Transreflective display apparatus and driving method thereof

1. Field of Invention

The present invention relates to a display apparatus, and, in particularly, relates to a transreflective display apparatus and driving method thereof.

2. Description of Related Art

There are more and more electronic devices have display devices, such as cell phones, personal digital assistants (PDAs), and laptop computers. The display devices are requested to be thin and/or light in order to save the volume and the cost of the electronic devices. To satisfy these requirements, various flat panel displays (FPDs) have been developed as alternatives to more conventional cathode ray tube displays.

The display panels of the FPDs are classified as transmissive display panels, reflective display panels, and transreflective display panels. The transmissive display panel uses a backlight module disposed at the back thereof to serve as a light source. The reflective display panel uses ambient light or a light source in the front of the panel. The transreflective display panel can use a backlight module and/or the ambient light as the light source.

FIG. 1 illustrates a diagram of a transreflective display panel. Each pixel of the transreflective display panel includes a reflective area, made of reflective material, and a transmissive area, made of transparent material. When the ambient light intensity around the display panel is strong enough, e.g. higher than a threshold value, the display panel is in a reflective mode that the ambient light is used as the light source and the display panel emanates lights from the reflective area. When the ambient light intensity is not strong, the display panel is in a transmissive mode that the backlight module is used as the light source and the display panel emanates lights from the transmissive area.

However, while the transreflective display panel is in the transmissive mode, the backlight module is started to provide a backlight, but the ambient light still exists to be reflected from the reflective area. Hence, some gray levels representing the darker pixels can not be displayed distinguishably. FIG. 2 shows a voltage-to-transparency (V-T) curve of the transreflective display panel. The dashed line L′ shows the distorted V-T curve, compared to the original solid line L without distortion. That is, while the voltage V 0 is applied to the pixel, transparency T 0 ′ of the distorted V-T curve L′ is actually displayed, instead of the expected transparency T 0 in the original V-T curve L, due to the reflected ambient light. Therefore, the low gray levels corresponding below the transparency T 0 ′ can not be distinguishably displayed as dark as desired. Therefore, it needs a good driving method for improving the above problems and further providing other advantages.

The present invention provides a driving method for a transreflective display apparatus which has a dual mode display panel. By this driving method, images can be displayed normally both in a reflective mode and in a transmissive mode, and the display quality of the display apparatus can be enhanced. In addition, the present invention also provides a transreflective display apparatus having the said advantages.

A driving method for a transreflective display apparatus is provided in the present invention. In the driving method, an ambient light intensity of the display apparatus is detected for determining a display mode of the display apparatus. If the ambient light intensity is greater than a predetermined value, the display mode is set to a reflective mode, else the display mode is set to a transmissive mode. Then, one of a plurality of voltage-to-transparency curves is selected according to the display mode and the ambient light intensity for driving the display apparatus.

In an embodiment of the foregoing driving method, the V-T curves include a transmissive mode V-T curve and a reflective mode V-T curve. If the display mode is the transmissive mode, and there exists some ambient light affecting the display quality (or the ambient light intensity is larger than a low threshold), the transmissive mode V-T curve is selected.

A transreflective display apparatus is provided in the present invention. The display apparatus includes a display panel, an ambient light detector, a backlight module, a timing controller and a gamma voltage generator. The display panel having dual display mode is used for display an image. The ambient light detector detects an ambient light intensity of the display apparatus, and thereby determines a display mode of the display apparatus according to the ambient light intensity, wherein the display mode is either a transmissive mode or a reflective mode. The backlight module provides a backlight when the display mode is the transmissive mode. The timing controller selects one of a plurality of voltage-to-transparency (V-T) curves according to the display mode and the ambient light intensity. Then, the timing controller controls the gamma voltage generator generates a plurality of gamma voltages according to the selected V-T curve.

In an embodiment of the foregoing display apparatus, the ambient light detector includes a photo sensor and a light controller. The photo sensor detects the ambient light intensity of the display apparatus to output an electronic signal. The light controller converts the electronic signal into a detection signal with digital form, such that the ambient light controller can determines the display mode according to the detection signal.

The present invention provides a driving method and a transreflective display apparatus that selects a proper voltage-to-transparency (V-T) curve to drive pixels on the display panel according to the ambient light intensity and the display mode. When the display apparatus is in the transmissive mode, the pixels having the lower gray levels can not be displayed distinguishably as a result of the existence of the ambient light. Hence, considering the influence of the ambient light, the V-T curves are designed for different display modes, even there are several V-T curves designed for the transmissive mode according to different ambient light intensity. Therefore, the display quality of the display apparatus can be enhanced by referring the proper voltage-to-transparency (V-T) curve.

It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 illustrates a diagram of a transreflective display panel.

FIG. 2 shows a voltage-to-transparency curve of the transreflective display panel.

FIG. 3A shows two voltage-to-transparency curves for the display apparatus according to an embodiment of the present invention.

FIG. 3B illustrates a flow chart of a method for selecting the V-T curve according to an embodiment of the present invention.

FIG. 4 shows a diagram of a plurality of the V-T curves according to an embodiment of the present invention.

FIG. 5 shows a block diagram of a transreflective display apparatus according to an embodiment of the present invention.

Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

In embodiments of the invention, a transreflective display apparatus has a display panel and a backlight module serving as a light source, wherein the backlight module can emit light into the display panel. FIG. 3A shows two voltage-to-transparency (V-T) curves VT 1 and VT 2 for the display apparatus according to an embodiment of the present invention. The display apparatus provides two different V-T curves, VT 1 and VT 2 , respectively for different display mode. Each V-T curve is determined by one set of gamma voltages, which are provided to the digital-to-analog converter of a source driver, such as the gamma voltages V 1 through Vn in the first V-T curve VT 1 , and the gamma voltages V 1 ′ through Vn′ in the second V-T curve VT 2 .

In order to distinguish the lower gray levels, one or more gamma voltages corresponding to the lower gray levels in the first V-T curve VT 1 are different to those corresponding to the same gray levels in the second V-T curve VT 2 . In FIG. 3A , the gamma voltage Vn corresponding to the lowest gray level of the first V-T curve VT 1 is different from the gamma voltage Vn′ corresponding to the lowest gray level of the second V-T curve VT 2 . In other words, for displaying the lowest gray level, the gamma voltage Vn′ provided by referring the second V-T curve VT 2 is greater than the gamma voltage Vn provided by referring the first V-T curve VT 1 . In an alternative embodiment, it should be noted that the digital-to-analog converter may generate more additional gamma voltages by interpolating the received gamma voltages V 1 , V 2 , . . . and Vn/Vn′, such that the lower gray levels corresponding between V(n−1) to Vn are different from the lower gray levels corresponding between V(n−1) to Vn′. The gamma voltages are generated by a resistor string for example. As shown in FIG. 3A , a terminal of a resistor string is coupled to a reference voltage Vref, and the other terminal of the resistor string is coupled to a ground voltage GND. According to the voltage division theorem, the resistor string can output several analog gamma voltages for driving the pixels on the display panel. Each of the gamma voltages drives the pixel at a corresponding transparency of the display panel. The first V-T curve VT 1 is determined by the first set of the gamma voltages V 1 through Vn; while the second V-T curve VT 2 is determined by the second set of the gamma voltages V 1 ′ through Vn′, wherein in the V-T curves VT 1 and VT 2 , the same reference numbers affixed to the symbol “V”, e.g. V 1 and V 1 ′, V 2 and V 2 ′, or Vn and Vn′, correspond to the same gray level. In this embodiment, although only one gamma voltage corresponding to the lowest gray level (representing the darkest pixel) is different between the two V-T curves VT 1 and VT 2 , in the alternative embodiments, more than one gamma voltages may be different between the two V-T curves VT 1 and VT 2 .

In the embodiment of the present invention, the display apparatus selects one of the V-T curves according to the display mode and the intensity of the ambient light. FIG. 3B illustrate a flow chart of a method for selecting the V-T curve. First, in step 301 , the display mode is determined, for example, by detecting the ambient light intensity. When the ambient light intensity is higher than a predetermined value, the display mode is set to the reflective mode, or else the display mode is set to the transmissive mode. In the reflective mode, the backlight module of the display apparatus is turned off, and the first V-T curve is applied for the digital-to-analog converter of the display apparatus to generate the proper gamma voltages. In the transmissive mode, the backlight module of the display apparatus is turned on.

In step 305 , it is detected whether there is still some ambient light. If there is still some ambient light, the ambient light may cause the darker pixels, having lower gray levels, indistinguishable. Hence, the second V-T curve VT 2 is applied for the display apparatus in step 307 , else the first V-T curve VT 1 is applied in step 303 . In the embodiment of the present invention, the gamma voltages provided by referring the second V-T curve VT 2 can drive the pixel at the transparencies which are above the critical transparency T 0 ′, and having small difference each other. In the transmissive mode with some ambient light, applying the second V-T curve VT 2 can display the lower gray levels distinguishably. In other embodiment, the step 305 is optional, and the transmissive mode uses the second V-T curve regardless of the ambient light. Some ambient light is defined if the intensity of the ambient light is larger than a low threshold.

As the foregoing description, although the said embodiment provides two V-T curves VT 1 and VT 2 for enhancing the display quality of the display apparatus under different display modes, in consideration with the ambient light intensity, a plurality of V-T curves can be also designed when the display apparatus is in the transmissive mode. In other word, when the display apparatus is set to the transmissive mode, the critical transparency T 0 ′ is changed as the ambient light intensity, which results in that the pixels driven by the gamma voltages, lower than a certain gamma voltage driving the pixel at the critical transparency T 0 ′, are displayed indistinguishably. The more the ambient light is, the higher the critical transparency T 0 ′ is, and the more the lower gray levels are displayed indistinguishably. Hence, more appreciate V-T curves are required to design.

FIG. 4 shows a diagram of a plurality of V-T curves according to an embodiment of the present invention. Referring to FIG. 4 , the plural V-T curves may be provided by the resistor string as illustrated in FIG. 3A or a programmable gamma voltage generator 402 as illustrated in FIG. 4 . There are three V-T curves, VT 1 , VT 2 and VT 3 illustrated in FIG. 4 , but more V-T curves may be used so that the present invention is not limited thereto. The V-T curve VT 3 is determined by the gamma voltages V 1 ″ through Vn″. Compared with the V-T curve VT 2 , the gamma voltages V(n−1)″ and Vn″ corresponding to the gray levels are different to the gamma voltages V(n−1)′ and Vn′ corresponding to the same gray levels. Similarly, the display apparatus determines which V-T curves to be applied to display images based on the display mode and/or the ambient light intensity. The programmable gamma voltage generator 402 is controlled by the timing controller 401 of the display apparatus for generating the gamma voltages based on the selected V-T curve.

FIG. 5 shows a block diagram of a transreflective display apparatus according to an embodiment of the present invention. The display apparatus includes a display panel 501 , a backlight module, an ambient light detector, a timing controller 401 and a programmable gamma voltage generator 402 . The ambient light detector includes a photo sensor 510 and a light controller 520 . The photo sensor 510 detects the ambient light to output the detection current I to the light controller 520 . The light controller 520 includes a current-to-voltage converter 502 and an analog-to-digital converter 503 for converting the detection current I into a detection signal and outputting the detection signal to the timing controller 401 . The ambient light detector then determines the display mode of the display apparatus, which is either the transmissive mode or the reflective mode, by the intensity of the ambient light. When the display mode is the transmissive mode, the backlight module would provide a backlight to the display panel, else the backlight module is turned off. The timing controller 401 selects one of the V-T curves based on the display mode and/or the intensity of the ambient light. The timing controller 401 receives the intensity of the ambient light and thereby controls the programmable gamma voltage generator 402 to generate a set of gamma voltages corresponding to the selected V-T curve. In another embodiment, the light controller 520 and the timing controller 401 can be integrated into an integrated circuit (IC).

In summary, the transreflective display apparatus can determine the display mode to be the transmissive mode or the reflective mode according to the ambient light intensity detected by the ambient light controller. When the display apparatus is in the transmissive mode, the darker pixels having the lower gray levels may not be displayed distinguishably, so that a plurality of V-T curves for different display modes are provided in the said embodiment, and a proper one among them can be selected according to the display mode and the ambient light intensity to drive the display panel. With regard to the V-T curve of the transmissive mode, the gamma voltages provided by referring the V-T curve of the transmissive mode can drive the pixels at the transparencies which are above the critical transparency associated with the ambient light intensity, and have small difference each other. As a result, the darker pixels can be displayed distinguishably and the display quality can be enhanced.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing descriptions, it is intended that the present invention covers modifications and variations of this invention if they fall within the scope of the following claims and their equivalents.