This disclosure relates generally to LED microdisplay devices and methods for operating the same. In particular, this disclosure relates to devices and methods for transmitting data to and for driving a LED microdisplay device.
LED displays are used in various applications ranging from outdoor large display panels to microdisplays for hand-held display devices. While large display panels may employ arrays of discreet LEDs, a microdisplay often uses monolithic LED arrays to for their small sizes and fine pixel pitches. U.S. Pat. No. 8,557,616 discloses methods of making a microdisplay mounted on an active matrix panel. However, the turn-on voltages of LEDs on an active matrix vary according to the distance between each LED and n-electrode, which leads to variations in the lifetime and emitting wavelength of individual LEDs in the microdisplay. Accordingly, there is a need for micro LED display that has a uniform color purity, good durability, and high power efficiency.
In addition, there are numerous ways to operate LED display panels. U.S. Pat. Nos. 9,747,872 and 9,704,430 disclose an electrical system that include a transmitter (aka sendbox) for distributing data (e.g., video data), a bridge chip (aka first receiver), which receives data from the transmitter and further transmits the data to the receiver chips (aka second receiver.) The receiver chips further process and send data to the array of LED drivers. Data is transmitted among the transmitter and numerous receivers through SerDes links. However, the LLP SerDes speed is slow, e.g., 307.2 Mbps. The bridge chip is needed to distribute 1 Gbps data to several SerDes links. In addition, such a system has a relative large footprint because, for example, each second receiver carries a flash memory.
A large display is assembled together with relative large a plurality LED modules, i.e., LED tiles. Each of these tiles have its designated receiver chip(s) that performs functions such as R/G/B calibrations and gamma calculation. Data communication amongst the tiles are through the cables. This configuration allows the replacement of an individual LED tile with its associated receiver chip(s). Further, power consumption for a large LED display, although an important performance consideration, is not necessarily a constraint. However, for a microdisplay not much larger than a person's palm and powered by a small battery, small size and low power consumption is crucial. Accordingly, there is a need for LED display device that has a simply electrical system and a lower power consumption.
In some embodiments, the microdisplay of this disclosure employs one or more array of quantum dot LEDs or organic LEDs with spacing-saving topology and direct current driver architecture, delivering high video brightness dynamics and power efficiency. Its modular design also allows manufacturing different size displays using the same module.
In further embodiments, the LED array may be arranged in a common anode scan configuration, in which anodes of a plurality of LEDs of a same color in a same row are operatively connected to a power source via a switch while cathodes of the plurality of LEDs of the same color in a same column are tied to the output of a current driver circuit. As such, the LEDs have a same supply voltage. In such a configuration, an NMOS driver is often used as the current sink. An NMOS is preferable over a PMOS because NMOS has a larger current capacity and a lower Rds(on) for a given design geometry.
Alternatively, the LED display may use a common cathode topology, in which cathodes of a plurality of LEDs in a same row are connected to a scan switch via a common cathode bus (i.e., a scan line) and the anodes of a plurality of LEDs of a same color in a same column are connected to a driver circuit via a common anode bus.
One embodiment of the LED panel of the current disclosure has a first layer comprising an LED array having rows and columns of interconnected LED pixels, a second layer comprising a plurality of driver circuits, and a plurality of cathode buses and a plurality of anode buses disposed between the first layer and the second layer. Each driver circuit is connected to a power source and comprises an on-off switch. Each LED pixels have a red LED, a green LED, and a blue LED, and each LED has a cathode and an anode. Each of the plurality of driver circuits outputs a constant current to one of the plurality of cathode buses or to one of the plurality of anode buses.
In a further embodiment of a common cathode configuration, each anode bus connects anodes of LEDs of a same color in a column while each cathode bus connects cathodes of the red LEDs, the green LEDs, and the blue LEDs in a row. Each anode bus receives a constant current outputted from the driver circuit and each cathode bus is connected to the on-off switch in the driver circuit.
In some embodiments, the driver circuit includes a plurality of pulse width modulation (PWM) engines, a register that stores driver circuit settings, and a plurality of gain adjustable current sources. The register provides gray scale values to the PWM engines and global gain adjustment settings to the current sources. The PWM engine receives gray scale values from the configuration register. It also receives R/G/B PWM data, a global clock signal from the receiver circuitry. The PWM engine then provides signals to the gain adjustable current sources. The current sources provide a plurality of current outputs to drive the LED array.
In one of the embodiments in this disclosure, the LED display device contains an electrical system and an LED display having one or more arrays of LED pixels. The electrical system includes a transmitter, a plurality of receiver chips each having a receiver circuitry, and a plurality of driver chips each having a driver circuitry. Alternatively, the receiver circuitry and the driver circuitry are integrated on a chip (i.e., “LPU,” “LPU chip,” or “integrated receiver/driver chip”) so that the electrical system contains a number of LPU chips. The transmitter has a memory storing a Gamma correction lookup table and a buffer for storing a LED calibration data. The transmitter receives data packets from a data source, performs Gamma encoding and LED calibration to the data packets. The receiver circuitry is coupled to the transmitter and receives the data packets from the transmitter and sends PWM data to a group of LED drivers, which provides current sources to drive the LED array.
In another embodiment, the transmitter is coupled to a flash memory storing the Gamma correction lookup table and the LED calibration data. The flash memory provides the Gamma correction lookup table and the LED calibration data to the transmitter upon power up.
In certain embodiments, the transmitter and the plurality of receivers are serially connected using a plurality of transformerless serial links, e.g., SerDes links.
In further embodiments, the array of LED pixels are bonded to a number of LPU chips and the group of LED drivers on the LPU chips are connected to the array of LED pixels. The LPU chips in turn are bonded to a substrate. The substrate has the transmitter mounted thereon and a plurality of connection points for receiving external feeds to the LED display device, such as a human interface cable, a power cable, or a video source cable. The LED array is a monolithic quantum dot LED array or a monolithic organic LED array. The LED array is connected to the driver circuitry in either a common anode or a common cathode configuration.
In still other embodiments, the receiver circuitry receives data packets from a data source and generates PWM data. It has an analog front-end circuit that performs signal sampling, clock recovery, and de-serialization of the data stream, an alignment circuit for aligning the de-serialized data stream, a decoder for decoding the data stream from the alignment circuit, and a first-in-first-out circuit coupled to the decoder for outputting the decoded data stream. The decoded data stream is then assembled to generate PWM data.
In still additional embodiments, the driver circuitry contains a double buffer receiving PWM data and the clock signal from the receiver circuitry, a plurality of PWM engines coupled to the double buffer and receive the PWM data and the clock signal form the double buffer, a plurality of current sources coupled to and driven by the plurality of PWM engines, and a plurality of current gain adjustment circuits coupled to the plurality of current sources. The current sources are gain adjustable and can output constant current to drive the LED array.
The teachings of the present invention can be more readily understood by considering the following detailed description in conjunction with the accompanying drawings.
Reference will now be made in detail to embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. It is noted that wherever practicable, similar or like reference numbers may be used in the drawings and may indicate similar or like elements.
The drawings depict embodiments of the present disclosure for purposes of illustration only. One skilled in the art would readily recognize from the following description that alternative embodiments exist without departing from the general principles of the present disclosure.
Used herein, the term “couple,” “couples,” “connect,” or “connects” means either an indirect or direct electrical connection unless otherwise noted. Thus, if a first device couples or connects to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices or connections. Further, an “LED module” refers to a standard-size array of LED pixels that can be assembled together to form a larger LED panel. In addition, “an LED array” means an array of LED pixels. A receiver means a receiver circuitry, either on a chip that does not contain a driver circuitry or on a chip having both the receiver circuitry and a driver circuitry. Likewise, a driver means a driver circuitry, either on a chip that does not have a receiver circuitry or on a chip having both a receiver circuitry and the driver circuitry.
This disclosure presents LED display devices made of LED modules, including monolithic LED modules for making microdisplays. Certain embodiments of the monolithic LED array and assemblies thereof in this disclosure are described with reference to
The QD-LED array can be processed to form electronic devices.
Accordingly, the intermediate layer contains a plurality of scan lines arranged in parallel in the Y-direction and a plurality of parallel common cathode buses arranged in parallel in the X-direction. The plurality of scan lines may reside in a same depth relative to each other, i.e., the first depth. The plurality of common cathode buses may be in another same depth relative to each other, i.e., the second depth. But the first depth and the second depth are not the same.
Further, each scan line is connected to a scan bonding pad (not shown) via a through hole in the intermediate layer (36). The anode bonding pads and the scan bonding pads are connected to the driver circuitry on the driver chip (not shown). The QD-LED array and the intermediate layer may be manufactured on a same wafer using known photolithographic methods. The driver chips may also be fabricated on a wafer, e.g., a Si wafer, which is coupled with the intermediate layer at corresponding bonding pads. The bonding process can be done by semiconductor wafer bonder with the proper placement precision.
The QD-LED array in
In other embodiments of the current disclosure, the LED array may use organic LED (OLED) instead of QD-LEDs. In such cases, each QD-LED in the QD-LED array shown in
One aspect of the current disclosure is that the LED microdisplay is made by assembling multiple LED modules. For example, a 4K microdisplay with 3840×2160 pixels can be constructed using two LED modules of 1920×2160 pixels each, as shown in
The size of LED module is primarily determined by practical manufacturing limitations for high yield processes, including the wafer size of LED, OLED, driver wafer and pixel yields. Since the LED or OLED wafers are different from the Si driver wafer in these aspects, the size of a basic LED or OLED module may differ from that of the driver chip module.
For example, an LED module of about 40 mm by 40 mm has 1920×2160 pixels of 20 micron pitch size. A driver chip of about 4 mm by 20 mm in size can drive 192×1080 pixels so that 10 driver chips may drive 1920×1080 pixels and a 4K microdisplay requires 40 such driver chips.
An LED display device, particularly an LED microdisplay, requires an electrical system of small footprint and low power consumption.
Referring to
In the embodiment of
In a power up stage, the controller (904) sends the calibration data into a line buffer (906) and sends the Gamma correction data to a SRAM (902). The raw video data is Gamma encoded according to the Gamma correction data in the SRAM. The Gamma encoded data is then calibrated with calibration data from the line buffer (906) to obtain the R/G/B data. The RGB data is further distributed to SerDes link ports (SerDes_0 to SerDes_n) and from there sent via the SerDes downlink (
The receiver circuitry on the LPU receives the Gamma encoded, calibrated video data from the SerDes downlink, and performs clock recovery, data alignment, and data decoding. The decoded data is sent to the driver circuitry. In this embodiment, the decoded data is encoded again to have a different ID and passed on the LPUs downstream.
The de-serialized data is aligned, i.e., in “byte align” step. In this step, the boundary between consecutive 10-bit symbols is determined and the de-serialized data is aligned to the boundary. The aligned data packet is further sent to the “106/8B decoder” and decoded to 8-bit data. The 8-bit data enters a FIFO circuit and is passed downstream to be assembled into PWM data, i.e., in the “PWM data assembled” step. The PWM data include the 18-bit data for R, G, and B LEDs, respectively, as well as the clock data (“RCV_DW_CLK”) and SRAM Write Enable control signal (“SRAM_WR_EN”). Examples of the configuration of the D-word based data packet from the FIFO have been disclosed elsewhere, e.g., in U.S. Pat. No. 9,747,872. As such, the receiver circuitry sends write-enable PWM R/G/B data to the LED driver circuitry.
In the LED driver circuitry, the PWM data is written into a double buffer (“LED Driver SRAM Frame Buffer Ping” and “LED Driver SRAM Frame Buffer Pong”), under the control of the “Set_ping” signal, using the double buffering technique. Data from the double buffer is combined in a multiplexer and sent to the LED driver circuitry (i.e., “LED PWM Current Driver Circuitry”), which drives the LED array. Since the receiver circuitry and the driver circuitry are both integrated on one chip, parallel data from the receiver circuit can be directly written into the double buffer.
The control settings for receiver circuitry and for the LED driver circuitry are stored in their respective registers. Both registers are accessible through an I2C slave.
Referring back to
Embodiments of the present disclosure have been described in detail. Other embodiments will become apparent to those skilled in the art from consideration and practice of the present disclosure. Accordingly, it is intended that the specification and the drawings be considered as exemplary and explanatory only, with the true scope of the present disclosure being set forth in the following claims.
This application claims the benefit of priority under 35 U.S.C. § 119 to U.S. Provisional Application No. 62/461,500, filed on Feb. 21, 2017, the entire contents of which are incorporated herein by reference.
Number | Date | Country | |
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62461500 | Feb 2017 | US |