Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2003-08-12
2004-11-16
Vannucci, James (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169300, C315S169400, C345S060000
Reexamination Certificate
active
06819055
ABSTRACT:
The invention relates to a plasma display panel addressing and driving method.
Document JP 10-171399 (HITACHI) describes a coplanar-type plasma panel comprising:
a rear plate provided with a first array of electrodes;
a front plate, parallel to the first, provided with a second array of pairs of electrodes orthogonal to the electrodes of the first array, the electrodes of each pair leaving between them discharge spaces positioned at the intersections of the electrodes of the first array and of the pairs of electrodes of the second array.
The addressing and the driving of a plasma display panel of this type generally comprise the following steps:
activation of a discharge in each of the intersection regions to be activated, by applying, at least, an address voltage pulse between the electrode of the rear plate and an electrode of the front plate which intersect in this region;
re-activation of a series of discharges in this region by applying a series of sustain voltage pulses between the same electrode of the front plate and the paired electrode of this same plate.
According to this method, the address discharge extends essentially perpendicular to the plates in the space, filled with discharge gas, which separates the plates; in contrast, the sustain discharges extend essentially parallel to the plates, along the front plate.
According to this conventional method, the instantaneous frequency of the sustain pulses is generally about 100 to 300 kHz and determines the luminosity of the panel; the sustain is called “positive” if the two electrodes of the pair always have a positive or zero potential with respect to the address electrodes and, in the opposite case, called “negative” or “bipolar” if this potential is alternately positive and negative (the sustain signals of the electrodes of the same pair are then offset by a half-phase).
The address pulses may be grouped together in groups of rows and are then also very close together.
To address and drive a panel of this type, document JP 10-171399 (HITACHI) also proposes to use pulses of very high frequency, substantially greater than 10 MHz.
If, as indicated in FIG. 3 of that document, the first array of electrodes comprises electrodes A
1
, A
2
, . . . , A
6
, and if the second array comprises pairs (X, Y
1
), (X, Y
2
), . . . , (X, Y
n
), referring now to FIG. 1 of that document, the addressing and driving of the coplanar plasma display panel then comprise the following steps:
addressing or writing (phase IV) during the address voltage pulse resulting from the difference between the signal 107 applied to the electrode Y
m
and the signal 108 applied to the electrode A;
bipolar sustain by applying signals 101 generating conventional “low-frequency” sustain voltage pulses between the electrode Y
m
and the paired electrode X;
according to the invention presented in that document, a very-high-frequency “RF” signal 100 is furthermore applied during this sustain phase, on the side of that one of the electrodes Y
m
or X which serves as cathode; the application of this signal corresponds here to the sustain step VII.
According to that document, the purpose of applying a very-high-frequency signal, once the charges have formed between the electrodes after a conventional sustain discharge, is to prevent the ionic charges reaching the cathode and to vibrate the ionic charges between the electrodes, as shown schematically in FIG. 4-VII of that document; referring to FIG. 5, said document teaches:
that it is necessary to start applying the RF signal 100 before the conventional sustain discharge corresponding to the pulse 101 has resulted in the complete inversion of the charges on the dielectric layer which covers the electrodes; thus, the time t
d
separating the pulse front 101 from the first front of the RF signals must be substantially shorter than the cumulative time of the sustain discharge and of the complete invention of the charges;
that it is necessary for the half-period t
w
of the RF signal 100 to be short enough for the ionic charges not to have time to return to the cathode during a half-period; this condition generally results in very high frequencies difficult to employ.
According to that document, under these conditions, a discharge stabilized by the RF signal is obtained, which emits light with a luminous efficiency very much greater than that obtained with conventional discharges of lower frequency.
As an example, according to that document, when the distance separating two sustain electrodes at the point of the discharge is about 100 &mgr;m, when the discharge gas is an Ne/Xe mixture at a pressure of 0.4×10
5
Pa, the abovementioned conditions are as follows: t
d
<1 &mgr;s approximately; t
w
<0.1 &mgr;s approximately, corresponding to frequencies of greater than 20 MHz.
According to that document, in the method of driving the plasma display panel, each sustain step comprises a succession of conventional sustain discharges and of stabilized discharges:
a first discharge, generated by a conventional sustain pulse, intended to create ionic charges in the activated region, and
a stabilized discharge, generated by a pulse train with a high frequency suitable for stabilizing the ionic charges created in the activated region.
Thus, the sustain discharge is used to activate or “ignite” the stabilized discharge.
The use of high frequencies poses major electronic problems which limit the use of this method for driving plasma display panels; to obtain stabilized discharges at a lower frequency, it is necessary to increase the distance separating the electrode X and the electrode Y of each pair, but the voltage required to obtain the conventional sustain discharge then increases, creating other drawbacks.
More Precisely:
to apply the conventional “low frequency” sustained signal that serves to initiate a discharge before application of the “high frequency” signal, it is beneficial to use electrodes close enough to limit the voltage needed for initiation;
to apply the “high frequency” signal, it is beneficial to use electrodes far enough apart as to prevent the ions from reaching one of the electrodes during the period of one alternation and thus obtain the desired stabilization effect for a frequency that is not too high.
Document U.S. Pat. No. 5,233,272, in particular FIG. 2, describes a plasma panel similar to a coplanar panel comprising, for each discharge space, an anode 40 and an auxiliary electrode 50 that are coplanar and carried by the same plate, and a cathode 60 carried by the other plate; unlike conventional coplanar panels, which have a lasting memory effect, no dielectric layer separates the electrodes so it is possible to obtain only a short-duration pseudomemory effect, that is to say a memory effect of conditioning by the previous discharge or by an adjacent source of primary particles; to drive such a panel, according to that document, pulses of high enough amplitude to obtain a succession of discharges are applied between the anode and the cathode; during application of these pulses, similar to sustained pulses, pulses of higher frequency are applied, between the coplanar electrodes 40 and 50, so as to disturb the movements of the ions and make them diffuse between the electrodes (column 2, lines 20-21 and 40-41; column 3, lines 38-39 and 57-58); this disturbance leads merely to the extension of the path of the ions between the electrodes (column 3, line 66 to column 4, line 4) and not to stabilization of these ions, as in document JP 10-171399; here, the purpose of applying the higher-frequency pulses is to improve the short-duration memory effect and to lower the pulse amplitude needed to obtain discharges (column 5); according to that document (especially “table” column 4) and the figures, to obtain the desired effect it is therefore important for the distance separating the electrodes between which the higher-frequency signal is applied (in this case the anode and the auxiliary electrode) to be less than the distance separating the electrodes between which the conventional sustain-type signal
Fried Harvey D.
Thomson Licensing S.A.
Tripoli Joseph S.
Vannucci James
Verlangieri Patricia A.
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