Active matrix LCD based on diode switches and methods of improving display uniformity of same

• US 6,738,035 B1
• Filed: 06/01/2000
• Issued: 05/18/2004
• Est. Priority Date: 09/22/1997
• Status: Expired due to Fees

• Current Assignee: Rd&Ip LLC
• Original Assignee: Nongqiang Fan
• Inventors: Fan, Nongqiang
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): LESPERANCE, JEAN E
• Application Number:
  US09/584,951
• Time in Patent Office: 1,447 Days
• Field of Search: 345/87, 345/88, 345/89, 345/90, 345/91, 345/92, 345/205, 345/206, 315/169.1, 315/169.2, 315/169.3
• US Class Current: 345/87
• CPC Class Codes: G09G 2300/088 using a non-linear two-terminal element
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

An active matrix LCD using two-terminal non-linear elements as switching elements is disclosed. This new kind of active matrix LCD comprises a matrix of pixel elements, and each pixel element comprises a first two-terminal non-linear element (5), a second two-terminal non-linear element (5′), and a capacitor (8) for holding the voltage on the LCD cell. When both the first and the second two-terminal non-linear elements are in the conducting state, the voltage on the capacitor (8) can be changed. When both the first and the second two-terminal non-linear elements are in the non-conducting state, the voltage on the capacitor (8) can be maintained. To improve the display uniformity of an active matrix LCD based on two-terminal non-linear elements, the display characteristics of each pixel is measured and stored in a calibration memory (70), and the correct driving parameters for each pixel are calculated based on the display characteristics of the pixel fetched from the calibration memory (70). Finally, the correct driving parameters for each pixel is used to drive the active matrix LCD. The correct driving parameters for each pixel can be stored in a video memory (80).

Claims

1. A method for creating a video data signal compensated for the non-uniformity of an LCD having a matrix of pixels, comprising the steps of:

measuring the display characteristics of each pixel, having an LCD cell, in the matrix of pixels;

deriving at lest one calibration parameter for each pixel in the matrix of pixels from the measured display characteristics of the corresponding pixel;

storing into a calibration memory at least one calibration parameter for each pixel in the matrix of pixels;

obtaining the compensated video word for each pixel in the matrix of pixels by using the calibration parameter for the corresponding pixel fetched from the calibration memory;

storing into a video memory having a matrix of memory-cells the compensated video word for each pixel in the matrix of pixels;

creating the compensated video data signal by fetching the compensated video word for each pixel from the video memory; and

wherein each pixel including

(a) a capacitor having a first terminal and a second terminal,

(b) a first non-linear element having a first terminal connecting to the first terminal of said capacitor,

(c) a second non-linear element having a first terminal connecting to the first terminal of said capacitor,

(d) a third non-linear element having a first terminal connecting to the second terminal of said capacitor, and

(e) a resistive element having a first terminal connecting to the second terminal of said capacitor.

2. A method of claim 1 wherein

said step of deriving further comprises the step of determining the calibration parameters of each pixel based on a device model by using the measured display characteristics of the corresponding pixel as the row data; and

where said step of obtaining further comprises the step of calculating the correct driving parameters by using a device model as the algorithm and by using the calibration parameters of the corresponding pixel from the calibration memory as the raw data.

3. A method of claim 1 wherein the video memory is a video RAM.

4. A method of claim 1 wherein the video memory is a VRAM.

5. An active matrix LCD with improved display uniformity, comprising:

an array of row driving lines;

a first array of column driving lines being perpendicular to said array of row driving lines;

a second array of column driving lines being in parallel with said first array of column driving lines;

a matrix of pixel elements wherein a pixel element comprising,

(a) a capacitor having a first terminal and a second terminal,

(b) a first non-linear element having a first terminal connecting to the first terminal of said capacitor and having a second terminal connecting to a column driving line in said first array of column driving lines,

(c) a second non-linear element having a first terminal connecting to the first terminal of said capacitor, and having a second terminal connecting to a common voltage,

(d) a third non-linear element having a first terminal connecting to the second terminal of said capacitor and having a second terminal connecting to a row driving line in said array of row driving lines,

(e) a resistive element having a first terminal connecting to the second terminal of said capacitor and having a second terminal connecting to a column driving line in said second array of column driving lines;

a calibration memory having at least one calibration parameter for said pixel element stored therein;

electronic circuitry for obtaining the correct driving parameters for said pixel element by using the calibration parameter for said pixel element fetched from said calibration memory;

electronic circuitry for driving said pixel element with the correct driving parameters for said pixel element;

a video memory having the compensated video word for said pixel element stored therein; and

electronic circuitry for converting the compensated video word into the correct driving parameter for said pixel element.

6. The active matrix LCD of claim 5 wherein the video memory is a video RAM.

7. The active matrix LCD of claim 5 wherein the video memory is a VRAM.

8. An active matrix LCD comprising:

an array of row driving lines;

a first array of column driving lines being perpendicular to said array of row driving lines;

a second array of column driving lines being in parallel with said first array of column driving lines; and

a matrix of pixel elements wherein a pixel element comprising,

(a) a capacitor having a first terminal and a second terminal,

(b) a first non-linear element having a first terminal connecting to the first terminal of said capacitor and having a second terminal connecting to a column driving line in said first array of column driving lines,

(c) a second non-linear element having a first terminal connecting to the first terminal of said capacitor, and having a second terminal connecting to a common voltage,

(d) a third non-linear element having a first terminal connecting to the second terminal of said capacitor and having a second terminal connecting to a row driving line in said array of row driving lines, and

(e) a resistive element having a first terminal connecting to the second terminal of said capacitor and having a second terminal connecting to a column driving line in said second array of column driving lines.

9. An active matrix LCD of claim 8 wherein said first non-linear element, said second non-linear element and said third non-linear element are selected from a group consisting of metal-insulator-metal diode, pn diode, diode complex comprising a metal-insulator-metal diode and a resistor, diode complex comprising a pn diode and a resistor, avalanche diode complex comprising two thin film pn diodes connecting inversely to each other in series, and any combination thereof.

10. An active matrix LCD of claim 8 further comprising:

a calibration memory having at least one calibration parameter for each pixel element in said matrix of pixel elements stored therein.

11. An active matrix LCD of claim 10 wherein

the calibration parameter for each pixel element being the correct data-voltages for a gray levels of that pixel element;

and

said calibration memory having the correct data-voltages for all gray levels of each pixel element stored therein as a complete lookup table.

12. An active matrix LCD of claim 10 wherein

the calibration parameter for each pixel element being the correct data-voltages for a gray levels of that pixel element;

and

said calibration memory having the correct data-voltages for selected gray levels of each pixel element stored therein as a partial lookup table.

13. An active matrix LCD of claim 10 wherein

the calibration parameter for each pixel element being a set of fitting parameters for the display characteristics of the corresponding pixel element based on a device model.

14. An active matrix LCD of claim 10 further comprising:

electronic circuitry for determining the calibration parameter for each pixel element in said matrix of pixel elements.

15. An active matrix LCD of claim 10 further comprising:

electronic circuitry for calculating the correct driving parameter for each pixel element by fetching the calibration parameter for the corresponding pixel element from said calibration memory.

16. An active matrix LCD of claim 15 further comprising:

a video memory having the compensated video word for each pixel element stored therein, where the compensated video word for each pixel element being derived from the correct driving parameter for the corresponding pixel.

17. An active matrix LCD of claim 16 wherein

the calibration parameter for each pixel element being the correct data-voltages for a gray levels of that pixel element;

and

said calibration memory having the correct data-voltages for all gray levels of each pixel element stored therein as a complete lookup table.

18. An active matrix LCD of claim 16 wherein

the calibration parameter for each pixel element being the correct data-voltage for a gray levels of that pixel element;

and

said calibration memory having the correct data-voltages for selected gray levels of each pixel element stored therein as a partial lookup table.

19. An active matrix LCD of claim 16 wherein

the calibration parameter for each pixel element being a set of fitting parameters for the display characteristics of the corresponding pixel element based on a device model.