Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Patent
1996-10-28
2000-05-30
Luu, Matthew
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
345100, G09G 336
Patent
active
060696052
DESCRIPTION:
BRIEF SUMMARY
FIELD OF TECHNOLOGY
This invention pertains to a driving method for a liquid crystal panel and, in particular, a driving method for a TFT liquid crystal panel.
BACKGROUND TECHNOLOGY
A number of different driving methods for TFT liquid crystal panels are already known. For example, as stated in "Driver LSI Problems Solved by low Voltage Single Power Supply", Flat Panel Display 1991 (Nov. 26, 1990, Nikkei Business Publications, Inc., p. 168 to p. 172), TFT liquid crystal panel drivers (liquid crystal driving devices) can be broadly divided into two types: digital and analog. The typical structure of a conventional analog line sequential driver is shown in FIG. 38. This conventional driver contains shift register 2000, level shifter 2002, switches (analog switches) 2004 to 2018, sampling capacitors 2020 to 2026, hold capacitors 2028 to 2034, and analog buffers 2036 to 2042. Shift register 2000 shifts in synchronization with the shift clock, the output is input into level shifter 2002, and the voltage is shifted. Switches 2004 to 2010 are sequentially turned off (opened) based on the output of level shifter 2002, resulting in the sequential sampling of video signals by capacitors 2020 to 2026. When video signal sampling is finished, the output enable signal becomes valid and switches 2012 to 2018 simultaneously turn on (close). When this happens, the sampled voltages are held by capacitors 2028 to 2034 through capacitive coupling between capacitors. The voltage that is held is then buffered by analog buffers 2036 to 2042 and is output to the signal lines of the liquid crystal panel as display signals. Analog buffers 2036 to 2042 are constructed, for example, by connecting operational amplifiers to voltage followers.
The configuration of the pixel region of the liquid crystal panel is shown in FIG. 39. Signal line 2050 is connected to the source region of TFT (Thin Film Transistor) 2054, scan line 2052 is connected to the gate electrode of TFT 2054, and pixel electrode 2054 is connected to the drain region of TFT 2054. When TFT 2054 is selected by scan line 2052, the voltage difference between the voltage applied to pixel electrode 2056 and the counter voltage (common voltage) applied to the counter electrode is supplied to liquid crystal element 2058, thereby driving liquid crystal element 2058.
Liquid crystal elements degrade when direct current voltage is applied to them for extended periods. This property makes necessary a driving means in which the polarity of the voltage applied to the liquid crystal elements is inverted after a specified period of time. As shown in FIG. 40A to FIG. 40D, such known driving methods include frame inversion driving (hereafter referred to as "1V inversion driving" for the sake of convenience), scan line inversion driving (hereafter referred to as "1H inversion driving" for the sake of convenience), signal line inversion driving (hereafter referred to as "1S inversion driving" for the sake of convenience), and dot inversion driving (hereafter referred to as "1H+1S inversion driving" for the sake of convenience).
In 1V inversion driving, as shown in FIG. 40A, the polarity of the applied voltage in all pixels is the same within a single vertical scanning period (1 field, 1 frame); and the polarity of all pixels is inverted after each vertical scanning period. While 1V inversion driving has the advantage of having driver circuits that are simple and easy to control and, moreover, does not suffer from line nonuniformity, this driving means does suffer from extremely conspicuous screen flicker.
In 1H inversion driving, as shown in FIG. 40B, the polarity of the applied voltage differs for each scan line; and, under these conditions, polarity is inverted after each vertical scanning period. The advantage of 1H inversion driving is that flicker is not conspicuous and cross-talk in the vertical direction is inhibited. Conversely, however, it suffers from the drawbacks of susceptibility to horizontal cross-talk and visible horizontal stripes in video displays. This driving method is
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Nikkei Business Publications, Inc., "Driver LSI Problems Solved by Low Voltage Single Power Supply", Flat Panel Display 1991, Nov. 26, 1990, pp. 168-172.
Nikkei Business Publications, Inc., "A 13-inch EWS High-Definition TFT Liquid Crystal Panel With Improved Picture Quality by Means of Dot Inversion Driving", Flat Panel Display 1993, Dec. 10, 1992, pp. 120-123.
Electronics and Communications in Japan, Part II: Electronics, "Poly-Si TFT and Driver Integration Technology," H. Ohshima et al.; vol. 77, No. 7, Jul. 1994, New York, pp. 46-54.
Review of the Electrical Communication Laboratories, "A 10-In. Diagonal Active Matrix Monochrome Liquid-Crystal Display," S. Sakai et al.; vol. 36, No. 4, Jul. 1988, Tokyo, pp. 395-401.
Luu Matthew
Seiko Epson Corporation
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