Backlight module and display device thereof

Abstract

The invention discloses a backlight module and a display device thereof. The backlight module includes a white light emitting diode, a first light emitting diode driver, and a second light emitting diode driver. The white light emitting diode comprises a blue light crystal grain, a green light crystal grain and a red color conversion material. The first light emitting diode driver provides a first driving current for driving the blue light crystal grain based on the first control signal. The second light emitting diode driver provides a second driving current for driving the green light crystal grain based on the second control signal. And when the brightness of the white backlight is greater than or equal to the preset brightness, the ratio of the second driving current to the first driving current is fixed as a preset ratio. When the brightness of the white backlight is smaller than the preset brightness, the ratio of the second driving current to the first driving current is increased along with reduction of the brightness.

Description

Technical Field

[0001] The present invention relates to a light emitting device, and in particular to a backlight module and a display device thereof. Background Art

[0002] As we all know, white light is a mixture of multiple colors. White light-emitting diodes (LEDs) are light-emitting components that produce white light by combining three wavelengths of light: red, green, and blue. Alternatively, a blue LED (such as gallium nitride, InGaN) is combined with a green LED (such as gallium nitride, GaN) and a red color-conversion material is added. By adjusting the brightness ratio of the blue and green lights and the concentration of the red color-conversion material, the desired white light effect can be achieved.

[0003] The light mixing method of dual-die white light emitting diodes (LEDs) with a red color conversion material effectively leverages the human eye's sensitivity to different wavelengths, creating an effect visually close to natural white light. For example, a dual-die design consists of a blue LED (e.g., InGaN) + a green LED (e.g., GaP). Current dual-die white LEDs (blue + green) are driven using direct current (DC) mode. When the brightness is reduced to low levels, the wavelength of the green light shifts, causing a significant color shift, resulting in a noticeable reddish tint. Summary of the Invention

[0004] The present invention provides a backlight module and a display device thereof, which can reduce the problem of obvious reddishness when the backlight brightness is low.

[0005] The backlight module of the present invention includes at least one white light emitting diode, a first light emitting diode driver, and a second light emitting diode driver. The white light emitting diode is used to provide a white backlight and includes a blue light emitting diode, a green light emitting diode, and a red color conversion material. The first light emitting diode driver is coupled to the blue light emitting diode and receives a first control signal to provide a first driving current for driving the blue light emitting diode based on the first control signal. The second light emitting diode driver is coupled to the green light emitting diode and receives a second control signal to provide a second driving current for driving the green light emitting diode based on the second control signal. When the brightness of the white backlight represented by the first control signal and the second control signal is greater than or equal to the preset brightness, the ratio of the second driving current to the first driving current is fixed to the preset ratio. Moreover, when the brightness of the white backlight represented by the first control signal and the second control signal is less than the preset brightness, the ratio of the second driving current to the first driving current increases from the preset ratio as the brightness decreases.

[0006] A display device according to the present invention includes a control circuit and a backlight module. The control circuit receives a brightness control signal to provide a first control signal and a second control signal. The backlight module is coupled to the control circuit and includes at least one white light emitting diode (LED), a first LED driver, and a second LED driver. The white light emitting diode (LED) provides white backlight and includes a blue light emitting diode (LED), a green light emitting diode (LED), and a red color conversion material. The first LED driver is coupled to the blue light emitting diode (LED) and receives a first control signal to provide a first drive current for driving the blue light emitting diode based on the first control signal. The second LED driver is coupled to the green light emitting diode (LED) and receives a second control signal to provide a second drive current for driving the green light emitting diode based on the second control signal. When the brightness of the white backlight indicated by the first and second control signals is greater than or equal to a preset brightness, the ratio of the second drive current to the first drive current is fixed at a preset ratio. Furthermore, when the brightness of the white backlight indicated by the first and second control signals is less than the preset brightness, the ratio of the second drive current to the first drive current increases from the preset ratio as the brightness decreases.

[0007] Based on the foregoing, the backlight module and display device of the present invention, when the brightness of the white backlight is lower than a predetermined brightness, controls the ratio of the second drive current to the first drive current via the first and second control signals to increase from the predetermined ratio as the brightness decreases. This results in the chromaticity, which would otherwise decrease significantly with the current reduction, being improved due to the increase in the brightness of the green light caused by the increase in the second drive current. Consequently, the color shift of the image caused by reducing the brightness of the white backlight can be alleviated.

[0008] In order to make the above features and advantages of the present invention more clearly understood, embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 FIG. 1 is a system diagram of a display device according to an embodiment of the present invention.

[0010] Figure 2 FIG. 4 is a system diagram of a display device according to another embodiment of the present invention.

[0011] Description of reference numerals:

[0012] 10, 20: Host system

[0013] 100, 200: Display device

[0014] 110, 210: Control circuit

[0015] 111, 211: Timing controller

[0016] 120, 130, 220, 230: LED drivers

[0017] 140: White light emitting diode

[0018] 141: Blue light crystal

[0019] 142: Green Light Crystal

[0020] 143: Red color conversion material

[0021] 150: Scan driver

[0022] 160: Data drive

[0023] 170: Display panel

[0024] 212: Microcontroller

[0025] BLM1, BLM2: backlight modules

[0026] Data_im: image data

[0027] Data_p: Display data

[0028] Idef1, Idef2: preset current values

[0029] Idr1, Idr2: driving current

[0030] Lwb: white backlight

[0031] PWMi1, PWMi2, PWMa1, PWMa2: pulse width signals

[0032] PWMin: input pulse width signal

[0033] Scan: Scan signal

[0034] SETi1, SETi2: current setting signal

[0035] Vdata: data voltage

[0036] Xsc1, Xsc2: control signals DETAILED DESCRIPTION

[0037] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. It will be further understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and the present invention, and will not be interpreted as idealized or overly formal unless explicitly defined as such herein.

[0038] It should be understood that although the terms "first," "second," "third," etc., may be used herein to describe various elements, components, regions, layers, and / or portions, these elements, components, regions, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or portion from another element, component, region, layer, or portion. Thus, a "first element," "component," "region," "layer," or "portion" discussed below may be referred to as a second element, component, region, layer, or portion without departing from the teachings herein.

[0039] The terms used herein are for the purpose of describing specific embodiments only and are not restrictive. As used herein, unless the content clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms, including "at least one". "Or" means "and / or". As used herein, the term "and / or" includes any and all combinations of one or more of the relevant listed items. It should also be understood that when used in this specification, the terms "include" and / or "including" specify the presence and / or parts of the features, regions, entireties, steps, operations, elements, components and / or parts, but do not exclude the presence or addition of one or more other features, regions, entireties, steps, operations, elements, components and / or combinations thereof.

[0040] Figure 1 This is a system diagram of a display device according to an embodiment of the present invention. Figure 1 In this embodiment, the display device 100 includes, for example, a control circuit 110, LED drivers 120 and 130 (corresponding to a first LED driver and a second LED driver), at least one white light LED 140 (one is shown here as an example), a scan driver 150, a data driver 160, and a display panel 170, wherein the LED drivers 120, 130, and the white light LED 140 are used to constitute a backlight module BLM1.

[0041] The control circuit 110 is coupled to the host system 10 to receive a brightness control signal (e.g., an input pulse width signal PWMin) and image data Data_im from the host system 10, and provides a first control signal (e.g., a pulse width signal PWMi1 (corresponding to a first pulse width signal) and a current setting signal SETi1 (corresponding to a first current setting signal)) and a second control signal (e.g., a pulse width signal PWMi2 (corresponding to a second pulse width signal) and a current setting signal SETi2 (corresponding to a second current setting signal)) based on the input pulse width signal PWMin, and provides display control signals Xsc1 and Xsc2 and display data Data_p based on the image data Data_im.

[0042] The scan driver 150 is coupled between the control circuit 110 and the display panel 170 to provide a plurality of scan signals Scan to the display panel 170 based on the display control signal Xsc1, thereby driving the display panel 170. The data driver 160 is coupled between the control circuit 110 and the display panel 170 to provide a plurality of data voltages Vdata to the display panel 170 based on the display control signal Xsc2 and display data Data_p, thereby writing an image into the display panel 170.

[0043] The white light emitting diode 140 is used to provide white backlight Lwb to the display panel 170 and includes a blue light emitting chip 141, a green light emitting chip 142, and a red color conversion material 143. The light emitting diode driver 120 is coupled between the control circuit 110 and the blue light emitting chip 141, and receives a pulse width signal PWMi1 and a current setting signal SETi1. Based on the pulse width signal PWMi1 and the current setting signal SETi1, the driver 120 provides a driving current Idr1 (corresponding to a first driving current) for driving the blue light emitting chip 141.

[0044] The LED driver 130 is coupled to the control circuit 110 and the green chip 142 and receives the pulse width signal PWMi2 and the current setting signal SETi2 to provide a driving current Idr2 (corresponding to the second driving current) for driving the green chip 142 based on the pulse width signal PWMi2 and the current setting signal SETi2.

[0045] When the brightness of the white backlight Lwb represented by the pulse width signal PWMi1 and / or the pulse width signal PWMi2 (equivalent to the brightness value represented by the input pulse width signal PWMin) is greater than or equal to the preset brightness (for example, 40%), the ratio of the driving current Idr2 to the driving current Idr1 is fixed to a preset ratio (for example, 62.5%), and when the brightness of the white backlight Lwb represented by the pulse width signal PWMi1 and / or the pulse width signal PWMi2 is less than the preset brightness (for example, 40%), the ratio of the driving current Idr2 to the driving current Idr1 increases from the preset ratio (for example, 62.5%) as the brightness decreases.

[0046] As mentioned above, dual-die white light-emitting diodes typically use a blue LED (e.g., gallium nitride, InGaN) die and a green LED (e.g., gallium nitride, GaN) die mixed with a red color conversion material. Color shift is a characteristic of nitride LEDs. Due to the quantum confinement Stark effect (QCSC) / screening effect, the energy gap in the well region increases, shortening the wavelength of light. Due to the wavelength difference, green light is more affected than blue light. Consequently, the wavelength of the light wave increases at low currents, and the chromaticity decreases significantly as the current decreases, resulting in color shift. Therefore, when the brightness of the white backlight Lwb is less than a predetermined brightness (e.g., 40%), the ratio of the driving current Idr2 to the driving current Idr1 increases from the predetermined ratio (e.g., 62.5%) as the brightness decreases. This results in a chromaticity that would otherwise decrease significantly with current reduction, but is improved by the increased green light brightness caused by the increased driving current Idr2. This can alleviate the color shift in the image caused by reducing the brightness of the white backlight.

[0047] In this embodiment, the control circuit 110 includes a timing controller 111. The timing controller 111 provides display control signals Xsc1 and Xsc2 and display data Data_p based on image data Data_im, and sequentially provides pulse width signals PWMi1 and PWMi2 based on an input pulse width signal PWMin, and sequentially provides current setting signals SETi1 and SETi2.

[0048] In this embodiment, the LED driver 120 provides a driving current Idr1 based on the pulse width signal PWMi1 and a preset current value Idef1 (corresponding to a first preset current value), and the LED driver 130 provides a driving current Idr2 based on the pulse width signal PWMi2 and a preset current value Idef2 (corresponding to a second preset current value). The preset current value Idef1 is stored in the LED driver 120, and the preset current value Idef2 is stored in the LED driver 130.

[0049] In this embodiment, the pulse width signals PWMi1 and PWMi2 correspond to the brightness of the white backlight Lwb. For example, when the brightness of the white backlight Lwb is 40%, the pulse widths of the pulse width signals PWMi1 and PWMi2 are 40%, and so on.

[0050] In this embodiment, the LED driver 120 sets a preset current value Idef1 based on the current setting signal SETi1, and the LED driver 130 sets a preset current value Idef2 based on the current setting signal SETi2. Specifically, as shown in Tables 1 and 2, the preset current value Idef1 is fixed at an upper current limit (e.g., 16 milliamperes (mA)). When the brightness of the white backlight Lwb is greater than or equal to a preset brightness (e.g., 40%), the preset current value Idef2 is fixed at a starting current value (e.g., 10 milliamperes (mA)) that is less than the upper current limit (e.g., 16 milliamperes (mA)). When the brightness of the white backlight Lwb is less than the preset brightness (e.g., 40%), the preset current value Idef2 increases from the starting current value (e.g., 10 milliamperes (mA)) to the upper current limit (e.g., 16 milliamperes (mA)) as the brightness decreases. For example, when the brightness of the white backlight Lwb is greater than or equal to the preset brightness (for example, 100-40%), the preset current value Idef1 is 16 mA, and the preset current value Idef2 is 10 mA; when the brightness of the white backlight Lwb is greater than or equal to the preset brightness (for example, 30%), the preset current value Idef1 is still set to 16 mA, and the preset current value Idef2 is set to 10.1 mA. The rest can be referred to as shown in Table 1 and Table 2, and will not be repeated here.

[0051] Table 1

[0052]

[0053]

[0054] Table 2

[0055]

[0056] Figure 2 This is a system diagram of a display device according to another embodiment of the present invention. Figure 1 and Figure 2 , wherein the display device 200 is substantially the same as the display device 100, and the difference lies in the control circuit 210, and the LED drivers 220, 230, wherein the LED drivers 220, 230 and the white light emitting diode 140 are used to constitute the backlight module BLM2, wherein the same or similar components are labeled with the same or similar numbers.

[0057] In this embodiment, the control circuit 210 is coupled to the host system 20 to receive an input pulse width signal PWMin and image data Data_im from the host system 20, to provide a first control signal (e.g., a pulse width signal PWMa1 (corresponding to the first pulse width signal)) and a second control signal (e.g., a pulse width signal PWMa2 (corresponding to the second pulse width signal)) based on the input pulse width signal PWMin, and to provide display control signals Xsc1 and Xsc2 and display data Data_p based on the image data Data_im.

[0058] The control circuit 210 includes a timing controller 211 and a microcontroller 212. The timing controller 211 provides display control signals Xsc1 and Xsc2 and display data Data_p based on image data Data_im, and the microcontroller 220 sequentially provides pulse width signals PWMa1 and PWMa2 based on an input pulse width signal PWMin.

[0059] The LED driver 220 is coupled between the control circuit 210 and the blue chip 141 and receives a pulse width signal PWMa1 to provide a driving current Idr1 (corresponding to a first driving current) based on the pulse width signal PWMa1 and a preset current value Idef1 (corresponding to a first preset current value). The LED driver 230 is coupled between the control circuit 210 and the green chip 142 and receives a pulse width signal PWMa2 to provide a driving current Idr2 (corresponding to a second driving current) based on the pulse width signal PWMa2 and a preset current value Idef2 (corresponding to a second preset current value). The preset current value Idef1 is stored in the LED driver 220, and the preset current value Idef2 is stored in the LED driver 230. Furthermore, the preset current values ​​Idef1 and Idef2 are fixed to a current upper limit (e.g., 16 milliamperes (mA)).

[0060] In this embodiment, as shown in Tables 3 and 4, the pulse-width signal PWMa1 corresponds to the brightness of the white backlight Lwb. Furthermore, when the brightness of the white backlight Lwb is greater than or equal to a predetermined brightness (e.g., 40%), the pulse-width signal PWMa2 corresponds to the brightness of the white backlight Lwb. Furthermore, when the brightness of the white backlight Lwb is less than the predetermined brightness (e.g., 40%), the pulse-width signal PWMa2 corresponds to the product of the brightness of the white backlight Lwb and a pulse-width adjustment value, where the pulse-width adjustment value increases as the brightness decreases and is less than or equal to 1. For example, when the brightness of the white backlight Lwb is 40%, the pulse width of the pulse-width signal PWMa1 is 40%, and the pulse width of the pulse-width signal PWMa2 is 40%×0.625. When the brightness of the white backlight Lwb is 20%, the pulse width of the pulse-width signal PWMa1 is 20%, and the pulse width of the pulse-width signal PWMa2 is 20%×0.669. The rest can be referred to as shown in Tables 3 and 4, and will not be repeated here.

[0061] Table 3

[0062]

[0063] Table 4

[0064]

[0065]

[0066] In summary, the backlight module and display device of the present invention, when the brightness of the white backlight is lower than a predetermined brightness, controls the ratio of the second drive current to the first drive current via the first and second control signals to increase from the predetermined ratio as the brightness decreases. This results in the chromaticity, which would otherwise decrease significantly with the current reduction, being improved due to the increase in the brightness of the green light caused by the increase in the second drive current. Consequently, the color shift of the image caused by reducing the brightness of the white backlight to a low brightness can be alleviated.

[0067] Although the present invention has been disclosed above with reference to the embodiments, they are not intended to limit the present invention. Any person skilled in the art may make slight changes and modifications without departing from the concept and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A backlight module, comprising: At least one white light emitting diode, for providing a white backlight, and comprising a blue light die, a green light die, and a red color conversion material; a first LED driver coupled to the blue light chip and receiving a first control signal to provide a first driving current for driving the blue light chip based on the first control signal; as well as a second LED driver coupled to the green light chip and receiving a second control signal to provide a second driving current for driving the green light chip based on the second control signal; When the brightness of the white backlight indicated by the first control signal and the second control signal is greater than or equal to a preset brightness, a ratio of the second driving current to the first driving current is fixed to a preset ratio, and When the brightness of the white backlight indicated by the first control signal and the second control signal is lower than the preset brightness, the ratio of the second driving current to the first driving current increases from the preset ratio as the brightness decreases.

2. The backlight module according to claim 1 , wherein the first control signal comprises a first pulse width signal, and the first LED driver provides the first driving current based on the first pulse width signal and a first predetermined current value, and The second control signal includes a second pulse width signal, and the second LED driver provides the second driving current based on the second pulse width signal and a second preset current setting.

3. The backlight module according to claim 2 , wherein the first control signal further comprises a first current setting signal, and the first LED driver sets the first preset current value based on the first current setting signal, and The first control signal further includes a second current setting signal, and the second LED driver sets the second preset current value based on the second current setting signal.

4. The backlight module as claimed in claim 3, wherein the first preset current value is fixed to a current upper limit value, and When the brightness of the white backlight is greater than or equal to the preset brightness, the second preset current value is fixed to a current starting value that is less than the current upper limit value, and when the brightness of the white backlight is less than the preset brightness, the second preset current value increases from the current starting value to the current upper limit value as the brightness decreases. 5 . The backlight module as claimed in claim 4 , wherein the first pulse width signal and the second pulse width signal correspond to the brightness of the white backlight.

6. The backlight module as claimed in claim 2, wherein the first pulse width signal corresponds to the brightness of the white backlight, and When the brightness of the white backlight is greater than or equal to the preset brightness, the second pulse width signal corresponds to the brightness of the white backlight, and when the brightness of the white backlight is less than the preset brightness, the second pulse width signal corresponds to the product of the brightness of the white backlight and a pulse width adjustment value, wherein the pulse adjustment value increases as the brightness decreases, and the pulse width adjustment value is less than or equal to 1.

7. A display device comprising: a control circuit receiving a brightness control signal to provide a first control signal and a second control signal; A backlight module is coupled to the control circuit and includes: At least one white light emitting diode, for providing a white backlight, and comprising a blue light die, a green light die and a red color conversion material; a first LED driver coupled to the blue light chip and receiving the first control signal to provide a first driving current for driving the blue light chip based on the first control signal; and a second LED driver coupled to the green light chip and receiving the second control signal to provide a second driving current for driving the green light chip based on the second control signal; When the brightness of the white backlight indicated by the first control signal and the second control signal is greater than or equal to a preset brightness, a ratio of the second driving current to the first driving current is fixed to a preset ratio, and When the brightness of the white backlight indicated by the first control signal and the second control signal is lower than the preset brightness, the ratio of the second driving current to the first driving current increases from the preset ratio as the brightness decreases.

8. The display device of claim 7 , wherein the first control signal comprises a first pulse width signal, and the first LED driver provides the first driving current based on the first pulse width signal and a first predetermined current value, and The second control signal includes a second pulse width signal, and the second LED driver provides the second driving current based on the second pulse width signal and a second preset current setting.

9. The display device as claimed in claim 8, wherein the first control signal further comprises a first current setting signal, and the first LED driver sets the first preset current value based on the first current setting signal, and The first control signal further includes a second current setting signal, and the second LED driver sets the second preset current value based on the second current setting signal. 10 . The display device as claimed in claim 9 , wherein the control circuit comprises a timing controller for sequentially providing the first pulse width signal and the second pulse width signal, and sequentially providing the first current setting signal and the second current setting signal.

11. The display device as claimed in claim 9, wherein the first preset current value is fixed to a current upper limit value, and When the brightness of the white backlight is greater than or equal to the preset brightness, the second preset current value is fixed to a current starting value that is less than the current upper limit value, and when the brightness of the white backlight is less than the preset brightness, the second preset current value increases from the current starting value to the current upper limit value as the brightness decreases. 12 . The display device as claimed in claim 11 , wherein the first pulse width signal and the second pulse width signal correspond to the brightness of the white backlight.

13. The display device as claimed in claim 8, wherein the first pulse width signal corresponds to the brightness of the white backlight, and When the brightness of the white backlight is greater than or equal to the preset brightness, the second pulse width signal corresponds to the brightness of the white backlight, and when the brightness of the white backlight is less than the preset brightness, the second pulse width signal corresponds to the product of the brightness of the white backlight and a pulse width adjustment value, wherein the pulse adjustment value increases as the brightness decreases, and the pulse width adjustment value is less than or equal to 1. 14 . The display device as claimed in claim 13 , wherein the control circuit comprises a microcontroller for providing the first pulse width signal and the second pulse width signal.

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