Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-11-13
2003-07-08
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S204000
Reexamination Certificate
active
06590557
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device such as a liquid crystal display device used for AV (audio and visual) apparatuses and OA (office automation) apparatuses, and a method for driving such a display device. More specifically, the present invention also relates to a display device incorporating dual-terminal nonlinear elements and a method for driving such a display device, in which appropriate corrections are performed corresponding to an ambient temperature around the device and corresponding to the characteristics of the elements.
2. Description of the Related Art
Recently, liquid crystal display devices are used for a variety of purposes, for example, as display devices for AV and OA apparatuses. Low-end apparatuses incorporate passive type liquid crystal display devices such as TN (twisted-nematic) display device and STN (super-twisted-nematic) display device. High quality apparatuses incorporate liquid crystal display devices driven according to an active matrix approach, in which three-terminal nonlinear elements represented by TFTs (thin-film-transistors) or dual-terminal nonlinear elements represented by MIMs (metal-insulator-metal) are used as switching elements.
Such liquid crystal display devices driven according to the active matrix approach provide thinner and lighter devices which have a color reproduction quality superior to that of CRTs (cathode-ray-tube), and reduced power consumption, and therefore use of such liquid crystal display devices is rapidly increasing. Using TFTs as switching elements, however, requires 6 to 8 steps of thin film forming processes and photolithography processes during production of the display devices. Therefore, solutions for cost reduction are highly sought.
On one hand, liquid crystal display devices incorporating dual-terminal nonlinear elements as switching elements have been developed rapidly since they are advantageous to TFTs in terms of cost and advantageous to passive type liquid crystal display devices in terms of display quality.
The dual-terminal nonlinear element is known for changing its characteristics depending on an ambient temperature. As illustrated in
FIG. 2
, when the ambient temperature increases, the characteristics of the dual-terminal nonlinear element change from the characteristics indicated by a solid line a to characteristics indicated by a dashed line b, i.e., to low resistance characteristics, and when the ambient temperature decreases, the characteristics of the dual-terminal nonlinear element change from the characteristics indicated by a solid line a to characteristics indicated by a dashed line c, i.e., to high resistance characteristics.
As the characteristics of the dual-terminal nonlinear element change depending on the ambient temperature, a voltage-transmittance characteristic of the display device incorporating the dual-terminal nonlinear element also changes depending on the ambient temperature. This means that the display condition of the display device changes depending on the ambient temperature, which is a fatal problem for display devices used in certain temperature ranges.
In order to improve such a temperature characteristic of the dual-terminal nonlinear element, studies has been made for obtaining a better material and a better structure for the dual-terminal nonlinear element, but no outstanding effects have as yet been achieved. Another solution is to incorporate an independent heating device or a cooling device together with the display device so as to maintain the display section at a constant temperature. This, however, increases the cost and the size of the apparatus.
As methods for improving the temperature characteristic by means of changing the manner in which the display is driven, it has been conventional to change a driving voltage value or a bias value applied to the liquid crystal. Regarding a display device incorporating dual-terminal nonlinear elements, for example, Japanese Laid-open Publication No. 5-53092 discloses a driving method in which a rate of change depending on the temperature is varied between a bias potential, a data amplitude voltage, and the maximum selection potential. In Japanese Laid-open Publication No. 5-53092, the maximum selection potential means the maximum potential during a selection period, the bias potential means the time average of the potential during a nonselection period, and the data amplitude voltage means the difference of the selected pulse between operation time and nonoperation time of the liquid crystal panel. A correction of the temperature is performed based on the following three criteria: (1) the bias potential is always at a non-zero value; (2) the temperature-dependent variation rate of the maximum selection potential is set to be greater than the temperature-dependent variation rate of the bias potential; and (3) the temperature-dependent variation rate of the data amplitude voltage is set to be smaller than the temperature-dependent variation rate of the maximum selection potential.
The above method, however, requires alteration of the bias potential during a nonselection period, and therefore requires a variety of potentials. It may also increase the power consumption since the energy loss in the power supply circuit is great due to the variable amplitudes.
Moreover, it is difficult in the above method to change the characteristics of dual-terminal nonlinear element so as to obtain display devices for specified uses, e.g., display devices emphasizing uniformity, display devices emphasizing contrast, or the like.
SUMMARY OF THE INVENTION
In one aspect of the invention, a method for driving a display device includes a pair of substrates disposed so as to face each other with a display medium inserted therebetween, one of the substrates including: a first wiring of either a plurality of scanning lines or a plurality of signal lines; and at least one dual-terminal nonlinear element which is connected to the first wiring and functions as a switching element for selecting matrix-like pixels, and the other substrate including a second wiring of the other of the plurality of scanning lines or the plurality of signal lines provided in a direction perpendicular to the first wiring, the method including the step of altering an amplitude of a supply voltage applied to each of the pixels during a selection period and an amplitude of a modulated voltage applied to each of the pixels during a nonselection period, corresponding to an ambient temperature level, wherein the amplitude of the supply voltage and the amplitude of the modulated voltage are decreased in a case where the ambient temperature increases, and the amplitude of the supply voltage and the amplitude of the modulated voltage are increased in a case where the ambient temperature decreases, and the rate of amplitude change of the modulated voltage to the change of the ambient temperature is greater than the rate of amplitude change of the supply voltage to the change of the ambient temperature.
In another aspect of the invention, a method for driving a display device includes a pair of substrates disposed so as to face each other with a display medium inserted therebetween, one of the substrates including: a first wiring of either a plurality of scanning lines or a plurality of signal lines; and at least one dual-terminal nonlinear element which is connected to the first wiring and functions as a switching element for selecting matrix-like pixels, and the other substrate including a second wiring of the other of the plurality of scanning lines or the plurality of signal lines provided in a direction perpendicular to the first wiring, the method including the step of altering a pulse width of a supply voltage applied to each of the pixels during a selection period and a pulse width of a modulated voltage applied to each of the pixels during a nonselection period, corresponding to an ambient temperature, wherein the pulse width of the supply voltage and the pulse width of the modulated voltage are decre
Birch & Stewart Kolasch & Birch, LLP
Said Mansour M.
Shalwala Bipin
Sharp Kabushiki Kaisha
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