Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Patent
1995-02-22
1998-07-21
Tung, Kee M.
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
345 90, G09G 336
Patent
active
057840393
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an AC-drive method for an active matrix liquid crystal display and, more particularly, to an AC-drive method which is intended to lessen display flicker and reduce power consumption by combining a bias voltage with a display drive voltage.
The display image quality by the active matrix liquid crystal display (hereinafter referred to as AMLCD) has been drastically improved in recent years. The prior art device has, however, a problem of flicker and a problem that a fixed image is printed immediately after being displayed; various solutions to these problems have been reported. In view of its use such as a liquid crystal TV or the like, it is desirable that the AMLCD be driven with as low power consumption as possible.
Solutions to the flicker problem are disclosed in Japanese Pat. Laid-Open Gazette Nos. 29893/86 and 59493/86. The methods proposed therein, however, do not compensate for a DC voltage which is caused by the dielectric anisotropy of the liquid crystal material used and a parasitic capacitance in the AMLCD itself, and hence do not reduce the flicker for each display pixel but merely lessen apparent flicker all over the display screen.
A method for reducing the power consumption of the source driver is proposed in Japanese Pat. Laid-Open Gazette No. 116923/87, for instance, but the proposed method does not compensate for the DC voltage caused by the dielectric anisotropy either.
Drive method which compensate for the DC voltage attributable to the dielectric anisotropy are set forth in "Compensation of the Display Electrode Voltage Distortion" (Japan Display '86, p. 191-195; this will hereinafter be referred to as literature 1) and "COMPENSATIVE ADDRESSING FOR SWITCHING DISTORTION IN A-SI TFTLCD" (Euro Display '87, p. 107-110; this will hereinafter be referred to as literature 2).
Literature 1 proposes a method which compensates for the DC voltage by changing the amplitude of an image signal voltage between positive and negative sides of its amplitude center. This method is defective in that the positive-negative amplitude ratio needs to be changed in accordance with the magnitude of the image signal. Literature 2 proposes a method which applies a correcting pulse via a capacitance provided in an adjacent gate line; the above-mentioned DC voltage is not generated in principle. Both methods compensate for the DC voltage but do not provide any improvements in the reduction of power dissipation of the source driver.
A method which cuts the power consumption of the source driver as well as compensates for the DC voltage is proposed in Japanese Pat. Laid-Open Gazette No. 157815/90. This method has, however, such a defect as mentioned below. After writing into pixel capacitors image signals corresponding to the positions of the pixels, it is necessary to turn OFF TFTs (thin film transistors) to hold therein the written charges. To perform this, the voltage that is applied to the gate of each TFT to turn it OFF needs to have a potential which sufficiently reduces it source-drain current I.sub.DS. According to the disclosure of Pat. Laid-Open Gazette No. 157815/90, the write of the image signals into the pixel capacitors is followed by the application of a pulse V.sub.e(+) or V.sub.e(-). This impairs the charge retaining characteristic of the pixels.
Incidentally, the method of literature 2 uses, as a pulse -V.sub.E, the pulse identified by V.sub.e(-) in Pat. Laid-Open Gazette No. 157815/90, and hence has the same defect as does the latter.
A first object of the present invention is to provide a method for AC-driving a liquid crystal display which provides an improved charge retaining characteristic of the pixels, and a liquid crystal display using the method.
A second object of the present invention is to provide a method for AC-driving a liquid crystal display which reduces the output power of the source driver, and a liquid crystal display using the method.
A third object of the present invention is to provide a method for AC-driving a liquid crystal di
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Hosomichi Masanori
Kamiya Takeo
Yasui Masaru
Hosiden Corporation
Suraci John
Tung Kee M.
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