Patent Application
20170177147
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2015-244848, filed Dec. 16, 2015, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a display device.
A display device which has the function of detecting an object in proximity to a display area has been in practical use. As an example of a detection method, there is a capacitive detection method in which the proximity of the object is detected based on a change in the capacitance between a detection electrode and a drive electrode facing each other with a dielectric interposed therebetween.
The detection electrode is formed of, for example, conductive lines such as metal lines. If such detection electrodes are arranged in such a manner as to overlap the display area, the conductive lines interfere with pixels included in the display area, and fringes (so-called moiré) may occur.
As a moiré prevention method, for example, a method of randomly distributing intersections of the conductive lines extending at different angles may be adopted. In this method, since there is no regularity of the interference between the conductive lines and the pixels, moiré can be prevented.
However, the pattern of the detection electrodes having randomized intersections will include numerous frequency components. If external light is made incident on a display device comprising such detection electrodes, the reflected light is visually recognized as glare resulting from the detection electrodes, and consequently the display quality will be degraded.
In general, according to one embodiment, a display device comprises pixel electrodes, a drive electrode, a detection electrode, and a detection module. The pixel electrodes are provided for respective pixels arrayed in a display area. The drive electrode forms an electric field for image display with the pixel electrodes. The detection electrode is opposed to the drive electrode. And The detection module detects an object in proximity to the display area based on a signal obtained from the detection electrode. In the display device, the detection electrode includes conductive lines extending parallel to each other, and the conductive lines are arranged at randomized pitch.
According to another embodiment, the detection electrode includes conductive lines extending parallel to each other, and slits are provided in random positions in the conductive lines.
According to another embodiment, the detection electrode includes conductive lines extending parallel to each other and dummy patterns arranged in random positions between the conductive lines and electrically unconnected to the conductive lines.
Embodiments will be explained with reference to the accompanying drawings.
Note that the disclosure is presented for the sake of exemplification, and any modification and variation conceived within the scope and spirit of the invention by a person having ordinary skill in the art are naturally encompassed in the scope of invention of the present application. In addition, in some cases, in order to make the description clearer, the drawings may be more schematic than in the actual modes, but they are mere examples, and do not limit the interpretation of the present invention. In each drawing, like or similar elements disposed sequentially may not be denoted by reference numbers or symbols. In the specification and drawings, components that fulfill same or similar functions are denoted by the same reference number and their overlapping descriptions may be omitted.
As an example of a display device and a touch detection device, a display device having the function of displaying an image using a liquid crystal display element and the function of touch detection will be described in the embodiments. However, the embodiments do not preclude the application of individual technical ideas disclosed in the embodiments to display devices using display elements other than the liquid crystal display element. As the display devices, for example, a self-luminous display device comprising an organic electroluminescent display element, or an electronic-paper type display device comprising a cataphoretic element may be considered. The touch detection device may be independent of the display device and attached to the display device.
First, the structure common to the embodiments to be described later will be described with reference to
The display device 1 comprises a display panel 2, drive electrodes TX (TX1 to TXn), detection electrodes RX (RX1 to RXm) opposed to the drive electrodes TX, a driver IC 3 serving as a driver module, and a touch detection IC 4 serving as a detection module. For example, n and m are integers not less than two. The drive electrodes may also be referred to as common electrodes.
The display panel 2 comprises a rectangular array substrate AR (first substrate) and a rectangular counter-substrate CT (second substrate) smaller in outer shape than the array substrate AR. In the example of
In an area where the array substrate AR and the counter-substrate CT are opposed, the display panel 2 comprises a display area (active area) DA where an image is displayed and a peripheral area FA between the display area DA and the end of the display panel 2. In the example of
In the display area DA, the drive electrodes TX1 to TXn extend in the first direction X and are arranged in the second direction Y. The drive electrodes TX1 to TXn can be formed of a transparent conductive film of, for example, indium tin oxide (ITO). For example, the drive electrodes TX1 to TXn are formed inside the display panel 2, i.e., in the array substrate AR. In the display area DA, the detection electrodes RX1 to RXm extend in the second direction Y and are arranged in the first direction X. For example, the detection electrodes RX1 to RXm are formed on a surface of the counter-substrate CT, which is opposite to a surface opposed to the array substrate AR. The drive electrodes TX1 to TXn may extend in the second direction Y and be arranged in the first direction X and the detection electrodes RX1 to RXm may extend in the first direction X and be arranged in the second direction Y.
The driver IC 3 executes control related to image display, and is mounted in the terminal area NA. In the terminal area NA, a mounting terminal 5 is formed. A first flexible printed circuit 6 which supplies image data to the display panel 2 is connected to the mounting terminal 5.
A mounting terminal 7 is formed at an end of the counter-substrate CT along the terminal area NA. A second flexible printed circuit 8 which outputs detection signals from the detection electrodes RX1 to RXm is connected to the mounting terminal 7. In the example of
In the example of
In the example of
The counter-substrate CT comprises a second insulating substrate 20 as a transparent substrate, a light-shielding layer 21, color filters 22, an overcoat layer 23 and a second alignment film 24. The light-shielding layer 21 is formed on a surface of the second insulating substrate 20 on the array substrate AR side to define the sub-pixels SPX. The color filters 22 are formed on the surface of the second insulating substrate 20 on the array substrate AR side and colors corresponding to the sub-pixels SPX are applied to the color filters 22. The overcoat layer 23 covers the color filters 22. The second alignment film 24 covers the overcoat layer 23.
A liquid crystal layer LC including liquid crystal molecules is formed between the first alignment film 13 and the second alignment film 24. The detection electrodes RX are formed on a surface of the second insulating substrate 20 which is not opposed to the array substrate AR. The dummy electrodes DX are also formed on the surface of the second insulating substrate 20 which is not opposed to the array substrate AR. The drive electrodes TX are formed in the array substrate AR in the example of
Next, an example of the principle of detection of an object in proximity to the display area DA by the drive electrodes TX and the detection electrodes RX will be described with reference to
Capacitance Cc exists between the drive electrode TX and the detection electrode RX which are opposed to each other. When a drive signal Stx is supplied to the drive electrodes TX, a current flows through the detection electrodes RX via the capacitance Cc, and thus, a detection signal Srx is obtained from each detection electrode RX.
When an object O, which is a conductor such as a user's finger, approaches the display device 1, capacitance Cx is produced between the object O and a detection electrode RX in proximity to the object O. When the drive signal Stx is supplied to the drive electrodes TX, a waveform of a detection signal Srx obtained from the detection electrode RX in proximity to the object O changes under the influence of the capacitance Cx. That is, the touch detection IC 4 can detect the object O in proximity to the display device 1 based on the detection signal Srx obtained from each detection electrode RX. The touch detection IC 4 can also detect a position of the object O in the first direction X and the second direction Y, based on the detection signal Srx obtained from each detection electrode RX in each time phase when the drive signal Stx is sequentially supplied to the drive electrodes TX in a time-division manner. The above-described method is referred to as a mutual-capacitive method, a mutual-detection method or the like.
Next, image display by the display device 1 will be described.
The scan lines G extend in the first direction X and are arranged in the second direction Y in the display area DA. The signal lines S extend in the second direction Y and are arranged in the first direction X in the display area DA. The scan lines G and the signal lines S are formed in the array substrate AR. Each scan line G is connected to the first gate driver GD1 and the second gate driver GD2. Each signal line S is connected to the selector SD.
In the example of
Each sub-pixel SPX comprises a thin-film transistor TFT (switching element) formed in the array substrate AR. The thin-film transistor TFT is electrically connected to the scan line G, the signal line S and the pixel electrode PE. At the time of display, the drive electrodes TX are set at a common potential and function as so-called common electrodes.
The first gate driver GD1 and the second gate driver GD2 sequentially supply a scanning signal to the scan lines G. The selector SD selectively supplies a video signal to the respective signal lines S under the control of the driver IC 3. When a scanning signal is supplied to a scan line G connected to a certain thin-film transistor TFT and a video signal is supplied to a signal line S connected to the same thin-film transistor TFT, a voltage corresponding to the video signal is applied to the pixel electrode PE. At this time, an electrical field is produced between the pixel electrode PE and the drive electrode TX, which changes the alignment of the liquid crystal molecules in the liquid crystal layer LC from an initial alignment state where the voltage is not applied. Through the above-described operation, an image is displayed in the display area DA.
The display device 1 having the above-described structure may be a transmissive display device which displays an image using light from a backlight provided on the back surface (surface which is not opposed to the counter-substrate CT) of the array substrate AR, a reflective display device which displays an image using reflected external light which enters from the outer surface (surface which is not opposed to the array substrate AR) of the counter-substrate CT, or a display device which has the functions of both the transmissive display device and the reflective display device.
Next, the pixels PX and the detection electrodes RX will be described in detail.
The detection electrode Rx is constituted by conductive lines CL. For example, the conductive lines CL have a single layer structure or a multilayer structure which includes a layer formed of at least one of the following metal materials: aluminum (Al), copper (Cu), silver (Ag), and an alloy thereof. The use of the metal material as the conductive lines CL makes it possible to reduce the resistance of the conductive lines CL as compared to the case of forming the conductive lines CL only of a transparent conductive material such as ITO.
More specifically, the detection electrode RX shown in
The pattern of the detection electrode RX is not limited to the example shown in
More specifically, the conductive lines CL3 shown in
The conductive lines CL (CL1, CL2 and CL3) formed of the metal material have higher light-shielding effect than a transparent conductive film such as ITO. Accordingly, if the detection electrodes RX having the pattern shown in
In addition, the conductive lines CL formed of the metal material may reflect external light, which may cause glare in the display area DA. The principle of occurrence of glare will be explained with reference to a model shown in
Part of light that enters from an external light source to the display panel 2 is reflected by the conductive lines CL of the detection electrodes RX. Glare occurs when the user sees diffracted light (primary light, secondary light, . . . ), not specular light (zero-order light). That is, glare seen at the viewpoint is caused by diffracted light from the pattern of the detection electrodes RX, i.e., part of a Fourier pattern obtained by performing a Fourier transform on the pattern.
As shown in
An example of methods for moiré and glare evaluation will be described with reference to
The Fourier transform is performed to obtain distribution of diffracted light with respect to the observation angles θx and θy. For example, the Fourier pattern I2 indicates distribution of intensity of diffracted light in a plane in which the horizontal axis is the observation angle θx and the vertical axis is the observation angle θy. The Fourier pattern I2 corresponds to glare visually recognized by human eye. Therefore, glare caused by the detection electrodes RX can be evaluated based on the Fourier pattern I2.
In general, spectra along straight lines passing through the origin O (θx=0, θy=0) appear in the Fourier pattern I2. A width Δθ of the straight line spectrum can be used as one of indexes for glare evaluation. That is, glare increases as the width Δθ becomes larger and decreases as the width Δθ becomes smaller.
Considering a one-dimensional pattern in the first direction X, for example, in the case where the visual distance L shown in
Δθmax=Δx/L=1 mm/100 mm*180/π≈0.6°
where π is the circular constant. In the case of using Δθmax obtained in this way, glare can be determined to be within the allowable range if Δθ<0.6.
In the moiré evaluation, a Fourier pattern I3 is generated by performing a gray scale transform on the actual image I0 which is a color image, and then performing a Fourier transform (FFT) on the image after the gray scale transform. The Fourier transform is performed to obtain distribution of a first spatial frequency in the first direction X and a second spatial frequency in the second direction Y. For example, the Fourier pattern I3 indicates distribution of frequency in a plane in which the horizontal axis is a first spatial frequency and the vertical axis is a second spatial frequency.
Next, a frequency domain I4 of a resolution visible to humans is extracted from the Fourier pattern I3. The visibility of humans depends on a contrast and a spatial frequency of an image. That is, the pattern tends to be more visible as the contrast and the spatial frequency of the pattern increases. For example, the frequency domain I4 can be extracted by filtering the Fourier pattern I3 by a contrast sensitivity function defined in consideration of the visibility.
After the frequency domain I4 is extracted, a moiré image I5 is generated by performing an inverse Fourier transform (IFFT) on the frequency domain I4. Fringes visible to humans appear in the moiré image I5. Therefore, the degree of moiré of the actual image I0 can be evaluated based on the moiré image I5. For example, the degree of moiré can be visibly determined. Alternatively, the degree of moiré can be determined by obtaining a standard deviation with respect to the moiré image I5 and determining whether the standard deviation belongs to a predetermined allowable range.
A specific operation method of the filtering using the contrast sensitivity function and the moiré evaluation using the standard deviation is disclosed in, for example, JP 2014-219973 A. The operation method disclosed in the literature can be arbitrarily used for the moiré evaluation explained with reference to
An example of evaluation in the above-described glare evaluation method is described.
Two groups of dots aligned like straight lines passing through the origin O appear in the Fourier pattern I2 of
As explained above, glare is low in the detection electrode RX in which conductive lines CL are regularly arranged as shown in
As a measure to avoid moiré, the regularity of the pattern of the detection electrode RX may be lessened.
Two groups of dots aligned like straight lines passing through the origin O appear in a Fourier pattern I2 of the detection electrode RX of
As explained above, if the pattern of the detection electrode RX is designed to prevent moiré, there is a possibility that glare is increased. Therefore, the detection electrode RX should have a pattern that can prevent both moiré and glare.
In the following first to third embodiments, examples of a pattern of the detection electrode RX that can prevent moiré by having irregularity and also prevent glare.
The degree of moiré changes according to angles 74 1 and θ2. In order to prevent moiré, for example, angles θ1 and θ2 should preferably be angles from 30 to 40° or from 50 to 60°. The line width of the first conductive lines CL1 and the second conductive lines CL2 is constant in
In the present embodiment, the pattern of the detection electrode RX is provided with irregularity by randomizing pitch SA ( . . . SAi−1, SAi, SAi+1 . . . ) between adjacent first conductive lines CL1 and pitch SB ( . . . SBj−1, SBj, SBj+1 . . . ) between adjacent second conductive lines CL2.
For example, pitch SA and pitch SB are determined by the following equations:
SA=SA0±ΔSA (1)
SB=SB0±ΔSB (2)
where SA0 and SB0 are constant values, and ΔSA and ΔSB are deviations from constant values SA0 and SB0. Deviations ΔSA and ΔSB are, for example, random numbers. As a generation method of such random numbers, various methods such as a method using Fibonacci numbers may be adopted. Deviations ΔSA and ΔSB may be randomly selected from predetermined candidates.
If deviations ΔSA an ΔSB are too small, the pattern of the detection electrode RX cannot be provided with sufficient irregularity. If deviations ΔSA and ΔSB are too large, unevenness in density of conductive lines CL1 and CL2 in the detection electrode RX is increased, which may affect detection performance and result in nonuniformity in brightness of the display area DA. Therefore, deviations ΔSA and ΔSB should preferably satisfy the following equations:
0.01<ΔSA/SA0<0.1 (3)
0.01<ΔSB/SB0<0.1 (4)
For example, the dummy electrode DX shown in
The pattern of the detection electrode RX including wavy conductive lines CL3 shown in
In the example of
For example, the dummy electrode DX used together with the detection electrode RX of
Since the patterns of the detection electrode RX shown in
In the same manner as the first embodiment, angles θ1 and θ2 should preferably be angles from 30 to 40° or from 50 to 60°. The line width of the first conductive lines CL1 and the second conductive lines CL2 is constant in
In the present embodiment, the pattern of the detection electrode RX is provided with irregularity by providing slits SL in the first conductive lines CL1 and the second conductive lines CL2. The slits SL are provided at random positions. The specific positions of the slits SL can be determined based on random numbers generated by using, for example, Fibonacci numbers. The slits SL may be provided only in the first conductive lines CL1 or only in the second conductive lines CL2.
If an electrically floating portion is generated in the pattern of the detection electrode RX by providing the slits SL, the portion does not contribute to detection of an object, which may result in a decrease in detection performance. In addition, if the slits SL are concentrated in a certain position, the light transmittance in this position increases, which may result in nonuniformity in brightness of the display area DA. Therefore, the density and the positions of the slits SL may be adjusted so as to avoid the generation of the electrically floating portion and the nonuniformity in brightness.
If the slits SL are provided at the intersections of the first conductive lines CL1 and the second conductive lines CL2, current paths are greatly reduced in the pattern of the detection electrode RX, which may result in high resistance of the detection electrode RX. Thus, in the example of
The dummy electrode DX shown in
The pattern of the detection electrode RX can be provided with irregularity by the slits SL of the present embodiment. As a result, moiré caused by interference with the pixel pattern can be prevented. In addition, the slits SL are provided along the first conductive lines CL1 or the second conductive lines CL2 and regularity of the intersections of the conductive lines CL1 and CL2 is maintained. In this case, the Fourier pattern I2 of the detection electrode RX includes straight line spectra having small width Δθ in the same manner as
In the case of the detection electrode RX including wavy conductive lines CL3 shown in
In the same manner as the first embodiment, angles θ1 and θ2 should preferably be angles from 30 to 40° or from 50 to 60°. The line width of the first conductive lines CL1 and the second conductive lines CL2 is constant in
In the present embodiment, the pattern of the detection electrode RX is provided with irregularity by providing dummy patterns DP in addition to the first conductive lines CL1 and the second conductive lines CL2. Each dummy pattern DP is arranged in a rectangular closed pattern formed by two first conductive lines CL1 and two second conductive lines CL2, and is not electrically connected to the first conductive lines CL1 and the second conductive lines CL2. The dummy patterns DP are formed of a metal material similarly to the conductive lines CL1 and CL2, and exhibit the same degree of light-shielding effect as the conductive lines CL1 and CL2. For example, the shape of the dummy patterns DP is a circle having a diameter substantially equal to the width of the conductive lines CL1 and CL2, but may be a circle having a diameter greater or less than the width of the conductive lines CL1 and CL2 or may be other shapes such as an ellipse or a rectangle.
For example, the dummy patterns DP are arranged at random positions in a virtual line V. The virtual line V is a straight line extending between two first conductive lines CL1 and parallel to the first extension direction D1. The specific positions of the dummy patterns DP in the virtual line V can be determined based on random numbers generated by using, for example, Fibonacci numbers. Alternatively, the dummy patterns DP may be arranged at random positions in a virtual line parallel to the second extension direction D2 of the second conductive lines CL2. The dummy electrode DX can be provided with irregularity by randomly arranging the dummy patterns DP.
The dummy patterns DP may be randomly arranged in the virtual line V so as to overlap sub-pixels SPX of a particular color. The particular color is, for example, a color possessing the maximum luminosity for human eye, of the colors of the sub-pixels SPX included in the pixel PX. Among red, green, and blue, the color possessing maximum luminosity for human eye is green. Thus, if the pixel PX is constituted by a red sub-pixel SPXR, a green sub-pixel SPXG and a blue sub-pixel SPXB, the dummy patterns DP are arranged to overlap the green sub-pixels SPXG.
The sub-pixels SPX of the color possessing high luminosity tend to cause moiré. Therefore, if the dummy patterns DP are arranged to overlap the sub-pixels SPX of the color possessing the maximum luminosity, the overlap between the sub-pixels SPX of the color and the detection electrodes RX becomes irregular and moiré can be efficiently reduced.
The pattern of the detection electrode RX including wavy conductive lines CL3 shown in
In the example of
The pattern of the detection electrode RX can be provided with irregularity by providing the dummy patterns DP as in the present embodiment. As a result, moiré caused by interference with the pixel pattern can be prevented. In addition, the dummy patterns DP are arranged in the virtual line V parallel to the first extension direction D1 or the second extension direction D2, and regularity of the intersections of the conductive lines CL1 and CL2 (or connecting points between the first portions P1 and the second portions P2) is maintained. In this case, the Fourier pattern I2 of the detection electrode RX includes straight line spectra having small width Δθ in the same manner as
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. These novel embodiments can be carried out in various other modes, in which various omissions, substitutions and variations may be carried out within the scope and spirit of the technology. Such changes and modifications are encompassed by the scope and spirit of the technology, and naturally fall within the scope and its equivalency of the technology recited in the claims.
For example, each embodiment shows a mesh-like detection electrode RX constituted by first conductive lines CL1 and second conductive lines CL2 and a detection electrode RX constituted by conductive lines CL3 meandering like waveforms. However, various other patterns can be adopted as the detection electrode RX. For example, the detection electrode RX may include a polygonal closed pattern formed by conductive lines and other than a rectangle, or may include curved conductive lines.
The pattern of the detection electrode RX may be provided with irregularity by a method other than randomizing pitch of the conductive lines, providing slits at random positions in the conductive lines and providing dummy patterns at random positions. In this case, too, both moiré and glare can be reduced if the pattern of the detection electrode RX is designed such that the width Δθ of a straight line spectrum is less than about 0.6° in a Fourier pattern I2 obtained by performing a Fourier transform on the pattern of the detection electrode RX.
In each embodiment, the drive electrode TX is used for object detection as well as for image display. However, an electrode for object detection and an electrode for image display may be separately provided instead. In that case, for example, the touch sensing device may be configured by forming the drive electrodes TX on one main surface of a transparent substrate such as a glass substrate, and forming the detection electrodes RX on the other main surface of the substrate.
In each embodiment, a mutual-capacitive method of detecting an object by the detection electrode RX and the drive electrode TX is described. However, the object detection method may be other methods such as a method of detecting an object by using the capacitance of the detection electrode RX itself (referred to as a self-capacitance detection method or the like).
The technical thoughts disclosed in the embodiments can be arbitrarily combined. That is, the detection electrode RX may be configured by adopting two or three of the following methods: a method of randomizing pitch of the conductive lines; a method of providing slits at random positions in the conductive lines; and a method of providing dummy patterns at random positions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-244848 | Dec 2015 | JP | national |
