 is sent to the selection circuit 303x, and the loop coil 160-1 is connected to the transmission / reception switching circuit 304x.

The transmission / reception switching circuit 304x switches the loop coil 160-1 to the driving circuit 314x and the amplifier 315 based on the transmission / reception switching signal B described above.
x is alternately controlled to be switched to x.
In the transmission period of μsec, 5 seconds as shown in FIG.
The 16 sine wave signals of 00 kHz are sent to the loop coil 160-1.

The switching between the transmission and the reception is repeated seven times for one loop coil, here 160-1, as shown in FIG. 10 (b). The seven transmission and reception repetition periods correspond to one loop coil selection period (448 μsec).

At this time, an induced voltage is obtained from the output of the amplifier 315x every 7 reception periods for 7x one loop coil, and this induced voltage is applied to the reception timing switching circuit 306 as described above.
Are transmitted to the bandpass filter 307 via the averaging unit, and are averaged.
The signal is sent to the control circuit 301 through 3.

The control circuit 301 performs A / D conversion of the output value of the low-pass filter 309, inputs the converted value, and temporarily stores it as a detection voltage depending on the distance between the pen 2 and the loop coil 160-1, for example, Vx1.

Next, the control circuit 301 sends information for selecting the loop coil 160-2 to the selection circuit 303x, and connects the loop coil 160-2 to the transmission / reception switching circuit 304x.
The detection voltage Vx2 depending on the distance to −2 is obtained and stored. Thereafter, the loop coils 160-2 to 160-48 are similarly connected to the transmission / reception switching circuit 304x in the same manner, and FIG. As shown in the figure, the detection voltages Vx1 to Vx48 depending on the distance of each loop coil from the pen 2 in the X direction (however, only a part thereof is shown in an analog expression in FIG. 10C) are stored. I do.

The actual and detected voltages are obtained only in a few loop coils before and after the center (xp) where the pen 2 is placed as shown in FIG.

The control circuit 301 checks whether or not the voltage value of the stored detection voltage is equal to or higher than a certain detection level. If the voltage value is equal to or lower than the certain detection level, the control circuit 301 again selects each loop coil in the X direction and detects the voltage. If the detection level is equal to or more than the predetermined detection level, the process proceeds to the next process.

Next, the control circuit 301 sends selection information in the Y direction to the XY switching circuit 305 and the reception timing switching circuit 306, switches the selection circuit 303y and the transmission / reception switching circuit 304y in the same manner as described above, and reduces the reduction filter when transmitting and receiving radio waves. The pen 2 obtained by A / D conversion of the output value of 309 and each loop coil 170-1 in the Y direction
The detection voltage depending on the distance to 170-48 is temporarily stored. Thereafter, a level check is performed in the same manner as described above.
If it is below a certain detection level, the process returns to the selection and voltage detection of each loop coil in the X direction. If it is above a certain detection level, the pen 2 is used as described later based on the stored voltage value. Is calculated at the designated position in the X and Y directions.

Next, the control circuit 301 controls the loop coil 160- in the X direction.
1-160-48 (or loop coil 170-1 to 170 in the Y direction)
-48), the information for selecting the loop coil for which the maximum detection voltage is obtained is sent to the selection circuit 303x (or 303y),
The transmission / reception of the radio wave is repeated a plurality of times, for example, seven times. At this time, the output values obtained from the reduction filters 312 and 313 are A / D
Then, as described above, it is detected whether any of these values is equal to or greater than a predetermined value, and the on / off state of the switch 251 is identified.

The on / off identification result of the switch 251 is transferred to the computer 900 together with the coordinate values of the designated positions of the pen 2 in the X and Y directions.

When the first coordinate detection operation and state identification operation are completed in this way, the control circuit 301 performs the X-direction loop coil 160-1 as the second and subsequent coordinate detection operations as shown in FIG. Of the loop coil from which the maximum detection voltage was obtained, a constant number before and after that, for example, information for selecting only 10 loop coils is sent to the selection circuit 303x. Loop coil 170
Out of -1 to 170-48, with the loop coil at which the maximum detection voltage is obtained as the center, a constant number before and after the loop coil, information for selecting only 10 loop coils is sent to the selection circuit 303y, and the same as above. To obtain the output value, to detect the coordinates of the pen 2 in the X and Y directions, and to turn on / off the switch 251.
The off-state identification operation is performed, and the obtained coordinate values and identification result are transferred to the computer 900, and thereafter, these operations are repeated.

In addition, if the level check described above is explained in detail,
Check whether the maximum value of the detection voltage has reached the detection level and which loop coil has the maximum value of the detection voltage, and stop the subsequent coordinate calculation and the like if the detection level has not been reached. This is a process of setting the center of the loop coil to be selected in the next coordinate detection operation and state identification operation.

X-direction or Y-direction coordinate values, for example, as one method of calculating the coordinate value xp, approximate the waveform near the maximum value of the detection voltage Vx1 ~ Vx48 with a suitable function, the coordinates of the maximum value of the function There is a way to ask.

For example, in FIG. 10 (c), the maximum detection voltage Vx3
And the detection voltages Vx2 and Vx4 on both sides thereof can be calculated as follows by approximation by a quadratic function (however, the coordinate values of the center values of the loop coils 160-1 to 160-48 are x1 to
x48, and the interval is Δx. First, from each voltage and coordinate value, Vx2 = a (x2-xp) ² + b (1) Vx3 = a (x3-xp) ² + b (2) Vx4 = a (x4-xp) ² + b ... (3) Here, a and b are constants (a <0). X3−x2 = Δx (4) x4−x2 = 2Δx (5) Substituting the expressions (4) and (5) into the expressions (2) and (3) and rearranging them, xp = x2 + Δx / 2 ｛(3Vx2-4Vx3 + Vx4) / (Vx2-2Vx3 + Vx4)｝ (6) .

Therefore, the maximum value of the detection voltage obtained at the time of the level check and the detection voltages before and after that are extracted from each of the detection voltages Vx1 to Vx48, and these and the one of the loop coil from which the maximum value of the detection voltage is obtained are extracted. The coordinate value xp of the designated position of the pen 2 can be calculated by performing an operation corresponding to the above-described equation (6) from the coordinate value (known) of the previous loop coil.

Each coordinate value thus detected is displayed on the liquid crystal display panel 50 under the control of the display panel control circuit 500 for each detection.

FIG. 13 shows the details of the display control circuit 500, and the position data consisting of the X-direction data and the Y-direction data sequentially instructed by the sensing unit 10 is input to the computer 900, and then the display memory 501 The position data is stored in a predetermined order, and the position data is stored in the controller 50 as a display processor.
The signals are sequentially read out by the timing pulses from 2, and output to the X-direction driver 503 and the Y-direction driver 504.

The scanning pulse generated by the scanning pulse generator 505 is input to the X-direction driver 503 and the Y-direction driver 504 in synchronization with the timing pulse of the controller 502. And the position data in the Y direction are input, whereby the position indicated by the pen 2 is displayed on the sensing unit 10 at the same position on the liquid crystal display panel 50. Therefore, the handwriting of a character or a figure drawn with the pen 2 from the top of the liquid crystal display panel 50 superimposed on the sensing unit 10 is the same handwriting on the liquid crystal display panel 50, and the backlight 60 provided below the sensing unit 10 The display is made bright by the action of the light guide plate 70.

Further, when the backlight 60 is turned on, the inverter circuit 600 operates, and noise is generated by harmonics of the clock signal CK2. As shown in the relationship between the input / output signal strength and frequency of the bandpass filter 307 in FIG. The frequency of the harmonic of the clock signal CK2 is the same as the frequency of the clock signal CK1.
Never match f1. Also, it is not included in the pass frequency band of the bandpass filter 307. Therefore, the clock signal CK
No malfunction due to detection of noise due to harmonics of 2.

Note that the number of loop coils and the arrangement thereof in the embodiment are merely examples, and it is needless to say that the present invention is not limited to this. Also, a cursor can be used instead of the stylus pen.

Further, in the present embodiment, the coordinate input device having the backlight is used, but the present invention is not limited to the backlight,
A similar effect can be obtained with a coordinate input device having a lighting device provided with an inverter circuit.

Further, in the present embodiment, the sensing unit 10 is arranged below the liquid crystal display panel 50, and the backlight 60 is arranged therebelow. However, the present invention is not limited to this. Can be obtained.

Further, in the above-described embodiment, the coordinate input device that transmits a radio wave to the position indicator from the tablet side and receives the reflected radio wave to perform position detection and the like is used, but the radio wave transmitted from the tablet side is used by the position indicator side. It is also possible to use a well-known electromagnetic induction type coordinate input device or the like, which receives the radio wave transmitted from the position indicator side on the tablet side.

(Effect of the Invention) As described above, according to the present invention, the first frequency used as a signal for coordinate detection does not match the second frequency used for lighting the illuminator, and Since the harmonic of the second frequency does not exist within a predetermined frequency band centered on the first frequency, the second harmonic generated from the illuminator is not detected when detecting coordinates. However, there is an advantage that the accuracy of coordinate detection can be prevented from deteriorating due to the influence of noise composed of the harmonics.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an outline of a coordinate input device of the present invention, FIG. 2 is a sectional view of an input display section, FIG. 3 (a) is a schematic view of a transparent substrate, and FIG. 3 (b) is a transparent substrate. FIG. 4 is a detailed configuration diagram of a loop coil group in the X direction and the Y direction of the sensing unit, FIG. 5 is a cross-sectional view of a stylus pen, FIG. 6 is a block diagram of a control device, FIG. 7 is a block diagram showing details of a tuning circuit, a position detecting circuit, an inverter circuit, and a clock signal generating circuit of the stylus pen. FIG. 8 is a signal waveform diagram of each part in FIG. 7, and FIG. Flow chart of processing in the control circuit, FIGS. 10 (a) and 10 (b)
FIG. 11C is a timing chart showing a basic position detection operation in the position detection circuit. FIG. 11 is a view showing detection voltages obtained from each loop coil at the time of the first position detection operation.
FIG. 12 is a timing chart showing the position detection operation and the state identification operation after the second time, FIG. 13 is a display control circuit diagram,
14 (a) and 14 (b) are diagrams showing the relationship between the input / output signal strength of the bandpass filter and the frequency. DESCRIPTION OF SYMBOLS 1 ... Input display part, 2 ... Stylus pen, 3 ... Control device, 4 ... Power supply device, 10 ... Sense part, 50 ... Display panel, 60 ... Backlight, 300 ... Position detection circuit, 500: Display control circuit, 600: Inverter circuit, 700: Clock signal generation circuit, 900: Electronic computer.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G06F 3/03 G06F 3/033

Claims (1)

(57) [Claims] 1. A coordinate input device in which a tablet using a radio wave of a first frequency as a signal of coordinate detection and an illuminator driven by a signal of a second frequency are combined. Different from the second frequency, and the first and second frequencies are set such that harmonics of the second frequency are outside a predetermined frequency band around the first frequency, A coordinate input device, characterized in that: