Active matrix electroluminescent display device

• US 6,441,560 B1
• Filed: 08/18/2000
• Issued: 08/27/2002
• Est. Priority Date: 08/19/1999
• Status: Expired due to Term

• Current Assignee: Beijing Xiaomi Mobile Software Co., Ltd. (Xiaomi Corp.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Hunter, Iain M.
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Vu, Jimmy T.
• Application Number:
  US09/642,257
• Time in Patent Office: 739 Days
• Field of Search: 315/169.1, 315/169.3, 315/169.4, 315/169.2, 313/505, 313/506, 313/509, 313/512, 345/76, 345/77, 345/56
• US Class Current: 315/169.1
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/088 using a non-linear two-terminal element
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 2360/148 the light being detected by light detection means within each pixel
• CPC Class Codes: G09G 3/32 semiconductive, e.g. using light-emitting diodes [LED]
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: H10K 59/13 comprising photosensors that control luminance

Abstract

An active matrix electroluminescent display device comprises an array of display pixels (10) which each include a current-driven electroluminescent display element (20) connected to a driving device (22) controlling the current flowing through the display element in a drive period according to a voltage stored on a capacitance (36) and determined by a data signal applied in a preceding address period. In order to compensate for ageing effects in the display element, electro-optic devices (45, 40) are included in the pixel for adjusting the voltage stored on the capacitance in dependence on the light output of its display element during the address period.

Claims

1. An active matrix electroluminescent display device comprising an array of display pixels with each pixel comprising an electroluminescent display element and a driving device for controlling the current through the display element based on a drive signal applied to the pixel during an address period and stored as a voltage on a storage capacitance connected to the driving device, characterised in that each pixel includes electro-optic adjustment means which is responsive to light produced by the display element during an address period and arranged to adjust in the address period the voltage signal stored on the capacitance in the address period in accordance with the light output level of the display element.

2. An active matrix electroluminescent display device according to claim 1, characterised in that the electrooptic adjustment means regulates a current flowing in the pixel during the address period according to an applied data signal, upon which current the voltage stored on the storage capacitance following the address period is dependent.

3. An active matrix electroluminescent display device according to claim 1, characterised in that the electro-optic means comprises an electro-optic device arranged to shunt an electrical current flowing through the storage capacitance during the addressing period according to the display element light output.

4. An active matrix electroluminescent display device according to claim 3, characterised in that the electro-optic device is connected to the storage capacitance via a switch device which is operated during a pixel address period so as to connect the electro-optic device in parallel with the storage capacitance.

5. An active matrix electroluminescent display device according to claim 3, characterised in that the electro-optic device comprises a photodiode.

6. An active matrix electroluminescent display device according to claim 1, characterised in that the driving device comprises a thin film transistor.

7. The active matrix electroluminescent display device according to claim 1 wherein the array of pixels is connected to a plurality of respective row lines and to a plurality of respective column lines, said active matrix electroluminescent display device further comprising;

a row address circuit coupled to said row lines, and

a column data driver circuit coupled to said column lines.

8. An active matrix electroluminescent display device according to claim 2, characterised in that the electro-optic means comprises an electro-optic device arranged to shunt an electrical current flowing through the storage capacitance during the addressing period according to the display element light output.

9. The active matrix electroluminescent display device according to claim 1 wherein the drive device for each pixel comprises a drive transistor coupled to its associated pixel display element, and

the electro-optic adjustment means for each pixel comprises an electro-optic device, and each pixel further comprises;

an address transistor coupled to the electro-optic device and to a control electrode of the drive transistor, and

a further switch transistor coupled to the storage capacitance and to the electro-optic device.

10. The active matrix electroluminescent display device according to claim 9 wherein the address transistor and the further switch transistor are coupled in series between a column data line and the control electrode of the drive transistor,

the electro-optic device is coupled to a circuit point between the address transistor and the further switch transistor,

control electrodes of the address transistor and the further switch transistor are coupled to a row address line, and

the storage capacitance is coupled to a circuit point between the further switch transistor and the control electrode of the drive transistor.

18. The active matrix electroluminescent display device according to claim 1, wherein each pixel driving device comprises a respective transistor coupled to the storage capacitance and to its associated electroluminescent display element and electrically controlled at its control electrode by the voltage stored on its respective storage capacitance.

19. The active matrix electroluminescent display device according to claim 1, wherein each pixel further comprises;

an address transistor coupled to a control electrode of the driving device via a switch device, and

said address transistor and said switch device are operated in synchronism from a row address circuit.

20. The active matrix electroluminescent display device according to claim 1, wherein the driving device of each pixel comprises a drive transistor and each pixel also comprises an address transistor controlled by a row address circuit, and the drive transistor is controlled by the stored voltage on the storage capacitance, which stored voltage is determined by a data signal from a column data driver circuit.

11. An active matrix electroluminescent display device comprising:

an array of display pixels with each pixel comprising an electroluminescent display element and an associated driving device for controlling current through the associated display element based on a drive signal applied to the pixel from a data drive circuit during an address period and stored as a voltage on an associated storage capacitance connected to the associated driving device, wherein

each pixel includes an electro-optic device which is responsive to light produced by the display element during an address period and the electro-optic device adjusts, in the address period, a voltage stored on the storage capacitance in accordance with the light output level of the associated display element.

12. The active matrix electroluminescent display device according to claim 11 wherein the electro-optic device controls a current flowing in the pixel display element during the address period according to an applied data signal so that the voltage stored on the storage capacitance following the address period is dependent on said current.

13. The active matrix electroluminescent display device according to claim 11 wherein the electro-optic device is connected to the storage capacitance via a switch device which is operated during a pixel address period so as to connect the electro-optic device in parallel with the storage capacitance.

14. The active matrix electroluminescent display device according to claim 13 wherein each pixel further comprises;

an address transistor coupled to a control electrode of the driving device via the switch device, and

said address transistor and said switch device are operated simultaneously from a row address circuit.

15. The active matrix electroluminescent display device according to claim 11 wherein the data drive circuit applies a data current signal to the pixel during the address period.

16. The active matrix electroluminescent display device according to claim 11 wherein each pixel driving device comprises a switch transistor arranged to operate in saturation.

17. The active matrix electroluminescent display device according to claim 13 wherein the pixel switch device is turned off during a drive period of the pixel thereby to effectively electrically isolate the electro-optic device from the storage capacitance.