Driving method for a gas-discharge display panel and display systems using such a method
4/l97l Mayer et al. 340/324 M O Unlted States Patent 91 1111 3,877,006  
 Reboul et al. Apr. 8, 1975 [54] DRIVING METHOD FOR A 3.6l8.07l ll/l97l Johnson et al. 340/324 M G S SC DISPLAY PANEL AND 3,665,455 5/1972 Schmersal et al. 340/324 M DISPLAY SYSTEMS USING SUCH A 3.668.688 6/l972 Schmersal 340/324 M METHOD Primary Examiner-John W. Caldwell Inventors: J pp Reboul; J ques Assistant Examiner-Marshall M. Curtis Pm&#39;tmanns both of Pans, France Attorney, Agent, or FirmRoland Plottel, Esq, [73] Assignee: Thomas-CSF, Paris, France 22 Filed: on. 31, 1972 [571 fABSTRA&#39;CT d I A driving method or gas-discharge isp ay panels [21] Appl&#39; 3024l3 consisting of a network of cells, the ionisation of which is controlled by signals applied between elec- [30] Foreign Application P i it D t trodes arranged in lines and columns, consists in utilis- Nov. 5 1971 France 71.39795 ing driving Signals in Parts drive the I I various display cells of a panel, and for example, to 52 us. c1. 340/324 M- 340/173 PL write them as to cause them take P in the 1 1111. C1. H05b 41/24 Play or to erase them- A first P is applied indiscrim- [58] Field of Search 340/324 M 173 inately to all the cells which it ionise, thus rendering 315/169 them active. A second part, which is different in accordance with the command to be carried out, acts se- [56] References Cited lectively upon the cells which &#39;it leaves active or which UNITED STATES PATENTS neutralses&#39; 3,573,542 8 Claims, 11 Drawing Figures nrcoupuus CIRCUITS 1 p 91 92 93 81 i i 1 PILOT HOLDINGSIGNAL 96 QAAMPUFIER F 3 5 *9 OSCILLATOR GENERATDR &#34;(SELECTOR i www. 2 m 774 j o o ol l 99 98 1 1 2 i i 1.7 6 5 con&#39;biiioiiifls LINE 3 Qi QKQ&#39;Q H SIGNAL SELECTOR isstr TOR 4 1; 1 GENERATOR 0 0 O t i 79% V 1; it i 22.3. i l 1 l o Q -11 VOLTAGE i i W GEN ATDR I l DECDUPLINB I 1 cmcuns I v i t i g y J F g I &#39;wm unsn 1 i J 104 105 l I s, t i. COLUMN SELECTOR B GX iMODULATDR M 80 srnrmoa 102.31 1  
 i (Vii Inf  DRIVING METHOD FOR A GAS-DISCHARGE DISPLAY PANEL AND lDllSPLAY SYSTEMS USING SUCH A METHOD The present invention concerns an improved method of driving a gaseous discharge display panel, providing simplified driving circuits due to the use of particular and original command signals; it also conserns display systems utilising such a method.  
  Gas discharge display-panels, also called plasma display panels, are used to present in visual form informa tion such as letters, numbers, symbols, diagrams, curves, graphs in other words, two-dimentional images, obtained by combinations of zones or points of a surface, the points being rendered luminous by appropriate driving means; they are used, for example, in the input and output terminals of computer systems, in sys tems for the remote visualisation of information, highspeed printing, etc.  
  Such panels can consist of a large number of gasfllled cells, constituting the aforementioned points, ar ranged in lines and columns at right angles and capable of being selectively energised in such a way as to emit light when they are the site of a gaseous discharge.  
  For this purpose, in certain methods of constructions, a matrix perforated with holes arranged in a network of lines and columns-at right angles and filled with a suitable gas, is clamped between two thin plates of an electrically insulating material, at least one of these plates being transparent so as to allow the gas cells to be seen. The outerfaces of these two plates carry networks of conducting electrodes which do not hinder observation of the cells and which are crossing onto the axes of said cells. These electrodes allow an electric field to be applied to each cell, causing ionisation of the gas and, as a result, a small luminous spot at the corresponding point on the panel. Other methods of construction to which the invention is equally applicable are briefly described hereinafter.  
  These panels are generally of a convenient use. Their luminosity is very high. Their addressing can be carried out in a relatively simple manner by conventional digital methods. In addition, and it is possibly here that their essential advantage lies, the different cells of these panels have an intrinsic memory which allows them to retain information written in, stored in the memory for a certain time, it being possible very simply to prolong this time for as long as is desired, by means of signals, called holding signals, applied to the electrodes for as long as the information needs to be memorised.  
  In general, whatever the method of technology employed in the construction of a gas discharge display panel, the application of a suitable driving signal to a cell, through the agency of the two associated electrodes, causes ionisation of the gas in the cell. Electrical charges appear in the gas and are deposited upon the walls of the cell, creating a potential between these walls known as memory potential, capable of remaining in store for a relatively long period.  
  A cell having such a memory potential is referred to as an active cell, in the following part of the text; its state is referred to as state 1. This state 1 is stable; once established, it is retained in the absence of any control signal, for relatively long periods, depending chiefly upon the construction of the panel.  
  On the other hand, a cell having no electrical charges upon its walls and consequently having zero potential is referred to as non-active; its state is referred to as state 0. It is, of course, stable.  
  In order to make a cell visible, it is necessary, on the one hand, to render it active, that is to say, to cause it to pass from state 0 to state 1, and on the other hand, to maintain the gaseous discharge; this latter point is realised through the agency of the holding signals.  
  In order to erase a cell, it is necessary to cause it to pass from state 1 to state 0.  
  One serious problem set by gas discharge display panels is that of driving them. Various solutions have already been proposed. In a general way, they consist of applying specifically to the cell or cells which are to be driven, that is to say, which are to be caused to pass from state 0 to state 1 (writing-in) or from state 1 to state 0 (erasing), a driving signal, for Write or erase&#34; respectively, or, more precisely an electric field resulting from a signal of this kind. The solutions known up to the present are distinguished from one another principally by the nature of these driving signals and notably by their amplitude, their form and frequency. In all cases, the application of these signals to the panels gives rise to delicate problems, either these signals need to have very high amplitudes, necessitating particularly expensive application circuits which is all the more inconvenient, the greater is the number of points which the panel has, or the tolerances of error on these signals may be very narrow, or again, the energising circuits may be of a particularly complex construction.  
  The present invention concerns a method for driving such panels which makes use of driving signals having a particular form and which applies them in a novel manner to the different cells of the panel, permitting effective driving without needing complicated and expensive driving circuits for this purpose, and permitting a greater degree of scatter, not only in the characteristics of the panel itself, but also in those of the associated circuits.  
  According to the invention, a method for driving a display panel composed of display cells filled with a gas becoming luminescent when ionisation is produced by the application to the said cells of a driving signal applied between two electrodes associated with each cell and forming part of a network of intersecting elec trodes disposed in lines and columns, the said cells being capable of memorising in the form of electrical charges creating between their walls a potential known as memory potential, the information which produced their ionisation, these cells being termed active, in contrast to cells which have no electrical charges upon their walls, this method consisting for providing writing, that is to say for rendering active certain prespecified cells of the panel, in using a driving signal S, composed of a first part S termed the activation signal, applied indiscriminately to all the cells of the panel with an amplitude such that all the said cells are then active, and ofa second part S termed the selection signal, the said selection signal comprising a first signal known as the write signal applied to the said prespecified cells so as to consolidate them in their active cell state, state 1, and a second signal known as the neutralisation signal applied to the cells in the panel other than the said prespecified cells so as to render them inactive, state 0, that is to say, so as to cause them to revert to their initial state, the state which they occupied before the application of the activation signal.  
  A similar method is employed in order to provide erasing. The driving signal is then composed of the same first activation signal S, and of a second selection signal S which in this case comprises an erasing signal applied to the cells which are to be erased in such a manner as to do-energise them and to cause them to pass into the state 0, and the abovementioned second neutralisation signal applied to the cells of the panel other than the above-mentioned cells to be erased, in such a manner as to suppress the effect of the activation signal and to cause them to revert to their initial state, that is to say the state which they presented before the application of the said activation signal S,.  
  A two-part driving signal of this kind, a first part S always the same, and always applied to the whole of the cells and a second part S differentiated as to its nature, write in, neutralisation, erasing, and as to its application or addressing, may be obtained in various ways.  
  The description which follows describes some of these ways and describes display systems which make use of the method in accordance with the invention in certain of its variations. It is given as a non-limitative example and is illustrated by the attached figures which show:  
  FIG. 1, an &#39;exploded&#34; diagramatic view in perspective of a gas discharge display panel;  
  FIG. 2, curves which assist in the understanding of the general operating of gas discharge display cells;  
  FIGS. 3, 4 and 5, curves showing the form of driving signals on the method in accordance with the invention;  
 FIG. 6, a graph summarising the various driving signals in accordance with the invention;  
  FIGS. 7, 9 and 11, block diagrams for three display systems making use of the method in accordance with the invention;  
  FIGS. 8 and 10, graphs illustrating two variations for obtaining driving signals for the method in accordance with the invention.  
  FIG. 1 diagramatically shows in an exploded view, the essential parts of a conventional panel with gas discharge display cells.  
  A matrix I, made from an insulating material, is perforated with an intersecting network, here shown intersecting at right angles, of cylindrical holes, 2 for example, perforating said matrix from side to side, and arranged in lines L,, L and in columns C C the number of these holes generally being very large, some thousands for example. This matrix 1 is clamped between two plates 3 and 4 of an insulating and transparent material, thin glass for example, which provide for the sealing of the panel by means of a peripheral seal and which carry on their outer faces networks of trans parent conducting electrodes, intersecting on the centre-lines of the holes such as 2 and being parallel, for electrodes such as EL,, EL, to the lines L L and, for electrodes as EC,, EC t the columns C The whole of the matrix 1 is filled with a gas, neon, argon, etc. or possibly with a mixture of such gases, preferably the mixture known as Penning one.  
  More elaborate techniques allow panels to be constructed with different forms which modify the appearance but keep the same operating principle.  
  For example, the assembly can be inserted between two glass slabs, ensuring rigidity.  
  The conducting electrodes can be embodied directly upon the internal surfaces of these slabs by means of metallic deposition. With regard to the insulating plates 3 and 4, they can be replaced by deposited dielectric material which covers the electrodes.  
  The matrix 1 may be omitted; the gas-filled cells then no longer are materially delimited and the discharges are limited only by the spread of the electric field.  
 The networks of intersecting electrodes EL, EC  
 . allow electrical fields to be applied, through the agency of energisation circuits not shown here, to the display cells causing ionisation of the gas and, consequently, luminescence of the corresponding cells which then become active.  
  A brief review of the operating mode of such cells, and particularly of their hereinabove mentioned memory function is given below, with the aid of the curve of FIG. 2, which are curves of voltage V as a function of time t.  
  Curve 21 represents a sinusoidal voltage which would be applied between the two electrodes intersecting on the centreline of a cell creating, in the absence of any reaction from the cell, an electric field which is also sinusoidal. When the field so applied reaches a sufficient value, corresponding to a firing potential V,,, reached at the instant t,, the gas in the cell is ionised and the resulting electrical charges, under the influence of the applied field, charge the dielectric walls which enclose the cells.  
  These surface charges create a memory potential within the cell which is opposed to the external voltage 21. This memory potential in turn sets up an electric field having a polarity opposite to that of the applied field, and increasing very rapidly until the difference of the two fields corresponds to the gas extinguishing potential V Curve 22 in FIG. 2 represents the variations of the memory potential V,,, of the cell as a function of the variation in the applied voltage. It has been shown here with the memory potential V,,,, symmetrical to V,,,, in such a fashion that the part contained between the two curves 21 and 22 (area 25 marked with parallel vertical lines) represents the resulting actual field at every instant.  
  Thus, at the instant t when the resulting field corresponds to the extinguishing potential V,,, arrow 23, the cell is extinguished and retains the memory potential V,,, acquired at the instant t the case is, of course, that of an active cell whose state is state 1 as defined above.  
  During the succeeding half-wave of 21, the memory potential V,,, is added to the applied voltage and ionisation takes place at a time r for an external voltage 21 lower than the firing potential V,,, but for a resulting field, arrow 24, corresponding to that potential V,,. The cell is then lit until the instant t, when the resulting field, arrow 26, again corresponds to the extinguishing potential V,.. The sequence is continued similarly.  
  In addition, it should be noted that since the charges accumulated on the walls increase with the time derivative of the applied voltage 21, symmetry of the surface charges appears rapidly after a few half-waves. The memory potential V,,, changes sign with each halfwave, but rapidly assumes a constant amplitude V It should further be noted that a cell which is active, or in state 1, is lit only during very brief instants (t, to r I, to t, which are repeated periodically in time with the applied voltage 21, twice per cycle.  
  Thus, in order for an active cell to be visible and to take a proper part in the display it must be subjected, after having been rendered active by the application of a driving signal with amplitude at least equal to the firing potential V to an alternating holding signal of an amplitude sufficient to light the said cell twice per cycle. The amplitude of this holding signal is, however, lower than the firing potential V so that this signal may be applied to all the cells in the panel without rendering active the cells which are not taking part in the display, that is to say, which are in the 0 state.  
  Each half-wave of the holding signal provides, on the one hand, regeneration of the memory potential whose sign atternately reverses, thus avoiding an erasing, i.e. avoiding any passage from state I to state 0, which otherwise would occur by the progressive dissipation of the charges accumulated on the surfaces of the active cells, and, on the other hand, the emission of a pulse of light having a short duration compared with the period of the holding signal.  
  The method for driving such panels, which is the subject of the present invention, will now be described with the aid of FIG. 3; variations of this method will be given subsequently. Display systems making use of these methods in accordance with the invention will finally be described, particularly in their novel features.  
  In the two graphs (a) and (b) of FIG. 3, the curves shown in full line represent the signals applied between the electrodes which intersect at the cells, for example, by means of semi-voltages in a manner known in itself, whilst the curves made up of a succession of signs represent the opposite of the memory potential which results from the charges accumulated upon the cell walls under the action of the signals which are applied to them.  
  In the example described here, the holding signal 5,; is a square-wave signal. It could also equally well have some other form, and be, for example, trapezoidal or sinusoidal. In order to make suitable use of the method of driving in accordance with the invention, it is always applied to the panel but it is omitted when a driving signal 8,. is applied.  
  It should be noted that the polarities indicated for the various voltages, on the graphs of FIGS. 3 to 6, are only thus for the purpose of example; arrangements which are symmetrical with respect to the zero ordinate are equivalent.  
  Part (a) of FIG. 3 illustrates the method used to cause a cell to pass from state 0 to state 1, that is to say to effect writing-in on this cell, with the aid of a driving signal S,., whilst part (12) illustrates the method used in order to retain a cell in state 0 despite these particular driving signals.  
  In fact, in order to effect writing-in on a panel of gasdischarge cells, it is necessary to render certain prespecified cells ((1) active and to leave the others inactive (b).  
  In order to obtain this result, the method in accordance with the invention makes use of two-part driving signals.  
  A first part S is applied to the whole of the cells in the panel and has an amplitude V higher than or equal to the firing potential so as to render all the cells of the panel active, the walls of which then become charged as is indicated by the curves shown in for the parts (a) and (b), to&#39;a potential V higher in absolute value than V This signal S, will be termed the activation signal.  
  The second part S of the driving signal 8,, termed hereinbelow the selection signal differs in its nature as well as in the way it is applied.  
  This selection signal S here comprises signal known as the write-in signal which is applied selectively to the cells which are needed to participate in the display and thus must remain active, part (a) of FIG. 3, and further comprises a signal known as the neutralisation signal which is applied to the other cells so as to cause them to become inactive again, part (b) of FIG. 3.  
  The various functions, write-in or neutralisation, of the selection signal S are obtained by signals 8,, of different amplitudes.  
  The amplitude of the write-in signal, V in FIG. 3 (a), is such that the difference IV V is smaller than the firing potential so that the cell which is to be written retains the memory potential V conferred by the activation signal S this potential being subsequently rendered symmetrical about the axis V 0 by the holding signal 8,, as explained above (the curves represented here being very diagramatic, this process of rendering symmetrical is supposed instantaneous).  
  With regard to the amplitude of the neutralisation signal, V in FIG. 3 (b), it is such that the difference IV V l is slightly greater than the firing potential, so that the cell ionise and that no charge remains upon its walls, that is to say, it again becomes inactive with a zero memory potential.  
  It is clearly apparent that the potentials V and V may vary within relatively wide limits whilst still retain ing their function, which is an important advantage of this method and facilitates the construction of the driving circuits of the panel.  
  In addition, these potentials V and V have relatively low amplitudes which also allows the circuits for their application to the various electrodes of the panel to be simplified. Only the potential V, has a high amplitude; but this potential being-applied in all cases to the whole of the cells and therefore to all of the electrodes simultaneously, the more elaborate and higher quality circuits which are necessary for it are greatly reduced in number, for example, two, one for the line electrodes, one for the column electrodes, whilst one driving circuit per electrode is often necessary for the potentials V and V Additional details concerning these circuits are given in the latter part of this description.  
  The method just described permits the writing-in of a display panel with good conditions of quality and speed.  
  Erasing may, of course, be effected in the conventional manner, for example, by applying a driving signal to the whole of the line or column electrodes which brings the whole of the cells into the 0 state. Such a driving method is simple to realise but leads to a global erasing, which is not always desired.  
  Erasing can be carried out in a more advantageous manner, particularly being selective, that is to say, affecting only certain cells, by means of the method described above, utilised as indicated in FIG. 4.  
  It is a matter here of causing a cell to pass from state 1, that is to say having a memory potential V alternatively positive and negative as the holding signal, into state 0. For this purpose, a driving signal made of two parts 8, and S equivalent to those of the signal in FIG. 3 is applied during an interruption of the holding signal.  
 The activation signal S, is the same as previously, which simplifies the circuits and is likewise applied to the whole of the panel. It has no effect on the state of the cells to be erased, while cells have already, at the time when it is applied, a memory potential V and which retain it. The selection signal S is in this case a signal known as the erasing signal and it has an amplitude V, such that the cell is ionised. The effect of this V, amplitude signal is equivalent to that of the V amplitude signal of FIG. 3 (b); their amplitudes are different since the memory potentials are also different, V in one case, V, in the other.  
  The application of such a signal S of amplitude V, to the whole of the panel causes global erasing.  
  In order to effect a selective erasing, it is sufficient to apply to the cells which it is desired not to erase, a signal S having amplitude V (see FIG. 3 (b)), that is to say a neutralisation signal. The cells which were in state will remain in this state as shown in FIG. 3 (b); those which were in state 1 will remain there as shown in FIG. 5, Since lV I It should be remarked here, concerning this selective erasing, that it can only be carried out if |V e |V For this reason, the polarity of the signal S, will preferably be selected to be the same as that of the last half wave of the holding signal, it being possible for both these latter to be either positive or negative.  
  In this way, the method in accordance with the invention allows the operations both of writing and erasing, global or selective, due to the driving signals consisting of a first part 8,, the activation signal which is always the same and is always applied to the whole of the cells, and of a second part 8,, the selection signal, of a different amplitude in accordance with the operations to be carried out, and applied selectively to the cells to be operated on. It is taken for granted that various methods can be used to obtain such a selection signal 8-,, modulated in amplitude so as to have three different values V V, or V,. These methods will be dealt with in the description of display systems and their driving circuits.  
  One important point must now be noted concerning the application of this driving method. In fact, it is known in the present methods of utilising certain gasdischarge display panels,-to periodically apply (every millisecond, for example) a signal, generally known as the conditioning signal&#34;, to the whole of a panel whilst functioning. The purpose of such a signal is to ionise briefly the cells in state 0 in order that there may always be a sufficient number of electrons within the gas, necessary for the ionisation of the cells to render them active in order to effect a display. In fact, generally speaking, write driving signals are of short duration and it is only possible for them to be effective at all times if there are such electrons existing in the gas.  
  Clearly, if the conditioning signal has to cause ionisation of the cells in state 0, it must neither change the state of these latter nor of the cells in state I. In order to obtain this effect, a conditioning signal generally consists of a first part, of an amplitude sufficient to ionise the cells in state 0 and of such a polarity, in relation to the last half-wave of the holding signal that it does not ionise the cells in state I and of a second part, of an amplitude such that it brings the memory potential of the cells ionised by the first part back to zero level and such that it produces no change in the memory potential of the cells in state 1.  
  Such a signal is equivalent to some of the driving signals of the method of the invention. In fact, considering FIG. 3 (b) and 5, the effect produced by the driving signal having a first amplitude V, and then a second amplitude V, are those which have just been stated for the conditioning signal.  
  Two variations of this driving method are then possible. In a first variation, the conditioning is effected independently of the driving means which provide writing-in and erasing. It is applied, for example, to the whole of the panel by a signal generator which is provided for said conditioning, at instants which are appropriate for it and which can be completely independent of the driving signals. In the extreme case, in certain types of panels, it can even be effected by other means than the application of electrical signals. This case particularly covers panels where conditioning is carried out directly by the provision of particles which are not electrically neutral, the panel possibly comprising for that a certain quantity of radio-active material.  
 In a second variation of the method in accordance with the invention, the conditioning signal is considered as being a driving signal in the same way as the write or erase driving signals. Like them, it consists of an activation signal 8,, followed by a selection signal 8-,, this selection signal being here always a neutralisation signal with amplitude V applied, like 8,, to all the cells. In such a variant, the conditioning signal does not have to be applied to the panel when a write or erase driving signal is applied to it. In fact, these driving signals themselves bring about a conditioning when their activation signal is applied.  
  FIG. 6 summarises briefly the various aspects of the driving signals which have just been described. The activation signal S, is identical whatever is the command to be carried out. The selection signal S will provide different commands according to the level of its amplitude in relation to the level V, of the signal S, it will provide a write command in the P, amplitude band, a conditioning, or a neutralisation in the P amplitude band, an erasing in the P amplitude band and, again a write command in the I amplitude band.  
  It is clearly apparent from this figure that the amplitude of the driving signals, in addition to their relatively low value where 8,, is concerned, can vary within farily wide limits without risk of causing erroneous com mands.  
  The erasing amplitude band is the alone band which is rather narrow.  
  The amplitudes of these bands relative to the zero axis can be different; they are in fact determined with reference to the level V, which can be different. Polarities for the various selection signals 8, which are different from those shown here may result from this.  
  It should be noted that all these diagrams show voltages of perfect square-wave form having infinitely steep rising flanks. In practice, matters are somewhat different, without, be it understood, altering the functioning described. However, this can facilitate the realisation of erasing signals, the results, that is to say the absence of charges on the walls of an erased cell depending not only on the amplitude of the signal 8,, but also upon its form and particularly on its slope. As has already been indicated at the beginning of this discussion, the electrical charge on the walls of a cell depends opon the slope of the signal which is applied to it whilst it is ionised. The compromise to be established between the amplitude of an erasing signal and its slope, in order to obtain the best results, depends particularly on the type of panel concerned.  
  Generally speaking, the various signals may be other than square-wave; they may for example be trapezoidal or even sinusoidal.  
  FIGS. 7, 9 and 11 diagrammatically show various display systems with gas-discharge panels P driven in accordance with the method of the invention, using driving circuits represented in these figures in block form. The details of the circuits themselves present no diffi culties; their realisation is within the reach of the specialist conversant with present-day driving techniques for such panels. In these figures, the same reference numbers refer to identical elements.  
  These figures represent display systems where the panel P consists of n X m cells disposed in n lines and m columns, with n m 5, in this case, by way of example, each cell being driven by the application of suitable voltages between the line electrodes EL, EL, and the column electrodes EC, EC intersecting on this cell.  
  A transcoder component 71 receives, through an input terminal 70, general driving information such as, for example, indications of the number, letter, symbol or curve to be displayed. The component 71 supplies various specific items of information through different outputs: for example, at 72, synchronisation information necessary for the correct functioning of the circuit assembly; at 73 and/or 74, information relating to the driving signals S, and S proper; at 75 and 76, the address respectively of the line and of the column whose intersection defines the cell which is to be driven that is to say which is to be written, to be erased or to be neutralised in accordance with the method of the invention. These addresses drive a line selector 77 and a column selector 78 in the conventional manner. These selectors also receive, at 79 and 80 for example, for FIG. 7, the driving signals to be applied to the addressed line and column electrodes and deliver them over their appropriate output. The whole of these operations of addressing and of switching driving signals is carried out in a completely conventional manner by digital techniques. It should also be noted that the commands can be carried out point by point, as is the case here, but that they may equally well be carried out line by line or column by column with conventional parallel addressing making use of registers to drive the lines and columns.  
  The driving signal supplied by the selectors 77 and 78 are applied to the line electrodes EL, EL and column electrodes EC, EC by way of decoupling circuits 81 to 90, diode-type for example, allowing the high-voltage signals which are the holding signal S,;, the activation signal S, and a certain number of other signals depending upon the constructional variant under consideration, to be applied to these electrodes.  
  In the three variants here illustrated, the synchronisation output 72 of the transcoder component drives a generator of periodic signals. or clock 91, having frequency H serving as the frequency pilot for the whole of the circuit. In all three cases, this clock controls the delivery of the holding signal 5,; by a square-wave signal generator 92, for example. These signals have a relatively high amplitude, in the hundreds of volts, for ex ample. They are applied through the intermediary of a selector 93 with two inputs 96 and 97, to a line amplifier 94 and to a column amplifier 95 whose outputs supply the line electrodes and the column electrodes re spectively through decoupling components 81 to 85 and 86 to 90. The holding signal S is applied in accordance with a technique which is well known in itself by means of half-voltages to the line electrodes which are brought to a potential V /2 and the column electrodes which are then brought to a potential V /Z, for example. The two outputs of the selector 93 symbolise these two potentials V,.;/2 and V /Z which can be elaborated at any required level of the circuit, and by the amplifiers 94 and 95 themselves, for example.  
  The second input 97 of the selector 93 receives one or another among several signal, more explicity referred to subsequently (being dependent upon the variants), which are simultaneously applied to the whole of the electrodes by means of the amplifiers 94 and 95, for example by means of symmetrical half-voltages. The selector 93 is such that when a signal is present at its input 97, the holding signal S,- is no longer applied to the amplifiers 94 and 95.  
  The variant illustrated in FIG. 7 will now be described more completely.  
  This variant applies the method of the invention in two separate special ways.  
  On the one hand, the conditioning signal C is supplied by a generator 98 independent of the write and erase driving signals. The generator 98 is frequencypiloted by the clock 91 through a frequency-divider 99 supplying a signal of frequency H/n which is the conditioning frequency. The output from the generator 98 is applied to a first input 100 ofa selector 102, the output of which is connected to the input 97 of the selector 93.  
  On the other hand, the second part 8, of the driving signals is obtained by simple modulation of a D.C. level.  
  The first part of these driving signals, or activation signal S,, is obtained by means of agenerator 103 supplying a high-voltage signal with an amplitude V, greater than the amplitude V,; of the holding signal. The delivery of these signals being controlled by the transcoder component 71 (output 74) and monitored by the clock 91. The output of this generator 103 is applied to the second input 101 of the selector 102 which thus delivers, at 97, either the conditioning signal C or the activation signal 8,, it being understood that when S, is applied, the conditioning signal is not. A generator 104 driven by the generator 103, for example, delivers a DC. signal S, with a much lower amplitude than that of S,, at the termination of the signal S,, and applies it to a modulator 105. This modulator receives a signal, from the output 73 of the transcoder component, which signal is characteristic of the level V V or V, which the signal which it delivers must have in order to apply a selection signal, which. may be a write, erase or neutralisation signal, to the cell concerned in the panel. Here again the modulator 105 in fact delivers two symmetrical half-voltages applied respectively through the intermediary of the selectors 77 and 78 and of the decoupling components, to the: line and column electrodes for driving the cell the address of which is defined by the outputs&#39; 75 and 76 of the transcoder component 71.  
  FIGS. 9 and 11 diagramatically illustrate the principle of construction of two other variants of display systems in accordance with the invention.  
  Each of these two variants differs from the first (FIG. 7) in two different aspects. The first concerns the conditioning signals; the second relates to the method of formation of the selection signal S and to its application to the panel electrodes. It should be noted that a conditioning signal such as that elaborated in FIG. 7 can be employed in the variants shown in FIGS. 9 and 11. Conversely, a conditioning signal produced as in FIGS. 9 and 11, that is to say from driving signals S, S, S can be employed in FIG. 7.  
  In the systen s illustrated by FIGS. 9 and 11, the selection signal S composed of write signals, erase signals and neutralisation signals is obtained, not be modulating the amplitude of a DC. signal but by applying to the electrodes, in addition to a DC. level S of relatively low amplitude supplied by a generator 104, auxiliary signals formed from pulses of a relatively low and constant amplitude, the respective phases of which are caused to vary in dependence on the information from the transcoder component, in such as manner as to obtain signals on the desired amplitude for write, erase or neutralise. FIGS. 9 and 11 give two examples of construction making use of this method of production of the selection signal. FIGS. 8 and 10 show, in graph form, the auxiliary signals applied to the line and column electrodes, the resulting signals for the cells and the results produced on these cells, as a function of different relative delays of the line and column signals. In these two examples the DC. level S of the selection signal has been choosen to be equal to the write potential V In this case, writing-in takes place when the resulting auxiliary signal 8,, is zero, erasing when it has an amplitude such that the total selection signal S S 5,, has an amplitude equal to V that is to say when lS,,l IV V2 and neutralisation when |S,,| |V v-zl In the first of these two variations illustrated by FIG. 8 and 9, the auxiliary signals supplied to the line electrodes S and the auxiliary signals applied to the column electrodes S,, are each composed of a positive pulse having an amplitude v and a duration T and being able of occupying one or other of the positions marked p =0, 1,2,3, 4, 5, during the time T given to the selec tion signal 5 It should be noted that the ratio of the duration T of a pulse to the period T can be different from that given here. But this duration T must be equal to the smaller phase difference between the different possible positions for these pulses, so that they do not overlap.  
  In the example illustrated in FIG. 8, conditioning or neutralisation is effected by the application to the line electrode concerned of an auxiliary signal S,, with phase p= and of an auxiliary signal S,, (the inverse of which is shown here) with phase p 2, to the column electrode which is also concerned, as is indicated by column (1) of FIG. 8. The resulting selection signal S is composed oftwo pulses bringing the DC level to V that is to say, providing conditioning.  
  Erasing is effected as is indicated in column (2), by applying a line signal S,,, with phase p l and a column signal S with phase p l, the resulting signal S having an amplitude V writing-in is effected, see (3), by eliminating the two auxiliary line and column signals, leaving the level of the resulting signal S at V Columns (4), (5), (6), and (7) of the graph verify that, in a line and a column of which at least one cell is subjected to writing-in or erasing, the cells which are not subjected to writing-in or erasing are subjected to a selection signal of neutralisation which is equivalent to a conditioning signal.  
  FIG. 9 gives an example of a display system which functions as described above.  
  The activation signal S, supplied by thegenerator 103, which here is also utilised to form the conditioning signal, is controlled at the frequency I-I/n by the frequency-divider 99 and applied at to one of the two inputs of a selector 111 whose output 112 supplies the input 97 ofthe selector 93 already described in connection with FIG. 7. The signal S, is thus applied at a frequency H/n to the whole of the panel. The end of this signal 5, controls, on the one hand, t he generator 104 which supplies the DC. component S of the selection signal, here equal to V and applied to the second input of the selector 111, and on the other hand, it controls a pulse generator 113 the signals from which are applied to a variable delay device 114 delivering a pulse with amplitude v and phase 0, 2 and 1, through three outputs marked 0, 2 and l, in order to form the auxiliary signals.  
  The outputs 0 and 2 of the device 1 14 which supply auxiliary signals permitting the neutralisation signals to be formed are applied, in order to complete the conditioning signal which is partly produced at the output 112 of the selector 111, to the line and column amplifiers, 94 and 95 respectively. The conditioning signal is thus formed and applied at a frequency H/n to all of the cells in the panel.  
  In regard to the driving signals proper, that is to say the write signals and erase signals, they are produced and applied in the following manner.  
  The signal S and the dc. component S of the selection signal S are formed and applied as described previously. The signals supplied by the outputs 0 and 2 of the device 114 are prevented to be applied to the amplifiers 94 and 95 by the transcoder component, for example by means of electronic gates, not shown for not over-looking the figure; the application of a neutralisation signal to the whole of the panel is thus prevented.  
  When erasing is wanted, the output 73 of the transcoder component 71 controls the supply of an auxiliary signal by the device 114 at the output l, which is connected to the inputs 115 and 116 of the line and column selectors 77 and 78 so as to apply to the cells which are to be erased a signal of amplitude V, as in (2) of FIG. 8. The outputs 0 and 2 are themselves connected respectively to input 117 and 118 of these two selectors 77 and 78 so as to allow the neutralisation of the cells which do not need to be cancelled.  
  When writing is wanted, the output 73 of the transcoder component 71 controls the elimination of the pulses supplied by the generator 113 so as to obtain zero auxiliary signals. Here again, the cells which need not be written are neutralised by signals delivered by the outputs 0 and 2 of the device 114 and applied to the selectors 77 and 78.  
  The second variant for the production of selection signals S consisting in adding line and column auxihary signals with variable phases to a DC. component S equal to V for example, is illustrated by FIGS. 10 and 11, transposed from FIGS. 8 and 9.  
  The essential difference consists in making use of line auxiliary signals S and column auxiliary signals S each composed of two symmetrical pulses, displaced in phase by a constant quantity relative to each other, and of equal amplitude, as is shown by FIG. 10. Here again, the subdivision of the time T allotted to the selection signal S into 14 intervals marked p=0, l 14 is arbitrary. The only point of importance is that the disposition of the auxiliary signal pulses indicated in FIG. 10 should be adhered to.  
  Column (1 indicates the respective phases of the signals S applied to the line electrodes and of the signals S applied to the column electrodes so as to obtain conditioning or neutralisation. Columns (2) and (3) correspond respectively to erasing and to writing-in. Columns (4) to (7) are equivalent to columns (4) to (7) of FIG. 8. They demonstrate that in all cases the panel is properly driven.  
  One important advantage of this variant, compared with that&#39;of FIG. 8. is that it is not necessary to eliminate the auxiliary signals in order to secure writing-in, which renders the commands more homogenous with each other.  
  FIG. 11 gives an example of display system functioning in accordance with the statements which have just been made, and particularly in accordance with FIG. 10.  
  The greater part of the components of this system being equivalent to those in FIG. 9, their description is not repeated here.  
  The difference principally consist in the pulse generator 113 which permits the auxiliary signals to be produced and in the variable delay device 114.  
  The generator 113 supplies elementary auxiliary signals with their two pulses symmetrical and fixed in relation to each other. It does not include any control for eliminating these pulses.  
  The variable delay device 114 supplies, through five outputs marked 0, 8, 4, 6, 2, the lines and col umn auxiliary signals required to produce selection signals S as in columns (1), (2) and (3) in FIG. 10.  
  The outputs and 8 which serve for conditioning and for neutralisation are applied, like the outputs 0 and 2 in FIG. 8, to the line and column amplifiers 94 and 95, on the one hand, and on the other hand, to the selectors 77 and 78.  
  The output 4 which permits writing-in to be effected (as in column (3) of FIG. 10) is applied to the two selectors 77 and 78.  
  The outputs 6 and 2, permitting erasing to be ef fected, are likewise applied to the selectors 77 and 78, as shown in the figure.  
  It should be noted that, in order to simplify the figures, the outputs of the device 114 take no account of the polarities of the line and column signals.  
  It is to be understood that the three display systems just described have the advantages already mentioned for the driving method in accordance with the invention.  
  The two latter systems have the advantage, in addition, of further increasing the tolerances on the circuits by permitting the *selection part of the driving signals to be realised, not by means of voltages of different amplitudes applied by means of symmetrical half-levels at the electrodes, but by signals of constant amplitude subjected to variable delays. From this there results a greater reliability of driving for the same quality of circuit. Such a driving method permits greater degrees of scatter in the characteristics of the panels and of the asssociated circuits.  
 What I claim is: V  
  l. A control system for controlling a gas-discharge display panel having display cells filled with a gas which become luminescent when ionised by the application of a suitable signal between two electrodes associated with each cell and forming part of an array of crossed line and column electrodes, said cells when ionised becoming active cells with a memory potential due to electrical charges stored by said cells, the presence of such a memory potential for an active cell defining a state 1, while the absence of such a memory potential for a non-active cell defines a state 0, said control system comprising:  
 means including a transcoder component and an addressing circuit for receiving information to be dis played on said panel and for distributing signals between the line and column electrodes of said panel,  
 high voltage source means controlled by said transcoder component for providing a high voltage activation signal S which is applied between all the line and column electrodes of said panel, the amplitude V of said activation signal being high enough for setting all the display cells of the panel in their state 1,  
 and low voltage source means for providing different low voltage selection signals S which are selectively applied between said line and column electrodes, said different low voltage selection signals S being:  
 a write signal having an amplitude V such that, when applied by corresponding electrodes to cells set in their state 1 by said activation signal 5,, said cells stay in their state 1, and  
 a neutralization signal having an amplitude V such that, when applied by corresponding electrodes to cells set in their state 1 by said activation signal S a neutralization occurs and said cells are reset in their state 0,  
 said low voltage source means being synchronized with said high voltage source means so that said selection signals are selectively applied after said activation signal has been applied between all said electrodes.  
  2. A control system according to claim 1 further comprising a holding signal generator applying between all the line and column electrodes of said display panel a periodic signal having an amplitude lower than that which would provide ionisation of a cell in the state 0 and at least equal to that which provides ionisation of a cell in the state 1, means for inhibiting application of said holding signal 8,; to the panel when a control signal made of an activation signal followed by a selection signal is applied to the panel, said inhibition being initiated when the polarity of said holding signal is the same as the polarity of said activation signal 5,; said holding signal providing a periodic ionisation of cells which have been set in state I by a control signal made of an activation signal followed by a write signal, said cells being thus displayed.  
  3. A control system according to claim 2 wherein said low voltage source means further delivers a third selection signal S which is an erasing signal having an amplitude V, such that, when applied by corresponding electrodes to cells previously set in their state I and periodically ionised by said holding signal S an ionisation occurs and said cells are reset in their state 0, being thus erased, said low voltage source means being controlled by said transcoder component for applying to said cells to be erased said erasing signal and to the other cells said neutralisation signal.  
  4. A control system according to claim 2 wherein an electrical conditioning of the panel is effected by means for periodically applying to all the cells of the panel, at a frequency which is a sub-multiple of the frequency of the holding signal, a conditioning signal made of said activation signal 8, followed by said neutralisation signal.  
  5. A control system according to claim 3 further comprising a clock synchronised by said transcoder component and synchronising said control system,  
 wherein said addressing circuit comprises a line selector and a column selector controlled by said transcoder component for applying to said selected line and column electrodes the said different selection signals S that said line selector and column selector receive from said low voltage source means,  
 wherein said high voltage source means comprises a high voltage generator which applies said activation signal S, between all the electrodes of the panel through at least one line amplifier and one column amplifier,  
 and wherein said low voltage source means comprises a DC. low voltage generator whose output is connected to an amplitude modulator controlled by said transcoder component for delivering to said line and column selectors of said addressing circuit said selection signals S 6. A control system according to claim 3 further comprising a clock synchronised by said transcoder component and synchronising said control system.  
 wherein said addressing circuit comprises a line selector and a column selector controlled by said transcoder component for applying to said selected line and column electrodes the said different selection signals S that said line selector and column selector receive from said low voltage source means,  
 wherein said high voltage source means comprises a high voltage generator which applies said activation signal 5, between all the electrodes of the panel through at least one line amplifier and one column amplifier,  
 and wherein said low voltage source means comprises a DC. voltage generator delivering a DC.  
 level S applied between all the line and column electrodes of the panel and an auxiliary signal generator controlled by said D.C. voltage generator for delivering auxiliary signals simultaneously with the deliverance by said DC. voltage generator of said D.C. level and by said transcoder component for delivering line and column auxiliary signals, said line and column auxiliary signals being applied between selected line and column electrodes through said line and column selector, said line and column auxiliary signals being pulse signals, the control of the amplitude of the resulting signal applied between line and column electrodes being provided by controlling the relative phase shift between said line and column auxiliary signals.  
  7. A control system according to claim 6 wherein said auxiliary signal generator comprises a pulse generator delivering pulse signals to a variable delay device controlled by said transcoder component, said variable delay device delivering said line and column auxiliary signals shifted in phase relative to each other.  
  8. A control system according to claim 1 wherein said low voltage source is controlled by said transcoder component for applying to selected ones of said electrodes said write signal, and between other electrodes said neutralization signal.