CN110941370A

CN110941370A - Capacitive touch sensor and display device

Info

Publication number: CN110941370A
Application number: CN201811115923.6A
Authority: CN
Inventors: 于子鹏; 杨洋
Original assignee: Shenzhen Honghe Innovation Information Technology Co Ltd
Current assignee: Shenzhen Honghe Innovation Information Technology Co Ltd
Priority date: 2018-09-25
Filing date: 2018-09-25
Publication date: 2020-03-31

Abstract

The invention discloses a capacitive touch sensor and a display device, wherein the capacitive touch sensor comprises: a first electrode including a first pattern and a first connection line; the second electrode comprises a second pattern and a second connecting line; in the grid formed by the first electrode and the second electrode, the shape characteristics of the first pattern and/or the second pattern are arranged so as to adaptively change the facing area between the first pattern and the adjacent second pattern in each electrode node according to the resistance difference on different signal paths; and/or setting the lengths of the first connecting line and/or the second connecting line so as to adaptively change the gap between the first pattern and the adjacent second pattern in each electrode node according to the resistance difference on different signal paths, so that the resistance-capacitance time constant of each signal path is in a preset consistency level. The capacitive touch sensor has good data consistency at the receiving side and can be well suitable for large-size display devices.

Description

Capacitive touch sensor and display device

Technical Field

The invention relates to the technical field of capacitive touch sensing, in particular to a capacitive touch sensor and a display device.

Background

Projected capacitive touch sensors generally include a substrate, and patterned X and Y electrodes disposed on the substrate, the X and Y electrodes being interdigitated to form a detection grid. When a conductor or finger touches the projected capacitive panel, which results in a decrease in mutual capacitance but an increase in capacitance, the touched position can be detected by detecting this change.

As the projected capacitive touch sensor increases in size, the resistance of each electrode increases linearly, and since the X and Y electrode patterns (e.g., both equal prismatic shapes) and the spacing between the patterns are substantially the same, the resistances in series on the signal paths are different, and thus the time constants of the resistance and the capacitance of different signal paths differ greatly. The more resistors are connected in series on the signal path, the longer the mutual capacitance charging time of the corresponding node is when the detection driving side starts scanning the signal path, and thus the data collected on the detection receiving side is uneven.

Disclosure of Invention

The invention mainly aims to provide a capacitive touch sensor, and aims to solve the technical problem that data reflected by a receiving side during detection are not uniform due to poor charging time consistency of nodes of the conventional capacitive touch sensor.

In order to achieve the above object, the present invention provides a capacitive touch sensor, including:

the first electrodes extend along a first direction and comprise a plurality of first patterns and first connecting lines which are arranged in a staggered mode along the first direction and are electrically connected with each other;

the plurality of second electrodes extend along the second direction and comprise a plurality of second patterns which are arranged in a staggered manner along the second direction and are electrically connected with one another and second connecting lines;

the second direction and the first direction are arranged in a crossed mode to form a matrix, wherein each first pattern is located in an even row, and each second pattern is located in an odd row;

wherein, in the grid composed of the first electrode and the second electrode, the first electrode and the second electrode are connected by a first electrode

Setting the appearance characteristics of the first pattern and/or the second pattern to adaptively change the facing area between the first pattern and the adjacent second pattern in each electrode node according to the resistance difference on different signal paths; and/or

Setting lengths of the first connection lines and/or the second connection lines to adaptively change gaps between the first patterns and the adjacent second patterns in each electrode node according to a resistance difference on different signal paths,

so that the rc time constants of each of the signal paths are at a predetermined level of uniformity. .

Preferably, facing areas between the first pattern and the adjacent second pattern decrease in order in a direction away from the driving side.

Preferably, the first pattern has a first side edge adjacent the second pattern, the second pattern has a second side edge adjacent the first pattern;

the first side edge is parallel to the second side edge, and the vertical projection of the first side edge to the second side edge completely falls on the second side edge;

the length of the first side of each of the first patterns is successively shortened in a direction away from the driving side.

Preferably, the first pattern is hexagonal or octagonal and the second pattern is prismatic or hexagonal.

Preferably, a gap between the first pattern and the adjacent second pattern is kept constant in a direction away from the driving side.

Preferably, a length of each of the first connection lines of the first electrodes and a length of each of the second connection lines of the second electrodes are kept constant in a direction away from the driving side.

Preferably, gaps between the first pattern and the adjacent second pattern become larger in order in a direction away from the driving side.

the lengths of the first connection lines of the first electrodes are successively shortened in a direction away from the driving side.

Preferably, the length of the first side of each of the first patterns is kept constant in a direction away from the driving side.

Preferably, the facing area between the first pattern and the adjacent second pattern is constant.

The invention further provides a display device, which comprises a display panel, a touch panel and a glass protection layer, wherein the touch panel is located between the display panel and the glass protection layer, the touch panel comprises a capacitive touch sensor, and the capacitive touch sensor comprises:

so that the rc time constants of each of the signal paths are at a predetermined level of uniformity.

Preferably, the surface between the touch panel and the glass protective layer is completely attached; and/or the surface between the display panel and the touch panel is completely attached.

Preferably, the screen size of the display device is above 50 inches.

The capacitive touch sensor adjusts the opposite area between the first pattern and the second pattern in each node of the first electrode and the second electrode; and gaps between the first pattern and the second pattern enable mutual capacitance of corresponding nodes of the signal path to be smaller as the signal path is longer in signal paths with different lengths transmitted to the receiving side along the driving side, so that the resistance of the path is matched with the relatively larger resistance, and the capacitance-resistance time constant of the signal path is adjusted, so that the resistance-capacitance time constant (RC) of each signal path in a matrix formed by the first pattern and the second pattern is in a preset consistency level, and further data collected by the receiving side is more uniform and consistent during detection.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.

FIG. 1 is an assembled schematic view of a prior art capacitive touch sensor;

FIG. 2 is a schematic diagram of electrode nodes of the capacitive touch sensor of FIG. 1;

FIG. 3 is a schematic structural diagram of a capacitive touch sensor according to an embodiment of the invention;

FIG. 4 is an enlarged view of a portion of FIG. 3 at A;

FIG. 5 is an enlarged view of a portion of the alternate embodiment shown at A in FIG. 3;

fig. 6 is an electrical diagram of the detection of the capacitive touch sensor of the present invention.

The reference numbers illustrate:

reference numerals	Name (R)	Reference numerals	Name (R)	Reference numerals	Name (R)
						100	Capacitive touch sensor	111b	The first side edge	2	Second electrode
1	A first electrode	11c	First pattern	21	Second pattern
						11a	First pattern	111c	The first side edge	211	Second side edge
111a	The first side edge	12a	First connecting wire	22	Second connecting line
						11b	First pattern	12b	First connecting wire

The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that, if directional indications (such as up, down, left, right, front, and back … …) are involved in the embodiment of the present invention, the directional indications are only used to explain the relative positional relationship between the components, the movement situation, and the like in a specific posture (as shown in the drawing), and if the specific posture is changed, the directional indications are changed accordingly.

In addition, if there is a description of "first", "second", etc. in an embodiment of the present invention, the description of "first", "second", etc. is for descriptive purposes only and is not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present invention.

Fig. 1 is an assembly diagram illustrating a conventional capacitive touch sensor in which X-axis electrodes and Y-axis electrodes have the same pattern and are diamond-shaped.

Referring further to fig. 2, fig. 2 is a schematic diagram of an electrode node of the capacitive touch sensor in fig. 1, and fig. 2 is a model of resistance and mutual capacitance of the node.

Because the pattern matrix formed by the X-axis electrode and the Y-axis electrode is of a symmetrical structure, mutual capacitance of each node is relatively consistent, each node has a resistor Rb + Rd, and the serial node resistances of different nodes are different during detection, so that the capacitance charging time of the nodes at the edge of the principle is prolonged, capacitance values of different nodes calculated by a receiving end are slightly different due to different time constants of the resistors and the capacitors, and further, the difference of data values after arrangement is large, namely, the data is represented to be non-uniform.

The invention provides a capacitive touch sensor.

In an embodiment of the present invention, as shown in fig. 3 to 5, the capacitive touch sensor includes:

a plurality of first electrodes 1 extending in a first direction, the first electrodes 1 including a plurality of first patterns (11a,11b,11c) and first connection lines (12a, 12b) alternately arranged in the first direction and electrically connected to each other;

a plurality of second electrodes 2 extending along the second direction, the second electrodes 2 including a plurality of second patterns 21 and second connection lines 22 alternately arranged along the second direction and electrically connected to each other;

the second direction is arranged crosswise to the first direction to form a matrix with each first pattern (11a,11b,11c) in an even row and each second pattern 21 in an odd row;

wherein, in the grid composed of the first electrode 1 and the second electrode 2, the first electrode and the second electrode are connected by a wire

The outline characteristics of the first patterns (11a,11b,11c) and/or the second patterns 21 are set so as to adaptively change the facing areas between the first patterns (11a,11b,11c) and the adjacent second patterns 21 in each electrode node according to the resistance differences on different signal paths; and/or

The lengths of the first connection lines (12a, 12b) and/or the second connection lines 22 are set to adaptively change the gaps between the first patterns (11a,11b,11c) and the adjacent second patterns 21 in each electrode node according to the difference in resistance on different signal paths,

so that the rc time constants of the signal paths are at a predetermined level of uniformity.

In the present embodiment, the number of the first electrodes 1 and the second electrodes 2 is generally set appropriately according to the application, and for example, when applied to a large-sized display device, each of the first electrodes 1 and all of the second electrodes 2 are configured to form 200 or more nodes. For example, in 86-inch and 75-inch display devices, each row has 216 nodes, and the line resistance of the first electrode 1 made of nano-silver in the row is 12K Ω for 86 inches, and 10K Ω for 75 inches, so that the charging time of the mutual capacitance of each node is very different if the mutual capacitances of the nodes are the same.

It will be appreciated that in common applications, in order to reduce the thickness, the first electrode 1 and the second electrode 2 are generally formed by etching a metal film, such as an ito (indium Tin oxides) film or a nano silver film. For use in conjunction with light transmissive display applications, a light transmissive ito (indium Tin oxides) film may be used. The first patterns (11a,11b,11c), the second patterns 21, the first connection lines (12a, 12b), and the second connection lines 22 may be made of the same material or different materials.

In addition, the first electrode 1 and the second electrode 2 may be disposed in the same layer, or may be disposed in different layers, for example, the first electrode 1 and the second electrode 2 are disposed on the same surface of the substrate, and thus, the first connection lines (12a, 12b) and the second connection lines 22 need to be connected in an insulating manner. If one or more interlayers are present between the first electrode 1 and the second electrode 2, no overlap is required.

The first direction and the second direction are arranged to intersect each other so that the first electrode 1 and the second electrode 2 form a matrix for detection, and the intersection may be a vertical intersection or an oblique intersection.

By setting the shapes of the first patterns (11a,11b,11c) and/or the second patterns 21, the relative position relationship between the adjacent sides of the first patterns (11a,11b,11c) and the second patterns 21 can be adjusted, so that the facing area between the first patterns (11a,11b,11c) and the adjacent second patterns 21 is changed, namely the size of mutual capacitance is changed, for example, when the facing area is reduced, the corresponding mutual capacitance is reduced.

Similarly, by changing the lengths of the first connection lines (12a, 12b) and/or the second connection lines 22, the gaps between the adjacent sides of the first patterns (11a,11b,11c) and the second patterns 21 can be adjusted, so as to change the mutual capacitance, for example, if the facing area is reduced, the corresponding mutual capacitance becomes smaller.

It is understood that the shape of the first pattern (11a,11b,11c) and/or the second pattern 21 and the length of the first connection line (12a, 12b) and/or the second connection line 22 may be simultaneously set to vary the magnitude of the corresponding and node capacitance.

In order to better understand the technical scheme of the invention, a common mutual capacitance detection method is described below.

In brief, 2 sensors for sending and receiving signals are used to detect the reduction degree of the capacitance on the signal receiving side when the finger touches.

A mutual capacitance detection scheme is to measure the change in mutual capacitance of a row and a column. Suppose that the mutual capacitance between the first electrode 1 and the second electrode 2 decreases by C after the finger touches_F1By detecting the change of the mutual capacitance, whether the finger touches or not can be detected.

Mutual capacitance detection methods have transmit and receive electrodes arranged in an orthogonal matrix, which is the only way a projected capacitive touch screen reliably reports and tracks two or more concurrent touch points. In a mutual capacitance detection scheme, the drive and sense lines are in different directions, and if a drive voltage is applied in a first direction, signal detection is performed in a second direction, and vice versa.

Referring to fig. 3 and 6, assuming that the first direction electrodes are driving lines and the second direction electrodes are detection lines, the first direction driving lines are scanned line by line during detection, and the sensing signals on each detection line are read in time during scanning of each line of driving lines, so that each intersection of the row and column can be scanned through one scanning cycle, and X × Y signals can be obtained through scanning. In a mutual capacitance based measurement system, each touch point is represented by a pair of (X, Y) coordinates. Each clock cycle is divided into two phases, precharge and measurement. If the charging of the capacitors of the nodes cannot be consistently completed in the pre-charge stage, the uniformity of the data in the measurement stage is affected.

The capacitive touch sensor of the invention adjusts the opposite area between the first pattern (11a,11b,11c) and the second pattern (21) in each node of the first electrode (1) and the second electrode (2); and the gaps between the first patterns (11a,11b,11c) and the second patterns 21 are such that the longer the signal path is, the smaller the mutual capacitance of the corresponding nodes of the signal path is, so as to match the relatively larger resistance of the path, and the time constant of capacitance and resistance of the signal path is adjusted, so that the time constant of Resistance and Capacitance (RC) of each signal path in the matrix formed by the first patterns (11a,11b,11c) and the second patterns 21 is at a preset consistency level, and further, when detecting, the data collected by the receiving side is more uniform and consistent.

Referring to fig. 3, the resistance of the signal path a is smaller than that of the signal path B, and when the first electrode 1 of the second row is scanned, since the node mutual capacitance on the signal path a is adjusted to be smaller than that on the signal path B, the RC time constant (τ) on the signal path a is equal to that on the signal path B by this offset. The first electrode 1 and the second electrode 2 make the rc time constants of the signal paths at a predetermined consistency level by matching the node capacitances.

Further, referring to fig. 4, facing areas between the first patterns (11a,11b,11c) and the adjacent second patterns 21 decrease in sequence in a direction away from the driving side.

In this embodiment, the relative positional relationship between the adjacent sides of the first pattern (11a,11b,11c) and the second pattern 21 can be adjusted, and the length of the facing sides can be adjusted when the adjacent sides are parallel to each other; or directly adjusting the included angle between two adjacent sides, thereby changing the facing area between the first pattern (11a,11b,11c) and the adjacent second pattern 21. The facing areas between the first patterns (11a,11b,11c) and the adjacent second patterns 21 are sequentially reduced. The mutual capacitance of the nodes on each signal path can be guaranteed to be adjusted.

Further, the first pattern (11a,11b,11c) has a first side (111a, 111b, 111c) adjacent to the second pattern 21, and the second pattern 21 has a second side 211 adjacent to the first pattern (11a,11b,11 c); the first side edges (111a, 111b, 111c) are parallel to the second side edge 211, and the perpendicular projection of the first side edges (111a, 111b, 111c) to the second side edge 211 completely falls on the second side edge 211; the lengths of the first sides (111a, 111b, 111c) of the first patterns (11a,11b,11c) are successively shortened in a direction away from the driving side.

In the present embodiment, as shown in fig. 4, among the three first patterns (11a,11b,11c) from left to right, the second sides 211 of the adjacent second patterns 21 are the same in length, but in each first side (111a, 111b, 111c) of each first pattern (11a,11b,11c), S1> S2> S3, so that the facing areas decrease from left to right. Only the shape of the first pattern (11a,11b,11c), and particularly only the length of the first side (111a, 111b, 111c), is adjusted, so that the corresponding manufacturing process can be simplified and the process cost can be reduced.

Further, the first pattern is hexagonal or octagonal and the second pattern is prismatic or hexagonal.

In this embodiment, the hexagons of the first pattern (11a,11b,11c) may match the prisms of the second pattern 21; or the hexagon of the first pattern is matched with the hexagon of the second pattern; the first pattern and the second pattern are set to be relatively regular shapes, so that a capacitor network model and a resistor network model corresponding to the capacitive touch sensor are simplified, and the corresponding resistor-capacitor time constant is adjusted more accurately.

Further, in the direction away from the driving side, the gap between the first pattern (11a,11b,11c) and the adjacent second pattern 21 is kept constant.

In the present embodiment, as described earlier, in each first side (111a, 111b, 111c) of each first pattern (11a,11b,11c) in fig. 4, S1> S2> S3, the area so facing decreases sequentially from left to right, and since the gap between the first pattern (11a,11b,11c) and the second pattern 21 remains unchanged, the mutual capacitance decreases sequentially everywhere. By keeping the gap between the first pattern (11a,11b,11c) and the second pattern 21 constant, at least the dimensional positioning of the manufacturing is thereby easier to perform, and the corresponding production process is thus more compact.

Further, the length of each first connection line (12a, 12b) of the first electrode 1 and the length of each second connection line 22 of the second electrode 2 are kept constant in a direction away from the driving side.

In the present embodiment, the distances between two adjacent second electrodes 2 in the first direction are the same, and thus, the ratio of the second pattern 21 to the second connection line 22 in the first direction is also the same; similarly, the distances between two first electrodes 1 adjacent in the second direction are the same, and thus the ratio of the sizes of the first patterns (11a,11b,11c) to the first connecting lines (12a, 12b) in the second direction is also the same. Thus, the electrode nodes are uniformly arranged throughout the first direction, and the electrode nodes are uniformly arranged throughout the second direction. Preferably, the length of the first electrical connection line is the same as that of the second electrical connection line, and each electrode node forms a grid cell in a square shape.

Further, referring to fig. 5, in the direction away from the driving side, the gaps between the first patterns 11a and the adjacent second patterns 21 become larger in sequence.

In the present embodiment, the gap between the first pattern 11a and the adjacent second pattern 21 can be increased by adjusting the distance between the adjacent two first patterns 11a and/or adjusting the distance between the adjacent two second patterns 21. It is also possible to reduce the size of the first pattern 11a proportionally in the direction away from the driving side to increase the gap between the first pattern 11a and the adjacent second pattern 21.

Further, the first pattern 11a has a first side 111a adjacent to the second pattern 21, and the second pattern 21 has a second side 211 adjacent to the first pattern 11 a; the first side 111a is parallel to the second side 211, and a perpendicular projection of the first side 111a to the second side 211 completely falls on the second side 211; the lengths of the respective first connecting lines (12a, 12b) of the first electrode 1 are successively shortened in a direction away from the driving side.

In this embodiment, specifically, as shown in fig. 5, in three first patterns 11a from left to right, the length S1 of each first side 111a is S2 is S3, the second sides 211 of adjacent second patterns 21 are also equal, but the length of the left first connection line 12a is shorter than the length of the right first connection line 12b, so that the distance between the two right first patterns 11a is increased, so that d1 is less than d2, and the mutual capacitances at all positions are decreased from left to right.

Further, the length of the first side 111a of each first pattern 11a in the direction away from the driving side is kept constant.

In this embodiment, the adjustment of the first pattern 11a is reduced to achieve the purpose of adjusting the time constant of the corresponding node resistor and capacitor, thereby simplifying the corresponding manufacturing process. Preferably, the shape and size of each first pattern 11a on the first electrode 1 are consistent, and the etching formation of each first pattern 11a can be achieved by a stepwise offset.

In this embodiment, similarly, by setting the first pattern 11a and the second pattern 21 to be relatively regular shapes, it is beneficial to simplify the capacitance network model and the resistance network model corresponding to the capacitive touch sensor, so that the adjustment of the corresponding resistance-capacitance time constant is more accurate.

Further, the facing area between the first pattern 11a and the adjacent second pattern 21 is not changed. In the present embodiment, the gap between the first pattern 11a and the adjacent second pattern 21 can be adjusted only by adjusting the length of the second connection line 22 between the adjacent second patterns 21 and/or the length of the first connection line (12a, 12b) between the adjacent first patterns 11a, and the corresponding manufacturing process is simpler, i.e., easier to implement.

The present invention further provides a display device, which includes a display panel, a touch panel and a glass protection layer, wherein the touch panel is located between the display panel and the glass protection layer, the touch panel includes, for example, a capacitive touch sensor, and the specific structure of the capacitive touch sensor refers to the above embodiments.

In this embodiment, the display panel is used for displaying light and shadow information, and the glass protection layer is disposed outside the touch panel to prevent scratching the touch panel and resist deformation. To avoid light blocking, the first electrode 1 and the second electrode 2 of the touch sensor are preferably made of a transparent conductive material.

Furthermore, the surface between the touch panel and the glass protective layer is fully attached; and/or the surface between the display panel and the touch panel is fully attached.

In this embodiment, the use of surface bonding can improve the display effect of the display device and reduce the thickness of the display device by shortening the optical path. Although the full-lamination process can cause greater interference to the touch panel, the consistency of the resistance-capacitance time constants of all paths in the pattern matrix of the capacitive touch sensor is high, and accordingly the data acquisition consistency is better, so that the capacitive touch sensor has better anti-interference capability after being applied to the full-lamination process.

Further, the screen size of the display device is over 50 inches. By way of example, the screen size of the display device may be 55 inches, 60 inches, 65 inches, 70 inches, 75 inches, 86 inches. As described above, as the size of the display device increases, the resistance of each electrode increases accordingly, and the influence of the linear increase of the resistance on the touch detection is more prominent. However, by adopting the capacitive touch sensor of the embodiment, the linear increase of the resistance can be compensated, so that the mutual capacitance charging time of each node tends to be consistent, and better data acquisition consistency is obtained.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the contents of the present specification and the accompanying drawings, or directly/indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims

1. A capacitive touch sensor, comprising:

2. The capacitive touch sensor of claim 1, wherein facing areas between the first pattern and the adjacent second pattern decrease sequentially in a direction away from the driving side.

3. The capacitive touch sensor of claim 2,

the first pattern has a first side edge adjacent the second pattern, the second pattern has a second side edge adjacent the first pattern;

4. The capacitive touch sensor of claim 3, wherein the first pattern is hexagonal or octagonal and the second pattern is prismatic or hexagonal.

5. The capacitive touch sensor of any of claims 2-4, wherein a gap between the first pattern and the adjacent second pattern remains constant in a direction away from the drive side.

6. The capacitive touch sensor of claim 5,

the length of each of the first connection lines of the first electrodes and the length of each of the second connection lines of the second electrodes are kept constant in a direction away from the driving side.

7. The capacitive touch sensor of claim 1, wherein gaps between the first pattern and the adjacent second pattern become larger in order in a direction away from the driving side.

8. The capacitive touch sensor of claim 7,

9. The capacitive touch sensor of claim 8, wherein a length of the first side of each of the first patterns remains constant in a direction away from the drive side.

10. The capacitive touch sensor of claim 9, wherein the first pattern is hexagonal or octagonal and the second pattern is prismatic or hexagonal.

11. The capacitive touch sensor of any of claims 7-10, wherein the facing area between the first pattern and the adjacent second pattern is constant.

12. A display device comprising a display panel, a touch panel and a glass protective layer, the touch panel being located between the display panel and the glass protective layer, wherein the touch panel comprises the capacitive touch sensor according to any one of claims 1 to 11.

13. The display device according to claim 12, wherein the touch panel is fully attached to the glass protective layer; and/or the surface between the display panel and the touch panel is completely attached.

14. A display device as claimed in claim 12 or 13, characterised in that the screen size of the display device is above 50 inches.