Active matrix electroluminescent display device

(54) ACTIVE MATRIX ELECTROLUMINESCENT DISPLAY DEVICE

(75) Inventors: John M. Shannon, Whyte Leafe (GB);

Alan G. Knapp, Crawley (GB)

(73) Assignee: Koninklijke Philips Electronics N.V.,

Eindhoven (NL)

( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 188 days.

(21) Appl. No.: 09/658,925

(22) Filed: Sep. 11, 2000

(30) Foreign Application Priority Data

Sep. 11, 1999 (GB) 9921425

Mar. 13, 2000 (GB) 0005811

(51) Int. C I. G09G 3/30

(52) U.S. CI 345/76; 345/77; 315/169.3

(58) Field of Search 345/74.1, 75.1,

345/75.2, 76, 77, 78, 79, 80, 81, 82, 83;

315/169.1, 169.3

(56) References Cited

U.S. PATENT DOCUMENTS

FOREIGN PATENT DOCUMENTS

EP 0653741 Al 5/1995 G09G/3/30

EP 0717446 A2 6/1996 H01L/27/15

EP 0923067 Al 6/1999 G09G/3/30

WO W09636959 11/1996 G09G/3/30

WO WO9965012 12/1999 G09G/3/30

* cited by examiner

Primary Examiner—-Xiao Wu

(57) ABSTRACT

An active matrix electroluminescent display device in which the drive current through an electroluminescent display element (20) in each pixel (10) in a drive period is controlled by a driving device (22) based on a drive signal applied during a preceding address period and stored as a voltage on an associated storage capacitor (36). In order to counteract the effects of display element ageing, through which the light output for a given drive signal level diminishes over time, the pixel includes electro-optic discharging means (40) coupled to the storage capacitor and responsive to the display element's light output to leak stored charge and to control the integrated light output of the display element in the drive period. For improved control, the discharging means is arranged to rapidly discharge the capacitor at a controlled point in the drive period, upon the drive of the display element falling to a low level. A photoresponsive transistor can conveniently be utilised for this purpose.

5 Claims, 6 Drawing Sheets