GB2224153A - Matrix display devices - Google Patents

Abstract

In a matrix display having an electro-optical display element e.g. LCD, connected in series with a non-linear device at each matrix point between associated row and column conductors 14, 15, the overall number of conductors is reduced by arranging the picture elements into groups of at least two elements 12 with the associated non-linear devices 11 connected in series between a row or a column conductor and one of the elements 12 with intermediate connections to the other elements and by arranging the selection signal provided by the driving means 20 to have different and predetermined levels corresponding to the number of elements in a group. The non-linear devices 11 connected to a row are progressively turned off one by one by the selection signal after the data supplied via a switching circuit 30 are loaded into the related picture elements. A group may be formed from picture elements in one or more rows or columns, and each group may be connected via a separate string of non-linear devices to adjacent rows. The non-linear devices may be diode rings, MIMs or back to back diodes. <IMAGE>

Description

DESCRIPTION MATRIX DISPLAY SYSTEM This invention relates to a matrix display system comprising sets of row and column address conductors carried respectively on two supporting plates, a plurality of picture elements arranged in rows and columns and defined by opposing electrodes on the supporting plates with an electro-optical display medium therebetween, the picture elements being connected in series with a non-linear device between associated row and column conductors, and driving means for applying selection and data voltage signals to the row and column conductors selectively to load each picture element individually with display information.

A matrix display system of this kind is suitable for displaying alpha-numeric or video (for example, TV) information using passive electro-optical display material such as liquid crystal material. Such active matrix addressed display systems may typically consist of a matrix array of a very large number, for example around 200,000 or more, picture elements.

In a known example of such a matrix display system in which the electro-optical medium comprises liquid crystal material, each picture element is defined by a respective electrode carried, together with row conductors, on one of two supporting plates and a facing portion of a column conductor which is common to all picture elements in the same column and-carried on the other supporting plate. The non-linear devices comprise bidirectional devices such as diode rings, MIMs (Metal-Insulator-Metal devices) or the like and are arranged laterally of their respective picture element electrodes on the one supporting plate in an array of row and columns extending between the picture element electrodes with one terminal of the non-linear device being connected to its associated picture element electrode.The other terminals of all non-linear devices associated with one row of picture elements are connected to a respective one of the set of row conductors. Each picture element is therefore associated with a unique combination of a row conductor and a column conductor. The non-linear devices exhibit a threshold characteristic and act as swithes- in-se-fls' wth--their picture elements A predetermi-ned voltage appAied-acrosssthe series combination of a picture element and a non-linear device causes the-devi-ce to operate in the conductive, "on", part of its characteristic curve. At lower voltage levels the device is substantially non-conductive, and in its "off" state.

Examples of known matrix addressed liquid crystal display systems using non-linear devices such as diode rings, MIMs and the like are described in US Patent Specification No. 4,223,308 and British Patent Specification Nos. 2,147,135 and 2,091,468.

In order to obtain a full colour display, a colour filter mosaic of red, green and blue filter elements is carried on the other substrate to colour light transmitted by the picture elements. The elements of the filters are registered with the picture elements so that each picture element is dedicated to one of the three primary colours. Groups of juxtaposed red, green and blue picture elements constitute colour triplets whose primary colour outputs combine to provide a multi-colour display capability. By driving the array of picture elements with the appropriate red, green and blue data signals, a full colour picture is produced.

It will be appreciated that with the above-described display system the minimum number of row and column conductors necessary corresponds to the number of rows and columns respectively of picture elements. In addition to the need to devote a proportion of the overall display area to the accommodation of the row and column conductors, there is also a possiblity that in view of the large number of conductors involved one or more could prove defective, perhaps rendering the device unusable. Obviously, the more conductors employed; the greater this possibility becomes so that with comparatively large area display systems yields can be seriously effected.

Furthermore, the large numbers of row and column conductors necessary can also cause problems with the production of small area display systems, for example of the kind used in projection systems. In order to provide the desired display resolution after projection, the display system generating the image should have adequate numbers of rows and columns of picture elements. Ideally a display system having a very compact array of picture elements is required to provide sufficient picture element density.

It is an object of the present invention to provide an active matrix addressed display system in which fewer address conductors need be provided.

It is another object of the present invention to provide an active matrix addressed display system which can, if desired, be fabricated either with a compact array of picture elements, thus rendering it suited to use in a projection display system, or with a high density of picture elements to provide a high resolution display.

According to the present invention a matrix display system of the kind referred to in the opening paragraph is characterised in that the picture elements are formed into groups of at least two picture elements in each of which groups the picture elements are addressed via the same row and column conductors, the non-linear devices associated with the picture elements of a group being interconnected in a series arrangement whereby a first picture element of the group is connected to an address conductor through its associated non-linear device, a second picture element is connected to that address conductor through its associated non-linear device in series with the non-linear device associated with the first picture element, and so on if each group comprises more than two picture elements, and in that the selection signal provided by the driving means has different and predetermined levels according to the number of picture elements in each group.

As a result of the non-linear devices of the group being interconnected in a series arrangement then the number of non-linear devices which are in effect turned "on" and rendered conductive by the application of a voltage across the group's associated address conductors will depend upon the level of that voltage.The non-linear devices have substantially uniform threshold charac-teristi-cs,-aL-though small' variations -rnght exist as a result of fabrircation processes employe-d.- By usi-ng,--in conjunction with a data signal, a selectio'n-- signat- 'whose" level changes in predetermined manner over a selected amplitude- range, the non-linear devices associated with the pi-:cture elements of each group can be selectively controlled.

A suitably high voltage level selection signal will result in the plurality of non-linear devices being turned "on". A subsequent decrease in the voltage level of the selection signal to a value below that required for switching one of the non-linear devices will result in that one non-linear device being turned "off" whilst the one or more other non-linear devices of the group remain "on".

A further decrease in the voltage level of the selection signal to another, lower, selected level will result in one of the other non-linear devices, assuming there are three or more non-linear devices associated with each group, being turned "off", and so on.

In this way, therefore, each of the non-linear devices of a picture element group can be operated selectively. By applying data voltages to the other address conductor associated with the group appropriately in synchronism with the changing selection signal, each of the picture elements of the group is left charged to a value dependent on the data voltage upon its associated non-linear device being turned "off" by the disappearance of the required selection signal voltage level. Thus each picture element in the group is set individually to produce a desired individual display effect independently of the display effect produced by other picture elements of the group. The resulting visible display is equivalent to that which would be obtained by a corresponding number of picture elements independently driven via respective unique pairs of address conductors and non-linear devices.

It will be appreciated that by grouping and driving the picture elements in the aforementioned manner, the number of address conductors necessary is reduced. This leads in turn to a beneficial reduction in the number of address conductor connections necessary.

Each group of picture elements may comprise picture elements located adjacent one another in the same row, leading to a reduction in the number of column conductors necessary, or located in different, adjacent rows, whilst still being driven via the same row conductor and the same column conductor, leading to a reduction in the number of row conductors necessary. For example, in the case where each group comprises three adjacent picture elements of the same row, the number of column conductors which need be provided is reduced by a factor of three.Each column conductor would therefore have a width corresponding to the distance across the group of three picture elements which offers the advantage of greater reliability whilst also avoiding problems due to resistivity of the conductor material as found in conventional panels where the width of a column conductor corresponds to a single picture element. Moreover, as the picture elements of each group are associated with for example only one column conductor packing of the picture elements closer together is facilitated enabling higher densities of picture elements to be achieved. Thus either a higher resolution display or a compact array type display system suitable for use in a projection system can more easily be obtained.Alternatively, in certain embodiments, space which becomes available through reducing the number of address conductors could if desired be utilised instead to provide at least some duplicated conductors for redundancy purposes.

In a preferred embodiment where each group of picture elements is addressed through a single row conductor and a single column conductor, the driving means is arranged to provide each of the required number of selection voltage levels to each row conductor in turn, each row conductor address period being divided into sub-periods during which respective voltage levels are applied.

The number of picture elements provided in the groups may be varied. The upper limit is determined bearing in mind that a certain period is needed to allow each picture element to be charged to a respective required value through the same row and column conductor. Considering, for example, the situation where each-group comprises-picture elements in the samegrow-and the and th'e- system is intended to display PAL standard-TV pictures, then the: row energisation-period available, namely 64 microseconds, needs ,to- be divided into sub-periods during which data slgnals are. apptied to charge each of the picture elements, the number of such sub-periods corresponding to the number of picture elements in the group.The possible duration of these sub-periods is therefore dependent on the operating characteristics of the picture elements with their associated non-linear devices.

In the case of the display device being intended to produce full colour displays, the number of picture elements in each group is preferably three, and each picture element in a group is arranged to provide a display in a respective one of the primary colours, namely red, green and blue. This offers the advantage that each colour triplet of the display system need require only one row conductor and one column conductor, thus greatly simplifying construction.

The non-linear devices may, as in known matrix display devices, comprise bidirectional devices, such as diode rings, MIMS, or other diode structures with a substantially symmetrical voltage/current relationship, which enable each group of picture elements to be associated with a single row conductor and a single column conductor. However, the invention is applicable also to a kind of system using the so-called Lechner addressing scheme, as described in the article entitled "Liquid Crystal Matrix Displays" by B. J. Lechner et al published in Proceedings of the IEEE, Vol.

59, No. 11, November 1971, at page 1566, in which each picture element is addressed using three address conductors, one from one set, e.g. a column conductor, and two adjacent address conductor's from the other set, e.g. two row conductors, with the picture element being connected to the two adjacent row conductors via respective unidirectional non-linear devices. In a further embodiment of the invention, therefore, which employs the Lechner addressing scheme, the non-linear devices associated with the group of picture elements and connected to an address conductor are unidirectional devices and the picture elements are connected also to an adjacent address conductor through associated further unidirectional non-linear devices, the further non-linear devices being similarly interconnected in a series arrangement but in the opposite sense to the first-mentioned series arrangement.

Embodiments of matrix display systems in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic circuit diagram of a matrix display system according to the present invention intended to be used for displaying video information and having a liquid crystal display panel with picture elements in a column and row array and associated with bidirectional non-linear devices; Figure 2 shows diagrammatically in plan view, and in greater detail, a part of the display panel of the system of Figure 1 in which the picture elements of the panel are arranged in groups, the particular part shown comprising a typical group consisting of three juxtaposed picture elements in one row of the panel;; Figures 3a and 3b show by way of example typical selection signal and data signal waveforms respectively applied to the group of three picture elements shown in Figure 2; Figure 4 is a view, similar in respects to that of Figure 2, showing a typical group of three picture elements of a modified form of the display panel of Figure 1 in which picture elements are arranged in groups using picture elements from adjacent rows; Figures 5a and b illustrate alternative forms of non-linear devices which can be used in the displays systems of Figure 1, 2 and 4; and Figure 6 shows diagrammatically in plan view a typical part of the display panel of another embodiment of matrix display system according to the invention, the display panel in this case having groups of picture elements connected to two adjacent row conductors and using unidirectional non-linear devices.

Referring to Figure 1, there is shown in simplified form a block diagram of a matrix display system intended for displaying TV pictures which includes an-active matrix addressed liquid crystal display: p-anel' 10 consisting of m rows (1 to m) 'with n harizontal, and vertically - aligned,wpicture-elements 12 C1 to'n)--in-ea'c-h row, only a few of which are indicated in figure f for simplicity; In practice, the total number of picture elements -(m x n) in then column and row matrix array may be 200,000 or more.Each pictures element consists of a pair of spaced-electrodes 16 and 17 with liquid crystal material therebetween, and has an associated two-terminal bidirectional resistance device with a non-linear and symmetrical current/voltage relationship acting as a switch for controlling operation of the picture element. Groups of three of these non-linear devices associated with groups of three adjacent picture elements in each row are indicated in Figure 1 by the blocks 11. The non-linear devices throughout the panel have substantially similar current/voltage characteristics, although small variations in thresholds may be present due to materials or technological factors.

The non-linear devices associated with all picture elements in the same row are connected to a respective row conductor 14 to which selection (scanning) voltage signals are applied. Data (video information) signals are applied to the picture elements through column conductors 15.

The row conductors 14, the non-linear devices and picture element electrodes 16 are all carried on one supporting plate of the panel. The column conductors 15 and picture element electrodes 17, constituted by portions of the conductors 15 overlying the picture element electrodes 16, are carried on a further supporting plate extending parallel to, and spaced from, the one supporting plate with TN liquid crystal material being disposed between the plates. The opposing plates, which may be of glass, are provided with polariser and analyser layers in conventional manner.In operation of the panel, the liquid crystal material modulates light depending upon a voltage applied the reac ross with each picture element, being individually operable to vary light transmission through the panel in accordance with a drive voltage applied across its respective electrodes. For simplicity the picture elements 12 in Figure 1 are represented by capacitors denoting the picture element capacitance.

The picture elements 12 are addressed by repetitively scanning the row conductors 14 in sequential fashion with a selection signal so that each row of picture elements is driven in turn and applying data signals to the column conductors 15 in synchronism appropriately. By virtue of the selection signal the non-linear devices associated with a row of picture elements are turned "on" in a selective manner as will be described. During the remainder of the field period, that is, until a row of picture elements is next selected, the non-linear devices are "off" and their function is to keep the video voltage across their associated picture elements by virtue of the natural capacitance of the picture elements.

The general constructional and operational aspects of active matrix address liquid crystal display panels employing non-linear devices as switching elements are well known and have been widely described and documented elsewhere. For this reason, it is not considered necessary to describe here these general aspects in detail. For further information in this respect, reference may be made for example to US Patent Specification No. 4,223,308 and British Patent Specifications Nos. 2,147,135 and 2,091,468 describing display devices using diode structures, diode rings and MIMs.

The row conductors 14 are driven by a digital shift register circuit 20 supplied with regular timing pulses from a timing and control circuit 21. The timing and control circuit 21 in turn is supplied with synchronisation signals, X, derived from received TV signals via a tuner, IF circuit, video amplifier and synchronisation separator circuits (not shown). Video information signals, T, from the video amplifier are applied, via a video processing circuit 22, to a sample and hold circuit 23 controlled by a shift register circuit 24 which is fed with timing signals from the timing and control circuit 21.The shift register and sampte-and: hold circuits'23- and 24, which are of known- -type' as conventionatly used,- and-acc-orwdingly shown here in simple btock form, act as a -serial to paralle'L -converS-i'on circuit appropriates to the row at a time addressing of the panel and sample one line of the video information signal at a time and place the relevant voltages on the column conductors 15 via a switching' circuit 30 whose function will become apparent. The particular sample and hold circuit 23 employed depends upon whether the display system is to provide a half or full vertical resolution, colour or monochrome, TV display.In all forms, however, the circuit 23 samples the incoming video information signal at n points during each TV line period and applies these voltages respectively to n output lines, where n corresponds to the number of picture elements in each row of the panel 10. The n output lines from the circuit 23 are fed into the switching circuit 30 which comprises a series of solid state switches whose operation is controlled by the timing and control circuit 21. The circuit 30 has n/3 outputs, each of which is coupled to a respective one of the column conductors 15 and is switchably connected in predetermined sequence, via an associated one of the solid state switches, to each one of a group of three adjacent outputs of the circuit 23 in turn.

When selected the picture element electrodes 16 of a row charge up to a value according to the level of the selection signal. At the same time the data signals are applied to the electrodes 17 and when the selection signal is removed from the row conductor 14, the picture elements are isolated and charge is stored on the elemental capacitors whose value is dependent on the respective data signals. The picture elements thus stay in the state into which they were driven until the next time they are addressed, which, in the case of a TV display, will be in the subsequent frame period.

In order to avoid electrochemical degradation of the liquid crystal material, the polarity of the drive voltages applied to the picture elements is, in accordance with known practice, inverted periodically, although the means by which this is achieved has been omitted from Figure 1 for simplicity.

Referring now also to Figure 2, there is shown a typical portion of the display panel 10 in greater detail. In accordance with the invention, the picture elements are formed into groups, with each group, such as that indicated by the dotted line 18, comprising a plurality of juxtaposed picture elements 12 sharing the same row conductor 14 and column conductor 15, the latter being shown in Figure 2 in dashed line form. In the illustrated embodiment, each group comprises three picture elements located adjacent one another in the row direction, their electrodes here referenced 16', 16'' and 16"'. Although shown as oblong other electrode shapes, such as squares, could be employed.Respective portions of a column conductor 15 overlying the electrodes 16', 16" and 16"' constitute the opposing electrodes 17 of the picture elements. The three non-linear devices associated with the three picture elements, corresponding to a block 11 in Figure 1, are referenced 34, 35 and 36, and are arranged to one side of the electrodes. The non-linear devices 34, 35 and 36 are interconnected in a series arrangement. A first terminal of the device 34 is connected to a row conductor 14 and its second terminal connected to the electrode 16'. The device 35 is connected in series between the electrode 16" and the second terminal of the device 34.

Similarly, the device 36 is connected in series between the electrode 16"' and the device 35. Thus, the electrodes 16" and 16"' are connected to the row conductor 14 through the devices 34 and 35 in series and the devices 34, 35 and 36 in series respectively.

As the column conductor 15 is shared by the group 18 of three picture elements (and likewise other similar groups of picture elements in the same columns as these picture elements) the number of column conductors is reduced compared with known panels having one column conductor for each column of picture elements, and only n/3 column conductors 15 are needed.

The non-linear devices 34, 35 and 36 are selectively controllable so that video information can be loaded into the three picture elements'individually as appropriate. In this respect because the non-linear devices of this' group (and:- likewise corresponding non-linear devices in other groups) are arranyed in series, respective different, and defined, vo-ltage Levels 'of: the' selection signal are applied to the row conductor.l4 in order to exceed their thresholds and render them conductive.Thus, at a certain voltage level on the conductor 14, the non-linear device 34, (and correspondingly-positioned non-linear devices of other groups in the same row), will be turned "on". At a higher voltage level, non-linear device 35, (and again other correspondingly-positioned non-linear devices of other groups in the same row), will be turned "on" as well. At an even higher voltage level, the non-linear device 36, will also be turned "on", so that at this voltage level all three non-linear devices in each group, and thus all non-linear devices of the row, will be turned "on" simultaneously.

Figure 3a shows part of a typical waveform for the selection signal, Vs, applied to a single row conductor 14. At the beginning of a selected row energisation period, the switching signal Vs is at a high level. At a certain time thereafter the signal Vs drops to an intermediate voltage level and then, after another predetermined period, to a low level before finally dropping to zero, or some other hold level, at which time a similar waveform is applied to the next row conductor 14 to be energised. The duration of this sequence of high, intermediate and low voltage levels corresponds approximately with the duration of row energisation, which for a TV display will be equal to the line period, that is, around 64 microseconds for PAL standard, and each level is maintained for a similar period, approximately one third of the line period.During the next TV field period, this sequence is repeated, and so on. The time interval between these sequences for a TV display is around 20 ms.

In synchronism with these selection signal sequences, and similarly under the control of the timing and control circuit 21, video information (data signals), D, for the three picture elements of the group are applied to the relevant column conductor 15.

Similarly video information signals for the three picture elements of all other groups in the same row are applied to their respective column conductors 15. Figure 3b illustrates a typical example of video information waveform for the group of three elements shown in Figure 2 where the voltages to be supplied to the picture elements are designated S3, S2 and S1 respectively. The polarity of the data voltages and likewise the selection signal is inverted for row energisations in successive fields. During the interval between the two successive sets of information signals shown in Figure 3b intended for the group 18, similar information signals will be applied to the same column conductor 15 for other groups of picture elements of the panel in the same columns, but these have been omitted for simplicity.

Loading the group of three picture elements shown in Figure 2 will now be described in greater detail. At the beginning of the selection signal, Vs, sequence, the information signal S1 is applied to the associated column conductor 15 by the circuits 23, 24 and 30 and all three non-linear devices are turned "on" as at this high voltage level the voltage obtained across the devices exceeds their threshold voltages, so that the picture element electrode 16"' is charged according to the level of Vs. The electrodes 16' and 16" are similarly charged at this time.When the selection signal voltage drops to its intermediate level, the non-linear device 36 turns "off" as this intermediate level produces a voltage across this device below its threshold voltage but is sufficient to keep the other two non-linear devices 34 and 35 on". The picture element associated with the device 36 is then isolated and left charged to a desired level according to the value of signal S1. Simultaneously with this intermediate selection signal level, the information signal applied to column conductor 15 is changed to S2 by switching of the circuit 30.Upon the switching signal voltage dropping further to its low level, the voltage across the non-linear device 35 drops below its threshold voltage so that device 35 turns "off" and only device 34 remains on. The: picture element associated wi-th the device 35 is- thus ist-ated and left charged to a value dependent on the signal S2.- The video information signal on columm 15 again charlge-s-at- this point to S3 by operation of. the circuit 30 so that when the low level selection signal is removed, and device 34;turns "off", -the picture element associated with the device 34 is left charged according to the value of S3.

The picture elements are then set in the required state and remain in their respective set states until the next time the row is energised with a further selection signal sequence in the subsequent field period and fresh information signals are applied in a similar manner.

Although during this loading procedure some of the picture elements are supplied temporarily with video information not specifically intended for those elements, the duration of the periods involved is so small that a visible effect in the display picture should not be perceived.

It will be appreciated that the picture elements of other groups in the same row are loaded with the proper video information during the row energisation period in a similar manner via their associated, different, column conductors 15. The remaining rows of picture elements are loaded sequentially in similar fashion.

Whereas in the particular embodiment described above each group of picture elements consists of three elements, the numbers of elements in the groups may be varied. For example each group may comprise two or four or more elements. The maximum number of elements in a group is determined by the preset duration of the available loading time, corresponding to a TV line period, and by the operational characteristics of ttle non-linear devices and the charging characteristics of the picture elements.

Groups of three picture elements are particularly advantageous in a full colour display system. In this case, a filter sheet comprising a matrix of red, green and blue filter elements is carried on the same supporting plate as the column conductors 15 and overlies the picture element electrodes with correspondingly-positioned elements in the groups being in registration with a respective colour filter element. For example, the three picture elements defined by the electrodes 16', 16" and 16"' may respectively display red, green and blue video information. Each group thus forms a colour triplet having a red, green and blue picture element and similar in respects to those of a colour CRT's phosphor screen.Conveniently therefore, using the described loading procedure, each colour triplet of the display panel is loaded using only one row and one column conductor.

Obviously in such a full colour display system the sample and hold circuit 23 is modified and fed with appropriate R, G and B video signal components from the processing circuit 22 in a known manner for supply in the relevant order to its n output lines in accordance with the chosen order of colours in the triplets.

In the above-described embodiment of display system according to the invention, the picture elements of the display device are arranged in groups comprising picture elements of the same row.

However, different group configurations are possible involving picture elements of different rows leading to a reduction in the number of row conductors necessary.

Referring to Figure 4, there is shown in plan diagrammatic form a typical part of the display panel of another embodiment of the display system according to the invention in which a different group configuration is employed. The display panel shares many similarities with that of the Figures 1 and 2 embodiment and accordingly the same reference numerals have been used to designate like components. The main difference between this display panel and that of Figure 2 is that each group comprises picture elements from adjacent rows of picture elements, in this case pairs of elements from two rows. One such group is shown bordered by the dotted lines 50.

As before, each picture element has an associated bidirectional non-linear device, here referenced at 51 and 52, and the non-linear devices of a group are interconnected in a series arrangement. Thus, the non-linear device 51 associated with the upper picture element is connected in series between the electrode, 16', of that-*Lement and! a row conductor 14. The: non-tinear device 52 associated -wi-th the lower-picture element is connected between: the electrode 16" of the lower element and the non-linear device.

51 so that this electrode 16'' is connected to the row conductor'- 14 through the two non-linear devices 51 and SI in series.

Operation of this display device is similar in respects to that previously described with reference to the embodiment of Figures 1 and 2. A selection signal Vs sequence having two rather than three different steps of predetermined voltage levels chosen in accordance with the threshold levels of the two non-linear devices of each group is applied to each row conductor 14 in turn.

Appropriate data signals are applied to the column conductors 15 in synchronism with the stepping of the selection signal sequence as previously so that at the end of the row selection period each of the two picture elements of each of the groups in a line is loaded according to the relevant video information. It will be seen therefore that two rows of picture elements are loaded in one row addressing energisation period. Successive pairs of rows of picture elements are subsequently loaded in similar fashion in turn to build up a complete display picture in one field period.

In view of the different group configuration compared with that described with regard to Figure 2, the drive circuits are modified appropriately. More particularly, as two rows of picture elements of the device are effectively driven simultaneously, that is, at least in the same row addressing period, the sample and hold circuit 23 is capable in this case of sampling and holding data signals for two TV lines at a time and the switching circuit 30 is suitably configured with regard to the outputs from circuit 23 for supplying the relevant data signals to the column conductors 15 in the required order. It will be appreciated that with this form of display system, the number of row conductors 14 is halved compared with the previous embodiment and a conventional display system and the shift register circuit 20 is arranged to energise sequentially only m/2 row conductors 14.Each row conductor 14 is addressed by this circuit 20 with a selection signal sequence within an interval corresponding to two TV line periods. As such, the duration of each of the two individual signal levels required in the sequence may be increased close to a TV line period. The number of column conductors 15 required is, however, double that of the previous embodiment and corresponds to the number of columns of picture elements, namely n. Of course, the switch circuit 30 is no longer necessary in this case.

Whilst groups of two picture elements have been specifically described for this embodiment, each group may have three or more picture elements taken from a corresponding number of adjacent rows.

Some of the space which becomes available through the reduction in the number of row conductors necessary may be utilised to provide duplicate row conductors each of which runs alongside a respective row conductor 14 and is connected electrically in parallel therewith. This duplicate conductor provides a back up in the event of the associated row conductor 14 proving defective.

The defective conductor, or a portion thereof, may be disconnected from the circuit by a laser scribing technique.

It is envisaged that, in another embodiment of display system, each group of picture elements could consist of two or more picture elements from one row together with one or more picture elements from an adjacent row, with each group of picture elements still being addressed through a single row conductor and a single column conductor thereby leading to a reduction in the overall numbers of both the row and column conductors. This embodiment shares similarities with the above-described embodiments, and the necessary driving circuit will combine features of the driving circuits of these two embodiments.

The bidirectional non-linear devices used in the above embodiments may be of any suitable known type exhibiting a threshold characteristic such as diode rings, MIMs or back to back diodes. Figures 5a and 5b illustrate by way of example, the circuit configuration of non-linear devices comprising diode rings andMIMs respectivety associated with a' group' of picture elements as shown in Figure 2.

Whilst in the above- embodimentsleach row of picture elements -is addressed via a single row conductor ánd the- non-binear devices used are bidirectional in operation, the invention is applicable as well to display systems using the so-called Lechner addressing scheme in which each row of picture elements is associated wi-th two- row conductors through which the row of elements are selected' and- using unidirectional non-linear devices, data signals being applied to column conductors as before. Figure 6 shows schematically a part of the display panel of another embodiment of liquid crystal display system in accordance with the invention which uses the Lechner addressing scheme.Referring to this figure, it is seen that the picture elements are each connected to two associated row conductors, for example Xn and Xn'. Each row of picture elements shares the same two, respective, row conductors. As in the embodiment of Figure 1 and 2, the picture elements are formed into groups of three, as indicated by the dotted line 60 for example, and are connected to a row conductor, Xn, through associated non-linear devices 61, 62 and 63 respectively, which in this case are unidirectional non-linear devices each comprising a plurality of series-connected diode elements. Like the non-linear devices of Figure 2, these non-linear devices 61, 62 and 63 are interconnected in a series arrangement.

In addition, the three picture elements of the group are connected also to the row conductor Xn' through further associated unidirectional non-linear elements 64, 65 and 66, which again are interconnected in a series arrangement, but with opposite polarities to the devices 61, 62 and 63.

The non-linear devices 61-66 are shown for simplicity as consisting of two series connected diode elements. However, taking into account the forward direction threshold voltage of a diode element and the need to match the non-linear device characteristics with the operating characteristics of a liquid crystal picture element each non-linear device would in practice typically comprise a larger number of diode elements, for example, around six.

Each column conductor 15, like those of the embodiment of Figures 1 and 2, overlies a respective column of groups with portions of the column conductor in registration with the picture element electrodes 16', 16" and 16"'. Thus the display system uses n/3 column conductors where n is the number of picture elements in a row.

The operation of this display system is similar in many respects of that of the embodiment of Figures 1 and 2 except that the use of two row conductors with respective unidirectional non-linear devices necessitates some changes. The three picture elements of each group are again loaded in turn during one row address period. Considering the group of picture elements in the upper row of picture elements in Figure 6, a multi-level row selection signal is applied to the row conductors Xn and Xn' simultaneously with an appropriate data signal waveform to the column conductor 15. The selection signal starts with a high voltage level pulse being supplied to the row conductor Xn which results in the three non-linear devices 61-63 being turned "on" and charging of all those picture elements.This pulse then disappears and a negative voltage level is applied to the row conductor Xn' which is not sufficiently low to turn device 66 "on". Thus the electrodes 16' and 16" are discharged and the picture element associated with the devices 63 and 66 is left charged to a value dependent on the instantaneous value of the data signal to provide a desired display effect. Thereafter a lower level voltage pulse is applied to row conductor Xn turning on devices 61 and 62, but not device 63, to charge up the electrodes 16' and 16" followed by a negative voltage pulse of decreased magnitude applied to the row conductor Xn' which is sufficient to turn "on" the non-linear device 64 only. This leaves the picture element associated with the devices 62 and 65 charged to a value dependent on the instantaneous value of the data signal to provide a desired display effect.Finally, a further, yet lower, voltage level pulse is applied to the row conductor Xn to turn "on" the device 61 alone to selecvt the associated picture eLement which, upon removed of this putse,- :is left charged to the desired va;Lue.

Each row of picture elements is addressed in this manner in sequence to build up a display picture. In:the':successive'field period and immediately before the above described selection and addressing procedure for each individual row, a high level negative voltage pulse is applied to the lower row electrode of a row, for example Xn', to turn "on" the associated non-linear devices in that row and discharge the picture element prior to them being charged again to their required values.

Whilst in the above embodiments the non-linear devices have been described as situated serially between the picture elements and the row (selection) conductors, it is envisaged that they may instead be situated serially between the picture elements and the column (data) conductors, the column conductors in this case extending between columns of picture element electrodes and the row conductors being of a width to provide the opposing electrodes of the picture elements.

Although the use of liquid crystal material has been described in particular, other electro-optical media having appropriate electrical characteristics may be employed instead.

Claims (12)

CLAIM(S)

1. A matrix display system comprising sets of row and column address conductors carried respectively on two supporting plates, a plurality of picture elements arranged in rows and columns and defined by opposing electrodes on the supporting plates with an electro-optical display medium therebetween, the picture elements being connected in series with a non-linear device between associated row and column conductors, and driving means for applying selection and data voltage signals to the row and column conductors selectively to load each picture element individually with display information, characterised in that the picture elements are formed into groups of at least two picture elements in each of which groups the picture elements are addressed via the same row and column conductors, the non-linear devices associated with the picture elements of a group being interconnected in a series arrangement whereby a first picture element of the group is connected to an address conductor through its associated non-linear device, a second picture element is connected to that address conductor through its associated non-linear device in series with the non-linear device associated with the first picture element, and so on if each group comprises more than two picture elements, and in that the selection signal provided by the driving means has different and predetermined levels according to the number of picture elements in each group.

2. A matrix display system according to Claim 1, characterised in that each group of picture elements consists of picture elements located adjacent one another in the same row.

3. A matrix display system according to Claim 1, characterised in that each group of picture elements consists of picture elements located adjacent one another in adjacent rows.

4. A matrix display system according to any one of Claims 1 to 3, characterised in that the driving means is arranged to supply each of the required number of selection voltage levels to each row conductor in turn, each row conductor address period being divided into sub-periods during which respective voltage levels are app L;edt

5. A matrix di-splay system according to any one. of Claims 1' to 4, characterised in that each group comprises three picture elements and each picture element in a groups arranged to provide a display effect in a respective one of the primary colours.

6. A matrix display system according to any one of Claims 1 to 5, characterised in that each group of picture elements is addressed using a single row conductor and a single column conductor.

7. A matrix display system according to Claim 6, characterised in that each non-linear device comprises a bidirectional device.

8. A matrix display system according to Claim 7, characterised in that the non-linear devices comprise diode rings, MIMs, or back to back diodes.

9. A matrix display system according to any one of Claims 1 to 5, characterised in that each group of picture elements is addressed using a single address conductor from one set and two address conductors from the other set, in that the non-linear devices comprise unidirectional devices connected to one of the two address conductors of the other set and in that the picture elements are connected also to the other of the two address conductors of the other set through associated further unidirectional non-linear devices being similarly interconnected in a series arrangement but in opposite sense to the first-mentioned series arrangement.

10. A matrix display system according to Claim 9, characterised in that the unidirectional non-linear devices comprise diode structures.

11. A matrix display system according to any one of the preceding claims, characterised in that the electro-optical medium comprises liquid crystal material.

12. A matrix display system substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.