Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1997-10-08
2001-09-25
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S087000, C345S090000, C345S103000
Reexamination Certificate
active
06295044
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to electro-optic displays.
BACKGROUND OF THE INVENTION
Many computer displays have a limited physical resolution—typically 70-100 dots per inch (2.76 to 3.94 dots per mm). Since the display is composed of an array of rectangular pixels, each of which is either ON or OFF, the edges of text, lines, etc that are displayed may often have a jagged “staircase” effect which is visually disturbing.
There have been several attempts to solve this problem in a variety of ways e.g. by grey scale rendering or anti-aliasing. Some display technologies such as Twisted Nematic Liquid Crystal Displays (TN LCDs), cathode ray tubes, etc.,allow the intensity of the whole area of a pixel to be varied. In these types of display, the intensity of each pixel may be selected in proportion to the area of the pixel that should be ON. Whilst this can reduce the visually disturbing staircase effect, it can make edges in the displayed image appear blurred, especially when viewed from close to the display.
Other display technologies do not allow a range of intensities over the whole area of the pixel display, in which case a range of intensities may be simulated by rapidly turning the pixel ON and OFF, sufficiently fast so that the eye sees the average intensity. This may be used with Super Twisted Nematic (STN) LCDs. Alternatively, each pixel may be divided into sub pixels, and a varying number turned on according to the desired intensity. The display must then be viewed from such a distance that the eye cannot resolve the sub pixels, or some optical blurring introduced to average out the intensity over the whole pixel. An example of this type of technique is described in JP-A-3142260, where each pixel is effectively divided into four sub pixel slices. The image to be displayed is analysed and two-bit pixel data is added to each pixel to turn on selected sub pixel slices during a pixel sub-scanning period. This allows a range of intensities to be displayed by varying the area of the pixel that is ON, in four discrete steps. However, by its nature this system is only capable of modulating the pixel output slice-wise and in many instances this will not give good smoothing, particularly where the edge to be smoothed is nearly perpendicular to the slice direction of the pixels.
A similar technique is disclosed in U.S. Pat. No. 4,824,218, which relates principally to Ferroelectric LCDs. Here a variable width portion of a pixel is turned on by driving a potential gradient across the width of the pixel by means of metal electrodes running along the edges of resistive transparent column electrodes. To allow the complete area of the pixel to be driven, whilst preventing crosstalk (i.e. unintentionally affecting other pixels in the same row), and to avoid a wasted area of the pixel nearest the “reference” metal electrode, the pixel is driven in two phases, swapping the role of the two metal electrodes between “reference” and “data”. This technique relies on the fact that a Ferroelectric Liquid Crystal (FLC) material stores its state and can be written to again, adding to the area that has already been turned ON, which is not true for all bistable materials. This scheme also requires a blanking pulse to clear the whole pixel before the two writing phases. U.S. Pat. No. 4,824,218 also refers to an extension of this technique in which the display has row and column transparent resistive electrodes each with metal electrodes on either side. A four field drive scheme is described in which the display is scanned four times, following a blanking pulse, to make up a frame. As before the metal electrodes swap roles between data and reference electrodes. Because alternate electrodes are set to a fixed reference this arrangement does not allow great flexibility in the creation of sub pixel shapes.
SUMMARY OF THE INVENTION
Accordingly, in one aspect, this invention provides a display comprising:
a first substrate having thereon a plurality of row electrode means,
a second substrate having thereon a plurality of column electrode means,
a layer of electro-optic material disposed between said first and said second substrate,
row drive means associated with said first substrate for applying a respective selected voltage profile across each row electrode means in a direction transverse to the thickness of said layer,
column drive means associated with said second substrate for applying a respective selected voltage profile across each column electrode means in a direction transverse to the thickness of said layer,
whereby the electrical field in each pixel in the direction transverse to the thickness of the electro-optic layer may be selected to provide a non-uniform optical output.
In a particularly preferred arrangement, each of said column electrode means and said row electrode means comprises a group of generally parallel conductive tracks.
We have found that the multiple track architecture for each of the row and column electrodes provides important and unexpected advantages when used in conjunction with drive means which apply a selected voltage profile across each of the groups of tracks making up an electrode. In this way the magnitude of the electrical field across the pixel may be varied in a direction transverse to the thickness of the electro-optic layer to provide a non-uniform optical output across the pixel. By contrast to the arrangements of U.S. Pat. No. 4,824,218, which use resistive electrodes driven by metal electrodes to either side, the multiple conductive tracks of the present invention may be driven by electrical contacts well away from the image area, thus considerably improving the aperture ratio of the display. Also, the previous arrangement of U.S. Pat. No. 4,824,218 requires accurate alignment of fine metal electrodes with each of the transparent resistive electrodes, whereas in the present invention the conductive tracks in each group may be coupled together by a resistive element in contact with the end regions of the conductive tracks to one side of the display, and an input electrode provided at each end of the resistive element. Here the accuracy of alignment of the tracks and the resistive elements is not so important as the resolution of the conductive tracks may be effectively decoupled from that of the resistive elements.
Thus, in one embodiment, the resistive elements may be formed on the first and second substrates, in electrical contact with the respective conductive tracks. Alternatively, the row and column resistive elements may be formed on separate substrates which are then placed in contact with the first and second substrates.
For both the rows and the columns, the series of resistive elements driving the groups of conductive tracks may be replaced by a single resistive element in electrical contact with a substantial proportion of, or all the conductive tracks making up the complete set of row/column electrodes, with the drive means including an input electrode means between each group of conductive tracks.
Preferably, said drive means includes means for applying an adjustable voltage across each of said resistive elements, so that the voltage profile across the group of conductive tracks is a ramp of positive, negative or zero slope. Instead of resistance coupling, the drives to the groups of tracks may be inductively or capacitively coupled.
By the above arrangements, the electrical field may be configured to generate a wide range of different non-uniform outputs of selected shape for a pixel, to turn on an arbitrary portion of the pixel, so that the required edge of the line portion of the text character etc is maintained within the area of the pixel.
In one preferred drive scheme, each of a set of predetermined voltage profiles is applied across a row electrode means in successive phases, and the columns driven in parallel with the required voltage profiles. In this way a broad range of pixel shapes may be provided in either a single write (i.e. just one of the phases) or a multiple write where the pixel output is incrementally rendered
Geisow Adrian Derek
Rudin John Christopher
Hewlett--Packard Company
Nguyen Jimmy H.
Shalwala Bipin
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