Liquid crystal display with integrated frame buffer

• US 5,471,225 A
• Filed: 05/17/1994
• Issued: 11/28/1995
• Est. Priority Date: 04/28/1993
• Status: Expired due to Term

• Current Assignee: Dell USA LP (Dell Technologies Inc.)
• Original Assignee: Dell USA LP (Dell Technologies Inc.)
• Inventors: Parks, Terry J.
• Primary Examiner(s): Weldon, Ulysses
• Application Number:
  US08/245,801
• Time in Patent Office: 560 Days
• Field of Search: 307/247.1, 307/571, 307/573, 359/57, 359/58, 359/59, 345/85, 345/98, 345/205, 345/90
• US Class Current: 345/98
• CPC Class Codes: G02F 1/1368 in which the switching element is a three-electrode device G02F1/136277 takes precedence
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0857 Static memory circuit, e.g. flip-flop
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

An improved liquid crystal display (LCD) is provided having a static random access memory located within each liquid crystal control cell and between each display electrode and corresponding bit and word lines. The memory cell, or storage cell, includes a pass-gate transistor which, upon activation via word line, forwards bit line video data to a memory circuit, such as a latching circuit, placed between the pass-gate transistor and the display electrode. The latching circuit may consist of two thin-film transistors connected as cross-coupled inverters for latching video data upon the display electrode for virtually an indefinite period of time or until the pass-gate transistor is again activated. By utilizing a storage cell with buffer capability adjacent each display electrode, problems associated with large data line current can be minimized. Moreover, the static memory can rid the host processor of having to continuously refresh the LCD active matrix.

Claims

1. A storage cell capable of storing video data within a liquid crystal display, comprising:

a display electrode arranged within said liquid crystal display;

a storage element arranged within said liquid crystal display, said storage element comprising;

a source-drain path for receiving video data when said source-drain path is conductive; and

a memory circuit having first and second transistors, each of said transistors having a gate and first and second terminals, said first terminals being connectable to a power supply, said second terminals being grounded, said first terminal of said first transistor being further connected to said gate of said second transistor and said source-drain path, said first terminal of said second transistor being further connected to said gate of said first transistor and said display electrode, thereby storing said video data and providing driving current and voltage to charge said display electrode.

2. The storage cell as recited in claim 1, wherein said storage cell and connected said display electrode are arranged as a matrix across a glass plate, and each said display electrode is exposed to a liquid crystal material hermetically sealed within said liquid crystal display.

3. The storage cell as recited in claim 1, wherein said video data is transmitted over a conductive bit line, and said bit line is routed to said source-drain path.

4. The storage cell as recited in claim 1, wherein said source-drain path is rendered conductive during times in which a word line, routed to a gate region of a pass-gate transistor having said source-drain path, is active.

5. The storage cell as recited in claim 1, wherein said first and second transistors are metal oxide semiconductor field effect transistors and said first terminal is a drain and said second terminal is a source.

6. A liquid crystal display device having a plurality of storage cells arranged in a matrix and operatively coupled to red and write video data into and from, respectively, the liquid crystal display, the plurality of storage cells comprising:

a substantially transparent glass material;

a plurality of bit lines substantially parallel to each other extending across at least a portion of said glass material;

a plurality of word lines substantially parallel to each other and substantially perpendicular to said bit lines extending across at least a portion of said glass material;

a plurality of display electrodes arranged coplanar with each other and extending across at least a portion of said glass material;

a plurality of pass-gate transistors, each pass-gate transistor having a first terminal connected as an output, a second terminal connected to one of said plurality of bit lines, and a gate connected to one of said plurality of word line, whereby one of said plurality of pass-gate transistors is capable of reading video data on one of said plurality of bit lines from said respective second terminal to said respective first terminal during times in which one of said plurality of word lines is active; and

a plurality of memory circuits in corresponding relation with said plurality of pass-gate transistors and said plurality of display electrodes, each of said memory circuits having first and second corresponding transistors, each of said transistors having a gate and first and second terminals, said first terminals being connectable to a power supply, said second terminals being grounded, said first terminal of each of said first transistors being further connected to said gate of said corresponding second transistor and said second terminal of said corresponding pass-gate transistor, said first terminal of each of said second transistors being further connected to said gate of said corresponding first transistor and said corresponding display electrode, whereby each of said memory circuits is capable of storing said video data voltage to charge said corresponding display electrode.

7. The liquid crystal display device as recited in claim 6, further comprising a substantially planar common electrode, a dielectric material, and a liquid crystal material capable of polarizing a light beam, said liquid crystal material being interposed between said substantially planar common electrode and said dielectric material, said dielectric material covering each bit line, each word line, each transistor and each memory circuit.

8. The liquid crystal display device as recited in claim 6, further comprising a substantially planar common electrode and a liquid crystal material capable of polarizing light, said crystal material being interposed between said substantially planar common electrode and said plurality of display electrodes arranged coplanar with each other.

9. The liquid crystal display device as recited in claim 6, wherein said bit lines and said word lines are conductive and transparent.

10. The liquid crystal display device as recited in claim 6, wherein said bit lines and said word lines comprise indium tin oxide.

11. The liquid crystal display device as recited in claim 6, wherein said plurality of pass-gate transistors are responsive to an activated word line for erasing said video data stored in said memory circuit.

12. The liquid crystal device as recited in claim 6, wherein said pass-gate transistors, said first transistors, and said second transistors are thin film metal oxide semiconductor field effect transistors and said first terminal is a drain and said second terminal is a source.

13. A liquid crystal display comprising:

a first glass material having a common electrode extending across a substantial portion of one surface of said first glass material;

a second glass material having one surface adapted for receiving;

a plurality of spaced, substantially coplanar display electrodes;

a plurality of pass-gate transistors, each of said pass-gate transistors having a source-drain path and a gate terminal, wherein a data signal is passed through said source-drain path when said gate terminal of said pass-gate transistor is activated;

a plurality of latching circuits, each of said latching circuits comprising a pair of cross-coupled first and second transistors, each of said transistors having a gate, a drain connected to a pull-up resistor, and a source connected to a ground, wherein said drain of said first transistor is connected to said display electrode and to said gate of said second transistor and wherein said drain of said second transistor is connected to said drain of said pass-gate transistor and to said gate of the first transistor;

a liquid crystal material interposed between said common electrode and said plurality of display electrodes; and

a dielectric material interposed between said liquid crystal material and said plurality of pass-gate transistors and latching circuits, each of said plurality of latching circuits storing and providing driving current and voltage to charge a respective one of said plurality of display electrodes.

14. The liquid crystal display as recited in claim 13, wherein each said display electrode is arranged in close proximity to one of said plurality of pass-gate transistors and one of said plurality of latching circuits to form a pixel region.

15. The liquid crystal display as recited in claim 14, wherein said pixel region is arranged adjacent other pixel regions to form an array of pixels extending across the surface of said second glass material.

16. The liquid crystal display as recited in claim 13, wherein said video data is transmitted over a conductive word line, and said word line is routed to said source-drain path.

17. The liquid crystal display as recited in claim 13, wherein said source-drain path is rendered conductive during times in which a bit line, routed to said gate terminal of said pass-gate transistor having said source-drain path, is active.

18. The liquid crystal display as recited in claim 13, wherein said pass-gate transistors and said cross-coupled first and second transistors are thin film metal oxide semiconductor field effect transistors.