HK1167922B - Backlight module and controlling method thereof - Google Patents

Description

Backlight module and control method thereof

Technical Field

The present invention relates to backlight and ambient light sensing, and more particularly, to backlight and ambient light sensing using Light Emitting Diodes (LEDs).

Background

Liquid Crystal Displays (LCDs) are widely used in a variety of electronic devices and facilities ranging from small handheld mobile phones to large flat panel televisions. Generally, liquid crystal displays include three main types, each type of liquid crystal display having different characteristics suitable for different devices. These three LCD types include: transmissive, reflective and transflective liquid crystal displays. The transmissive and transflective liquid crystal displays to which the present invention is closely related will now be further described.

Transmissive liquid crystal displays provide high brightness, contrast and color saturation and are characterized by the use of a backlight (i.e., an internal light source located behind the liquid crystal display) to provide illumination. The backlight of a transmissive liquid crystal display is generally composed of white Light Emitting Diodes (LEDs). The power consumption of these backlit leds is relatively high because they are typically driven with sufficient power to obtain sufficient light output to compete with the strongest outdoor light environment in which the device is operating, such as an outdoor environment where sunlight may be strong.

One approach to solving this high power consumption problem is to place and position an ambient light sensor on the outer surface of the liquid crystal display. The ambient light sensor is used to estimate the ambient light condition of the current usage environment of the lcd, which is then used to adjust the brightness of the leds of the backlight to adapt to, rather than greatly exceed, the brightness required by the ambient light condition. While this approach can improve power consumption, the addition of ambient light sensors increases the cost of the display and increases its overall size. In addition, conventional transmissive display devices utilizing ambient light sensors do not take into account the amount of light the display's own screen adds to the sensed estimated ambient light condition. The brightness of the screen is often adjusted to a less preferred setting.

A transflective liquid crystal display combines a transmissive function and a reflective function in one display. In case of darkness or low ambient light levels, the backlight is activated and the image is displayed mainly in transmissive mode. In bright ambient light conditions, such as in intense sunlight, the reflective mode is primarily active to illuminate the LCD, the backlight is activated to assist in displaying the image or the backlight is turned off to save energy. In the reflective mode, the liquid crystal display is illuminated by an external light source whose light passes through the front of the liquid crystal display and is reflected back by an embedded reflector behind the liquid crystal display. Since the transflective lcd operating in the reflective mode relies on an external light source for image display, it consumes less power and has better readability in high ambient light environments.

In order to estimate the current ambient light condition such that the brightness of the backlight may be reduced in a brighter environment to allow the reflective mode of the transflective display to take over, an ambient light sensor is typically used. As previously mentioned, while this approach can improve power consumption, it increases cost and increases the overall size of the display.

Therefore, there is a need for an apparatus and method for ambient light condition estimation for liquid crystal displays that does not require conventional ambient light sensors and eliminates the disadvantages associated therewith.

Disclosure of Invention

According to an aspect of the present invention, there is provided a backlight module including:

a Light Emitting Diode (LED) array; and

a backlight controller for forward biasing the LED array to provide backlight for a Liquid Crystal Display (LCD) and reverse biasing the LED array to sense ambient light level.

Preferably, the backlight controller includes:

a pulse width modulator for providing a Pulse Width Modulated (PWM) signal, wherein each cycle of the PWM signal includes an on time and an off time; and

and the light emitting diode array driver is used for forward biasing the light emitting diode array at the on time of the pulse width modulation signal and reversely biasing the light emitting diode array at the off time of the pulse width modulation signal.

Preferably, the backlight controller further comprises:

and the bias voltage generator is used for providing a forward bias voltage to the LED array driver to forward bias the LED array during the on time of the pulse width modulation signal and providing a reverse bias voltage to the LED array driver during the off time of the pulse width modulation signal to reverse bias the LED array.

Preferably, the backlight controller controls the bias generator to supply the reverse bias voltage to the light emitting diode array at an off time of the selected period of the pulse width modulation signal.

Preferably, the backlight controller controls the bias voltage generator to supply the reverse bias voltage to the light emitting diode array driver only for an off-time of one period every N periods of the pulse width modulation signal, where N is an integer.

Preferably, the led driver reverse biases only a portion of the led array during the off time of the pwm signal.

Preferably, the backlight controller further comprises:

and the brightness controller is used for cooperating with an image controller of the liquid crystal display to ensure that the ambient light can penetrate through the liquid crystal display at the closing time of the pulse width modulation signal.

Preferably, the backlight controller further comprises:

and the brightness controller is used for modulating the duty ratio of the pulse width modulation signal according to the ambient light brightness sensed by the LED array.

Preferably, the backlight controller further comprises:

and the brightness controller is used for modulating the duty ratio of the pulse width modulation signal according to the ambient light brightness sensed by the LED array and information received from an image controller of the liquid crystal display.

Preferably, the information received from the image controller includes information related to a current arrangement of one or more liquid crystal display molecules, the one or more liquid crystal display molecules corresponding to one or more pixels of the LCD.

Preferably, the information received from the image controller includes information related to a plurality of pixels of an LCD whose luminance is within two or more luminance ranges when displaying one or more images.

According to an aspect of the present invention, there is provided a method of controlling a backlight assembly including a Light Emitting Diode (LED) array, comprising:

forward biasing an array of light emitting diodes to provide backlight for a Liquid Crystal Display (LCD); and reverse biasing the array of light emitting diodes to sense ambient light brightness.

Preferably, the method further comprises:

providing a Pulse Width Modulated (PWM) signal, wherein each cycle of the PWM signal includes an on time and an off time,

during the on time of the pulse width modulation signal, the light emitting diode array is forward biased to provide backlight for the liquid crystal display; during the off time of the pulse width modulated signal, the led array is reverse biased.

Preferably, the array of light emitting diodes is reverse biased only at off times of selected periods of the pulse width modulated signal.

Preferably, the array of light emitting diodes is reverse biased only during the off time of one period of every N periods of the pulse width modulated signal, where N is an integer.

Preferably, only a portion of the led array is reverse biased during the off time of the pwm signal.

Preferably, the method further comprises:

an image controller of the liquid crystal display is adjusted to ensure that the external light is able to pass through the liquid crystal display at the off time of the pulse width modulation signal.

Preferably, the method further comprises:

and modulating the duty ratio of the pulse width modulation signal according to the ambient light brightness sensed by the light emitting diode array.

Preferably, the method further comprises:

the duty ratio of the pulse width modulation signal is modulated according to the ambient light brightness sensed by the LED array and information received from an image controller of the LCD.

Preferably, the information received from the image controller includes information related to a current arrangement of one or more liquid crystal display molecules, the one or more liquid crystal display molecules corresponding to one or more pixels of the LCD.

Preferably, the information received from the image controller includes information related to a plurality of pixels of an LCD whose luminance is within two or more luminance ranges when displaying one or more images.

Drawings

The principles of the present invention are further explained below in conjunction with the drawings and the description of the drawings to enable those skilled in the art to understand and use the present invention.

FIG. 1 is an exploded view of an exemplary liquid crystal display;

FIG. 2 is a partial block diagram of a liquid crystal display using a conventional ambient light sensor;

FIG. 3 is a block diagram of an LCD using a back-lit ambient light sensor according to an embodiment of the present invention;

FIG. 4 illustrates an exemplary backlight module according to an embodiment of the invention;

FIG. 5 illustrates an exemplary method for adjusting the brightness of a liquid crystal display according to the ambient light condition sensed by a backlight ambient light sensor, according to an embodiment of the present invention.

The invention will be described below with reference to the accompanying drawings. The left-most digit(s) of a corresponding reference number identifies the figure in which the element first appears.

Detailed Description

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention, including the structures, systems and methods, may be practiced without these specific details. The specific details described herein are those ordinarily skilled in the art. In other instances, well-known methods, procedures, compositions and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present invention.

Reference throughout this specification to "one embodiment," "an example embodiment," or the like, includes a number of specific features, structures, or characteristics of the present invention, but not all embodiments necessarily include the particular features, structures, or characteristics. Moreover, such phrases are not intended to refer to the same embodiment. Further, it will be apparent to one skilled in the art that after a particular feature, structure, or characteristic has been described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in other embodiments whether or not explicitly described.

1. Examples of operating environments

FIG. 1 is an exploded view of an exemplary transmissive or transflective LCD 100, in which the embodiments of the invention may be implemented in the LCD 100. The liquid crystal display 100 includes a backlight assembly 110, a first polarizing film 120, a liquid crystal intermediate layer 130, and a second polarizing film 140. The liquid crystal display 100 may be used in a variety of different devices including, for example, a mobile phone, a video camera, a television, or a display.

In operation, the liquid crystal intermediate layer 130 is controlled by an image controller (not shown) to allow different amounts of light from the backlight assembly 110 to pass through different portions of the second polarizing film 140. By controlling the amount of light transmitted through the respective portions of the second polarizing film 140, the liquid crystal display 100 can generate a desired image, which will be explained below.

To generate light that can be filtered by the LC interlayer 130, the backlight assembly 110 includes an array of LEDs (not shown) positioned along one or more edges of the back-plane of the LCD 100 or dispersed over the back-plane area of the LCD 100. The light generated from the backlight assembly 110 first passes through the first polarizing film 120, and the first polarizing film 120 converts the light into light having a single polarity. For example, the first polarizing film 120 may be a wire grid polarizer capable of passing the horizontal component of light while absorbing and/or reflecting the vertical component. In general, the first polarizing film 120 may be disposed to transmit any single polarization angle.

The polarized light from the first polarizing film 120 is then processed by the liquid crystal intermediate layer 130, the liquid crystal intermediate layer 130 having been broken down on the right side of fig. 1 to further illustrate and describe its composition. In particular, the liquid crystal interlayer 130 includes (starting from the component closest to the back of the liquid crystal display 100) a first glass plate 150, a back electrode 155, a first polymer layer 160, a front electrode/second polymer layer 165, an RGB panel 170, and a second glass plate 175.

After the first polymer layer 160 and the second polymer layer 165 are filled with liquid crystal (e.g., nematic liquid crystal), certain optical properties of the liquid crystal can be controlled by an applied electric field. More specifically, in one embodiment, a twisted state (e.g., a helical structure) of liquid crystal molecules is formed between two polymer layers separated by a series of spacers (not shown). The surface of each polymer layer has "grooves" which are 90 ° with respect to each other, so that both ends of each arrangement of liquid crystal molecules will be aligned with the grooves, and each arrangement will be twisted by 90 ° without the application of an applied electric field. The twist of each configuration of liquid crystal molecules can redirect or bend 90 degrees the light passing through the first polarizing film 120 and the first glass plate 150 to finally pass through the second glass plate 175 and the second polarizing film 140 such that the phase angle of the final outgoing light is 90 degrees from the angle of the first polarizing film 120.

By applying an applied electric field to the liquid crystal layer between polymer layers 160 and 165, each twisted configuration of liquid crystal molecules will be untwisted and aligned parallel to the direction of the electric field. Controlling the intensity of the applied electric field can control the amount of untwisting, and thus ultimately the amount of light passing through the second polarizing film 140.

In particular, the back electrode 155 and the front electrode 165 are used to generate and apply an electric field applied to the liquid crystal layer. For example, in one embodiment, the display area of the liquid crystal display 100 is divided into two-dimensional pixel arrays, each of which is further divided into three areas. The back electrode 155 and the front electrode 165 generate and apply a unique controlled electric field that controls each portion of the liquid crystal intermediate layer to which the electric field is applied, the portions corresponding to three regions of each pixel. After passing through the three regions of each pixel, the light is then processed by the RGB panel 170, and the RGB panel 170 filters the light passing through the three regions of each pixel using red, green, and blue color filters. Accordingly, the back electrode 155 and the front electrode 165 can be controlled to adjust the amounts of red, green, and blue light, which constitute each mixed pixel color displayed by the LCD 100 and then a final image is displayed.

In one embodiment, the liquid crystal display 100 employs an active matrix scheme to generate and apply different electric fields at different portions of the liquid crystal layer. In another embodiment, a passive matrix scheme is employed.

Note that an image controller for controlling the back electrode 155 and the front electrode 165 is not shown in fig. 1. It is further noted that the LCD 100 is merely representative of one exemplary LCD in which embodiments of the present invention may be implemented. For example, to those skilled in the art, embodiments of the invention may be implemented in any reasonable transmissive or transflective liquid crystal display that is backlit using an array of LEDs.

2. Conventional ambient light sensor

In general, liquid crystal displays, such as the backlight in liquid crystal display 100, have relatively high power consumption associated with their light emitting diodes because they are typically driven with sufficient power to obtain sufficient light output to compete with the strongest outdoor light environment in which the device operates, such as an outdoor environment where sunlight may be strong.

One approach to solving this high power consumption problem is to place and position an ambient light sensor on the surface of the liquid crystal display. The ambient light sensor is used to estimate the ambient light condition of the current usage environment of the lcd, which is then used to adjust the brightness of the leds of the backlight source to meet, rather than greatly exceed, the brightness required by the ambient light condition.

FIG. 2 is a block diagram of an exemplary control structure 200, the control structure 200 using a conventional ambient light sensor 285 as described above to control the LCD 100. In particular, the control structure 200 includes an image controller 210, the image controller 210 controlling the back electrode 155 through a gate driver 220 and a source driver 225; the control structure 200 further comprises a backlight controller 230 for controlling an array of light emitting diodes 240, wherein the array of light emitting diodes 240 comprises light emitting diodes for generating light 250 through the back electrode 155.

In one embodiment, the back electrode 155 operates as an active matrix and further includes an array of pixel elements 260, each pixel element corresponding to one color (i.e., red, green, or blue) in a complete pixel. Specifically, each pixel element includes a transistor and a capacitor (one end of the capacitor is provided on the front electrode 165 shown in fig. 1). This transistor/capacitor pair is commonly referred to as a Thin Film Transistor (TFT).

The gate driver 220 drives the gate of the transistor in each pixel element 260 through a series of scan lines 270, enabling the transistor to be turned on and off. The source driver 225 uses a series of data lines 280 to drive the source or drain of the transistor in each pixel element 260 to effect charging of each associated capacitor when the transistor is turned on. Image controller 210 is operative to control gate driver 220 and source driver 225 to turn selected pixel elements 260 on and off, and to charge each capacitor in pixel elements 260 to a desired voltage. The voltage across each capacitor comprises an equalizing electric field across a corresponding region of the liquid crystal layer, which in turn changes the orientation or twist of the liquid crystal molecular arrangement in that region. As discussed previously, the amount of twist in the liquid crystal arrangement affects the amount of light 250 that is ultimately displayed by the output to the liquid crystal display 100. Accordingly, by appropriately controlling the amount of charge stored in each capacitor of the pixel element 260, the image controller 210 can control the output display of the liquid crystal display 100, thereby realizing the display of a desired image.

It should be noted that the active matrix scheme discussed above represents only one possible way of controlling the orientation of each liquid crystal associated with each pixel element 260. Other possible control schemes will be apparent to those skilled in the art without departing from the scope and spirit of the invention. For example, in another embodiment, a passive matrix scheme is employed.

The control structure 200 also includes a backlight controller 230, the backlight controller 230 being configured to supply power to the light emitting diode array 240 and to control the brightness of the light emitting diode array 240 using a Pulse Width Modulation (PWM) dimming technique. The backlight controller 230 modulates the turn-on time of the light emitting diodes in the light emitting diode array 240 by a Pulse Width Modulation (PWM) driving signal 295 using a PWM dimming technique. The brightness of the liquid crystal display is approximately equal to the duty cycle of the pulse width modulated drive signal 295.

The brightness control function is combined with the conventional ambient light sensor 285, so that the brightness of the led array 240 can be adjusted according to the brightness condition of the current environment in which the device is used. For example, in a room where the ambient light level 290 is sensed to be relatively high, the backlight controller 230 may adjust the duty cycle of the pulse width modulated drive signal 295 to provide a higher brightness level. Conversely, when the ambient light level 290 in the room is low, the backlight controller 230 may adjust the duty cycle of the pulse width modulated drive signal 295 to provide a low level of brightness.

While sensing ambient light conditions to control brightness can improve power consumption, the addition of the conventional ambient light sensor 285 increases the cost of the display and increases its overall size. In addition, many display devices that use ambient light sensors, such as ambient light sensor 285, do not consider the amount of light the display itself adds to the sensed estimated ambient light condition. The brightness of the screen is often adjusted to a less preferred setting.

The embodiments of the present invention now discussed relate to an apparatus and method for estimating the ambient light conditions of a liquid crystal display, while estimating whether a conventional ambient light sensor, such as ambient light sensor 285, is required, and its associated disadvantages.

3. Backlight ambient light sensor

Fig. 3 is a block diagram of an exemplary control structure 300 for controlling the liquid crystal display 100 according to an embodiment of the present invention. In particular, the control structure 300 includes substantially similar components as the control structure 200 of FIG. 2. However, the conventional ambient light sensor 285 is eliminated and replaced with a back-lit ambient light sensor (BALS, not shown). In addition, the backlight controller 230 of fig. 2 is replaced with a modified backlight controller 310.

In operation, the backlight controller 310 powers the LED array 240 and controls the brightness of the LED array 240 using a Pulse Width Modulation (PWM) dimming technique. Using pulse width modulation dimming techniques, the backlight modulation controller 310 modulates the LED firing time in the LED array 240 using a pulse width modulation drive signal 295. The brightness of the liquid crystal display is approximately equal to the duty cycle of the pulse width modulated drive signal 295.

In an embodiment, one or more of the LEDs in the LED array 240 used to perform backlighting are also used by the backlight controller 310 as ambient light sensors, and thus as Backlight Ambient Light Sensors (BALS). The additional function of ambient light sensing is performed by reusing one or more LEDs, thereby eliminating the conventional ambient light sensor. In order for the LEDs to perform the dual functions described above, the backlight modulation controller 310 forward biases the LEDs to emit light and reverse biases the LEDs to sense ambient light.

In another embodiment of the invention, one or more dual function LEDs in the LED array 240 are reverse biased during the phase of the pulse width modulated drive signal 295 that normally turns off the LEDs and is used as an ambient light sensor. As a variation of this embodiment, one or more of the dual-function LEDs are reverse biased and used as ambient light sensors only during selected periods of the PWM drive signal 295, that is, only during some but not all of the periods of the PWM drive signal 295. For example, one or more dual-function LEDs are reverse biased for use as ambient light sensors in one of every N cycles of the pulse width modulated drive signal 295, where N is an integer. In another example, one or more dual function LEDs are reverse biased for use as ambient light sensors every M periods of N periods of the pwm drive signal 295, where M and N are integers and M is less than N.

The brightness of the LED array 240 may be adjusted based on the current ambient light conditions sensed by one or more LEDs in the LED array 240. For example, in a room where the sensed ambient light level 320 is relatively high, the backlight controller 310 may adjust the duty cycle of the pulse width modulated drive signal 295 to provide a higher brightness level. However, when the sensed ambient light level 320 is low in the room, the backlight modulation controller 310 may adjust the duty cycle of the pulse width modulated drive signal 295 to provide a low level of brightness.

In another embodiment of the present invention, the backlight modulation controller 310 utilizes additional control logic to receive and utilize information regarding the crystalline material state of the liquid crystal display 100 to determine and/or adjust the ambient light level sensed by one or more dual function LEDs. More specifically, when one or more dual function LEDs sense ambient light brightness, the current orientation or twist state of the liquid crystal molecules corresponding to one or more pixel elements 260 of LCD 100 can also be used to determine and/or adjust the sensed ambient light brightness 320.

For example, if the current orientation or twisted state of the liquid crystal molecules is such that less light is allowed to be transmitted through the LCD display than is otherwise possible, the sensed ambient light level is increased and/or analyzed to correspond to an actual ambient light level that is higher in brightness than the actual sensed ambient light level. The state information of the crystalline material in the liquid crystal display 100 may be represented by the voltage of a capacitor corresponding to one or more pixel elements 260, or by the amount of charge stored on the capacitor; the state information of the crystalline material in the liquid crystal display 100 may be received by the backlight controller 310 from the image controller 210 through the image correction signal 330 in fig. 3.

In another embodiment, the backlight controller 310 may further utilize additional control logic to receive and use the brightness information of the plurality of pixel elements 260 in the LCD 100 to analyze and/or adjust the ambient light level sensed by the one or more dual function LEDs. For example, the brightness or brightness of Pixel element 260 may be calculated by image controller 210 based on the sum of the weights of the red, green, and blue components (e.g., Pixel brightness Pixel _ Luma ═ 3R + B +4G, where R, G, B are the red, green, and blue components, respectively, in displaying a given image). The image controller 210 may calculate the brightness of a plurality of pixel elements 260 in one or more images displayed by the liquid crystal display 100; image controller 210 can also record the number of pixel elements having a luminance in two or more luminance ranges. That is, the image controller 210 can generate a statistical histogram including the number of pixel elements having luminance in two or more luminance ranges. These data representing the number of pixel elements having a brightness in two or more brightness ranges may be sent to the backlight controller 310 for analysis and/or adjustment of the sensed ambient light brightness 320.

In yet another embodiment, the backlight controller 310 may send a signal to the image controller 210 via the image correction signal 330 to adjust the crystal material to ensure that a portion of the external ambient light is able to pass through the liquid crystal display 100 such that the external ambient light is able to be sensed by the LEDs of the LED array 240 during the off-state time of the one or more pulse width modulated drive signals 295. In a variation of this embodiment, backlight controller 310 can send a signal to image controller 210 via image correction signal 330 to ensure that a portion of the ambient light outside the display passes through by adjusting only the crystalline material corresponding to a particular region or pixel in liquid crystal display 100.

Fig. 4 is an exemplary block diagram of the backlight module 110 according to the embodiment of the invention, which includes a backlight controller 310 and an led array 240. As shown in fig. 4, the backlight controller 310 includes a bias voltage generator 410, a pulse width modulator 420, a brightness controller 430, and a light emitting diode array driver 440.

In operation, the pulse width modulator 420 provides a Pulse Width Modulated (PWM) signal 450 to the led array driver 440. Each period of the pulse width modulated signal 450 includes an on time and an off time. The light emitting diode array driver 440 is configured to forward bias one or more LEDs in the light emitting diode array 240 for an on time of a Pulse Width Modulation (PWM) signal 450 and to reverse bias one or more LEDs in the light emitting diode array 240 for at least a partial off time of the Pulse Width Modulation (PWM) signal 450.

During a portion of the time that one or more of the LEDs in the LED array 240 are forward biased, the LEDs are illuminated and the liquid crystal display 100 is illuminated. Ambient light is sensed during a portion of the time that one or more LEDs in the LED array 240 are reverse biased. In general, one or more LEDs in the LED array 240, when reverse biased, convert into a photodiode and generate a current, referred to as a photocurrent, that is approximately proportional to the amount of light that passes through the surface of the various layers in the liquid crystal display 100. Brightness controller 430 can measure or sense this current via ambient light level signal 320 as shown in fig. 3.

In one embodiment, the brightness controller 430 is configured to modulate the duty cycle of the pulse width modulation signal 450 according to the ambient light level sensed by the LED array 240. For example, in a room where the ambient light level 320 is sensed to be relatively high, the brightness controller 430 may adjust the duty cycle of the pulse width modulated signal 450 to provide a higher brightness level; conversely, when the ambient light level 320 in the room is sensed to be low, the brightness controller 430 may adjust the duty cycle of the pulse width modulated signal 450 to provide a low brightness level. In particular, the duty cycle may be adjusted according to the pulse width control signal 470 as shown in FIG. 4.

In another embodiment, brightness controller 430 may further utilize additional control logic to receive and utilize crystalline material state information about liquid crystal display 100 to analyze and/or adjust the ambient light level sensed by one or more dual function LEDs. More particularly, the current orientation or twist of the liquid crystal molecules corresponding to one or more pixel elements 260 in the liquid crystal display 100 during the ambient light level sensed by one or more dual function LEDs can also be used to determine and/or adjust the sensed ambient light level 320.

For example, if the current orientation or twisted state of the liquid crystal molecules is such that light transmitted through the LCD display is less than the other various possible states, the sensed ambient light level is increased and/or analyzed to correspond to an actual ambient light level that is higher in brightness than the actual sensed ambient light level. The state information of the crystalline material in the liquid crystal display 100 may be represented by the voltage of a capacitor corresponding to one or more pixel elements 260, or by the amount of charge stored on the capacitor; the state information of the crystalline material in the liquid crystal display 100 may also be received by the brightness controller 430 from the image controller of the liquid crystal display 100 through the image correction signal 330 in fig. 4.

In another embodiment, the brightness controller 430 may further utilize additional control logic to receive and use brightness information of a plurality of pixel elements in the LCD 100 to analyze and/or adjust the ambient light level sensed by one or more dual function LEDs. For example, the brightness or brightness of a Pixel element may be calculated by image controller 210 from the sum of the weights of the red, green, and blue components (e.g., Pixel brightness Pixel _ Luma ═ 3R + B +4G, where R, G, B are the red, green, and blue components, respectively, in displaying a given image). The image controller 210 may calculate the brightness of a plurality of pixel elements 260 in one or more images displayed by the liquid crystal display 100; image controller 210 can also record the number of pixel elements having a luminance in two or more luminance ranges. That is, the image controller 210 can generate a statistical histogram including the number of pixel elements having luminance in two or more luminance ranges. These data representing the number of pixel elements having a brightness in two or more brightness ranges may be sent to brightness controller 430 for analysis and/or adjustment of the sensed ambient light brightness 320.

In yet another embodiment, the brightness controller 430 may send a signal to the image controller via the image correction signal 330 to adjust the crystal material to ensure that a portion of the ambient light is able to pass through the liquid crystal display 100 such that the ambient light is able to be sensed by the LEDs of the LED array 240 during the off state of the one or more pulse width modulation signals 450. In a variation of this embodiment, the brightness controller 430 sends a signal to the image controller via the image correction signal 330, which can adjust only the crystalline material corresponding to a specific region or pixel in the lcd 100 to ensure that part of the external ambient light can pass through the display.

The bias voltage generator 410 is used to provide a forward bias voltage for forward biasing the led array 240 to the led array driver 440 during the on time of the pwm signal 450 and a reverse bias voltage for reverse biasing the led array 240 to the led array driver 440 during the off time of the pwm signal 450. In particular, the two BIAS voltages are provided to the LED array driver 440 via the V-BIAS signal 460 as shown in FIG. 4.

In one embodiment, the brightness controller 430 further controls the bias voltage generator 410 via the BALS enable signal 480 to provide a reverse bias voltage to the LED array driver 440 only during the off time of a selected period or interval of the PWM signal 450. For example, the backlight controller 430 controls the bias voltage generator 410 to provide the reverse bias voltage to the led array driver 440 only every N periods of the off-time of the pwm signal 450, where N is an integer. In another example, the backlight controller 430 controls the bias voltage generator 410 to provide the reverse bias voltage to the led array driver 440 every mth period of the N periods of the pwm signal 450, where M and N are integers and M is less than N.

It should be noted that the pulse width modulated drive signal 295 generated by the led array driver 440 is substantially identical and identical to the pulse width modulated signal 450. But the pwm drive signal 295 is stronger in intensity to achieve forward and reverse biasing of the led array 240.

FIG. 5 is a flowchart illustrating an exemplary method 500 for adjusting the brightness of the LCD 100 according to the ambient light condition sensed by the back-lit ambient light sensor (BALS) according to an embodiment of the present invention. The method 500 is in accordance with the features described above and shown in fig. 4.

The method 500 shown in fig. 5 begins at step 510 and proceeds to step 520. In step 520, it is determined whether the pwm signal 450 is currently in an off state. If the pwm signal 450 is not currently in the off state, the method 500 continues to step 520 until the pwm signal 450 is determined to be in the off state. If the pwm signal 450 is currently in the off state, go to step 530.

At step 530, it is determined whether the current ambient light condition is sensed. If not, the method 500 jumps to step 520 and waits for the next off state of the pwm signal 450; if step 530 determines that the current ambient light condition is sensed, then the method 500 jumps to step 540.

At step 540, one or more light emitting diodes in the light emitting diode array 240 are reverse biased. When reverse biased, one or more of the light emitting diodes in the light emitting diode array 240 operate as photodiodes and produce a current that is approximately proportional to the amount of ambient light impinging on the surface of the light emitting diodes. The method 500 proceeds to step 550 after step 540.

At step 550, the magnitude of the current generated by one or more LEDs in the LED array 240 is sensed and analyzed. In one embodiment, this analysis process includes using state information of crystalline material in the liquid crystal display 100 as described above, or using information associated with a plurality of pixel elements of the liquid crystal display 100 whose brightness is within two or more brightness ranges when displaying one or more images. After the sensed information is analyzed, the method 500 proceeds to step 560.

In step 560, the brightness of one or more LEDs in the LED array 240 is adjusted according to the sensed information. In one embodiment, the duty cycle of the pulse width modulated signal 450 is modulated in accordance with the sensed information. For example, in a room where ambient light levels are sensed to be relatively high, the duty cycle of the pulse width modulated signal 450 is adjusted to provide a higher brightness level; conversely, when a low ambient light level is sensed in the room, the duty cycle of the pulse width modulated signal 450 is adjusted to provide a low level of brightness.

4. Conclusion

It is to be understood that the claims are to be interpreted by the above description of specific embodiments and not in the abstract. The abstract of the specification sets forth only one or more, but not all exemplary embodiments of the invention, and thus, is not intended to limit the invention and the claims.

The present invention has been described in detail with reference to functional block diagrams illustrating embodiments of specific functions and relationships thereof. Boundaries of these functional block diagrams are arbitrarily defined for the convenience of the description. The boundaries of the functional block diagrams may be changed so long as the specific functions and relationships thereof are appropriately performed.

While the invention has been described with reference to several particular embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope.

It is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims (10)

1. A backlight module, comprising:

an array of light emitting diodes;

a pulse width modulator for providing a pulse width modulated signal, wherein each cycle of the pulse width modulated signal has an on time and an off time;

a light emitting diode array driver for forward biasing the light emitting diode array to provide backlight for the liquid crystal display at the on time of the pulse width modulation signal and reverse biasing the light emitting diode array to sense ambient light brightness at the off time of the pulse width modulation signal; and

a brightness controller for modulating a duty cycle of the pulse width modulated signal according to ambient light brightness sensed by the light emitting diode array; and is

The current orientation or twist state of the liquid crystal molecules corresponding to one or more pixel elements in the liquid crystal display is used to determine and/or adjust the sensed ambient light level.

2. The backlight module according to claim 1, wherein the brightness controller is further configured to utilize additional control logic to receive and use information about a current orientation or twist state of liquid crystal molecules corresponding to one or more pixel elements in the liquid crystal display when ambient light brightness is sensed by one or more dual-function light emitting diodes in the array of light emitting diodes to analyze and/or adjust the ambient light brightness.

3. The backlight module according to claim 1, further comprising: and the bias voltage generator is used for providing a forward bias voltage to the LED array driver to forward bias the LED array during the on time of the pulse width modulation signal and providing a reverse bias voltage to the LED array driver during the off time of the pulse width modulation signal to reverse bias the LED array.

4. The backlight module according to claim 3, wherein the bias voltage generator is configured to provide a reverse bias voltage to the LED array at an off time of a selected period of a pulse width modulation signal.

5. The backlight module according to claim 3, wherein the bias voltage generator is configured to provide a reverse bias voltage to the LED array driver only during an off-time of one period of every N periods of the PWM signal, where N is an integer.

6. The backlight module as claimed in claim 3, wherein the brightness controller is further configured to cooperate with an image controller of the LCD to ensure ambient light can pass through the LCD during the OFF time of the PWM signal.

7. The backlight module of claim 1, wherein the brightness controller is further configured to modulate a duty cycle of a pulse width modulation signal according to a current arrangement of one or more liquid crystal molecules in the liquid crystal display corresponding to one or more pixels.

8. A method of controlling a backlight module, the backlight module comprising an array of light emitting diodes, the method comprising:

providing a pulse width modulated signal, wherein each cycle of the pulse width modulated signal has an on time and an off time;

forward biasing the light emitting diode array at the turn-on time of the pulse width modulation signal to provide backlight for the liquid crystal display;

reverse biasing the LED array at the turn-off time of the PWM signal to sense ambient light brightness; and

modulating a duty cycle of the pulse width modulated signal according to ambient light brightness sensed by the light emitting diode array; and is

The current orientation or twist state of the liquid crystal molecules corresponding to one or more pixel elements in the liquid crystal display is used to determine and/or adjust the sensed ambient light level.

9. The method of claim 8, further comprising: receiving and using information about a current orientation or twist state of liquid crystal molecules in the liquid crystal display corresponding to one or more pixel elements when ambient light brightness is sensed by one or more dual-function light emitting diodes in the array of light emitting diodes to analyze and/or adjust the ambient light brightness.

10. The method of claim 8, wherein the array of light emitting diodes is reverse biased only for an off time of one period of every N periods of the pulse width modulated signal, N being an integer.