Patent Application
20070132706
In liquid crystal display (LCD) devices, such as those used in laptop computers and flat panel televisions, an image is formed by manipulating liquid crystal material disposed between a substrate and a glass cover at discrete points on the display to selectively pass light through the liquid crystal material. At each discrete point, an individually-controllable electro-optical element that defines a pixel of the image is created by forming a common electrode on the substrate and patterning a pixel electrode on the glass cover. The liquid crystal material reacts in response to the electric field established between the common electrode and pixel electrode to control the electro-optical response of the pixel.
For example, the pixel electrodes in LCD devices are typically driven by a matrix of thin film transistors (TFTs). Each TFT individually addresses a respective pixel electrode to load data representing a pixel of an image into the pixel electrode. The loaded data produces a corresponding voltage on the pixel electrode. Depending on the voltages applied between the pixel electrode and the common electrode, the liquid crystal material reacts at that electro-optical element to either block or transmit the incoming light. In some applications, the pixel electrodes can be driven with voltages that create a partial reaction of the liquid crystal material so that the electro-optical element is in a non-binary state (i.e., not fully ON or OFF) to produce a “gray scale” transmission of the incoming light.
A traditional illumination device that is used in color LCD devices is a backlight unit that provides a uniform field of light to each of the electro-optical elements in the display. The backlight unit may be illuminated by red, blue and green light emitting diodes (LEDs) that are mixed to produce white light. However, the light intensity of LEDs degrades differently over time. Therefore, some LCD devices include an optical feedback system that measures the degradation of each LED and compensates for the LED degradation by adjusting the intensity of each LED, for example, by pulse width modulation of the LED drive current. Typically, an optical sensor fitted with a color filter is positioned adjacent the backlight unit to measure the intensity of light produced by each LED.
However, the color sensors available on the market today are typically complicated and expensive. In addition, measuring the light in the backlight unit does not take into account any changes in the spectral content resulting from the light passing through the liquid crystal material. Therefore, what is needed is a display device including a low cost, simple optical feedback system that compensates for degradation of the light due to the LCD.
Embodiments of the present invention provide a display device for providing optical feedback. The display device includes light sources, each for emitting light in a different respective wavelength range, electro-optical elements defining pixels of an image, each for selectively passing light in one of the wavelength ranges and a sensor for measuring the intensity of light output from a portion of the electro-optical elements. To provide optical feedback, the display device further includes a controller for activating at least one of the light sources, altering those electro-optical elements within the portion of the electro-optical elements that are arranged to pass light in the wavelength range of a select one of the light sources and reading out the measured intensity from the sensor. Based on the measured light intensity, the controller adjusts an illumination parameter associated with the select light source.
In one embodiment, the controller includes an illumination drive circuit operable to individually drive each of the light sources, a pixel controller operable to individually drive each of the electro-optical elements and a display controller operable to control the illumination drive circuit to activate one of the light sources and to adjust the illumination parameter. The display controller is further operable to control the pixel controller to alter the electro-optical elements. In addition, the display controller is operable to control the sensor to read out the measured intensity of light output from the electro-optical elements.
In an exemplary embodiment, the display controller is further operable to compare the measured intensity to a known intensity associated with the select light source, estimate a degradation value associated with the select light source based on the comparison between the measured intensity and the known intensity and adjust a duty factor of the pulse width modulation of the select light source to compensate for the degradation value.
Embodiments of the present invention further provide a method for providing optical feedback in a display. The method includes providing electro-optical elements defining pixels of an image, in which each of the electro-optical elements selectively passes light in one of a plurality of different wavelength ranges. The method further includes illuminating the electro-optical elements with light in at least a select one of the wavelength ranges, altering select ones of the electro-optical elements to pass the light in the select one of said wavelength ranges and measuring a measured intensity of light output from the select ones of the electro-optical elements. Based on the measured intensity, the method further includes adjusting an illumination parameter associated with the select one of said wavelength ranges.
The disclosed invention will be described with reference to the accompanying drawings, which show sample embodiments of the invention and which are incorporated in the specification hereof by reference, wherein:
The liquid crystal device 50 includes a two-dimensional array of electro-optical elements (not specifically shown) defining pixels of an image displayed on the display device 10. Adjacent the liquid crystal device 50 is a color filter array (CFA) 60 formed of a number of color filters, each designed to absorb light within a particular wavelength range in order to pass light in other wavelength ranges. The color filters are spatially arranged in the CFA 60 to provide a one-to-one optical coupling between color filters and electro-optical elements within the liquid crystal device 50. For example, in one embodiment, the CFA 60 includes a checkerboard pattern of red filters, green and blue color filters, each optically coupled to one of the electro-optical elements. The CFA 60 can be included within the liquid crystal device 50, disposed between the backlight unit 40 and the liquid crystal device 50 or laid over the liquid crystal device 50 on the opposite side from the backlight unit 40, the latter being illustrated in
The illumination device 30, backlight unit 40, liquid crystal device 50 and CFA 60 are mounted in a display casing 20, such that a portion 55 of the liquid crystal device 50 is covered by the display casing 20. Between the CFA 60 and the edge of the display casing 20 covering the portion 55 of the liquid crystal device 50 is located an optical sensor 70 having an active area 75 spatially arranged to provide optical coupling between the portion 55 of the liquid crystal device 50 and the optical sensor 70. The active area 75 of the optical sensor 70 is operable to measure the intensity of light output from the portion 55 of the liquid crystal device 50 and to produce measurement data representing the measured intensity.
Although the optical sensor 70 is shown within the display casing 20 in
The display device 10 further includes a controller 100 operable to control the display device 10 and provide optical feedback in the display device 10. More specifically, the controller 100 includes an illumination drive circuit 110 for controlling the illumination device 30, an LCD controller 120 for controlling the liquid crystal device 50 and a display controller 130 for controlling the illumination drive circuit 110 and LCD controller 120 in response to measurement data output from the sensor 70. As used herein, the term “controller” includes any hardware, software, firmware, or combination thereof. As an example, the controller 100 could include one or more processors that execute instructions and one or more memories that store instructions and data used by the processors. As another example, the controller 100 could include one or more processing devices, such as microcontrollers, Field Programmable Gate Arrays (FPGAs), or Application Specific Integrated Circuits (ASICs), or a combination thereof
In accordance with one embodiment of the present invention, the illumination drive circuit 110 is capable of individually activating (“turning on”) each of the LEDs within the illumination device 30 to enable the optical sensor 70 to measure the intensity of light output from the liquid crystal device 50 in response to illumination by one of the LEDs. In addition, the LCD controller 120 is capable of altering the electro-optical elements within the portion 55 of the liquid crystal device 50 to allow light emitted from one of the LEDs to pass through the liquid crystal device 50 and into the optical sensor 70. In embodiments in which a white LED is used in combination with red, blue and green LEDs, the white LED can be driven separately to measure the intensity of white light or in series with one or more of the red, blue and/or green LEDs to measure the intensity of the combination of white light with red, blue and/or green light.
In accordance with another embodiment of the present invention, with each electro-optical element being optically coupled to only one color filter within the CFA 60, the LCD controller 120 is capable of altering only those electro-optical elements within the portion 55 that are optically coupled to a color filter corresponding to a particular LED wavelength. For example, since red color filters only pass red light (and not blue or green light), the LCD controller 120 can be operable to alter only those electro-optical elements within the portion 55 that are optically coupled to red color filters. In this embodiment, the illumination drive circuit 110 can either simultaneously activate multiple ones of the LEDs within the illumination device 30 while measuring red, blue or green light by altering only those electro-optical elements that pass red, blue or green light, respectively, or sequentially activate the red, blue and green LEDs within the illumination device 30 to sequentially measure red, blue or green light, respectively.
The light passing through each electro-optical element and associated color filter impinges on the active area 75 of the optical sensor 70, where the intensity of the light is measured. For example, in one embodiment, the active area 75 of the optical sensor 70 is a single measurement sensor capable of measuring the intensity of light output from the electro-optical elements within the portion 55. In this embodiment, a color filter array 60 may not be necessary if the LEDs within the illumination device 30 are sequentially activated. In another embodiment, the active area 75 of the optical sensor 70 includes a respective measurement sensor for each color filter and associated electro-optical element within the portion 55. In other embodiments, the active area 75 of the optical sensor 70 includes a respective measurement sensor for a predetermined number of color filters and associated electro-optical elements within the portion 55. Each measurement sensor measures the intensity of light received at that measurement sensor and produces measurement data representing that measured intensity. Thus, each measurement sensor measures the actual light as measured on the observer side of the display, which takes into account degradation of the LED, as well as changes in the spectral transmissivity of the liquid crystal material and color filters.
The measurement data produced by the measurement sensor(s) in the optical sensor 70 is read out by the display controller 130 to provide optical feedback indicating the light intensity degradation of a particular LED in the illumination device 30. Based on the measurement data, the display controller 130 adjusts one or more illumination parameters associated with that particular LED, and provides the parameter adjustments to the illumination drive circuit 110 for storage and later use. For example, in one embodiment, the display controller 130 is operable to compare the measured intensity, as determined from the measurement data, to a known or initial intensity of an LED and estimate a degradation value (e.g., the percentage of combined LED and LCD degradation over time) for the LED based on the comparison between the measured intensity and the known intensity. The display controller 130 uses the estimated degradation value to adjust the duty factor of the pulse width modulation of the LED or the magnitude of the drive current to compensate for the perceived degradation of that LED.
In another embodiment, the display controller 130 is further operable to measure the light transmitted by the electro-optical elements as a function of the drive voltage applied to the electro-optical elements. For example, the display controller 130 can instruct the LCD controller 120 to drive the electro-optical elements within the portion 55 of the liquid crystal device 50 with voltages that create a partial reaction of the liquid crystal material so that one or more of the electro-optical elements are in a non-binary state (i.e., not fully ON or OFF) to produce a “gray scale” transmission of light emitted from one of the LEDs into the optical sensor 70. From the measurement data provided by the optical sensor 70, the display 5 controller 130 is able to determine the transmission of each color independently as a function of the signal applied to the liquid crystal material. As such, the display controller 130 can compensate for subtle changes in the response of the liquid crystal material to “partial” or “gray” level inputs by altering the “gamma correction” applied to each LED on an independent basis.
The illumination device 40 includes light sources 210a, 210b and 210c for emitting light. In
The liquid crystal device 50 includes a two-dimensional array of electro-optical elements 230 forming pixels (P1-P12) of an image. The electro-optical elements 230 are spatially arranged in a pattern 235 corresponding to the pattern 245 of color filters 240 in the CFA 60, such that each color filter 240 is optically coupled to receive light from only one electro-optical element 230. The output of the combination of an electro-optical element 230 and associated color filter 240 within the portion 55 is received by a respective corresponding sensor 250 (S1-S12) within an active area 75 of the optical sensor 70.
Thus, each electro-optical element 230/color filter 240 optically couples light of a particular wavelength (e.g., blue, green or red) to only a single sensor 250. For example, in
As discussed above in connection with
In an exemplary embodiment, the LCD controller 120 correlates the electro-optical elements 230 with light sources 210a, 210b and 210c according to color. Each electro-optical element 230 is first correlated with the color of the color filter 240 that is optically coupled to that electro-optical element 230. For example, in
As a result, in order to provide optical feedback for the red LED 210a, the LCD controller 120 loads data that allows only the red electro-optical elements (e.g., elements P1, P3, P9 and P11) to pass light. Thereafter, when the illumination drive circuit 110 activates all of the light sources 210a, 210b and 210c, since only the red electro-optical elements 230 are altered to allow transmission, only red light is passed to the optical sensor 70. For example, in
In another exemplary embodiment, the illumination drive circuit 110 individually activates (“turns on”) each of the LEDs 210a-210c within the illumination device 30 to enable the optical sensor 70 to measure the intensity of light output from the liquid crystal device 50 in response to illumination by one of the LEDs 210a-210c. For example, to provide optical feedback for the red LED 210a, the illumination drive circuit 110 activates the red LED 210a to illuminate the electro-optical elements 230 with red light via the backlight unit. The LCD controller 120 loads data into the electro-optical elements that allows all of the electro-optical elements (e.g., elements P1-P12) to pass the red light. However, since the red light is filtered by the green and blue color filters 240 in the CFA 60, only the red color filters associated with electro-optical elements P1, P3, P9 and P11 pass the red light to the optical sensor 70. In other embodiments, the LCD controller 120 can alter only the red electro-optical elements (e.g., P1, P3, P9 and P11) within the portion 55 of the liquid crystal device 50 to allow the red light emitted from the red LED 210a to pass through those altered electro-optical elements (e.g., P1, P3, P9 and P11) and into the optical sensor 70.
The measurement data produced by the measurement sensors in the optical sensor 70 is read out by the display controller 130 to provide optical feedback indicating the light intensity degradation of a particular LCD/LED 210a-210c in the illumination device 30. Continuing with the above example, sensors S1, S3, S9 and S11 in the optical sensor 70 would output measurement data representing the intensity of red light measured at that sensor. The display controller 130 determines an overall measured intensity of the red light at the optical sensor 70 from the measurement data (e.g., an average intensity, maximum intensity, minimum intensity, mean intensity or other measured intensity gleaned from the measurement data), and uses the measured intensity to adjust one or more illumination parameters associated with the red LED 210a. For example, in one embodiment, the display controller 130 is operable to compare the measured intensity, as determined from the measurement data, to a known or initial intensity of the red LED 210a and estimate a degradation value (e.g., the percentage of combined LED and LCD degradation over time) for the red LED 210a based on the comparison between the measured intensity and the known intensity. The display controller 130 uses the estimated degradation value to adjust the duty factor of the pulse width modulation of the red LED 210a in the illumination drive circuit 110 to compensate for the perceived degradation of the red LED 210a.
The liquid crystal device 50 includes a substrate 330 on which a two-dimensional array of pixel electrodes 365 are located. The pixel electrodes 365 are spatially arranged in a pattern 235 corresponding to the pattern of color filters, as shown in
The pixel electrodes 365 in combination with pixel drive circuitry 370, common electrode 350, liquid crystal material 340 and polarizers 380 and 390 form the respective individual electro-optical elements (230, shown in
In one embodiment, the electro-optical elements allow light of a particular polarization to be transmitted or not transmitted. In another embodiment, the pixel electrodes 365 can be driven with voltages that create a partial reaction of the liquid crystal material 340 so that the electro-optical element is in a non-binary state (i.e., not fully ON or OFF) to produce the “gray scale” transmission. For example, the voltages that create a partial reaction of the liquid crystal material 340 are typically produced by applying signals on the pixel electrode 365 and common electrode 350 that not fully in or out of phase, thereby creating a duty cycle between zero and 100 percent, as understood in the art.
Thereafter, to provide optical feedback, at block 420, the electro-optical elements are illuminated with light from one or more LEDs, and at block 430, the electro-optical elements are selectively altered to pass only the light in a particular wavelength range corresponding to one of the LEDs. For example, in one embodiment, all of the LEDs are activated to illuminate the electro-optical elements with white light containing red, blue and green light. To pass only light from a particular LED (e.g., the red LED), only the electro-optical elements having a red color filter are altered so as to pass only red light. In another embodiment, the electro-optical elements are illuminated with light from only a single LED (e.g., the red LED), and at least those electro-optical elements having a red color filter are altered to enable the red light to be passed.
At block 440, the intensity of the light output from the electro-optical elements is measured, and at block 450, the measured intensity is used to adjust an illumination parameter associated therewith. For example, in one embodiment, the measured intensity is compared to a known or initial intensity of a particular LED, and a degradation value (e.g., the percentage of combined LED and LCD degradation over time) is estimated for that LED based on the comparison between the measured intensity and the known intensity. The estimated degradation value is used to adjust the duty factor of the pulse width modulation of the particular LED to compensate for the perceived degradation. At block 460, this process is repeated for each color of LEDs in the display device. Once the feedback is complete, the adjusted illumination parameters are stored for future use at block 470.
The innovative concepts described in the present application can be modified and varied over a wide rage of applications. Accordingly, the scope of patented subject matter should not be limited to any of the specific exemplary teachings discussed, but is instead defined by the following claims.
