Patent Application
20220199035
This disclosure relates to a display device, and specifically to a display device with bonding pads where each bonding pad receives data signals for multiple columns of micro organic light emitting diode (OLED) pixels.
A display device is often used in a virtual reality (VR) or augmented-reality (AR) system as a head-mounted display (HMD) or a near-eye display (NED). The display device may include an array of OLED pixels that emits light. To display a high resolution image, the display device may include a large number of OLED pixels in the array that are driven with a high frame rate. As a result of high frame rate, there may be signal settling errors that cause deterioration in image quality. Further, HMD and NED need to be portable and compact to be worn by users, so there is limited space on a chip for arranging bonding pads and signal lines for routing data signals and timing control signals for operating the pixels. To reduce area of the chip, adjacent bonding pads may be disposed with a smaller pitch in between or arranged into rows. However, these alternative layouts involve a complex process flow for manufacturing and may result in yield loss. Further, when bonding pads are placed close to each other, there may be an increase in signal noise due to crosstalk. Alternatively, a larger chip may be used to fit the large number of OLED pixels, signal lines, and bonding pads, but using a larger chip increases the cost and size of the display device.
Embodiments relate to a display device including a display element with a plurality of pixels and a display driver circuit that generates data signals for the display element, where the display element includes a plurality of bonding pads each of which receives data signals for multiple columns of pixels in the display element. Since one bonding pad is used for receiving data voltages for multiple columns of pixels that each includes multiple columns of subpixels, the display element includes a demultiplexer and sample and hold circuits for providing data signals for driving the columns of pixels in a time-divisional manner. The demultiplexer routes data signals for a column of pixels to a corresponding sample and hold circuit that samples data signals at the bonding pad, stores the sampled data signal value, and sends the stored value to the column of pixels for driving the column of pixels.
In some embodiments, the display element includes a first source driver that drives a first column of pixels and a second source driver that drives a second column of pixels that are connected to the same bonding pad. Each of the first source driver and the second source driver is connected to a set of sample and hold circuits. The set of sample and hold circuits is connected in parallel between the corresponding source driver and the bonding pad, where the set of sample and hold circuits includes a plurality of capacitors that stores data signals for the corresponding column of pixels, a first set of switches that connects or disconnects the capacitors and the bonding pad to sample and store the data signal value in the capacitors, and a second set of switches that connects or disconnects the capacitors and the corresponding source driver to send the stored value to the column of pixels. At a given time, no more than one of the first set of switches may be closed at a time to charge no more than one capacitor at a time. However, a switch from the first set of switches and a switch from the second set of switches may be closed at the same time such that a period during which one capacitor is charged overlaps with a period during which another capacitor transfers data voltage to the source driver, allowing for a compact operation time of the display device.
The figures depict embodiments of the present disclosure for purposes of illustration only.
Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the various described embodiments. However, the described embodiments may be practiced without these specific details. In other instances, well-known methods, procedures, components, circuits, and networks have not been described in detail so as not to unnecessarily obscure aspects of the embodiments.
Embodiments relate to a display device with a reduced number of bonding pads in a display element. Instead of having a bonding pad for each column of pixels, a bonding pad may be connected to a plurality of columns of pixels and send data signals to the plurality of columns of pixels in a time-divisional manner. The bonding pad is connected to the plurality of columns of pixels through a set of sample and hold circuits, and the set of sample and hold circuits samples data signals at the bonding pad, stores the sampled data signal value, and sends the stored value to the appropriate column of pixels.
Embodiments of the invention may include or be implemented in conjunction with an artificial reality system. Artificial reality is a form of reality that has been adjusted in some manner before presentation to a user, which may include, e.g., a virtual reality (VR), an augmented reality (AR), a mixed reality (MR), a hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include completely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, haptic feedback, or some combination thereof, and any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional effect to the viewer). Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, e.g., create content in an artificial reality and/or are otherwise used in (e.g., perform activities in) an artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a head-mounted display (HMD) connected to a host computer system, a standalone HMD, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.
The NED 100 shown in
The display assembly 210 may direct the image light to the eye 220 through the exit pupil 230. The display assembly 210 may be composed of one or more materials (e.g., plastic, glass, etc.) with one or more refractive indices that effectively decrease the weight and widen a field of view of the NED 100.
In alternate configurations, the NED 100 may include one or more optical elements (not shown) between the display assembly 210 and the eye 220. The optical elements may act to, by way of various examples, correct aberrations in image light emitted from the display assembly 210, magnify image light emitted from the display assembly 210, perform some other optical adjustment of image light emitted from the display assembly 210, or combinations thereof. Example optical elements may include an aperture, a Fresnel lens, a convex lens, a concave lens, a filter, or any other suitable optical element that may affect image light.
In some embodiments, the display assembly 210 may include a source assembly to generate image light to present media to a user's eyes. The source assembly may include, e.g., a light source, an optics system, or some combination thereof. In accordance with various embodiments, a source assembly may include a light-emitting diode (LED) such as an organic light-emitting diode (OLED).
The waveguide display 300 may include, among other components, a source assembly 310, an output waveguide 320, and a controller 330. For purposes of illustration,
The source assembly 310 generates image light. The source assembly 310 may include a source 340, a light conditioning assembly 360, and a scanning mirror assembly 370. The source assembly 310 may generate and output image light 345 to a coupling element 350 of the output waveguide 320.
The source 340 may include a source of light that generates at least a coherent or partially coherent image light 345. The source 340 may emit light in accordance with one or more illumination parameters received from the controller 330. The source 340 may include one or more source elements, including, but not restricted to light emitting diodes, such as micro-OLEDs, as described in detail below with reference to
The output waveguide 320 may be configured as an optical waveguide that outputs image light to an eye 220 of a user. The output waveguide 320 receives the image light 345 through one or more coupling elements 350 and guides the received input image light 345 to one or more decoupling elements 360. In some embodiments, the coupling element 350 couples the image light 345 from the source assembly 310 into the output waveguide 320. The coupling element 350 may be or include a diffraction grating, a holographic grating, some other element that couples the image light 345 into the output waveguide 320, or some combination thereof. For example, in embodiments where the coupling element 350 is a diffraction grating, the pitch of the diffraction grating may be chosen such that total internal reflection occurs, and the image light 345 propagates internally toward the decoupling element 360. For example, the pitch of the diffraction grating may be in the range of approximately 300 nm to approximately 600 nm.
The decoupling element 360 decouples the total internally reflected image light from the output waveguide 320. The decoupling element 360 may be or include a diffraction grating, a holographic grating, some other element that decouples image light out of the output waveguide 320, or some combination thereof. For example, in embodiments where the decoupling element 360 is a diffraction grating, the pitch of the diffraction grating may be chosen to cause incident image light to exit the output waveguide 320. An orientation and position of the image light exiting from the output waveguide 320 may be controlled by changing an orientation and position of the image light 345 entering the coupling element 350.
The output waveguide 320 may be composed of one or more materials that facilitate total internal reflection of the image light 345. The output waveguide 320 may be composed of, for example, silicon, glass, or a polymer, or some combination thereof. The output waveguide 320 may have a relatively small form factor such as for use in a head-mounted display. For example, the output waveguide 320 may be approximately 30 mm wide along an x-dimension, 50 mm long along a y-dimension, and 0.5-1 mm thick along a z-dimension. In some embodiments, the output waveguide 320 may be a planar (2D) optical waveguide.
The controller 330 may be used to control the scanning operations of the source assembly 310. In certain embodiments, the controller 330 may determine scanning instructions for the source assembly 310 based at least on one or more display instructions. Display instructions may include instructions to render one or more images. In some embodiments, display instructions may include an image file (e.g., bitmap). The display instructions may be received from, e.g., a console of a virtual reality system (not shown). Scanning instructions may include instructions used by the source assembly 310 to generate image light 345. The scanning instructions may include, e.g., a type of a source of image light (e.g. monochromatic, polychromatic), a scanning rate, an orientation of scanning mirror assembly 370, and/or one or more illumination parameters, etc. The controller 330 may include a combination of hardware, software, and/or firmware not shown here so as not to obscure other aspects of the disclosure.
According to some embodiments, source 340 may include a light emitting diode (LED), such as an organic light emitting diode (OLED). An organic light-emitting diode (OLED) is a light-emitting diode (LED) having an emissive electroluminescent layer that may include a thin film of an organic compound that emits light in response to an electric current. The organic layer is typically situated between a pair of conductive electrodes. One or both of the electrodes may be transparent.
As will be appreciated, an OLED display can be driven with a passive-matrix (PMOLED) or active-matrix (AMOLED) control scheme. In a PMOLED scheme, each row (and line) in the display may be controlled sequentially, whereas AMOLED control typically uses a thin-film transistor backplane to directly access and switch each individual pixel on or off, which allows for higher resolution and larger display areas.
Anode 420 and cathode 480 may include any suitable conductive material(s), such as transparent conductive oxides (TCOs, e.g., indium tin oxide (ITO), zinc oxide (ZnO), and the like). The anode 420 and cathode 480 are configured to inject holes and electrons, respectively, into one or more organic layer(s) within emissive layer 450 during operation of the device.
The hole injection layer 430, which is disposed over the anode 420, receives holes from the anode 420 and is configured to inject the holes deeper into the device, while the adjacent hole transport layer 440 may support the transport of holes to the emissive layer 450. The emissive layer 450 converts electrical energy to light. Emissive layer 450 may include one or more organic molecules, or light-emitting fluorescent dyes or dopants, which may be dispersed in a suitable matrix as known to those skilled in the art.
Blocking layer 460 may improve device function by confining electrons (charge carriers) to the emissive layer 450. Electron transport layer 470 may support the transport of electrons from the cathode 480 to the emissive layer 450.
In some embodiments, the generation of red, green, and blue light (to render full-color images) may include the formation of red, green, and blue OLED sub-pixels in each pixel of the display. Alternatively, the OLED 400 may be adapted to produce white light in each pixel. The white light may be passed through a color filter to produce red, green, and blue sub-pixels.
Any suitable deposition process(es) may be used to form OLED 400. For example, one or more of the layers constituting the OLED may be fabricated using physical vapor deposition (PVD), chemical vapor deposition (CVD), evaporation, spray-coating, spin-coating, atomic layer deposition (ALD), and the like. In further aspects, OLED 400 may be manufactured using a thermal evaporator, a sputtering system, printing, stamping, etc.
According to some embodiments, OLED 400 may be a micro-OLED. A “micro-OLED,” in accordance with various examples, may refer to a particular type of OLED having a small active light emitting area (e.g., less than 2,000 μm2 in some embodiments, less than 20 μm2 or less than 10 μm2 in other embodiments). In some embodiments, the emissive surface of the micro-OLED may have a diameter of less than approximately 2 μm. Such a micro-OLED may also have collimated light output, which may increase the brightness level of light emitted from the small active light emitting area.
In some embodiments, the display active area 530 may have at least one areal dimension (i.e., length or width) greater than approximately 1.3 inches, e.g., approximately 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.25, 2.5, 2.75, or 3 inches, including ranges between any of the foregoing values, although larger area displays are contemplated.
Backplane 520 may include a single crystal or polycrystalline silicon layer 523 having a through silicon via 525 for electrically connecting the DDIC 510 with the display active area 530. In some embodiments, display active area 530 may further include a transparent encapsulation layer 534 disposed over an upper emissive surface 533 of active matrix 532, a color filter 536, and cover glass 538.
According to various embodiments, the display active area 530 and underlying backplane 520 may be manufactured separately from, and then later bonded to, DDIC 510, which may simplify formation of the OLED active area, including formation of the active matrix 532, color filter 536, etc.
The DDIC 510 may be directly bonded to a back face of the backplane opposite to active matrix 532. In further embodiments, a chip-on-flex (COF) packaging technology may be used to integrate display element 540 with DDIC 510, optionally via a data selector (i.e., multiplexer) array (not shown) to form OLED display device 500. As used herein, the terms “multiplexer” or “data selector” may, in some examples, refer to a device adapted to combine or select from among plural analog or digital input signals, which are transmitted to a single output. Multiplexers may be used to increase the amount of data that can be communicated within a certain amount of space, time, and bandwidth.
As used herein, “chip-on-flex” (COF) may, in some examples, refer to an assembly technology where a microchip or die, such as an OLED chip, is directly mounted on and electrically connected to a flexible circuit, such as a direct driver circuit. In a COF assembly, the microchip may avoid some of the traditional assembly steps used for individual IC packaging. This may simplify the overall processes of design and manufacture while improving performance and yield.
In accordance with certain embodiments, assembly of the COF may include attaching a die to a flexible substrate, electrically connecting the chip to the flex circuit, and encapsulating the chip and wires, e.g., using an epoxy resin to provide environmental protection. In some embodiments, the adhesive (not shown) used to bond the chip to the flex substrate may be thermally conductive or thermally insulating. In some embodiments, ultrasonic or thermosonic wire bonding techniques may be used to electrically connect the chip to the flex substrate.
The display active area 530 may include a plurality of pixels (e.g., m rows by n columns) with each pixel including a plurality of subpixels (e.g., a red subpixel, a green subpixel, a blue subpixel). Each subpixel may be connected to a gate line and a data line and driven to emit light according to a data signal received through the connected data line when a corresponding gate signal is provided through the connected gate line. Each row of pixels may be connected to an emission line that controls when the row of pixels is to emit light by sending emission line control signal to the row.
The backplane 520 may include conductive traces for electrically connecting the pixels in the display active area 530, the gate driver 635, the source drivers 645, and the bonding pads 640. The bonding pads 640 are conductive regions on the backplane 520 that are electrically coupled to signal lines 624 of the DDIC 510 to receive timing control signals from the timing controller 610, data signals from the data processing unit 615, and bias and reference voltages from the bias and reference voltage unit 620. The bonding pads 640 are connected to the source drivers 645 and the gate driver 635 as well as other circuit elements in the backplane 520. In the embodiment illustrated in
The gate driver 635 may be connected to a plurality of gate lines (GL1 to GLm) and provide gate-on signals to the plurality of gate lines at appropriate times. In some embodiments, each subpixel in the display active area 530 may be connected to a gate line. For a given subpixel, when the subpixel receives a gate-on signal via the corresponding gate line, the subpixel can receive a data signal to emit light.
The source drivers 645 provide data signals to the display active area 530. Each of the source drivers 645 is connected to a column of pixels which includes a plurality of columns of subpixels. For example, each source driver 645 is connected to a column of red subpixels, a column of green subpixels, and a column of blue subpixels. A source driver 645 may be connected to a demultiplexer (demux) that receives an input from the source driver 645 and outputs data signals to an appropriate column of subpixels. The demux may be a 1:3 demux that outputs to the column of red subpixels, the column of green subpixels, or the column of blue subpixels in a time-divisional manner.
The DDIC 510 may include a timing controller 610, a data processing circuit 615, a bias and reference voltage unit 620, an input/output (I/O) interface 625, a mobile industry processor interface (MIPI) receiver 630, and signal lines 624. In other embodiments, one or more components of the DDIC 510 may be disposed in the display element 540.
The I/O interface 625 is a circuit that receives control signals from other sources and sends operation signals to the timing controller 610. The control signals may include a reset signal RST to reset the display element 540 and signals according to serial peripheral interface (SPI) or inter-integrated circuit (I2C) protocols for digital data transfer. Based on the received control signals, the I/O interface 625 may process commands from a system on a chip (SoC), a central processing unit (CPU), or other system control chip.
The MIPI receiver 630 may be a MIPI display serial interface (DSI), which may include a high-speed packet-based interface for delivering video data to the pixels in the display active area 530. The MIPI receiver 630 may receive image data DATA and clock signals CLK and provide timing control signals to the timing controller 610 and image data DATA to the data processing unit 615.
The timing controller 610 may be configured to generate timing control signals for the gate driver 635, the source drivers 645, and other components in the backplane 520. The timing control signals may include a clock, a vertical synchronization signal, a horizontal synchronization signal, and a start pulse. However, timing control signals provided from the timing controller 610 according to embodiments of the present disclosure are not limited thereto.
The data processing unit 615 may be configured to receive image data DATA from the MIPI receiver 630 and convert the data format of the image data DATA to generate data signals input to the source drivers 645 for displaying images in the display active area 530.
The bias and reference voltage unit 620 provides a bias voltage Vbias and a reference voltage Vref to circuit elements to the bonding pads 640 in the display element 540.
When the first distance D1 between two adjacent bonding pads 640 is small, there can be signal noise due to crosstalk that causes degraded image quality. A possible solution to increase the first distance D1 is to arrange the bonding pads into two rows such that adjacent bonding pads 640 are offset. However, this involves a complex layout and a larger surface area for the display element 540A, which increases manufacturing costs and size of the display device 600. Another possible solution is to reduce a number of bonding pads 640 by connecting multiple source drivers to a single bonding pad 640 and driving pixels using time division. This approach is described below with respect to
As illustrated in
The bonding pad 640 of the display element 540B receives data signals from the DDIC 510B via the signal line 624. The bonding pad 640 is connected to a second demultiplexer 822 that is connected to a plurality of sample and hold circuits 824. A demultiplexer circuit 828 includes a second demultiplexer 822 and a plurality of sample and hold circuits 824A through 824D (collectively referred to as “sample and hold circuits 824” and also referred to individually as “sample and hold circuit 824”) connected to the second demultiplexer 822. Each sample and hold circuit 824 corresponds to a different column of pixels 730. An example demultiplexer circuit 828 that corresponds to four columns of pixels 730A, 730B, 730C, and 730D is illustrated in detail in
For example, a first sample and hold circuit 824A is connected in between a first source driver 645A and the bonding pad 640A to sample and store data signals at the bonding pad 640A. The sampled data signal is used for driving a first column of pixel 730A including a column of red subpixels 728R, a column of green subpixels 728G, and a column of blue subpixels 728B. The first sample and hold circuit 824A includes a first red sampling switch S_1R connected to a first red capacitor C_1R. The first red capacitor C_1R is configured to store data signals for the column of red subpixels 728R of the first column of pixels 730A. The first red sampling switch S_1R connects the first red capacitor C_1R to sample data signal transmitted to the bonding pad 640A by the DDIC 510B and disconnects the first red capacitor C_1R after it has been charged. The first red capacitor C_1R is also connected to a first red transfer switch T_1R that connects the first red capacitor C_1R to the first source driver 645A to transfer the data signal stored in the first red capacitor C_1R to the first source driver 645A and disconnects after completing the data signal transfer.
The first sample and hold circuit 824A also includes a first green capacitor C_1G and a first blue capacitor C_1B that are connected or disconnected from the bonding pad 640A by a first green sampling switch S_1G and a first blue sampling switch S_1B, respectively. The first green sampling switch S_1G and the first blue sampling switch S_1B sample and store data signals for its corresponding column of subpixels. After being charged, the first green capacitor C_1G and the first blue capacitor C_1B are connected or disconnected from the first source driver 645A by a first green transfer switch T_1G and a first blue transfer switch T_1B, respectively, to transfer data signal to the first source driver 645A.
The first red transfer switch T_1R, the first green transfer switch T_1G, and the first blue transfer switch T_1B are connected to an input of the first source driver 645A. The input of the first source driver 645A is also connected to a reference switch Sref that connects or disconnects the first source driver from a reference voltage Vref. The reference switch Sref prevents the input from floating by closing at times when none of the transfer switches T_1R, T_1G, T_1B are connected to the first driver 645A and fixes the input to the reference voltage Vref. Floating input could lead to deteriorated image quality, but by applying the reference voltage Vref, unexpected variations in image may be prevented.
During a subframe, the sampling switches are sequentially opened and closed to charge the capacitors with no more than one sampling switch closed at a time. A switch is closed when its timing signal is in high state and open when its timing signal is in low state. In the embodiment illustrated in the timing diagram 1000, the four red sampling switches S_1R, S_2R, S_3R, S_4R are sequentially closed and then opened to charge its corresponding capacitor, followed by the four green sampling switches S_1G, S_2G, S_3G, S_4G, and then the four blue sampling switches S_1B, S_2B, S_3B, S_4B.
After the four red capacitors C_1R, C_2R, C_3R, C_4R have been charged, the four red transfer switches T_1R, T_2R, T_3R, T_4R may be closed to transfer the data signals to the source driver 645A. As shown in
The timing signal for the reference switch Sref is the inverse of the respective transfer switches that it is connected to. For example, for the reference switch Sref connected to the first sample and hold circuit 824A, control signal for the reference switch Sref is in a high state when none of the control signals for the first red transfer switch T_1R, the first green transfer switch T_1G, and the first blue transfer switch T_1B are in a high state. Therefore, the input to the first source driver 645A is set to the reference voltage Vref only when the input is not connected to one of the first red capacitor C_1R, the first green capacitor C_1G, and the first blue capacitor C_1B.
The first red capacitor C_1R, the first green capacitor C_1G, and the first blue capacitor C_1B are connected to the same first source driver 645A. The first source driver 645A outputs data signals to one of the three columns of subpixels within the first column 730A at a time. Each subpixel may be connected to a gate line and a data line and driven by according to a data signal provided to the connected data line in response to a gate signal provided through the connected gate line. Each subpixel may include a storage capacitor that stores charge according to the data signal provided by the first source driver 645A until the subpixel is configured to emit light.
Each row of pixels 728 in the display active area 530 may be connected to an emission line configured to receive an emission line control signal (e.g., EM_ROW0, EM_ROW1, . . . EM_ROWN−1) that corresponding to the row. When the emission line control signal is in a high state, pixels 728 in the row emits light. Accordingly, the emission period for a row of pixels occurs after all of the transferring switches complete transferring the charge in the capacitors of the sample and hold circuit 828 to the subpixels in the row. For example, referring to row 0 of the display active area 530, the sample and hold circuit 828 samples data signals for the pixels 728 in row 0 during subframe 0 and transfers the data signals to the pixels 728 in row 0 during a portion of subframe 0 and subframe 1. After the completion of transferring data signals to the pixels 728 in row 0, the pixels 728 in row 0 emit light when the emission line control signal EM_ROW0 is in a high state during subframe 1 and subframe 2.
During the subsequent subframes of the frame, display device 600 iteratively samples data signals, transfers the data signals, and emits light based on the data signals from the corresponding row of pixels 728. The display device 600 scans vertically from top to bottom until all n rows of pixels 728 emit light and repeats the process for a next frame.
The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the disclosure be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments is intended to be illustrative, but not limiting, of the scope of the disclosure, which is set forth in the following claims.
