Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-07-21
2004-10-12
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S103000
Reexamination Certificate
active
06803899
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based on Japanese Patent Application Nos. 11-212348, 11-225177, and 11-274594 filed in Japan on Jul. 27, 1999, Aug. 9, 1999, and Sep. 28, 1999, respectively, the entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to a liquid crystal display apparatus and its driving method, and more particularly, to a liquid crystal display apparatus equipped with a liquid crystal display using liquid crystal having a memory capability, and to the driving method for said apparatus.
2. Description of the Related Art
Using a conventionally known liquid crystal display in which a liquid crystal that exhibits a cholesteric phase at room temperature, such as a cholesteric liquid crystal or a chiral nematic liquid crystal, is sandwiched between two substrates, display may be performed by alternating the state of the liquid crystal between a planar state and a focal conic state.
In other words, when the liquid crystal is in a planar state, where the helical pitch is deemed (P) and the average refractive index is deemed (n), light having the wavelength &lgr;=P·n is selectively reflected. Where the liquid crystal is in a focal conic state, when the selective reflection wavelength of the liquid crystal is in the infrared range, the liquid crystal scatters the light, and when the selective reflection wavelength is in the range shorter than the infrared range, the liquid crystal allows visible light to pass through. As a result, by setting the selective reflection wavelength to be in the visible range, and by locating a light-absorbing layer on the side of the element opposite the side that is observed, display of the selectively reflected color may be obtained when the display is in the planar state, while black is displayed when the display is in the focal conic state.
Where the selective reflection wavelength is set to be within the infrared range and the light-absorbing layer is located on the side of the element opposite the side that is observed, a black display is obtained because light having a wavelength within the infrared range is reflected but light in the visible range passes through when the liquid crystal is in the planer state. Consequently, a white display can be obtained through scattering of the light when the display is in the focal conic state.
By using three stacked elements set to selectively reflect red, green and blue, respectively, a color display may be obtained.
This type of liquid crystal display may be alternated between a planar state and a focal conic state through the application of voltage. If the threshold voltage required to eliminate the twist in the liquid crystal is deemed Vth
1
, when Vth
1
is applied for a sufficient amount of time, and then the voltage is reduced to a lower voltage Vth
2
, the display enters a planar state. When a voltage between Vth
2
and Vth
1
is applied for a sufficient amount of time, the display enters a focal conic state. These two states remain stable even after the application of voltage is stopped. It is also known that these two states may coexist, enabling halftone display.
Incidentally, the display state of the liquid crystal generally depends on the ambient temperature. Chiral nematic liquid crystal in particular has a temperature characteristic in which the display state (the Y value, i.e., the luminous reflectance) changes in accordance with the surrounding temperature. This is caused mainly by the fact that the viscosity of the chiral nematic liquid crystal falls as its temperature rises. Therefore, when the display is driven by means of a pulse voltage having a constant voltage level and pulse width at all times, chiral nematic liquid crystal entails the problem that its display state changes depending on the temperature.
With ordinary nematic liquid crystal, the drive voltage must be continuously applied to maintain the display, and real-time ambient temperature information from a temperature detection unit must be incorporated as a drive condition. However, the incorporation of this real-time temperature information imposed a substantial burden on the control unit (i.e., the CPU), and entails high power consumption. On the other hand, when the liquid crystal used has a memory capability that can maintain a display even if the application of drive voltage is stopped—such as cholesteric liquid crystal or chiral nematic liquid crystal—the proper timing and frequency of the incorporation of the temperature information have not yet been determined.
In addition, chiral nematic crystal is known to have a unique hysterisis phenomenon. Therefore, in order to avoid the occurrence of problems arising due to this hysterisis phenomenon, when performing driving, it is desired that the desired pixels be set to the desired state after a first reset pulse signal is applied to the liquid crystal and that the liquid crystal be reset to the homeotropic state. However, because the reset pulse signal to reset the liquid crystal to the homeotropic state as described above requires more energy than the selection pulse signal used to set the liquid crystal to the desired reflection state, multiple pulse signals that entail different amounts of energy are normally required to drive chiral nematic liquid crystal. Therefore, temperature compensation must be performed for each of these pulse signals, and the problem arises that the driving method and drive circuit become more complex.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to provide a layered liquid crystal display apparatus that can avoid display state variation regardless of changes in the surrounding temperature.
Another object of the present invention is to provide a liquid crystal display apparatus and associated driving method in which good display can always be performed regardless of changes in the surrounding temperature and in which the driving method and drive circuit are simplified.
Yet another object of the present invention is to provide a liquid crystal display apparatus and associated driving method that reduce the burden on the control unit and efficiently incorporate temperature information while reducing power consumption.
In order to attain these and other objects, the liquid crystal display apparatus reflecting a first aspect of the present invention comprises: a liquid crystal display including a liquid crystal material having a memory capability; a temperature detection unit that detects a temperature of the liquid crystal display or a temperature of the environment surrounding the liquid crystal display; and a control unit connected with the liquid crystal display and the temperature detection unit, the control unit applying drive pulse signals to the liquid crystal display to draw a first image on the liquid crystal display and leaving the liquid crystal without applying a drive pulse signal to maintain the first image by using the memory capability of the liquid crystal, wherein the control unit incorporates temperature information from the temperature detection unit before the drawing of the first image.
The liquid crystal display apparatus described above may also include (i) a first display mode under which the control unit applies the drive pulse signals to the liquid crystal display to draw the first image on the liquid crystal display and leaving the liquid crystal without applying a drive pulse signal to maintain the image by using the memory capability of the liquid crystal; and (ii) a second display mode under which the control unit successively draws a second image to an n-th image data on the liquid crystal display. In this case, when the first display mode is active, the control unit incorporates temperature information from the temperature detection unit before the drawing of the first image, while when the second display mode is active, the temperature information is incorporated by the control unit before the drawing of the second image, and thus incorporated temperat
Asai Katsuhiko
Mandai Makiko
Masazumi Naoki
Anyaso Uchendu O.
Minolta Co. , Ltd.
Saras Steven
Sidley Austin Brown & Wood LLP
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