Patent Application
20140184667
The present disclosure relates generally to the field of display devices and more specifically to the field of light-emitting diode display panels.
An Organic Light-Emitting Diode (OLED) display consists of a matrix of Organic Light-Emitting Diode (OLED) pixels that generate light upon electrical activation. Conventionally, luminance of each OLED increases with more current flowing to it. Typically, this continuous current flow is controlled by at least two transistors at each pixel, one to start or stop the charging of a storage capacitor and the second to provide a voltage source at the level needed to create a constant current to the pixel. In a commonly adopted RGB color model, each light emitting element, i.e., pixel, comprises a red (R) OLED element, a green (G) OLED element, and a blue (B) OLED element for emitting red color, green color and blue color light, respectively. A pixel can express a desired color in a certain frame by mixing light of the three colors from respective light emitting elements. Typically, a system encodes pixel color values by devoting 8 bits to each of the R, G, and B components for control.
One approach to achieve control of an OLED display is to use an active matrix thin-film-transistor (TFT) backplane in an Active matrix Organic Light-Emitting Diode (AMOLED) display. The active matrix functions as switches to control the current flowing to each individual color element in each frame. Conventionally, the current flowing to each OLED is continuous and controlled by at least two TFTs, the first one for activating and deactivating the charging of a storage capacitor, and the second one for providing a voltage required to drive a constant current of intended level to control the luminance of the color element. Since the second transistor operates in its linear region, a considerable fraction of the power can be consumed by the internal resistance of the second transistor which wastes a significant amount of valuable power, especially when used in a mobile computing device fitted with a limited size battery. For example, the TFT transistors in an AMOLED display device may consume 40-60% of the power supplied to drive the AMOLED display device.
Further, in a conventional design, since luminance of each OLED is driven by a continuous current through an associated transistor, the binary color values, e.g. in the format of a 8:8:8 byte, usually have to be converted to analog data through a Digital-Analog-Converter (DAC) in a timing controller, which complicates the circuit design in the timing control logic.
Moreover, a display device for a portable device is often used in a wide range of ambient light levels. Conventionally, as the ambient light level increases, the luminance contrast decreases due to a fixed brightness emitted from the display panel. Although setting the display panel luminance constantly at its maximum level would ensure the images are visible in the widest range of ambient light levels, the unnecessarily brightness increases power consumption, and shortens operating lifetime of the display panel. Also, excessive contrast between the displayed images and dark ambient environments may cause eye discomforts.
Therefore, it would be advantageous to reduce the power consumed by the transistors in an AMOLED display device and thereby increase power consumption efficiency of the display device. It would also be advantageous if the timing control logic for such a device can be simplified. Moreover, it would be also advantageous to be capable of adjusting the global luminance of a display panel in response to ambient light level.
Accordingly, embodiments of the present disclosure provide a mechanism to reduce power consumption by using transistors operating in a binary on/off mode to drive an array of OLEDs. The mechanism also allows for simplified designs of timing control logic and global luminance control of the display device. Embodiments of the present disclosure advantageously include an AMOLED layer with each color element comprising a discrete array of OLED junctions coupled to a plurality of transistors. Thus, luminance of the color element can be digitally controlled by turning on a selected combination of the transistors and thereby activating luminance of the associated OLED junctions. The plurality of OLED junctions of a respective color element vary in size in accordance with the value of the binary digit to which they are controlled. In one embodiment, the plurality of junctions that make up a color element may vary in size according to 2n, where n is the junction number and may correspond to a bit position of a control color bit that that controls the junction. The color bit is located within a color byte for controlling the entire color element.
In one embodiment of the present disclosure, a flat panel display apparatus comprises a cathode layer, an anode layer, an OLED layer and a plurality of sets of transistors coupled to the OLED layer. The OLED layer comprises a plurality of pixels arranged in a matrix. Each pixel comprises a plurality of color elements, and each of the plurality of color elements comprises a plurality of diode junctions arranged in a pattern. Each transistor controls a corresponding diode junction in a binary mode by a respective bit of a respective binary color value. A nominal luminance of each diode junction of a color element may correspond to a binary value represented by a respective bit position of a respective bit in a corresponding binary color value. Each transistor may be further coupled to a storage device operable to store the binary color value. The global luminance of the pixels may be adjustable by adjusting a voltage across the cathode and anode of the display panel. The transistors may be integrated on a thin film transistor TFT layer.
In another embodiment of the present disclosure, a system comprises a memory, a display panel and a display control logic, where the display panel comprises a cathode layer, an anode layer an AMOLED layer and a plurality of switches coupled to the AMOLED layer. The AMOLED layer comprises a plurality of pixels. Each of the plurality of pixels comprises a plurality of color element and each color element comprises a plurality of diode junctions coupled to a set of switches. The display control logic is operable to control luminance of each diode junction of respective color element by controlling a respective switch. The switches may be configured by transistors operating in on/off mode. Each of the transistors may have the gate coupled to a bit of corresponding binary color value provided by the display control logic, the drain coupled to the anode layer, and a source coupled to an associated diode junction. The total number of the plurality of diode junctions in a respective color element may be equal to a total number of bits in a corresponding binary color value, and each diode in a respective color element may have nominal luminance proportional to 2n, where n is the bit position of the bit controlling the diode. The system may further comprise a plurality of flip-flops coupled to the plurality of switches.
In another embodiment of the present disclosure, a method for displaying images on a display device comprises receiving image data that comprises a binary number representing luminance of a color element of a corresponding pixel of the display device and the color element comprises a plurality of discrete illuminating units. The method further comprises controlling each discrete illuminating unit individually between a first state and a second state with a respective bit of the binary number. The discrete illuminating units may comprise OLEDs coupled to transistors. The transistors may be configured to receive a respective bit of a binary number and provide binary control to the associated OLED. Each discrete illuminating unit in a color element may have nominal luminance proportional to 2n, where n indicates a bit position of a respective bit of the binary number used to control the illuminating unit.
The foregoing is a summary and thus contains, by necessity, simplifications, generalizations and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of the present invention, as defined solely by the claims, will become apparent in the non-limiting detailed description set forth below.
Embodiments of the present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing figures in which like reference characters designate like elements and in which:
Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of embodiments of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the embodiments of the present invention. The drawings showing embodiments of the invention are semi-diagrammatic and not to scale and, particularly, some of the dimensions are for the clarity of presentation and are shown exaggerated in the drawing Figures. Similarly, although the views in the drawings for the ease of description generally show similar orientations, this depiction in the Figures is arbitrary for the most part. Generally, the invention can be operated in any orientation.
It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the present invention, discussions utilizing terms such as “processing” or “accessing” or “executing” or “storing” or “rendering” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories and other computer readable media into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. When a component appears in several embodiments, the use of the same reference numeral signifies that the component is the same component as illustrated in the original embodiment.
Referring to
The discrete nature of each color element advantageously eliminates the need for linear drive on the current or voltage applied to each color element, thereby saving power consumed on the associated controlling elements, e.g. the transistors. In addition, the elimination of linear control advantageously eliminates the need for digital-analog conversion as required to generate a linear control value by the prior art, and consequently leads to significantly simplified timing control logic.
In some embodiments, each of the discrete segments may be a separate diode junction. In some other embodiments, each of the discrete segments may further comprise a number of discrete diode junctions.
In some embodiments, each color element may comprise a different number of segments from the number of bits in a control byte. In such cases, the control byte may be converted, e.g. via encoding or decoding, to a binary number in order to control the segments to operate in binary mode correctly. In some other embodiments, more than one segment may be grouped together and controlled by a control bit as a unity.
The TFTs may be formed by a well known variety of substrates, including crystalline silicon, poly-silicon and amorphous silicon, where poly-silicon substrates may be processed under low and high temperature. Low-Temperature Poly-Silicon (LTPS) can be built on common low-cost glasses, while High Temperature Poly-Silicon (HTPS) needs quartz plate.
According to the illustrated embodiment in
The global luminance of the display panel 300 can be advantageously adjusted in response to the ambient light level detected by the ambient light sensor 328. For example, if the ambient light sensor senses the ambient light becomes brighter, the global control logic 327 can instruct the anode regulator 326 to output a reduced voltage on the anode layer 314. As a result, the luminance of the display panel 310 decreases. This global brightness value can be adjusted in analog fashion.
In some embodiments, the organic active layers 312 may be formed based on small-molecules technology by thermal evaporation. In some other embodiments, the organic active layers 312 may be polymer layers processed by spin coating. In some other embodiments, the OLED display panel may include a diffusive layer (not shown).
In this configuration, when the gate of an individual transistor 420 receives a logic “1” from a corresponding bit of the byte 440, the corresponding transistor 420 acts as a very low resistance, and allows the anode of the associated diode junction to be substantially at the voltage of Vdd, thereby activating the associated diode 410 to illuminate. On the other hand, if the gate of the transistor 420 receives a logic “0”, the associate diode remains off. Thus, each diode 410 works between an “on” and an “off” mode due to the binary mode operation of the associated transistor.
In some embodiments, as illustrated in
In some embodiments, the flip-flops may be integrated on the TFT layer. In some other embodiments, they may be disposed in the driver or other suitable integrated circuits in the system.
An AMOLED display panel comprising binary mode discrete illuminating segments in each color pixel in accordance with the present disclosure can be applied in any type of devices that require a display panel, such as a laptop, a cell phone, a personal digital assistance (PDA), a touchpad, a desktop monitor, a game display panel, TV, a controller of a machine, etc.
According to the illustrated embodiment in
The main processor 621 can be implemented as one or more integrated circuits and can control the operation of mobile computing device 600. In some embodiments, the main processor 621 can execute a variety of operating systems and software programs and can maintain multiple concurrently executing programs or processes. The storage device 624 can store user data and application programs to be executed by main processor 621, such as video game programs, personal information data, media play back programs. The storage device 624 can be implemented using disk, flash memory, or any other non-volatile storage medium.
Network or communication interface 627 can provide voice and/or data communication capability for mobile computing devices. In some embodiments, network interface can include radio frequency (RF) transceiver components for accessing wireless voice and/or data networks or other mobile communication technologies, GPS receiver components, or combination thereof. In some embodiments, network interface 627 can provide wired network connectivity instead of or in addition to a wireless interface. Network interface 627 can be implemented using a combination of hardware, e.g. antennas, modulators/demodulators, encoders/decoders, and other analog/digital signal processing circuits, and software components.
I/O interfaces 625 provide communication and control between the mobile computing device 600 with other external I/O devices (not shown), e.g. a computer, an external speaker dock or media playback station, a digital camera, a separate display device, a card reader, a disc drive, in-car entertainment system, a storage device, user input devices or the like.
Although certain preferred embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the spirit and scope of the invention. It is intended that the invention shall be limited only to the extent required by the appended claims and the rules and principles of applicable law.
