The present invention relates to a flat-panel display device such as a liquid crystal display device, and a display method of the same.
A flat-panel display device has characteristics of being thin and light-weight, and low power consumption, and is widely used in various fields as display devices of personal computers or word processors, display devices of television receivers, car navigation systems or game machines, and display devices of projection type, because of the characteristics.
In particular, research and development of an active matrix liquid crystal display device in which switch elements are electrically connected to display pixels has been vigorously effected due to the feature that an excellent display image can be obtained without cross-talk between adjacent pixels.
In the active matrix liquid crystal display device, a plurality of thin film transistors (TFTs) are formed near intersections between scanning lines and signal lines, and used as switching elements each for selectively driving a corresponding one of the pixel electrodes. In each TFT, the gate is connected to a scanning line, the drain is connected to a signal line and the source is connected to a pixel electrode. The TFT supplies a signal voltage from the signal line to the pixel electrode, when it is turned on upon rise of a scanning pulse supplied from the scanning line. Thus, a liquid crystal capacitance between the pixel electrode and a common electrode is charged, and the charge is maintained even after the TFT is turned off upon fall of the scanning pulse.
When the electric field in a liquid crystal cell is maintained in one direction, materials other than the liquid crystal are moved in the liquid crystal cell by the electric field and concentrated at one electrode side. This is a factor of making the lifetime of the liquid crystal cell short. Conventionally, there is a frame-inversion technique known as a measure for solving the above problem by inverting the polarity of a signal voltage with respect to the potential of the common electrode such that the direction of the electric field is reversed in every frame period. Further, there is a line-inversion technique of inverting the polarity of the signal voltage also in every horizontal scanning to reduce flicker. Moreover, there is a common inversion driving technique which causes a common electrode drive circuit to output a common electrode drive signal whose polarity is positively inverted with respect to a reference potential in synchronism with a frame-inversion period and a line-inversion period, for the purpose of preventing an increase in amplitude of the signal voltage. In this case, the signal voltage is level-inverted with reference to the center level thereof, and the common electrode drive signal is inverted from one of a high-level driving signal and a low-level driving signal to the other, every time the signal voltage is level-inverted.
In the case of a flat-panel display device, the number of scanning lines is preset to a specific value for the device. However, if such a display device having a preset number of scanning lines performs a display operation on the basis of a video signal having scanning lines the number of which exceeds the preset number, a simplified image is generally displayed in the entire display area by thinning out an excessive number of scanning lines from the video signal during multiple scannings.
For example, if a display device having only 234 scanning lines for the NTSC system performs a display operation on the basis of a video signal having an increased number of scanning lines for the PAL system or the like, there is a technique in which specific lines of a video signal each corresponding to one of successive six lines, for example, are canceled in one field.
Further, it is known that the regularity in the thin-out operation can be moderated by alternately canceling one of six lines and one of eight lines.
Under the circumstances, it was discovered through the assiduous research of the present inventors that display failure or shortening of the lifetime of liquid crystal may occur due to the regularity of the thin-out operation.
USPTO Backgrounds
USPTO Backgrounds