(12) United States Patent ao) Patent No.: Us 7,106,290 B2
Inukai et al. (45) Date of Patent: Sep. 12,2006
(54) METHOD OF DRIVING EL DISPLAY DEVICE
(75) Inventors: Kazutaka Inukai, Kanagawa (JP);
Mitsuaki Osame, Kanagawa (JP);
Tomoyuki Iwabuchi, Kanagawa (JP)
(73) Assignee: Semiconductor Energy Laboratory
Co., Ltd., Atsugi (JP)
( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 231 days.
(21) Appl. No.: 09/944,085
(22) Filed: Sep. 4, 2001
(65) Prior Publication Data
US 2002/0047852 Al Apr. 25, 2002 (30) Foreign Application Priority Data
Sep. 4, 2000 (JP) 2000-267164
A method of driving an EL display device in which pseudo contours are difficult to be seen is provided. A method of driving an EL display device in which a plurality of pixels, each having a first TFT, a second TFT, a third TFT, and an organic EL element, are formed has the following: n+m display periods (where n and m are both natural numbers) appear in one frame period; the n+m display periods each correspond to one bit of a digital video signal among n bits of the digital video signal; a plurality of display periods, among the n+m display periods, correspond to the same bit of the digital video signal; and display periods corresponding to other bits of the digital video signal, among the n+m display periods, appear during the plurality of display periods.