KR20070076078A - Apparatus and method controlling dimming frequency in lcd - Google Patents

Abstract

A method and an apparatus for controlling a dimming frequency in an LCD(Liquid Crystal Display) are provided to automatically adjust the dimming frequency of an inverter by referring to the frame frequency of a displayed image. An apparatus for controlling a dimming frequency in an LCD includes a refresh rate controller(100), a frequency setting unit(130), a brightness controller(140), and an inverter(150). The refresh rate controller reads a changed frame frequency of the LCD and/or frame frequency information of various LCDs. The frequency setting unit determines an optimal PWM frequency for the LCD based on the read result from the refresh rate controller. The brightness controller outputs the optimal PWM(Pulse Width Modulation) frequency, which is provided from the frequency setting unit. The inverter delivers an input voltage to an LCD lamp in synchronization with the variable PWM frequency from the brightness controller.

Description

Frequency control device and method for brightness control of liquid crystal display {Apparatus and Method Controlling Dimming Frequency in LCD}

In order to better understand the drawings used in the detailed description of the invention, a brief description of each drawing is provided.

1 is a block diagram of a frequency adjusting device for adjusting brightness of a liquid crystal display when the frame frequency of the same liquid crystal display is changed according to a preferred embodiment of the present invention.

2 is a view for explaining the configuration of the frequency control device for adjusting the brightness of the liquid crystal display when applying a plurality of liquid crystal display according to another embodiment of the present invention.

<< Explanation of symbols for main part of drawing >>

100, 200: refresh rate control unit 110, 210: video controller

120, 220: liquid crystal display 130, 230: optimal PWM frequency selection unit

140, 240: brightness controller 150, 250: inverter

160, 260: liquid crystal display lamp

The present invention relates to a brightness control device for a liquid crystal display, and more particularly, to a frequency control device for controlling brightness of a liquid crystal display for converting a PWM frequency of an inverter for adjusting the brightness of the liquid crystal display to a frame frequency of the liquid crystal display. It is about.

Liquid crystal displays (LCDs) are increasingly in demand due to their low power consumption and low space consumption compared to conventional CRTs (Cathod Ray Tubes). LCD displays are widely applied to portable devices such as notebook computers and PDAs, and have recently been favored as display devices of desktop computers.

Since portable devices such as notebook computers and PDAs are portable, they have to be frequently used with batteries. Therefore, power consumption should be minimized in order to increase battery life. Therefore, in recent years, in order to increase the battery life of a portable device, the frame frequency of the liquid crystal display is changed according to the usage environment of the system. For example, by checking whether the portable device is a battery environment or an AC adapter power environment, the frame frequency of the liquid crystal display is randomly changed.

In this case, when a digital mode inverter (Brust Mode) using the "fixed PWM frequency" is used as the brightness control information of the liquid crystal display, a screen defect may occur due to the mutual interference between the PWM frequency and the frame frequency of the liquid crystal display. Therefore, the PWM frequency of the inverter is generally set by referring to the frame frequency of the liquid crystal display. However, when setting one kind of liquid crystal display, there was no problem, but when using various kinds of liquid crystal displays, it is difficult to set an optimal PWM frequency for each liquid crystal display, which may cause noise in a specific display.

The present applicant has filed an application No. 34498 on May 29, 2003 for the brightness control device of the liquid crystal display that solves the above problems.

Briefly, in the prior application, when the frame frequency of the liquid crystal display is changed, the changed frame frequency of the liquid crystal display is read in order to prevent a screen defect from occurring due to mutual interference with the changed frame frequency. The digital mode inverter enables conversion to an arbitrary PWM frequency without affecting the frame frequency, thereby enabling a variable frame frequency method of the liquid crystal display.

The refresh rate controller programmed to change the frame frequency to a predetermined frame frequency is controlled by the video controller to change the frame frequency, and outputs constant brightness control information to the brightness controller in proportion to the variable PWM information and the variable PWM frequency. The brightness controller outputs the existing brightness control information and the variable PWM frequency information to the PWM converter separately configured. PWM converter designed to output the optimum PWM frequency according to the output information of the brightness control unit converts each information and outputs to the inverter.

However, in such a configuration, when a voltage within a predetermined range is variably input to the LCD display brightness adjusting device, a PWM conversion circuit having a predetermined variable amount and designed to be changed to a frequency within a predetermined range is additionally included. Therefore, the structure and configuration of the liquid crystal display brightness adjusting device is complicated, and the provision of additional hardware has a problem of increasing the volume and manufacturing cost of the device.

Accordingly, an object of the present invention is to provide a frequency control device and a method for adjusting the brightness of the liquid crystal display for variably adjusting the PWM frequency of the inverter for controlling the brightness of the liquid crystal display in conjunction with the frame frequency of the liquid crystal display.

Another object of the present invention is to provide a frequency control device and method for controlling brightness of a liquid crystal display for driving various types of liquid crystal displays at an optimal PWM frequency of a light emitting device using one type of inverter.

Still another object of the present invention is to provide a frequency control device and method for adjusting the brightness of a liquid crystal display which outputs an optimal PWM frequency according to the frame frequency of the liquid crystal display on a program basis without additional hardware.

According to a feature of the present invention for achieving the above object, the present invention provides a refresh rate control unit for reading frame frequency information from a variable frame frequency of the liquid crystal display and / or a plurality of liquid crystal display, the refresh rate control unit A frequency selector for selecting an optimal PWM frequency suitable for the liquid crystal display, a brightness controller for outputting an optimal PWM frequency provided from the frequency selector, and an input voltage in synchronization with a variable PWM frequency of the brightness controller. It is configured to include an inverter that delivers to the display lamp.

The frequency selecting unit includes table information defining an optimum PWM frequency according to the frame frequency, and includes a frequency selecting processor for combining an optimal PWM frequency suitable for the frame frequency provided from the refresh rate control unit.

The frequency selector includes a calculator that calculates an optimal PWM frequency by using the frame frequency provided from the refresh rate controller.

The apparatus may further include a video controller configured to variably control the frame frequency of the liquid crystal display according to the frame frequency of the refresh rate controller.

According to another feature of the present invention, the present invention provides a method of reading a frame frequency from at least one liquid crystal display, selecting an optimal PWM frequency suitable for the frame frequency of the read liquid crystal display, and outputting the selected optimal PWM frequency. And synchronizing the input voltage with the selected optimal PWM frequency and supplying the same to the liquid crystal display lamp.

The step of selecting the optimum PWM frequency includes combining the optimal PWM frequency which does not affect the frame frequency of the liquid crystal display based on the table information defining the optimum PWM frequency according to the frame frequency.

The step of selecting the optimum PWM frequency includes calculating an optimum PWM frequency using the frame frequency read from the liquid crystal display.

By the above configuration, the frequency adjusting device and method for brightness adjustment of the liquid crystal display according to the present invention, when applying various types of liquid crystal display or to change to an arbitrary frame frequency, without using a separate drive circuit, the frame Automatic conversion to the optimum PWM frequency does not affect the frequency. As a result, the configuration and structure of the brightness control system portion of the liquid crystal display can be simplified, and the manufacturing cost can be reduced while reducing the volume and weight.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of a frequency control device for adjusting brightness of a liquid crystal display when the frame frequency of the same liquid crystal display is changed according to a preferred embodiment of the present invention.

Frequency control apparatus for brightness adjustment of the liquid crystal display of the present invention, the refresh rate control unit 100, the video controller 110, the liquid crystal display 120, the optimum PWM frequency selection unit 130, brightness control unit 140, inverter 150 ) And the liquid crystal display lamp 160.

The refresh rate control driver 100 stores a program for arbitrarily changing the frame frequency of the liquid crystal display 120. When the frame frequency of the liquid crystal display 120 is changed, the refresh rate controller 100 supplies information about the variable frame frequency to the optimum PWM frequency selecting unit 130.

The optimal PWM frequency selecting unit 130 includes table information in which an optimum PWM frequency is defined according to the frame frequency, and selects an optimal PWM frequency for the frame frequency supplied from the refresh rate controller 100 based on the table information. .

The optimum PWM frequency selecting unit 130 calculates an optimal PWM frequency that does not affect the frame frequency using the variable frame frequency information from the refresh rate control unit 100.

The brightness controller 140 receives optimal PWM frequency information from the optimum PWM frequency selecting unit 130 to generate an optimal PWM frequency suitable for the frame frequency of the variable liquid crystal display and outputs the optimal PWM frequency to the inverter 150. The brightness controller 140 uses a microcomputer or SMSC processor.

The inverter 150 supplies a brightness output waveform to the liquid crystal display lamp 160 by synchronizing the input voltage for brightness control with the optimum PWM frequency supplied from the brightness controller 140.

The liquid crystal display lamp 160 is a light emitting device that is turned on to adjust the brightness of the liquid crystal display 120. Therefore, the brightness of the liquid crystal display 120 is controlled differently according to the brightness control voltage output supplied from the inverter 150.

The liquid crystal display 120 displays various display signals under the control of the video controller 110. In addition, the video controller 110 receives variable frame frequency information from the refresh rate controller 100 to variably control the frame frequency of the liquid crystal display 120. The liquid crystal display 120 represents a display device used for a notebook computer, a PDA, or a desktop computer.

Hereinafter, a process of selecting an optimal PWM frequency by the frequency adjusting device for brightness adjustment of the liquid crystal display according to the present invention having the above configuration will be described step by step.

When the frame frequency of the same liquid crystal display 120 is changed from 60 Hz to 57 Hz and 45 Hz, the refresh rate controller 100 controls the video controller 110 to change the frame frequency of the liquid crystal display 120 from 60 Hz to 57 Hz to 45 Hz. Variable control is performed by the procedure. The refresh rate controller 100 reads the variable frame frequency and supplies it to the optimum PWM frequency selector 130.

The optimum PWM frequency selecting unit 130 selects an optimum PWM frequency suitable for the variable frame frequency supplied from the refresh rate control unit 100 through table information and automatic calculation that define the optimum PWM frequency for each frame frequency.

The optimal PWM frequency information selected from the optimum PWM frequency selecting unit 130 is transmitted to the brightness controller 140. The brightness controller 140 outputs the selected PWM frequency to the inverter 160 together with the brightness control information.

The inverter 160 supplies a voltage adjusting waveform for controlling the brightness of the liquid crystal display 120 to the liquid crystal display lamp 160 in synchronization with the optimum PWM frequency provided from the brightness controller 140. The liquid crystal display lamp 160 is brightness-controlled by a voltage output waveform for brightness adjustment supplied from the inverter 150.

Therefore, in the above process, the frame frequency of the liquid crystal display and the PWM frequency of the inverter are varied in conjunction with each other.

For example, when the brightness controller 140 is an SMSC processor, nine types of PWM frequencies output by the SMSC processor are 122 Hz, 128 Hz, 162.8 Hz, 183.1 Hz, 244 Hz, 275 Hz, 326 Hz, 366 Hz, and 407 Hz. As a result, it is impossible to generate the kind of PWM frequency output as shown in Table 1, but it is possible to select 2 ~ 6 PWM frequency of SMSC suitable for each frame frequency. That is, two frame selections of 275Hz and 326Hz are possible at the frame frequency of 60Hz, and six frame selections of 122Hz, 128Hz, 162.8Hz, 183.1Hz, 275Hz and 326Hz are possible at the frame frequency of 50Hz.

The reason for the above selection is that, when the frame frequency is 60 Hz, the optimal brightness control frequencies corresponding to the nth integer multiples are 90 Hz, 150 Hz, 210 Hz, 270 Hz, 330 Hz, and 390 Hz. There is no single. However, considering the allowable range of each optimum PWM frequency, the difference between the optimum PWM frequency and 15 can be selected.

TABLE 1

Formulating the likelihood of noise due to frequency interference,

f = ABS [PWM frequency-(frame frequency × n)],

Where n = 1, 2, 3, ...

If f> 15, it is stable. If f <15, it is unstable, and there is a possibility that a screen defect occurs in the liquid crystal display. The smaller the value, the greater the possibility.

If the output PWM frequency of the SMSC processor set as the inverter's brightness control frequency is set to 275Hz, a 5Hz difference occurs from the optimal brightness control frequency 270Hz, and if it is set to 326Hz, it is 4Hz different from 330Hz. The output PWM frequency is 326 Hz. If you confirm this through the above equation,

f = ABS {326-(60 × n)], n = 1,2,3,4,5,6, ...

f = 266 if n = 1,

f = 206 if n = 2,

f = 146 if n = 3,

f = 86 if n = 4,

f = 26 if n = 5,

f = 34 if n = 6,

If n = 7, f = 94, and no matter how much n increases, it is not an condition less than 26, so it is an optimal condition that is not subject to frequency interference.

In the same way, when the frame frequency is 57Hz, the selectable SMSC processor output PWM frequencies are 128Hz, 244Hz, 326Hz, and 366Hz, of which 366Hz is optimal. If you verify this in the same way,

f = ABS {366-(57 × n)], n = 1,2,3,4,5,6, ...

f = 309 if n = 1

f = 252 if n = 2,

f = 195 if n = 3,

f = 138 if n = 4,

f = 81 if n = 5,

f = 24 if n = 6,

If n = 7, f = 33, and no matter how much n increases, there is no condition less than 24, so it is an optimal condition that is not subject to frequency interference.

When the frame frequency is 45 Hz, 244 Hz is optimal among the output PWM frequencies of the selectable SMSC processors of 122 Hz, 162.8 Hz, and 244 Hz.

f = ABS {244-(45 × n)], n = 1,2,3,4,5,6, ...

f = 199 if n = 1,

f = 154 if n = 2,

f = 109 if n = 3,

f = 64 if n = 4,

f = 19 if n = 5,

f = 26 if n = 6,

If n = 7, f = 71 and no matter how much n is increased, no condition is less than 19. Therefore, it is an optimal condition that is not subject to frequency interference.

Table 2 shows the optimal SMSC processor output PWM frequency for each frame frequency.

The optimum PWM frequency selecting unit 130 includes the optimum PWM frequency for each frame frequency as shown in Table 2 as table information, and receives the information that the frame frequency of the liquid crystal display is 60 Hz from the refresh rate controller 100. The PWM frequency selecting unit 130 selects an optimal PWM frequency as 326 Hz based on the table information in Table 2 above. The optimum PWM frequency information selected by the above method is output to the brightness controller 140.

TABLE 2

The brightness controller 140 generates an optimal PMW frequency of 326 Hz with brightness control information (On Time Duty) and outputs the same to the inverter 150.

The inverter 150 transmits the brightness output waveform corresponding to the brightness control information of 326 Hz to the liquid crystal display lamp 160 in synchronization with the optimum PWM frequency. In order to check the influence due to mutual interference, if f> 15 condition is sufficiently satisfied, the minimum value of f is 26, so it operates stably.

When the frame frequency of the liquid crystal display is changed to 57 Hz, the optimal PWM frequency selecting unit 130 selects 366 Hz as the optimal PWM frequency suitable for the frame frequency and outputs the brightness to the brightness controlling unit 140, and the brightness controlling unit 140 adjusts the brightness control information. 366Hz is generated together with the inverter 150.

The inverter 150 supplies the brightness output waveform corresponding to the brightness control information of 366 Hz to the liquid crystal display lamp 160 in synchronization with the optimum PWM frequency. The minimum value of f that satisfies the condition f> 15 for reading the influence of mutual interference is 24, resulting in stable operation.

When the frame frequency of the liquid crystal display is changed to 45 Hz, the optimum PWM frequency selecting unit 130 selects 244 Hz as the PWM frequency suitable for the frame frequency and provides the brightness control unit 140 to the brightness control unit 140 with the brightness control information. An optimum PWM frequency of 244 Hz is generated and output to the inverter 150.

The inverter 150 supplies the brightness output waveform corresponding to the brightness control information of 244 Hz to the liquid crystal display lamp 160 in synchronization with the optimum PWM frequency. The minimum value of f, which satisfies the condition f> 15 for reading the influence of mutual interference, is 19, resulting in stable operation.

4 is a configuration diagram of a frequency control device for adjusting brightness of a liquid crystal display when applying a plurality of liquid crystal displays according to another embodiment of the present invention. Since the configuration of the apparatus is as shown in FIG. 3, only the parts that are differentiated in operation will be described using the case where the brightness controller 240 is an SMSC processor.

When the frame frequencies of the various liquid crystal displays are 45 Hz, 57 Hz, and 60 Hz, the refresh rate controller 200 reads the frame frequencies and provides them to the optimum PWM frequency selecting unit 230.

The optimum PWM frequency selecting unit 230 selects 244Hz, 366Hz, and 326Hz as the optimum PWM frequencies that do not cause screen defects on the respective liquid crystal displays with reference to the table information of Table 2. The selected optimal PWM frequency information is output to the brightness controller 240.

The brightness controller 240 generates each optimal PWM frequency together with the brightness control information and provides it to the inverter 250 of the corresponding LCD display.

The inverter 250 is synchronized to the optimum PWM frequency, and converts the input voltage for brightness adjustment into voltage output waveforms for brightness control of 244 Hz, 366 Hz, and 326 Hz to be supplied to the liquid crystal display lamp 260.

As described above, when varying the frame frequency of the liquid crystal display according to an embodiment of the present invention or when applying a plurality of liquid crystal display, the frequency of the optimum brightness control of the interlock is automatically adjusted according to each frame frequency, the frame It is possible to prevent the display defect of the liquid crystal display due to the interference between the frequency and the frequency for adjusting the brightness of the inverter. In addition, it is possible to variably apply the PWM frequency of the inverter, which is the brightness information of the liquid crystal display, without fixing it.

By applying the variable frame frequency method as described above it is possible to reduce the power consumption of the liquid crystal display, it is possible to increase the battery life of the portable device.

In addition, while using one type of inverter element, it is possible to effectively provide an optimal PWM frequency for different frame frequency characteristics of various types of liquid crystal displays.

In addition, since only the programming technique is used without additional hardware for PWM frequency conversion, the configuration of the LCD controller may be simplified and manufacturing cost may be reduced.

Therefore, the present invention is applicable to all products using a liquid crystal display such as a portable computer such as a notebook computer, a PDA, and a desktop computer, a mobile display.

As described above, the present invention has been described with reference to the embodiments shown in the drawings, which are merely exemplary, and a person of ordinary skill in the art without departing from the spirit and scope of the present invention. It will be apparent that various modifications, changes, and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (7)

In a system having at least one liquid crystal display capable of adjusting the brightness by each independent PWM frequency, A refresh rate controller which reads a variable frame frequency of the liquid crystal display and / or frame frequency information from a plurality of the liquid crystal displays; A frequency selector configured to receive an optimal PWM frequency suitable for the liquid crystal display from the refresh rate controller; A brightness controller outputting an optimal PWM frequency provided from the frequency selector; And And an inverter configured to transmit an input voltage to the liquid crystal display lamp in synchronization with the variable PWM frequency of the brightness control unit. The method of claim 1, wherein the frequency selection unit, And a frequency selection processor having table information defining an optimum PWM frequency according to the frame frequency, and combining the optimal PWM frequency with the frame frequency provided from the refresh rate control unit. Adjustable frequency regulator. The method of claim 1, wherein the frequency selection unit, And a calculator configured to calculate an optimal PWM frequency by using the frame frequency provided from the refresh rate controller. The method of claim 1, And a video controller for variably controlling the frame frequency of the liquid crystal display according to the frame frequency of the refresh rate controller. Reading a frame frequency from at least one liquid crystal display; Selecting an optimum PWM frequency suitable for the frame frequency of the read liquid crystal display; Outputting the selected optimal PWM frequency; And And synchronizing an input voltage with the selected optimal PWM frequency and supplying the same to the liquid crystal display lamp. The method of claim 5, wherein the selecting the optimal PWM frequency, A method of adjusting the brightness for adjusting the brightness of a liquid crystal display, comprising the step of combining an optimal PWM frequency that does not affect the frame frequency of the liquid crystal display based on the table information defining the optimum PWM frequency according to the frame frequency. . The method of claim 5, wherein the selecting the optimal PWM frequency, Comprising a step of calculating the optimum PWM frequency using the frame frequency read from the liquid crystal display frequency adjustment method for brightness control of the liquid crystal display.

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