JPH04337824A - Coordinate input device - Google Patents

Abstract

PURPOSE:To set coordinate detection precision to be uniform for a whole surface in a coordinate detection area by providing auxiliary electrodes. CONSTITUTION:When a position detection pen 8 is brought near the surface of a liquid crystal panel 1, voltage induced by the detection pen 8 is amplified by an amplifier 9 and is given to a coordinate detection circuit 10 by stray capacity between an electrode provided at the tip of the detection pen 8 and electrodes X and Y to which voltage is impressed. Electrodes X-1, X0, Xm+1, Xm+2, Y-1, Y0, Yn+1 and Yn+2 in the liquid crystal panel 1 are the auxiliary electrodes and they are formed on the same plane as the common electrode Y or the segment electrode X beyond the area of the display area of the liquid crystal panel 1. They do not have to contribute to display which an operator requires. Since the auxiliary electrodes are provided, the coordinate can highly precisely be detected near the boundary of the coordinate detection area. Even if the auxiliary electrodes are provided, it does not affect the display of the display panel and the coordinate can highly precisely be detected while high display quality is kept.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coordinate input device such as a so-called tablet used for inputting characters, figures, etc. into a personal computer, word processor, or the like.

0002

[Prior Art] As a means of inputting handwritten characters and figures into computers, word processors, etc., for example, a liquid crystal display and an electrostatic induction tablet are combined.
Input devices have been put into practical use in which characters, figures, etc. input to an electrostatic induction tablet are inputted by an operator as if they were written on paper with a writing utensil, and are displayed on a liquid crystal display.

[0003] Electrostatic induction tablets used for such purposes have conventionally been formed by forming a transparent electrode of indium oxide or the like on a transparent glass or plastic film, or by forming a thin wire of several micrometers as an electrode. Generally, pulse voltages are applied sequentially, and for example, there is a structure shown in FIG. 6.

Coordinate input section 3 of this electrostatic induction tablet
1 is a glass substrate 32 on which transparent electrodes X1, X2, ..., Xm (indicated collectively by X) are formed, and a transparent electrode Y1.
, Y2, . placed on top.

The transparent electrodes X, Y are connected to a column electrode shift register 34 and a row electrode shift register 35, respectively, and further, these two shift registers 34, 35
is connected to the timing generation circuit 36. From this timing generation circuit 36, the shift register 34,
Shift data and clock signals are sent to the column electrode shift register 34 to the electrodes X1, X2, ..., Xm, and the row electrode shift register 35 to the electrodes Y1, Y2, ...
, Yn are sequentially applied with a pulse voltage.

When a position detection pen (hereinafter simply referred to as detection pen) 37 is brought close to the surface of the coordinate input section 31, stray capacitance between the electrode provided at the tip of the detection pen 37 and the electrodes X and Y causes , a voltage is induced in the electrode at the tip of the detection pen 37. The voltage induced in the detection pen 37 is amplified by the amplifier 38, and the X coordinate detection circuit 39 and the Y coordinate detection circuit 39 and
It is input to the coordinate detection circuit 40.

The X-coordinate detection circuit 39 and Y-coordinate detection circuit 40 detect the X-coordinate and Y-coordinate, respectively, based on the output from the amplifier 38 and the timing signal from the timing generation circuit 36. The liquid crystal display (not shown) displays the coordinates indicated by the detection pen 37 on the display based on the coordinate signals from the electrostatic induction tablet.

However, in the case of this electrostatic induction tablet, the reflectance and transmittance are different between the portions of the coordinate input section 31 where the transparent electrodes X and Y are present and the portions where the transparent electrodes are not. visible, causing a drop in the quality of the LCD display.

[0009] Therefore, as a tablet that eliminates these drawbacks, a display-integrated tablet as shown in FIG. 7 has recently been proposed.

[0010] In this display-integrated tablet, the display electrode of the liquid crystal display also serves as a position detection electrode, and position detection and display are performed in a time-sharing manner.

In FIG. 7, a liquid crystal panel 501 includes common electrodes Y1 to Yn (indicated by Y when collectively referred to) and segment electrodes X1 to Xm (indicated by X when collectively referred to) arranged in directions that intersect with each other. A liquid crystal layer is interposed therebetween, and the liquid crystal layer at the intersection of each common electrode Y and segment electrode X forms each pixel. That is, here, pixels of n×m dots are arranged in a matrix. The area where the pixels of this nxm dot are arranged is the display area 501 as shown in FIG.
d, and is a position detection area.

[0012] This display-integrated tablet has the advantage that the grid-like electrode pattern is no longer visible and the screen is easier to see, compared to the above-mentioned tablet placed on the liquid crystal display. This has the advantage of reducing costs and making it easier to reduce size and weight.

A common drive circuit 502 for driving the common electrode Y and a segment drive circuit 503 for driving the segment electrode X are connected to a display control circuit 505 and a position detection control circuit 506 via a switching circuit 504. It is connected to the. The switching circuit 504 is switched and controlled by the control circuit 507, and the display control circuit 505 is switched during the display period.
The output from the position detection control circuit 506 is output to the drive circuits 502 and 503 during the position detection period.

During the display period, the display control circuit 505 outputs shift data S, inverted signal FR, clock CP1, clock CP2, and display data D0 to D3.

The clock CP1 is a clock whose period is equal to the scanning period for scanning one row of pixels, and
The signal is inputted from the output terminal CP10 of No. 4 to the clock input terminal CK of the common drive circuit 502 and the latch pulse input terminal LP of the segment drive circuit 503. The shift data S is a pulse signal for specifying each common electrode Y, and is output from the output terminal S0 of the switching circuit 504, and is synchronized with the clock CP1 from the shift data input terminal D101 of the common drive circuit 502. is input.

According to the shift of the shift data S, a drive signal is outputted to the common electrode Y from the output terminal of the common drive circuit 502 corresponding to the shift position. This drive signal is generated based on bias voltages V0 to V5 supplied from the DC power supply circuit 512. The clock CP2 is a clock whose cycle is a period obtained by dividing a scanning period for scanning one column of pixels into a plurality of parts, and is output from the output terminal CP20 of the switching circuit 504, and is outputted from the output terminal CP20 of the switching circuit 504.
It is input to the clock input terminal XCK of No. 3.

Display data D0 to D3 are transferred to the switching circuit 504.
is outputted from the output terminal Dout of the segment drive circuit 503, inputted to the input terminals D0 to D3 of the segment drive circuit 503, and sequentially taken into the register inside the segment drive circuit 503. When display data corresponding to one row of pixels is captured, these display data are latched at the timing of clock CP1 input to the latch pulse input terminal LP, and drive signals corresponding to each display data are segment driven. The signal is output from the output terminal of the circuit 503 to the segment electrode X. This drive signal is also generated based on bias voltages V0 to V5 supplied from the DC power supply circuit 512. Note that the inversion signal FR is a signal for periodically inverting the polarity of the voltage applied to the liquid crystal layer to prevent deterioration of the liquid crystal due to electrolysis.

By the operations of the common drive circuit 502 and the segment drive circuit 503, the pixels of the liquid crystal panel 501 are driven in accordance with the row order, and an image corresponding to display data is displayed on the liquid crystal panel 501.

On the other hand, during the position detection period, the position detection control circuit 506 outputs the shift data Sd, the inverted signal FRd, the clocks CP1d and CP2d, and the drive data D0d to D0d.
3d respectively.

The clock CP1d is a clock whose cycle is equal to the scanning period for scanning one row of common electrodes, and is a clock whose cycle is equal to the scanning period for scanning one row of common electrodes.
2 clock input terminal CK and segment drive circuit 50
It is input to the latch pulse input terminal LP of No. 3. Also,
The shift data Sd is a pulse signal for specifying each common electrode Y, and is output from the output terminal S0 of the switching circuit 504, and is input from the shift data input terminal D101 of the common drive circuit 502 in synchronization with the clock CP1d. Ru.

According to the shift of the shift data Sd,
A drive signal is output to the common electrode Y from the output terminal of the common drive circuit 502 corresponding to the shift position. This drive signal is generated based on bias voltages V0 to V5 supplied from the DC power supply circuit 512. clock CP2
d is a clock whose cycle is the scanning period for scanning one column of segment electrodes X, and is output from the output terminal CP20d of the switching circuit 504 and input to the clock input terminal XCK of the segment drive circuit 503.

The drive data D0d to D3d are transferred to the switching circuit 5.
04, is input to the input terminals D0 to D3 of the segment drive circuit 503, and is sequentially taken into the register inside the segment drive circuit 503. 1
When the drive data corresponding to the segment electrodes X for the rows are taken in, these drive data are latched at the timing of the clock CP1d input to the latch pulse input terminal LP, and the drive signals corresponding to each drive data are The signal is output from the output terminal of the segment drive circuit 503 to the segment electrodes X. This drive signal is also created based on bias voltages V0 to V5 supplied from the DC power supply circuit 512. Note that the inversion signal FRd is a signal for periodically inverting the polarity of the voltage applied to the liquid crystal layer to prevent deterioration of the liquid crystal due to electrolysis.

FIG. 9 is a timing chart showing the driving timing of the display-integrated tablet during the position detection period. As shown in FIG. 9, the position detection period is
The period is divided into a coordinate detection period and a Y-coordinate detection period that follows. During the X-coordinate detection period, a number of segment electrodes X are sequentially driven, and during the Y-coordinate detection period, b common electrodes Y are sequentially driven. The reason why a plurality of pulse voltages are applied simultaneously is to improve the detection accuracy by increasing the induced voltage of the detection pen 508 and to shorten the detection period. The induced voltage of the detection pen 508 is detected by the amplifier 509.
The output of this amplifier 509 and the control circuit 507
Based on the timing signal from
10 detects the X coordinate, and a Y coordinate detection circuit 511 detects the Y coordinate.

[0024]

[Problems to be Solved by the Invention] The display-integrated tablet using the liquid crystal panel 501 has the problem that the display electrodes
, Y also serve as scanning electrodes for coordinate detection. That is, as shown in FIG. 10, in the liquid crystal panel 501, segment electrodes X and common electrodes Y, which are transparent electrodes, are formed on transparent substrates 24 and 23, and a distance of, for example, several micrometers between the electrodes is formed.
A gap of m is filled with liquid crystal. Furthermore, a polarizing plate 2 is provided on the surface of the transparent substrates 24 and 23 opposite to the electrode formation surfaces.
1 and 22 are arranged.

In the case of a duty-driven liquid crystal panel, the display electrode also serves as a lead wire to the electrode, and the intersection of both electrodes becomes a pixel of the liquid crystal display. In other words, in FIG. 8, the area 501d indicated by the dashed line is the display area. be. Display area 501
The electrode width in areas other than d is the same as the display electrode width in the display area 501d. However, in consideration of connection with the liquid crystal drive circuit, there are cases where the area is slightly fan-shaped outside the display area. Moreover, its length is also about 5 mm.

When such a liquid crystal panel 501 is used as a display device, the presence of the aforementioned electrodes outside the display area, that is, the lead wire portions does not pose a particular problem in terms of display function, but when used as a tablet, the function may be affected. It becomes a hindering factor.

FIG. 11 shows the state of capacitive coupling between the detection pen 508 and the segment electrode X when the detection pen 508 is brought into contact with the vicinity of the segment electrode X1, and FIG. , for example, shows the state of capacitive coupling between the detection pen 508 and the segment electrode X when it is brought into contact with the segment electrode Xm/2. Figure 1
2, the detection pen 508 has segment electrodes...,X
It is electrostatically coupled to i-1, Xi, Xi+1, Xi+2,..., and when voltage is applied sequentially to the segment electrodes,
A voltage as shown in FIG. 12 (2) is induced in the detection pen 508, and after amplification and passing through a low-pass filter, the voltage shown in FIG. 12 (3) is induced.
) A voltage with the waveform shown in is obtained. Furthermore, after the pulse is binarized by a comparator, the X coordinate can be detected based on the timing of generation of the pulse.

In FIG. 11, the detection pen 508 is only connected to segment electrodes X1, X2, X3, . . . , and there are no segment electrodes to the left of segment electrode X1 in the drawing. Therefore, segment electrode X1,
When voltage is applied sequentially to X2, X3,..., the detection pen 5
A voltage with a waveform as shown in Fig. 11 (2) is induced in 08, and after amplification and passing through a low-pass filter, it becomes as shown in Fig. 11 (3).
A voltage with the waveform shown in is obtained.

However, when the detected voltage waveform shown in FIG. 11 (3) is output, the peak value is lower than that shown in FIG. 12 (3), and therefore, when the reference voltage of the comparator is low, may not be detected. Furthermore, even if the comparator can perform the binarization process, the output voltage waveform is asymmetrical as shown in FIG.

In the actual liquid crystal panel 501, as shown in FIG. 11, the area where the coordinate detection accuracy is low is the display area 501d.
The distance is approximately 5 mm inward from the end, and as shown in FIG. 12, coordinates can be detected with high precision in the area inward of this area, as in the center of the display area.

FIGS. 13 and 14 respectively show the detection pen 508 and the common electrode Y disposed on the lower side in the drawing.
FIG. FIG. 13 shows the state of capacitive coupling when the detection pen 508 is brought into contact with the vicinity of the border of the display area 501d, and FIG. 14 shows the state of capacitive coupling when the detection pen 508 is brought into contact with the vicinity of the center of the display region 501d. The situation is shown below.

As shown in FIG. 14, when the detection pen 508 is brought into contact with the vicinity of the center of the display area 501d, the detection pen 508 and the common electrode Y are connected to a plurality of segment electrodes X.
They are electrostatically coupled through the gap. In FIG. 14,
Although the electrode width and electrode spacing are written in a one-to-one ratio,
In reality, the ratio is about 10:1, and the gap (distance between electrodes) is extremely small. Therefore, when scanning is performed by sequentially applying a scanning voltage to the common electrode Y, the detection voltage obtained from the detection pen 508 is the same as that of the segment electrode X if the applied voltage is the same as that of the segment electrode X. Although the waveform is significantly lower than that when electrically coupled, the waveform is almost the same.

However, as shown in FIG. 13, when the detection pen 508 is brought into contact with the vicinity of the boundary of the display area 501d, the lead wire portion 25 of the common electrode Y is not covered with the segment electrode X and is therefore exposed. , the electrostatic coupling in this lead wire portion 25 is extremely large. Therefore, when sequential scanning voltages are applied to the common electrode Y,
As shown in FIG. 2, an extremely high induced voltage is induced in the detection pen 8 due to the close electrostatic coupling with the lead wire portion 25. In FIG. 13(3), the voltage is about twice that shown in FIG. 14(3), but it may exceed 10 times.

As described above, coordinates cannot be detected near the boundary of the display area 501d due to the high voltage induced by the lead wire portion 25. The area where the coordinate detection accuracy is low is about 5 mm inward from the vicinity of the border of the display area 501d, and in the inner area, it is as high as near the center of the display area 501d, as shown in FIG. Coordinate detection can be performed with high precision.

As described above, in the case where the electrodes are formed to spread out in a fan shape in the lead wire portion 25, if the angle is large, the detection accuracy will further deteriorate.

An object of the present invention is to provide a coordinate input device that can solve the above technical problems and make the coordinate detection accuracy uniform over the entire coordinate detection area.

[0037]

[Means for Solving the Problems] The present invention provides a display panel that has a plurality of segment electrodes arranged in parallel and a plurality of common electrodes arranged in parallel, and is driven by a duty drive method, and the display panel a detection pen having an electrode at its tip that is coupled by stray capacitance between the segment electrodes and the common electrode of the display panel; a display control circuit that outputs a display control signal and display data for displaying an image; a position detection control circuit that outputs a scan control signal for scanning segment electrodes and common electrodes of the display panel; In a display period, a switching circuit outputs a display control signal and display data from the display control circuit, and in a position detection period following the display period, a switching circuit outputs a scanning control signal from the position detection control circuit; In the period, a common electrode drive signal for sequentially selecting the common electrodes is generated based on the display control signal from the switching circuit, and in the position detection period, the common electrode driving signal is generated in the pixel matrix based on the scanning control signal from the switching circuit. a common drive circuit that outputs a common electrode scanning signal for sequentially scanning the common electrodes without displaying an image; and a common drive circuit that outputs a common electrode scanning signal for sequentially scanning the common electrodes without displaying an image; A segment electrode drive signal is output for displaying pixels related to the common electrode selected by the signal, and during the position detection period, the segment electrode is moved without displaying an image on the pixel matrix based on the scan control signal from the switching circuit. a segment drive circuit that outputs a segment electrode scanning signal for sequentially scanning the area; and application timing of the common electrode scanning signal and the segment electrode scanning signal applied to the common electrode and the segment electrode during the position detection period;
a coordinate detection circuit that detects the coordinates indicated by the tip of the detection pen on the display panel based on the induced voltage induced in the electrode of the detection pen, and outputs an X coordinate signal and a Y coordinate signal. In the coordinate input device, a plurality of auxiliary electrodes parallel to the common electrode and the segment electrodes are provided outside the display area of the display panel, and during the position detection period, an electrode scanning signal is sequentially applied to the auxiliary electrode, the common electrode, and the segment electrode. This is a coordinate input device characterized by applying .

Further, the present invention is characterized in that the potential of the scanning signal applied to the auxiliary electrode during the position detection period is made the same as the potential of the scanning signal applied to the common electrode and the segment electrode within the display area.

Further, in the present invention, the auxiliary electrode is connected to a common drive circuit and a segment drive circuit, and in the position detection period, the auxiliary electrode, the common electrode, and the auxiliary electrode are connected in the order of the auxiliary electrode, the segment electrode, and the auxiliary electrode. In the order of
It is characterized by being scanned in a predetermined arrangement direction.

The present invention is also characterized in that an electrode scanning signal of the same potential is applied to a plurality of adjacent auxiliary electrodes arranged in parallel at the same timing.

Further, in the present invention, the common drive circuit and the segment drive circuit each include a shift register, and the shift register is controlled during scanning of the auxiliary electrode and during scanning of the common electrode or the segment electrode in the position detection period. It is characterized by having the same clock and data.

Further, in the present invention, the shift register of the drive circuit has a data interrupt function, and during the display period of the display panel, the shift register operates by interrupting data from the middle to scan the auxiliary electrodes. It is characterized by the fact that there is no

Further, in the present invention, the coordinate detection circuit converts the coordinate values calculated including the auxiliary electrodes into coordinate values in an effective coordinate input area constituted by the intersection of the common electrode and the segment electrode. It is characterized by

Further, in the present invention, the auxiliary electrode is formed on the same plane as the common electrode or the segment electrode, and the width and formation interval of the auxiliary electrode are selected to be the electrode width and formation interval of the common electrode or the segment electrode. Features.

The present invention is also characterized in that the length in the width direction of the auxiliary electrode in the auxiliary electrode array area is selected to be larger than the distance between the detection pen and the common electrode or the segment electrode when instructing coordinate input to the display panel. shall be.

The present invention is also characterized in that the auxiliary electrode is formed on a plane different from that of the segment electrode or the common electrode.

The present invention is also characterized in that the auxiliary electrode is made of the same material as the segment electrodes and the common electrode, and is formed in the same manufacturing process.

[0048]

[Operation] According to the present invention, an auxiliary electrode is provided on the outer side in the arrangement direction of the common electrode and segment electrode of the display panel,
In a position detection period that is set subsequent to the display period of the display panel, the auxiliary electrode, the common electrode, and the segment electrode are scanned by applying a scanning voltage line-sequentially. This reduces the capacitive coupling between the detection pen and the common electrode or segment electrode when the detection pen is brought into contact near the display area border of the display panel, and when the detection pen is brought into contact near the center of the display panel. The state can be almost the same as that of electrostatic coupling. Therefore, highly accurate coordinate detection is possible over almost the entire display area, that is, the coordinate detection area.

Further, according to the present invention, since the auxiliary electrodes are driven by the common drive circuit and the segment drive circuit, highly accurate coordinate detection is possible without adding any new circuits. In this case, as the number of electrodes to be driven increases, the scanning period for scanning the electrodes becomes longer during the display period of the display panel, and if the display of the display panel is affected, the shift register included in the drive circuit The electrodes are scanned by switching the clock. That is, the auxiliary electrode portion is scanned with a faster clock than the clock used to scan the display electrode portion. This can prevent the display quality of the display panel from deteriorating.

Further, according to the present invention, the shift register included in the drive circuit has a data interrupt function,
During the position detection period, drive data is input from the beginning of the shift register, and during the display period, data is input from the middle of the shift register, that is, from the register corresponding to the display electrode. As a result, the auxiliary electrode portion is not scanned during the display period, and it is possible to prevent the display quality of the display panel from deteriorating due to the addition of the auxiliary electrodes described above.

[0051]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the configuration of a coordinate input device according to an embodiment of the present invention. This coordinate input device is a so-called display-integrated tablet, in which the display electrode of the liquid crystal display also serves as a position detection electrode, and position detection and display are performed in a time-sharing manner.

In FIG. 1, the liquid crystal panel 1 includes common electrodes Y1 to Yn (indicated by Y when collectively referred to) and segment electrodes X1 to Xm (indicated by X when collectively referred to) arranged in directions crossing each other. A liquid crystal layer is interposed between them, and the liquid crystal layer at the intersection of each common electrode Y and segment electrode X forms each pixel. That is,
In the liquid crystal panel 1 of this embodiment, pixels of n×m dots are arranged in a matrix.

[0053] This display-integrated tablet has the advantage that the grid-like electrode pattern is no longer visible compared to the tablet placed on the liquid crystal display, making it easier to see. This has the advantage of reducing costs and making it easier to reduce size and weight.

The common drive circuit 2 for driving the common electrode Y and the segment drive circuit 3 for driving the segment electrode X are connected to a display control circuit 5 and a position detection control circuit 6 via a switching circuit 4. and is connected to. This switching circuit 4 is switched and controlled by a control circuit 7, and during the display period, the output from the display control circuit 5 is transferred to the drive circuits 2 and 3.
During the position detection period, the output from the position detection control circuit 6 is output to the drive circuits 2 and 3.

During the display period, the display control circuit 5 outputs the shift data S, the inverted signal FR, and the clock C from the output terminal.
P1, CP2, and display data D0 to D3 are output respectively.

The clock CP1 is a clock whose cycle is the scanning period for scanning one row of pixels, and the latch pulse is transmitted from the output terminal CP10 of the switching circuit 4 to the clock input terminal CK of the common drive circuit 2 and the segment drive circuit 3. It is input to input terminal LP. Further, the shift data S is a pulse signal for specifying each common electrode Y, and is output from the output terminal S0 of the switching circuit 4, and is sent from the shift data input terminal D101 of the common drive circuit 2 to the clock CP1.
input in synchronization with

According to the shift of the shift data S, a drive signal is outputted to the common electrode Y from the output terminal of the common drive circuit 2 corresponding to the shift position. This drive signal is a bias voltage V0 supplied from the DC power supply circuit 12.
- Generated based on V5. Clock CP2 divides the scanning period for scanning one column of pixels into a plurality of periods into one period.
It is a clock with a period, and the output terminal CP of the switching circuit 4
20 and input to the clock input terminal XCK of the segment drive circuit 3.

The display data D0 to D3 are output from the output terminal Dout of the switching circuit 4, input to the input terminals D0 to D3 of the segment drive circuit 3, and are inputted to the input terminals D0 to D3 of the segment drive circuit 3.
Sequentially loaded into internal registers. When display data corresponding to one row of pixels is captured, these display data are latched at the timing of clock CP1 input to the latch pulse input terminal LP, and drive signals corresponding to each display data are segment driven. The signal is output from the output terminal of the circuit 3 to the segment electrode X. This drive signal is also created based on bias voltages V0 to V5 supplied from the DC power supply circuit 12. Note that the inversion signal FR is a signal for periodically inverting the polarity of the voltage applied to the liquid crystal to prevent deterioration of the liquid crystal due to electrolysis.

By the operations of the common drive circuit 2 and the segment drive circuit 3, the pixels of the liquid crystal panel 1 are driven in row order, and an image corresponding to display data is displayed on the liquid crystal panel 1.

On the other hand, during the position detection period, the position detection control circuit 6 outputs the shift data Sd and the inverted signal FR from the output terminal.
d, clocks CP1d, CP2d, and drive data D
Output 0d to D3d, respectively.

The clock CP1d is a clock whose cycle is equal to the scanning period for scanning one row of common electrodes Y, and connects the output terminal CP10 of the switching circuit 4 to the clock input terminal CK of the common drive circuit 2 and the segment drive circuit 3. It is input to the latch pulse input terminal LP of. Further, the shift data Sd is a pulse signal for specifying each common electrode Y, and is output from the output terminal F0 of the switching circuit 4, and is output from the shift data input terminal D101 of the common drive circuit 2 in synchronization with the clock CP1d. is input.

According to the shift of the shift data Sd,
A drive signal is output to the common electrode Y from the output terminal of the common drive circuit 2 corresponding to the shift position. This drive signal is a bias voltage V supplied from the DC power supply circuit 12.
Generated based on 0 to V5.

The clock CP2d is a clock whose cycle is equal to the scanning period for scanning one column of segment electrodes X, and is output from the output terminal CP20d of the switching circuit 4 and input to the clock input terminal XCK of the segment drive circuit 3. Ru.

The drive data D0d to D3d are transferred to the switching circuit 4.
The signal is output from the output terminal Dout of the segment drive circuit 3, inputted to the input terminals D0 to D3 of the segment drive circuit 3, and sequentially taken into the register inside the segment drive circuit 3. When drive data corresponding to one row of segment electrodes X is taken in, the clock CP1 is input to the latch pulse input terminal LP.
At timing d, these drive data are latched,
A drive signal corresponding to each drive data is input to the segment electrode X from the output terminal of the segment drive circuit 3. This drive signal is also created based on bias voltages V0 to V5 supplied from the DC power supply circuit 12. Note that the inversion signal FRd is a signal for periodically inverting the polarity of the voltage applied to the liquid crystal to prevent deterioration of the liquid crystal due to electrolysis.

A position detection pen (
8 (hereinafter simply referred to as a detection pen) approaches, the stray capacitance between the electrode provided at the tip of the detection pen 8 and the electrodes X and Y to which voltage is applied causes the electrode at the tip of the detection pen 8 to voltage induced. The voltage induced in the detection pen 8 is amplified by an amplifier 9 and applied to a coordinate detection circuit 10.

FIG. 2 is an enlarged plan view of the liquid crystal panel 1. As shown in Figure 2, the electrodes X-1, X0, Xm+1,
m+2 and electrodes Y-1, Y0, Yn+1, and Yn+2 are auxiliary electrodes, and outside the display area 1d of the liquid crystal panel 1, on the same plane as the common electrode Y or segment X,
In other words, they are formed on the same substrate, and from a structural point of view, the area in which the common electrodes and segment electrodes are formed is expanded, but they do not need to contribute to the display of information required by the operator. In this embodiment, two auxiliary electrodes are provided on the outside of the display area 1d, and the width and spacing of each electrode are approximately the same as the display electrodes in the display area 1d.

In FIG. 2, two auxiliary electrodes are arranged on the outer side of the display area 1d, but the auxiliary electrode formation areas R1 and R2 in the actual liquid crystal panel 1 are
It is determined based on the tip shape of the liquid crystal panel 1 and the distance between the liquid crystal layer and the detection pen 8, including the upper glass substrate of the liquid crystal panel 1, the polarizing plate, the protection plate (not shown), etc., but at least the distance between the detection pen 8 and the scanning electrode (common The distance from the electrode or segment electrode group is necessary, and is usually selected to be about 3 mm.

Since the auxiliary electrode forming regions R1 and R2 are regions that do not contribute to display, there is no need to fill the space between the auxiliary electrodes with liquid crystal, and an insulating film or an adhesive for bonding two glass substrates is not required. may be intervened. Also,
During the display period of the liquid crystal panel 1, if a scanning voltage for display is applied to these auxiliary electrodes, the scanning time, that is, the display period becomes longer, so the scanning of the auxiliary electrodes (
drive) is not necessary.

FIG. 3 is a timing chart showing the drive timing of each electrode during the position detection period. As shown in FIG. 3, the position detection period is divided into an X-coordinate detection period and a Y-coordinate detection period that follows. The b electrodes Y are sequentially driven. Furthermore, in the liquid crystal panel 1 of this embodiment, since the auxiliary electrodes are formed, the electrodes before the auxiliary electrode X0 are driven before the segment electrodes X1 to Xa are driven, and the segment electrodes Xm-a to Xm are driven. Subsequently, the electrodes after the auxiliary electrode Xm+1 are driven. Similarly, common electrodes Y1~
Prior to Yb, the electrodes before the auxiliary electrode Y0 are driven, and following the driving of the common electrodes Yn-b to Yn, the auxiliary electrode Y
The auxiliary electrodes after n+1 are driven (scanned).

As explained above, the auxiliary electrode is necessary only for position detection, and furthermore, for electrode scanning during position detection,
As shown in FIG. 3, since a or b electrodes are scanned together, there is no need to connect an independent drive circuit to each electrode. In other words, if multiple electrodes are connected in a comb shape at one end of the electrodes and connected to a drive circuit, even with the drive method of this embodiment, the functionality can be greatly improved with only a slight increase in the number of drive circuits. improves. The connection may be made outside the liquid crystal panel 1.

The display electrode and the auxiliary electrode are transparent electrodes such as indium oxide or tin oxide. The electrodes are first formed uniformly over the entire surface of the glass substrate by sputtering or the like, and then only the necessary electrode portions are left by photographic technology and etching. Therefore, the auxiliary electrodes are also formed at the same time as the display electrodes in the same manufacturing process.

In the position detection period, the coordinates are calculated based on the scanning of all electrodes including the auxiliary electrode, so the origin of the calculated coordinates is set outside the display area (coordinate detection area) 1d. , in practical use, the display area 1
Coordinates outside d are not only unnecessary but also inconvenient for display and other processing.

Therefore, the coordinate detection circuit 10 outputs the detected coordinates by shifting the detected coordinates so that, for example, the lower left of the display area 1d becomes the origin. Further, near the boundary of the display area 1d, the coordinates may be calculated as being outside the display area 1d depending on the reading accuracy, etc., but in such a case, it is appropriate to correct the coordinates to be within the display area 1d.

As described above, the common drive circuit 2 and the segment drive circuit 3 each have an increased number of output terminals compared to the conventional drive circuit by the amount supplied to the auxiliary electrodes.
The internal structure is basically the same as the conventional one.

However, if conventional electrode drive circuits are used as they are, each drive circuit 2, 3 has a shift register containing the auxiliary electrodes therein, although scanning by the auxiliary electrodes is not required during the display period. Therefore, the display period becomes longer by the time it takes to scan the auxiliary electrode portion. However, since the time for scanning the auxiliary electrode is much shorter than the time for scanning the display area 1d, it can be practically ignored.

Therefore, the conventional electrode drive circuit can be used as is without designing and manufacturing a new integrated circuit dedicated to the coordinate input device of this embodiment, which has a greater effect of reducing costs. .

However, if the above-mentioned scanning time of the auxiliary electrode is relatively long, it may cause a decrease in the contrast of the liquid crystal panel 1, and if higher quality contrast is required, measures must be taken. . Some countermeasures will be explained below.

One of them is that the display control circuit 5 prepares two clocks, a display clock and a high-speed scanning clock whose frequency is higher than that of the display clock, and the auxiliary electrode portion is scanned by the high-speed scanning clock. do. Thereby, the scanning time of the auxiliary electrodes can be shortened, and a decrease in display contrast of the liquid crystal panel 1 can be suppressed. Further, by simply making changes to the display control circuit 5, the conventional electrode drive circuit can be used as is.

Another countermeasure will be explained with reference to FIG. This countermeasure requires each shift register of drive circuits 2 and 3 to
An interrupt function is provided that allows data to be interrupted midway. That is, during the coordinate detection period,
Data D10 input to the shift register in the drive circuit
1 and drive data D0 to D3 are input from the beginning of the shift register, and therefore the drive circuit sequentially scans including the auxiliary electrode. During the display period, display data is input from the middle of the shift register, and only the display electrodes are driven.

In FIG. 4, the shift register is composed of an auxiliary electrode register 44 and a display electrode register 43. The output control unit 45 outputs each electrode drive signal based on the data stored in the shift register. A 3-status gate 46 is provided between the memories S0 and S1 constituting the shift register, and a 3-status gate 48 is provided between the input terminal TD and the memory S1. A control signal I from the input terminal TI is applied to the gate 46 via an inverting circuit 47, and a control signal I from the input terminal TI is similarly applied directly to the gate 48. Therefore, by setting the control signal I applied from the input terminal TI to a low level, the gate 46 is provided with a high level signal which is an inverted signal of the control signal I, and is turned off, and the gate 48 is controlled at a low level. When signal I is applied, it is turned on. As a result, drive data applied from the input terminal TD is sequentially shifted to the memories on the right side of the drawing in the order of memories S1, S2, . . . .

Conversely, by setting the control signal I applied from the input terminal TI to a high level, a low level signal which is an inverted signal of the control signal I is applied to the gate 46, and the gate 46 is turned on. is turned off by being given a high-level control signal I. Therefore, the drive data given from the input terminal TD is transmitted to the memory S-1,
S0, S1, . . . are sequentially shifted to the memory on the right side of the drawing.

Therefore, during the display period, data is input from the memory S1, and during the coordinate detection period, data is input from the memory S1.
Input from -1. As a result, the auxiliary electrodes are not driven during the display period, making it possible to prevent the display contrast of the display panel 1 from deteriorating.

In the drive circuits 2 and 3 in actual use, several stages of elements are connected in cascade, but if the connection exists between the memories S0 and S1 in FIG. 4, external connection is possible. be.

FIG. 5 is a sectional view for explaining another embodiment of the present invention. The feature of this embodiment is that the shielding member 17 is formed outside the liquid crystal panel 1, that is, between the glass substrate 15 and the polarizing plate 16. In this case, the shielding member 17 serves to shield the electric field from the lead wire portion 18. Although this embodiment is inferior in functionality to the previous embodiments, it is most suitable for low-priced popular tablets because there is no need to manufacture a dedicated liquid crystal panel and a conventional liquid crystal panel can be used as is.

Furthermore, the shielding member 17 may be provided on the polarizing plate 16. Since this part is usually covered with, for example, a plastic case, it may be sufficient to adhere a conductive tape, or it may be formed with a conductive member or electroless plating on the inside of the plastic case.

[0086] In the above explanation, the display electrodes of the liquid crystal panel were used as electrodes for coordinate detection, but an EL (electroluminescence) display panel that serves both as an electrode extraction part and a display electrode may be applied to a tablet. It can be applied even if

[0087]

As described above, according to the present invention, even if the detection pen is brought into contact with the border of the display area of the display panel, which is the coordinate detection area, the electrostatic coupling between the auxiliary electrode and the detection pen The voltage waveform output from the detection pen is approximately equal to the voltage waveform output from the detection pen when the detection pen is brought into contact with, for example, near the center of the display area. Therefore, coordinate detection can be performed with high accuracy even near the boundary of the coordinate detection area. Further, even if such an auxiliary electrode is provided, the display on the display panel is not affected, and coordinates can be detected with high precision while maintaining high display quality.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of a display-integrated coordinate input device that is an embodiment of the present invention.

2 is an enlarged plan view of the liquid crystal panel 1 used in the coordinate input device shown in FIG. 1. FIG.

FIG. 3 is a timing chart showing operations during a coordinate detection period in the coordinate input device of the present invention.

4 is a circuit diagram showing the configuration of a shift register provided in the common drive circuit 2 or the segment drive circuit 3 shown in FIG. 1. FIG.

FIG. 5 is a sectional view showing another embodiment of the present invention.

FIG. 6 is a block diagram showing the configuration of a conventional electrostatic induction tablet.

FIG. 7 is a block diagram showing the configuration of another conventional electrostatic induction tablet.

FIG. 8 is an enlarged plan view of a liquid crystal panel used in a conventional tablet.

FIG. 9 is a timing chart illustrating operations during a position detection period in a conventional electrostatic induction tablet.

FIG. 10 is a diagram for explaining the principle of an electrostatic induction tablet.

FIG. 11 is a diagram for explaining electrostatic coupling between a detection pen and an electrode.

FIG. 12 is a diagram for explaining electrostatic coupling between a detection pen and an electrode.

FIG. 13 is a diagram for explaining electrostatic coupling between a detection pen and an electrode.

FIG. 14 is a diagram for explaining electrostatic coupling between a detection pen and an electrode.

[Explanation of symbols]

1.LCD panel 2 Common drive circuit 3 Segment drive circuit 4 Switching circuit 5 Display control circuit 6 Position detection control circuit 7 Control circuit 8 Detection pen 10 X coordinate detection circuit 11 Y coordinate detection circuit 25 Auxiliary electrode X segment electrode Y Common electrode

Claims (11)

[Claims] 1. A display panel having a plurality of segment electrodes arranged in parallel and a plurality of common electrodes arranged in parallel and driven by a duty drive method, and a display panel including a plurality of segment electrodes and a common electrode arranged in parallel. a detection pen having an electrode at its tip that is coupled by stray capacitance between the pens; and a display control for displaying an image on a pixel matrix formed by an intersection area between a plurality of segment electrodes and a plurality of common electrodes of the display panel. a display control circuit that outputs signals and display data; a position detection control circuit that outputs a scan control signal for scanning segment electrodes and common electrodes of the display panel; and during a display period of the display panel, the display control circuit a switching circuit that outputs a display control signal and display data from the position detection control circuit, and outputs a scan control signal from the position detection control circuit in a position detection period following the display period;
Generating a common electrode drive signal for sequentially selecting the common electrodes based on a display control signal from a switching circuit, and displaying an image on the pixel matrix in the position detection period based on a scanning control signal from the switching circuit. a common drive circuit that outputs a common electrode scanning signal for sequentially scanning the common electrodes without scanning; and in the display period,
A segment electrode drive signal for displaying the pixel related to the common electrode selected by the common electrode drive signal is output based on the display control signal and display data from the switching circuit, and during the position detection period, the scanning from the switching circuit is a segment drive circuit that outputs a segment electrode scanning signal for sequentially scanning segment electrodes without displaying an image on the pixel matrix based on a control signal;
During the position detection period, the tip of the detection pen is adjusted based on the application timing of the common electrode scanning signal and the segment electrode scanning signal applied to the common electrode and the segment electrode, and the induced voltage induced in the electrode of the detection pen. In a coordinate input device comprising a coordinate detection circuit that detects coordinates specified on a display panel and outputs an X coordinate signal and a Y coordinate signal, a plurality of electrodes parallel to a common electrode and a segment electrode are provided outside the display area of the display panel. A coordinate input device characterized in that an auxiliary electrode is provided, and during the position detection period, an electrode scanning signal is sequentially applied to the auxiliary electrode, a common electrode, and a segment electrode. 2. The electric potential of the scanning signal applied to the auxiliary electrode during the position detection period is made the same as the electric potential of the scanning signal applied to the common electrode and the segment electrode within the display area. coordinate input device. 3. The auxiliary electrode is connected to a common drive circuit and a segment drive circuit, and in the position detection period, the auxiliary electrode, the common electrode, and the auxiliary electrode are connected in the order of the auxiliary electrode, the segment electrode, and the auxiliary electrode are connected in the order of the auxiliary electrode, the segment electrode, and the auxiliary electrode. 2. The coordinate input device according to claim 1, wherein the coordinate input device scans in a predetermined arrangement direction. 4. A plurality of auxiliary electrodes arranged in parallel,
2. The coordinate input device according to claim 1, wherein electrode scanning signals of the same potential are applied to a plurality of adjacent auxiliary electrodes at the same timing. 5. The common drive circuit and the segment drive circuit each include a shift register, and the clock and data of the shift register are controlled during scanning of the auxiliary electrode and during scanning of the common electrode or segment electrode in the position detection period. 2. The coordinate input device according to claim 1, wherein the coordinate input device has the same coordinates. 6. The shift register of the drive circuit has a data interrupt function, and during the display period of the display panel, the shift register has a data interrupt function.
It operates by interrupting data from the middle of the shift register,
6. The coordinate input device according to claim 5, wherein the coordinate input device does not scan the auxiliary electrode. 7. The coordinate detection circuit converts the coordinate values calculated including the auxiliary electrodes into coordinate values in an effective coordinate input area formed by the intersection of the common electrode and the segment electrode. The coordinate input device according to claim 1. 8. The auxiliary electrode is formed on the same plane as the common electrode or the segment electrode, and the auxiliary electrode width and formation interval are selected to match the electrode width and formation interval of the common electrode or the segment electrode. A coordinate input device according to claim 1. 9. The widthwise length of the auxiliary electrode in the auxiliary electrode arrangement area is selected to be larger than the distance between the detection pen and the common electrode or the segment electrode when instructing coordinate input to the display panel. Coordinate input device according to item 1. 10. The coordinate input device according to claim 1, wherein the auxiliary electrode is formed on a plane different from that of the segment electrode or the common electrode. 11. The coordinate input device according to claim 1, wherein the auxiliary electrode is made of the same material as the segment electrodes and the common electrode, and is formed in the same manufacturing process.