A plasma display panel (hereinafter, referred to simply as the panel) as a representative of an image display device having a large number of pixels arrayed in a planar form is provided with a large number of discharge cells serving as pixels in a space between a front plate and a rear plate disposed oppositely. Regarding the front plate, plural pairs of scanning electrodes and sustaining electrodes, each pair forming a display electrode, are formed on the front glass substrate to be parallel to each other, and a dielectric layer and a protection layer are formed to cover these display electrodes. Regarding the rear plate, plural data electrodes are formed on the rear glass substrate in parallel with each other, and a dielectric layer is formed to cover these data electrodes, plus plural partition walls are formed on the dielectric layer in parallel with the data electrodes. A phosphor layer is formed on the surface of the dielectric layer and the side surfaces of the partition walls. The front plate and the rear plate are encapsulated while being disposed oppositely in such a manner that the display electrodes and the data electrodes spatially intersect with each other, and a discharge gas is sealed in a discharge space in the interior thereof. A discharge cell is formed in a portion where the display electrode and the data electrode oppose each other. A color display is enabled on the panel of the configuration as described above by generating UV rays through a gas discharge within each discharge cell to give rise to excited luminescence in fluorescent materials of the respective colors in the RGB representation with the UV rays.
The sub-field method is used as a method of driving the panel. This is a method of performing luminance display by dividing one field period into plural sub-fields and by controlling each discharge cell to emit light or not to emit light in each sub-field. Each sub-field has an initialization period, a writing period, and a sustaining period. In the initialization period, the discharge cell performs an initialization discharge to form a wall electric charge needed for the following writing operation. In the writing period, a scanning pulse is applied successively to the scanning electrodes and a writing pulse corresponding to an image signal to be displayed is applied to the data electrodes at the same time for selectively giving rise to a writing discharge between the scanning electrode and the data electrode, thereby forming a wall electric charge selectively. In the following sustaining period, a sustaining pulse is applied between the scanning electrode and the sustaining electrode a specific number of times corresponding to the display luminance at which light is to be emitted for selectively giving rise to a discharge in the discharge cell having formed the wall electric charge by the writing discharge to emit light. A ratio of the display luminances for each sub-field is referred to as luminance weight.
As means for driving the panel, a scanning electrode driving circuit to drive the scanning electrodes, a sustaining electrode driving circuit to drive the sustaining electrodes, and a data electrode driving circuit to drive the data electrodes are provided, and the respective electrode driving circuits apply necessary driving waveforms to the corresponding electrodes. Among these electrode driving circuits, because the data electrode driving circuit needs to form a driving waveform independently for each data electrode according to an image signal, it is normally formed using an IC for exclusive use. Meanwhile, when viewed from the data electrode driving circuit side, each data electrode is a capacitive load having a combined capacity with the adjacent data electrode, the scanning electrode, and the sustaining electrode. It is therefore necessary to charge and discharge this capacity in order to apply a driving waveform to the respective data electrodes. It is, however, necessary to reduce power consumption of the data electrode driving circuit as much as possible in order to realize the driving circuit in the form of an IC. In addition, the proportion of power consumption of the data electrode driving circuit in total power consumption of the plasma display apparatus is by no means small. Hence, in terms of reducing power consumption of the plasma display apparatus, there has been a need to reduce power consumption of the data electrode driving circuit.
Power consumption of the data electrode driving circuit increases as a charge and discharge current for the capacity of the data electrode increases, and the charge and discharge current largely depends on an image signal to be displayed. For example, because the charge and discharge current is 0 when the writing pulse is applied to none of the data electrodes, power consumption becomes a minimum. Likewise, because the charge and discharge current is also 0 when the writing pulse is applied to all the data electrodes, power consumption is small. However, when the writing pulse is applied to the data electrodes at random, the charge and discharge current becomes larger, and in particular, when the writing pulse is applied alternately to the adjacent data electrodes, an electrostatic capacity between the adjacent data electrodes and an electrostatic capacity between the scanning electrode and the sustaining electrode are charged and discharged, which makes power consumption extremely large.
Given these circumstances, as a method of reducing power consumption of the data electrode circuit, for example, a method of detecting an image signal that consumes large power and replacing this image signal with an image signal consuming less power is disclosed in Japanese Patent Unexamined Publication No. 2002-23694. Also, a method of detecting power consumption of the data electrode driving circuit and limiting the levels of grayscale to be displayed when power consumption becomes large is disclosed in Japanese Patent Unexamined Publication No. 2003-271094.
When these methods are implemented, however, the size of the signal processing circuit becomes larger. Hence, there are problems that not only the circuit costs are increased, but also the resolution of luminance display becomes insufficient under some circumstances by displaying an image different from the original image that should be displayed or by limiting the levels of grayscale to be displayed.
USPTO Backgrounds
USPTO Backgrounds