1. Field of Invention
The present invention relates to an apparatus and method for driving a display device, and more particularly to an apparatus and method for driving a display device via a single driving voltage generating circuit.
2. Description of Related Art
Since liquid crystal display (LCD) has many advantages such as light, thin, short, and small, with low energy consumption and low radiation, it has come to be widely used in recent years.
In the liquid crystal panel of an LCD display, the relationship between the voltage applied to the liquid crystal molecule (referred as driving voltage below) and the light transmittance of a pixel is a gamma curve, rather than a linear relationship. By correcting the gamma curve, the gray scale signal of the pixel and the light transmittance of the liquid crystal molecule can be made to have a near linear relation, thus, the displayed image for an LCD is more desirable.
In an LCD display, each display unit, i.e. a pixel, consists of three sub-pixels. Each sub-pixel is used to display one of the three primary colors of red (R), green (G), and blue (B). Depending on which primary color a sub-pixel displays, the corresponding gamma curve will be different. Referring to
In order to obtain different driving voltages to display red, green and blue, in the conventional technology, three R/G/B look-up tables and three gamma voltage generating circuits are used respectively to obtain three sets of driving voltages corresponding to the R/G/B gray scale signals to drive the liquid crystal molecules. However, this prior art requires a relatively large memory space for storing three look-up tables, and three gamma voltage generating circuits will dramatically increase the area of the drive circuit.
Thus, it is preferred to have an apparatus and method for driving a liquid crystal display, which only needs a relatively small storage space for a look-up table and a gamma voltage generating circuit to generate the required three sets of driving voltages.
One of the objects of the present invention is to provide an apparatus and method for a display device, which uses fewer look-up tables and small-size gamma voltage generating circuits to generate three sets of driving voltages.
In order to achieve the above object, the present invention provides an apparatus and method for a display device. A plurality of difference values between the gamma curves R, G, and B and the reference curve is stored in a look-up table. The reference curve can be any combination of the gamma curves R, G, and B, a calculation result of the gamma curves R, G, and B, or a combination thereof.
According to the look-up table, an identification bit and a gray scale signal, a selection signal SEL can be obtained. The selection signal is the binary value of the difference value. The identification bit is used for identifying that the gray scale signal is a red (R) gray scale signal, a green (G) gray scale signal, or a blue (B) gray scale signal. A most significant bit (MSB) signal is extracted from the gray scale signal. The MSB signal is the most significant bit of the gray scale signal.
N analog voltages are generated from a voltage source through voltage division, where, n=2(p+q), and p and q are respectively the number of bits of the selection signal and the MSB signal.
The selection signal and the MSB signal are decoded, so as to select one from the analog voltages and convert it to a driving voltage that is used to drive the display device.
With the above techniques and features, fewer look-up tables, small-size gamma voltage generating circuit and a digital-to-analog conversion circuit are required in the present invention to generate the three sets of driving voltages required by sub-pixels to display red, green, or blue. Thus, the circuit area can be significantly saved.
In order to make aforementioned and other objects, features and advantages of the present invention more comprehensible, preferred embodiments accompanied with appended drawings are described in detail as below.
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.
a shows a characteristic view of gamma curves R/G/B and the reference curve ref to the light transmittance.
b shows an enlarged view of a part of
In the present invention, a reference curve is found out according to three common or predetermined gamma curves R/G/B. The reference curve can be any combination of the three gamma curves, or a calculation result (such as average value) of the three gamma curves or a combination thereof. Then, the difference values between the reference curve and each gamma curve at every gray scale value are found out, and then are all stored in a look-up table. Thus, the signals required for gamma correction can be obtained according to the difference values between the reference curve and each corresponding gamma curve. Then, simpler source driving circuit is used to generate the driving voltages required by pixels to display red, green, or blue.
Again referring to
Then, difference values between the three gamma curves R, G, B and the reference curve ref at each gray scale value are found out. Taking
In the above Table 1, R difference value represents the difference values between the gamma curve R and the reference curve ref; G difference value represents the difference values between the gamma curve G and the reference curve ref; and B difference value represents the difference values between the gamma curve B and the reference curve ref. In Table 1, “0” represents that there is no difference between the gamma curve and the reference curve at that gray scale value. In this embodiment, the maximum of the difference value is 7, and the minimum is 0. For the sake of simplicity, only the R/G/B difference values corresponding to some gray scale values are listed in Table 1, and the R/G/B difference values corresponding to other gray scale values can be known with reference to
Referring to
Referring to
To sum up, it can be known that, in the present embodiment, the three gamma curves R/G/B can be derived by looking up the table so long as each of the difference values are stored. In the present embodiment, there is no need to store the three gamma curves R/G/B respectively, thus saving much more memory space.
Referring to
Then, a 3-bit selection signal SEL can be obtained via the LUT 210. The selection signal SEL is the binary value of the difference value in Table 1. In this embodiment, a 6-bit MSB (most significant bit) is extracted from the 8-bit gray scale signal IN by the MSB extracting unit 215. The architecture of the MSB extracting unit 215 is not particularly restricted herein, as long as it can achieve the required functionality. The 6-bit MSB and the 3-bit selection signal SEL will be input into the DAC 230.
A plurality of analog voltages V1-Vn (in this embodiment, n=29) is generated from the voltage source VDD by the gamma voltage generating circuit 220. For example, the gamma voltage generating circuit 220 includes n serial-connected resistors R_1-R_n. The analog voltages V1-Vn can be obtained from a voltage division on the voltage source VDD by the resistors R_1-R_n and then they are input into the DAC 230. The gamma voltage generating circuit 220 must be conformed to the reference curve ref, so as to perform gamma correction.
The DAC 230 receives the 6-bit MSB and the 3-bit selection signal SEL, and then combines them together to obtain a 9-bit signal. Then, the DAC 230 decodes the 9-bit signal, and selects one analog voltage from the analog voltages V1-Vn, and outputs an analog driving voltage V_driving.
The driving voltage V_driving generated by DAC 230 is provided to drive the sub-pixels of the liquid crystal display (LCD) panel of the display device.
Therefore, in this embodiment, the gamma correction is performed on the gray scale signal IN via the combination of the gamma voltage generating circuit 220 (conformed to the reference curve ref) and the DAC 230 (especially, receiving the 3-bit selection signal SEL), such that a near linear relationship exists between the gray scale signal IN and the light transmittance of the pixel.
In this embodiment, it is supposed that the gray scale signal is 8-bit. However, those skilled in the art will know that the present invention also can be applied to the gray scale signals of other bits. Besides, reference curve ref can also be defined as the smallest one, or any combination of the three gamma curves R, G, and B at each corresponding gray scale value.
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, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
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