Methods and systems for compensating row-to-row brightness variations of a field emission display

• US 6,822,628 B2
• Filed: 06/28/2001
• Issued: 11/23/2004
• Est. Priority Date: 06/28/2001
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Candescent Intellectual Property Services, Inc., Candescent Technologies Corporation (Canon Inc.)
• Inventors: Cummings, William, Stanners, Colin, Liu, Jun (Gordon), Cressi, Lee, Dunphy, James C., Hansen, Ronald L., Spindt, Christopher J.
• Primary Examiner(s): Liang, Regina
• Assistant Examiner(s): Nguyen, Jennifer T.
• Application Number:
  US09/895,985
• Publication Number:
  US 20030011537A1
• Time in Patent Office: 1,244 Days
• Field of Search: 345/75.2, 345/63, 345/77, 345/211, 345/102, 345/531, 345/204, 345/207, 345/74.1, 345/75.1, 315/169.1, 315/169.3
• US Class Current: 345/75.2
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/0285 using tables for spatial correction of display data
• CPC Class Codes: G09G 3/22 using controlled light sources

Abstract

Methods for compensating for brightness variations in a field emission device. In one embodiment, a method and system are described for measuring the relative brightness of rows of a field emission display (FED) device, storing information representing the measured brightness into a correction table and using the correction table to provide uniform row brightness in the display by adjusting row voltages and/or row on-time periods. A special measurement process is described for providing accurate current measurements on the rows. This embodiment compensates for brightness variations of the rows, e.g., for rows near the spacer walls. In another embodiment, a periodic signal, e.g., a high frequency noise signal, is added to the row on-time pulse in order to camouflage brightness variations in the rows near the spacer walls. In another embodiment, the area under the row on-time pulse is adjusted to provide row-by-row brightness compensation based on correction values stored in a memory resident correction table. In another embodiment, the brightness of each row is measured and compiled into a data profile for the FED. The data profile is used to control cathode burn-in processes so that brightness variations are corrected by physically altering the characteristics of the emitters of the rows.

Claims

1. In a field emission display (FED) device comprising:

rows and columns of emitters; and

an anode electrode, a method of measuring display attributes of said FED device comprising the steps of;

a) in a scan fashion, individually driving each row and measuring the current drawn by each row, wherein a settling time is allowed after each row is driven;

b) measuring a background current level during a vertical blanking interval;

c) correcting current measurements taken during said step a) by said background current level to yield corrected current measurements;

d) averaging multiple corrected current measurements taken over multiple display frames to produce averaged corrected current values for all rows of said FED device;

e) generating a memory resident correction table based on said averaged corrected current values; and

f) measuring an RC decay function of said FED device at the last driven row of a frame; and

g) using said RC decay function to further correct values of said memory resident correction table.

2. A method as described in claim 1 wherein said step a) comprises the steps of:

a1) in a first frame, sequentially driving odd rows and measuring said current drawn by each odd row;

a2) simultaneous with said step a1) sequentially not driving even rows to create settling times between said odd rows;

a3) in a second frame, sequentially driving even rows and measuring said current drawn by each even row; and

a4) simultaneous with said step a3), sequentially not driving odd rows to create settling times between said even rows.

3. A method as described in claim 1 wherein said steps a)-e) are performed each time said FED device is turned on as part of an initialization and calibration sequence.

4. A method as described in claim 1 wherein said current is measured at said step a) for a given row by measuring the current at said faceplate in time correlation with driving said given row.

5. A method as described in claim 1 comprising the step of individually driving each row in a progressive scan fashion to display an image on said FED device, wherein said memory resident correction table is used to adjust the relative brightness of each row to a uniform level.

6. A method as described in claim 5 wherein the row driving voltage is adjusted, for each row, by said memory resident correction table.

7. A method as described in claim 5 wherein the row on-time period is adjusted, for each row, by said memory resident correction table.

8. A method as described in claim 1 comprising the step off) individually driving each row in a scan fashion to display an image on said FED device, wherein said memory resident correction table is used to adjust the relative brightness of each row to a uniform level and wherein step f) comprises the steps of:

f1) generating a correction signal that is periodic in nature;

f2) adding said correction signal to a row driving pulse to generate a corrected row driving pulse, wherein said row driving pulse is adjusted by said correction table;

f3) using said corrected row driving pulse to drive a row of said rows for a row on-time period; and

f4) generating a display frame by repeating steps f1)-f3) for each of said rows.