This claims priority under 35 U.S.C. § 119 of Taiwan patent application No. 94109765, filed Mar. 29, 2005.
This invention relates to color displays, and more specifically, to a drive system and method for color displays.
In general, the light transmittance of a display such as a liquid crystal display (LCD) is different depending upon whether the viewer is looking at the picture (displayed image) squarely (directly) in front of the LCD or at an angle. This is because the incident light from different angles results in different retardation in the liquid crystal layer. Hence, the refractive index influence in the transmitted light will change according to different viewing angles and result in different transmittance when viewing from different angles. Consequently, an image displayed by the LCD may appear to have different brightnesses when viewed from different angles.
When various color pixels of the LCD (e.g., red pixel, green pixel, and blue pixel) having different brightnesses are mixed and viewed at different angles, color shift may occur, which means that the colors of a displayed image may look different at different angles.
a to 2c are curves showing the correlation between gray level value and the normalized light transmittance of red light, green light, and blue light at different viewing angles.
a illustrates dark state and bright state display signals for various pixels, according to a conventional driving technique.
b schematically illustrates a relationship between driving voltage and the display gray scale value.
c illustrates a relationship between the voltage across the upper and lower substrates of a liquid crystal panel and the light transmittance of liquid crystal molecules in the liquid crystal display.
In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments are possible.
In a color display device, such as a liquid crystal display (LCD), each of the three primary colors—e.g., red, green, and blue—produces different color shift at different gray levels.
As shown in
Similarly, in
In
As shown in
As shown in
Usually, in a color display, one picture is displayed during one frame time (or frame period). A “frame” represents a complete image or image of a series of images. A “frame period” contains an active period and a blanking period, where the active period is the time period to drive all pixels of an LCD panel, and the blanking period is used to match the period for blanking performed in CRT (cathode ray tube) monitors. The frame time is divided into two sub-frame times (or sub-scan periods). The color display displays an image according to signals driven in sub-frame 1 during the first sub-frame period, and displays an image according to signals driven in sub-frame 2 during the second sub-frame period. As shown in
As further shown in
c illustrates the relationship between the voltage across the upper and lower substrates of a liquid crystal panel and the light transmittance of the liquid crystal molecules. In
The light transmittance of liquid crystals is associated with the voltage between the two sides of the liquid crystals but generally is not affected by the polarity of the voltage supplied to the two sides of the liquid crystals. The relationship between the voltage across the upper and lower substrates of the liquid crystal panel and the light transmittance of the liquid crystals is a Gamma curve which is generally symmetric with respect to Vcom in the center. Therefore, in response to two Gamma voltages of the same amplitude but different polarities—for example Gamma voltage Va with positive polarity and Gamma voltage Vb with negative polarity, the light transmittance T0 of the liquid crystals of the pixel is generally identical. In other words, assuming there are two pixels which have the same voltage Vcom at the upper substrate but different voltages (Va and Vb) at the lower substrate, the two pixels will generally exhibit the same brightness although they have different voltages at the lower substrate.
If each pixel is continuously supplied with voltage of the same polarity, the liquid crystal molecules of the pixel will be damaged. Therefore, the liquid crystal molecules can be protected by alternating the polarity of the voltage across the two substrates. In other words, when a pixel needs to continuously show a consistent brightness, this can be achieved by controlling the lower substrate of the pixel by alternately changing the polarity of the voltage across the upper and lower substrates. In this way, the liquid crystal molecules of the pixel will not be damaged due to continuously displaying consistent brightness.
In relation to the common voltage polarity signal level (Vcom), the bright state display signal (e.g., bright state gray scale value 190) has a positive Gamma voltage polarity (+V190) and a negative Gamma voltage polarity (−V190) to show the bright state display signal; and the dark state display signal (e.g., dark state gray scale value 0) has a positive Gamma voltage polarity (+V0) and a negative Gamma voltage polarity (−V0) to show the dark state display signal.
Take red pixel 111 of the first pixel group 11 and the red pixel 121 of the second pixel group 12 shown in
To reduce flickering or degraded resolution of the displayed image, a driver system according to some embodiments for a color display device enables the sequences of pixel signals for adjacent pixels of the same color to be identical. A “sequence” of display signals (or more simply “signals”) refers to a time sequence of signals each corresponding to a bright state or dark state gray scale value and each having a positive or negative polarity. Each pixel is driven by two signals in respective sub-scan periods (or “sub-periods”) of a frame, wherein a dark state display signal is driven in one sub-scan period and a bright state display signal is driven in the other sub-scan period. The dark state display signal and bright state display signal are “combined” (based on viewing or perception by a user) to achieve the original gray scale value. In other words, although the pixel actually displays the dark state and bright state gray scale values corresponding to respective dark state and bright state display signals in two successive sub-scan periods of a frame, the user perceives the original gray scale value based on the user perceiving the combined dark state and bright state gray scale values. A sequence of signals for driving a pixel can include signals in two sub-scan periods, or alternatively, signals in four sub-scan periods.
The driver system 40 includes a display signal controller 41, a voltage polarity controller 44, and a timing controller 45. Although the controllers are depicted as separate blocks, it is contemplated that the controllers can be integrated in one device, or alternatively, the controllers can be implemented in plural devices. The display signal controller 41 includes a first lookup table 411, a second lookup table 412, and a data selector 413. After an original display signal is sent from the signal end (S) to be input into the first lookup table 411 and the second lookup table 412, the original display signal is converted into a first display signal (for example, a bright state display signal) and a second display signal (for example, a dark state display signal) by the first and second lookup tables 411 and 412, respectively. Then the data selector 413 selects one of the first display signal and the second display signal as a first input signal. The voltage polarity controller 44 receives the first input signal and sets the Gamma voltage polarity of the first input signal. The signal is sent by the timing controller 45 to the data driver 46 to drive a selected pixel group. The timing controller 45 also activates the scan driver 47 to enable the color display 30 to display the selected pixel group. Note that the arrangement of the display signal controller 41 and the Gamma voltage polarity controller 44 may be different in other embodiments. For example, display signal controller 41 and the Gamma voltage polarity controller 44 can be combined with the data driver 46.
The display signal controller 41 and voltage polarity controller 44 cooperate to provide sequences of signals to drive respective pixels, as described below for some embodiments.
A. Driving Sequence +H, −L, +H, −L
The following embodiments involve color pixels driven by the sequence +H, −L, +H, −L in two consecutive frames N, N+1, as discussed further below. Note that the sequence of display signals in frame N (+H, −L) is a repeat of the sequence of display signals in frame N+1.
As depicted in Table 1 of
The Gamma voltage polarity controller 44 provides a first sub-Gamma voltage polarity to be received by a color pixel of the pixel group in the first sub-scan period, and a second Gamma voltage polarity to be received by the color pixel of the pixel group in the second sub-scan time.
For example, in sub-frame 1 (first sub-scan period) of frame N (Nth scan period), the Gamma voltage polarity of the red pixel R11 of the first pixel group is positive (hereafter expressed as +), and in sub-frame 2 (second sub-scan period) of frame N, the Gamma voltage polarity of the red pixel R11 of the first pixel group is negative (hereafter expressed as −). In sub-frame 1 of frame N+1, the Gamma voltage polarity of the red pixel R11 of the first pixel group is positive (+), and in sub-frame 2 of frame N+1, the Gamma voltage polarity of red pixel R11 of the first pixel group is negative (−). The Gamma voltage polarity controller 44 is thus used to set a plurality of Gamma voltage polarities for the color pixels in a plurality of sub-scan periods.
The display signal controller 41 provides a plurality of first display signals in the first sub-scan period, to be received by the color pixels of the corresponding pixel group, and a plurality of second display signals in the second sub-scan period, to be received by the color pixels of the corresponding pixel group. A first display signal and a second display signal include the bright state display signal and the dark state display signal of a color pixel to be combined into a combined display signal (the desired original display signal). In other words, a first display signal received in the first sub-scan period is combined with a second display signal received in the second sub-scan period to derive the combined display signal. Note that the combination is based on user perception and not actually electrical combination by circuitry in the display device.
For example, in sub-frame 1 (first sub-scan period) of frame N (Nth scan period), the red pixel R11 of the first pixel group is a bright state display signal (hereafter expressed as H), and in sub-frame 2 (second sub-scan period) of frame N, the red pixel R11 of the first pixel group is a dark state display signal (hereafter expressed as L) which is combined with the bright state display signal (H) to form a combined display signal. In sub-frame 1 of frame N+1, the red pixel R11 of the first pixel group is a bright state display signal (H), and in sub-frame 2 of frame N+1, the red pixel R11 of the first pixel group is a dark state display signal (L) which is combined with the brighter state display signal (H) to form a combined display signal.
The Gamma voltage polarity controller 44 and the display signal controller 41 provide display signals at predetermined Gamma voltage polarities in a driving sequence so that color pixels receive the display signals at respective Gamma voltage polarities. For example, the driving sequence for the red pixel R11 in the first pixel group is as follows: the first sub-Gamma voltage polarity in the first sub-scan period is positive (+), and the first display signal in the first sub-scan period is the bright state display signal (H) of the red pixel R11; the second sub-Gamma voltage polarity in second sub-scan period is negative (−), and the second display signal in the second sub-scan period is the dark state display signal (L) of the red pixel R11. Therefore, in frames N and N+1, which include four sub-scan periods, the driving sequence for the red pixel R11 is +H, −L, +H and −L (corresponding to display signals and polarities in the following sequence of time periods: (1) frame N, first sub-scan period; (2) frame N, second sub-scan period; (3) frame N+1, first sub-scan period; and (4) frame N+1, second sub-scan period).
In accordance with some embodiments, the Gamma voltage polarity controller 44 and the display signal controller 41 collectively provide display signals at respective Gamma voltage polarities in the same driving sequence for the red pixel R12 of the second pixel group, which is adjacent to the first pixel group. The red pixel R12 receives the same sequence of display signals at respective Gamma voltage polarities, except with an offset of one sub-scan period. Thus, adjacent red pixels R11 and R12 are driven by the same sequences of display signals, which helps to reduce flickering effects.
The first sub-Gamma voltage polarity for the red pixel R12 of the second pixel group in the first sub-scan period is negative (−), and the first display signal in the first sub-scan period is the dark state display signal (L) of the red pixel R12; and the second sub-Gamma voltage polarity in the second sub-scan period is positive (+), and the second display signal of in the second sub-scan period is the bright state display signal (H) of the red pixel R12. The driving sequence for the red pixel R12 in the second pixel group is −L, +H, −L, +H.
As indicated above, the driving sequence for the red pixel R11 of the first pixel group is +H, −L, +H and −L, while the driving sequence for the red pixel R12 of the adjacent second pixel group is −L, +H, −L and +H. The driving sequences for R11 and R12 are the same but with an offset of one sub-scan period (one sub-scan period ahead or behind). The driving sequences for the other red pixels (such as R21 and R22) in adjacent pixel groups are also the same. The following illustrates sequences in multiple frames (e.g., frame N, N+1, N+2, N+3, etc.) for the four red pixels R11, R12, R21, and R22:
R11: +H, −L, +H, −L, +H, −L, +H, −L, . . .
R12: −L, +H, −L, +H, −L, +H, −L, +H, −L, . . .
R21: −L, +H, −L, +H, −L, +H, −L, +H, −L, . . .
R22: +H, −L, +H, −L, +H, −L, +H, −L, . . .
The underlined sequences above indicate that the sequences for the four red pixels are identical, except that the sequences for R12 and R21 are offset with respect to the sequences for R11 and R22 by one sub-scan period.
Table 2 of
In the second driving embodiment, the driving sequence for the green pixel G11 of the first pixel group is: −L, +H, −L and +H, and the driving sequence for the green pixel G12 of the second pixel group is: +H, −L, +H and −L. The driving sequences for G11 and G12 are the same but with an offset of one sub-scan period (one sub-scan period ahead or behind).
In the second driving embodiment, the driving sequence for the blue pixel B11 of the first pixel group is: +H, −L, +H and −L, and the driving sequence for the blue pixel B12 of the second pixel group is: −L, +H, −L and +H. The driving sequences are the same but with an offset of one sub-scan period (one sub-scan period ahead or behind).
Table 6 of
Table 7 of
In the driving embodiment of Table 7, the driving sequence for the blue pixel B11 of the first pixel group is: +H, −L, +H and −L, and the driving sequence for the blue pixel B12 of the second pixel group is: −L, +H, −L and +H. The driving sequences are the same but with an offset of one sub-scan time.
Similarly, in the driving embodiment of Table 10 depicted in
B. Driving Sequence −H, +L, −H and +L
The driving sequence −H, +L, −H, +L is based on the following sequence: the first sub-Gamma voltage polarity in the first sub-scan period is negative (−), and the first display signal in the first sub-scan period is the bright state display signal (H) of the corresponding color pixel; the second sub-Gamma voltage polarity in the second sub-scan period is positive (+), and the second display signal in the second sub-scan period is the dark state display signal (L) of the corresponding color pixel. Therefore the driving sequence is −H, +L, −H and +L in two consecutive frames N, N+1.
This driving sequence also repeats every frame—the sequence in frame N is the same as the sequence in frame N+1.
In the driving embodiment of Table 1 (
In the driving embodiment of Table 1, the driving sequence for the blue pixel is −H, +L, −H and +L, while the driving sequence for the red pixel is +H, −L, +H and −L, which is different from that for the blue pixel. However, as long as the same color pixels in adjacent pixel groups are driven in the same sequence, the different color pixels in the adjacent pixel groups can be driven in different sequences.
In the driving embodiment of Table 6 (
In the driving embodiment of Table 10 (
C. Driving Sequence +H, +L, −H and −L
The sequence +H, +L, −H, −L are driven in two consecutive frames (e.g., frame N and frame N+1), where each frame corresponds to a “scan period” (frame N is the first scan period, and frame N+1 is the second scan period). This driving sequence is as follows: the first sub-Gamma voltage polarity in the first sub-scan period of the first scan period is positive (+), and the display signal of the first sub-scan period of the first scan period is the bright state display signal (H) of the corresponding color pixel; the second sub-Gamma voltage polarity in the second sub-scan period of the first scan period is positive (+), and the display signal in the second sub-scan period of the first scan period is the dark state display signal (L) of the corresponding color pixel; the first sub-Gamma voltage polarity in the first sub-scan period of the second scan period is negative (−), and the display signal in the first sub-scan period of the second scan period is the bright state display signal (H) of the corresponding color pixel; the second sub-Gamma voltage polarity in the second sub-scan period of the second scan period is negative (−), and the display signal in the second sub-scan period of the second scan period is the dark state display signal (L) of the corresponding color pixel.
Unlike the previous two driving sequences, this driving sequence repeats every two frames (rather than every frame).
In the driving embodiment of Table 3, depicted in
R11: +H, +L, −H, −L, +H, +L, −H, −L, . . .
R12: −H, −L, +H, +L, −H, −L, +H, +L, . . .
R21: −H, −L, +H, +L, −H, −L, +H, +L, . . .
R22: +H, +L, −H, −L, +H, +L, −H, −L, . . .
The underlined sequences are identical.
In the driving embodiment of Table 3, the driving sequence for the green pixel G11 of the first pixel group is: −H, −L, +H and +L, and the driving sequence for the green pixel G12 of the second pixel group is: +H, +L, −H and −L. The driving sequences are the same but with an offset of two sub-scan periods. The driving sequences for the adjacent green pixels G21 and G22 are also the same.
In the driving embodiment of Table 3, the driving sequence for the blue pixel B11 of the first pixel group is: +H, +L, −H and −L, and the driving sequence for the blue pixel B12 of the second pixel group is: −H, −L, +H and +L. The driving sequences are the same but with an offset of two sub-scan periods. The driving sequences for the adjacent blue pixels B21 and B22 are also the same.
In the driving embodiment of Table 4 (
In the driving embodiment of 8 (depicted in
In the driving embodiment of Table 8, the driving sequence for the green pixel G11 of the first period group is: −H, −L, +H and +L, and the driving sequence for the green pixel G12 of the second pixel group is: +H, +L, −H and −L. The driving sequences are the same but with an offset of two sub-scan periods.
In the driving embodiment of Table 8, the driving sequence for the blue pixel B11 of the first pixel group is: +H, +L, −H and −L, and the driving sequence for the blue pixel B12 of the second pixel group is: −H, −L, +H and +L. The driving sequences are the same but with an offset of two sub-scan periods.
In the driving embodiment of Table 9 (depicted in
In the driving embodiment of Table 11 (
In the driving embodiment of Table 11, the driving sequence for the green pixel G11 of the first pixel group is: −H, −L, +H and +L, and the driving sequence for the green pixel G12 of the second pixel group is: +H, +L, −H and −L. The driving sequences are the same but with an offset of two sub-scan periods.
In the driving embodiment of Table 11, the driving sequence for the blue pixel B11 of the first pixel group is: +H, +L, −H and −L, and the driving sequence for the blue pixel B12 of the second pixel group is: −H, −L, +H and +L. The driving sequences are the same but with an offset of two sub-scan periods.
In the driving embodiment of Table 12 (
In the driving embodiment of Table 13 (
In the driving embodiment of Table 14 (
In the driving embodiment of Table 15 (
D. Driving Sequence +H, −L, −H and +L
The driving sequence +H, −L, −H and +L is as follows: the first sub-Gamma voltage polarity in the first sub-scan period of the first scan period is positive (+), and the display signal in the first sub-scan period of the first scan period is the bright state display signal (H) of the corresponding color pixel; the second sub-Gamma voltage polarity in the second sub-scan period of the first scan period is negative (−), and the display signal in the second sub-scan period of the first scan period is the dark state display signal (L) of the corresponding color pixel; the first sub-Gamma voltage polarity in the first sub-scan period of the second scan period is negative (−), and the display signal in the first sub-scan period of the second scan period is the bright state display signal (H) of the corresponding color pixel; the second sub-Gamma voltage polarity in the second sub-scan period of the second scan period is positive (+), and the display signal in the second sub-scan period of the second scan period is the dark state display signal (L) of the corresponding color pixel.
Again, this driving sequence repeats every two frames.
Similarly, in the driving embodiment of Table 14 (
The driving sequences for some color pixels according to various driving embodiments have been discussed above. The driving sequences for the red, green, and blue pixels according to the various driving embodiments are summarized in the table below:
In the above table, driving embodiments 1-15 correspond to the driving embodiments of Tables 1-15 of
The driver system for a color display according to some embodiments is thus able to match sequences of bright state display signals (H) and dark state display signals (L) at respective positive Gamma voltage (+) or the negative Gamma voltage (−) in adjacent pixel groups such that adjacent color pixels are driven by the same driving sequence (albeit offset by at least one sub-scan period). For example, with the driving sequence of +H, −L, +H and −L, it takes one frame time (+H, −L) in order to achieve the same driving sequence as the same color pixel in the adjacent pixel group. As a result, picture flickering or resolution degradation is reduced, while at the same time allow reduction of color shift due to wide viewing angles
In another example, assume the driving sequence of +H, −L, −H and +L. Two frame times (+H, −L, −H and +L) are needed for driving in the same driving sequence as the same color pixel in the adjacent pixel group.
Therefore, whether the same driving sequence is achieved in one frame or two frame times, picture flickering or resolution degradation can be reduced, while achieving reduced color shift at wide viewing angles by driving pixels using bright state display signals and dark state display signals.
In the driving embodiment of Table 7 (
Similarly, in the driving embodiment of Table 7, the driving sequence of the green pixel G11 of the first pixel group is: −L, +H, −L and +H, and the driving sequence of the green pixel G12 of the second pixel group is: +H, −L, +H and −L. The driving sequence of the green pixel G21 of the third pixel group is: −L, +H, −L and +H, and the driving sequence of the green pixel G22 of the fourth pixel group is: +H, −L, +H and −L. The driving sequences of the green pixels of the four adjacent pixel groups are thus the same.
In the driving embodiment of Table 7, the driving sequence of the blue pixel B11 of the first pixel group is: +H, −L, +H and −L, and the driving sequence of the blue pixel B12 of the second pixel group is: −L, +H, −L and +H. The driving sequence of the blue pixel B21 of the third pixel group is: +H, −L, +H and −L, and the driving sequence of the blue pixel B22 of the fourth pixel group is: −L, +H, −L and +H. The driving sequences of the blue pixel of the four adjacent pixel groups are the same.
In the driving embodiment of Table 7, the driving sequences of three color pixels (red, green and blue) in the four adjacent pixel groups are the same (SR11=SR12=SR21=SR22=SG11=SG12=SG21=SG22=SB11=SB12=SB21=SB22), and the best display effect is achieved. SR11 represents the driving sequence for pixel R11; SR12 represents the driving sequence for pixel R12; and so forth. Similarly, in the driving embodiments of Tables 3, 8, and 11, the driving sequence of three color pixels (red, green and blue) in the four adjacent pixel groups are the same (SR11=SR12=SR21=SR22=SG11=SG12=SG21=SG22=SB11=SB12=SB21=SB22), and the best display effect is achieved as well.
While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover such modifications and variations as fall within the true spirit and scope of the invention.
Number | Date | Country | Kind |
---|---|---|---|
94109765 A | Mar 2005 | TW | national |
Number | Name | Date | Kind |
---|---|---|---|
5717474 | Sarma | Feb 1998 | A |
5847688 | Ohi et al. | Dec 1998 | A |
6611246 | Ito et al. | Aug 2003 | B1 |
20020149598 | Greier et al. | Oct 2002 | A1 |
20040246216 | Hosaka | Dec 2004 | A1 |
20050225545 | Takatori et al. | Oct 2005 | A1 |
Number | Date | Country | |
---|---|---|---|
20060221029 A1 | Oct 2006 | US |