Display device

1. Field of the Disclosure

The present disclosure is related to a display device, and more particularly to a display device including a plurality of illumination portions.

2. Description of the Prior Art

Presently, passive matrix (PM) and active matrix (AM) driving methods have been adopted as two primary methods for driving light-emitting components. Despite the complicated process for fabricating an active matrix, each pixel in the active matrix can be driven continuously and independently, and driving signal of each pixel can be recorded without using a high pulse current for a long time to drive each pixel. Therefore, the active matrix is able to provide higher efficiency and extending a service life of a light-emitting component in comparison to the passive matrix driving method.

In the prior art, the active matrix driving method mainly drives the light emitting components through currents of different sizes, so that the light emitting component can emit light of different brightness. For example, the display panel can continuously drive the light emitting component with a corresponding current in a present frame, and drive the light emitting component with the updated current in the next frame period. Therefore, the light emitting component can present the brightness required for each frame. In this case, if it is desired to increase the number of luminance grey levels presented by the light-emitting components, it would be necessary to drive the light-emitting components with a small current to present the grey level of low brightness. However, when the light-emitting component is driven by a small current, the light emitted from the light-emitting component easily undergoes a significant color shift, resulting in poor picture quality.

One embodiment of the present disclosure discloses a method for expressing a grey level of a sub-pixel in a display device.

The method includes providing at least one light emitting unit in the sub-pixel, and the light emitting unit includes a plurality of illumination portions. Each illumination portion is illuminated independently. The method further includes illuminating at least one of the plurality of illumination portions to express the grey level of the sub-pixel according to a data signal.

Another embodiment of the present disclosure discloses a display device. The display device includes a plurality of sub-pixels.

One of the plurality of sub-pixels includes at least one light emitting unit and a plurality of driving units. The at least one light emitting unit includes a plurality of illumination portions. Each of the driving units is coupled to a corresponding illumination portion of the plurality of illumination portions, and drives the corresponding illumination portion to express a plurality of grey levels in different frames.

These and other objectives of the present disclosure will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the embodiment that is illustrated in the various figures and drawings.

FIG. 1 shows a display device according to one embodiment of the present disclosure.

FIG. 2 shows the arrangement of the illumination portions in the light emitting unit according to one embodiment of the present disclosure.

FIG. 3 shows the sub-pixel in FIG. 1 according to one embodiment of the present disclosure.

FIG. 4 shows the amplitude of the current when expressing four different grey levels according to one embodiment of the present disclosure.

FIG. 5 shows a sub-pixel according to another embodiment of the present disclosure.

FIG. 6 shows the structure of an LED according to one embodiment.

FIG. 7 shows the duty ratios of the current for expressing different grey levels according to one embodiment of the present disclosure.

FIG. 8 shows a sub-pixel according to another embodiment of the present disclosure.

FIG. 9 shows a method 400 for operating a sub-pixel in a display device according to one embodiment.

FIG. 1 shows a display device 10 according to one embodiment of the present disclosure. The display device 10 includes a plurality of sub-pixels 100 ( 1 , 1 ) to 100 (M,N), where M and N are positive integers. Each of the sub-pixels 100 can emit light at a plurality of grey levels in different frames.

In FIG. 1 , sub-pixels disposed in the same row can be coupled to the same scan line, and sub-pixels disposed in the same column can be coupled to the same data lines. For example, sub-pixels 100 ( 1 , 1 ) to 100 ( 1 ,N) can be coupled to the scan line SCL 1 , and sub-pixels 100 (M, 1 ) to 100 (M,N) can be coupled to the scan line SCLM. Also, sub-pixels 100 ( 1 , 1 ) to 100 (M, 1 ) can be coupled to the data lines DLA 1 to DLE 1 , and sub-pixels 100 ( 1 ,N) to 100 (M,N) can be coupled to the data lines DLAN to DLEN.

In some embodiments, the sub-pixels 100 ( 1 , 1 ) to 100 (M,N) have the same structure. For example, the sub-pixel 100 ( 1 , 1 ) includes a light emitting unit 110 , and a plurality of driving units 120 A, 120 B, 120 C, 120 D, and 120 E. The light emitting unit 110 includes a plurality of illumination regions 110 A, 110 B, 110 C, 110 D, and 110 E, and the illumination portions 110 A, 110 B, 110 C, 110 D, and 110 E can have different sizes and/or different shape. In one embodiment, the shape of the illumination portion may be, for example but not limited to, a circle, a rectangular, a square, or a free shape. In some embodiments, each of the illumination portions 110 A, 110 B, 110 C, 110 D, and 110 E may include a light emitting diode (LED), the LED could be an organic LED or inorganic LED (such as quantum-dot LED, Mini-LED, or Micro-LED), and the sizes of the LEDs in the illumination portions 110 A, 110 B, 110 C, 110 D, and 110 E are different. That is, the maximal brightness of the illumination portions 110 A, 110 B, 110 C, 110 D, and 110 E are different, and the sub-pixels 100 ( 1 , 1 ) to 100 (M,N) can present different grey levels with modulated illumination portions.

Also, each of the driving units 120 A, 120 B, 120 C, 120 D, and 120 E is coupled to a corresponding illumination portion of the plurality of illumination portions 110 A, 110 B, 110 C, 110 D, and 110 E, and can be used to drive the corresponding illumination portion to express a plurality of grey levels according to the data signal received in different frames. For example, the driving unit 120 A can be coupled to the illumination portion 110 A for driving the illumination portion 110 A, and the driving unit 120 E can be coupled to the illumination portion 110 E for driving the illumination portion 110 E.

That is, in FIG. 1 , each of the sub-pixels 100 may have 5 illumination portions and each illumination portion can emit light at a plurality of grey levels. Consequently, by driving different illumination portions with different intensities, each of the sub-pixels 100 can emit light at a variety of grey levels without complicated control of the current.

For example, the area of the illumination portion 110 B can be N times the area of the illumination portion 110 A, the driving unit 120 A can drive the illumination portion 110 A to emit light at N grey levels, the driving unit 120 B can drive the illumination portion 110 B to emit light at N grey levels. In this case, the illumination portions 110 A and 110 B are able to present a total of N 2 grey levels, where N is an integer greater than 1.

FIG. 2 shows the arrangement of the illumination portions 110 A, 110 B, 110 C, 110 D, and 110 E in the light emitting unit 110 according to one embodiment. In some embodiments, the size ratio of the illumination portions 110 A, 110 B, 110 C, 110 D, and 110 E can be 1:4:16:64:256, and each of the illumination portions 110 A, 110 B, 110 C, 110 D, and 110 E can present 4 different grey levels. If the 4 different grey levels are represented by 2 bits, then the grey level presented by the illumination portions 110 A, 110 B, 110 C, 110 D, and 110 E can be determined by 10 bits. In this case, the illumination portion 110 A would be controlled by the 2 least significant bits of the 10 bits, and the illumination portion 110 E would be controlled by the 2 most significant bits of the 10 bits. Therefore, the sub-pixel 100 would be able to present 2 10 ( 1024 ) grey levels in total.

FIG. 3 shows the sub-pixel 100 ( 1 , 1 ) according to one embodiment of the present disclosure. In FIG. 3 , each of the driving units 120 A, 120 B, 120 C, 120 D, and 120 E can drive the corresponding illumination portion 110 A, 110 B, 110 C, 110 D, and 110 E to emit light at the plurality of grey levels by adjusting the amplitudes of the current according to the data signal.

The driving units 120 A, 120 B, 120 C, 120 D, and 120 E can have the same structure. For example, the driving unit 120 A includes a scan transistor 122 , a capacitor 124 , and a driving transistor 126 . The scan transistor 122 has a first terminal coupled to a data line DLA, a second terminal, and a control terminal coupled to a scan line SCL 1 . The capacitor 124 has a first terminal coupled to the second terminal of the scan transistor 122 , and a second terminal for receiving the voltage V 1 . The driving transistor 126 has a first terminal for receiving a voltage V 2 , a second terminal coupled to the LED of the illumination portion 110 A, and a control terminal coupled to the second terminal of the scan transistor 122 .

In this case, when the scan transistor 122 is turned on, the driving transistor 126 can adjust the current according to the data signal SIG DA . That is, by adjusting the voltage of the data signal SIG DA transmitted on the data line DLA, the driving transistor 126 can generate the current with the desired intensity so as to drive the illumination portion 110 A to emit light at the corresponding grey level. In some embodiments, the capacitor 124 can keep the voltage of the data signal SIG DA to stabilize the current generated by the driving transistor 126 .

FIG. 4 shows the amplitude of the current I D when expressing four different grey levels according to one embodiment. In some embodiments, to present four different grey levels, the data signal may be at four different voltages, and the driving transistor 126 would generate the current I D with amplitude of four different levels A 0 , A 1 , A 2 , and A 3 . In FIG. 4 , the ratio of the four levels can be A 0 , A 1 , A 2 , and A 3 , for example but not limited to, 0:1:2:3, and the ratio of the brightness presented by the four grey levels would also be 0:1:2:3.

In FIG. 3 , since the illumination portions 110 A, 110 B, 110 C, 110 D, and 110 E are controlled and illuminated independently, the driving units 120 A, 120 B, 120 C, 120 D, and 120 E can be coupled to different data lines DLA 1 , DLB 1 , DLC 1 , DLD 1 , and DLE 1 . Furthermore, in some embodiments, since the sizes of the illumination portions 110 A, 110 B, 110 C, 110 D, and 110 E are different, the sizes of the driving transistors 126 of the driving units 120 A, 120 B, 120 C, 120 D, and 120 E may also be different. For example, the driving transistor 126 in the driving unit 120 B and the driving transistor 126 in the driving unit 120 A can have the same channel length, but the channel width of the driving transistor 126 in the driving unit 120 B can be four times the channel width of the driving transistor 126 in the driving unit 120 A.

Furthermore, in some embodiments, the anode of at least one of illumination portions 110 A, 110 B, 110 C, 110 D, and 110 E may be coupled to the P-type doped layer through the region of the first ohmic contact. FIG. 6 shows the structure of an illumination portion according to one embodiment. In FIG. 6 , the illumination portion can include a P-type doped layer PL 1 , an active layer AL 1 , an N-type doped layer NL 1 , a buffer layer BL 1 , and a sapphire layer SL 1 . In this case, the anode AN 1 of the illumination portion can be coupled to the P-type doped layer PL 1 through the region RA 1 of the first ohmic contact OC 1 , and the cathode CA 1 of the LED can be coupled to the N-type doped layer NL 1 through the region RA 2 of the second ohmic contact OC 2 . The ohmic contacts OC 1 and OC 2 can be formed by Indium Tin Oxide (ITO) or other suitable materials, and is adopted as an intermediate conductor between two different materials, that is, the metal material of the anode AN 1 and the cathode CA 1 and the semiconductor material of the P-type doped layer PL 1 and the N-type doped layer NL 1 .

In this case, the area of the region RA 1 of the first ohmic contact OC 1 contacting with the P-type doped layer PL 1 will affect the actual current density received by the illumination portion. Therefore, the areas of regions RA 1 (or RA 2 ) of the ohmic contacts OC 1 (or 0 C 2 ) contacting to the P-type doped layer PL 1 (or the N-type doped layer NL 1 ) of the illumination portions 110 A, 110 B, 110 C, 110 D, and 110 E can also be different and can correspond to the area ratio of the illumination portions 110 A, 110 B, 110 C, 110 D, and 110 E so as to adjust the amplitude of the current density. For example, the area of the region RA 1 of the ohmic contact OC 1 contacting the P-type doped layer in the first illumination portion 210 A can be different from the area of the region RA 1 of the ohmic contact OC 1 contacting the P-type doped layer in the second illumination portion 210 B.

Also, the area of the region RA 2 of the second ohmic contact OC 2 contacting with the N-type doped layer NL 1 may also affect the actual current density received by the LED. Therefore, in some other embodiments, the area of the region RA 2 of the second ohmic contact OC 2 contacting the N-type doped layer NL 1 in the first illumination portion 210 A may also be different from the area of the region RA 2 of the another ohmic contact OC 2 contacting the N-type doped layer NL 1 in the second illumination portion 210 B.

In addition, in some embodiments, since sizes of the illumination portions 110 A and 110 E may be quite different, the display device 10 may further include a diffuser for diffusing the light emitted from the sub-pixels 100 ( 1 , 1 ) to 100 (M,N) so as to mitigate the issue of mura caused by the repeated patterns of the illumination portions of the sub-pixels 100 ( 1 , 1 ) to 100 (M,N).

In FIG. 2 , the driving units 120 A, 120 B, 120 C, 120 D, and 120 E can drive the groups of LEDs 110 A, 110 B, 110 C, 110 D, and 110 E with currents of different intensities to present different grey levels, however, in some other embodiments, the driving units 120 A, 120 B, 120 C, 120 D, and 120 E can drive the groups of LEDs 110 A, 110 B, 110 C, 110 D, and 110 E with different duty ratios to emit light at different grey levels.

FIG. 5 shows a sub-pixel 200 according to one embodiment of the present disclosure. In some embodiments, the sub-pixel 200 can be used in the display device 10 to replace each of the sub-pixels 100 ( 1 , 1 ) to 100 (M,N). In FIG. 5 , each of the driving units 220 A, 220 B, 220 C, 220 D, 220 E can drive the corresponding illumination portion 210 A, 210 B, 210 C, 210 D and 210 E to emit light at the different grey levels with a constant current by adjusting the duty ratio of the constant current according to a data signal.

The driving units 220 A, 220 B, 220 C, 220 D, and 220 E can have the same structure. For example, the driving unit 220 A can include a pulse width modulation circuit 222 and a driving circuit 224 . The pulse width modulation circuit 222 can receive the data signal SIG DA and generate a pulse signal SIG PA with a duty ratio determined by the data signal SIG DA . The driving circuit 224 is coupled to the pulse width modulation circuit 222 and the LED of the corresponding illumination portion. The driving circuit 224 can generate a constant current with the duty ratio according to the pulse signal SIG PA .

FIG. 7 shows the duty ratios of the current I D for expressing different grey levels according to one embodiment. In FIG. 7 , the duty ratios can be calculated by B/A, C/A, D/A, while A represents the time length of a frame, and B, C, and D represent the time lengths that the LED is driven.

In FIG. 7 , when the data signal SIG DA is corresponding to the brightest grey level, the pulse width modulation circuit 222 may generate the pulse signal SIG PA with a 100% duty ratio. When the data signal SIG DA is corresponding to the second brightest grey level, the pulse width modulation circuit 222 may generate the pulse signal SIG PA with a 66.7% duty ratio. When the data signal SIG DA is corresponding to the third brightest grey level, the pulse width modulation circuit 222 may generate the pulse signal SIG PA with a 33.3% duty ratio. Also, when the data signal SIG DA is corresponding to the least grey level, the pulse width modulation circuit 222 may generate the pulse signal SIG PA with a 0% duty ratio.

In this case, the driving unit 220 A can control the illumination portion 210 A to express four different grey levels by adjusting the duty ratio of the constant current I D . Therefore, the amplitude of the current I D can be predetermined properly, preventing the color shift issue caused by small currents.

Also, in FIG. 5 , the driving units 220 A, 220 B, 220 C, 220 D, and 220 E can be coupled to different data lines DLA, DLB, DLC, DLD, and DLE, and the data signals SIG DA to SIG DE can be serial digital signals for reducing the number of input ports of the driving units 220 A, 220 B, 220 C, 220 D, 220 E and simplifying the routing.

In FIG. 3 and FIG. 5 , the sub-pixels 200 and 300 both include five illumination portions, however, in some other embodiments, the sub-pixel may include more or less illumination portions according to the system requirement.

FIG. 8 shows a sub-pixel 300 according to one embodiment of the present disclosure. In some embodiments, the sub-pixel 300 can be used in the display device 10 to replace each of the sub-pixels 100 ( 1 , 1 ) to 100 (M,N). In FIG. 8 , each of the driving units 320 A, 320 B, 320 C, and 320 D can drive the corresponding illumination portions 310 A, 310 B, 310 C, and 310 D to emit light at the different grey levels by adjusting both the amplitude of the current and the duty ratio of the current.

In FIG. 8 , each of the driving units 320 A, 320 B, 320 C, and 320 D can be coupled to two data lines for receiving two data signal. For example, the driving units 320 A can be coupled to the data lines DLA 1 and DLA 2 , the driving units 320 B can be coupled to the data lines DLB 1 and DLB 2 , the driving units 320 C can be coupled to the data lines DLC 1 and DLC 2 , and the driving units 320 D can be coupled to the data lines DLD 1 and DLD 2 .

The driving units 320 A, 320 B, 320 C, and 320 D can have the same structure. For example, the driving unit 320 A can include a pulse width modulation circuit 322 and a driving circuit 324 . The pulse width modulation 322 can receive a first data signal SIG DA1 and generate a pulse signal SIG PA with a duty ratio determined by the first data signal SIG DA1 . Also, the driving circuit 324 can be coupled to the pulse width modulation circuit 322 and the LED of the corresponding illumination portion 310 A. The driving circuit 324 can generate the current I D according to a second data signal SIG DA2 , and output the current with the duty ratio determined by the pulse signal SIG PA . That is, the driving units 320 A, 320 B, 320 C, and 320 D can drive the illumination portions 310 A, 310 B, 310 C, and 310 D to express different grey levels by adjusting both the duty ratio and the amplitude of the current.

Furthermore, in some embodiments, the area ratio of the illumination portions 310 A, 310 B, 310 C and 310 D can be 1:8:64:512. Also, each of the driving units 320 A, 320 B, 320 C, and 320 D can drive the corresponding illumination portion to express eight grey levels. For example, the driving unit 320 A coupled to the illumination portion 310 A can drive the illumination portion 310 A to express eight grey levels, and the driving unit 320 B coupled to the illumination portion 310 B can drive the illumination portion 310 B to express eight grey levels. In this case, the illumination portions 310 A and 310 B will be able to present 64 grey levels, and the illumination portions 310 A, 310 B, 310 C, and 310 D will be able to present 4096 grey levels in total.

Table 1 shows the amplitude and the duty ratio of the current generated by the driving unit 320 A for presenting the eight grey levels.

That is, to present the brightest grey level, the driving unit 320 A can drive the illumination portion 310 A by providing the current with the first amplitude (1) and a 100% duty ratio. Also, the driving unit 320 A can drive the illumination portion 310 A to express a second grey level by providing the current with the second amplitude (6/7) and a 100% duty ratio, the driving unit 320 A can drive the illumination portion 310 A to express a third grey level by providing the current with the third amplitude (5/7) and a 100% duty ratio, and the driving unit 320 A can drive the illumination portion 310 A to express a fourth grey level by providing the current with the fourth amplitude (4/7) and a 100% duty ratio. Also, the driving unit 320 A can drive the illumination portion 310 A to express a fifth grey level by generating the current with the second amplitude (6/7) and a 50% duty ratio, the driving unit 320 A can drive the illumination portion 310 A to express a sixth grey level by providing the current with the fourth amplitude (4/7) and a 50% duty ratio, and the driving unit 320 A can drive the illumination portion 310 A to express a seventh grey level by providing the current with the third amplitude (5/7) and a 20% duty ratio.

In this case, by adjusting the duty ratio, the driving unit 320 A can drive the illumination portion 310 A to present eight grey levels with currents having amplitude of 4 different levels without using low current, thereby preventing the color shift issue caused by small currents.

Furthermore, in table 1, to present the least grey level, the driving unit 320 A can control the illumination portion 310 A by providing the current with the first amplitude (1) and a 0% duty ratio. However, in some other embodiments, the driving unit 320 may also simply not drive the illumination portion 310 A by not providing the current.

In some embodiments, the driving units 320 B, 320 C, and 320 D can use similar approaches to drive the illumination portions 310 B, 310 C, and 310 D. In this case, the 8 different grey levels presented by each illumination portion 310 A, 310 B, 310 C, and 310 D can be generated by 3 bits, then the grey level presented by the illumination portions 310 A, 310 B, 310 C, and 310 D can be determined by 12 bits. In this case, the illumination portion 310 A can be controlled by the 3 least significant bits of the 12 bits, and the illumination portion 310 D can be controlled by the 3 most significant bits of the 12 bits. Therefore, the sub-pixel 300 would be able to present 2 12 (4096) grey levels in total.

FIG. 9 shows a method 400 for operating a sub-pixel in a display device according to one embodiment. The method 400 includes steps S 410 and S 420 .

S 410 : providing at least one light emitting unit in the sub-pixel; and

S 420 : illuminating at least one of the plurality of illumination portions to express the grey level of the sub-pixel.

In some embodiments, the light emitting unit 110 can be provided in the sub-pixel 100 ( 1 , 1 ) in step S 410 , and the illumination portions 110 A, 110 B, 110 C, 110 D and 110 E can be illuminated in step S 420 . In some embodiments, step S 420 can be performed adjusting the amplitudes of the currents provided to the illumination portions 110 A, 110 B, 110 C, 110 D and 110 E. For example, the illumination portion 110 A can be driven to express different grey levels with currents of different amplitude as shown in FIG. 4 .

Furthermore, the illumination portions 110 A, 110 B, 110 C, 110 D and 110 E can be illuminated independently. For example, the current provided to the illumination portion 110 A and the current provided to the illumination portion 110 B may have different amplitude. In some other embodiments, if the method 400 is used to operate the sub-pixel 200 in FIG. 5 , then step S 420 can be performed by adjusting the duty ratios of the currents provided to the illumination portions 210 A, 210 B, 210 C, 210 D, and 210 E. For example, the illumination portion 210 A can be driven to express different grey levels with currents of different duty ratios as shown in FIG. 5 .

Also, the illumination portions 210 A, 210 B, 210 C, 210 D and 210 E can be illuminated independently. For example, the current provided to the illumination portion 210 A and the current provided to the illumination portion 210 B may have different duty ratios.

In some other embodiments, if the method 400 is used to operate the sub-pixel 300 in FIG. 8 , then step S 420 can be performed by adjusting the amplitudes and the duty ratios of the currents provided to the illumination portions 310 A, 310 B, 310 C, and 310 D. For example, the illumination portion 310 A can be driven to express different grey levels with currents of different amplitudes and different duty ratios as shown in table 1.

Also, the illumination portions 310 A, 310 B, 310 C, and 310 D can be illuminated independently. For example, the current provided to the illumination portion 310 A and the current provided to the illumination portion 310 B may have different amplitudes and different duty ratios.

In summary, the sub-pixels and the methods for expressing a grey level of a sub-pixel in a display device provided by the embodiments of the present disclosure can present different grey levels by controlling the brightness presented by a plurality of illumination portions. Therefore, the sub-pixels and the display device are able to present much more grey levels in different frames with a flexible design compared with prior art. Furthermore, by controlling the grey level of each illumination portion with the current having proper amplitude and a proper duty ratio, the color shift issue caused by small currents can be prevented.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the disclosure. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.