Patent Application
20090189841
1. Field of the Invention
The invention relates in general to a color management system for light emitting diode (LED) backlight module, and more particularly to an open-loop management system for LED backlight module.
2. Description of the Related Art
Along with increasing development of technology, light emitting diodes (LED) have been wildly used in backlight module of a LCD (Liquid Crystal Display). In the LED backlight module, LEDs with difference colors are used for providing light of different colors, so that the light of different colors is mixed to generate white light. Since the LEDs with different colors have different rates of luminance decay corresponding to the time-of-use of the backlight module and the surrounding temperature, a color management system for LED backlight module is needed for preventing the changing of the chromaticity of the backlight resulting from the different rates of luminance decay of the different colors LEDs.
In a conventional color management system, a close-loop control system is applied for driving the LEDs based on the luminance of red, green, and blue lights generated by the LEDs. However, in the conventional color management system, a large number of color filters, photo detectors, analog-to-digital (A/D) converters, and a micro-controller must be used for the close-loop control system. Therefore, the conventional color management system has the drawback of large component amount and high producing cost. Besides, it is time-consuming to adjust the parameters of the conventional color management system due to the large component amount.
The invention is directed to a color management system for light emitting diode (LED) backlight module having less elements number, lower producing and element-adjusting cost in comparison to the conventional color management system.
According to an aspect of the present invention, an open-loop color management system for light emitting diode (LED) backlight module is provided. The open-loop color management system comprises an indicating means, a controller and an LED driver. The indicating means is for indicating the operation status of the LED backlight module. The controller is for generating a control signal based on the operation status by reference to a look-up table. The LED driver drives the LED backlight module based on the control signal, so the chromaticity of the LED backlight module may be substantially constant over time.
The invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings.
The color management system of the invention is applied in a LCD, which includes a LED backlight module. The color management system of the invention is for controlling the luminance of the LED backlight module by referring to a look-up table in an open-loop control system.
Referring to
The color management system 10 drives the red, the green, and the blue LEDs and makes the luminance of the red, the green, and the blue LEDs be substantially constant over time. The substantially constant luminance of the red, the green, and the blue LEDs will make the chromaticity of the backlight substantially constant.
The color management system 10 includes an indicating means, a controller 14, a LED driver 16, and a memory 18. The indicating means is for indicating an operation status of the LED backlight module 20. The operation status is relevant to the change of the luminance of the red, green, and blue LEDs. The indicating means is, for example, a timer 12 for providing a time-of-use signal St to indicate the time-of-use of the LED backlight module 20, which is one of the operation statuses of the LED backlight module 20.
The memory 18 stores a look-up table for mapping the time-of-use signal St to a corresponding control signal SC. The controller 14 is coupled to the timer 12 and the memory 18 for receiving the time-of-use signal St from the timer 12 and providing the time-of-use signal St to the memory 18. Then, the controller 14 can get the corresponding control signal SC from the memory 18 based on the time-of-use signal St of the LED backlight module 20, then send the control signal SC to the LED driver 16. The LED driver 16 provides a driving signal SD to drive the red, the green, and the blue LEDs based on the control signal SC.
The instantaneous luminance of the red, the green, and the blue LEDs decreases with the increase of the time-of-use of the LED backlight module 20. In order to keep the average luminance of the red/green/blue LEDs constant, the color management system 10 adjust the driving signal SD with the increase of the time-of-use of the LED backlight module 20. In the embodiment, the color management system 10 generates the control signal SC according to the time-of-use signal St, and then generates the driving signal SD corresponding to the control signal SC. The values of the control signal SC, which correspond to the characteristics of the red/green/blue LEDs related to the time-of-use of the LED backlight module 20, stored in the look-up table are obtained by experience or experiment, for example.
For example, the driving signal SD may be of the form of a pulse width modulated (PWM) signal. The values of the control signal SC, which may correspond to the voltage level, the frequency, the amplitude or other characteristics of the control signal SC, related to the time-of-use signal St are stored in the look-up table. The value of the control signal SC and the duty cycle of the driving signal SD may increase with the increase of the time-of-use of the LED backlight module 20. With the increased duty cycle of the driving signal SD, the ratio of the time when the red/green/blue LEDs is turned on to the time when the red/green/blue LEDs is turned off is increased. Therefore, the average luminance of the red/green/blue LEDs can be kept constant by increasing the duty cycle of the driving signal SD after the red/green/blue LEDs have been used for a certain time period and the instantaneous luminance of the red/green/blue LEDs has even been already decreased.
As described above, the luminance of the red, green, and blue LEDs are all controlled by the driving signal SD, corresponding to the same control signal SC. In an alternative way, the red, green, and blue LEDs can be controlled by different driving signals corresponding to different control signals, which are generated based on different look-up tables. For example, the memory 18 could store three different look-up tables for mapping the time-of-use signal St to three different control signals for controlling the LED driver 20 to drive the red, green, and the blue LEDs individually Scg and Scb.
The color management system of the embodiment is for controlling the luminance of the different color LEDs in a LED backlight module by refer ring to the corresponding look-up table. By using the driving signal SD which corresponding to the time-of-use signal St, the luminance of the red, the green, and the blue LEDs after being used for a particular time are substantially the same with the original luminance of the red, the green, and the blue LEDs when they were manufactured. Therefore, the chromaticity of the backlight is substantially constant over time.
Furthermore, the color management system of the embodiment has less component number and lower producing cost in comparison to the conventional color management system. Besides, it is much more timesaving to adjust the parameters of the components of the color management system of the invention in comparison to the conventional color management system due to the less component number.
Referring to
After the temperature signal Se is generated by the temperature meter 32 and is transmitted to the controller 34, the controller 34 receives the control signals SC′ from the memory 38 and then send the control signals SC′ to the LED driver 36. The LED driver 36 provides corresponding driving signals SD′ to drive the red, the green, and the blue LEDs based on the control signals SC′. As a result, the color management system 30 of the embodiment can keep the luminance of the LEDs in a LED backlight module 40 substantially constant and therefore keep the chromaticity of the LED backlight constant. The color management system 30 of the embodiment has the advantages of less elements number needed, lower producing and element-adjusting cost in comparison to the conventional color management system.
In this embodiment, the red, green, and blue LEDs can be also controlled by different driving signals corresponding to different control signals, which are generated based on different look-up tables. The memory 38 can store three different look-up tables for respectively mapping the temperature signal Se to three control signals for controlling the LED driver 36 to drive the red, the green, and the blue LEDs individually.
Referring to
The controller 34′ receives the control signal SC″ from the memory 58 and then send the control signal SC″ to the LED driver 36′. The LED driver 36′ provides corresponding driving signals SD″ to drive the red, the green, and the blue LEDs based on the control signals SC″. As a result, the color management system of the embodiment can keep the luminance of the LEDs in a LED backlight module and the chromaticity of the backlight substantially constant. Besides, the color management system of this embodiment also has the advantages of less elements number needed, lower producing and element-adjusting cost in comparison to the conventional color management system.
In this embodiment, the red, green, and blue LEDs can be also controlled by different driving signals corresponding to different control signals, which are generated based on different look-up tables. The memory 58 can store three different look-up tables for respectively mapping the time-of-use signal St′ and the temperature signal Se′ to three control signals for controlling the LED driver 36′ to drive the red, the green, and the blue LEDs individually.
While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.
