1. Field of the Invention
The present invention relates to a method and apparatus for displaying a color on a matrix driven display by utilizing a plurality of fundamental colors, e.g., R (red), G (green) and B (blue) in combination with one another.
2. Description of the Related Art
A conventional liquid-crystal display device which makes use of a display element, such as a liquid crystal or the like, in conjunction with a light source and color filters so as to allow a display of colors.
A thin-film transistor-driven liquid-crystal display will be described below as an example of a matrix driven display device. A pixel for displaying one color by utilizing three fundamental colors of R, G and B in combination as dots is formed as a color filter and arranged within a display region in large numbers. Signal lines and scanning lines are wired in matrix form to drive each of the liquid crystals. Pixel electrodes are respectively disposed in regions partitioned by the signal lines and the scanning lines. The pixel electrodes are operated by thin-film transistors by applying electric fields to the liquid crystals corresponding to the respective dots. The transmissivity of each liquid crystal is changed so as to select a display or a non-display mode.
In a display used for a computer to which this type of liquid-crystal display is applied, i.e., a VGA-standard display for performing a display of 640 (horizontal).times.480 (vertical) dots, the number of pixels (each of which is formed by a set of respective one dots of R, G and B) used as display units is 640.times.480=307200. The pixels are represented in the form of a three-way RGB split RGB along the signal lines. Therefore, the number of the scanning lines and the number of the signal lines are 480 and 640.times.3=1920 respectively. Accordingly, the total number of dots is defined as 640.times.3.times.480=921600.
FIG. 9 shows a color liquid-crystal driven unit wherein a driving LSI is attached to the screen of this type of color liquid-crystal display. In the drawing, reference numeral 1 indicates a liquid-crystal element in which a liquid crystal is sealed between two transparent substrates, disposed in opposing relationship to one another. The first transparent substrate has common electrodes and color filters. The second transparent substrate has longitudinally-extending signal lines and transversely-extending scanning lines, wired in matrix form in large numbers. Pixel electrodes and thin-film transistors are respectively provided within the regions partitioned by the signal lines and the scanning lines. In the present example, a plurality of gate drivers Gd, for driving the scanning lines, are provided on the left side of the liquid-crystal element 1 and a plurality of source drivers Sd, for driving the signal lines, are respectively provided at the upper and lower sides thereof.
In the circuit of the present example, however, signal lines (S.sub.1, S.sub.2, S.sub.3, . . . ) arranged in a vertical row, and the scanning lines (G.sub.1, G.sub.2, G.sub.3, . . . ) arranged in a horizontal row, are formed in large numbers in an intersecting state. Furthermore, pixel electrodes 5 and thin-film transistors 6 are respectively provided within regions partitioned by the signal lines and the scanning lines. One region forming each pixel electrode 5 is defined as one dot and one pixel is constituted by a collection of three dots.
Thus, since a pixel 7 surrounded with the dot line shown in FIG. 10 is formed in the circuit shown in FIG. 9, 307200 pixels 7 are formed on one screen of the display of the VGA standards.
Since the source drivers Sd and gate drivers Gd attached to the liquid-crystal display element 1 having the number of the dots referred to above are normally constructed of a single LSI having about 240 output pins, ones mounted on the set of transparent substrates of the liquid-crystal element 1 are normally set to a TCP (Tape Carrier Package) configuration using a polyimide tape equipped with LSI or a COG (Chip-On Glass) configuration for directly mounting LSI on a substrate.
Thus, the number of the 240-pin source drivers Sd and the number of the 240-pin gate drivers GD needed to handle the 1920 signal lines and the 480 scanning lines, employed in the liquid-crystal display element 1, are eight (240.times.8=1920) and two (240.times.2=480) as shown in FIG. 9. Incidentally, an actual liquid-crystal display additionally needs circuits for supplying signals or the like to the drivers. However, the description of the circuits will be omitted herein.
The source drivers Sd are greater than the gate drivers Gd in power consumption:
(1) Driver power consumption is about 840 mW PA1 (2) Gate drivers: low--it is about 40 mW (20 mW.times.2) which accounts for 5% of the total power consumption; and PA1 (3) Source drivers: high--it is about 800 mW (100 mW.times.8) which accounts for 95% of the total power consumption.
It is also known that the normal unit price of the source drivers are about twice that of the gate drivers.
The power consumption of each source driver referred to above is typically one corresponding to 6 bits (64-step gradation) in a color display under the existing circumstances. When it is a 8-bit corresponding to one, both the price and power consumption become large values and the differences in cost and power consumption between the gate drivers and the source drivers tend to further increase.
It has been desirable to reduce the cost of a liquid crystal display device by reducing the required number of these expensive drivers. It has also been desirable to lessen the power consumption of the liquid-crystal display.