Display comprising organic smart pixels

• US 6,384,804 B1
• Filed: 11/25/1998
• Issued: 05/07/2002
• Est. Priority Date: 11/25/1998
• Status: Expired due to Term

• Current Assignee: Alcatel-Lucent USA, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Dodabalapur, Ananth, Sarpeshkar, Rahul
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): NGUYEN, FRANCIS N
• Application Number:
  US09/199,364
• Time in Patent Office: 1,259 Days
• Field of Search: 345/82, 345/76, 345/55, 345/205-206, 345/44-46, 313/483, 313/498, 315/169.1, 315/169.3, 315/169.4, 257/40
• US Class Current: 345/82
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than one capacitor
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2320/0219 Reducing feedthrough effects in active matrix panels, i.e. voltage changes on the scan electrode influencing the pixel voltage due to capacitive coupling
• CPC Class Codes: G09G 2320/029 by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements

Abstract

A display apparatus according to our invention comprises a multiplicity of nominally identical smart pixels, a given pixel comprising an organic light emitting diode and an organic or inorganic (e.g., amorphous or polycrystalline Si) pixel FET. The display also comprises drive/compensation circuitry adapted for mitigating or eliminating non-idealities associated with the organic components. Among the non-idealities are variations in mobility and/or threshold voltage of the pixel FET from transistor to transistor, change in mobility and/or threshold voltage with time in a given pixel FET, change over time of the LED characteristics, capacitive signal feed-through through the gate insulator of the pixel FETs by short rise/fall time pulses, poor on-off ratio of the pixel FET, and charge leakage through the gate dielectric. Exemplary drive/compensation circuitry is disclosed.

Claims

1. Display apparatus comprising:

a first substrate region having a multiplicity of nominally identical smart pixels; and

a smart pixel-free second substrate region; and

wherein each smart pixel comprises;

a) an organic light emitting diode; and

b) pixel circuitry for providing a current through the organic light emitting diode, the pixel circuitry comprising at least one field effect transistor connected in series with the organic light emitting diode;

characterized in that

c) the field effect transistors are organic transistors; and

d) the display apparatus comprises drive/compensation circuitry that mitigates one of transistor gate capacitive signal feed-through and transistor gate leakage currents that produce adverse effects on said smart pixels, a portion of said drive/compensation circuitry being disposed in said second substrate region.

2. Display apparatus according to claim 1, wherein said drive/compensation circuitry comprises C-MOS circuitry.

3. Display apparatus according to claim 1, wherein said drive/compensation circuitry mitigates gate capacitive signal feed-through in said field effect transistors.

4. Display apparatus according to claim 3, wherein said drive/compensation circuitry is selected to mitigate said capacitive signal feed-through by injection of a compensating charge into the gate terminal of the field effect transistor.

5. Display apparatus according to claim 1, wherein said drive/compensation circuitry corrects one or more of pixel-to-pixel brightness variations and time-dependent pixel-brightness variations.

6. Display apparatus according to claim 1, wherein said drive/compensation circuitry mitigates gate leakage currents in said field effect transistors.

7. Display apparatus according to claim 1 wherein said drive/compensation circuitry is selected to mitigate said charge leakage by setting a pixel ROW signal to an inactive high value and a pixel reset signal to a value above a drain supply voltage.

8. Display apparatus according to claim 1, wherein said drive/compensation circuitry measures, at predetermined intervals that are longer than a frame period of the display apparatus, one or more characteristics of each smart pixel and sets voltages applied to gates of said field effect transistors such that substantially all smart pixels have substantially the same light emission for a given signal provided to the display apparatus.

9. Display apparatus according to claim 8, wherein said drive/compensation circuitry mitigates the capacitive signal feed-through by injection of a compensating charge into the gates and mitigates the charge leakage by setting pixel ROW signals to inactive high values and pixel reset signals to values above a drain-supply voltage.

10. Display apparatus comprising:

a first substrate region having a multiplicity of nominally identical smart pixels; and

a smart pixel-free second substrate region; and

wherein each smart pixel comprises;

a) an organic light emitting diode; and

b) pixel circuitry for providing a current through the organic light emitting diode, the pixel circuitry comprising at least one field effect transistor connected in series with the organic light emitting diode;

characterized in that

c) the field effect transistors are organic transistors; and

d) the display apparatus comprises drive/compensation circuitry that mitigates adverse effects on said smart pixels by one or more non-idealities inherent to the organic transistors and/or organic light emitting diodes, a portion of said drive/compensation circuitry being disposed in said second substrate region, the drive/compensation circuitry being configured to measure a characteristic of each smart pixel.

11. Display apparatus according to claim 10, wherein said drive/compensation circuitry is configured to remeasure the characteristic of one of the smart pixels, at predetermined intervals that are longer than a frame period of the display apparatus.

12. Display apparatus according to claim 10, wherein said drive/compensation circuitry is configured to measure the characteristic of one of the smart pixels intermittently.

13. Display apparatus according to claim 10, wherein the drive/compensation circuitry is configured to store data on one of the smart pixels in a memory in response to measuring the characteristic of the one of the smart pixels.

14. Display apparatus according to claim 10, wherein said drive/compensation circuitry is configured to measure the characteristic of one of the smart pixels by applying pulses with different pulse heights to the one of the pixels.

15. Display apparatus of claim 10, wherein said drive/compensation circuitry sets voltages applied to gates of said field effect transistors in a manner that is responsive to said measurements on associated ones of said smart pixels.

16. Display apparatus of claim 10, wherein the drive/compensation circuitry is configured to mitigate one of transistor gate capacitive signal feed-through and transistor gate leakage current.