CA2153744A1 - Segmented counter-electrode, active matrix liquid crystal display device - Google Patents

Abstract

The liquid crystal display device includes a display screen having a thin layer of liquid crystal disposed between a planar counter electrode and electrodes arranged such that each of the pixels corresponds to a row and a column. Each electrode is connected to a control element. Each conductor assigned to a row of pixels in a line direction is common to a group having an integer n, greater than 1, of rows and comprises a single drive circuit, provided for successively applying several control voltages during 'a screen write cycle. Each conductor assigned to a row of pixels in the column direction attacks only one row. The counter-electrode is divided into n parts each provided with the same voltage switching element, each part being assigned to rows which are homologous to the groups of pixels. The switching elements bring the counter-electrode to a determined validation voltage for the times necessary to control a row from among n rows.

Description

~ 15374 ~

~, . .

LIQUID CRYSTAL, MATRIX DISPLAY DEVICE
ACTIVE AND WITH FRACTIONAL COUNTER ELECTRODE

The present invention relates to devices for liquid crystal display, of the so-called matrix type active, comprising a display screen having a thin layer liquid crystal disposed between a counter electrode plane and electrodes (each defining a capacitor and a picture element, or pixel, with the counter electrode) arranged so that each of the pixels corresponds to a row and a column, each electrode being connected to a control element, such as a thin film transistor, allowing or bringing it to the potential of a driver of column which is common to all the pixels of the column to which it belongs to, or to isolate it and render its floating potential, depending on the voltage that is applied to a line conductor common to all the elements of command of the same line.
Each control element thus constitutes a switching tor which, in the closed state, makes it possible to bring the electrode to the potential of the column conductor and, in the open state, isolates the electrode.
To avoid the accumulation of residual charges, which would give birth to ghost images, we reverse general the polarity of the voltage applied to the condensa-tors at regular intervals, for example at the frequency of ~ 1 ~ 37 ~

``

image refresh. So the average value, in the time, the voltage applied to the capacitor of each pixel is zero.
It will be mainly a question later, for the clarity of the presentation, of monochrome screens. But the invention is also applicable to color display screens, having at least three sets of pixels, respectively green, red and blue.
Each of the L line conductors and each of the C
column conductors is connected to a driver or "driver" which determines the voltage applied to the conductor.
L + C must therefore be attacked if there are LxC = P pixels.
Any increase in the number of attack circuits increases the price, complexity and risk of default of the device. These consequences are all the more serious as the screen is larger. Now the trend is currently make wide screens, for example having 1920x480 pixels in the case of colored screens.
The present invention aims to provide a device for type defined above responding better than those previous-known to the requirements of practice, especially in that it reduces the number of drive circuits.
To this end, the invention notably proposes a device characterized in that:
- each conductor assigned to a row of pixels in a first direction (line or column) is common to a group with an integer n, greater than 1, of rows .

and has a single driver, designed to apply successively several control voltages during a screen write cycle (or frame cycle) while each conductor assigned to a row of pixels in the second direction (column or row) only attacks one arrayed in said second direction, orthogonal to the first;
- in that the counter-electrode is split into n parts each provided with a voltage switching element, each part being assigned to homologous rows of pixel groups;
- in that said switching elements are provided each to bring the counter electrode to a voltage determined validation only during durations necessary for the control of a row among n rows; and - in this one of the conductors assigned to each pixel applies a tension which is a sum of terms of an orthogonal code weighted and the conductor assigned to the pixel, in the other direction, apply a voltage representative of the terms of the orthogonal code.
This arrangement makes it possible to reduce the number of drive circuits in one of two directions; Furthermore, it reduces the number of connections to be made between attack circuits and the screen itself, which also reflected in an increase in the opening rate of the screen, i.e. the ratio between the useful surface display area.

~ 153744 .

Because we have three pixels for each pixel control parameters (voltage applied to the conductors of line, voltage applied to the column conductors and counter electrode voltage) instead of two in the screens conventional, the light transmission value of a pixel (transparency in general) can be ordered individually well that two lines (or more generally n lines) are ordered by the same driver, or two columns (or more usually n columns) are ordered by the same driver.
Various modes of electrical control are possible. In a particularly advantageous embodiment when n is much greater than 1 and when said groups consist of lines:
- each common attack circuit with n lines is provided for, during a screen writing cycle, perform at minus n successive sequences of duration (Ti) comprising a first fraction (Ta) during which all group electrodes are brought to the column potential corresponding and a second fraction (Tm) during which the previous potential remains maintained;
- the switching elements of the counter parts electrode are provided for, during said sequences successive of the same cycle, apply successively voltages having either of two values (+ VCe) and (- Vce), the sequence of values applied to each part of counter electrode representing a zero mean value code ~ 1 ~ 3744 which is orthogonal to all the other part codes of counter electrode; and - the columns are ordered so as to be worn each successively, during the first fractions (Ta) of said sequences of the same cycle, at voltages successive represented, for each column, by the sum products of the light transmission values to give pixels belonging to the group and to the column by successive code terms assigned to pixels.
Instead of forming groups of lines, it is possible to create groups of columns. The mode of command can then be of the same kind as above, but transposed to the case of columns.
There is not a linear relationship between the transmission of pixel light from a liquid crystal display and the voltage across the capacitor that defines this pixel. Of more, the command mode shows an error quadratic. The latter can be corrected in particular by providing each drive circuit to achieve at least an n + th sequence, during which the conductors of column are brought to the product of the same tension of quadratic error correction by successive terms an additional binary code with zero mean value, orthogonal to other codes. This correction mode is possible because the error is the same for all group pixels assigned to the same column.
The above features, as well as others that 21537 ~ 4 ``

are advantageously usable with them, but can being independent ~ mm ~ nt, will appear better on reading the description which follows of particular embodiments, given by way of nonlimiting examples.
The description refers to the accompanying drawings, wherein :
- Figure 1 is a block diagram showing a known constitution of a fragment of a monochrome screen at liquid crystal and active matrix;
- Figure 2, similar to Figure 1, is a diagram of principle of a first device according to the invention, according to a particular embodiment, having a counter electrode in two parts only;
- Figure 3 is a plan view of a fragment screen, showing a possible aspect of the masks used to constitute a screen of the kind shown in FIG. 2;
- Figure 4 schematically shows a constitution interdigitated counter-electrode, usable in the device of Figure 5;
- Figure 5, similar to Figure 3, shows another possible distribution of the parts of a counter electrode in two parts ;
- Figure 6, similar to Figure 4, shows a constitution of the counter electrode in three parts;
- Figure 7, similar to Figure 4, shows masks usable in cooperation with a counter electrode in three parts of the genus shown in Figure 5;

215374 ~

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- Figure 8, similar to Figures 4 and 6, shows a possible constitution of two-level counter-electrode, allowing to use groups of four lines;
- Figure 9, similar to Figure 7, shows masks usable in the case of groups of three colonists nes;
- Figure 10 is a timing diagram of the signals of command of line groups;
- Figure 11 is a diagram showing side by side a block diagram of a group of six lines and a chrono-gram of voltages applied to the counter parts corresponding electrode; and - Figure 12, similar to Figure 11, corresponds to a group of six columns.
The classic active matrix display screen including a fragment is shown diagrammatically in FIG. 1 comprises a thin layer of liquid crystals placed between two transparent blades. In the case of a screen working in light transmission, the assembly thus formed is mounted between a polarizer and an analyzer. One of the blades carries a unique counter electrode, which is one of the armatures 20 of the capacitors each forming an element image or pixel. The other transparent blade has control electrodes 22 each defining a pixel and constituting capacitors with the counter electrode 20.
These electrodes can be formed by deposits transparent conductors. We will assume later that there 21 ~ 374 ~

a LxC pixels, distributed in L lines L1, L2, L3, ..., and C
columns, Cl, C2, Figure 1 also shows a conventional command mode.
than. Each pixel is controlled by an effect transistor thin-film field (usually denoted by the abbrevia-TFT). All the transistors Tll, Tl2, Tl3, dlune same line Ll are simultaneously made conductive by wearing the line conductor L1 corresponding to a deter-mined (for example +15 Volts) while the conductors of line of all the other lines are brought to a potential blocking of the transistors (for example -15 Volts). The conducting transistors communicate the voltage Vc of the conduc-column sensor corresponding to the associated electrode 22.
The information constituted by the applied voltage Vc is then kept for the duration of an image, the constant of the capacitor discharge time being chosen sufficiently long for this purpose.
Conventionally, the control of column conductors is performed from a shift register 24 consisting of killing line memory, in which the advance is caused by a clock signal from a time base 26.
The data input 28 of the shift register receives the signal via a sampler 30 also controlled by time base 26. once the set of the information corresponding to a received line, it is transferred to a buffer 32. The contents of all cells in this memory is simultaneously applied to `` 215374 ~

column conductors Cl, C2, ... by driver circuits that 341 ~ 342, ..., upon receipt of an order from the time base 26. The line that should receive the information is selected by addressing using circuits line conductors 36. The potential of the counter electrode is fixed by a source 37, generally in alternation at values + Vce and - Vce-In the particular embodiment of the invention illustrated in figure 2, where the elements corresponding to those in figure 1 are designated by the same reference number this, each line driver, or driver, is assigned to two lines, usually adjacent because this solution is the simplest in terms of connections with line drivers. For example the first release of driver 36 is connected to the conductor of lines Ll and L2, the second output to the conductor of lines L3 and L4, etc.
In return, the counter electrode is split into two parts CEl and CE2 assigned to the lines in such a way that the same line does not at the same time have the same conduct-line tester and the same counter electrode part.
When the groups have n = 2 lines only, it is possible to make the counter electrode in one etched conductive layer, retaining the same resistance electric for both parties.
The physical distribution of conductors and electro-and the distribution of the masks used to make them ., ~

can be those given schematically in Figure 3. The indicated ranges designate the electrodes that define the pixels, which can be red R, green V and blue B. Each electrode is extended by a projection 5 which constitutes the drain, such as D, of a layer transistor respective thin. The same column conductor, C1 by example, attack sources, such as S, of transistors field effect belonging to a single column. A track forming a line conductor constitutes the grids of 10 transistors of two adjacent lines. For example, the same line conductor L12 constitutes, in the case of the figure 3, the grid of pixel field effect transistors of two lines, generally successive, L1 and L2 of the matrix.
15The fractionation of the counter electrode is not necessarily the one shown in Figure 3: the Figure 5 shows another possible grouping, allowing to simplify the engraving of the two parts CE1 and CE2, using the line distribution of the line conductors and 20 of the parts of the counter electrode shown in FIG. 4, where the elements corresponding to those of FIG. 2 bear the same reference.
As mentioned above, it is possible to divide the lines into groups with an integer 25 any n of lines, n ~ being greater than 1. The counter electrode is then split into n parts CE1, ..., CEn.
In the case where n = 3, it is still possible to use 21537 ~
.

a counter-electrode in a single etched layer, giving in the third part CE3 a form in Greek, such as that of which a fragment is shown in FIG. 6. This solution however has the disadvantage of giving the part CE3 a higher impedance than that of the other two, unless intermediate supplies are provided under form of via in an insulating layer covering the counter electrode.
The command, by the same line conductor, such as L123, of three transistors belonging to three lines L1, L2, L3, can then be performed by a engraving of the kind shown in Figure 7, which allows to group the control transistors in a space requirement less since only one engraved track is necessary for 3 (and more generally n) lines.
Each column conductor, such as Cl, then has growths each of which constitutes the common source of three transistors belonging to the same column and to three successive lines. The electrodes of the three corresponding pixels ponds have growths constituting the drains Dl, D2 and D3 of the thin film control transistors.
To significantly reduce the number of circuits of attack, we will often have to adopt a number n greater than 3. In particular, in the case of a screen trichrome, we will often adopt n = 6, that is to say that each line conductor will be assigned to two sets of three pixels R, G and B.

21 ~ 3744 ``

When n is 4 or more, the extrapolation of the solution shown in figure 6 remains possible but at the cost high resistances for several parts. We can then adopt a distribution of the counter-electrode parts 5in two layers (usually of tin and indium oxide, or ITO) separated by a thin insulating film. The relative arrangement of elements CEl, CE2, CE3 and CE4 and that of some row and column conductors can then be for example that of FIG. 8, when n = 4.
10Other combinations than those described above and other modes of constitution of the transistors are possible wheat. A constitution using groups of n = 6 lines will be described later, along with a constitution possible from the electrical part of the device.
15Each part of the counter electrode can be made killed by a mosaic of separate paving stones, engraved on the same conductive layer and connected to respective conductors through via holes through an insulating film.
It is still possible to split a large screen 20size into several rectangular areas and use a of the above provisions in each zone.
As noted above, it is also possible to form groups of columns and not line groups. Examples of such groupings 25 will be given later, on the occasion of the description of particular constitution of the electrical part of the device. A relative provision possible, in the case ~ 1 ~ 37 ~ 4 of groups of three columns, is the one shown in figure 9.
It takes into account that these are always the column conductors which receive the voltages fixing the light transmission, line conductors not playing than a switch control role.
It is also possible to combine groups of columns and row groups, but at the cost of one increase in the number of counter parts required electrode. More specifically, the number of parts of counter electrode will be equal to the product of the number of columns grouped by the number of grouped lines.
The electrical assemblies, which will now be given as an example, can be used when the elements of control are constituted by transistors. In that case, - when the line conductor assigned to the transistor is brought to a control potential (conductive state of transistor), the pixel electrode takes the potential of the column conductor, - when the line conductor is carried to a poten-blocking electrode, the electrode is isolated and the voltage at terminals of the capacitor is retained, with a decrease due to the progressive discharge of the capacitor.

C ~ s ~ le grol ~ es ~ le l ~ anes We will consider the general case where we wish to give a transmission value represented by a coefficient ajgk at a pixel belonging to the ji ~ m ~ line of a group g of 21 ~ 3 ~ 44 .

n lines, located at the crossing with a column k. We are will, however, especially look for the case where n = 6, i.e.
groups of six lines and counter electrodes in six parts.
A particularly interesting solution uses not plus an individual and individual command for each line for a time equal to the frame duration Tr divided by the number of lines on the screen (followed by a hold time representing the rest of the frame time), but a command of each group in turn. During each frame duration Tr ~ all transistors in the group considered are blocked except during periods Ta affected tees to this group. As Figure 10 shows, it is possible to address each group of lines during durations which belong to the Tm periods of all the others groups.
Group lines are subject to at least n sequencing these successives of duration Ti each having:
- a first fraction T ~ during which the transistors of all lines in the group are rendered conductors, so as to bring the electrodes to the potential the respective column conductor;
- a second fraction Tm ~ much longer than T ~, during which all the transistors of the group consider déré are blocked.
As shown in Figure 10, it is possible to address each group of lines during the periods Tm common to other lines.
This command mode allows the use of orthogo-nals, which will often be binary, made up in this case of a determined number of terms + l and -1; in codes 5orthogonal:
- the sum of the squares of the terms of each code is equal to the same value, which can be reduced to 1 by standardization, - the sum of the term-to-term products of two codes 10any is void.
The VCej voltages applied to the counter parts electrode during successive fractions T ~ l, T ~ 2 will be then constituted by the product of the same value Vce by the terms of one of the orthogonal codes.
15The codes used will generally have a number of terms greater than the number n of lines per group, for have additional parameters. The number of frac-tions will be equal to n + l when using an alternation on the counter-electrode, n + 2 otherwise. For example, 20in the particular case of groups of n = 6 lines and six counter electrode parts, eight eight-term codes; six codes are then assigned to parts of the counter electrode and another to compensation a quadratic error, the last code remaining unused.
25In particular, the following codes can be used, including each is zero-sum, except the one f0 which remains unused.

- ~ 153744 Cod ~ T ~ mps Tl T2 T3 T4 T5 T6 T7 T ~ Somm ~
unused fO 1 1 1 1 1 1 1 1 8 fl (t) for com- 1 1 1 1 -1 -1 -1 -1 -1 0 thinking fl (t) 1 1 -1 -1 1 1 -1 -1 0 f2 (t) 1 1 -1 -1 -1 -1 1 1 1 0 f3 (t) 1 -1 1 -1 1 -1 1 -1 0 0 f4 (t) 1 -1 -1 1 1 -1 -1 1 1 0 f5 (t) 1 -1 1 -1 -1 1 -1 1 1 0 f6 (t) 1 -1 -1 1 -1 1 1 -1 0 During the eight periods T, to T8 between which is fractional Tr ~ the voltages Vcej are then the products of terms fl to f6, multiplied by Vce. For example, the tension of the CEl part will be, during the periods T ~ consecutive ves:

Tensions Til Ti2 Ti3 Ti4 Ti5 Ti6Ti7 Ti8 of against-elect trode CEl + Vce + Vce -Vce -Vce + Vce + Vce -Vce -Vce This distribution is that illustrated in FIG. 11.
During the corresponding periods T ~, the voltages Vck applied to the column conductors of order k, while group g is addressed, by:

~ 15374 ~

Ta1 Ta2 Ta3 Ta4 Ta5 Ta6 Ta7 Ta8 Voltage VC1 gk Vc2gk Vc3gk Vc4gk Vc5gk Vc6gk Vc7gk Vc8gk on the column Vck The indices 1 to 8 indicate only a staggering temporal.
So that the capacitors of pixels 1 to n of the same group of order g, corresponding to the same column k, have, during time T, radiometric values (generally appropriate light transmission values) 15 apply quadratic voltages to pixel capacitors appropriate medium ticks, since the transmission of light by a pixel of the line j of the group g at the crossing of line k is fixed by the mean square value (V ~ sjgk) 2 for the duration Tr.
20We will obtain, for n = 6 pixels of a column k, algk, a2gk, ..., a6gk values of a radiometric parameter, representative of the transmission to be given, but which can vary between -1 and +1, by applying, in column k, different voltages in at least six periods 25 successive, and generally more to carry out a correction.
In the previously mentioned case where we adopt eight periods, the voltage applied to a column conductor during an interval Ta will be constituted by the product of a reference voltage Vc by the sum of the products of parameters for each pixel, by the terms of the assigned code to the line (and to the counter-electrode part) corresponding dante.
In other words, the signals sent will be, if we abstracts from the quadratic error:

Vc. ~ + Algk + a2gk + a3gk + a4gk + a5gk + a6gk) Vc. (+ Algk + a2gk-a3gk-a4gk-a5gk-a6gk) Vc. (- algk-a2gk + a3gk-a4gk + a5gk-a6gk) Vc. (- algk-a2gk-a3gk + a4gk-a5gk + a6gk) (1) Vc. (+ Algk-a2gk + a3gk + a4gk-a5gk-a6gk) Vc. (+ Algk-a2gk-a3gk-a4gk + a5gk + a6gk) Vc. (- algk + a2gk + a3gk-a4gk-a5gk + a6gk) Vc. (- algk + a2gk-a3gk + a4gk + a5gk-a6gk) We will then obtain the values al for the pixel of the first line, and so on, because the tension (Vpix) jgk seen by the point located at the intersection of the column k and line (or counter electrode) j in the line group g, is given by (Vpix) jgk (t) = VCEj - VCk.
This voltage is readjusted during each period Ti by a new address during Ta. It remains at the adjusted value throughout the following Tm period. This takes place 8 = n + 2 times immediately during a frame period Tr.

- 21 ~ 3744 But, because the information received by a pixel of a group depends on that received by the other pixels of the group, signals (1) must be corrected for error due to the quadratic nature of the relation which fixes the transmission. Theoretically this error is:

S = ~ / ~ n- ~ a jgk2) We then obtain:

Vclgk = Vc. (+ Algk + a2gk + a3gk + a4gk + a5gk + a6gk + S) during Tal Vc2gk = Vc. (+ Algk + a2gk-a3gk-a4gk-a5gk-a6gk + s) during Ta2 Vc3gk = Vc. (- algk-a2gk + a3gk-a4gk + a5gk-a6gk + S) during Ta3 Vc4gk = Vc. (- algk-a2gk-a3gk + a4gk-a5gk + a6gk + S) during Ta4 Vc5gk = Vc. (+ Algk-a2gk + a3gk + a4gk-a5gk-a6gk-S) during Ta5 Vc6gk = Vc. (+ Algk-a2gk-a3gk-a4gk + a5gk + a5gk-S) during Ta6 Vc7gk = Vc. (- algk + a2gk + a3gk-a4gk-a5gk + a6gk-S) during Ta7 Vc8gk = Vc. (- algk + a2gk-a3gk + a4gk + aSgk-a6gk-S) during Ta8 These eight voltage values Vclgk, ..., Vc8gk are those to be applied to column k considered during each of the eight charge periods Ta of the six pixels of the column k and group g.
We see that the pixel of row j and column k in group g sees tension at all times:

~.

(Vpix) jgk = VCE. fj - Vcgk Note that all the codes given above are with zero average over a period Tr. The average value of (Vpix) jgk on Tr is then zero.
If a code is not at zero mean, it is possible to use the classic technique in addressing transis-thin film tors or TFT, called alternation. It is not necessary while n + 1 orthogonal functions to implement the invention.
As an example, we see that the quadratic value average for the pixel at the crossing of the fourth line of the group g and for column k is:

(VRM5jgk) = Vce + 6.Vc - 2.a4gk.Vce.Vc where a4gk is between -1 and +1, and can take any intermediate value, when desired a display with gray, black and white values, or unsaturated color. So, by choosing Vc and Vce, we can modulate the light transmission of the corresponding point dant at any value between the states off and on, i.e. (VRMs) jgk) 2 can take any what value between Vce2 + 6.Vc2 - 2.Vce.Vc and Vce2 + 6.Vc2 + 2.Vce.Vc.

'- `21 ~ 374 ~

C ~ s ~ e arouDes ~ e colo ~ nes It is also possible to form groups of n columns, this solution making it possible to reduce the number column driver circuits, more complex than line driver circuits.
We will consider the case of a group g of n columns 1, ..., k, ..., n and in particular the control of the pixel at the cross-ment of row j and column k of group g. The counter electrode is still cut into n parts or separate CEk elements. The first element CEl is placed in with respect to columns 1 of each of the groups defined. The second element CE2 is placed opposite columns 2 of each of the defined groups, and so on, until the nth CEn counter-electrode which is placed opposite the columns n of each of the defined groups. He is not here again it is necessary that the columns of the same group are contiguous, on an active matrix plate.
The parts of the counter electrode CEl are connected electrically together on the counter electrode plate. The CE2 counter electrode elements are electrically connected together on the counter electrode plate, and so continuation up to n, according to a provision which can be one of those given above.
Figure 12 shows, by way of example, a fragment of a device with groups of six columns. The corresponding pixels in ~ six lines only and one group of n = 6 columns have been depicted. The orthogonal codes indicated `215374'1 to the right of Figure 12 are the same as those mentioned upper.
The frame period Tr is further divided into periods Ti (eight in number, if using the code above, of which six are used and one is used to compensate for the quadratic error tick.
During the periods Tm of blocking of the transistors of each line j, it is possible to address any another line of the screen, only one at a time.
We still want to apply to six pixels, this time defined by column group g and row j, six light transmission values via values of mean square electrical voltages applied to each of the pixels. These voltage values quadratics vary depending on an intensity parameter ajgl, ajg2, ajg3, ajg4, ajg5, ajg6, with -l <ajgk <+ l.
The signal to send on the columns of group g during each of the eight periods Ti, without error correction theoretical quadratic, is defined in the same way as previously; he is during Tal = Vc. (+ ajgl + ajg2 + ajg3 + ajg4 + ajg5 + ajg6) during Ta2 = Vc. (+ & jgl + ajg2-ajg3-ajg4-ajg5-ajg6) during Ta8 = Vc. (- ajgl + ajg2-ajg3 + ajg4 + ajg5-ajg6) `` ~ 1537 ~

To correct the mean square error, it is necessary add a term S which is the same as in the case of line groups; successive tensions applied to the column k are then:

Vcjgl = Vc. (+ Ajgl + ajg2 + ajg3 + ajg4 + ajg5 + ajg6 + S) during Tal Vcjg2 = Vc. (+ Ajgl + ajg2-ajg3-ajg4-ajg5-ajg6 + S) during Ta2 Vcjg3 = Vc. (- ajgl-ajg2 + ajg3-ajg4 + ajg5-ajg6 + S) during Ta3 Vcjg4 = Vc. (- ajgl-ajg2-ajg3 + ajg4-ajg5 + ajg6 + S) during Ta4 Vcjg5 = Vc. (+ Ajgl-ajg2 + ajg3 + ajg4-ajg5-ajg6-S) during Ta5 Vcjg6 = Vc. (+ Ajgl-ajg2-ajg3-ajg4 + ajg5 + ajg6-S) during Ta6 Vcjg7 = Vc. (- ajgl + ajg2 + ajg3-ajg4-ajg5 + ajg6-S) during Ta7 Vcjg8 = Vc. (- ajgl + ajg2-ajg3 + ajg4 + ajg5-ajg6-S) during Ta8 These 8 voltage values are the ones you need apply to all columns of group g considered during each charge period Ta of the 6 pixels of line j.
We see that the number of column "drivers" is divided by a factor n, here 6, because all the columns of the same group receive exactly the same electrical signal. That decreases the number of column drivers and also the number of electrical connection points between these "drivers" and the cell.
During these 8 periods the voltages VCEk, applied to the 6 counter electrodes, are given by a table which is the same as for grouping of lines (if the codes are the same).

215374 ~

For example, during the addressing of line j:

Voltage Ta1 Ta2 Ta3 Ta4 Ta5 Ta6 Ta7 Ta8 of against-electrode VCE1 + Vce + Vce -Vce -Vce + Vce + Vce -Vce -Vce VCE2 + Vce + Vce -Vce -Vce -Vce -Vce + Vce + Vce VCE3 + Vce -Vce + Vce -Vce + Vce -Vce + Vce -Vce VCE4 + Vce -Vce -Vce + Vce + Vce -Vce -Vce + Vce VCE5 + Vce -Vce + Vce -Vce -Vce + Vce -Vce + Vce VCE6 + Vce -Vce -Vce + Vce -Vce + Vce + Vce -Vce Voltage Vcjg1 Vcjg2 Vcjg3 Vcjg4 Vcjg5 Vcjg6 Vcjg7 Vcjg8 on the group g from co-lonnes We will not describe the command and the correction any further.
of quadratic error, since it is the same as in the case of line groups.

Claims (8)

1. Liquid crystal display device, of the so-called active matrix type, comprising a display screen having a thin layer of liquid crystals disposed between a planar counter electrode and electrodes (defining each a capacitor and a picture element, or pixel, with the counter electrode) so that each of the pixels corresponds to a row and a column, each election trode being connected to a control element, such as a thin film transistor, allowing or carrying it to the potential of a column conductor which is common to all the pixels of the column to which it belongs, or else to isolate it and make its potential floating, according to the voltage which is applied to a common line conductor at all control elements on the same line, characterized in that:
- each conductor assigned to a row of pixels in a first direction (row or column) is common to a group with an integer n, greater than 1, of rows and has a single driver, designed to apply successively several control voltages during a screen write cycle (or frame cycle) while each conductor assigned to a row of pixels in the second direction (column or row) attacks only one arrayed in said second direction, orthogonal to the first;
- in that the counter-electrode is split into n parts each provided with a voltage switching element, each part being assigned to homologous rows of row groups;
- in that said switching elements are provided each to bring the counter electrode to a determined voltage born of validation during the periods necessary for the ordering a row from among n rows; and - in this one of the conductors assigned to each pixel apply a voltage which is a sum of terms of a code orthogonal weighted and the driver assigned to the pixel, in the other direction, apply a voltage representative of orthogonal code terms. 2. Device according to claim 1, characterized in what groups are made up of rows or columns. 3. Device according to claim 1, characterized in that the counter electrode consists of two parts in a single layer and interdigitated. 4. Device according to claim 1, characterized in that the counter electrode consists of at least three parts in a single layer, of which two interdigitated parts and the other or the others in the form of Greek. 5. Device according to claim 1, characterized in that the counter electrode consists of four parts distributed in two layers separated by an insulating film you. 6. Device according to any one of claims above, characterized in that each of the electrodes of capacitor is extended by a protrusion which constitutes the drain or source of a thin film transistor respective, in that the same column conductor attacks the sources or drains of field effect transistors belonging to the same group and in that a track forming a line conductor constitutes the grids of the n transis tors of this group. 7. Device according to claim 1, said groups each consisting of n lines, characterized in that:
- each common attack circuit with n lines is provided to, during a screen writing cycle, perform minus n successive sequences of duration (Ti) comprising a first fraction (Ta) during which all group electrodes are brought to the column potential corresponding and a second fraction (Tm) during which the previous potential remains maintained;
- the switching elements of the counter parts electrode are provided for, during said sequences successive of the same cycle, apply successively voltages having either of two values (+ Vce) and (- Vce), the sequence of values applied to each part of counter electrode representing a zero mean value code which is orthogonal to all the other part codes of counter electrode; and - the columns are ordered to be worn each successively, during the first fractions of the cycle, at successive voltages each represented, for each column, by the sum of the products of the values represented sentatives of parameters representing radiometric values What to give to pixels belonging to both the group and to the column by successive weighted terms from one of codes assigned to the lines. 8. Device according to claim 7, characterized in what the codes are at least n + 1 and include at least n + 1 terms, and in that each driver circuit column is provided to add, to each of said sums of products, a term consisting of the product of a term of quadratic error correction by the (n + 1) th term and for perform a (n + 1) th sequence, during which the respective column conductor is brought to a voltage constituted by the sum of the products of said values by the successive terms of the additional value binary code zero mean orthogonal to the other codes.