EP0105767B1 - Method of controlling a matrix display - Google Patents

Description

The present invention relates to a method for controlling a matrix imager. It finds mainly an application in the production of liquid crystal display devices, used in particular in the binary display of complex images or of alpha-numeric characters.

These matrix display devices generally consist of a material formed of several zones distributed in a matrix and interspersed in a system with crossed bands or, in English terminology, in a “crossbar” system. Such systems include a first family of p parallel electrode lines and a second family of q parallel electrode columns, the electrode lines and columns being crossed, an area ij of the material being defined by the overlap region between line i, where i is an integer such as 1 ≤ i ≤ p and by column j, where j is an integer such as 1 ≤ j ≤ q. These systems further comprise means making it possible to deliver on the rows and columns of electrodes appropriate excitation signals serving to excite an optical property of the material.

Numerous devices of this kind are known which use, for example as a sensitive material, a liquid crystal film, and in which the excitation is electric. The invention applies particularly well to such devices, but it applies more generally to any device comprising a material whose optical property can be modified by means of any excitation. This excitation can be of an electrical nature, as for liquid crystals, but also magnetic, thermal, electronic, etc. The material can be a solid or liquid body, amorphous or crystalline. The optical property can be an opacity, a refractive index, a transparency, an absorption, a diffusion, a diffraction, a convergence, a rotary power, a birefringence, an intensity reflected in a determined solid angle etc ...

The most commonly used method of controlling a matrix imager, for example with liquid crystals, consists in applying sequentially or successively to the electrode lines an electrical signal S _o, for example sinusoidal, and in applying in parallel or simultaneously to the columns electrode and during the addressing of a line, sinusoidal electrical signals S _j which can be either in phase opposition, or in phase with the signal S _o depending on whether or not it is desired to display the liquid crystal zone corresponding.

FIG. 1 shows an example of signals applied to the row electrodes and to the column electrodes of a matrix imager. The first signal, bearing the reference a, corresponds to the signal applied to line i; the second signal, bearing the reference b, corresponds to the signal applied to the column j and the third signal, bearing the reference c, corresponds to the signal, or voltage, seen by the area ij of the display material. The time T corresponds to the time during which the line i and the column j are addressed and the time t to the time containing the information necessary for the display or not of the area ij of the material. For a sequential addressing of the p lines, the time T corresponds to the addressing time of all the lines and it is governed by the equation T = pt.

This control method, which is easy to implement, can only be used for a limited number of lines (p close to 100), which limits its use. Indeed, in certain applications such as in pocket televisions, text display screens, ... the number of lines required is too large for this control method to be used; the use of this method results in insufficient contrast between the displayed points and the non-displayed points, leading to the production of a blurred image. This is linked to the reaction time of the display material, when it is excited, and / or to its memory effect.

For these applications, use is made of electrode structures and control signals which make it possible to keep the number of display points, or display areas, desired on the imager and to halve the number rows of electrodes addressed sequentially.

One of the solutions consists in using column electrodes of special geometry making it possible to control them in parallel and simultaneously control the line electrode i and the line electrode i + 1. This solution developed by Itachi was exhibited at the conference of the "Society for Information Display" in 1980. This solution is compatible with taking information on a video signal, with storage at line level . Unfortunately, the structure of the column electrodes is complex and their realization difficult.

Another solution described in document US-A-4 281 324 consists in using column electrodes having a horizontal discontinuity defining two identical sets of electrode columns.

The object of the present invention is precisely a method for controlling a matrix imager which makes it possible to remedy this drawback.

More specifically, the invention relates to a method for controlling a matrix imager comprising a material of which an optical characteristic can be modified, this material being interposed between a first family of p lines of parallel electrodes and a second family of q columns of parallel electrodes, the lines and the columns being crossed, an area ij of the material being defined by the region of the material covered by the line i, where i is an integer such that 1 <i <, p, and by column j, where j is an integer such as 1 <j <q, the rows and columns used to convey signals causing excitation of the material, the electrode columns having n horizontal discontinuities defining n + 1 identical sets of columns of electrodes. This method is characterized in that a signal I is applied to the line of electrode i and to the other lines of electrodes a zero signal, signal 1 being applied sequentially to the p electrode lines according to the increasing values of i, and in that a signal J is applied to the electrode columns, this signal J being applied simultaneously to the electrode columns of the first set, during the time of application of the signal I on the p / n + 1 first rows of electrodes, the columns of electrodes of the other sets receiving a zero signal, then on the columns of electrodes of the second set, during the time of application of the signal on the p / n +1 following electrode lines, the electrode columns of the first set and of the other games receiving a zero signal, and so on until excitation of the electrode columns of n + 1 ^th game.

The fact of sequentially controlling the electrode lines and according to the increasing values of i is compatible with taking information on a video signal. In addition, the use of electrode columns having horizontal discontinuities makes it possible to separately control the different sets of electrode columns formed and therefore to increase the multiplexing rate of the imager, that is to say its number of electrode lines. Furthermore, the electrode columns have a very simple structure.

According to a preferred embodiment of the invention, the signals I and J are rectangular signals with zero mean value. In addition, these signals I and J can be either in phase or in phase opposition.

According to another preferred embodiment of the invention, the material whose optical characteristic can be modified is a liquid crystal film, the excitation signals applied to the electrodes being electrical voltages.

Other characteristics and advantages of the invention will emerge more clearly from the description which follows, given purely by way of illustration and without limitation. For clarity, the description refers to a liquid crystal matrix display device, the optical property of which varies as a function of the electric field applied to it. However, as indicated above, the invention is of much more general application, but since this display device is currently well known and widely used, it is preferable to carry out the description on this example.

• - la figure 1, déjà décrite, représente la forme des signaux appliqués aux électrodes d'un imageur matriciel à bandes croisées selon l'art antérieur,
• - la figure 2 représente une vue éclatée et en perspective d'un imageur à cristaux liquides utilisant des électrodes à bandes croisées conformément à l'invention, et
• - la figure 3 représente la forme des signaux appliqués aux électrodes de l'imageur de la figure 2.

The description refers to appended figures, in which:

• FIG. 1, already described, represents the shape of the signals applied to the electrodes of a cross-band matrix imager according to the prior art,
• FIG. 2 represents an exploded and perspective view of a liquid crystal imager using crossed strip electrodes according to the invention, and
• FIG. 3 represents the shape of the signals applied to the electrodes of the imager of FIG. 2.

FIG. 2 represents a display device with crossed bands. It has walls 20 and 22, generally transparent, arranged on either side of a shim 24 of thickness, made of insulating material, defining a volume 26 which is occupied, when the device is mounted, by the material of which controls an optical characteristic such as for example a liquid crystal film. On the walls 20 and 22 are deposited two electrode systems each consisting of a series of semi-transparent parallel conductive strips, noted i for the rows and j for the columns. The useful surface of the liquid crystal is thus broken down into a mosaic of zones corresponding to the overlapping zones of the two electrode systems, each zone corresponding to the overlapping of two strips i and j, and which can therefore be identified by the ij notation.

The sensitization of a zone ij, that is to say the control of an optical characteristic of the liquid crystal contained in this zone, is carried out by applying to the electrodes i and j electric voltages which cause the appearance d 'an electric field within the liquid crystal. We thus see an image appear on the entire device by defining it point by point and by sensitizing the zones one after the other according to the known principles of sequential control.

According to the invention, the column electrodes j have n horizontal discontinuities 28 defining n + 1 identical sets of q columns of electrodes, q being the total number of columns of electrodes. In FIG. 2, only one discontinuity 28 has been shown defining two sets of electrode columns, an upper set bearing the reference d and a lower set bearing the reference e.

In FIG. 3, the shape of the signals applied to the line of electrode i and to the column of electrode j is shown, to sensitize the area ij of the display material, these signals being those used for n equal to 1 .

According to the invention, a signal I is applied to the electrode line i, using known means, and to the other electrode lines a zero signal. This signal I is preferably a rectangular signal with zero mean value as shown in FIG. 3. The excitation of all the lines i takes place sequentially and according to the increasing values of i. In other words, the signal is applied to the first line, then to the second line, then to the third line, etc., up to the p ^th line, p being the total number of lines. This is compatible with taking information on a video signal.

Likewise, a signal J is applied to the electrode column j. This signal can for example be a rectangular signal with zero mean value as shown in FIG. 3.

According to the invention, this signal J is applied simultaneously to the columns of electrodes of the first set during the addressing time, or time of application of the signal I, of the p / n + 1 first rows of electrodes, the columns electrodes of other games receiving a zero signal.

This signal J is then applied simultaneously to the electrode columns of the second set during the addressing time, or application of the signal I, p / n + 1 following electrode lines, the electrode columns of all the other games, including the first game receiving a zero signal. The appearance of an image on the entire device is obtained by exciting the electrode columns of all the sets, as before, and one after the other until the electrode columns of the n + 1 ^{th are} excited clearance. The excitation of the n + 1 sets of electrode columns is done using known means associated with each set of electrode columns.

When n is equal to 1 and p is equal to 10, the signal J is applied simultaneously to the columns of the set d (FIG. 2), during the sequential addressing of the lines 1, 2, 3, 4 and 5 respectively, the columns of the game e receiving a zero signal; then the signal J is applied simultaneously to the columns of the set e, during the sequential addressing of the lines 6, 7, 8, 9 and 10 respectively, the columns of the set d receiving a zero signal.

In FIG. 3, the time T corresponds to the addressing time of all the lines i sequentially, and the time t corresponds to the time containing the information, that is to say leading to the display or not of the area ij of the material; the time T is governed by the equation T = pt, p being the total number of lines. Zone ij is displayed when signal 1 and signal J are, in time t, in phase opposition and this zone is not displayed when signals I and J are in phase, as shown in this figure.

Furthermore, this figure shows a third signal K corresponding to the signal, or voltage, seen by the area ij of the display material.

It can be noted that the three signals I, J, K all present a zero value after a time T / 2. This time corresponds to the addressing time of p / 2 electrode lines and one of the two sets of electrode columns.

The fact of using discontinuous electrode columns and alternately addressing the different sets of electrode columns makes it possible to produce matrix imagers comprising a large number of electrode lines, and to obtain an image on these imagers. well contrasted.

Claims (4)

1. Process for controlling a matrix imager comprising a material an optical characteristic of which can be modified, this material being inserted between a first group of p parallel lines of electrodes and a second group of q parallel columns of electrodes, the lines and the columns intercrossing, a zone ij of the material being defined by the region of the material covered by the line i, where i is an integer such that 1 < i < p, and by the column j, where j is an integer such that 1 < j < q, the lines and the columns used to convey signals producing an excitation of the material, the columns of electrodes having n horizontal discontinuities defining n +1 identical sets of columns of electrodes, characterized in that a signal I is applied to the electrode line i and a null signal to the other lines of electrodes, the signal I being applied sequentially to the p lines of electrodes according to the increasing values of i, and in that a signal J is applied to the columns of electrodes, this signal J being applied simultaneously to the columns of electrodes of the first set (d) during the time of application of the signal I to the first p/n+1 lines of electrodes (1, 2, 3, 4, 5), the columns of electrodes in the other sets (e) receiving a null signal, and then to the columns of electrodes of the second set (e), during the time of application of the signal I to the next p/n+1 lines of electrodes (6, 7, 8, 9, 10), the columnes of electrodes of the first (d) set and of the other sets receiving a null signal, and so on to excitation of the columns of electrodes of the n +1 'th set.

2. Control process according to Claim 1, characterized in that the signals I and J are rectangular signals with a zero mean value.

3. Control process according to either of Claims 1 and 2, characterized in that the signals I and J are either in phase, or in opposite phase.

4. Control process according to any one of Claims 1 to 3, characterized in that the material is a liquid crystal film, the excitation signals applied to the electrodes being electrical voltages.

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