1. Field of the Invention
The present invention relates to a liquid crystal display device and, in particular, to a potential generation circuit in an active matrix liquid crystal display device.
2. Description of the Background Art
Drive schemes for active matrix liquid crystal display devices are roughly divided into two groups from the viewpoint of a common potential. The first one is generally called a line common inversion scheme where the polarity of the common potential is inverted every other gate line of a liquid crystal display device, and the polarities of the potentials of all data lines are inverted according to the polarity of the common potential. Here, the polarity inversion period may be every other multiple number of lines or may be every frame. The other one is generally called a dot inversion scheme where the common potential is kept constant at a DC potential and the polarities of the potentials of data lines are inverted with reference to the common potential. Although polarity is typically inverted so that adjacent pixels are provided with different polarities, it may be inverted every other multiple number of pixels.
For instance, for the case in the line common inversion scheme where the polarity of an applied voltage is inverted every other gate line of a normally white liquid crystal display device, the applied voltage attains a maximum value when the display provides a full black screen, and at that time a current consumed by a potential generation circuit (hereinafter referred to as a “common potential generation circuit”) is also at its maximum. On the other hand, in the dot inversion scheme, when the display provides a full black or white screen, potentials between adjacent pixels are cancelled out, so that a common potential generation circuit consumes little current. However, for example when adjacent pixels are displayed as black and white (typical adjacent pixels have different RGB colors, so adjacent pixels are actually displayed as purple, green, purple, and so on), the common potential generation circuit consumes more power as in the case of the line common inversion scheme. In the dot inversion scheme, polarity is averaged during display of a typical image, so that power consumption by the common potential generation circuit tends to be generally smaller than in the case of the line common inversion scheme.
Conventionally, there is a method that uses a charge recovery circuit in the line common inversion scheme so as to reduce power consumption by the common potential generation circuit that would consume a large amount of power (see, for example, Japanese Patent Application Laid-open No. 2004-69848.) There is also another method for reducing power consumption by the common potential generation circuit (see, for example, Japanese Patent Application Laid-open Nos. 2007-093696, 11-194320, 2001-282197, and 06-088955.)
Such conventional common potential generation circuits either fail to achieve sufficiently low power consumption or achieve low power consumption but only with a complicated circuit configuration.