Electroluminescent display device

• US 20030098828A1
• Filed: 11/22/2002
• Published: 05/29/2003
• Est. Priority Date: 11/28/2001
• Status: Active Grant

• Current Assignee: Beijing Xiaomi Mobile Software Co., Ltd. (Xiaomi Corp.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Johnson, Mark T., Childs, Mark J., Hunter, Iain M.
• Granted Patent: US 8,125,414 B2
• Time in Patent Office: Days
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2310/0221 with use of split matrices G09G3/3644 and G09G3/3666 take precedence
• CPC Class Codes: G09G 2320/046 Dealing with screen burn-in prevention or compensation of the effects thereof
• CPC Class Codes: G09G 2330/022 in absence of operation, e.g. no data being entered during a predetermined time
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/2074 using sub-pixels
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across the light-emitting element

Abstract

An EL display device is operable in analogue and digital modes. In the analogue mode a current is supplied to the EL display elements (2) in dependence on a data signal (6) supplied to the pixel, and in the digital mode one of two voltages is provided across the EL display elements in dependence on the data signal supplied to the pixel. This enables the display to have a low power standby mode in which a digital drive scheme is implemented. This is particularly appropriate for static images and preferably for images without grey scales. The first mode is the normal current addressing mode.

Claims

1. An electroluminescent (EL) display device comprising an array of display pixels, each display pixel comprising an EL display element and a driving circuit, wherein each pixel is operable in first and second modes, wherein in the first mode an analogue current is supplied to the EL display element by the driving circuit in dependence on a data signal supplied to the pixel and in the second mode one of two voltages is provided across the EL display element by the driving circuit in dependence on the data signal supplied to the pixel.

2. A device as claimed in claim 1, wherein the driving circuit comprises a current source section for supplying current to the EL display element, wherein in the first mode the current source section is supplied by a first voltage and supplies the analogue current to the EL display element and in the second mode the current source section is supplied by a second voltage and drives the EL display element to one of two states.

3. A device as claimed in claim 1 or 2, wherein the current source section of each driving circuit comprises a transistor connected between a supply voltage line and the EL element and wherein the gate voltage on the transistor is controlled in dependence on the data signal.

4. A device as claimed in claim 3, wherein a first voltage is provided by the supply voltage line in the first mode of operation, and a second voltage is provided by the supply voltage line in the second mode of operation.

5. A device as claimed in claim 4, wherein the first voltage and the range of levels of the-data signal in the first mode are selected such that the transistor is operable in the linear region, such that the current provided by the current source is a function of the data signal.

6. A device as claimed in claim 4 or 5, wherein the second voltage and the data signal levels in the second mode are selected such that the transistor is fully turned on or turned off, such that a fixed voltage dependent on the second voltage is supplied to or isolated from the EL element.

7. A device as claimed in any one of claims 3 to 6, wherein each pixel comprises a single voltage supply line, and switching means is provided for selecting the voltage on the voltage supply line.

8. A device as claimed in any one of claims 3 to 6, wherein each pixel comprises two voltage supply lines, and wherein a mode switching arrangement is provided for selecting which voltage supply line signal is used to supply the current source transistor.

9. A device as claimed in claim 8, wherein a mode switching arrangement is provided for a group of pixels.

10. A device as claimed in claim 9, wherein each voltage supply line is coupled to the current source transistor through a respective coupling transistor, and wherein the mode switching arrangement selectively provides a first output for switching a first coupling transistor on and a second coupling transistor off, or a second output for switching the first coupling transistor off and the second coupling transistor on.

11. A device as claimed in any preceding claim, wherein each EL display element comprises a polymer light emitting diode.

12. A device as claimed in any preceding claim, wherein the pixels are arranged in rows and columns, and wherein the data signal is provided on column conductors.

13. A device as claimed in claim 12, wherein each row of pixels shares a row conductor, and wherein each pixel comprises an address transistor coupled between the column conductor and the current source section.

14. A device as claimed in any preceding claim, further comprising means for applying a mode select to enable the mode to be selected for a pixel being addressed.

15. A device as claimed in claim 14, wherein the means for applying a mode select signal applies a signal to a region of the display, based on a measure of the amount of movement within the image for that region of the display.

16. A portable electronic device comprising a display device as claimed in any preceding claim.

17. A method of driving an electroluminescent (EL) display device comprising an array of pixels, each pixel comprising an electroluminescent (EL) display element and a drive circuit, the method comprising, for each pixel of the display:

selecting an analogue or a digital drive mode;

when the analogue mode is selected, supplying a data signal to the pixel thereby resulting in an analogue current being supplied to the EL display element;

when the digital mode is selected, supplying a data signal to the pixel thereby driving the EL display element to one of two states.

18. A method as claimed in claim 17, wherein the driver circuit comprises a current source section for supplying current to the EL display element, and wherein in the first mode the current source section is supplied using a first voltage and in the second mode the current source section of the pixel is supplied using second voltage.

19. A method as claimed in claim 17 or 18, wherein the analogue or the digital drive mode is selected for all pixels of the display within any frame period.

20. A method as claimed in claim 19, wherein the drive mode is selected in dependence on the display requirement.

21. A method as claimed in claim 19, wherein the digital drive mode is selected for the display of static images and the analogue drive mode is selected for the display of moving images.

22. A method as claimed in claim 17 or 18, wherein within a frame period, the digital and analogue drive modes may be selected independently for different regions of the display.

23. A method as claimed in claim 22, wherein the drive mode for each region of the display is selected in dependence on the amount of previous image movement within the region.

24. A method as claimed in claim 23, wherein the amount of previous image movement is derived from MPEG data.