Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-06-02
2001-06-26
Saras, Steven (Department: 2775)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S099000, C345S100000, C345S101000
Reexamination Certificate
active
06252566
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a compensation process for a disturbed capacitive circuit, more particularly to a compensation process for a circuit comprising at least one conductor at a specified potential, at least other conductors generating disturbances by capacitive coupling to the said conductor and a disturbance compensation bus capacitively coupled to the said conductor.
The present invention also relates to an application of this process to matrix-drive display screens. It therefore relates to a device for compensating potential for a display screen driven by an electrode array arranged in matrix fashion. It is more particularly relevant to liquid crystal screens, but other screens of the same type may also be used.
The present invention will be described by referring to a matrix-drive display screen, but it can be applied to all disturbed capacitive systems which require compensation, the latter being effected without adding a special measurement line.
In the case of a matrix-drive display screen, the latter consists, in the known manner, of a set of lines and of a set of parallel columns which are activatable, and are arranged perpendicular to one another. This type of screen can operate sequentially, the lines being activated one after the other, while the data are displayed on the columns or vice versa. In the case of line by line sequential operation, the line drive circuit imposes a first selection potential on the chosen line, the other lines being taken to a reference potential. For some of the duration corresponding to the line drive, the column drive circuits impose, on all the columns, a potential dependent on the data to be displayed, and therefore all the column drive circuits change state simultaneously. The simultaneous changes of state therefore produce a capacitive coupling between lines and columns which is all the stronger the larger the difference between drive impedance and load impedance in favour of the latter.
Thus, various solutions have been proposed for compensating for the capacitive couplings between the lines and columns of a matrix screen which uses line or column drive devices, more particularly those exhibiting a high or medium output impedance.
A compensation circuit of this type is described, for example, in French Patent Application No. 94 05987 filed on May 17, 1994 in the name of THOMSON-LCD. In this case, as represented in
FIG. 1
, an additional electrode is used, namely a column f capacitively coupled by capacitors Cf
j
to each of the lines of the screen as well as an additional line g, also capacitively coupled to the columns of the screen, which it crosses in order to effect the compensation. More specifically,
FIG. 1
diagrammatically a display screen with matrix array comprising columns i represents (i varying from 1 to n) and lines j (j varying from 1 to m) which are driven by line drive circuits Dj−1 for line j−1, Dj for line j and Dj+1 for line j+1. The column drive circuits i−1, i, i+1 are not represented in the drawing.
In this case, when the output of a line drive circuit Dj of a selection line j is not at low impedance, non-negligible capacitive couplings are brought about by the capacitors labelled Cij (i varying from 1 to n and j varying from 1 to m) between the lines i (i varying from 1 to n) and the columns j (j varying from 1 to m). These capacitive couplings may induce unacceptable voltages on the lines which may even cause a change of state of the transistors located, in the known manner, at the intersections of the lines and columns of the active matrix when the columns are quiescent.
Thus, as represented in
FIG. 1
, to remedy this drawback and compensate for the couplings, an additional column f is provided, capacitively coupled by the capacitors Cfj to each of the lines j (j varying from 1 to m) of the screen. The value of the capacitor Cfj is chosen to be almost equal to the sum of the coupling capacitances Ci between a line and the columns which they cross. The column f can be activated with each change of polarity on the columns, such as during frame reversals or line reversals for example. Moreover, as represented in
FIG. 1
, another possible means of driving the column f is to associate therewith, across a comparator
1
, a line g capacitively coupled by the capacitors Cgi to the columns i (i varying from 1 to n) which it crosses. This line g makes it possible to detect the couplings with the columns of the screen and to correct the potential of column f by virtue of the capacitive coupling Cfg between column f and line g. In this case, two additional electrodes are necessary, namely the line g for measuring the imbalance due to the capacitive coupling and the column f for compensating for this imbalance.
SUMMARY OF THE INVENTION
The purpose of the present invention is to propose an enhancement to the above device whereby it is possible to use just a single additional electrode or bus so as simultaneously to measure the imbalance and compensate for this imbalance. The use of a single bus makes it possible, especially for display screens, to limit their size, since the coupling capacitors such as Cfj and Cgi require a considerable area when they are made on the matrix itself.
Accordingly, the subject of the present invention is a compensation process for a circuit comprising at least one first conductor at a specified potential, at least one second signal conductor generating disturbance by capacitive coupling to the conductor and at least one disturbance compensation bus capacitively coupled to the said first conductor by a first capacitor (C
1
), characterized by the following steps:
measurement of the voltage (V
comp
) and of the current (I
comp
) on the compensation bus;
calculation of the voltage (V
dist
) on the first disturbed conductor, and
determination of the set-point voltage to be applied to the compensation bus in order to compensate for the disturbance.
According to a preferred embodiment, the value of the voltage on the first disturbed conductor is given by the following formula:
V
dist
=
[
V
comp
+
∫
I
comp
ⅆ
t
C
1
]
The value of integral ∫I
comp
dt is calculated from observation of the value of the voltage across the terminals of a second capacitor (C
2
) which is in series with the compensation bus and through which the same current I
comp
flows.
The subject of the present invention is also a display screen comprising an array of electrodes arranged in matrix fashion in lines and in columns, a coupling capacitor being associated with each line/column crossing, line and column drive circuits and at least one additional conductor bus crossing all the lines and capacitively coupled to each of them in such a way that the corresponding coupling capacitance has a value of the same order of magnitude as the sum of the coupling capacitances between a line or column and the columns or the lines which it crosses, characterized in that it uses a compensation process such as described above.
Preferably, this screen comprises a circuit for compensating the imbalances due to the line/column capacitive couplings during the drive phases, the input and output of which are coupled to the said additional bus.
REFERENCES:
patent: 5132819 (1992-07-01), Noriyama et al.
patent: 5583533 (1996-12-01), Moriyama
patent: 5701136 (1997-12-01), Huq et al.
patent: 5726678 (1998-03-01), Dingwall
patent: 5774100 (1998-06-01), Aoki et al.
patent: 5841411 (1998-11-01), Francis
patent: 5939896 (1999-08-01), Hedberg
patent: 5940057 (1999-08-01), Lien et al.
patent: 542 307 A2 (1993-05-01), None
patent: 564 263 A2 (1993-10-01), None
patent: 570 001 A2 (1993-11-01), None
patent: 572 079 A2 (1993-12-01), None
patent: 731 442 A2 (1996-09-01), None
patent: WO9500874 (1995-01-01), None
Alphonse Fritz
Fried Harvey D.
Henig Sammy S.
Saras Steven
Thomson-LCD
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