Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-10-10
2001-07-24
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S037000, C313S580000
Reexamination Certificate
active
06266031
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a cathode structure for a 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 ground and a suitable 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 ground at the lower surface of the cover sheet
6
. If a data drive electrode is at ground 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 ground, 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 is a twisted nematic liquid crystal material which rotates the plane of polarization of linearly polarized light passing therethrough by an angle which is a function of the electric field in the liquid crystal 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 liquid crystal 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 liquid crystal 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 liquid crystal 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 liquid crystal 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 the conventional PALC display panel, the electrodes are about 75 &mgr;m wide, independently of the width of the channel.
During operation of a PALC display panel, material is sputtered from the cathode and some of this material is deposited on the lower surface of the cover sheet and on the bottom of the channel. This deposited material partially blocks transmission of light by the panel elements and so as the sputtering continues, the transmission of the panel elements becomes progressively smaller. This progressive degradation in the transmission of the panel elements reduces the useful life of the display panel.
The rate at which material is sputtered from the cathode and deposited on the lower surface of the cover sheet and the bottom of the channel depends on the current supplied to the plasma. The current supplied to the plasma also affects the power consumption of the PALC panel.
SUMMARY OF THE INVENTION
It has been recognized in accordance with the invention that the current supplied to the plasma depends on the area of the cathode, so that by reducing the area of the cathode, the current supplied to the plasma is reduced, and the power consumption and the sputtering rate are reduced accordingly.
In accordance with a first aspect of the present invention there is provided an improved PALC panel comprising a channel member having a plurality of channels therein and a cathode and anode in each channel for establishing a plasma in the channel, wherein the improvement resides in that the cathodes are narrow.
In accordance with a second aspect of the present invention there is provided a PALC panel comprising a channel member having a plurality of channels therein and a cathode and anode in each channel for establishing a plasma in the channel, wherein the cathodes are substantially less than 75 &mgr;m in width.
REFERENCES:
patent: 5804920 (1998-09-01), Khan et al.
patent: 5821912 (1998-10-01), Miyazaki
patent: 5990619 (1999-11-01), Ilcisin et al.
patent: 6002382 (1999-12-01), Hayashi et al.
patent: 6028572 (2000-02-01), Ilcisin et al.
Hinchliffe Robert D.
Ilcisin Kevin J.
Hjerpe Richard
Nguyen Kimnhung
Smith-Hill John
Tektronix Inc.
Winkelman John D.
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