1. Field of Invention
The present invention relates to electro-optical devices, such as liquid crystal devices. More particularly, the present invention relates to a type of electro-optical device that has transistors to control the switching of pixel electrodes arranged in a matrix and that performs active-matrix driving by sequentially supplying scan signals to scan lines provided for corresponding pixel rows, a drive device and a drive method which are preferably used for such an electro-optical device, and an electronic apparatus having such an electro-optical device.
2. Description of Related Art
The electro-optical device of this type has, in an image display area on a substrate, pixel electrodes, thin-film transistors (hereinafter “TFTs”) to switch the pixel electrodes, scan lines to supply scan signals to the corresponding TFTs, data lines to supply image signals to the sources of the TFTs, storage capacitors connected to the pixel electrodes, and the like. Drive circuits, including a scan-line drive circuit to supply scan signals to the scan lines, a data-line drive circuit to supply image signals to the data lines, and a sampling circuit, are provided at peripheral regions located around the image display area.
More specifically, the scan-line drive circuit line-sequentially supplies a scan signal having a pulsed waveform for each scan line or each row. That is, scan signals are supplied such that, at the same time when TFTs that are connected to the mth row (m is a natural number) are turned off, TFTs that are connected to the (m+1)th scan line are turned on. In parallel, the data-line drive circuit supplies image signals to the respective data lines in each horizontal-scanning period so as to write the image signals to corresponding pixel electrodes from the sources of the TFTs that are turned on by the scan signals through the drains thereof. The supply of such scan signals and image signals then causes the writing of an image for one row in a single horizontal-scan period. In addition, the electro-optical device is configured such that the above write operation is sequentially performed on all the rows in a vertical scan period to thereby write an image corresponding to one frame.
However, since the TFTs, the scan lines, capacitance lines, the data lines, and the like are fabricated in gaps between the pixel electrodes that are arranged in a plain matrix, parasitic capacitances are generated between the pixel electrodes in the (m+1)th row and the drains of the TFTs, the scan lines, the capacitance lines, and the like in the mth row. As a result, when the TFTs in the (m+1)th row are turned on by using scan signals having a pulsed waveform at a moment when the TFTs in the mth row are turned off, a scan signal or the like in the (m+1)th row is introduced as noise into an image signal written into the pixel electrodes in the mth row. This causes the pixel potentials, which are essentially to be held by the corresponding pixel electrodes, to fluctuate. In particular, since the parasitic capacitances are different depending on pixel units, there is a problem in that pixel irregularities occur in an image that is eventually displayed.
Furthermore, the above problem becomes more severe as the pixel pitch is reduced so as to meet a common requirement for higher definition of a displayed image in the art, since the parasitic capacitances between the pixel electrode in the (m+1)th row and the drains of the TFTs, the scan lines, the capacitance lines, and the like in the mth row become relatively large as the pixel pitch is increased.
Additionally, the waveform of scan signals is rounded depending on the corresponding wire capacitances. Thus, the degree to which the waveform of scan signals is rounded is greater at the center portion, which is farther from the scan-line drive circuit, of the image display area than at a peripheral portion, which is adjacent to the scan-line drive circuit, of the image display region. Thus, the ON/OFF timings of the TFTs are different between the peripheral portion and the center portion, depending on the degree to which the waveform of the scan signals is rounded. As a result, the influences of noise due to the next row's scan signal that is introduced into an image signal when the TFTs are turned off, as described above, are also different from each other between the peripheral portion and the center portion. Thus, in particular, in order to prevent flicker and/or aging of liquid crystal and the like, when AC inversion driving in which a drive potential of each pixel electrode is inverted in each field period or the like is adopted, adjusting the potential of the opposing electrode such that no DC component is generated in a potential applied to the liquid crystal causes such a DC component to be generated at the peripheral portion. Conversely, adjusting the potential of the scan signal or the like such that no DC component is generated in a potential applied to the liquid crystal at the peripheral portion of the image display area causes such a DC component to be generated at the center portion. For these reasons, a problem occurs in that flicker is generated at the peripheral portion or the center portions.
Meanwhile, when the mth-row's scan line and the mth-row's TFTs that are driven therethrough are considered, the pulsed waveform of a scan signal affects the pixel potentials at the drains of the TFTs since parasitic capacitances exist between the scan line and the drains. Specifically, at a moment when the corresponding gates are turned off, a pulsed potential corresponding to a pulsed waveform in the scan line is superimposed as noise on the potential of an image signal and the resulting potential is held as a pixel potential. Thus, in this case, the influences of noise introduced to image signals are different from each other between the peripheral portion and the center portion, because the degrees to which the waveform of the scan signals is rounded are different between the peripheral portion and the center portion. As a result, potentials applied to the liquid crystal are different and the luminance levels are also different. A problem also occurs in that flicker is generated at either of the peripheral portion and the center portion. In order to reduce or prevent the generation of such flicker, Japanese Unexamined Patent Application Publication No. 6-110035 discloses a technique of shaping the rising waveform of a scan signal, not into a rectangular waveform, but into a ramp waveform or a stepped waveform. This approach, however, cannot prevent the generation of pixel irregularities and flicker which result from parasitic capacitances between the pixel electrodes in the (m+1)th row and the drains of the TFTs, scan lines, capacitance lines, and the like in the mth row.
USPTO Backgrounds
USPTO Backgrounds