CN101093300A - Apparatus and method of driving backlight of liquid crystal display - Google Patents

Abstract

The present invention employs a technique for driving a backlight of a liquid crystal display capable of minimizing wave noise in a backlight using a light emitting diode as a light source. To this end, an apparatus for driving a backlight includes: a pulse width modulation signal phase shifting unit that shifts the phases of pulse width modulation signals for red, green, and blue according to the backlight type, thereby outputting the phase shifted pulse width modulation signals for red, green, and blue; at least one light-emitting diode driving unit, which drives the light-emitting diode array by using phase-shifted pulse width modulation signals for red, green, and blue; and a plurality of The light emitting diode arrays each include a plurality of light emitting diodes, and each light emitting diode is turned on by each pulse width modulation signal provided by at least one light emitting diode driving unit so as to emit red light, green light and blue light.

Description

Device and method for driving backlight of liquid crystal display

technical field

The present invention relates to a technology for driving the backlight of a liquid crystal display, in particular, to a driving device and method for a backlight of a liquid crystal display, which can minimize wave noise on a liquid crystal panel by using a light emitting diode (LED) as the backlight of a light source.

Background technique

In general, applications of liquid crystal displays (hereinafter simply referred to as "LCDs") have spread to office automation equipment, audio/video devices, and the like due to characteristics such as light weight, small size, and low power consumption. The LCD displays desired images by controlling light transmittance of light generated from a backlight according to image signals applied to a plurality of control switches arranged in a matrix.

LCDs are not self-emitting displays, and thus each LCD includes a light source such as a backlight disposed on the back of the LCD. Generally, fluorescent lamps are used as the backlight of the LCD. LCDs are classified into direct-lit LCDs and edge-lit LCDs according to the arrangement of backlights. Light emitting diodes (LEDs) have been widely used as backlights for small LCDs used in personal digital assistants (PDAs), mobile phones, notebook computers, and the like.

FIG. 1 shows an arrangement of a backlight in a liquid crystal display using light emitting diodes as the backlight according to the related art. That is, FIG. 1A shows the structure of an edge-lit backlight, in which an LED array 12 is formed on the side of a lining cavity 11 of a diffusing film. FIG. 1B shows the structure of a direct type backlight, in which an LED array 12 is formed on the rear surface of a lining cavity 11 of a diffusing film.

2 and 3 illustrate an arrangement of light emitting diodes used as a backlight in a liquid crystal display according to the related art. That is, FIGS. 2A and 2B show schematic diagrams of a backlight implemented by using a small number of high-power light emitting diodes. FIG. 3 shows a schematic diagram of a backlight implemented by arranging normal light emitting diodes in an array.

FIG. 4 is a block diagram of a driving circuit of a backlight according to the related art. As shown in FIG. 4 , the device for driving the backlight includes LED driving units 41R, 41G, and 41B, which respectively drive LED arrays 42R, 42G, and 42B, and the LED arrays 42R, 42G, and 42B are driven by slave light emitting diodes. The pulse width modulation signals provided by the diode driving units 41R, 41G, and 41B are turned on respectively, and emit red light, green light, and blue light. The operation of the device for driving the backlight having the above structure will be explained with reference to FIG. 5 .

The light-emitting diode drive units 41R, 41G, and 41B drive the light-emitting diode arrays 42R, 42G, and 42B for green, red, and blue in pulse mode, respectively, wherein the red light-emitting diode LED_R, the green light-emitting diode LED_G, and the blue light-emitting diode LED_B are respectively in series with each other.

In addition, as shown in FIG. 5 , the LED driving units 41R, 41G, and 41B perform dimming control in a pulse mode by pulse width modulation signals PWM_R, PWM_G, and PWM_B for red, green, and blue.

When the light-emitting diode driving units 41R, 41G, and 41B output the pulse width modulation signals PWM_R, PWM_G, and PWM_B for red, green, and blue to the light-emitting diode arrays 42R, 42G, and 42B, for red, green, and blue The pulse width modulation signals PWM_R, PWM_G, and PWM_B are synchronized and output as shown in Figure 5.

Therefore, the red light emitting diode LED_R, the green light emitting diode LED_G, and the blue light emitting diode LED_B are lighted by the red, green, and blue pulse width modulation signals PWM_R, PWM_G, and PWM_B supplied from the light emitting diode driving units 41R, 41G, and 41B, respectively. , thereby emitting red, green, and blue light components. The red, green, and blue light components are mixed to generate white light to be supplied to the rear surface of the liquid crystal panel.

Here, as shown in FIG. 5 , the pulse width modulation signals PWM_R, PWM_G, and PWM_B have periods in which the signals overlap with each other. When the three PWM signals PWM_R, PWM_G, and PWM_B for red, green, and blue overlap with each other, the frequencies generated from the light-emitting diode driving units 41R, 41G, and 41B affect the data lines of the liquid crystal panel, which will cause the data Distortion of line charging time. Wave noise is generated on the LCD panel due to the distortion of the charging time of the data line. In order to prevent wave noise from occurring on the liquid crystal panel, a method of changing the PWM dimming frequency of the light emitting diode driving units 41R, 41G, and 41B has been applied. However, this method is difficult to fundamentally eliminate wave noise. In addition, due to the small frequency range, it is difficult to effectively prevent the generation of wave noise.

Contents of the invention

Accordingly, an object of the present invention is to provide an apparatus and method for driving a backlight capable of eliminating wave noise by changing a phase of a pulse width modulation signal in the backlight of a liquid crystal display using light emitting diodes as a light source.

In order to obtain these and other advantages and in accordance with the purpose of the present invention, as described in detail and broadly herein, there is provided an apparatus for driving a backlight, comprising: Phases of pulse width modulation signals for red, green, and blue, so as to output phase-shifted pulse width modulation signals for red, green, and blue; at least one light-emitting diode driving unit, by using the phase-shifted pulse width modulated signals for red, green, and blue drive the array of light emitting diodes; and a plurality of arrays of light emitting diodes, each comprising a plurality of light emitting diodes, each light emitting diode being modulated by a respective pulse width provided by at least one light emitting diode drive unit The signal lights up to emit red, green, and blue light.

To achieve these and other advantages and in accordance with the objects of the present invention, as described herein in particular and broadly, there is provided a method of driving a backlight comprising: shifting the pulse widths for red, green, and blue according to the type of backlight modulating the phase of the signal and minimizing overlap in the phase-shifted pulse-width-modulated signals for red, green, and blue; and driving light by using the phase-shifted pulse-width-modulated signals for red, green, and blue, respectively diode array.

The above and other objects, features, aspects and advantages of the present invention will be apparent from the following detailed description of the present invention in conjunction with the accompanying drawings.

Description of drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description explain the principles of the invention.

In the picture:

1A and 1B are perspective views showing the structure of an edge-lit backlight and the structure of a direct-type backlight, respectively;

2A and 2B show schematic diagrams of backlighting implemented by high power light emitting diodes;

Figure 3 shows a schematic diagram of backlighting implemented by normal light emitting diodes;

4 is a block diagram of a backlight drive circuit according to the related art;

FIG. 5 is a waveform diagram of pulse width modulated signals for red, green, and blue;

6 is a block diagram of an apparatus for driving a backlight of a liquid crystal display according to an embodiment of the present invention;

7 is a waveform diagram of phase-shifted pulse width modulated signals for red, green, and blue;

8 is a waveform diagram of pulse width modulated signals for red, green, and blue whose phases are shifted according to the LED array; and

FIG. 9 is a waveform diagram of pulse width modulation signals for red, green, and blue whose phases are shifted according to the LED array and the pulse width modulation signals for red, green, and blue.

Detailed ways

Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.

FIG. 6 is a block diagram of an apparatus for driving a backlight of a liquid crystal display according to an embodiment of the present invention. As shown in FIG. 6, the device for driving a backlight according to the embodiment of the present invention includes: a pulse width modulation signal phase shifting unit 61, which is used to appropriately shift red, green, and blue pulse width modulation signals according to the backlight type The phases of PWM_R, PWM_G, and PWM_B thus output phase-shifted pulse width modulation signals; the light-emitting diode drive units 62R, 62G, and 62B are used to use the phase-shifted pulse width modulation signals PWM_R, green, and blue for red, green, and blue. PWM_G, PWM_B drive LED arrays 63R, 63G, and 63B, respectively; PWM_B is turned on respectively, thereby emitting red light, green light, and blue light.

Hereinafter, an apparatus for driving a backlight having the above structure will be described in detail with reference to FIGS. 6 to 9 .

The PWM signal phase-shifting unit 61 appropriately shifts the phases of the externally provided PWM_R, PWM_G, and PWM_B PWM signals for red, green, and blue according to the type of backlight, thereby outputting phase-shifted PWM signals. That is, the PWM signal phase shifting unit 61 shifts the phases of the PWM signals PWM_R, PWM_G, and PWM_B for red, green, and blue according to the values calculated for the side-light type and the direct-type backlight to provide the LED driving unit 62R , 62G, and 62B output phase-shifted pulse width modulation signals PWM_R, PWM_G, PWM_B.

The PWM signal phase shifting unit 61 can shift the phases of the PWM signals PWM_R, PWM_G, and PWM_B for red, green, and blue by various methods.

For example, when the backlight type is the side-light type as shown in FIG. 1A, in a liquid crystal display using light-emitting diodes as the backlight, as shown in FIG. 7, the pulse width modulation signals PWM_R, PWM_G for red, green, and blue , The phase of PWM_B is sequentially shifted by a predetermined angle, and then a phase-shifted pulse width modulation signal is output. At this time, the angles of the phase shifts of the pulse width modulation signals PWM_R, PWM_G, PWM_B for red, green, and blue are determined by overlapping Set for the computation of partial minimization conditions. For example, as shown in FIG. 7, the PWM_R signal for red is output like the related art, the PWM signal PWM_G for green is delayed by about 120° and then output, and the PWM signal PWM_B for blue is delayed About 240° and then output. The calculation is performed on the basis of waveforms of pulse width modulation signals PWM_R, PWM_G, PWM_B for red, green, and blue applied to light emitting diodes used in edge-lit backlights in the related art, whereby three pulse width modulation The overlap among the signals PWM_R, PWM_G, PWM_B can be minimized.

In addition, the backlight type is a direct type as shown in FIG. 1B. As shown in FIG. Phase-shifted pulse-width modulated signal for diode array. In addition, according to another embodiment of the present invention, as shown in FIG. 9 , the phases of the pulse width modulation signals of the LED arrays 63R, 63G, and 63B are sequentially shifted by a predetermined angle, and at the same time, for red and green The respective phases of the pulse width modulation signals PWM_R, PWM_G, and PWM_B of , and blue are sequentially shifted by a predetermined angle, and then a phase-shifted pulse width modulation signal is output. For example, as shown in FIG. 8, the phases of the pulse width modulation signals for the respective LED arrays 63R, 63G, and 63B are shifted by 120°, or as shown in FIG. The phase of the PWM signal is shifted by 120°, and the phases of the PWM_R, PWM_G, and PWM_B signals for each of red, green, and blue are shifted by 120° at the same time, and then the phase-shifted PWM signal is output. Therefore, as shown in FIGS. 8 and 9 , overlapping frequencies in the LED arrays 63R, 63G, and 63B and overlapping frequencies in the pulse width modulation signals PWM_R, PWM_G, PWM_B for red, green, and blue are minimized. Therefore, the influence of frequencies generated from the light emitting diode driving units 62R, 62G, and 62B on the liquid crystal panel data lines is minimized, and the distortion of the charging time of the data lines is minimized. Therefore, wave noise that occurs on the liquid crystal panel when the LED is applied to the backlight is minimized. Here the angle of the phase shift is determined by calculation based on the frequency waveforms of the LED arrays 63R, 63G, and 63B and the pulse width modulation signals PWM_R, PWM_G, and PWM_B for red, green, and blue, thereby minimizing the frequency overlap in . In addition, as shown in FIG. 2, when the backlight is realized by using high-power light-emitting diodes, although not shown in the figure, the phases of the pulse width modulation signals PWM_R, PWM_G, and PWM_B for red, green, and blue are similar to those of the above-mentioned embodiment. sequentially offset by a predetermined angle

As shown in FIG. 3, when the backlight is realized by arranging normal light-emitting diodes into an array, although it is not shown in the figure, the phase shift of the pulse width modulation signal of each light-emitting diode array 63R, 63G, and 63B is predetermined. Angle and output a phase-shifted pulse-width modulated signal like the above embodiment.

In addition, the LED driving units 62R, 62G, and 62B drive the LED arrays 63R, 63G, and 63B in a pulse mode by using phase-shifted pulse width modulation signals PWM_R, PWM_G, and PWM_B for red, green, and blue. , in the light emitting diode arrays 63R, 63G, and 63B, the red light emitting diode LED_R, the green light emitting diode LED_G, and the blue light emitting diode LED_B are each connected in series with each other.

Therefore, as mentioned above, the phases of the PWM signals PWM_R, PWM_G, PWM_B are shifted according to the PWM signal, LED array, or their mixed type according to the backlight type, and the phase-shifted PWM signal is output, thereby effectively effectively eliminate wave noise. Therefore, the frequency range of the obtainable pulse width modulated signal is increased compared with the related art. That is, when compared with the related art method of only changing the PWM dimming frequency to minimize wave noise, the frequency margin increases because the frequency that can be changed according to the PWM signal or the LED array is wider according to the embodiment of the present invention. .

In addition, when the method according to the embodiment of the present invention is applied, the method of changing the PWM dimming frequency according to the related art may be applied. In this case, the margin of the PWM dimming frequency is also increased twice that of the related art (for example, ±10Hz→±20Hz).

As described in detail above, according to the embodiment of the present invention, by shifting the phase of the PWM signal used as the driving signal of the LED according to the backlight type, according to the PWM signal, the LED array, or a combination thereof, the phase of the PWM signal can be effectively eliminated. Wave noise thus outputs a phase-shifted pulse-width modulated signal in a backlight that uses light-emitting diodes as a light source in a liquid crystal display.

In addition, since wave noise can be effectively eliminated, the frequency margin of the PWM signal can be increased to twice that of the related art.

The present invention can be implemented in various forms without departing from the spirit or essential characteristics thereof. It should be understood that the above-described embodiments are not limited by any details described above, unless expressly stated otherwise, to be construed broadly within the spirit and scope of the appended claims, and all that falls within the claims and their equivalents accordingly Changes and modifications within the bounds and scope are intended to be embraced by the appended claims.

Claims (10)

1. A device for driving a backlight, comprising: The pulse width modulation signal phase shifting unit shifts the phases of the red, green, and blue pulse width modulation signals according to the backlight type, so as to output the phase shifted red, green, and blue pulse width modulation signals; at least one LED driving unit for driving the LED array by using phase-shifted pulse width modulation signals for red, green, and blue; and A plurality of light emitting diode arrays, each including a plurality of light emitting diodes, each light emitting diode is turned on by a respective pulse width modulation signal provided by at least one light emitting diode driving unit to emit red light, green light and blue light. 2. The device according to claim 1, characterized in that, When the backlight type is an edge-lit type, the pulse width modulation signal phase-shifting unit applies pulse widths for red, green, and blue to the edge-lit type backlight according to pulse width modulation signals for red, green, and blue The phases of the PWM signals for red, green, and blue are shifted on the basis of the frequency waveform of the modulating signal so that the overlapping portion of the PWM signals for red, green, and blue is minimized, and then the PWM signal The phase-shifting unit outputs phase-shifted pulse width modulation signals for red, green, and blue. 3. The device of claim 1, wherein: When the backlight type is a direct type, the pulse width modulation signal phase shifting unit shifts the pulse widths for red, green, and blue on the basis of the frequency waveform applied to the LED array of the direct type backlight according to the LED array The phase of the signal is modulated so as to minimize frequency overlap in the LED array, and then the PWM signal phase-shifting unit outputs phase-shifted PWM signals for red, green, and blue. 4. Apparatus according to claim 1 or 3, characterized in that When the backlight unit is a direct type, the pulse width modulation signal phase shifting unit is applied to the direct type backlight according to the pulse width modulation signals for red, green, and blue. Shifts the phases of the PWM signals for red, green, and blue on the basis of the frequency waveform so that the overlapping portion of the PWM signals for red, green, and blue is minimized, and then the PWM signal is phase-shifted by the unit Outputs phase-shifted PWM signals for red, green, and blue. 5. The device of claim 1, wherein: When the backlight is implemented by using high-power light-emitting diodes, the pulse width modulation signal phase shifting unit is used for red, green, and blue of the high-power light-emitting diodes according to the pulse width modulation signals for red, green, and blue. The phases of the PWM signals for red, green, and blue are shifted on the basis of the frequency waveform of the PWM signal so that the overlapping portions of the PWM signals for red, green, and blue are minimized, and then the pulse width The modulation signal phase-shifting unit outputs red, green, and blue phase-shifted pulse width modulation signals. 6. The device according to any one of claims 1 to 3 and 5, wherein the phase shift angle is 120 degrees. 7. A backlight driving method, comprising: shifting the phases of the pulse width modulated signals for red, green, and blue according to the backlight type and minimizing overlap in the phase shifted pulse width modulated signals for red, green, and blue; and The LED array is driven by phase-shifted pulse width modulation signals for red, green, and blue, respectively. 8. The method of claim 7, wherein: When the backlight type is an edge type, according to the pulse width modulation signal for red, green, and blue in the frequency waveform of the pulse width modulation signal for red, green, and blue applied to the edge type backlight The phases of the pulse width modulated signals for red, green, and blue are substantially shifted so that the overlap of the pulse width modulated signals for red, green, and blue is minimized. 9. The method of claim 7, wherein: When the backlight type is the direct type, the phases of the pulse width modulation signals for red, green, and blue are shifted based on the frequency waveform applied to the light emitting diode array of the direct type backlight according to the light emitting diode array, so that Frequency overlap is minimal in LED arrays. 10. A method according to claim 7 or 9, characterized in that, When the backlight unit is a direct type, based on the frequency waveforms of the pulse width modulation signals for red, green, and blue applied to the direct type backlight according to the pulse width modulation signals for red, green, and blue The phases of the pulse width modulated signals for red, green, and blue are shifted such that the overlapping portions of the pulse width modulated signals for red, green, and blue are minimized.

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