Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-11-03
2002-07-09
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S094000, C345S100000
Reexamination Certificate
active
06417830
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to display devices and methods of operation therefor, and more particularly, to liquid crystal display (LCD) devices and methods of operation therefor.
BACKGROUND OF THE INVENTION
Liquid crystal display (LCD) devices are used in a wide variety of consumer products such as portable game machines, portable computers and the like. A typical LCD comprises a panel including an array of LCD elements arranged in rows and columns. A respective LCD element includes a liquid crystal element that transmits light according to a voltage applied thereto. A color filter may be included to preferentially transmit a selected color, e.g., red, blue or green. In an active-matrix LCD element, a thin-film-transistor is used to control voltage applied to the liquid crystal element. The gates of a row of LCD elements are typically connected to a common gate line, while the source electrodes of a column of LCD elements are typically connected to a common source line that provides a video voltage.
The gate lines control application of the video voltages supplied by the source lines to the liquid crystal elements, typically using a sequential line scan. To scan a line, a gate line for a selected row of LCD elements is driven to select a row of the display, and a video voltage is supplied to each column of the selected row through a source driver. The polarity of voltages applied to the liquid crystal elements typically is periodically reversed to extend the life of the display by preventing migration of the liquid crystal material toward one direction.
One technique for applying voltages to a liquid crystal element involves controlling the voltage at both electrodes of the element, as illustrated in FIG.
1
. During a first time period a and a second time period b, the element turns white as a voltage difference between a first electrode and a second electrode of the liquid crystal element is relatively low. The element turns black during a third time period c, a fourth time period d, and a fifth time period e, when the voltage difference is increased. For the technique illustrated, the change in voltage applied to an electrode between periods is relatively small. However, as the voltage applied to both electrodes of the liquid crystal element is controlled, the driver design may be complex and it may be difficult to maintain picture quality.
An alternative driving technique is illustrated in FIG.
2
. According to this technique, a first one of the electrodes of the liquid crystal element is held at a constant reference voltage while a voltage applied to a second electrode is varied. Although this technique can produce superior picture quality, large positive and negative voltage swings can occur on the non-constant electrode. These large swings can cause delay in reaching the desired voltage amplitude and can increase power dissipation in the output driver that drives the liquid crystal element.
SUMMARY OF THE INVENTION
In light of the foregoing, it is an object of the present invention to provide methods and apparatus for driving liquid crystal displays (LCDs) that can provide decreased power dissipation.
This and other objects, features and advantage are provided according to the present invention by apparatus and methods for driving an LCD in which a group of gate lines, e.g., adjacent gate lines, are driven during a first time period to thereby cause a charge transfer between liquid crystal elements associated with the driven gate lines, and then all but one of the group of gate lines is deactivated during a succeeding second time period as a video voltage is applied to the liquid crystal element controlled by the remaining active gate line. The charge-sharing that occurs between liquid crystal elements during the first time period allows the voltages on the liquid crystal elements activated by the group of gate lines to float toward a medial value, reducing the amount of voltage swing that occurs during the second time period.
In particular, according to the present invention, an apparatus is provided for driving a liquid crystal display (LCD) device including an array of LCD elements arranged in rows and columns, a respective row of LCD elements connected to a respective gate line, and a respective column of LCD elements connected to a respective source line. A gate driver circuit is configured to connect to the gate lines of the LCD device and operative to simultaneously drive a group of gate lines during a first time period to thereby transfer charge between the rows of LCD elements connected to the group of gate lines. The gate driver circuit is also operative to drive a selected one gate line of the group of gate lines during a second time period. A source driver circuit is configured to connect to the source lines of the LCD device and operative to apply a video voltage to a source line connected to an LCD element in the row of LCD elements connected to the selected one gate line during the second time period.
In an embodiment according to the present invention, the gate driver circuit is operative to simultaneously drive a first gate line connected to a first row of LCD elements and a second gate line connected to a second row of LCD elements during the first time period. The gate driver circuit is operative to drive the first gate line during the second time period. The gate driver circuit is operative to simultaneously drive the second gate line and a third gate line connected to a third row of LCD element during a third time period following the second period. The gate driver circuit is operative to drive the second gate line during a fourth time period following the third time period. The source driver circuit is operative to apply a first video voltage to a source line connected to an LCD element of the first row of LCD elements during the second time period, and the source driver circuit is operative to apply a second video voltage to a source line connected to an element of the second row of LCD elements during the fourth time period.
According to method aspects of the present invention, a liquid crystal display (LCD) device is operated by simultaneously driving a group of gate lines during a first time period to thereby transfer charge between the rows of LCD elements connected to the group of gate lines. A selected one gate line of the group of gate lines is then driven while applying a video voltage to a source line connected to an LCD element in a row of LCD elements connected to the selected one gate line during a second time period. Improved operation of an LCD device is thereby provided.
REFERENCES:
patent: 5049865 (1991-09-01), Nakamura et al.
patent: 5315315 (1994-05-01), Nakamura
patent: 5748165 (1998-05-01), Kubota et al.
patent: 5793346 (1998-08-01), Moon
patent: 5867141 (1999-02-01), Asada et al.
Lewis David L.
Myers Bigel & Sibley & Sajovec
Samsung Electronics Co,. Ltd.
Shalwala Bipin
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