RU2117335C1 - Method for control of alternating current plasma display - Google Patents

Abstract

FIELD: computer engineering. SUBSTANCE: method involves application of high-frequency feed voltage which provides electron oscillation amplitude in discharge less than discharge gap. This results in possibility to keep high- frequency discharge with low loss and quasi-stationary state. Amplitude of blanking pulses depends on condition of plasma decay in gas. EFFECT: increased efficiency, increased brightness of display, possibility to use low-amplitude blanking pulses, simplified design. 12 cl, 1 dwg

Description

 The invention relates to technical physics, in particular to methods for controlling visual indicators made in the form of a gas discharge device with crossed electrodes, and can be used, for example, in information displays used in aircraft, television, personal computers, advertising, etc. .

 In recent years, the interest of researchers and developers of information displays in plasma displays as the most promising direction in the production of large-size displays has sharply increased. Structurally, the plasma display, as a rule, consists of two substrates on which the rows of electrodes are placed, while the substrates are oriented relative to each other so that the rows of electrodes placed on the substrates are mutually orthogonal. The intersection areas of the orthogonal electrodes form cells that are filled with a gas or mixture of gases. Excitation of the discharge in the gas filling the cells in a certain sequence allows the display of information. By the type of electric voltage (constant or variable) applied to the electrodes of the cells, plasma displays are divided into two large classes: DC displays and alternating current displays (in the first case, it refers only to unipolarity of the voltage, but the shape can be different).

 Widely known DC displays, in which the discharge is excited by a constant voltage applied to uninsulated electrodes [1-3].

 A common design feature of this class of displays is that the electrodes are in electrical contact with the gas discharge plasma, which in itself is a drawback, since the electrodes are sprayed under the influence of the plasma, which leads to a change in the composition and pressure of the gas in the gas discharge cell and, as a result, changing its electrical parameters. Another disadvantage of DC displays is the difficulty of realizing the memory property — maintaining the discharge in the cell after ignition — due to the negative current – voltage characteristics of the glow discharge. To eliminate this drawback, ballast resistances in the cells are used that reduce the efficiency [4], or a sequence of unipolar pulses [3] is used as the supporting voltage, which does not provide sufficient stability to maintain the discharge in the cells.

 In the class of DC displays, it is known to create designs and methods for controlling them based on the use of a positive discharge column as a source of ultraviolet radiation, which is much more effective than a negative glow (IEEE Trans, on Plasma Science, V. 19 (1991), N 6, p. 1042-1043).

 However, the inevitable increase in the length of the discharge leads either to an increase in the operating voltage, since a drop on the positive column of the discharge is added to the cathodic voltage drop, or to the complexity of the design — the introduction of additional electrodes and the complexity of the cell configuration.

 The best parameters were achieved in alternating current displays using a pulsed voltage of variable polarity with a characteristic pulse repetition rate of 10-100 kHz to excite a discharge in the cells, which is applied to electrodes isolated from the plasma by a dielectric layer. In this case, as a rule, along with the protection of electrodes from sputtering, the problem of increasing the secondary electron emission coefficient is solved [8, 5 and 6]. In these displays, the memory property is ensured by the accumulation of charge on the dielectric wall during the discharge at a voltage of one polarity and by adding the voltage created by this charge to the voltage of the next pulse of reverse polarity so that the total voltage is higher than the breakdown voltage, while the voltage of the supporting pulses alone not enough for the breakdown of the cell. Thus, once a lit cell will break through in each subsequent pulse of the supporting voltage, until it is extinguished by a special quenching pulse.

 A specific disadvantage of this type of display is the insufficient brightness due to the short duration of the discharge (tens of nanoseconds), compared with the pulse repetition period, as a result of which the discharge is not overwhelming most of the time in the cells.

 A known method of controlling an AC display [7], in which, in order to increase brightness, as well as simplify control, a relatively high pulse repetition rate (up to 8 MHz) is used, while refusing the memory property, since at such a pulse repetition rate the charge on the wall does not have time to form. The latter circumstance, however, significantly reducing the maximum time the cell is in the on state, practically eliminates the gain in brightness by increasing the repetition rate.

 The closest analogue to the developed method for the combination of similar essential features is a method for controlling an alternating current plasma display [8]. According to this method, the supporting voltage is applied to the isolated electrodes of the cells in the form of a sequence of pulses of variable polarity with a repetition rate of 10 - 100 kHz. Selective control of the state of the cells — excitation and quenching of the discharge in them — is carried out by applying to the corresponding electrodes — rows and columns — igniting voltage pulses and quenching voltage pulses.

 The disadvantages of this display control method as well as other known ones, regardless of the type of voltage used (constant or variable), are low efficiency, low integrated brightness of the display luminescence and high operating voltage, determined by the large amplitude of the pulses performing selective blanking of the cells. One of the main reasons for the low efficiency of the existing display control methods is the low efficiency of converting the electric energy absorbed in the cell into light radiation of the discharge, usually not exceeding 10%. This is due to the fact that the overwhelming majority of electrical energy is spent on heating the ions in the cathode region and ionizing the gas, which is necessary to compensate for the fast drift transfer of electrons from the discharge. The reason for the low brightness of the luminescence is concluded, as indicated above, in the high duty cycle of the current pulses in the cells or in the low pulse repetition rate of the supporting voltage. The need to use large-amplitude pulses for selective blanking of cells in known methods is connected with the fact that the supply of quenching pulses should ensure the breakdown of the respective cells, and the minimum breakdown voltage, determined by the type of gas and electrode material, for gas mixtures used in displays is about 200 V.

 Thus, the object of the invention is to develop a method for controlling an alternating current plasma display that provides improved operational characteristics of an alternating current plasma display, namely, high efficiency, increased brightness and low operating voltage, and which does not require complex, bulky and expensive structural solutions for its implementation.

 The essence of the developed method for controlling an AC plasma display is that it, like the control method, which is the closest analogue, includes supplying voltage and ignition voltage pulses to the electrodes of the plasma display cells, thereby exciting a discharge in the gas filling the cells, with the subsequent supply of quenching voltage pulses to the electrodes of the cells.

 New in the developed method is that the supporting voltage is formed high-frequency and the discharge in the gas is maintained high-frequency, while the amplitude of the electron vibrations in the discharge is less than the discharge gap, and the parameters of the quenching voltage pulses are selected from the condition of plasma decay in the gas.

 In a particular case, firing voltage pulses are fed to the main electrodes.

In a specific implementation of this particular case, ignition voltage pulses are generated in the form of video pulses whose amplitude exceeds the critical voltage at the cell electrodes at which the gas ionization frequency ν _i in the cell is determined by the ratio
ν _i ≥ (2V _e / L) lnN _e / N _o ,
Where
V _e is the electron drift velocity;
L is the distance between the electrodes;
N _e is the given concentration of electrons in the cell in the operating mode;
N ₀ - the initial concentration of electrons in the cell, while the duration τ ₁ video pulses is determined by the ratio
τ ₁ ≅ 10 / ν _i .
In another specific implementation, firing voltage pulses are generated in the form of radio pulses, the amplitude of which exceeds the breakdown voltage of the cell, the filling frequency of the radio pulses is determined by the condition for maintaining the amplitude of the electron vibrations in the discharge less than the discharge gap, and their duration τ ₂ is determined by the ratio
τ ₂ > {1 / (ν _i -ν _d )} lnN _e / N _o ,
Where
ν _d is the frequency of diffusion losses.

 In another particular case, the ignition voltage pulses are supplied to additional electrodes, while the amplitude of the ignition voltage pulses exceeds the breakdown voltage of the cell.

 In another particular case, firing voltage pulses are applied to the display cells selectively.

 In another particular case, firing voltage pulses are applied to all display cells simultaneously.

 It is advisable to apply damping voltage pulses to the display cells selectively.

In a particular implementation, quenching voltage pulses are applied to the main electrodes. In another specific implementation, quenching voltage pulses are applied to additional electrodes. In this case, when the electrodes are isolated, the amplitude U ₁ and the duration t _{1 of the} quenching pulses are determined by the relation U ₁ = L ² / b _e t ₁ , where b _e is the electron mobility, and when the electrodes are made non-insulated, the amplitude U ₂ and the duration t _{2 of the} quenching pulses are determined the ratio U ₂ = L ² / b _i t ₂ , where b _i is the mobility of ions.

 In the developed method for controlling an alternating current plasma display, applying to the electrodes of the cells a high-frequency supporting voltage at which the amplitude of the electron oscillations in the discharge is less than the discharge gap, it is possible to realize a high-frequency discharge in the display cells, which is characterized by low losses and quasi-stationarity. This ensures high efficiency and increased brightness of the display luminescence and makes it possible to use damping pulses of small amplitude for selective blanking of cells, the magnitude of which is determined by the decay condition of the plasma in the gas, and thereby allows to solve the problem that the invention is directed to, namely, to develop a control method that provides improved operational characteristics of an AC plasma display and not requiring complex, bulky and expensive structural solutions for its implementation.

 The drawing shows a variant of the structural diagram of the device with which the proposed method for controlling an alternating current plasma display can be implemented.

 The device comprises a support voltage source 1, a source of 2 ignition voltage pulses, and a source of 3 quenching voltage pulses. The outputs of sources 1, 2 and 3 are connected to the electrodes of the cells of the plasma display 4.

 Source 1 is designed to form a high-frequency supporting voltage. In a specific implementation, a standard RF generator operating in the megahertz frequency range can be used as source 1. In the general case, the parameters of the supporting voltage are determined by the condition of maintaining the amplitude of the oscillations of the electrons in the discharge of a smaller discharge gap and depend on the size of the display cells, the composition and pressure of the gas filling the cells, etc. These parameters can be calculated, for example, by the method (Yu.P. Raizer . and other High-frequency capacitive discharge. - M.: Nauka-Fizmatlit, 1995, S. 30-37). For typical cell parameters, it is advisable to use a supporting voltage with a frequency of more than 20 MHz.

Source 2 is designed to form ignition voltage pulses. In one particular case, source 2 provides the formation of video pulses, the amplitude of which exceeds the critical voltage at the cell electrodes, at which the gas ionization frequency ν _i in the cell is determined by the ratio
ν _i ≥ (2N _e / L) lnN _у / N _o ,
Where
V _e is the electron drift velocity;
L is the distance between the electrodes;
N _e is the given concentration of electrons in the cell in the operating mode;
N ₀ is the initial concentration of electrons in the cell.

The duration τ ₁ video pulses is determined by the ratio
τ ₁ ≅ 10 / ν _i .
In another particular case, the source 2 provides the formation of radio pulses, the amplitude of which exceeds the breakdown voltage of the cell. The filling frequency of the radio pulses is determined by the condition of maintaining the amplitude of the oscillations of the electrons in the discharge less than the discharge gap, and their duration τ ₂ is determined by
τ ₂ > {1 / (ν _i -ν _d )} lnN _e / N _o ,
Where
ν _d is the frequency of diffusion losses.

 Source 3 is intended for the formation of quenching voltage pulses in the form of single video pulses of a given duration and amplitude.

 As the plasma display 4, for example, an AC plasma display [8] or a display [6], or another similar one, can be used.

 The developed method for controlling an alternating current plasma display using a device, the structural diagram of which is shown in the drawing, is implemented as follows.

 A high-frequency supporting voltage is supplied to the main electrodes of the cells of the plasma display 4 using a source 1. The amplitude of this voltage is less than the breakdown value, therefore, the discharge in the gas filling the cells is not excited. Then, ignition pulses are energized using the source 2 to the main or additional electrodes of the cells.

 When applying firing voltage pulses to the main electrodes in one particular case, these pulses are formed in the form of video pulses, and in another particular case in the form of radio pulses. In the general case, the amplitude of these pulses exceeds the breakdown voltage of the cell. In addition, when generating ignition voltage pulses in the form of video pulses in the case when the electrodes are insulated, the amplitude and duration of these pulses are chosen so that, on the one hand, the concentration of the emerging plasma during the pulse reaches a value at which the diffusion of charged particles becomes ambipolar, and on the other hand, an electric charge did not have time to accumulate on the dielectric coating of the cathode, which may interfere with the maintenance of a high-frequency discharge in the cell. Moreover, in one embodiment of the method, firing voltage pulses are applied to all cells simultaneously, and in another, selectively. As a result, a discharge is excited in the gas filling the cells to which the firing voltage pulses are applied. After the end of the ignition pulse, the discharge is maintained high-frequency using a high-frequency supporting voltage, while the amplitude of the electron oscillations in the discharge is maintained smaller than the discharge gap. Maintaining the amplitude of electron oscillations in the rf field of a smaller discharge gap leads to the fact that the electrons remain in the plasma - their losses are due in this case to ambipolar diffusion, which is much less than the drift drift that occurs in low-frequency discharges. Therefore, the cost of electric energy for gas ionization, designed to compensate for the loss of charged particles, in an RF discharge is less than in an RF discharge. In addition, the voltage drop across the electrode layers is less, since the current in them is mainly transferred by the bias current, which reduces the energy loss due to heating of the ions. The result is a high plasma display efficiency. The high-frequency discharge is quasistationary, i.e., it emits continuously throughout the entire time while the supporting voltage is applied. Therefore, the maximum brightness of the RF display is higher than in alternating current displays, when the radiation of the cells consists of short pulses separated by large pauses.

The discharge state is maintained in the cells until the quenching voltage pulses are supplied. In one particular case, quenching voltage pulses are supplied to the main electrodes, and in the other to additional electrodes, which can be insulated or non-insulated. When applying quenching voltage pulses, the drift loss rate of electrons in the quenching pulse field exceeds the rate of gas ionization in the rf field, since the parameters of the pulses, in particular the amplitude, are selected from the condition of plasma decay in the gas. To ensure this condition for typical cell parameters, the amplitude of the quenching pulses is several volts, which is much less than the operating voltage in the known methods. When the quenching voltage pulses are selectively applied to the display cells when the electrodes are insulated, the amplitude U ₁ and the duration t _{1 of the} quenching pulses are determined by the ratio U ₁ = L ² / b _e t ₁ , where b _e is the electron mobility, and when the electrodes are made, the amplitude U _{2 is} non-insulated and the duration t _{2 of the} quenching pulses are determined by the relation U ₂ = L ² / b _i t ₂ , where b _i is the mobility of the ions. The indicated ratios of the parameters of the quenching pulses suppress the selected cells without changing the state of the remaining cells.

Claims (11)

 1. A method for controlling an alternating current plasma display, by which a supporting voltage is supplied to the main electrodes of the plasma display cells and igniting voltage pulses are supplied, thereby exciting a discharge in the gas filling the cells, followed by supply of quenching voltage pulses to the cell electrodes, characterized in that the supporting voltage is formed high-frequency and the discharge in the gas is maintained high-frequency, while the amplitude of the electron vibrations in the discharge is less than the discharge gap, and the parameters are quenched x pulse voltage is selected from the condition in a gas plasma decay.  2. The method according to claim 1, characterized in that the ignition voltage pulses are fed to the main electrodes. 3. The method according to claim 2, characterized in that the ignition voltage pulses are formed in the form of video pulses, the amplitude of which exceeds the critical voltage at the cell electrodes, at which the gas ionization frequency ν _i in the cell is determined by the ratio:
ν _i ≥ (2v _e / L) lnN _e / N _o ,
where V _e is the electron drift velocity;
L is the distance between the electrodes;
N _e is the given concentration of electrons in the cell in the operating mode;
N ₀ is the initial concentration of electrons in the cell,
the duration τ _{1 of the} video pulses is determined by the ratio τ ₁ ≅ 10 / ν _i .
4. The method according to claim 2, characterized in that the ignition voltage pulses are formed in the form of radio pulses, the amplitude of which exceeds the breakdown voltage of the cell, the frequency of filling of the radio pulses is determined by the condition of maintaining the amplitude of the oscillations of the electrons in the discharge less than the discharge gap, and their duration τ ₂ is determined by the ratio
τ ₂ > {1 / ν _i -ν _d )} lnN _e / N _o ,
where ν _d is the frequency of diffusion losses.  5. The method according to claim 1, characterized in that the ignition voltage pulses are supplied to additional electrodes, while the amplitude of the ignition voltage pulses exceeds the breakdown voltage of the cell.  6. The method according to claim 1, or 2, or 3, or 5, characterized in that the ignition voltage pulses are applied to the display cells selectively.  7. The method according to claim 1, or 2, or 3, or 4, or 5, characterized in that the ignition voltage pulses are supplied to all cells of the display at the same time.  8. The method according to claim 1, or 2, or 3, or 4, or 5, or 6, or 7, characterized in that the quenching voltage pulses are applied to the display cells selectively.  9. The method according to claim 1, or 2, or 3, or 4, or 5, or 6, or 7, or 8, characterized in that the quenching voltage pulses are supplied to the main electrodes.  10. The method according to claim 1, or 2, or 3, or 4, or 5, or 6, or 7, or 8, or 9, characterized in that the quenching voltage pulses are supplied to additional electrodes. 11. The method according to claim 9, or 10, characterized in that when the electrodes are insulated, the amplitude U ₁ and the duration t _{1 of the} quenching pulses are determined by the ratio
U ₁ = L ² / b _e t ₁ ,
where b _e is the electron mobility. 12. The method according to claim 9 or 10, characterized in that when the electrodes are not insulated, the amplitude U ₂ and the duration t _{2 of the} quenching pulses are determined by the ratio
U ₂ = L ² / b _i t ₂ ,
where b _i is the mobility of ions.