Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Patent
1995-11-30
1998-11-03
Wu, Xiao
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
345 96, 345100, 345 98, 345208, G09G 336
Patent
active
058315861
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
TECHNICAL FIELD
The present invention relates to a method of driving a liquid crystal display device suitable for a liquid crystal of high speed response.
Particularly, the present invention relates to a method of reducing crosstalk in a method of driving a passive matrix type liquid crystal display device wherein multiplex driving is conducted by a multiple line selection method (a MLS method, reference to U.S. Pat. No. 5262881).
DISCUSSION OF THE BACKGROUND
Control of Frame Response in Conventional Techniques
In this specification, a scanning electrode is referred to as a row electrode and a data electrode is referred to as a column electrode.
In a highly intelligence-oriented age, demands to media for information display are increasing. Liquid crystal displays (LCDs) have advantages of being thin, light weight and having low power consumption as well as good adaptability to semiconductor technology; hence, they will be increasingly used. With the propagation of LCD use, there are demands for a large picture surface, a highly precise picture, and a display having a large capacity. Amongst the several techniques, a STN (super-twisted nematic) method is simpler in manufacturing process and lower in cost than a TFT (thin film transistor) method, and accordingly, it is likely that the STN methods become the main stream for future liquid crystal displays.
In order to obtain a large capacity display with use of the STN method, a successive line multiplexed driving (a-line-at-a time scanning) method has been used. In this method, row electrodes are successively selected one by one while column electrodes are driven in correspondence to a pattern to be displayed. When all the row electrodes are selected, the display of one picture is finished.
In the successive line driving method, however, there is known a problem called a frame response which is caused when the capacity of display is large. In the successive line driving method, pixels are applied with relatively high voltages at the time of selection and relatively low voltages at the time of non-selection. The voltage ratio generally becomes large as the number of row electrodes is large (a high duty driving). Accordingly, a liquid crystal which has been responsible to the effective value of voltages (RMS voltage: root mean square voltage) when the voltage ratio is small, becomes responsive to the waveform of the voltages to be applied. Namely, the frame response is a phenomenon caused when the transmittance at the OFF time is increased due to a large amplitude of selection pulses and the transmittance at the ON time is decreased due to a long time interval of the selection pulses, as a result of which the contrast ratio is decreased.
In order to suppress the occurrence of the frame response, there has been known a method of increasing a frame frequency to thereby shorten the time interval of the selection pulses. However, such method has a serious problem. Namely, when the frame frequency is increased, the frequency spectrum of the waveform of applied voltage becomes high. Accordingly, the high-frequency driving method causes an unevenness of display, that is a lack of display uniformity and increase in power consumption. Thus, there is an upper limit in determination of the frame frequency in order to avoid the formation of selection pulses having a narrow width.
Recently, a new driving method has been proposed to overcome the problem without increasing the frequency spectrum. In U.S. Pat. No. 5262881, for instance, a multiple line selection method (MLS method) is described wherein a plurality of row electrodes (selection electrodes) are simultaneously selected. In this method, a plurality of row electrodes are simultaneously selected, and a display pattern in the direction of columns can be controlled independently, whereby the time interval of selection pulse can be shortened while the width of selection pulses can be kept constant. Namely, a display of high contrast can be obtained while th
REFERENCES:
patent: 5262881 (1993-11-01), Kuwata et al.
patent: 5489919 (1996-02-01), Kuwata et al.
WPAT, AN 92-333371/41, EP-A-507061, Oct. 7, 1992.
Hirai Yoshinori
Kuwata Takeshi
Nagai Makoto
Nakazawa Akira
Asahi Glass Company Ltd.
Wu Xiao
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