Computer graphics processing and selective visual display system – Display peripheral interface input device – Light pen for fluid matrix display panel
Reexamination Certificate
1997-06-30
2001-07-03
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Light pen for fluid matrix display panel
C345S088000, C345S089000
Reexamination Certificate
active
06256010
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to liquid crystal displays and more particularly to a method and means for dynamically correcting the LCD &ggr; - curve of such a display.
BACKGROUND OF THE INVENTION
Light transmission through a liquid crystal display (LCD) is non-linear when viewed from a central position with respect to the plane of the display. For example, as illustrated in
FIG. 1
, an LCD screen for a portable computer or a projection TV will normally have better transmittance and color rendition near the center of the display when viewed head-on than at the upper and lower edges, since the viewing angle is somewhat different for each scan line from top to bottom on the screen when viewed directly at an angle of 0° with the center line. The transmittance is a function of the applied voltage and is defined in the art by a V-T or &ggr; - curve. As the transmittance is variable with the angle &THgr; at which a scan line of the display is viewed, a different light transmittance or &ggr; - curve exists for each different viewing angle of the display, i.e., a curve exists for head-on viewing at 0°, for upward viewing at +10°, and when viewing downward at −10°, as shown in FIG.
2
. As a practical matter, one &ggr; - curve is selected for correcting purposes, and in the conventional method for correcting the &ggr; - curve of an LCD, the correction curve at 0° is used and is typically applied by means of a voltage divider resistance network such that the correction curve is fixed. Consequently, the best &ggr; - curve correction is typically not obtained, and poor color resolution results, in view of the fact that the head and tail of the curve are not straight so that the darkest and whitest spots cannot be seen.
Other attempts to deal with the problem of poor resolution at the edges have focused on the liquid crystal materials and the changing of their characteristics. There is normally a significant difference in the transmittance characteristics of the three LCD scan lines at −10°, 0°, and +10° viewing angle so that corrective approaches try to change their characteristics to cause overlap. This approach has been found to be very difficult to accomplish so that a satisfactory solution has not been found.
Another approach is directed to modifying the control circuitry for applying voltages to the LCD. One example of a prior art disclosure dealing with circuitry for gamma correction is found in U.S. Pat. No. 5,461,430 to J. G. Hagerman wherein a gamma correction circuit is directed to correcting the grey scale linearity of images displayed on a liquid crystal light valve and cathode ray tube combination using a plurality of amplifiers, each adapted to implement a predetermined transfer function, and configured to compensate for nonlinearity in the display. The gamma correction here is used in conjunction with dynamic threshold correction and involves the inclusion of current sources with the amplifiers.
It will therefore be seen from a consideration of the prior art that various approaches have been used to deal with the problem in the art of achieving a method and means that will improve &ggr; - curve correction in LCDs so as to achieve optimum transmittance and color resolution to a viewer over the face of the display.
It is accordingly an object of the present invention to provide a method and means for improving &ggr; - curve correction in LCDs whereby the transmittance and color resolution are optimized over the face of the display screen for a viewer observing the screen head on.
It is a further object of the present invention to provide a method and means for improving &ggr; - curve correction in LCDs using a non-material approach wherein correction is achieved by calculating a suitable correction curve and implementing its application with appropriate circuitry.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method and means are presented for correcting the &ggr; - curve of an LCD by calculating an inverse &ggr; - curve from the &ggr; - curve of the LCD measured by the manufacturer and producing a straight line V-T correction curve from the combination, the straight line is then compared to an ideal V-T curve and its errors from the ideal curve is calculated. If the errors are acceptable, the inverse &ggr; - curve is used to provide the set of corrected voltages for the different positions or viewing angles of the display. More specifically, the &ggr; - curve correction voltages at different viewing angles are determined for the horizontal scan lines of the LCD, using the measured values appropriately modified by the straight line curve, and stored in memory. These different stored &ggr; - curve correction voltages are then used to produce correct voltage values for creating light transmission at the different angles. The invention thus improves the &ggr; - curve correction efficiency at different viewing angles of the LCD. The horizontal scan and vertical scan signals of the display are used as references in “dynamically” controlling the timing of the outputting of the sets of corrected voltage values stored in memory for conversion from digital to analog form and application to the horizontal scan lines of the display.
In one embodiment, a timing control application specific integrated circuit (ASIC), with clock, Hsync, and Vsynch inputs, is used to time the outputting of the sets of &ggr; - curve correction voltage signals stored in high speed memories for application, after digital to analog conversion, to the horizontal scan lines of the LCD to be corrected. The ASIC also provides a set of latch enable signals to a set of data latches, which receive the correction voltage signals as input signals from the memories, and provide the corrected voltage outputs, through a set of digital to analog converters (DACs) to a number of output lines connected to the LCD.
REFERENCES:
patent: 5461430 (1995-10-01), Hagerman
patent: 5496106 (1996-03-01), Anderson
patent: 5585841 (1996-12-01), Hardin
patent: 5724036 (1998-03-01), Kobayashi et al.
patent: 5754150 (1998-05-01), Matsui
patent: 5764216 (1998-06-01), Tanaka et al.
patent: 5793885 (1998-08-01), Kasson
patent: 5847688 (1998-12-01), Ohi et al.
Chen Yen-Chen
Lin Chien-Ho
Wang Chih-Wei
Industrial Technology Research Institute
Nelson Alecia D.
Saras Steven
Tung & Associates
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