Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-06-25
2001-08-28
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S087000, C345S092000
Reexamination Certificate
active
06281871
ABSTRACT:
RELATED APPLICATIONS
The present invention claims priority from Japan Patent Application Serial No. Hei 9-174342, filed on Jun. 30, 1997, which is incorporated herein by this reference in its entirety.
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal drive circuit for applying video signals to a liquid crystal panel, particularly a liquid crystal drive circuit capable of regulating the DC voltage levels of signals for three primary colors of Red, Green and Blue (R,G and B respectively).
Generally, continuously charging a liquid crystal panel with DC voltage may cause deterioration or burn of the liquid crystal, which will finally lead to its destruction. For this reason, it is necessary to drive the liquid crystal panel with alternating current signals so as to prevent it from being charged with DC. Also, in the case of displaying a fully colored image by video signals, respective R, G and B signals are provided to the liquid crystal panel after they are converted into alternating current, but due to the fact that the center potential of the respective color signals differs from that of the opposed electrode, troubles occur, such as the above-mentioned burn, difference in white balance, or degradation of contrast.
SUMMARY OF THE INVENTION
Since the respective R, G and B signals require, as a matter of course, three video signal drive circuit systems, in order to make the center voltage even among the R, G and B signals, it is necessary to regulate each circuit or to minimize the difference between the respective circuits.
In accordance with one embodiment of the present invention, a liquid crystal drive circuit provides video signals to an active matrix type liquid crystal panel as two AC signals in relation to polarity inversion of an opposed electrode with an amplifier for delivering an inverted video signal and a non-inverted video signal and with a mixer circuit for offsetting AC components by mixing the inverted video signal and said non-inverted video signal, thereby regulating a DC level of said amplifier on the basis of an output signal from the mixer circuit.
An object of one embodiment of the present invention is to realize a greater reduction of the center potential difference in AC signal output between RGB than that in the prior art and, particularly in case of AC signals having outputs having a phase difference of 180°, effectively reducing the DC difference between them. To realize this object, a circuit for adding an inverted output and a non-inverted output of a video signal is provided, in which the potential resulted from the addition is compared with the reference potential and the error voltage is fed back to the center voltage of the inverted video signal and the non-inverted video signal, the center voltage of the AC signals is set to an approximate value of the reference voltage. Also, the inverted video signal and the non-inverted video signal are amplified to a level at which they are applied to the liquid crystal panel, in order to further reduce the center potential voltage, in the stage prior to a multiplexer which mixes the inverted video signal and the non-inverted video signal to form a drive signal symmetrical to the center voltage.
REFERENCES:
patent: 5815134 (1998-09-01), Nishi
patent: 5835074 (1998-11-01), Didier et al.
patent: 5903247 (1999-05-01), Howard et al.
patent: 6121945 (2000-09-01), Tanaka et al.
patent: 6133895 (2000-10-01), Huang
patent: 6140989 (2000-10-01), Kato
Fish & Richardson P.C.
Hguyen Kimnhung
Hjerpe Richard
Sanyo Electric Co,. Ltd.
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