FR2505072A1 - IMAGE DISPLAY CONTROL METHOD, IN PARTICULAR ALTERNATING CURRENT LIGHT EMITTING DISPLAY - Google Patents

Abstract

THE PRESENT INVENTION RELATES TO A PROCESS FOR CONTROL OF IMAGE DISPLAY. THIS PROCESS WHICH APPLIES IN PARTICULAR TO A TWO-DIMENSIONAL ALTERNATIVE CURRENT ELECTROLUMINESCENT DISPLAY INCLUDING A MATRIX COMPOSED OF X AND Y ELECTRODES, IS CHARACTERIZED IN THAT THE MODULATION IS APPLIED TO BOTH THE POSITIVE PULSES AND THE NEGA PULSES CONTROL OF THE DISPLAY, BY CHANGING THE PHASES OF THE MODULATION PULSES AND THE SELECTION PULSES.

Description

The present invention relates to a display control method

  image, in particular of a two-dimensional AC light-emitting display, comprising a matrix constituted by X and Y electrodes and based on the thin-film technique, according to which: a modulation voltage is used which is preferably less than half of the total control voltage;

  we apply selective pulses to the elec-

  trodes X to one electrode at a time, while the other electrodes X are floating, and

  modulation pulses are applied to

  Y trodes while most X electrodes are floating.

  The method according to the invention is intended to be used for trimming the luminance of the display elements of an AC electroluminescent display, in particular a display based on the thin film technique.

  The particular characteristics of such a display device

  The reason for this is that: the control voltage is an alternating voltage; the required modulation voltage is less than half of the total control voltage; the capacitive impedance of the display is high, usually of the order of 10 to 200 p F / mm 2, and

  from the point of view of excitation circuits, the

  image is a two-dimensional matrix constituted by electrodes X and Y. In order to illustrate the prior art, reference is made to the following publications:

  (1) Gielow A, Holly R H: Image display.

  DELET Report TR-79-0251-1, September 1980, 17 p. (2) Takeda et alia: Technologies for the practical application of thin-film electroluminescent panels International Symposium SID 1980 Summary of Technical Papers, Vol XI,

p 66 to 67.

  In the control system described in the

  cation (1) above, each electrode X in turn receives a selection voltage pulse, while the other electrodes X are floating. The modulation of light takes place in such a way that a modulation voltage pulse of an amplitude corresponding to the desired luminance is applied simultaneously to each electrode Y, the polarity of this modulation voltage pulse being inverted with respect to the selection pulse of the electrode X After all the electrodes X have received pulses With equal polarity selection, inverse pulses are applied simultaneously to all X electrodes. In the method described in the publication (2) referred to, the display control pulses comprise four steps: precharge control; discharge control of non-selected picture elements; writing command; and

reconditioning order.

  In this method, the modulation pulses are always of the same polarity.

  voltage are necessary both for the control of the electri-

  X trodes and for the control of electrodes Y. It is well known that the luminance of an electroluminescent ac display, based on the thin film technique, depends on the peak-to-peak value of the control voltage. devices according to the prior art, the modulation is always applied to pulses of a

  same polarity, taken from the positive and negative impulses

  This produces a high modulation voltage pulse and a voltage of

  which has a DC component.

  The use of a high modulation voltage requires high voltage control circuits, the integration of which is all the more telling and difficult that the required voltage tolerance is narrower. A high modulation voltage also results in a high power consumption. energy since, in known manner, the energy consumption is proportional to the square of the amplitude when the capacitive impedance is controlled by means of square pulses. It is also well known that the presence of Gure DC component in the control voltage This display decreases the service life

of the last.

  In devices according to the prior art, high current peaks occur when the capacitive impedance of the entire display is simultaneously charged or discharged; These high current peaks require the use of corteux switches, able to withstand strong peaks of

  The current spikes also cause disturbances

  bations, in the form of interference radiation.

  The present invention aims to eliminate the disadvantages of the method and technology according to the prior art and to provide a control method of a display

  electroluminescent, and in particular of an electronic display

AC luminescent.

  The invention is based on the following ideas selection pulses are applied to X electrodes one electrode at a time, while

other electrodes are floating.

  The modulation is applied to both the positive and the negative pulses of the control voltage of the display, by changing the phases of the pulses of the display.

  modulation and selection pulses.

  Modulation pulses are applied to

  Y electrodes, whereas most X electrodes are

  aunts. More particularly, the method according to the invention is characterized in that the modulation is applied to both the positive pulses and the negative pulses of the control voltage of the display, by changing the phases of the

  modulation pulses and selection pulses.

  The invention makes it possible to obtain sensible advantages.

  Thus, the required modulation voltage is equal to half

  the modulation voltage required in the known methods.

  As a result, lower energy consumption is achieved and

better integrability.

  The display control voltage can be a

  fully symmetrical alternating voltage, without any

  This increases the service life of the display. The level of discharge of the capacitive impedances of the display may be the same as the highest or the lowest level of the modulation voltage, without a DC component being included in the control voltage of the display. to a single number of modulation voltage sources and simplifies the control circuits of

necessary modulation.

  The control circuits do not have to deal with strong current peaks. This makes it possible to use control circuits that are less expensive and more easily integrated.

  reduces the interference radiation.

  In addition to the foregoing, the invention also includes other provisions, which will emerge from the

description that will follow -

  The invention will be better understood by means of the

  description which will follow, which refers to the drawings

  in which: FIG. 1a illustrates the principle of the control pulses of a display according to the prior art, in the non-selection situation;

  FIG. 1b represents the pulses corresponding to

  dantes in a selection situation; FIG. 1c illustrates the principle of control pulses of a display device according to the present invention, in a non-selection situation;

  FIG. 1d shows oerresponent impulses

  dantes, in a selection situation; FIG. 2 diagrammatically represents an example of a 2 × 2 matrix display in which a display element is in a display situation, and

  Figure 3 illustrates in detail the impulses

  in accordance with the invention, in relation to the

  display device shown in Figure 2.

  It should be understood, however, that these drawings and the corresponding descriptive parts are given solely by way of illustration of the subject of the invention,

  which they do not constitute in any way a limitation.

  In FIG. 1b, the modulation pulses, indicated by truncations, form, in a selection situation,

  a layer at the top of the positive control pulses.

  As already mentioned, this causes, on the one hand, relatively high positive control pulses and, on the other hand, a

  troublesome component of direct current.

  In FIG. 1d, the modulation pulses are,

  in a selection situation, according to the invention, symmetrically

  triply divided by half on successive positive and negative control pulses, so that it does not form

  no DC component.

  FIG. 2 represents an exemplary display device comprising two X electrodes and two Y electrodes,

  the display element C 22 being in a display situation.

  Figure 3 illustrates control pulses of the

  display device of Figure 2.

  When, for example, the voltage pulses Uxlr Ux 2, Uyl and Uy 2, in accordance with FIG. 3, are applied to the electrodes X and Y, the values Ucll 'Uc 12' Uc 2 l and UC 22 are obtained as voltages. 3 shows that the peak-to-peak value of the voltage Uc 22 of

  the display element C 22, which is in a display situation

  chage, is U 1 + U 2 + U 3 The maximum voltage of the other ele

  In this way, the voltage of the display element in the display situation is 2 'U 3 greater than the maximum voltage of the display elements by

situation of non-selection.

  If, for example, U 1, U 2 and U 3 are chosen such that U 1 = U 3 + U 2 and U 1> U 3> -U 2, completely symmetrical control voltages without component can be obtained.

of direct current.

  In the example considered, the polarity of the control voltage has been reversed in the middle of the reconditioning cycle. It is clear that the polarity can also be reversed more frequently, for example each time the next electrode Y is selected. It is also possible to apply several AC pulses to the chosen electrode, at the same time as the phase is reversed at the electrode Y in synchronism with the alternating voltage of the electrode X. In this case, when controlling image displays, it is possible to use a pulse train length modulation

in the luminance setting.

  In known manner for the adjustment of the luminance, in addition to the pulse train length modulation,

  can also use amplitude modulation or modula-

  It is clear that the use of the method according to the invention makes it possible to implement these modes of modulation without forming a DC component in the control voltage of the display. amplitude modulation can be performed in that the modulation voltage UM corresponding to the desired luminance level is applied to the electrodes Y, the amplitude of this

  modulation voltage being between 0 and U 3,

  deriving from the fact that if the electrode X is at the negative voltage -U 2, the modulation voltage UM, corresponding to the luminance

  maximum is equal to U 3, and with the minimum luminance U = OV.

  M If the X electrode is at the positive voltage U 1, then we obtain at the maximum luminance, UM = OV, and at the luminance

minimum, UM = U 3.

  In the context of the invention, it is also conceivable

  see solutions that differ from the embodiments described above by way of example Thus, in the example of FIGS. 2 and 3, a single source of modulation U 3 has been used. It would also be possible to use two voltage sources of which one would for example have a positive voltage and the other a negative voltage, the absolute values of the voltages being equal. In addition to the electroluminescent display, the process according to the invention can also be applied, for example,

to the plasma display.

  As is apparent from the above, the invention is not limited to those of its modes of implementation, implementation and application which have just been described more explicitly; on the contrary, it embraces all the variants that may come to the mind of the technician in the field, without departing from the scope or scope of the

present invention.

8 +

Claims (7)

  1 Image display control method, in particular   particular of a two-dimensional electroluminescent display in   alternating current, comprising a matrix composed of electro-   X and Y and based on the thin film method, in which a modulation voltage is used which is preferably less than half of the total control voltage, selection pulses are applied to the X electrodes, at the same time, while the other X electrodes are floating, and modulation pulses are applied to   Y electrodes while most X electrodes are floating   which method is characterized in that the modulation   is applied to both positive impulses and impulse   the control voltage of the display, by buffering the phases of the modulation pulses and selection pulses.   Process according to Claim 1, characterized   in that the modulation pulses form symmetrical layers   at the top of successive positive and negative control pulses, so that no DC voltage component.   Process according to claim 1 or 2, characterized   rised in that the polarity of the control voltage is reversed   at least approximately in the middle of the reclamation cycle.   Process according to any one of the claims   tions, characterized in that a modula-   length of pulse train.   Process according to any one of the claims   tions, characterized in that a modula- amplitude.   Process according to any one of the claims   tions, characterized in that a modulation is used pulse width.   7 Process according to any one of the claims   tions, characterized in that a source is used modulation voltage.   Process according to any of the claims   cations 1 to 6, characterized in that two sources of modulation voltage are used, one of which has a positive voltage and the other a negative voltage, the absolute values of their voltages being equal.