Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1997-07-25
2003-02-11
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S093000, C345S090000, C345S087000, C345S098000, C345S100000
Reexamination Certificate
active
06518945
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to flat panel displays, and more particularly to flat-panel displays having redundant elements to replace defective circuit elements.
2. Description of the Background Art
As shown in
FIG. 1
, a typical flat-panel display (e.g., a liquid crystal display for use with a computer)
100
includes a number of pixel cells
110
(r,c) arranged in a rectangular array of m rows and n columns, a data bus driver
112
which asserts data signals on data lines
114
(c), and an address bus driver
116
, which sequentially asserts row-select signals on address lines
118
(r). Each pixel cell
110
includes a capacitor
120
, a transistor
122
, and a pixel electrode
124
. Transistor
122
has a gate terminal
126
coupled to address line
118
(
1
), a drain terminal
128
coupled to data line
114
(
1
), and a source terminal
130
coupled to capacitor
120
. When address bus driver
116
asserts a high signal on address line
118
(
1
), transistor
122
is turned on, allowing capacitor
120
to be charged or discharged, depending on the signal on data line
114
(
1
), thus storing the data signal. Capacitor
120
is coupled to pixel electrode
124
, and asserts the stored signal thereon. Pixel electrode
124
contacts an optically active pixel element (not shown), for example a liquid crystal cell, and the signal applied to the pixel electrode modulates the amount of light passing through the active pixel element.
Flat panel display
100
may be a reflective display or a transmissive display. In the case of a transmissive display, incident light passes through the optically active pixel element, the pixel electrode
124
, and the substrate upon which the display is formed. Therefore, in transmissive displays, the electronic elements such as transistor
122
and capacitor
120
must be formed in gaps between the pixel electrodes
124
(r,c), so as not to interfere with the light passing through the display. In a reflective display, light is reflected off the pixel electrode, and does not pass through the substrate. Therefore, in a reflective display, the electronic elements may be formed below the pixel electrode. In either case, broken data or address lines or defective electronic components can render one or more of the pixel cells inoperative, thus degrading the image generated by the display.
Because the display output is viewed as a complete image, corrective techniques typically employed in semiconductor memory devices to cope with defective array elements, e.g., the physical relocation of a row or column, are unsuitable for flat panel displays. Many attempts have been made to overcome the problem of defective elements in flat panel displays, but none have been completely successful. For example, U.S. Pat. No. 4,995,703, issued to Kesao Noguchi, describes the division of a single pixel into four separate pixels, each with its own pixel electrode and switching transistor. If a defect renders, for example, two of the four pixels inoperative, the remaining pixels may continue to function, rendering the defect less objectionable. However, this approach suffers from the disadvantage that twice as many data and address lines are required. More importantly, the four separate pixels must be separated by a finite gap, thus reducing the active pixel surface area, and causing a reduction in brightness.
Another technique is described in U.S. Pat. No. 4,680,580, issued to Yukito Kawahara. Kawahara describes a display wherein pixels whose scan or signal lines are broken are serviced by the scan or signal line of a neighboring pixel. While this technique yields a defect that is less objectionable than a row or column that is stuck on or off, it fails to completely compensate for a defective row or column, because the defective row or column is written with data intended for the neighboring row or column, and the original data intended for the defective row or column is lost.
What is needed is a display capable of replacing a defective row or column (e.g., broken row select lines, broken data lines, or defective circuit elements), while insuring that all pixels in the array, including the pixels of the defective rows or columns, are written with their intended data.
SUMMARY
A novel display, capable of replacing defective elements, for example broken row select lines, broken data lines, or defective circuit elements, by column and/or row shifting is described. The display generally includes a plurality of pixel cells, each having a pixel electrode in contact with an optically active element (e.g., a liquid crystal element), a primary storage element, and a switch for selectively coupling the pixel electrode with the primary storage element and at least one other storage element. The display may be either transmissive or reflective. In the case of a reflective display, the pixel electrodes are, for example, metallic mirrors, deposited over the switches and storage elements formed on a silicon substrate. The present invention recognizes that redundancy can be provided in the circuit elements, apart from the pixel electrodes and the optically active elements, such that replacement circuit elements can service a pixel electrode in its original position. Thus, no redundancy is necessary for the pixel electrodes or the optically active elements.
In one embodiment the display replaces defective elements by column shifting. A switch, for example a single bit multiplexer, selectively couples a pixel electrode with a primary storage element, for example an SRAM latch, and a storage element of an adjacent column. This embodiment further includes a controller, having a first voltage supply terminal, a second voltage supply terminal, a fuse, and a terminator. The fuse has a first end coupled to the first voltage supply and a second end coupled, via a control line, to the switch. The terminator is intercoupled between the second end of the fuse and the second voltage supply terminal, and operates to maintain a low voltage on the control line when the fuse is opened. Responsive to the low signal on the control line, the switch couples the pixel electrode with the storage element of the adjacent column. A data router, coupled to the control line, redirects data from the primary storage element to the adjacent storage element, responsive to the low signal on the control line.
Typically, any defective elements are identified and replaced during manufacturing. For instance, after the display has been fabricated, but before the display itself is completed, test data is conventionally written to and read from the storage elements of the display. Defects are identified by comparing the written to the read data. This information is then transferred to a computer controlled laser, which vaporizes the appropriate fuses, which are typically made of polysilicon or metal, of the controller, initiating the column shift. Optionally, the replacement of defective elements can occur in the field, by providing, for example, a software programmable controller. Of course other types of programmable elements can be substituted for the fuses.
In a second embodiment, the display replaces defective elements by row shifting. This embodiment includes a pixel electrode, a primary storage element, a second storage element, and a switch. The switch selectively couples the pixel electrode with the primary storage element and the second storage element, disposed in an adjacent row. This embodiment further includes a controller, coupled to the switch via a control line, for initiating a row shift. A row-select router, coupled to the control line, redirects row-select signals from the primary storage element to the second storage element.
In a third embodiment, the display replaces defective elements by column and row shifting. This embodiment includes a pixel electrode, a first switch, for example a two-bit multiplexer, a second switch, for example a two-level multiplexer, a primary storage element, a second storage element, a third storage element, and a fourth s
Aurora Systems, Inc.
Henneman & Saunders
Henneman, Jr. Larry E.
Nguyen Jimmy H.
Shalwala Bipin
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