Patent Grant
7088315
1. Field of the Invention
The present invention relates to a plasma display device employing a plasma display panel (hereinafter also referred to as a plasma panel or a PDP) and an image display system using the plasma display device. In particular, the present invention is useful for providing a display device capable of improving luminous efficacy and producing a high-contrast and high-quality image.
2. Description of Prior Art
Recently, plasma display devices have been expected as promising large-size thin color display devices. More specifically, an ac surface-discharge type PDP is the most common type among PDPs put to practical use because of its simple structure and high reliability. Although the present invention will be explained mainly by using a conventional PDP of the ac surface-discharge type, the present invention is equally applicable to other types of PDPs.
In the above, the X electrodes 22-1, 22-2 and the Y electrodes 23-1, 23-2 have been explained as transparent electrodes, this is because a lighter (high-brightness) panel can be obtained, and it is needless to say that they do not always need to be transparent. Magnesium oxide (MgO) is explained as a concrete material for the protective film 27, but material for the protective film 27 is not limited to magnesium oxide. The objects of the protective film 27 are to protect the display discharge electrodes and the dielectric 26 from bombarding ions and to promote initiation and sustenance of discharge with secondary electron emission caused by incident ions. Other materials can be used which are capable of achieving the above objects. The front glass substrate 21 combined in this way with the electrodes, the dielectric, the protective films in an integral structure is called a front plate.
On the other hand, formed on an upside of a rear glass substrate 28 are electrodes (hereinafter referred to as A electrodes or address electrodes) 29 such that they intersect the X electrodes 22-1, 22-2 and the Y electrodes 23-1, 23-2 at right angles with grade separation. The A electrodes 29 are covered with a dielectric 30, and barrier ribs 31 are formed on the dielectric 30 such that they extend in parallel with the A electrodes 29. Further, phosphors 32 are coated on inner surfaces of cavities formed by wall surface of the barrier ribs 31 and the upper surfaces of the dielectric 30. The rear glass substrate 28 combined in this way with the A electrodes and the dielectric in an integral structure is called a rear plate.
A plasma panel is fabricated by bonding the front and rear plates provided with the necessary constituent elements as described above, filling a gas (a discharge gas) for creating plasma, and then sealing the panel. It is needless to say that it is necessary to bond and seal the front and rear plates to ensure the hermeticity of the sealed package containing the discharge gas.
In
Here, the discharge space means a space where a display discharge, an address discharge, or a preliminary discharge (also called a reset discharge) is generated in operation of the plasma panel as described later. More specifically, the discharge space is a space which is filled with the discharge gas, has applied thereacross an electric field necessary for the discharge, and has a spatial expanse required for generation of the discharge. Further, a display discharge space means a space where a display discharge occurs, more specifically, a space which is filled with the discharge gas, has applied thereacross an electric field necessary for a display discharge, and has a spatial expanse required for generation of the display discharge. The discharge space and the display discharge space mean a space included in each of the discharge cells, or a collection of the spaces included in the discharge cells.
In a color PDP, usually three kinds of phosphors for red, green and blue are coated within the cells. A trio of cells coated with the three different kinds of phosphors serve as one pixel. A space having a plurality of such cells or pixels arranged continuously and periodically is called a display space. A set is called a plasma display panel or plasma panel which includes the display space and is provided with other necessary structures such as vacuum sealing and electrode leads for external connection. Hereinafter, the plasma panel is also referred to as the PDP.
In the plasma panel, a structure integrally fabricated to seal the discharge gas therein hermetically is referred to as the basic plasma panel. In the basic plasma display panel, a surface from which visible light for display is irradiated is called a display surface, and a space into which the visible light for display is irradiated is called a viewing space.
As described above, in the basic plasma panel, there is a space containing the plural discharge cells arranged continuously, which is hereinafter referred to as a display space. A projection of the display space onto the display surface is called a display region Rp, a projection of the discharge space onto the display surface is called a discharge region, and a projection of the display discharge space onto the display surface is called a display discharge region. A region other than the display discharge region in the display region Rp is called a non-display discharge region. A projection of the discharge cell onto the display surface is called a cell region.
A direction perpendicular to the display surface is called a height direction. In a case where the discharge cells include barrier ribs as their constituent components, a direction of a line connecting centers of two adjacent ones of the discharge cells arranged with one of the barrier ribs interposed therebetween is called a width direction, and a direction perpendicular to the width direction in a plane parallel with the display surface is called a length direction.
A barrier rib width is defined as a width of the barrier rib as measured in the width direction, and an average of the barrier rib width averaged over the height direction of the barrier rib is called an average barrier rib width Wrba.
In the conventional plasma panel shown in
By way of example,
As shown in portion II of
The preliminary discharge period 49 is a period for homogenizing conditions of all the cells (conditions for establishing their drive characteristics) and preparing to ensure stability and reliability in their subsequent operations. Usually, during the preliminary discharge period, a preliminary discharge, a reset discharge, or an overall-address discharge (a discharge for addressing the entire display region simultaneously) is performed.
In this way, each of the Y electrodes is supplied with the scan pulse once during the address discharge period 50, and the A electrodes 29 are supplied with the voltage V0 or ground potential in synchronism with the scan pulse according to whether they are to be lighted or not to be lighted, respectively. In the discharge cells where the address discharges have been generated, electric charges are formed by the discharges on the surfaces of the dielectric and the protective films covering the Y electrodes. ON and OFF of the display discharge described subsequently are controlled by the assistance of an electric field generated by the above-mentioned electric charge. That is to say, the cells which have generated the address discharge serve as lighted cells, and the remainder of the cells serve as non-lighted cells.
On the other hand, there is another driving method in which the cells which have generated the address discharge serve as non-lighted cells (in which a wall charge generated by the above-explained overall-address discharge is eliminated by the address discharge), and in which the remainder of the cells serve as lighted cells.
The pulses of the magnitude V3 (V) and the same polarity are applied alternately to the X electrodes and the Y electrodes, and as a result reversal of the polarity of the voltage between the X and Y electrodes is repeated. The discharge occurring in the discharge gas between the X and Y electrodes during this period is called the display discharge. Here, display discharges occur in pulses, and their polarities are alternated.
A display electrode-to-electrode voltage Vse(t) externally applied in a cell during the display period is expressed by
Vse(t)=Vy(t)−Vx(t) (1)
where Vx(t) and Vy(t) are voltage applied to the X and Y electrodes, respectively, during the display period, and t represents time.
A maximum applied display-discharge voltage Vsemax is defined as the maximum of the absolute value |Vset(t)| of the display electrode-to-electrode voltage Vse(t) during a time when the display discharge pulses are applied. In
Usually the means for generating the display discharge pulses is provided in the drive means shown in
In the above explanation, the display discharge has been explained in connection with a driving system in which the address discharge periods and the display periods are separated from each other, that is, the Address and Display Periods Separated Driving System, but the essence of the display discharge lies in intentional generation of light emission necessary for display, and therefore it is needless to say that such a discharge is recognized as the display discharge in other driving systems also.
For example, in the above-explained driving system (the Address and Display Periods Separated Driving System), the address discharge periods and the light-emission display periods are provided for the entire display region simultaneously, respectively. However, there is another driving system in which, while the address discharge periods are provided to some of the scanning electrodes (the Y electrodes), the light-emission display periods are provided to others of the scanning electrodes (the Y electrodes), and vice versa, and this driving system is called the Simultaneous Address and Display Driving System.
In the above-explained conventional techniques, the so-called progressive scanning drive system is employed, and all the discharge cells in the display region are used for displaying an image during each field period. On the other hand, the so-called interlaced scanning driving system can also be used. In the interlaced scanning driving system, the discharge cells of the plasma panel are divided into two kinds (group A and group B, for example), an image display is performed by alternately using the discharge cells of each of the group A and the group B on successive fields. For example, successive fields are divided into odd-numbered fields and even-numbered fields, and an image display is performed by using the discharge cells of the group A on the odd-numbered fields and using the discharge cells of the group B on the even-numbered fields. Further, in a third driving system, the same scanning electrodes (Y electrodes) may be used both for driving the odd-numbered fields and for driving the even-numbered fields. The plasma display device employing the plasma panel to which the interlaced scanning driving system or the above-described third driving system is applied is called the ALIS (Alternate Lighting of Surfaces) type plasma display device. The details of the ALIS type plasma display device have been reported in Kanazawa, Y., T. Ueda, S. Kuroki, K. Kariya and T. Hirose: “High-Resolution Interlaced Addressing for Plasma Displays,” 1999 SID International Symposium Digest of Technical Papers, Volume XXX, 14.1, pp. 154–157 (1999).
The plasma display device includes a plasma display panel having as its constituent element at least a plurality of discharge cells, creates plasmas in the discharge cells by discharge, and produces an image display by generating visible light by the action of the plasmas. Methods of generating visible light by using the action of the plasmas includes a method of utilizing visible light produced by the plasmas themselves, and a method of utilizing visible light emitted by phosphors excited by ultraviolet rays generated by the plasmas. Usually the latter method is employed for the plasma display devices.
A technical improvement most strongly desired in these plasma display devices is that on luminous efficacy h. The luminous efficacy h is the total luminous flux emitted from the display screen (which is proportional to a product of luminance, a display area and a solid angle) divided by the total electric power input to the display panel for producing the display, and are usually measured in lumens per watt. The higher the luminous efficacy, the brighter display screen can be realized with a small power input to the display panel. Consequently, the higher luminous efficacy is desired in the plasma display devices.
Among the important performance characteristics, of the plasma display devices, there is a contrast C. The contrast C is defined as below.
C=Bpon/Boff (2)
where
Bpon is a luminance value obtained when a display of the maximum luminance is produced,
Boff is a luminance value obtained when a black display is produced,
Bpon and Boff are expressed in cd/m2, and
luminance is usually measured by using a luminance meter.
The contrast C is classified into light-room contrast Cb and darkroom contrast Cd according to their measuring conditions. The light-room contrast Cb is a contrast as measured in a well-lighted environment (usually assumed to be a living room, that is, an ambient room illumination producing 150–200 lx), and the darkroom contrast Cd is a contrast as measured in a darkroom.
The higher the contrast calculated by using Equation (2), the clearer and more beautiful images can be produced. That is to say, the higher contrast is desired for the plasma display devices.
In the case of the plasma display devices, the luminance Boff is not always zero which is measured when a black display is produced in a darkroom. The reason is that light emission which is not always needed for displaying an image is produced by a preliminary discharge during the preliminary discharge period (also called a reset discharge or an overall-address discharge), or an address discharge during the address discharge period. Consequently, in the case of the plasma display devices, the darkroom contrast is not infinite, but finite, and is expressed by
Cd=Bpond/Boffd (3)
where
Bpond is a luminance (cd/m2) measured when a display of the maximum luminance is produced in a darkroom, and
Boffd is a luminance (cd/m2) measured when a black display is produced in the darkroom.
The darkroom contrast Cd is increased by increasing Bpond, or decreasing Boffd, and is determined by the structure of a cell or discharge characteristics.
On the other hand, the light-room contrast Cb is usually increased by using a filter having its transmission characteristics controlled. As described subsequently, when the transmission factor α is decreased so as to increase the light-room contrast Cb, a luminous efficacy in a case when the filter is employed, that is, a set luminous efficacy hs decreases with decreasing α. That is to say, in the case of the conventional plasma display devices, a tradeoff must be made between the set luminous efficacy hs and the light-room contrast Cb, and therefore it was difficult to achieve high values of both the high set luminous efficacy hs and the light-room contrast Cb at the same time.
The plasma display device in accordance with the present invention has reduced the restrictions imposed by the tradeoff between its luminous efficacy and its light-room display contrast, and realizes a plasma display device having a high set luminous efficacy (that is, which is capable of providing a high-brightness display image with a low power consumption) and producing a high light-room contrast.
The following explains the summaries of the representative ones of the inventions disclosed in this specification.
(27) A plasma display device according to (23), wherein a non-aperture-surface surface reflectance is 80% or more, where a solid wall surrounding said display discharge space is called an inner surface of said display discharge space, a portion of said inner surface of said display discharge space from which the visible light for a display is emitted into said viewing space is called an aperture surface, a portion of said inner surface of said display discharge space other than said aperture surface is called a non-aperture-surface, said non-aperture-surface surface reflectance is defined as a surface reflectance of said non-aperture-surface averaged over said non-aperture-surface.
(28) A plasma display device according to (24), wherein a non-aperture-surface surface reflectance is 80% or more, where a solid wall surrounding said display discharge space is called an inner surface of said display discharge space, a portion of said inner surface of said display discharge space from which the visible light for a display is emitted into said viewing space is called an aperture surface, a portion of said inner surface of said display discharge space other than said aperture surface is called a non-aperture-surface, said non-aperture-surface surface reflectance is defined as a surface reflectance of said non-aperture-surface averaged over said non-aperture-surface.
Before explaining the embodiments in accordance with the present invention, the results of various studies by the present inventors will be explained.
Usually a filter having its light transmission characteristics controlled is used to increase the above-described light-room contrast Cb.
In the configuration of
In the configuration of
Cb=(Bponm×α+Br×α2×β)/(Boffm×α+Br×α2×β) (4)
where
Bponm (cd/m2) is a luminance value obtained when a display of the maximum luminance is produced without a filter (that is, only by a plasma panel) in a darkroom, this is, a module luminance or a module peak luminance;
Boffm (cd/m2) is a luminance value obtained when a black display is produced without a filter, that is, only by a plasma panel, in the darkroom;
Br (cd/m2) is a luminance produced at an imaginary completely reflecting surface (a diffusing reflecting surface of 100% in surface reflectance) on a front surface (a viewer-side surface) of a filter, by external light in a light-room;
α is a transmission factor of the filter; and
β is a surface reflectance averaged over a surface in a display region of the plasma panel, that is, a display region surface reflectance.
When L (lx) is an ambient illuminance in the light-room, Br=L/π≈L/3.14 cd/m2.
In a system where part of light incident on a surface (an incident surface) of an object leaves the surface as the reflected light, the surface reflectance is the ratio of the reflected light energy to the incident light energy, and in a system where part of light incident on a surface (an incident surface) of an object is transmitted through the object as the transmitted light, the transmission factor is the ratio of the transmitted light energy to the incident light energy.
In principle, both the surface reflectance and the transmission factor can be defined and measured at arbitrary locations positioned with accuracy of the order of wavelengths of the incident light. Usually, both the surface reflectance and the transmission factor are measured as a function of positions on the incident surface by using a surface reflectometer and a transmissometer, respectively.
Usually, both the surface reflectance and the transmission factor are functions of wavelengths of incident light. Therefore, the surface reflectance β and the transmission factor α are average values determined by considering the spectrum in the range of ambient visible light in the home room and the standard luminosity curve of the human eye. For the sake of convenience, the surface reflectance β and the transmission factor α may be values averaged over the wavelength range of from 500 nm to 600 nm to which the human eye has a strong brightness sensation.
In Equation (4), it is assumed that there is no reflection of visible light on the surface of the filter.
When zero is substituted for Br in Equation (4), Cb gives the darkroom contrast Cd.
Cd=Bponm/Boffm (5)
In Equation (4), under the usual light-room condition (the light-room ambient illuminance L=150–200 lx),
Bponm×α>>Br×α2×β
Boffm×α<<Br×α2×β.
That is to say, the light-room contrast Cb increases in inverse proportion to the transmission factor α of the filter when the factor α is decreased with Bponm, Br and β being fixed. This is the principle on which the light-room contrast is increased by using the filter.
In the following the luminous efficacy will be discussed. The luminous efficacy h is divided into two kinds: the luminous efficacy hm for a case where no filter is employed (that is, the plasma panel only in
hm=α×Bponm×Sp/Pp (7)
hs=π×Bponm×α×Sp/Pp (8a)
=α×hm (8b)
where
hm is a luminous efficacy (lm/W) measured when no filter is employed, and is called a module luminous efficacy;
hs is a luminous efficacy (lm/W) measured when a filter is employed, and is called a set luminous efficacy;
π is the ratio of the circumference of a circle to its diameter;
Sp is an area (m2) of a light-emission display region;
Pp is an electric power (W) input to the plasma panel; and
light emission is assumed to be perfectly diffusing light emission.
Equations (7), (8a) and (8b) represent the cases when a display of the maximum luminance is produced, and the relationship of Equation (8b) holds for a display exhibiting arbitrary gray scale levels.
Among the above two kinds of the luminous efficacies, the ultimately important one is necessarily the set luminous efficacy. Equation (8b) shows that, even when the module luminous efficacy hm is kept constant, if the filter transmission α is decreased so as to increase the light-room contrast Cb, then the set luminous efficacy hs decreases in proportion to the filter transmission factor α.
That is to say, in the case of the conventional plasma display devices, there is a tradeoff between the set luminous efficacy hs and the light-room contrast Cb, and therefore it was difficult to achieve high values of both the high set luminous efficacy hs and the light-room contrast Cb at the same time.
An object of the present invention is to realize a plasma display device having a high set luminous efficacy (that is, which is capable of providing a high-brightness display image with a low power consumption) and producing a high light-room contrast.
In the following, initially techniques will be discussed which increase the luminous efficacy of the plasma display devices, and then techniques will be discussed which increase the light-room contrast also without decreasing the filter transmission factor α.
It is most important for increasing the luminous efficacy of the plasma display devices to increase the ultraviolet production efficiency hvuv by discharge. This is reported in the present inventors' published papers, Suzuki, K., N. Uemura, S. Ho, and M. Shiiki: “Ultraviolet Ray Production Efficiency of AC-PDPs,” Monthly Magazine Display, Vol. 7, No. 5, pp. 48–53 (May, 2001), and Suzuki, K., N. Uemura, S. Ho, and M. Shiiki: “Ultraviolet Production Efficiency of AC-PDPs and Ways to Increase It,” 3rd International Conference on Atomic and Molecular Data and Their Applications ICAMDATA, AIP Conference Proceedings, Vol. 636, pp. 75–84 (2002). The ultraviolet ray production efficiency hvuv is the ratio of the amount in terms of wattage of ultraviolet rays generated by discharge to an electric power input to a plasma panel.
The theoretical studies by the present inventors and others have made it clear that there are basically two ways for increasing the ultraviolet ray production efficiency: (1) lowering of the electron temperature Te of discharge, and (2) increasing of a Xe proportion aXe in the discharge gas. The studies were reported in the present inventors' published papers, Suzuki, K., Y. Kawanami, S. Ho, N. Uemura, Y. Yajima, N. Kouchi and Y. Hatano: “Theoretical formulation of the VUV production efficiency in a plasma display panel,” J. Appl. Phys., Vol. 88, pp. 5605–5611 (2000). In the above studies, the ultraviolet ray generating atoms in the discharge were assumed to be Xe atoms, as in a (Ne+Xe) gas mixture composed of Ne and Xe, and another gas mixture composed of Ne, Xe and another gas of other atoms or molecules.
The Xe proportion aXe in a discharge gas is defined as the ratio nXe/ng, where ng is a volume particle (atom or molecule) density of the discharge gas, and nXe is a volume particle density of a Xe gas contained in the discharge gas. The volume particle densities ng and nXe are measured by analyzing constituent atoms or molecules of the discharge gas using a mass spectrograph, for example. Conventionally, the Xe proportion aXe was usually 4% to 6%.
Further studies by the present inventors have made it clear that the most effective method for the lowering of the electron temperature Te of discharge in the above-mentioned (1) is (1a) increasing of the pd product in the discharge. The pd product is the product of the pressure p of the discharge gas and a distance d between the discharge electrodes. The pressure p of the discharge gas can be measured by a pressure gauge, for example. The distance d between the discharge electrodes is a distance between the X and Y electrodes which serve as display electrodes in the conventional plasma display shown in
The results of the studies by the present inventors are summarized as follows:
A1: The most effective method for increasing the luminous efficacy (ultraviolet ray production efficiency) of the plasma display device are basically divided into the two kinds: (1a) increasing of the product pd in discharge; and (2) increasing of the Xe proportion aXe of the discharge gas.
The important facts to be noted here are as follows:
A2: The display discharge voltage Vs is increased by both the two methods of increasing the luminous efficacy h, which are (1a) increasing of the product pd in discharge, and (2) increasing of the Xe proportion aXe of the discharge gas.
Here, the display discharge voltage Vs is an effective voltage to be applied between the display electrodes for sustaining a display discharge, and more specifically, it is approximately the maximum applied display discharge voltage Vsemax or is a display-discharge dc power supply voltage Vsdc. Conventionally, the display discharge voltage Vs was in a range of from 150 V to 180 V.
As shown in
The following will discuss the discharge electric power Pp input to the plasma panel.
The discharge electric power Pp input to the plasma panel is expressed by the following equations.
Pp=Nc×Pc (9)
Pc=2×Fdr×Cse×Vs2 (10)
where
The drive frequency Fdr is the number of times when a voltage is applied to the display electrode periodically per unit time (one second). The display-electrode capacitance Cse is a capacitance formed by the display electrode (the X or Y electrode) with a virtual electrode on a surface of the protective film 27 via the dielectric 26 and the protective film 27 within one discharge cell. The display-electrode capacitance Cse is expressed by
Cse=ε×Sse/Dsif (11)
where
Further from Equation (8a),
Bpons=hs×Pp/(π×Sp) (13)
Bpons=Bponsm×α (14)
Consequently, in the above-described methods, even when the display-electrode area Sse is reduced, if the discharge electric power Pp input to the plasma panel can be kept fixed, then the light emission luminance of the plasma display device can also be kept fixed.
It is usually thought that even if the luminous efficacy is increased, the employed method is not desirable because the display discharge voltage Vs is increased and thereby the cost of the circuit is increased. However, the various studies by the present inventors have made clear the following pronounced advantages as described above.
A3: When the display discharge voltage Vs is increased with at least the luminous efficacy hs being kept fixed, even if the display-electrode area Sse is reduced in inverse proportion to Vs2, the fixed amount of the discharge electric power Pp input to the plasma panel and the fixed light emission luminance can be ensured.
By further investigations based upon their own findings A1, A2 and A3 described above, the present inventors have invented a technique of realizing a plasma display device providing a high set luminous efficacy (i.e. producing a high-brightness display image at a low power consumption) and producing a high light-room contrast. In the following, its basic concept will be explained.
In the first place, the difficulties in developing the techniques are represented by Equations (6), (8b) and (14). As described above, even when the module luminous efficacy hm and the module luminance are kept fixed, if the filter transmission factor α is reduced so as to increase the light-room contrast Cb (see Equation (6)), the set luminous efficacy hs and the set luminance Bpons are decreased in proportion to α (see Equations (8b) and (14)).
However, by further investigations into Equations (6), (8b) and (14), the following is found.
A4: If the surface reflectance β of the display region of the plasma panel can be made smaller, the light-room contrast Cb can be increased without reducing the set luminous efficacy hs or the set luminance Bpons.
The surface reflectance β of the display region is an average surface reflectance averaged over the display region. The primary factor in increasing the surface reflectance β of the display region is the ratio (i.e. a discharge region area ratio) of an area (i.e. a discharge region area) of the display surface occupied by the discharge region to an area (i.e. a display region area) of the display surface occupied by the display region. Especially important is the ratio (i.e. a display discharge region area ratio) of a display discharge region area (an area of the display surface occupied by the display discharge region) to the display region area. The reason is that discharge spaces (especially display discharge spaces) forming discharge regions are spaces where display discharges are produced, and are provided with phosphors extending over wide areas for converting ultraviolet rays generated by display discharge into visible light.
Usually the phosphor layers have high reflectance so as to use the visible light produced by the phosphors effectively. That is to say, the phosphor layers appear white when viewed from the outside. Further, the structure itself of the discharge spaces is configured so as to emit the visible light produced by the phosphor layers efficiently into the viewing space. That is to say, the discharge spaces appear white when viewed from the outside, and therefore the reflectance of the discharge regions are high. Consequently, the surface reflectance β of the display region is increased when the discharge region area ratio (especially the display discharge region area ratio) is increased. The display discharge region area ratio Ad is expressed by
Ad=Sd/Sp (15)
where Sd=a display discharge region area (m2), and
Conventionally, the display discharge region area ratio Ad is 45% or more, and therefore, conventionally the surface reflectance β of the display region is 25% or more.
The display discharge region area ratio Ad and the surface reflectance β of the display region are determined by the display discharge region area Sd and the display-electrode area Sse within each of the discharge cells. That is to say,
A5: If the display-electrode area Sse is reduced, then the display discharge region area Sd is reduced, and as a result the surface reflectance β of the display region is made smaller.
The following fact A6 is understood only after putting together and understanding all the above facts A1 to A5 made clear successively in connection with the present invention.
A6: The luminous efficacy hs and the display discharge voltage Vs are increased by (1a) increasing the product pd in discharge or (2) increasing the Xe proportion aXe of the discharge gas, thereby the display discharge region area ratio Ad and the surface reflectance β of the display region of the plasma panel can be made smaller by reducing the display-electrode area Sse approximately in inverse proportion to Vs2. Consequently, this makes it possible to increase the set luminous efficacy hs, the set luminance Bpons and the light-room contrast Cb. This is the basic principle of the present invention.
As shown in
In the following, the embodiments in accordance with the present invention will be explained in detail by reference to the drawings. Throughout the figures for explaining the embodiments, the same reference numerals or symbols are used to designate functionally similar parts or portions in the above-explained prior art, and repetition of their explanation is omitted.
Embodiment 1
Wds(z) and Wrb(z) are a discharge space width and a barrier rib width, respectively, as measured in the width direction. The discharge space width Wds(z) and the barrier rib width Wrb(z) are functions of heights, that is, z coordinates. hds and hrb are a discharge space height and a barrier rib height, respectively, as measured in the height direction. An average discharge space width Wdsa is the discharge space width Wds(z) averaged over the discharge space height hds, an average barrier rib width Wrba is the barrier rib width Wrb(z) averaged over the barrier rib height hrb, and hph is a thickness of the phosphor layer. In the prior art, the average barrier rib width Wrba is selected to be as narrow as possible, and usually is 0.06 mm or less.
The following explains differences between Embodiment 1 shown in
To increase the ultraviolet ray production efficiency, the Xe proportion aXe of the discharge gas is selected to be 10% or more, 15% or more, 20% or more, or 50% or more according to desired individual specifications. As the Xe proportion aXe of the discharge gas is increased, the ultraviolet ray production efficiency is increased, and the discharge voltages of the reset discharge, the address discharge, and the display discharge are also increased. By taking the above into account, the optimum practical conditions are selected. If the increases in those discharge voltage are permissible, it is possible to use an approximately pure Xe gas (aXe≈100%) positively.
Moreover, the display electrode gap Wgxy is selected to be as great as possible. As a result, the display discharge voltage Vs, more specifically the maximum applied display-discharge voltage Vsemax or the display-discharge dc power supply voltage Vsdc, are selected to be 200 V or more, 220 V or more, 240 V or more, or 260 V or more according to desired individual specifications. However, due to the limitations imposed by the withstand voltages of device structures and their materials, the allowable display discharge voltage Vs is equal to or lower than 1000V.
As described above, the display discharge voltage Vs are increased, and consequently, the display-electrode area Sse in the discharge cell can be reduced, and therefore the light-room contrast can be improved.
First, as in the above discussion (A4), an example of the present embodiment will be explained in terms of the display region surface reflectance β.
Here, in the plasma panel, a surface from which visible light for display is irradiated is called the display surface, and a space into which the visible light for display is irradiated from the display surface is called the viewing space. A space containing plural discharge cells arranged continuously is called the display space, and a projection of the display space onto the display surface is called the display region Rp. The display region surface reflectance β is a ratio averaged over the display region Rp, where white light is entered into the display region Rp from the viewing space, and the ratio is the energy of light emitted from the display region Rp divided by the energy of the incident white light.
In this embodiment, it is desired to satisfy the following inequality:
0.02≦β≦0.2
For improvement of the light-room contrast, it is preferable to make the display region surface reflectance β smaller, but if the display region surface reflectance β is selected to be excessively small, the display luminance itself is lowered, and therefore β is selected to be in the above range.
As will be described later, when reduction in the display region surface reflectance β is realized by reducing the display discharge region area ratio Sd/Sp, or increasing a black region area ratio Sb/Sp, there is a practical lower limit to the display region surface reflectance β, and the above range for the display region surface reflectance β is a practical range. The more preferable range for the display region surface reflectance β is from 0.1 to 0.15.
Next, as in the above discussion (A4), another example of the present embodiment will be explained in terms of the display discharge region area ratio Ad, for improving the light-room contrast by the display region surface reflectance β.
When an area of the display region Rp is Sp, a discharge space used for display is called a display discharge space, a projection of the display discharge space onto the display surface is called the display discharge region, a collection of the display discharge regions in the display region Rp is called a display discharge region collection Rd, an area of the display discharge region collection Rd is Sd, it is desired to satisfy the following inequality:
0.05≦Ad≦0.4,
where the display discharge region area ratio Ad=Sd/Sp.
If the area Sd of the display discharge region collection Rd is selected to be excessively small, the light emission luminance becomes too low for the display device to function. If the sustain discharge voltage Vs is selected to be sufficiently high, the display discharge region area ratio Ad can be reduced accordingly. In a case where a practical range for the sustain discharge voltage Vs is expressed by
200 V≦Vs≦1000 V,
a practical range for the display discharge region area ratio Ad is expressed by
0.05≦Ad≦0.4.
Consequently, the display region surface reflectance β can be controlled within the above range. The more preferable range for Ad is from 0.2 to 0.3.
A projection of the discharge cell onto the display surface is called the cell region, and in at least some of the plural discharge cells, and a region other than the display discharge region in the cell region is called a non-display discharge region. When white light is entered into the non-display discharge region from the viewing space, the ratio of the energy of light emitted from the non-display discharge region to the energy of the incident white light may be made 0.2 or less. It is desirable to make the ratio as small as possible, and the practical range for the ratio is from 0.02 to 0.2 in view of the processing temperatures (usually a heat treatment of about 500° C.) and material costs.
The maximum applied display-discharge voltage Vsemax, the display-discharge dc power supply voltage Vsdc, the display discharge region area ratio Ad, and the display region surface reflectance β are selected depending the Xe proportion aXe of the discharge gas and dimensions of the cell structure such as display electrode gap Wgxy.
To realize the above-explained reflectance in the above-mentioned non-display discharge region concretely, in at least some of the discharge cells, the average barrier rib width Wrba is selected to be 0.1 mm or more, 0.15 mm or more, or 0.2 mm or more according to desired individual specifications.
Further, to make the display region surface reflectance β as small as possible, the barrier ribs or barrier rib tops (ends of the barrier ribs on their viewing space sides, i.e. their display-surface-sides) are made of black material, or black layers (usually called black stripes or a black matrix) in the form of and in register with the barrier ribs are provided in spaces displaced toward the viewing space from the barrier ribs. Here the black material and the black layers means material and layers exhibiting the surface reflectance of the above-mentioned values.
Next, another example of the present embodiment which has achieved the above-specified values of the display region surface reflectance β will be explained in terms of the black region area ratio.
Provided in at least some of the plural discharge cells are black regions in which, when white light is entered into the display surface from the viewing space, the ratio of the energy of light emitted from the display surface to the energy of the incident white light is equal to or smaller than 0.2. The black region area ratio Ab satisfies the following inequality:
0.95≧Ab≧0.5,
where
Ab=Sb/Sp,
Sp is an area of the display region Rp,
Rb denotes a collection of the black regions in the display region Rp, and
Sb is an area of the black region collection Rb in the display surface.
If the area Sb of the black region collection Rb is selected to be excessively large, the light emission luminance becomes too low for the display device to function. If the sustain discharge voltage Vs is selected to be sufficiently high, the black region area ratio Sb/Sp can be increased accordingly. In a case where a practical range for the sustain discharge voltage Vs is expressed by
200 V≦Vs≦1000 V,
a practical range for the black region area ratio Sb/Sp is expressed by
0.95≧Sb/Sp≧0.5.
The more preferable range for the black region area ratio Sb/Sp is from 0.7 to 0.8.
In this case also, when white light is entered into the black region, the smaller the ratio of the energy of light emitted from the black region to the energy of the incident white light, the better. However, the practical range for the ratio is from 0.02 to 0.2 in view of the processing temperatures (usually a heat treatment of about 500° C.) and material costs.
The following will explain another example of the present embodiment for realizing the above-specified values of the display region surface reflectance β, in which, in at least some of the discharge cells, there are provided a white region RW having a high surface reflectance to white light when viewed from the viewing space and a black region RB having a low surface reflectance to the white light when viewed from the viewing space, and the following conditions are satisfied.
Initially the reflectance is defined as follows: When white light is entered into the display surface from the viewing space, the reflectance is the ratio of the energy of light emitted from the display surface to the energy of the incident white light.
In the present embodiment, at least some of the plural discharge cells are provided with a black region having the reflectance equal to or smaller than 0.5×βmax, where βmax is the maximum of the reflectances in said at least some of the plural discharge cells, and the following conditions are satisfied.
Here, a space containing plural discharge cells arranged continuously is called the display space, a projection of the display space onto the display surface is called the display region Rp, an area of the display region Rp is Sp, a collection of the black regions RB in the display region Rp is denoted by Rb, and an area of the collection Rb of the black regions RB in the display surface is represented by Sb. The black region area ratio Ab=Sb/Sp is selected to satisfy the following inequality:
0.95≧Ab≧0.5
If the area Sb of the black region collection Rb is selected to be excessively large, the light emission luminance becomes too low for the display device to function. If the sustain discharge voltage Vs is selected to be sufficiently high, the black region area ratio Sb/Sp can be increased accordingly. In a case where a practical range for the sustain discharge voltage Vs is expressed by
200 V≦Vs≦1000 V,
a practical range for the black region area ratio Sb/Sp is expressed by
0.95≧Sb/Sp≧0.5.
The more preferable range for the black region area ratio Sb/Sp is from 0.7 to 0.8.
For a high-contrast display, it is desirable to make the black region area ratio Ab as small as possible, but its actual value is selected depending upon the Xe proportion aXe of the discharge gas, dimensions of the cell structure such as display electrode gap Wgxy, and the desired luminance value.
Embodiment 2
First, in the present embodiment, the barrier ribs are in the form of boxes. That is to say, the lengthwise directions of the barrier ribs extend in at least two directions DR1 and DR2, which are aligned with the arrows D1 and D2, respectively, in
In at least some of the discharge cells, the average barrier rib width Wrba of the barrier ribs with their lengthwise directions aligned in at least one of the above-explained two directions DR1, DR2 are selected to be 0.1 mm or more, 0.15 mm or more, or 0.2 mm or more according to desired individual specifications.
Another feature of the present embodiment is that a pair of display discharge electrodes (the X and Y electrodes) are arranged such that their major surfaces face each other. That is to say, the Y electrodes 230 and the Y bus electrodes 250 are disposed on the front glass substrate 21, and the X electrodes 220 are disposed on the rear glass substrate 28 to face the Y electrodes 250 spaced in the height direction from the X electrodes 220. The X electrodes X 220 disposed on the rear glass substrate 28 does not need to transmit visible light, and does not always need to be transparent electrodes. Both the X and Y electrodes are covered with the dielectric 26 and the protective film 27. The phosphors 32 are coated on the sidewalls of the barrier ribs 31 only, but not on the protective films 27 covering the X and Y electrodes. In
By arranging the display electrode pair opposite one another across the discharge space in this way, one (the X electrode) of the display discharge electrode pair and the display electrode gap Wgxy do not need to occupy portions of the display region. That is to say, the display discharge region area Sd becomes smaller, and therefore the display discharge region area ratio Ad can be reduced. Consequently, the display region surface reflectance β can be reduced easily.
As explained in connection with
The discharge space height h is realized by the structure explained below, for example. The z axis is drawn in the direction of the height of the plasma panel. When zX is the z-axis coordinate of the X electrode which is one of the display electrode pair, zY is the z-axis coordinate of the Y electrode, the absolute value |zY−zX| of a difference between the z-axis coordinates zX and ZY needs to be selected to be 0.2 mm or more, 0.4 mm or more, 0.6 mm or more, or 1.0 mm or more according to desired individual specifications.
Further, when the discharge space height h is increased, the discharge space aspect ratio Adsas=h/Wdsa also increases. When the discharge space aspect ratio Adsas is increased, visible light generated by the phosphors 32 enters the viewing space after multiple reflections by the surfaces of the phosphors 32 or the surfaces of the protective film 27 on the rear substrate (or the surface of the dielectric 26 on the rear substrate). Therefore it is necessary for effective utilization of the visible light to increase the surface reflectance of the surfaces of the phosphors 32 or the surfaces of the protective film 27 on the rear substrate (or the surface of the dielectric 26 on the rear substrate), and this surface reflectance is called the non-aperture-surface surface reflectance.
The non-aperture-surface surface reflectance is usually about 60%, and it is preferable to select the non-aperture-surface surface reflectance to be 80% or more, or 90% or more according to desired individual specifications. The greater the discharge space height h is selected to be, the higher the non-aperture-surface surface reflectance needs to be.
The non-aperture-surface surface reflectance is defined as follows. In the discharge cell, the solid wall surrounding the display discharge space is called the inner surface of the display discharge space, a portion of the inner surface of the display discharge space from which the visible light for a display is emitted into the viewing space is called the aperture surface, and a portion of the inner surface of the display discharge space other than the aperture surface is called the non-aperture-surface. The non-aperture-surface surface reflectance is defined as a surface reflectance of the non-aperture-surface averaged over the non-aperture-surface.
The present invention is capable of realizing a plasma display device having a high set-luminous-efficacy (i.e. producing a high-brightness display image at a low power consumption) and exhibiting a high light-room contrast.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-193765 | Jul 2003 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20040061669 | Kang et al. | Apr 2004 | A1 |
| 20040196216 | Shindo et al. | Oct 2004 | A1 |
| Number | Date | Country |
|---|---|---|
| 8-329843 | Dec 1996 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20050007308 A1 | Jan 2005 | US |
