Method for driving liquid crystal display device

Abstract

An object is to suppress deterioration of a displayed image even when a refresh rate is reduced in displaying a still image. A liquid crystal display device includes a pixel transistor electrically connected to a pixel electrode, and a capacitor having one electrode electrically connected to the pixel electrode and the other electrode electrically connected to a capacitor line. The pixel transistor is turned on and a voltage based on an image signal is supplied to the pixel electrode, and then, the pixel transistor is turned off so that a holding period during which the pixel electrode holds the voltage based on the image signal starts. A holding signal corresponding to change of the voltage based on the image signal in the pixel electrode in the holding period is supplied to the capacitor line so that a potential of the pixel electrode is constant.

1 . (canceled) 
     
     
         2 . A method for driving a liquid crystal display device, the liquid crystal display device comprising a transistor electrically connected to a pixel electrode, and a capacitor having a first electrode electrically connected to the pixel electrode and a second electrode electrically connected to a capacitor line, wherein a channel formation region of the transistor comprises an oxide semiconductor, and wherein an off-state current per micrometer of a channel width of the transistor is 10 aA/μm or less,
 the method comprising the steps of: 
 supplying an image signal to the pixel electrode through the transistor by turning on the transistor in a writing period; 
 holding a potential of the pixel electrode by turning off the transistor in a holding period; and 
 adjusting a potential of the capacitor line at least during the holding period. 
 
     
     
         3 . The method for driving a liquid crystal display device according to  claim 2 , wherein the potential of the pixel electrode is held for 60 seconds or longer. 
     
     
         4 . The method for driving a liquid crystal display device according to  claim 2 ,
 wherein the liquid crystal display device is capable of displaying a still image and a moving image, and   wherein a refresh rate during display of the still image is lower than a refresh rate during display of the moving image.   
     
     
         5 . The method for driving a liquid crystal display device according to  claim 2 ,
 wherein the liquid crystal display device comprises a plurality of pixels arranged in a column,   wherein each of the plurality of pixels comprises the transistor and the capacitor, and   wherein the second electrodes of the capacitors of the plurality of pixels arranged in the same column are electrically connected to the same capacitor line.   
     
     
         6 . The method for driving a liquid crystal display device according to  claim 2 ,
 wherein the liquid crystal display device further comprises a current source circuit being electrically connected to the second electrode of the capacitor through the capacitor line, and   wherein current flows in the current source circuit when the liquid crystal display device displays a still image.   
     
     
         7 . A method for driving a liquid crystal display device, the liquid crystal display device comprising a transistor electrically connected to a pixel electrode, and a capacitor having a first electrode electrically connected to the pixel electrode and a second electrode electrically connected to a capacitor line, wherein a channel formation region of the transistor comprises an oxide semiconductor, and wherein an off-state current per micrometer of a channel width of the transistor is 10 aA/μm or less,
 the method comprising the steps of: 
 supplying an image signal to the pixel electrode through the transistor by turning on the transistor in a writing period; and 
 holding a potential of the pixel electrode by turning off the transistor in a holding period, 
 wherein a potential of the capacitor line is changed at least in the holding period. 
 
     
     
         8 . The method for driving a liquid crystal display device according to  claim 7 , wherein the potential of the pixel electrode is held for 60 seconds or longer. 
     
     
         9 . The method for driving a liquid crystal display device according to  claim 7 ,
 wherein the liquid crystal display device is capable of displaying a still image and a moving image, and   wherein a refresh rate during display of the still image is lower than a refresh rate during display of the moving image.   
     
     
         10 . The method for driving a liquid crystal display device according to  claim 7 ,
 wherein the liquid crystal display device comprises a plurality of pixels arranged in a column,   wherein each of the plurality of pixels comprises the transistor and the capacitor, and   wherein the second electrodes of the capacitors of the plurality of pixels arranged in the same column are electrically connected to the same capacitor line.   
     
     
         11 . The method for driving a liquid crystal display device according to  claim 7 ,
 wherein the liquid crystal display device further comprises a current source circuit being electrically connected to the second electrode of the capacitor through the capacitor line, and   wherein current flows in the current source circuit when the liquid crystal display device displays a still image.   
     
     
         12 . A method for driving a liquid crystal display device, the liquid crystal display device comprising a transistor electrically connected to a pixel electrode, and a capacitor having a first electrode electrically connected to the pixel electrode and a second electrode electrically connected to a capacitor line, wherein a channel formation region of the transistor comprises an oxide semiconductor, and wherein an off-state current per micrometer of a channel width of the transistor is 10 aA/μm or less,
 the method comprising the steps of: 
 supplying an image signal to the pixel electrode through the transistor by turning on the transistor in a writing period; and 
 holding a potential of the pixel electrode by turning off the transistor in a holding period, 
 wherein one frame period comprises the writing period and the holding period, and 
 wherein a potential of the capacitor line is only lowered monotonically in the one frame period or is only raised monotonically in the one frame period. 
 
     
     
         13 . The method for driving a liquid crystal display device according to  claim 12 , wherein the potential of the pixel electrode is held for 60 seconds or longer. 
     
     
         14 . The method for driving a liquid crystal display device according to  claim 12 ,
 wherein the liquid crystal display device is capable of displaying a still image and a moving image, and   wherein a refresh rate during display of the still image is lower than a refresh rate during display of the moving image.   
     
     
         15 . The method for driving a liquid crystal display device according to  claim 12 ,
 wherein the liquid crystal display device comprises a plurality of pixels arranged in a column,   wherein each of the plurality of pixels comprises the transistor and the capacitor, and   wherein the second electrodes of the capacitors of the plurality of pixels arranged in the same column are electrically connected to the same capacitor line.   
     
     
         16 . The method for driving a liquid crystal display device according to  claim 12 ,
 wherein the liquid crystal display device further comprises a current source circuit being electrically connected to the second electrode of the capacitor through the capacitor line, and   wherein current flows in the current source circuit when the liquid crystal display device displays a still image.