Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-08-20
2001-12-11
Liang, Regina (Department: 2774)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
Reexamination Certificate
active
06329976
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a display device comprising an electro-optical material between two substrates of which at least one substrate is transparent, and a first substrate is provided with picture electrodes, in which each picture electrode is coupled via a switching element to a row electrode and a column electrode, and in which the picture electrode is capacitively coupled to a further electrode. The device further comprises drive means for providing the row electrodes with a selection signal and the row electrodes or the further electrode with a bias signal.
In this application, the term “capacitively coupled” is understood to mean that there is a coupling via an (auxiliary) capacitance, for example, by (partial) overlap of a picture electrode associated with a row and a part of the row electrode associated with a subsequent (or previous) row.
The second substrate may be provided with electrodes too (counter electrodes) defining at overlapping areas (a matrix of) picture elements. Picture elements may also be defined by picture electrodes in the same substrate (in plain switching).
Such display devices are used in, for example television and monitor applications.
A display device of the type mentioned in the opening paragraph is described in EP-A-0 657 864. This document describes how a DC component across the liquid crystal material is prevented in a liquid crystal display device by adaptation of a selection signal. To this end, the selection signal consisting of a gate pulse is extended with so-called gate-bias voltages applied during a gate-bias period. Where the selection signal is referred to in this application, the signal is understood which causes the switching element to conduct (generally the actual gate pulse of a TFT transistor). Where a bias signal or voltage, “(gate)-bias signal” or “(gate)-bias voltage” are mentioned, a bias signal or bias voltage as described in EP-A-0 657 864 is referred to, and therefore not the voltage across a row electrode during non-selection although when the gate-bias signal is presented to a selection electrode, although during a gate-bias period such a gate-bias signal may temporarily have a level which is equal to that of a non-selection signal. Instead of being presented to a row electrode, the bias signal may also be presented, for example, to a common connection for a number of capacitances within one row.
Due to the capacitive coupling between a picture electrode with an adjacent row electrode, it is true that the speed of the display device is considerably increased, but at this speed (and hence the transmission to be reached within one field period) flicker and artefacts (in moving images) still appear to occur frequently.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to provide a display device of the type described above in which the above-mentioned drawbacks are at least partly obviated.
To this end, a display device according to the invention is characterized in that the drive means comprise means for adapting the voltage level of the bias signal in dependence upon the temperature.
It has surprisingly been found that the level of the gate-bias signal has a considerable influence on the switching rate of the display elements, while the voltages to be used can be very well realized with ICs.
The capacitive division between an auxiliary capacitance and the capacitance of the pixel leads to a voltage across the pixel after the actual selection during switch-off of the gate-bias voltage. The switching rate of the pixel is also determined by this voltage. It appears that, dependent on the temperature, the pixel has a strongly varying dynamic behavior which gives rise to flicker and artefacts. By changing the gate-bias voltage also with the temperature, this change of dynamic behavior is substantially completely compensated.
The temperature measurement can be performed in different manners, for example, with one or more separate sensors or with a sensor integrated in the drive circuit.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.
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Johnson Mark T.
Van Der Put Adrianus A.
Laneau Ronald
Liang Regina
U.S. Philips Corporation
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