WO2008104229A1

WO2008104229A1 - Arrangement and method for backlighting a display device

Info

Publication number: WO2008104229A1
Application number: PCT/EP2007/051935
Authority: WO
Inventors: Andreas Huber; Oskar Schallmoser; Pavel Peka
Original assignee: Patent-Treuhand-Gesellschaft für elektrische Glühlampen mbH
Priority date: 2007-03-01
Filing date: 2007-03-01
Publication date: 2008-09-04

Abstract

The invention relates to an arrangement for backlighting a display device having a plurality of semiconductor light sources (Dl.l.l|-Dn.3.3) disposed in matrix elements (l.l-n.3), wherein the matrix elements are actuated using operating devices (Bl-Bn), and one or more operating devices are provided for supplying the matrix elements of a column of the matrix, and wherein one or more switching elements are provided in each line of the matrix, with a switching element being associated with one or more matrix elements of a line.

Description

description

Arrangement and method for backlighting a display device.

Technical area

The invention relates to a spatial and elekt ^¬ cal arrangement for backlighting a Anzeigevor- direction such as an LCD display. The invention also relates to an operating ^{method of} this arrangement.

State of the art

More recently, the LCD display is increasingly used in all areas of daily life. Especially applications that used to be tubes (CRTs - Cathode Ray Tubes) are now equipped with LCDs. Two ty ^¬ european applications are computer monitors and Fernsehgerä ^¬ te.

LCD displays are known to be relatively slow in image design. The switching speed of the pixels in an LCD display is in the ms range. In applications with moving images, eg video monitors or televisions or computer screens with fast games, slow blurring results in motion blur, which makes the picture appear blurred and unattractive. This is reinforced by the nature of the image on ^¬ superstructure of LCD displays. A pixel does not have to be controlled permanently, but it retains its color for the rest of the Bilddarstellungs- after one-time control time at. Therefore, LCD displays do not rebuild every image, but they rebuild it. That is, the pixel does not turn black between two images, but it is switched directly from the current color to the new color.

In order to improve the image quality, in GB 2 409 754, the cold cathode lamps (CCFL) of the backlighting were switched on at the rate of the frame rates and the illumination level of the image display was adapted. In addition, each image to its brightness ^¬ distribution is analyzed and adjusted the backlighting this brightness level. This means that if there are dark spots in the picture, then the lamp that is in this position will be dimmed or switched on for a shorter time in order to increase the contrast.

In order to dim the lamps individually, a separate control gear is provided for each lamp. Thus, if the backlighting device has 8 cold cathode lamps, ie if there are 8 areas in which the brightness can be regulated individually, then the device also requires 8 operating devices in order to operate the lamps.

However, this backlighting device has a serious disadvantage. Since the CCFL's are quite long, they usually cover the entire width of the previous display. That is, it can always only whole Zei ^¬ len in brightness are changed, which is often not sufficient for a cor ^¬ rect playback.

Therefore, more recently semiconductor ^light sources such as LEDs are used as backlighting for display devices. In this case, the LEDs can be matrix-shaped be arranged, and thus significantly refine the representation of light and dark parts of the picture. Since the LEDs also have to be controlled individually, a separate operating device is required for each LED. If the backlighting device consists, for example, of 64 individual segments with one or more LEDs, 64 operating devices are necessary for their activation. This is very expensive and expensive.

task

The invention is therefore the object of the reciprocating terleuchtung a display device to be designed so that it is less consuming and more cost-effective herzustel ^¬ len. At the same time, a further improvement of the image quality is to be achieved.

Presentation of the invention

The object is achieved by an arrangement having the features of patent claim 1 and an operating method according to claim 15.

An arrangement is proposed in which the display surface is divided into a matrix field. The Matri ^¬ ze is organized into rows and columns. Each die element may contain one or more semiconductor light sources. Each column is provided by an operating ^device . Preferably, the operating device is designed as a DC-DC converter. Each row is terminated by a switching element that closes the circuit to ground. The switching element is preferably a MOSFET. With this arrangement, the backlighting of the display device is no longer uniform over the entire surface, but line by line in several stages.

The process is synchronized with the image structure, i. the line-by-line switching takes place completely within an image, also called a frame. In order to clarify the context, the following explanations are related to the representation of a television picture. In the case of the prevailing PAL system in Europe, the image is displayed at 50 frames / second (50 frames / sec), in the US NTSC system at 60 frames / second. This means that a complete backlighting cycle for displaying a PAL image takes 1/50 second (20 ms).

In one cycle, all rows are sequentially turned on, that is, each row is turned on for a period towards ^¬ away 20ms speaks the (l / number of rows) * ^¬ ent.

As long as the switching element is closed, the top row can be illuminated. The die elements, the ^¬ ser line can preferably be dimmed to various Hellig ^¬ keitsstufen then, which correspond to the brightness of the overlying image part. The brightness of the image section lying above the matrix element is calculated by the control unit and sent to the corresponding operating devices. These regulate the semiconductor light sources to the predetermined dimming level and thus adapt the backlighting to the content of the preceding image detail. After a predetermined time, the switching element Sl is opened and the switching element S2 is closed. Now the second line is illuminated. The process repeats until all lines have been traversed. This time span corresponds exactly to the time span in which an image is displayed on the display. Thus, once the display image ^¬ repetition rate of 50 frames / second, 50 crossings / second will take place accordingly in the backlighting. Thereafter, a new image is built on the display, and the operation of the matrix elements begins again at the first line. Since the process of a complete pass is very fast, the human eye can not resolve it, and the display area appears backlit at the same time.

The matrix elements are only set stale ^¬ tet preferred if the display is not realized in switching. This results in a clear and clear image, even with fast change of image content.

Various methods can be used for the regulation of the semiconductor light sources. Firstly, the Rege ^¬ development with a current feedback loop. Preferably, however, the control is used with an optical feedback loop. However, it is also possible to use only one converter with an impressed current.

Short description of the drawing (s)

Fig. 1 example of an inventive arrangement with the electrical interconnection of the semiconductor light sources.

Fig. 2 Schematic representation of the signal processing Fig. 3 flowchart of the operating method according to the invention

Fig. 4 switching example of a branch of the inventive ^¬ Shen arrangement with a Stromrückkoppelschlei- fe.

Fig. 5 switching example of a branch of the inventive ^¬ Shen arrangement with an optical feedback loop.

6 shows a switching example of a branch of the arrangement according to the invention with an additional diode in FIG

Load circuit.

Fig. 7, the driving method of the formwork Tele ^¬ elements with the resulting current through the operating device

8 shows an example of another method of driving the switching elements with the resulting current through the operating device

Fig. 9 Three-dimensional representation of the geometric arrangement of the die elements.

Fig. 10 sectional view of the inventive arrangement in various embodiments.

Fig. 11 Electrical arrangement of the die elements.

Fig. 12 Various possible geometric arrangements of the die elements. Fig. 13 operating method of the LEDs in multi-color illuminated matrix elements.

Preferred embodiment of the invention

First embodiment

Fig. 11 shows the basic organization of the matrix elements in rows r and columns c. The elements are numbered, the first digit denotes the column, the second the row. Element 11 is therefore the first element. Element 32 denotes e.g. the third element in the second line, ie column 3, line 2.

Fig. 1 shows the electrical interconnection of the die elements. Each die element contains one or more monochrome or white light emitting semiconductor light sources. In order to identify the installation location of the semiconductor light sources, these are then numbered with a third digit. Di.i.3 is thus the third semiconductor light source of the first matrix element. Preferably, white-emitting light-emitting diodes are used. However, other semiconductor light sources such as OLEDs can also be used. Each column is supplied by a supply unit (Vi ... Vg) which contains at least one operating device (Bl, B2, ..., Bn). In this embodiment, in which the matrix elements are illuminated with white-emitting semiconductor light sources, the supply unit contains exactly one operating device. Each line is switched on via a switching ^¬ element. The switching elements (Sl, S2, ..., Sm) are preferably MOSFETs. The operating devices are designed as DC-DC converters.

The backlighting cycle is now as follows. As long as the switching element Sl is closed, the top line lights up. The matrix elements of this line can preferably be dimmed to different brightness ^¬ gradual then that correspond to the brightness of the darü- berliegenden image part. The brightness of the image detail above the matrix element is calculated by the control unit and sent to the supply units (V ₁ ... V _g ). They govern the semiconductor light sources to the preset dimming and so adjust the backlighting of the content of the vorgela ^¬ siege to image section. After a predetermined time, the switching element Sl is opened and the switching element S2 is closed. Now the second line is operated. The process repeats until all lines have been traversed. Thereafter, a new image is built on the display, and the operation of the matrix elements begins again at the first line. Since the process of a complete pass is very fast, the human eye can not resolve it, and the display area appears backlit at the same time. The total time span ^¬ a run corresponds exactly to the period of time, in which an image is displayed on the display al ^¬ as a frame. If the display has a frame rate of 50 frames / second, then 50 passes / second take place accordingly in the backlighting device.

Usually not all Pi ^¬ xel be at an LCD display switched on simultaneously but in groups. There- in the case of the groups consist of several pixel lines, which go across the screen. The switching of the display is thus also in a line-based process, which goes through from top to bottom. This is contrary to the backlighting method according to the invention, since in this case the line by line backlighting of the display can always take place where the display is currently not being switched over. The matrix elements are thus only switched on where the display is not in switching. The switching phase of the display thus always runs in the dark. This results in a sharp and kla ^¬ res image even during fast changes of image content.

In order to dimming the semiconductor light sources precisely, a current control is necessary. Various methods can be used for the current regulation. First, the control with a current feedback loop, as shown in Fig. 4. In this case, the actual current is measured with ^{¬ means of} a measuring element Sh and entered again in the DC-DC converter. This compares the actual value with a predetermined value, and regulates the current accordingly.

The control is preferably used with an optical Rückkop ^¬ pelschleife. This comprises a lichtempfindli ^¬ ches semiconductor element such that the radiated from the element arranged in the Matrizen- semiconductor light sources can receive light. Preferably, the photosensitive semiconductor element is a photodiode. The forward voltage of the ^¬ ser photodiode changes according to light intensity. The flux voltage is again input to the DC-DC converter, which can then regulate to a predetermined light intensity. An exemplary arrangement is shown in FIG. 5 for two matrix elements of a column. Such an arrangement achieves the most accurate adjustment to the desired dimming level.

Another important detail is disclosed in FIG. Many high-performance light-emitting diodes have a very low reverse voltage due to the technology. But they are very susceptible to voltage surges, which can destroy them in the worst case. Therefore, a normal diode is preferably switched through in series to the LEDs to this at such a voltage peak to Schütting ^¬ zen.

Fig. 2 shows the schematic representation of Signalauf ^¬ preparation of the method according to the invention. The received signal from an external source, for example, by a computer-ter or a DVD player or a satellite-tenreceiver of is inputted to the control unit (100) of the display device ^¬. The control unit is divided into a subunit for the display device, a buffer storing the data of an image, and a brightness analysis part (107). The latter undertakes a segment-by-segment brightness analysis per image and sends the brightness data together with a synchronization signal (V _sync ) to the backlight control unit (101). This consists of a memory for the entire brightness data, a phase locked loop and a logic (106) for driving the backlighting device. The column driver unit (104) with the Ver ^¬ supply units (Vi ... V _g) and the operating devices therein receives from the control unit each include a column current which corresponds to the current dimming value to which they are just driven Matrizen- dimming elements. The on and off times are set fixedly e- benfalls ^¬ from the control unit via the power profile. The row driver unit (105) switches the screened ^¬ de required line so that it is operated. The method of operation of the arrangement is now so (Fig. 3):

The method according to the invention runs in 2 control units

Parallel off. On the one hand in the brightness analysis part

(107), the so-called BAT. The BAT sends, as soon as a new image is built, the V _sync signal to the control ^¬ unit (101) of the backlight device (BLUC). As soon as the image memory is filled, the image content is analyzed and the brightness values in segments calculation ^¬ net. In the next step, they will be sent to the BLUC. Then a waiting loop is processed until a new image is created. Then the main ^{cycle is} over and the process begins again.

The procedure in the BLUC runs in two loops. Once in the outer main loop, which is traversed as per the BAT once per image. The inner loop is looped once per operation. For an image, the loop is thus traversed as many times as the backlighting device has lines. The matrix elements (1.1 ... nm) are switched through line by line by making the corresponding line switch conductive. The switching elements (si ... S _n ) are organized in a row driver unit (105). Each matrices ^¬ element is operated by the control logic (106) ^pre-¬ added brightness. This is achieved by a corresponding set column current. After the time specified by the drive logic (106), the last line off the current line remains a ^¬ connected. This is done by making all switches except the current one. Then it will be

T (V _S ) is still waiting until the time ^ - has expired. m This is the mth part of the frame rate, where m is the number of lines. Thereafter, the loop is re-run. Thus, during the display of an image on the display all lines of the matrix on and off again. As soon as the next image is displayed, the process begins again.

The aforementioned operating method describes a method with overlapping column currents according to FIG. 7. A current can thereby be set which is formed from the sum of the two partial currents during the times in which both switches are switched on. FIG. 7a shows this by way of example for equal partial flows. Fig. 7b shows the current waveform illustrative of different ^¬ Lich large partial flows, in which corresponding Dimmstel ^¬ lungs are taken into account. These current curves must supply the operating device of the respective column, these being specified by the control logic (106).

However, it can pass a time gap between the ex ^¬ turn one cell and turning on the next cell. The circuit sequence is shown in FIG. 8. Fig. 8a again shows the current course with equally large partial flows, Fig. 8b shows the current profile for different partial flows according to the Dimmstel ^¬ ments. Since the screen layout in typical LCD displays and line-oriented ^¬ going on, switching through the line of the backlighting can be synchronized with the display. It should avoid advertising to that the area in which the screen just makes a Su ^¬ alteration of the image content, is illuminated. For this purpose, the Vsync signal can be evaluated, which enables a line-by-line synchronization. As a result, a particularly sharp image reproduction is achieved, and otherwise visible blurring of the image is avoided.

In addition to the LEDs, photodiodes are also incorporated in the matrix, which measure the current light intensity. This measured value is in turn entered into the column driver (104). The measured value can also be entered into the control logic (106). Through this feedback loop, the LEDs can all be operated with a uniformly high current, which is necessary for a good life behavior.

The electrical and geometric arrangement of the die elements need not necessarily be the same. Fig. 12a shows an arrangement in which the geometric and the electrical arrangement is equal. In Fig. 12b, the first electrical element of each row is geometrically offset from the left by one column to the right. In Fig. 12c, the first electrical element of each row is geometrically offset from the right by one column to the left. In Fig. 12 e has the electrical arrangement dop ^¬ pelt as many columns as the geometric. This Kings ^¬ nen are always controlled two rows at a time, doubling the maximum image brightness. In Fig. 12f, the electrical arrangement has only half as many columns as the geometric, what supply units and thus ultimately saves equipment. This arrangement may be particularly advantageous in light-emitting diodes, which have a very high pulse strength, and the maximum power is limited only by the heat dissipation. Thus, the Bildhellig ^¬ ness can be kept the same at half the cost of operating devices with the diodes then be companies, with a more long break removal in which they can heat.

Fig. 12c is another variation of how the template elements can be geometrically arranged. In principle, any geometrical arrangement is conceivable as may result due to leakage ^¬ cleverly devised driving of many arrangements, a positive benefit.

The basic structure of the arrangement for backlighting a display device is shown in FIGS. 9 & 10. The die elements are disposed in ^¬ a frame which is mounted behind the display device, eg a display. To avoid over-coupling to the neighboring matrix elements are between the matrix elements opaque walls is ^¬ done. The walls may be configured in various ways, as shown in FIG. 10. Above the frame, a diffuser is mounted to even out the radiated light. The walls may thereby, as shown in FIG. 10, be straight and to the diffuser rei ^¬ chen. As a result, they may be visible as disturbing dark streaks in the image of the display. To avoid this, a certain distance between the diffu- is sorplatte and left walls, respectively, as ^¬ leads in Fig. 10b. Instead of the straight walls, funnel shaped structures are used. This is insbesonde ^¬ re useful when only a few semiconductor light sources are used per array element, and so the Platzbe ^¬ may be low. These structures can analogously again extend to the diffuser plate, as shown in Fig. 10c Darge ^¬ provides. But you can also have a distance to the diffuser plate to achieve a more uniform radiation, as shown in Fig. 10d.

The die elements may be operated such that for each image segment, the matrix element illuminated, the suitable brightness is calculated, and the entspre ^¬ sponding female mold is then dimmed on this brightness. This is done for each matrix element in the whole matrix for each frame.

Since the human eye usually concentrates on the image content in the middle of the image, the backlighting can also be made less complicated and thus more cost-effective. For this purpose, the individual brightnesses are calculated only for the matrix elements in the middle of the image content. The outer elements form a ring, a kind of frame around the middle elements. This variant is shown in FIG. 12 f. They are operated together and brought to only one dimming position, the z. B corresponds to the average brightness of all inner matrix elements. This value is a simple way to calculate the Helligkeitsana ^¬ lyseteil (107) since the middle brightness of the inner matrix elements are present and must take place only a mean value calculation of all these magnitudes. However, other suitable methods for image brightness determination can also be used. This can be computing power and also Circuit costs are saved, since the matrix elements of the outer columns and proportional elements of the outer rows are combined into one group and can be operated with ei ^¬ ner supply unit.

Second embodiment

The structure of the arrangement in the second embodiment is similar to that of the first embodiment. Therefore, only the differences from the first embodiment will be described.

In the first embodiment, it was assumed that the matrix elements are equipped with single-color LEDs. In this embodiment, several differently colored LEDs are used for a matrix element. This has the advantage that different light colors can be realized for the backlight device. A Matritzenelement can be equipped with three different ver ^¬ colored LEDs, for example, a red, a green and a blue. These can be operated individually with a given brightness. This can represent a large color space. Different color temperatures can be realized, eg 4000K, 5000K and 6000K.

The invention is not limited to the use of three different colored LEDs. For example, it is also possible to use five different-colored light-emitting diodes in order to additionally expand the displayable color space. For the implementation of this embodiment j operating devices are required per die element j, where j is the number of differently colored semiconductor light sources. A supply unit therefore contains j operating devices. The control logic (106) must therefore set the corresponding current conditions for the light-emitting diodes depending on the light color, so that this light color is also achieved. The light-emitting diode current corresponds de ^¬ ren performance, and depending on the power of different colored light emitting diodes each other, a desired light color and thus color temperature can be adjusted.

In the preferred embodiment, each Matrizen ^¬ element has an optical feedback. In order to regulate the Lichtfärbe ge ^¬ precisely, it is necessary to control each of the individual different colored LEDs individually in their performance. In order to measure the power, and thus the amount of light emitted, the differently colored light-emitting diodes are operated so that only one of the light-emitting diodes lights up at a certain time, as shown in FIG. 13 for three different light-emitting diodes. During the short time that only one LED is lit, its light intensity can be measured and then regulated to a desired intensity. This makes it possible to precisely regulate the light color of the matrix element.

Third embodiment The third embodiment is based on the second embodiment. Therefore, only the differences from the second embodiment will be explained.

The third embodiment is not limited to the reproduction of the color temperature for a display backlight. This embodiment actively supports the display (102) in color representation by adjusting the color of the backlighting in the corresponding matrix elements to the color of the currently displayed image content. Thus, the dynamic range of the color representation of the entire unit of display (102) and backlighting (103) can be significantly expanded. In order to achieve this, the brightness analysis unit (107) must calculate not only the average brightness of the image content ahead of the corresponding matrix element, but also its color. The control logic (106) controls the output of the differently colored LEDs then so that by the control unit counted he ^¬ color is generated in the corresponding matrix element. The fact that the resolution of the matrix for backlighting is significantly smaller than the resolution of the display can lead to the display of false colors, since the backlighting is no longer white.

This can be avoided by the brightness analysis unit (107) taking into account the color information sent to the control logic (106) and sending it to the LCD control part of the control unit (100). The Ansteu ^¬ erteil can control the display so that the addition of the backlighting color and the pixel color of the display together give the desired color to be displayed.

Claims

claims

An arrangement for backlighting a display device with a matrix, which is divided into columns (1 ... n) and rows (1 ... m), with a plurality of matrix elements (11, 12, .., nm), in those one or more semiconductor light sources

(1.1.1, 1.1.2, ..., nml) are arranged, wherein the matrix elements with supply units (Vi ... Vg) are controlled, characterized in that a supply unit (Vi ... V _g ) for the Ver - Supply of at least two die elements of a column of the die is provided, and each row is completed with a switching unit is wherein each switching unit at least two Matrizen ^¬ elements that are not supplied by the same supply unit (Vi ... V _g ) on a on the Common ^¬ mes potential.

2. Arrangement for backlighting a display device according to claim 1, characterized in that each supply unit (Vi ... V _g ) can comprise a plurality of operating devices (Bl ... Bn) for supplying the semiconductor light sources.

3. Arrangement for backlighting a display device according to claim 1 or 2 with a plurality of a Matrizenelement associated semiconductor light sources ^{zusammenge ¬} in series to a branch are switched, characterized in that ge to each series-connected branch of semiconductor light sources, an additional diode in series ^{¬ is} switched.

4. Lighting device according to claim 1, 2 or 3, characterized in that the geometric An ^¬ order of the matrix elements has the same number of columns and rows as the electrical arrangement.

5. Lighting device according to claim 1, 2 or 3, characterized in that the matrix elements of a row are arranged in ascending order from left to right.

6. Lighting device according to claim 4, characterized in that the geometric arrangement of the die elements is equal to the electrical arrangement.

7. Lighting device according to claim 5, characterized in that the geometric arrangement of the die elements is designed so that the first electrical matrix element of the line m is geo ^¬ metric at position m, and the element, which is located electrically at position nm, geometrically first place of the line is arranged.

8. Illumination device according to claim 5, characterized in that the geometric (ab) and the electrical (nm) arrangement of the Matrizenele ^¬ elements as follows correlate: The electrical Zei ^¬ lennummer m is equal to the geometric line number b. The electrical column number n is calculated as n = a + b-1 if a + b-1 is less than or equal to the maximum number of columns a _max , otherwise n is calculated as n = a + bla _max .

9. Lighting device according to claim 1, 2 or 3, characterized in that the geometric arrangement of the ^array elements ^¬ is designed so that two or more geometric lines correspond to an electrical line.

10. Lighting device according to claim 1, 2 or 3, characterized in that the geometric arrangement of the die elements is designed so that two or more electrical lines are arranged in a geometric row.

11. Lighting device according to claim 1, 2 or 3, characterized in that the geometric arrangement of the die elements is designed so that two or more electrical columns are arranged in a geometric line.

12. Lighting device according to claim 1, 2 or 3, characterized in that the geometric arrangement of the die elements is designed so that the inner geometric die elements are covered with an electrical matrix according to one or more of the preceding claims, and the outer die elements, the frame to form the inner Matrizenelemente be supplied with a zu ^¬ additional control gear.

13. Lighting device according to claim 10 or 11, characterized in that the two or more electrical lines or columns per geometric line are formed of different color illuminated semiconductor light sources.

14. Lighting device according to claim 1, 2 or 3, characterized in that the electrical and the geometric position can be in any relation to each other.

15. A method for operating a backlighting device for backlighting a display device, said backlighting device is divided into a matrix and the matrices ^¬ elements include one or more semiconductor light sources, characterized in that a ^¬ individual matrix elements of a row different ^¬ Lich light and / or can emit light of a different color, wherein the matrix is driven row by row, and the rows are switched so quick succession that the menschli ^¬ chen eye it appears the entire surface as illuminated ^¬.

16. A method for operating a backlighting device according to claim 15, marked thereby, that a passage of the line by line switching ^¬ happens within a time that corresponds to the display time of an image of the display device.

17. A method for operating a backlighting device according to claim 15, characterized in that the lines of the backlighting device are turned on only when no switching of the image content takes place at the relevant point in the display.

18. A method for operating a backlighting device according to any one of claims 15-17, characterized in that two or more lines can be operated simultaneously.

19. A method for operating a backlighting device according to any one of claims 17-18, characterized in that the image structure and the backlighting of the display are synchronized with each other in a manner that ensures that the display area in which just a switching of Image content does not take place ^¬ lights.

20. A method for operating a backlighting device according to one of the preceding claims, characterized in that the light output of the semiconductor light sources of the individual matrix elements is measured with a sensor and is input again into the operating device as an input variable.

21. A method for operating a backlighting device according to claim 20, characterized in that the sensor is a photodiode.

22. A method for operating a backlighting device according to claim 20 or 21, character- ized in that all the sensors of an electric ^¬ cal column are connected in parallel.