RU2319991C1 - Liquid-crystalline display - Google Patents

Abstract

FIELD: electromagnetic protection, in particular, electromagnetic protection of electronic devices, and may be used during engineering of liquid-crystalline displays.

SUBSTANCE: liquid-crystalline display is created with grounded conductive grid, having period of cells within range from 50 to 150 millimeters, positioned inside the illumination block and ensuring efficient screening of electromagnetic noise of liquid-crystalline displays within range of frequencies from 10 to 200 MHz without substantial damage to homogeneousness of illumination. In accordance to the invention, in liquid-crystalline display which includes body, liquid-crystalline light modulator which contains row and column controlling electrodes, illumination device, light source and diffuse plate, between the diffuse plate and the light source a metallic wire is positioned.

EFFECT: creation of a liquid-crystalline display, wherein a screening grid integrated in illumination device allows on one side to efficiently let through the light from illumination device, and simultaneously ensures electromagnetic safety of such a liquid-crystalline display.

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Description

The invention relates to the field of electromagnetic protection, namely, electromagnetic protection of electronic devices, and can be used in the design of liquid crystal displays (LCD).

It is known that electronic devices emit electromagnetic (EM) waves. Depending on the power, electromagnetic radiation (EMP) can affect the operation of surrounding electronic devices. Therefore, to prevent the harmful effects of spurious EMP, it is required to certify equipment according to the EM compatibility standard, for example, according to the FCC (US Federal Communications Commission) standard.

In particular, it is known that functioning LCDs are sources of spurious EMR. A typical LCD panel (FIG. 1.1) consists of an active matrix (AM) 1, a backlight (UP) device 2, and AM and UP control circuits connected to a power source (not shown). A typical UP in a large-format LCD panel may contain diffuse film 3, film 4, which improves brightness (BEF - brightness enhancement film), double film 5, which improves brightness (DBEF - dual brightness enhancement film), diffuse plate 6, lamps 7 (or LEDs ), reflector 8.

It is known that in a typical large-format LCD, the UP has a thickness of the order of several centimeters, and the control electrodes AM of the LCD are located quite far from the grounded rear plane of the UP. Such EM LCD protection is not effective enough for panels with a diagonal size of more than 30 inches, since the length of the horizontal and vertical electrodes is large, and when an electric field is applied to the AM, they begin to emit EM waves, which can affect the functioning of the surrounding devices. On the other hand, UE lamps (for example, widespread cold cathode lamps - CCFL), as well as UE and AM power boards can produce spurious EM noise during operation.

It is known that if the diffuse film is combined with a conductive network (see US Patent Application Laid-Open No. 20040004684 [1]), it is possible to obtain a diffuser capable of damping the power of electromagnetic waves passing through it. However, this method is not effective enough if the mesh cell size does not correlate well with the range of shielded EM waves.

Closest to the claimed invention is a liquid crystal display having an electromagnetic protective element (see US patent 7030546 [2]), in which the problem of spurious EM coupling between the UP and AM LCD lamps is solved by introducing a diffuse plate containing a conductive screen that is grounded to the device . This system is selected as a prototype of the claimed invention.

The disadvantages of the above analogue and prototype of the claimed invention are the lack of data on the influence of mesh cell sizes on its shielding ability, as well as the complexity and high cost of manufacturing.

The objective of the claimed invention is the creation of an LCD, in which a shielding grid integrated in the UE allows one to efficiently transmit light from the UE on the one hand, and at the same time provides EM safety for such an LCD.

The technical result of the claimed invention is the creation of an LCD with a grounded conductive grid having a cell period in the range from 50 to 150 mm, located inside the UE and providing effective shielding of EM noise in the LCD in the frequency range from 10 to 200 MHz without significant damage to the uniformity of the backlight.

The invention consists in the development of an improved design of a liquid crystal display, including a liquid crystal light modulator, comprising horizontal and column control electrodes, a backlight device, a light source and a diffuse plate, in which a metal wire is placed between the diffuse plate and the light source

As a light source, either a lamp or an LED is used.

Regarding the characteristics of the metal wire, it has been experimentally established that for the optimal implementation of the claimed invention it is important that the metal wire has a transverse size in the range from 0.1 to 0.5 mm, while the metal wire can be made either by cutting from a sheet, or made by printing, or made by winding.

It is also important that the metal wire is located by segments that lie in the plane of the display parallel to one another at a distance of up to 150 mm.

It is also advisable that the metal wire was located in segments that lie in the plane of the display in the form of a rectangular grid so that part of the segments are parallel to one another and the lower case control electrodes of the display, and the rest of the segments are parallel to one another and the column control electrodes display, and all segments are located at a distance of 150 mm.

In the claimed design, attention should be paid to the fact that the metal wire is either in contact, or built into the diffuse plate, or glued to the diffuse plate.

It is also necessary that the metal wire be grounded.

For a better understanding of the present invention, the following is a detailed description thereof with corresponding drawings.

Figure 1 - traditional (view 1.1) and improved in this invention (view 1.2) LCD structures, where 1 - AM LCD, 2 - UP, 3 - diffuse film, 4 - BEF, 5 - DBEF, 6 - diffuse plate, 7 - lamps, 8 - reflector, 9 - grounded conductive wire.

Figure 2 - the estimated normalized measured envelope of EMR noise for a 46 "LCD panel and the estimated radiation efficiency of an ideal conductive antenna (all noise envelopes were measured for a linear vertical monopole antenna and an estimate was made of the power of the radiative efficiency in the vertical plane - the radiation spectrum was normalized to maximum radiation value), where

21 is a measured envelope of the spectrum of EMR noise from the LCD UP,

22 is a measured envelope of the spectrum of EMR noise from the control electrodes AM LCD,

23 - the total measured envelope of the spectrum of EMP noise from the LCD UP and the control electrodes AM LCD,

24 - calculated radiative efficiency of an ideal conductor,

25 is the relative spectral power distribution of spurious EMI noise from the LCD UP and AM LCD 23 multiplied by the calculated radiative efficiency of the ideal conductor 24.

Figure 3 is a grid model, where:

31 is a rectangular grid

32 - LCD matrix with control electrodes,

33 - grounded rear plane,

34 - UP lamp

35 is an equivalent noise generator simulating noise from the LCD control electrodes,

36 is an equivalent noise generator simulating noise from the LCD UP,

37 - radiation from lamps passing through AM LCD,

38 - frontal radiation from the control electrodes of the LCD,

a is the horizontal period of the grid,

b is the vertical period of the grid,

d1 is the distance from the grid to the plane of the LCD control electrodes,

d2 is the distance from the grid to the grounded rear plane of the LCD 33.

Figure 4 - spectrum attenuation of the grid in the vertical plane for different 20 sizes (vert. × horiz.) Cell grid (in relation to the radiation of the LCD panel without a grid), where:

41 - attenuation of radiation from AM LCD for a grid with a cell size of 200 × 285 mm,

42 - attenuation of radiation through AM LCD for a grid with a cell size of 200 × 285 mm,

43 - attenuation of radiation from AM LCD for a grid with a cell size of 100 × 140 mm,

44 - attenuation of radiation through AM LCD for a grid with a cell size of 100 × 140 mm,

45 - attenuation of radiation from AM LCD for a grid with a cell size of 50 × 70 mm,

46 - attenuation of radiation through AM LCD for a grid with a cell size of 50 × 70 mm,

47 — attenuation of radiation from and through the AM LCD for a grid with a cell size of 25 × 35 mm.

The wire mesh 9 shown in Fig.1.2, creates a blocking screen against EMI noise emitted by the lamp (or LED) UP, electrodes AM LCD, as well as power boards, control AM LCD and backlight. Also, grid 9 lowers the impedance of the control electrodes of the AM LCD, which as a result reduces the EMR from these electrodes.

The conducted EMR study of the noise of the LCD panel made it possible to estimate the noise spectrum of the emitted LCD panel and to compose an equivalent computer model that made it possible to select the parameters of the screening grid. In particular, computer calculation made it possible to evaluate the spectrum and radiative efficiency of a separately controlling electrode and UE for an LCD model with a diagonal of 46 inches. It is known that the radiative efficiency of LCD control electrodes is proportional to the gain of the equivalent conductive antenna monopole. Thus, the spectral gain in the vertical plane was calculated for a vertical antenna monopole having a length that corresponds to the height of the panel. Then the gain was converted to spectral emissivity and is presented in figure 2. Curves 21-25 in figure 2 are normalized to their own maximum values. The broadband spectral averaged noise described by envelope 21 is caused by CCFL UE lamps, which are considered to be conductors in the calculation. Further, the broadband spectral averaged noise described by envelope 22 is caused by the control electrodes of the LCD matrix. The time-averaged envelopes 21 and 22 of noise are added to the noise envelope 23. Further, the spectral power of the control signals supplied to the LCD and the UP panel 23 was multiplied by the radiative efficiency of the conductor 24 and the resulting envelope of noise 25 was obtained. Envelope 25 is associated with spurious noise, which can be eliminated by appropriate EMR shielding. At the same time, noise with an envelope of 25 is critical in the frequency range from 10 to 200 MHz and is characteristic of LCD panels of medium and large diagonal sizes, which is proved experimentally. Thus, the computer simulation performed reflects the general nature of EMR noise in LCD panels.

One way to protect the panel from spurious EMI is to use a mesh screen or mesh. Such a grid can be made in the form of linearly stretched wires (for example, as shown in Fig. 1.2) or in a rectangular form (see Fig. 3). The grid parameters are determined by the frequency range of the suppressed noise and the optical characteristics of the control unit, since the grid can reduce the aperture and uniformity of illumination.

The example shown in FIG. 3 illustrates the calculated attenuation produced by a rectangular grid, which is included in the LCD package with a diagonal size of 46 inches. The grid 31 has the following parameters: horizontal period a, vertical period b, wire diameter D (not shown), distance between the grid and the LCD control electrode d1, distance between the grid and the grounded plane of the LCD case d2. A grid 31 of wire having a diameter of D = 0.1 mm was located between the light source 34 and AM of the LCD 32 at a distance of d1 = 1 cm and d2 = 3 cm. The wire segments were parallel to the vertical and horizontal electrodes of the LCD matrix, respectively. Further, using the computer simulation package NEC (Numeric Electromagnetic Currents), the grid parameters a and b were optimized.

In this model, two main sources of EMR noise were used: 32 LCD control electrodes and 34 UP lamp (here, CCFL). The mentioned noise sources were equivalently modeled by the respective noise generators: the noise generator 35 was between the ground plane 33 and the LCD control electrodes 32, the noise generator 36 was between the ground plane 33 and the lamps 34. The noise spectrum 37 emitted by the UE and the noise spectrum 38 emitted by the electrodes LCDs correspond to curves 21 and 22 in FIG. 2, respectively.

The EMR noise level of the constructed LCD model with grid 31 was compared with the noise level of the LCD model without grid 31, and the difference, i.e. the attenuation coefficient of the grid was shown in FIG. 4, which shows the spectral attenuation coefficients of grids with different periods from 25 to 285 mm. Curve 41 corresponds to attenuation of radiation from AM LCD 38 by a grid with a 200 × 285 mm cell, curve 42 to attenuation of radiation 37 through AM LCD for a grid with a cell of 200 × 285 mm, curve 43 — attenuation of radiation 38 from AM LCD to a grid with a cell size 100 × 140 mm, curve 44 - attenuation of radiation 37 through AM LCD for a grid with a cell of size 100 × 140 mm, curve 45 - attenuation of radiation from AM LCD 38 for a grid with a cell of size 50 × 70 mm, curve 46 - attenuation of radiation 37 through AM LCD for a grid with a cell size of 50 × 70 mm, curve 47 - attenuation of radiation 37 from and through AM LCD for I have a mesh with a cell size of 25 × 35 mm.

Thus, it was found that a grid with a period of 50 to 150 mm (for both horizontal and vertical b periods) and a wire diameter D in the range of 0.1 to 0.5 mm is optimal in terms of the attenuation efficiency of the shielded EMR noise and ensuring the characteristics of UP LCD. So, the attenuation coefficient up to -10 dB is achieved in the range from 35 to 190 MHz, and the attenuation coefficient up to -20 dB is achieved in the frequency range from 55 to 120 MHz.

It is important to note that, in the case where the UE contains LEDs or other types of light sources, the grid is also an effective screen against the EMP emitted by such light sources.

Consider specific examples of the implementation of the claimed invention (Figure 3).

Example 1

In the LCD panel with a diagonal size of 46 inches (Samsung LTA46 model), which has a CCFL-based LED unit, a rectangular grid of metal wire with a diameter of D = 0.1 mm was grounded and grounded at a distance of 10 mm from the plane of the control electrodes of the AM LCD. The period between the wire segments was a = 285 mm and b = 200 mm located parallel to the horizontal and column electrodes of the LCD. The described grid provides shielding EMR noise to a maximum of -12 dB.

Example 2

In the LCD panel with a diagonal size of 46 inches (Samsung LTA46 model), which has a CCFL-based CB at a distance of 10 mm from the plane of the control electrodes of the AM LCD, a rectangular grid of metal wire with a diameter of D = 0.1 mm was stretched and grounded. The period between the wire segments was a = 50 mm and b = 70 mm, located parallel to the horizontal and column electrodes of the LCD. The described grid provides shielding of EMR noise to a maximum of -25 dB.

The technology is compatible with modern mass production technology of LCD and LCD UP. Mentioned mesh can be made by printing, winding wire, or cutting from a sheet of foil and then embedded in the LCD by gluing to a diffuse plate or embedding in UP LCD. The resulting grid is grounded to achieve maximum shielding effect of spurious EMP.

Although the above embodiments of the invention have been set forth to illustrate the present invention, it is clear to those skilled in the art that various modifications, additions and substitutions are possible without departing from the scope and meaning of the present invention disclosed in the attached claims.

Claims (11)

1. A liquid crystal display including a housing, a liquid crystal light modulator, comprising horizontal and column control electrodes, a backlight device, a light source and a diffuse plate, in which a metal wire is placed between the diffuse plate and the light source. 2. The liquid crystal display according to claim 1, characterized in that the light source contains a lamp. 3. The liquid crystal display according to claim 1, characterized in that the light source contains an LED. 4. The liquid crystal display according to claim 1, characterized in that the metal wire has a transverse dimension of from 0.1 to 0.5 mm. 5. The liquid crystal display according to claim 1, characterized in that the metal wire is located in segments that lie in the plane of the display parallel to one another at a distance of up to 150 mm. 6. The liquid crystal display according to claim 1, characterized in that the metal wire is arranged in segments that lie in the plane of the display in the form of a rectangular grid so that part of the segments are parallel to one another and the lowercase control electrodes of the display, and the rest of the segments are parallel to both one to the other, as well as columnar control electrodes of the display, and all segments are located at a distance of up to 150 mm. 7. The liquid crystal display according to claim 1, characterized in that the metal wire is made by cutting from a sheet. 8. The liquid crystal display according to claim 1, characterized in that the metal wire is made by winding. 9. The liquid crystal display according to claim 1, characterized in that the metal wire is in contact with or integrated into said diffuse plate. 10. The liquid crystal display according to claim 1, characterized in that the metal wire is glued to said diffuse plate. 11. The liquid crystal display according to claim 1, characterized in that the metal wire is grounded.

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