Display device

The present application claims priority from Japanese Patent Application JP 2017-194202 filed on Oct. 4, 2017, the content of which is hereby incorporated by reference into this application.

(1) Field of the Invention

The present invention relates to a display device, specifically to a display device that is installed with a touch panel function and a Near Field Communication (NFC) function.

(2) Description of the Related Art

Recently, display devices that include touch panel function for input means are increasing in the small size and the middle size liquid crystal display devices. One type of those displays is that a touch panel is formed separately from the display panel; then, the touch panel and the display panel are assembled. Another type is a so called in-cell touch panel where touch panel function is installed in the display panel. In the in-cell touch panel, the Rx electrodes (receiver electrodes) are formed outside of the counter substrate; the Tx electrodes (transfer electrodes) are formed inside of the TFT (Thin Film Transistor) substrate.

In the meantime, it has been put to practical use that a Near Field Communication (NFC) function is installed in a mobile terminal of the liquid crystal display device. The NFC enables to access to the digital contents or to connect with the instruments only by putting e.g. the liquid crystal display device having the NFC function near to the instruments.

The patent document 1 (Japanese patent laid open 2014-57243) and the patent document 2 (WO 2014/038209) describe the NFC technology.

The liquid crystal display device has a structure that the TFT substrate and the counter substrate oppose to each other and the liquid crystal layer is sandwiched between them; wherein the TFTs (Thin Film Transistor), the pixel electrodes, the counter electrodes, the scanning lines, and the video signal lines are formed on the TFT substrate.

In the in-cell touch panel, Rx electrodes (receiving electrodes) are formed outside of the counter substrate to extend in e.g. the same direction that the scanning lines extend (the lateral direction). In addition, the counter electrode, which is formed at the liquid crystal layer side of the TFT substrate, is divided to form the Tx electrodes (transferring electrodes), which extend in orthogonal to the direction that scanning lines extend (the longitudinal direction). The touch position is detected by measuring the static capacitance Ct formed between the Rx electrode and the Tx electrode.

In such a structure, the counter electrode has both a role of the common electrode in the liquid crystal display device and a role of the Tx electrodes in the touch panel. In the in cell touch panel system, one frame is divided into the display period and the touch panel period. Namely, the voltages being applied to the counter electrode must be switched. However, a noise is generated when this switching operation is made.

On the other hand, the liquid crystal display device compatible to the NFC, in which an NFC antenna is installed in the display device, communicates with the electrical instruments at close range. Therefore, if a noise is generated when the display operation is switched to the touch panel operation or when the touch panel operation is switched to the display operation, this noise causes malfunction of the NFC operation.

The purpose of the present invention is to countermeasure the malfunction of the NFC operation due to the noise, which is generated when the display operation is switched to the touch panel operation or when the touch panel operation is switched to the display operation, in the liquid crystal display device installed with the touch panel function and the NFC function.

The above problem has been explained taking an example of the liquid crystal display device; however, the same problem exists in the organic EL display device and the like, which the in cell touch panel function and the NFC function are installed.

The present invention overcomes the above explained problem; the concrete structures are as follows:

A display device having a Near Field Communication (NFC) function and a display panel installed with touch panel function comprising: a plurality of display electrodes are formed in a display area of the display panel, a first circuit having a plurality of first switches for changing between a voltage for an image display and for a touch panel operation, formed at a first side of the display area, a second circuit having a plurality of second switches for changing between applying the voltage for an image display and not applying the voltage for the image display at a second side opposite to the first side of the display area,

the first circuit selects one of the plural display electrodes successively, applying the voltage for the touch panel operation to a selected display electrode and applying the voltage for the image display to the plurality of display electrodes other than the selected display electrode,

the second circuit selects one of the plural display electrodes successively, and not applying the voltage for the image display to the selected display electrode.

FIG. 1 is an exploded perspective view of the liquid crystal display device according to the present invention;

FIG. 2 is a perspective view of the liquid crystal display panel;

FIG. 3 is a plan view of the layout of the display area when the common electrode is used as electrodes of one side of the touch panel;

FIG. 4 is an equivalent circuit as the comparative example when the present invention is not used;

FIG. 5A is an example of the timing of the gate voltage that changes between the display operation and the touch panel operation;

FIG. 5B is an example of the timing of the gate voltage that controls supplying voltages to the Tx electrode for the touch panel operation;

FIG. 6 is an example of NFC signals when the present invention is not used;

FIG. 7 is an equivalent circuit that shows the function of the present invention;

FIG. 8 is a plan view of the layout of the liquid crystal display device according to the present invention;

FIG. 9 is a third switch circuit diagram that shows the third shift register and the third selector switch;

FIG. 10 is a second switch circuit diagram that shows the second shift register and the second selector switch;

FIG. 11 is a timing chart according to the present invention;

FIG. 12 is an example of the signal of the NFC according to the present invention.

The present invention will be described in detail referring to the following embodiment. The following explanations are made in an example of the liquid crystal display device; however, the explanation is applicable to the organic EL display device and the like, in which the in cell touch panel function and the NFC function are installed.

FIG. 1 is an example of an exploded perspective view of the liquid crystal display device according to the present invention. The liquid crystal display device in FIG. 1 has functions of the image display, the touch panel, and the NFC. In FIG. 1 , the touch panel function is installed in the liquid crystal display panel 6 . The protection glass 7 is disposed over the liquid crystal display panel 6 . The frame like light shielding area 25 is formed outside of the display area 20 of the protection glass 7 . The back light 5 is disposed at the rear of the liquid crystal display panel 6 .

The antenna 4 for the NFC is disposed underneath of the back light 5 . The NFC operates in the frequency band having 13.56 MHz as the center frequency to transfer data between the liquid crystal display device and other electronical instruments. The circuit substrate 2 is disposed under the NFC antenna 4 ; the circuit substrate 2 includes the circuits or a battery to make work whole of the liquid crystal display device. Since the NFC utilizes the electro-magnetic induction, the magnetic sheet 3 is disposed between the NFC antenna 4 and the circuit substrate 2 to prevent interference between the circuit substrate 2 and the antenna 4 . All of those components are contained in the metal frame 1 . The electro-magnetic wave radiates in the direction toward the liquid crystal display panel 6 .

FIG. 2 is a perspective view of the liquid crystal display panel 6 . In FIG. 2 , the counter substrate 200 is disposed over the TFT substrate 100 . The TFT substrate 100 and the counter substrate 200 are adhered to each other by the sealing material; the liquid crystal is sandwiched between the TFT substrate 100 and the counter substrate 200 . The display area 20 is formed at the area that the TFT substrate 100 and the counter substrate 200 overlap.

The TFT substrate 100 is made bigger than the counter substrate 200 ; the terminal area 30 is formed in the area that the TFT substrate 100 and the counter substrate 200 do not overlap. The driver IC 31 , which drives the liquid crystal display panel 6 , is installed on the terminal area 30 ; the flexible wiring substrate 32 is connected to the terminal area 30 to supply signals to the liquid crystal display panel 6 and the driver IC 31 .

In FIG. 2 , the Rx electrodes for the touch panel are formed on the major surface of the outer side of the counter substrate 200 . The Rx electrodes extend in the x direction and are arranged in the y direction. The flexible wiring substrate 33 for the touch panel connects to the counter substrate 200 to connect the Rx electrodes and the touch panel driving circuit.

The Tx electrodes for the touch panel are formed on the surface of the TFT substrate 100 that faces the liquid crystal layer. The Tx electrodes extend in the y direction and are arranged in the x direction. The Tx electrodes are formed by dividing the counter electrode of the liquid crystal display panel 6 . Namely, the counter electrode has a role as the common electrode for the image display and a role as the Tx electrodes of the touch panel in the liquid crystal display panel 6 .

In FIG. 2 , the antenna 4 for the NFC is set under the liquid crystal display panel 6 and opposite side to the terminal area 30 . The electromagnetic wave from the antenna 4 radiates in the direction toward the liquid crystal display panel 6 . Therefore, if a source of noise exists near the side opposite to the terminal area 30 , a malfunction of the NFC tends to occur.

FIG. 3 is a plan view of the TFT substrate 100 . In FIG. 3 , the scanning lines 11 extend in the x direction and are arranged in the y direction; the video signal lines 12 extend in the y direction and are arranged in the x direction. The pixel 13 is formed in the area surrounded by the scanning lines 11 and the video signal lines 12 . The pixel electrode, the TFT, and the through hole to connect the pixel electrode and the TFT are formed in the pixel 13 .

In FIG. 3 , the counter electrode 110 is formed in a plurality of pixels in common. In the normal liquid crystal display device, the counter electrode 110 is formed in common for all of the pixels; in the in cell touch panel type, however, the counter electrode 110 is divided so that it also can function as Tx electrodes. In FIG. 3 , the stripe of the Tx electrode, which has a width of four pixels, extends in the y direction.

In FIG. 3 , the width of the Tx electrode is a width of summation of four pixels in the X direction; however, number of the pixels in width direction can be bigger or smaller according to a necessity of the resolution of the touch panel. Generally, the video signal line 12 forms a boundary between the pixels 13 ; in addition to that, in FIG. 3 , the narrow stripe shaped region, where the counter electrode 110 does not exist, extends over the video signal line 12 in every four pixels. The Tx electrodes are insulated to each other at this narrow stripe shaped region where the common electrode does not exist.

The counter electrode 110 of FIG. 3 has a role of a common electrode for the image display and a role of the Tx electrodes in the in cell touch panel. In concrete, one frame is divided into the display period and the touch panel period: in the display period, the common voltage Vcom is applied to the counter electrode 110 ; in the touch panel period, the transfer voltages (Tx voltage) for touch panel operation are applied successively to each of the Tx electrodes.

FIG. 4 is an equivalent circuit that shows this function. FIGS. 5A and 5B are timing charts that correspond to FIG. 4 . In FIG. 4 , n lines of Tx electrodes extend in the y direction in the display area 20 . The number n is e.g. 35. The Tx electrodes are formed by dividing the counter electrode 110 . Various circuits are installed in the liquid crystal display device; however, in FIG. 4 , the circuits that do not directly relate to the present invention are not shown. The following drawings are also the same.

In FIG. 4 , the first selector switch SW 1 , which supplies a common voltage Vcom to each of the Tx electrodes, is disposed at the upper side of the display area 20 . The first selector switch SW 1 is constituted by N type TFT array to connect to each of the Tx electrodes. Each of the TFTs that constitute the first selector switch SW 1 is switched simultaneously by the voltage Vgsw 1 .

FIG. 5A is a timing chart of Vgsw 1 . In FIG. 5A , The period tf of one frame is divided into the period td of the image display period and the period tt of the touch panel operation. The periods are e.g. td:tt=2:1. The gate voltage Vgsw 1 is High during the period td, and is Low during the period tt. In FIG. 4 , when the Vgsw 1 is High, all the TFTs of the first selector switch SW 1 become ON, consequently, the common voltage Vcom is supplied to all the Tx electrodes; on the other hand, when the Vgsw 1 is Low, the common voltage Vcom, which is to be supplied from the upper side of the display area, is cut off.

Back to FIG. 4 , the second selector switch SW 2 is disposed at the lower side of the display area 20 . The second selector switch SW 2 comprises pairs of switches of SW 2 n - 1 and SW 2 n - 2 ; in each of the pairs, the two switches are connected in parallel. Each of the pair of switches of SW 2 n - 1 and SW 2 n - 2 is connected to each of the Tx electrodes. The voltage Vt for touch panel operation is supplied to the source electrode of the TFT switch SW 21 - 1 ; the drain of the TFT switch SW 21 - 1 is connected to the Tx electrode. On the other hand, the common voltage Vcom for image display is supplied to the source electrode of the TFT switch SW 21 - 2 ; the drain of the TFT switch SW 21 - 2 is connected to the Tx electrode commonly with the TFT switch SW 21 - 1 .

The gate electrodes of SW 21 - 1 and SW 21 - 2 are commonly supplied with e.g. the gate voltage Vbg 1 . Each of similar pairs e.g. SW 22 - 1 and SW 22 - 2 through SW 2 n - 1 and SW 2 n - 2 in the second selector switch SW 2 is connected to each of the electrodes Tx 1 through Txn as the same manner as the pair of SW 21 - 1 and SW 21 - 2 . The gate voltages Vbg 1 through Vbgn are successively applied to the gate electrodes of each pairs of the second selector switch SW 2 .

The operation is explained taking an example of the left most pair of SW 21 - 1 and SW 21 - 2 . The SW 21 - 1 is comprised of N type TFT, while the SW 21 - 2 is comprised of P type TFT. The voltage Vt for the touch panel is applied to the source of the SW 21 - 1 ; The common voltage Vcom is applied to the source of the SW 21 - 2 .

When the gate voltage Vbg 1 becomes High, the switch SW 21 - 1 becomes ON, at the same time, the switch SW 21 - 2 becomes OFF. Consequently the voltage Vt is applied to the electrode Tx 1 . When the gate voltage Vbg 1 becomes Low, the switch SW 21 - 1 becomes OFF, at the same time, the switch SW 21 - 2 becomes ON. Consequently the common voltage Vcom is applied to the electrode Tx 1 . The functions of the second pair from the left and subsequent pairs, namely, pairs of SW 2 n - 1 and SW 2 n - 2 , are the same as explained for the pair of the switch SW 21 - 1 and SW 21 - 2 .

FIG. 5B is a timing chart of the gate voltages that are applied to each of the switching pairs in the touch panel operation period tt in the second selector switch SW 2 . The gate voltages Vbg 1 through Vbgn are applied to the switches in the second selector switch SW 2 in synchronizing with the selector switch SW 1 at the upper side of the display area 20 . Namely, in a timing that the selector switch SW 1 at the upper side of the display area becomes OFF, one of the gate voltages of Vbg 1 , Vbg 2 , Vbg 3 and so on are successively applied to the switch pairs in the second selector switch SW 2 ; consequently, the touch panel voltage Vt is applied to the selected electrode Tx. The pulses Vbg 1 , Vbg 2 , Vbg 3 and so on are formed by the shift register.

Each of the electrodes of Tx 1 , Tx 2 , Tx 3 and so on depicted in FIG. 5B are selected once or plural times in one frame period; all the electrodes of Tx 1 to Txn are selected successively. The period tt 1 of the selecting pulse and the width tt 2 of the selecting pulse in FIG. 5B can be changed according to how many times the electrodes of Tx 1 , Tx 2 , Tx 3 and so on are selected in one frame period.

By the way, in FIG. 4 , during the voltage Vt is applied to the electrode Tx 1 for the touch panel operation, the gate voltages Vbg 2 through Vbgn are low. Therefore, the common voltage Vcom is applied to the electrode Tx 2 through Tx 3 ; thus, black can be displayed; consequently, the contrast of the screen is not deteriorated.

The operation of FIG. 4 , however, has the following problems. In FIG. 4 , when a change is made by the switch SW 1 between the image display period td and the touch panel period tt, the ON or OFF of the common voltage Vcom is applied to all of n lines of the Tx electrodes all at once. A large noise is generated when a change of ON or OFF of the common voltage Vcom occurs in all the n lines of Tx electrodes simultaneously. This large noise is generated every time when the change is made between the image display period td and the touch panel period tt.

In the display device installed with the NFC, this noise is superimposed to the carrier wave cw of the NFC; consequently, it becomes a cause of malfunction of the NFC. The sin wave in FIG. 6 is a carrier wave for the NFC signal; the frequency of the carrier wave is e.g. 13.56 MHz. In FIG. 6 , the ordinate is a value of the carrier wave cw; the abscissa is the time t. When the common voltage Vcom is cut off from each of the Tx electrodes by the first selecting switch sw 1 at the time t 1 , the noise of Vnoise is generated, the carrier wave is modulated by the noise of Vnoise. Namely, as depicted in FIG. 6 , the center of the sin wave shifts by a magnitude of Vnoise; this can be a cause of malfunction of the NFC.

FIG. 7 is an equivalent circuit of the present invention. The structure of the display area in FIG. 7 is the same as the display area in FIG. 4 . Namely, n lines of the Tx electrodes extend in the y direction and are arranged in the x direction. The second selector switch SW 2 is disposed at the lower side in the y direction of the display area 20 . The structure and the function of the second selector switch SW 2 are the same as FIG. 4 .

In FIG. 7 , the third selector switch SW 3 is disposed at the upper side in the y direction of the display area 20 . The third selector switch SW 3 is different from the first selector switch SW 1 of FIG. 4 . The third selector switch SW 3 is comprised of the TFT array of N type TFTs of SW 31 through SW 3 n. Each of the sources of SW 31 through SW 3 n connects with Vcom; the drains of SW 31 through SW 3 n connect with the Tx electrodes Tx 1 through Txn.

The voltages Vug 1 , Vug 2 , . . . , Vugn are successively applied to the gates of SW 31 , SW 32 , SW 33 , . . . , SW 3 n. Each of pulse voltages of Vug 1 , Vug 2 , . . . , Vugn is supplied from the shift register. Since SW 3 is constituted by N type TFT, the common voltage Vcom is cut off from the Tx electrodes Tx 1 through Txn when the voltages of Vug 1 , Vug 2 , . . . , Vugn become Low.

On the other hand, the function of the second selector switch SW 2 , which is disposed at the lower side in the y direction of the display area 20 in FIG. 7 , is the same as the SW 2 of FIG. 4 . In FIG. 7 , the voltages Vug 1 , Vug 2 , . . . , Vugn are applied in synchronized with the voltages Vbg 1 , Vbg 2 , . . . , Vbgn respectively. FIG. 11 shows the timing chart that shows the relation between the voltages Vug 1 , Vug 2 , . . . , Vugn and the voltages Vbg 1 , Vbg 2 , . . . , Vbgn.

Namely, in regard to a certain Tx electrode, when the common voltage Vcom is cut off in the SW 3 , which is disposed at the upper side in the y direction of the display area 20 , the SW 2 , which is disposed at the lower side in the y direction of the display area 20 , becomes ON at the same time; consequently, the Tx voltage Vt is applied to the Tx electrode. The feature of FIG. 7 is that: when the change between the display period td and the touch panel period tt is made by the switch SW 3 , which is located at the upper side of the display area 20 , the ON or OFF of the common voltage Vcom is not applied to all the Tx electrodes at once; however, the ON or OFF of the common voltage Vcom is applied only to the Tx electrode that the Tx voltage is applied. Therefore, the noise, generated in the switch SW 3 of FIG. 7 , becomes 1/n of the noise, generated in the switch SW 1 of FIG. 4 ; thus, malfunction of the NFC can be avoided.

FIG. 8 is a plan view of the TFT substrate that shows concrete layout of the FIG. 7 . The scanning line driving circuits 21 are located at both sides of the display area 20 . The third selector switch SW 3 and the upper shift register USR that supplies selecting signals to the third selector switch SW 3 are located at the upper side of the display area 20 . BUF is a buffer amplifier for the signals that are input to the shift register USR. The second selector switch SW 2 and the lower shift register BSR that supplies selecting signals to the second selector switch SW 2 are located at the lower side of the display area 20 .

In FIG. 8 , the electrode Tx 1 through the electrode Txn serving as the counter electrodes 110 extend in the y direction and arranged in the x direction in the display area 20 . The electrodes Tx 1 through Txn are spread all over the display area 20 . The common voltage Vcom is applied to all the electrodes Tx 1 through Txn during the display period. On the other hand, either one of the electrodes Tx 1 through Txn are selected to be applied with the Tx voltage during the touch panel operation; the common voltage Vcom is applied to the other Tx electrodes that are not selected. All the electrodes of Tx 1 through Txn are selected once or plural times in one frame period.

As shown in FIG. 2 , the liquid crystal display panel comprises the TFT substrate 100 and the counter substrate 200 . The scanning line driving circuit 21 , the third selector switch SW 3 , the upper shift register USR, the second selector switch SW 2 , and the lower shift register BSR are disposed in the area where the TFT substrate 100 and the counter substrate 200 overlap. The TFT substrate 100 is made bigger than the counter substrate 200 ; the region of the TFT substrate 100 , where the counter substrate 200 does not overlap the TFT substrate 200 , is a terminal area 30 ; the driver IC 31 is installed in the terminal area 30 . The driver IC 31 supplies the start signal SDST, the clock signal SDCK, the reset signal XDISC and so on, which control the upper shift register USR, the lower shift register BSR and so on. In the meantime, the driver IC 31 supplies the video signals that constitute the images.

FIG. 9 is a circuit of the third selector switch SW 3 and the upper shift register USR that controls the third selector switch SW 3 . In FIG. 9 , the number of the shift register units SR 31 through SR 3 n is the same as the number of the Tx electrodes. The signals Vug 1 through Vugn, which drive the third switch SW 3 , are supplied from the output terminal of each of the shift register units SR 31 through SR 3 n. Each of the output terminals of the switches SW 31 through SW 3 n in the third selector switch SW 3 connects with each of the electrodes of Tx 1 through Txn.

In FIG. 9 , XDISC is a reset signal, which determines operating state or non-operating state of the shift register USR. SDCK is a clock signal, which determines a timing of the operation of the shift register USR. In FIG. 9 , when the start signal SDST is applied to the first shift register unit SR 31 , the voltage Vug 1 is supplied to the third selector switch SW 31 from the first shift register unit SR 31 .

The output from the first shift register unit SR 31 is the in-put to the second shift register unit SR 32 . The voltage Vug 2 is supplied to SW 32 of the third selector switch SW 3 from the second shift register unit SR 32 . The output from the second shift register unit SR 32 is the in-put to the third shift register unit SR 33 . As the same token, the switch signals Vug 1 through Vugn are successively supplied to the third selector switch of SW 31 through SW 3 n.

FIG. 10 is a circuit of the second selector switch SW 2 and the lower shift register BSR that controls the second selector switch SW 2 . In FIG. 10 , the number of the shift register units SR 21 to SR 2 n is the same as the number of the Tx electrodes. The signals Vbg 1 through Vbgn, which drive the second selector switch SW 2 , are supplied from the output terminal of each of the shift register units of SR 21 through SR 2 n. Each of the output terminals of the switches SW 21 through SW 2 n in the second selector switch SW 2 connects with each of the electrodes of Tx 1 through Txn.

In FIG. 10 , XDISC is a reset signal, which determines operating state or non-operating state of the shift register BSR. SDCK is a clock signal, which determines a timing of the operation of the shift register USR. In FIG. 10 , when the start signal SDST is applied to the first shift register unit SR 21 , the voltage Vbg 1 is supplied to the second selector switch SW 21 from the first shift register unit SR 21 .

The output from the first shift register unit SR 21 is the in-put to the second shift register unit SR 22 . The voltage Vbg 2 is supplied to SW 22 of the second selector switch from the second shift register unit SR 22 . The output from the second shift register unit SR 22 is the in-put to the third shift register unit SR 23 . As the same token, the switch signals Vbg 1 through Vbg 2 n are successively supplied to the switches of SW 21 through SW 2 n in the second selector switch of SW 21 .

FIG. 11 is a timing chart of the operation of the structures of FIGS. 8 through 10 . In FIG. 11 , SDST is a start signal to the shift register; SDCK is a clock signal; XDISC is a reset signal. SDST, SDCK and XDISC are commonly supplied to the upper shift register USR and the lower shift register BSR. Since XDISC is the state of High, the shift register is in a state of operation. In FIG. 11 , the display period dt and the touch panel operation period tt are the same.

In FIG. 11 , when the start signal SDST is applied to the upper shift register USR, the upper shift register unit SR 31 begins to work, then the gate voltage Vug 1 is supplied to the switch SW 31 from the output terminal of the upper shift register unit SR 31 . Since the switch SW 31 is constituted by N type TFT, the switch SW 31 becomes OFF when the gate signal Vug 1 is Low; consequently, the common voltage Vcom from the upper side of the screen is cut off. By the way, the signal Vug 1 is simultaneously applied to the input terminal of the shift register unit SR 32 .

On the other hand, when the start signal SDST is applied to the lower shift register BSR, the lower shift register unit SR 21 begins to work, then the signal High is supplied to the lower switch SW 21 . Since the lower switch SW 21 is constituted by the structure as shown in FIG. 7 , the common voltage Vcom is cut off when the gate signal is High; consequently, the Tx signal for the touch panel is applied to the electrode Tx 1 . In the meantime, the signal Vbg 1 is simultaneously supplied to the input terminal of the shift register SR 22 .

Supplying Low pulse to the upper switch SW 3 from the upper shift register USR and supplying High pulse to the lower switch SW 2 from the lower shift register BSR are made simultaneously. After supplying Low pulse from the upper shift register USR and supplying High pulse from the lower shift register BSR are completed; the subsequent clock period is for a image display period, in which the common voltage Vcom is applied to all the electrodes Tx 1 through Txn.

During the voltage for the touch panel is applied to the electrode Tx 1 , the common voltage Vcom is applied to the electrodes Tx 2 through Txn from both of the upper side and the lower side of the screen. Namely, in the present invention, since the common voltage Vcom is applied from the upper side of the screen and the lower side of the screen to the electrodes other than the electrode Tx 1 , a gradation of brightness or a gradation of contrast in the screen can be avoided.

After the images are displayed for a certain period, when the next clock signal is applied to the upper shift register USR and the lower shift register BSR, the same operation is made in the electrode Tx 2 , and the touch panel voltage is applied to the electrode Tx 2 . In this time, too, the common voltage Vcom is applied to all the Tx electrodes except the electrode Tx 2 . In the function of FIG. 11 , each of the Tx electrodes is selected once or more times in one frame period.

FIG. 11 is an example that one frame period is divided into the display period dt and the touch panel operation period tt where tt:td=1:1. The present invention, however, is operable in a condition that e.g. the display period is ⅔ and the touch panel operation period is ⅓, and the like. Further, the present invention is operable even in the case that one frame is divided into three or more periods.

FIG. 12 is the figure that shows the effect of the present invention. The abscissa t and the ordinate cw of FIG. 12 are the same as explained in FIG. 6 . Namely, the sin wave in FIG. 12 is a carrier wave cw for the NFC signal; the frequency of the carrier wave is e.g. 13.56 MHz. In FIG. 12 , the ordinate is a value of the carrier wave cw; the abscissa is the time t. When the common voltage Vcom is cut off from each of the Tx electrodes by the third selecting switch sw 3 at the time t 1 , the noise of Vnoise is generated, the carrier wave is modulated by the noise of Vnoise. In the present invention, however, the source of the noise is the switching circuit corresponding to the only one Tx electrode. In other words, the noise due to the switching in Vcom is 1/n in FIG. 12 compared with the noise in FIG. 6 . Therefore, as depicted in FIG. 12 , the malfunction of the NFC can be avoided since the modulation due to the noise in the carrier wave can be smaller in the present invention.

Furthermore, as depicted in FIG. 2 , the antenna for the NFC is located at the side opposite to the terminal area 30 of the liquid crystal display device. In such a case, if the switches of the voltages for the Tx electrodes are located at the side opposite to the terminal area 30 , the influence to the wave for the NFC is more serious. At this point, the present invention is further effective since the present invention can counter measure the noise generated at the switches of the voltages for the Tx electrodes, which are located at the side opposite to the terminal area 30 .

In the meantime, in the touch panel operation, the common voltage Vcom is applied to all the electrodes Tx except the electrode Tx that the voltage for the touch panel operation is applied. Further, the common voltage Vcom is applied from the upper side and the lower side of the screen in the present invention; thus, a gradation of the common voltage Vcom can be avoided, consequently, the gradation of the contrast can be avoided.

The N type TFT and the P type TFT can be interchangeable as well as the combination of the N type TFT and the P type TFT. For example, it is possible to make SW 1 by P type, SW 2 n - 1 by P type, SW 2 n - 2 by N type and SW 3 by P type. In this case, the wave form of the timing chart in FIG. 11 is reversed.

In the above explanations, the present invention has been explained in regard to the liquid crystal display device. The present invention, however, is applicable to the organic EL display device. Namely, the touch panel function can be installed in the organic EL display device, too. For example, the cathode is generally formed in common in all the pixels; however, the cathode can be divided to form the Tx electrodes, which work as the electrodes of one side of the touch panel, namely, e.g. as Tx electrodes.

In such a case, either one of the cathode voltage for the image display or the voltage for the touch panel operation can be applied by timely switching to each of the electrodes formed by dividing cathode. When the NFC function is installed in such an organic EL display device, the same problem as explained in the liquid crystal display device arises. Therefore, the malfunction of the organic EL display device, in which the touch panel function and the NFC function are installed, can be avoided by applying the structure of the present invention explained above.