Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-06-28
2002-06-04
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S060000, C345S061000, C345S062000, C345S064000, C345S065000, C345S066000, C345S067000, C345S068000, C345S069000, C345S087000
Reexamination Certificate
active
06400345
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of operating a plasma addressed liquid crystal (PALC) panel.
U.S. Pat. No. 5,077,553 discloses apparatus for addressing data storage elements. A practical implementation of the apparatus shown in U.S. Pat. No. 5,077,553 is illustrated schematically in
FIG. 1
of the accompanying drawings.
The display panel shown in
FIG. 1
comprises, in sequence from below, a polarizer
2
, a channel member
4
, a cover sheet
6
(commonly known as a microsheet), a layer
10
of electro-optic material, an array of parallel transparent data drive electrodes (only one of which, designated
12
, can be seen in the view shown in FIG.
1
), an upper substrate
14
carrying the data drive electrodes, and an upper polarizer
16
. In the case of a color display panel, the panel includes color filters (not shown) between the layer
10
and the upper substrate
14
. The panel may also include layers for improving viewing angle and for other purposes. The channel member
4
is typically made of glass and is formed with multiple parallel channels
20
in its upper main face. The channels
20
, which are separated by ribs
22
, are filled with an ionizable gas, such as helium. An anode
24
and a cathode
26
are provided in each of the channels
20
. The channels
20
are orthogonal to the data drive electrodes and the region where a data drive electrode crosses a channel (when viewed perpendicularly to the panel) forms a discrete panel element
28
. Each panel element can be considered to include elements of the layer
10
and the lower and upper polarizers
2
and
16
. The region of the upper surface of the display panel that bounds the panel element constitutes a single pixel
30
of the display panel.
When the anode
24
in one of the channels is connected to a reference potential and a suitably more negative voltage is applied to the cathode
26
in that channel, the gas in the channel forms a plasma which provides a conductive path to the reference potential at the lower surface of the cover sheet
6
. If a data drive electrode is at the reference potential, there is no significant electric field in the volume element of electro-optic material in the panel element at the crossing of the channel and the data drive electrode and the panel element is considered to be off, whereas if the data drive electrode is at a substantially different potential from the reference potential, there is a substantial electric field in that volume element of electro-optic material and the panel element is considered to be on.
It will be assumed in the following description, without intending to limit the scope of the claims, that the lower polarizer
2
is a linear polarizer and that its plane of polarization can be arbitrarily designated as being at 0° relative to a reference plane, that the upper polarizer
16
is a linear polarizer having its plane of polarization at 90°, and that the electro-optic material rotates the plane of polarization of linearly polarized light passing therethrough by an angle which is a function of the electric field in the electro-optic material. When the panel element is off, the angle of rotation is 90°; and when the panel element is on, the angle of rotation is zero.
The panel is illuminated from the underside by an extended light source
34
which emits unpolarized white light. A rear glass diffuser
18
having a scattering surface may be positioned between the light source and the panel in order to provide uniform illumination of the panel. The light that enters a given panel element from the source is linearly polarized at 0° by the lower polarizer
2
and passes sequentially through the channel member
4
, the channel
20
, the cover sheet
6
, and the volume element of the electro-optic material toward the upper polarizer
16
and a viewer
32
. If the panel element is off, the plane of polarization of linearly polarized light passing through the volume element of electro-optic material is rotated through 90°, and therefore the plane of polarization of light incident on the upper polarizer element is at 90°. The light is passed by the upper polarizer element and the pixel is illuminated. If, on the other hand, the panel element is on, the plane of polarization of the linearly polarized light is not changed on passing through the volume element of electro-optic material. The plane of polarization of light incident on the upper polarizer element is at 0° and therefore the light is blocked by the upper polarizer element and the pixel is dark. If the electric field in the volume element of electro-optic material is intermediate the values associated with the panel element being off and on, light is passed by the upper polarizer element with an intensity which depends on the electric field, allowing a gray scale to be displayed.
In a practical implementation of the PALC display panel, the channel member
4
is etched back around the area in which the channels are formed in order to provide a plateau
36
in which the channels
20
are formed, and the cover sheet
6
is secured to the channel member by an endless frit bead
38
in a rabbet
40
extending around the periphery of the plateau. An upper substrate assembly, including the upper substrate
14
and the data drive electrodes
12
carried thereby, is attached to the channel member
4
by means of a glue bead
42
.
When the PALC display panel disclosed in U.S. Pat. No. 5,077,553 is used as a raster scan display panel for displaying a raster scan video signal, the panel is oriented so that the channels extend horizontally and the data drive electrodes. extend vertically. The horizontal line interval can conveniently be divided into an initiation interval, during which the plasma is formed in the channel; a sustain interval, during which the voltage of the strobe pulse is less than during the initiation interval but is sufficient to sustain the plasma; and a decay interval, which starts when the strobe pulse is removed and during which the gas reverts to its non-conductive state.
The data drive electrodes are driven to the voltage levels associated with line N+1 of the video signal during a capture interval which starts after the end of the decay interval of line N and ends before the end of the sustain interval of line N+1, so that the data drive electrodes are at the proper levels at the end of the sustain interval for line N+1 but the change in voltage levels, from the levels for line N to the levels for line N+1, does not affect the panel elements of line N.
In the conventional PALC panel, the electro-optic material may be a liquid crystal material operating in a twisted nematic (TN) mode. The upper surface of the cover sheet is provided with an alignment layer oriented parallel to the plane of polarization of the lower polarizer
2
(0°) and the lower surface of the data drive electrode
12
is provided with an alignment layer oriented parallel to the plane of polarization of the upper polarizer
16
(90°). The molecules that are in contact with the alignment layers are aligned with the respective alignment layers. When the display element is off, and there is no significant electric field in the volume element of liquid crystal material, the molecules that are distant from the alignment layers tend to align themselves with their neighboring molecules. Therefore, the axes of the molecules are generally parallel to the upper surface of the cover sheet and the orientation of the liquid crystal molecules spirals through the range from 0° to 90° as a function of distance from the lower alignment layer to the upper alignment layer. When linearly polarized light passes through the liquid crystal material, its plane of polarization rotates by 90°.
When there is an electric field in the volume element of liquid crystal material, the axes of the liquid crystal molecules tend to become aligned with the electric field. When there is a potential difference between the data drive electrode and the channel electrodes, the electric field tends to force the liq
Buzak Thomas S.
Ilcisin Kevin J.
Hjerpe Richard
Lesperance Jean
Smith-Hill John
Tektronix Inc.
Winkelman John D.
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