Display device

• US 6,806,857 B2
• Filed: 05/01/2001
• Issued: 10/19/2004
• Est. Priority Date: 05/22/2000
• 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 Mcintosh, Johnson, Mark Thomas, Sempel, Adrianus, Young, Edward Willem Albert
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): NGUYEN, KIMNHUNG T
• Application Number:
  US09/846,420
• Publication Number:
  US 20010052606A1
• Time in Patent Office: 1,267 Days
• Field of Search: 345/45, 345/46, 345/55, 345/74.1, 345/76, 345/89, 345/92, 315/169.1, 315/169.3, 315/169.4
• US Class Current: 345/92
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0866 by means of changes in the pixel supply voltage
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• 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 3/3241 the current through the light-emitting element being set using a data current provided by the data driver, e.g. by using a two-transistor current mirror
• CPC Class Codes: G09G 3/325 the data current flowing through the driving transistor during a setting phase, e.g. by using a switch for connecting the driving transistor to the data driver

Abstract

Grey scale linearity and power efficiency in active matrix (O) LEDs are enhanced by storing the grey value in a memory circuit, coupled to an adjusting circuit, preferably via a current mirror.

Claims

1. A display device comprising:

a matrix of pixels at the area of crossings of row and column electrodes, each pixel including a current adjusting circuit based on a memory element and a luminescent element in series with the current adjusting circuit; and

a switch between a plurality of the luminescent elements and a connection point for an operating voltage,

wherein the column electrode can be electrically coupled to a current source, and wherein the current adjusting circuit includes a further circuit arranged between the column electrode and a connection point of the memory element such that the current adjusting circuit substantially does not conduct during adjustment of a value of the current through the luminescent element.

2. A display device as claimed in claim 1, wherein the memory element comprises a TFT transistor and a capacitor between the gate electrode and a further connection of the TFT transistor, and wherein the further circuit comprises at least one TFT transistor with a gate electrode connected to a row electrode.

3. A display device as claimed in claim 2, wherein the further circuit comprises two series arranged TFT transistors between the column electrode and the memory element, which transistors have their gate electrodes connected a common row electrode, the common point of the two series-arranged TFT transistors being connected in an electrically conducting manner to an electrode of the luminescent element.

4. A display device as claimed in claim 1, wherein the further circuit is electrically detachable from the memory element, and wherein, in a coupled state, the further circuit constitutes a current mirror with the memory element.

5. A display device as claimed in claim 4, wherein the current mirror is asymmetrical.

6. A display device comprising:

a matrix of pixels at the area of crossings of row and column electrodes, each pixel including a current adjusting circuit based on a memory element and a luminescent element in series with the current adjusting circuit; and

a switch between a plurality of the luminescent elements and a connection point for an operating voltage, wherein said display device comprises drive means for varying the time during which the switch is closed.

7. A display as claimed in claim 6, wherein the drive means for luminescent elements of a different color can close associated switches during different periods of time.

8. A display device, comprising:

a plurality of pixels arranged in a matrix of rows and columns, wherein each pixel includes;

a luminescent element; and

current adjusting means for adjusting a current flowing through the luminescent element said current adjusting means including a memory element and being connected to a first terminal of the luminescent element;

a plurality of row lines each connected to one of the rows of pixels;

a plurality of column lines each connected to one of the columns of pixels;

current supply means for supplying current through the column lines to the plurality of pixels; and

switching means being operatively controlled to close a circuit carrying said current flowing through at least one of the luminescent elements during a first period, and to open the circuit and prevent said current from flowing through said at least one luminescent element during a second period.

9. The display device of claim 8, wherein the switching means is operatively connected between a supply voltage terminal and a second terminal of said at least one luminescent element, to close the circuit.

10. The display device of claim 8, the current adjusting means comprises at least one switching element between a column line and the memory element.

11. The display device of claim 8, wherein the memory element comprises a transistor and a capacitor between the gate electrode and one of a source or drain electrode of the transistor, the other of the source or drain electrode being connected to the first terminal of the luminescent element.

12. The display device of claim 8, wherein the switching means comprises a plurality of switches, each switch being connected between one or more of the pixels and a supply voltage terminal, each switch being individually controllable such that a first group of pixels has the current flowing through corresponding luminescent elements during the first period, and a second group of pixels does not have the current flowing through the corresponding luminescent elements during the first period.

13. A display device, comprising:

a plurality of pixels arranged in a matrix of rows and columns, wherein each pixel includes;

a luminescent element; and

current adjusting means for adjusting a current flowing through the luminescent element, said current adjusting means including a memory element and being connected to a first end of the luminescent element;

a plurality of row lines each connected to one of the rows of pixels;

a plurality of column lines each connected to one of the columns of pixels;

current supply means for supplying current through the column lines to the plurality of pixels; and

switching means connected between a second end of each of the luminescent elements and a fixed voltage.

14. The display device of claim 13, wherein the current adjusting means comprises at least one switching element between a column line and the memory element.

15. The display device of claim 13, wherein the memory element comprises a transistor and a capacitor between the gate electrode and one of a source or drain electrode of the transistor, the other of the source or drain electrode being connected to the first terminal of the luminescent element.

16. The display device of claim 13, wherein the switching means comprises a plurality of switches, each switch being connected between the second terminal of one or more of the luminescent elements and the fixed voltage, each switch being individually controllable such that a first group of luminescent elements is connected to the fixed voltage during a first period, and a second group of luminescent elements is not connected to the fixed voltage during the first period.