Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-09-03
2001-12-25
Hjerpe, Richard (Department: 2774)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S087000, C349S072000
Reexamination Certificate
active
06333728
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of liquid crystal display devices, and, more particularly, to a novel liquid crystal display structure having optimized on-off contrast ratio for implementation as part of a liquid crystal display panel.
2. Discussion of the Prior Art
Normally, a liquid crystal cell gap thickness is determined and built, and the applied voltage placed across the liquid crystal will determine the amount of optical transmission. Since the on-off contrast ratio is the maximum to minimum light transmission ratio, a small voltage shift in the liquid crystal optical transmission versus voltage characteristics, for example, can change the minimum transmission enormously and degrade the on-off contrast ratio. In addition, the future trend in scaling to ever higher bit (more gray levels) displays produces a more stringent requirement on the hysteresis of the transmission versus voltage characteristics. One such change in the transmission versus voltage characteristics can occur as a result of a change in operating temperature. A second such change in the transmission versus voltage characteristics will result if a light valve designed with a liquid crystal cell gap for one wavelength of light (or color) is used with another wavelength of light.
There exists liquid crystal display devices that employ temperature sensing to control the optical transmission properties of screen displays. U.S. Pat. No. 5,717,421 describes a system for correcting display panel drive signals based on a detected current signal associated with a pixel. In the system described, parameters are measured to determine current threshold characteristics of a pixel and the display is accordingly corrected based on detected threshold data and sensed temperature data of the display panel.
U.S. Pat. No. 5,694,147 describes a system for controlling the temperature of the liquid crystal material utilizing a temperature sensor and a servo external to the liquid crystal display. In the system described, temperature sensing circuitry implements a resistive Wheatstone bridge for incorporation in proximity to a liquid crystal display panel. A control circuit is provided to control the liquid crystal display temperature, and implements a bipolar transistor and a resistive heating element. Because of this system's external and non-integrated approach for maintaining temperature control, this technique is relatively inefficient and expensive to implement.
Thus, it would be highly desirable to provide a on-off contrast ratio optimization technique employing a temperature compensation and control system for a liquid crystal display device that is efficient, cost-effective, and integrated as part of high-contrast liquid crystal panel displays.
SUMMARY OF THE INVENTION
The present invention is directed to a method and apparatus for obtaining the optimum on-off contrast ratio for liquid crystal displays using either an on display panel or off display panel temperature sensing and compensation circuit. The temperature sensing is accomplished by a liquid crystal capacitor, a diode, or any other device where the temperature characteristics are known. The advantage of using a liquid crystal capacitor is that it is inherent to the liquid crystal display element, i.e., forms part of a pixel element, thus requires no extra fabrication techniques to implement. Another advantage of using a liquid crystal capacitor is that it has a one to one transfer function when relating the sensed temperature to the liquid crystal pixels. A compensation circuit is provided to monitor the temperature and provide feedback to a heat producing element (such as a resistor, etc.) to stabilize the temperature to some determined value. Since on-off contrast ratio is most sensitive to the transmission (or reflection) in the off state, a scheme is deployed to monitor the off state of the liquid crystal capacitor.
According to the principles of the invention, there is provided an apparatus for providing optimal on-off contrast ratio in a liquid crystal display panel including liquid crystal elements having optical transmission properties dependent upon applied voltage and temperature, the apparatus comprising: a temperature sensing means for sensing the temperature of liquid crystal display pixels and having an input voltage applied thereto, the temperature sensing means outputting a voltage according to an applied input voltage and a sensed temperature; a means for monitoring output voltage of the temperature sensing means and obtaining a peak voltage corresponding to a maximum change of the voltage output from the temperature sensing means; a means for measuring a difference between the peak voltage with a predetermined reference voltage, and outputting a signal representing said difference; and, means for applying heat to the flat panel display in accordance with the measured temperature difference whereby the temperature sensing means is part of a liquid crystal display element.
Advantageously, the method and apparatus for real-time liquid crystal transmission versus voltage characteristics optimization methodology may be effectively employed in high gray scale resolution projection displays or high contrast ratio projection displays. Additionally, a projection system designed with three light valves for optimizing the on-off contrast ratios as a function of light color, can be further reduced to one light valve with the disclosed method.
REFERENCES:
patent: 4128311 (1978-12-01), Smith et al.
patent: 4239346 (1980-12-01), Lloyd
patent: 4298866 (1981-11-01), Hodemaeker
patent: 4387963 (1983-06-01), Brennan
patent: 4460247 (1984-07-01), Hilsum et al.
patent: 4775221 (1988-10-01), Baumgartner
patent: 5012274 (1991-04-01), Dolgoff
patent: 5029982 (1991-07-01), Nash
patent: 5088806 (1992-02-01), McCartney et al.
patent: 5300942 (1994-04-01), Dolgoff
patent: 5489918 (1996-02-01), Mosier
patent: 5597223 (1997-01-01), Watanabe et al.
patent: 5602679 (1997-02-01), Dolgoff et al.
patent: 5608422 (1997-03-01), Ikeda
patent: 5694147 (1997-12-01), Gaalema et al.
patent: 5717421 (1998-02-01), Katakura et al.
patent: 5936603 (1999-08-01), Lippmann et al.
patent: 62-23024 (1987-01-01), None
patent: 4-131829 (1992-05-01), None
IBM Technical Disclosure Bulletin, vol. 36, No. 10 (Oct. 1993) “Compensation of Liquid Crystal Display Contrast and Brightness for Temperature Variation”, pp. 381-382/.
Libsch Frank R.
Yang Kei-Hsiung
Eisen Alexander
Hjerpe Richard
International Business Machines - Corporation
Scully Scott Murphy & Presser
Underweiser, Esq. Marian
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