LED driver voltage considering temperature estimation

Abstract

A method for controlling a pixel array based on temperature estimation is provided, the method including sampling an anode voltage of each LED of a plurality of pixels to generate a sampled voltage, determining an average voltage based on the sampled voltages, and determining a total voltage to provide to the pixel based on the average voltage and voltage data from a memory coupled to a controller, the voltage data including one or more of a three sigma value, a driver headroom value, a resistance value, or a k-factor value.

Description

[Technical Field]

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 289,682, filed December 15, 2021, which is incorporated herein by reference in its entirety.

[0002] The present disclosure relates generally to light emitting diode (LED) junction-level temperature estimation and corresponding voltage level setting in monolithic or segmented LED dies. [Background technology]

[0003] The use of micro LED displays or projectors is an emerging technology in the lighting and display industry. Micro LED arrays can contain arrays of thousands to millions of actively emitting tiny LED pixels. The micro LEDs in the array can be individually controlled. Compared to other display technologies, micro LED arrays can have higher brightness and better energy efficiency, making them attractive for a variety of applications, such as television displays or backlighting, automotive lighting, or mobile phone lighting. [Brief explanation of the drawings]

[0004] [Figure 1] 1 shows an LED display system including an LED array that supports individual pixel temperature measurement. [Figure 2] 1 is a representative graph of forward voltage shift versus junction temperature. [Figure 3] 1 shows one embodiment of a representative circuit for driving two pixels, including temperature measurement capability. [Figure 4] 1 illustrates an embodiment of a system that adjusts LED driver voltages by taking into account an average temperature estimate of an LED array. [Figure 5] 1 illustrates one embodiment of a procedure for measuring pixel temperature. [Figure 6]1 illustrates an example of a system with a micro LED control module. [Figure 7] 1 shows a detailed chip-level implementation of a system with a micro LED control module. DETAILED DESCRIPTION OF THE INVENTION

[0005] Unfortunately, the color or intensity of the emitted light in a micro LED array is a function of LED temperature. Temperature variations across the die or substrate supporting the micro LEDs can result in unacceptable micro LED color or intensity variations. When the display is uniform, these variations are visible as color or light intensity streaks, bright spots, or dark spots within the display. In smaller LED pixel arrays, control of intensity variations due to temperature variations can be achieved by using feedback sensors. However, such control systems are generally not available for larger micro LED matrix pixel arrays, which already face additional operating power and data management challenges not experienced by smaller LED pixel arrays. If technology for smaller micro LED arrays worked on larger micro LED arrays, it would be possible to monitor and adjust the individual light intensity of thousands or millions of emitting pixels to compensate for temperature. Such a task would be impractical at higher display refresh rates due to the pixel count.

[0006] The LED temperature determines the current level, I, at which a given LED should be driven. LED (and associated voltage levels (V LED ) is just one of many parameters to consider when determining the current level at which to drive the LED. Other influencing factors that may be considered when determining the current level at which to drive the LED are duty cycle, driver headroom (V LDO ), the forward voltage V of the micro LEDs in the array fvoltage drops due to circuit losses in metal planes, traces, or other interconnects or electrical components; whether the LED is changing from dark to bright or vice versa; or a combination of these.

[0007] The duty cycle determines the average pixel current, which in turn determines the temperature of the LED, thus affecting the forward voltage and ultimately the LED's operation. As the duty cycle increases, the LED's temperature increases, with a corresponding decrease in the LED's forward voltage. As the duty cycle decreases, the LED's temperature decreases, with a corresponding increase in the LED's forward voltage.

[0008] Driver headroom is the voltage drop across the pixel driver of the corresponding pixel. Driver headroom in the context of the driver for the LEDs in a micro LED array is approximately 190 millivolts in some specific implementations and varies for different driver implementations. Driver headroom varies significantly between driver designs. Different driver configurations and different silicon fabrications of the driver result in different driver headroom.

[0009] A voltage drop across a metal plane, trace, or other interconnect manifests itself as a temperature rise in the LED (or other component). This voltage drop causes a rise in temperature and therefore a drop in the LED's forward voltage.

[0010] The K factor determines how much V is affected when there is an expected change in the content provided by the LED. LED The content change can be brightness, color, etc.

[0011] The duty cycle indicates how long the LED is operated relative to the total time available. For example, a 50% duty cycle means that the LED produces light 50% of the time.

[0012] FIG. 1 illustrates an LED display system 100 including an LED array 110. As illustrated, each box in the array 110 defines a pixel 102 whose temperature can be individually estimated using a system controller 120 supporting a temperature monitor and control system 122. The temperature monitor and control system 122 for the LED array 110 can include a circuit-based driver that enables measurement of bus voltage (sometimes referred to as anode voltage). The bus voltage measurement can be used to determine the LED forward voltage, which can be mapped to the corresponding temperature of the pixel. The system controller 120 can be used to make adjustments to the LED array 110 based on the detected temperature. Adjustments can include changing the pixel intensity, color, and on / off state of individual pixels 102 or selected groups of pixels, such as by adjusting the pulse-width modulation (PWM) duty cycle of one or more colors.

[0013] In some embodiments, the LED array 110 can be formed from one or more arrays of micro LEDs (sometimes referred to as "μLEDs" or "uLEDs"). Micro LEDs can support a high density of pixels with lateral dimensions of less than 100 micrometers (μm) by 100 μm. In some embodiments, micro LEDs with diameter or width dimensions of about 50 μm or less can be used. Such micro LEDs can be used to fabricate color displays by closely aligning micro LEDs emitting at multiple visible wavelengths, e.g., red, blue, and green wavelengths. In some embodiments, the micro LEDs can be defined on a monolithic gallium nitride (GaN) or other semiconductor substrate, segmented and formed on a partially or fully divided semiconductor substrate, or individually formed or panel-assembled as a group of micro LEDs. In some embodiments, the LED array 110 can include a small number of micro LEDs positioned on a substrate with an area on the centimeter scale or larger. In some embodiments, the LED array 110 can support a micro LED pixel array having hundreds, thousands, or millions of LEDs positioned together on a centimeter-scale area substrate or smaller. In some embodiments, the micro LEDs can include LEDs sized between 30 microns and 500 microns. In some embodiments, the micro LED pixel array can be formed from LEDs of various types, sizes, and layouts. In some embodiments, a one-dimensional (1D) or two-dimensional (2D) matrix array of individually addressable LEDs can be used. In general, an N×M array can be used, where N and M are between 2 and 1000, respectively. The individual LED structures can have square, rectangular, hexagonal, polygonal, circular, arcuate, or other surface shapes. The array of LED assemblies or structures can be geometrically arranged in linear rows and columns, staggered rows or columns, curved lines, or quasi-random or random layouts.LED assemblies that can include multiple LEDs formed as an array of individually addressable pixels are also supported. In some embodiments, radial or other non-rectangular grid arrangements of conductive lines to the LEDs may be used. In other embodiments, curved, winding, serpentine, and / or other suitable non-linear arrangements of conductive lines to the LEDs may be used.

[0014] FIG. 2 is a representative graph 200 of forward voltage shift versus junction temperature, illustrating temperature determination using forward voltage shift measurements. As can be seen in graph 200, an LED formed with a PN junction is supplied with a current that can induce a forward voltage shift in the LED. The associated forward voltage shift measurement for an LED has a negative temperature coefficient of a few millivolts per degree Celsius, typically -2 mV / °C. FIG. 2 shows an example curve illustrating forward voltage shift as a function of LED junction temperature at a particular current value.

[0015] FIG. 3 illustrates one embodiment of a pixel-level circuit 300 that enables measuring pixel temperature. In this circuit 300, two representative pixels 330, 332 may be from a micro LED array that supports thousands to millions of pixels. Each pixel 330, 332 has a respective driver and a respective LED 338, 340. The illustrated circuit 300 includes current sources 334, 336 and pulse-width modulation (PWM) switches 342, 344 that combine to form a driver, although alternative current and control systems for providing current to drive individual LED pixels may be used. Another switch 346 is connected to the anode of the LED 338 of pixel 330, and similarly, a switch 348 is connected to the anode of the LED 340 of pixel 332. The other terminals of both switches 346, 348 are shown connected to a common power node bus 350.

[0016] In operation, the control block 352 can scan the micro LED array by electrically turning on the switches 346, 348 connected to each LED 338, 340 one at a time. For example, when the control block 352 turns on switch 346 and turns off switch 348, while simultaneously turning off all other switches connected to other pixels, the voltage on bus 350 is equal to the LED forward voltage of LED 338. The bus 350 of LED 338 of pixel 330 can be sent to the control block 352 for processing and / or storage in memory. When switch 346 and all other switches of other pixels in the LED array are turned off and only switch 348 is turned on, the forward voltage of LED 340 of pixel 332 can be measured on bus 350 and processed by the control block 352. In this manner, the LED voltages on bus 350 of the pixels in the matrix can be measured one at a time.

[0017] Control block 352 can be controlled by a higher level controller, such as temperature monitor and control system 122 (see FIG. 1) or command and control module 716 (see FIG. 7). Command and control module 716 of FIG. 7 can include or implement the functionality of temperature monitor and control system 122, and vice versa.

[0018] Figure 4 shows an example of how to compensate for the estimated temperature. LED4 shows a block diagram of one embodiment of a system 400 for setting the temperature. This compensation may be independent of an actual measurement of temperature, such as with a thermometer. The illustrated system 400 includes a pixel 440, a memory 448, and a controller 488. The controller 488 may be similar to the control block 352 of FIG. 3. The pixel 440 may be similar to the pixels 330 and 332. The pixel 440 includes a driver 490 and an LED 492 (e.g., a single LED) electrically coupled to the driver 490. The pixel 440 may provide a voltage 442 supplied to the LED 492 in response to a row select (RS) and a column select (CS) being asserted. A gate 496 (e.g., an AND gate in the example of FIG. 4) may be used to sense when RS and CS for a given pixel 440 are asserted. A switch 494 may be closed in response to the assertion of RS and CS.

[0019] At operation 444, the controller may maintain a running sum of an average voltage 446 of the last N sampled voltages 442 (represented by operation 444). The average voltage 446 is the sum of the last N sampled voltages divided by N, where N is the number of pixels 440 in the micro LED array 110 (see FIG. 1 ). The voltages 442 may be stored in a memory, such as memory 448, which may be a different memory. The average voltage 446 may be stored in a memory, such as memory 448 or a different memory. The average voltage 446 is a running average of the anode 493 voltages of all pixels 440. This value varies with temperature and the globally set pixel current Ibias (bias current 480). The number of voltage 442 samples used for the running average may be configurable. For diagnostic purposes and to invalidate unreliable average voltages 446, voltage 442 values ​​outside a user-defined window of acceptable voltages may be excluded from the calculation of the average voltage 446. Sampling the voltage 442 of the anode 493 (closing the switch 494) can be done intermittently, on a repeating schedule, during a predetermined time, etc. This allows for continuous, occasional, or scheduled adjustment of the micro LED pixel voltage, for example to compensate for temperature.

[0020] 4 includes a 3-sigma value 450 of the voltage 442, a driver headroom value 452, a resistance value 454, and a k-factor value 456. The 3-sigma value 450 is three times the standard deviation of the forward voltage of the pixel 440. The standard deviation can be programmed during testing of the micro LED array 110.

[0021] The driver headroom value 452 is the V LED V f190 millivolts is a typical value for driver headroom. The driver headroom value 452 can be programmed when testing the micro LED array 110.

[0022] Resistance value 454 is an estimate of the equivalent resistance used to determine the I*R losses from the backplane. The I*R losses are converted to heat, which is then used to calculate V f The losses are from metal planes, traces, or other structures not considered elsewhere. The estimated voltage drop due to IR losses is from IR losses in the backplane and surrounding package. The backplane and surrounding package are shown in FIG. 7 and include circuitry coupled to the active matrix 720. The "R" value 454 can be programmed during testing of the micro LED array 110. The "I" value of IR losses can be calculated by multiplying the sum of the PWM values ​​(duty cycle values) of all pixels by the globally set bias current 480, Ibias.

[0023] The k factor value of 456 ensures that V LED For example, if display frame data 464 indicates that LED 492 is bright (or dim) and display frame data 474 indicates that LED 492 is dim (or bright), then k factor value 456 will increase V accordingly. LED The k factor value 456 can be used to adjust any V to account for expected changes in brightness or intensity. LED A constant indicating whether a change is required.

[0024] Display frame data 464 for the current frame may be provided or retrieved, such as from a memory of display frame data. The display frame data 464 indicates the duty cycle δ of each pixel 440, 102 of the micro LED array 110. The controller 488 may determine (by operation 466) an estimate of the input current 468 for the current frame as the sum of the duty cycles of all of the pixels in the micro LED array 110. Similarly, the controller 488 may determine (by operation 476) an estimate of the input current 478 for the immediately preceding frame (based on the previous display frame data 474) as the sum of the duty cycles of all of the pixels in the micro LED array 110 in providing the immediately preceding frame. A frame is provided by operating the micro LEDs 492 of the pixels 102 of the micro LED array 110 according to the duty cycles defined in the frame data 464, 474 for a particular amount of time.

[0025] The bias current 480 may be multiplied by an estimate of the input current 468 via multiplier 470 to generate a bias current estimate 471. The bias current 480 may be multiplied by an estimate of the input current 478 via multiplier 482 to generate a biased previous current estimate 479. The biased previous current estimate 479 may be low-pass filtered by low-pass filter 484 to generate a low-pass filtered estimate 481 of the biased previous current estimate 479. The low-pass filter 484 helps suppress extreme changes in intensity that may result in visible flashing in the display provided by the micro LED array 110.

[0026] A current difference 473 between the low pass filtered current estimate 481 and the biased current estimate 471 can be determined by the controller 488 in the subtractor 472. The current difference 473 is multiplied by the k factor value 456 in the multiplier 462 to produce a V that accounts for the brightness or intensity difference between the previous frame data 474 and the current frame data 464. LED An adjustment 491 may be provided. The resistance value 454 may be multiplied by the bias current estimate 471 via a multiplier 458 to determine the I*R loss 489.

[0027] The controller 488 calculates the average voltage 446, the 3 sigma value 450, the driver headroom value 452, the I*R loss 489, and the V LED Adjustment 491, or a combination of these, to sum up the calculated V LED 486 can be determined.

[0028] 5 illustrates one embodiment of a method 500 for estimating a voltage to provide to an LED driver taking pixel temperature into account. The illustrated method 500 includes sampling an anode voltage of each LED of a plurality of pixels to generate a sampled voltage at operation 550, determining an average voltage based on the sampled voltages at operation 552, and determining a total voltage to provide to the pixel based on the average voltage and voltage data from a memory coupled to the controller at operation 554, where the voltage data includes one or more of a 3-sigma value, a driver headroom value, a resistance value, or a k-factor value.

[0029] The voltage data may further include data indicative of a respective duty cycle for each of the plurality of pixels in a current display frame and an immediately preceding display frame. Method 500 may further include estimating a first total current in the current display frame as a sum of the duty cycles for the plurality of pixels in the current display frame. Method 500 may further include determining a total voltage based on the first total current.

[0030] The voltage data may include a global bias current. The method may further include multiplying the first total current by the global bias current to generate a first bias current. Method 500 may further include multiplying the first bias current by a resistance value to generate an I*R loss. Method 500 may further include determining a total voltage further based on the I*R loss.

[0031] The method 500 may further include estimating a second total current in the immediately preceding display frame as a sum of duty cycles for the plurality of pixels in the immediately preceding display frame. The method 500 may further include determining a total voltage based on the second total current. The method 500 may further include multiplying the second total current by a global bias current to generate a second bias current. The method 500 may further include determining a bias current difference between the first bias current and the second bias current. The method 500 may further include determining a total voltage based on the bias current difference.

[0032] Method 500 may further include multiplying the second bias current by a k factor value to generate an LED voltage adjustment. Method 500 may further include determining a total voltage based on the LED voltage adjustment. Method 500 may further include low-pass filtering the second bias current to generate a low-pass filtered bias current before determining the bias current difference. Method 500 may further include determining the bias current difference as the difference between the first bias current and the low-pass filtered bias current. The total voltage may be determined as the sum of the average voltage, a 3-sigma value, a driver headroom value, an I*R loss, and the LED voltage adjustment.

[0033] FIG. 6 shows an example of a lighting matrix control system 600 with a suitable lighting logic and control module and / or pulse-width modulation module to enable separately controlled and adjusted pixel intensities by setting appropriate ramp times and pulse widths. Such adjusted pixel intensities, ramp times, or pulse widths can help compensate for thermal issues or potential thermal problems. Addressable LED pixel activation can be used to provide patterned illumination, reduce color or intensity variations, and provide various pixel diagnostic functions. A micro LED array, such as that shown in FIG. 6, can include an array of thousands to millions of individually controlled, actively emitting LED pixels. To emit light in a pattern or sequence that results in the display of an image, the current levels of micro LED pixels at different locations on the array can be individually adjusted according to a specific image. This can involve pulse-width modulation (PWM), which turns pixels on and off at a specific frequency. During PWM operation, the average direct current (DC) current through a pixel is the product of the PWM duty cycle, which is the ratio between the conduction time and the period or cycle time, and the current amplitude.

[0034] Processing modules that facilitate efficient use of the system 600 are shown in Figure 6. The system 600 includes a control module 602 that can implement pixel-level or group-pixel-level control of amplitude and duty cycle for the micro LED array. In some embodiments, the system further includes an image processing module 604 for generating, processing, or transmitting images, and a processor, e.g., an I / O module, configured to transmit control data and / or instructions. 2 C(inter-integrated circuit)(I 2and a digital control interface 606 such as a synchronous, multi-reader, multi-follower, packet-switched, single-ended serial communication bus. The digital control interface 606 and control module 602 may include a system microcontroller and any type of wired or wireless module configured to receive control inputs from external devices. By way of example, wireless modules may include Bluetooth, Zigbee, (registered trademark) , Z-wave, mesh, WiFi, near field communication (NFC), and / or peer-to-peer modules may be used. The microcontroller may be any type of dedicated computer or processor that may be incorporated into the LED lighting system and configured or configurable to receive inputs from wired or wireless modules or other modules in the LED system and provide control signals to the other modules based thereon. Algorithms implemented by the microcontroller or other suitable control module 602 may be implemented in a computer program, software, or firmware embodied in a non-transitory computer-readable storage medium for execution by the dedicated processor. Examples of non-transitory computer-readable storage media include read-only memory (ROM), random-access memory (RAM), registers, cache memory, and semiconductor memory devices. The memory may be included as part of the microcontroller or may be implemented elsewhere, either on or off a printed circuit board or electronics substrate.

[0035] As used herein, terms such as module, block, or circuit may refer to electrical and / or electronic components located on individual circuit boards that may be soldered to one or more electronics substrates. However, the term module may also refer to electrical and / or electronic components that provide similar functionality but that may be individually soldered to one or more circuit boards, either in the same area or in different areas. The electrical and / or electronic components may include one or more transistors, resistors, capacitors, diodes, amplifiers, inductors, power supplies, memory, analog-to-digital converters (ADCs), digital-to-analog converters (DACs), switches, multiplexers, logic gates (e.g., AND, OR, XOR, negate, or buffers), processor devices (e.g., central processing units (CPUs), graphics processing units (GPUs), field programmable gate arrays (FPGAs), or application-specific integrated circuits (ASICs)), or the like.

[0036] As previously mentioned, the control module 602 further includes an image processing module 604 and an image processing module 606, e.g., 2 and a digital control interface 606, such as may be implemented using C. In some embodiments, image processing calculations may be performed by the control module 602 through direct generation of a modulation image. Alternatively, standard image files may be processed or otherwise converted to provide modulation matching images. Image data, primarily including PWM duty cycle values, may be processed for every pixel within the image processing module 604. Since amplitude is typically a fixed value or a value that changes infrequently, amplitude-related commands may be sent over a different digital interface (e.g., a separate I 2The digital data may be provided separately via a standard Ethernet interface (NIC), a controller area network (CAN), a universal asynchronous receiver / transmitter (UART), a serial peripheral interface (SPI), a universal serial bus (USB), or the like. The control module 602 interprets the digital data, which may be used by a PWM generator 1210 of the control module 602 to generate a PWM signal 610 for the pixel, and by a digital-to-analog converter (DAC) signal 612 to generate a control signal for generating the required current source amplitude.

[0037] In some embodiments, discrete temperature sensors (T1-T4) may be used for temperature monitoring, which may supplement or provide calibration for the described pixel-level temperature monitoring systems and methods. In an embodiment, pixel matrix 620 of FIG. 6 may include m pixels capable of supporting pixel-level temperature measurements. In an embodiment, the pixels are connected to current sources 334, 336 and PWM switches 342, 344, for example, as described above with respect to FIG. 3.

[0038] The control module 602 may be controlled by a higher level controller, such as the temperature monitor and control system 122 (see FIG. 1) or the command and control module 716 (see FIG. 7). The control module 602 may include or implement the functionality of the control block 352, the controller 488, or vice versa.

[0039] 7 shows in more detail one chip-level implementation of a system 700 that supports functionality such as those described with respect to FIGS. 1-6. The system 700 includes a command and control module 716 that can provide temperature control monitoring and control, as well as implement pixel-level or group-pixel-level control of amplitude and duty cycle for the pixel circuits. In some embodiments, the system 700 further includes a frame buffer (FRAME BUF.) 710 for holding generated or processed images that can be fed to an active LED matrix 720. Other modules, such as an I / O module, are configured to transmit necessary control data or commands. 2 A digital control interface such as a C serial bus 712 or an SPI interface 714 may be included.

[0040] In operation, the system 700 can accept image or other data from a vehicle or other source arriving via the SPI interface 714. Continuous image or video data can be stored in an image frame buffer 710. When image data is not available, one or more standby images held in a standby image buffer (STBY FRAME BUF.) 711 can be directed to the image frame buffer 710. Such standby images can include, for example, an intensity and spatial pattern that matches a vehicle's legally permitted low-beam headlamp radiation pattern, or a default light radiation pattern for architectural lighting or display.

[0041] In operation, pixels in an image are used to determine the response of corresponding LED pixels in the active matrix, and the intensity and spatial or temporal modulation of the LED pixels are based on the image. To reduce data rate issues, in some embodiments, a group of pixels (e.g., a K x L block of pixels, where K and L are integers greater than 1) can be controlled as a block. In embodiments, high speed and data rate operation is supported, allowing pixel values ​​from successive images to be loaded as successive frames in an image sequence at a rate between 30 Hz and 100 Hz, with 60 Hz being typical. PWM can be used to control each pixel to emit light in a pattern and intensity that depends at least in part on the image held in the image frame buffer 710.

[0042] In some embodiments, the system 700 may allocate logic power to V dd and V ss The active matrix receives power for controlling the LED array through multiple VLEDs and V CathodeThe SPI interface 714 can provide full-duplex mode communication using a master-slave architecture with a single master. The leader device originates frames for reading and writing. Multiple follower devices are supported via selection on individual follower select (SS) lines. Input pins can include leader-out-follower-in (MOSI), leader-in-follower-out (MISO), chip select (SC), and clock (CLK), all connected to the SPI interface 714. The SPI interface connects to an address generator, a frame buffer, and a standby frame buffer. The pixels can have parameters set and their signal or power modified by the command and control module (e.g., by power gating before input to the frame buffer or after output from the frame buffer via pulse-width modulation or power gating). The SPI interface 714 can be connected to an address generation module 718, which provides row and address information to the active matrix 720. The address generator module 718 can then provide frame buffer addresses to the frame buffer 710.

[0043] In some embodiments, the command and control module 716 2 The command and control module 716 can be externally controlled via a C serial bus 712. 7-bit addressing of clock (SCL) and data (SDA) pins can be supported. The command and control module 716 can include a digital-to-analog converter (DAC) and two analog-to-digital converters (ADC). These respectively control the V bias, which are used to set the maximum Vf and to help determine the system temperature. An oscillator (OSC) is also connected to set the pulse width modulated oscillation (PWMOSC) frequency of the active matrix 720. In embodiments, bypass lines are also present to allow addressing of individual pixels or blocks of pixels within the active matrix for diagnostic, calibration, or test purposes. The active matrix 720 may be further supported by row and column selects used to address individual pixels supplied with data lines, bypass lines, PWMOSC lines, Vbias lines, and Vf lines.

[0044] As will be appreciated, in some embodiments, the described circuitry and active matrix 720 can be packaged and optionally include a submount or printed circuit board connected to power and control light generation by the semiconductor LEDs. In certain embodiments, the printed circuit board can also include electrical vias, heat sinks, ground planes, electrical traces, and flip-chip or other mounting systems. The submount or printed circuit board can be formed from any suitable material, such as ceramic, silicon, or aluminum. If the submount material is conductive, an insulating layer is formed on the substrate material, and a metal electrode pattern is formed on the insulating layer. The submount can serve as mechanical support, provide an electrical interface between the electrodes on the LEDs and a power source, and also provide heat sinking.

[0045] More generally, emissive active matrix pixel arrays such as those described herein can support applications that benefit from fine-grained intensity, spatial, and temporal control of light distribution. This can include, but is not limited to, precise spatial patterning of emitted light from pixel blocks or individual pixels. Depending on the application, the emitted light can be spectrally distinct, adaptive over time, and / or environmentally responsive. The emissive pixel array can provide pre-programmed light distributions with various intensity, spatial, or temporal patterns. The emitted light can be based at least in part on received sensor data and can be used for optical wireless communication. The associated optics can be distinct at the pixel level, pixel block level, or device level. An example emissive pixel array can include a device with a commonly controlled center block of high-brightness pixels with associated common optics, while edge pixels can have separate optics. Typical applications supported by emissive pixel arrays include video lighting, automotive headlights, architectural and area lighting, street lighting, and information displays.

[0046] Light-emitting matrix pixel arrays can be used to selectively and adaptively illuminate buildings or areas for improved visual display and to reduce lighting costs. Light-emitting pixel arrays can also be used to project media facades for decorative motion or video effects. Along with tracking sensors and / or cameras, selective illumination of areas around pedestrians can be enabled. Spectrally distinct pixels can be used to adjust the color temperature of the lighting and support specific wavelengths of horticultural lighting.

[0047] Street lighting is one important application that could greatly benefit from the use of emissive pixel arrays. A single type of emissive array can be used to mimic various streetlight types, allowing, for example, switching between a Type I linear streetlight and a Type IV semicircular streetlight by appropriate activation or deactivation of selected pixels. Furthermore, street lighting costs can be reduced by adjusting the intensity or distribution of the light beam according to environmental conditions or time of use. For example, the light intensity and distribution area can be reduced when pedestrians are absent. If the pixels of the emissive pixel array are spectrally distinct, the respective color temperatures of the lights can be adjusted according to daylight, twilight, or nighttime conditions.

[0048] Light-emitting arrays are also well suited to support applications requiring direct or projected displays. For example, warning signs, emergency signs, or information signs can all be displayed or projected using light-emitting arrays. This allows, for example, color-changing or flashing exit signs to be projected. When a light-emitting array is composed of many pixels, text or numerical information may be presented. Directional arrows or similar indicators may also be provided.

[0049] Vehicle headlamps are an application of light-emitting arrays that require a large pixel count and a high data refresh rate. Automotive headlights that actively illuminate only selected portions of the road can be used to reduce problems associated with glare or dazzling for oncoming drivers. Using an infrared camera as a sensor, a light-emitting pixel array can activate only the pixels necessary to illuminate the road while deactivating pixels that may dazzle pedestrians or oncoming drivers. Also, off-road pedestrians, animals, or signs can be selectively illuminated to enhance the driver's environmental awareness. When the pixels of a light-emitting pixel array are spectrally distinct, the respective color temperatures of the lights may be adjusted according to daylight, twilight, or nighttime conditions. Some pixels may be used for optical wireless vehicle-to-vehicle communications.

[0050] Notes and Examples

[0051] Example 1 includes a control system including a plurality of pixels, each pixel of the plurality of pixels including a pixel driver and a corresponding light emitting diode (LED); a memory storing voltage data, the voltage data including one or more of a three sigma value, a driver headroom value, a resistance value, or a k-factor value; and a controller coupled to the memory and the pixels, the controller configured to: sample an anode voltage of each LED of the plurality of pixels to generate a sampled voltage; determine an average voltage based on the sampled voltages; and determine a total voltage to provide to the pixel based on the average voltage and the voltage data.

[0052] In Example 2, Example 1 further includes: the voltage data further includes data indicative of a respective duty cycle for each of the plurality of pixels in a current display frame and an immediately preceding display frame.

[0053] In Example 3, Example 2 further includes: the controller is configured to estimate a first total current in the current display frame as a sum of the duty cycles for the plurality of pixels in the current display frame, and the total voltage is determined based on the first total current.

[0054] In Example 4, Example 3 further includes: the voltage data includes a global bias current; and the controller is configured to multiply the first total current by the global bias current to generate a first bias current, multiply the first bias current by the resistance value to generate an I*R loss, and determine the total voltage further based on the I*R loss.

[0055] In Example 5, Example 4 further includes: the controller is configured to estimate a second total current in the immediately preceding display frame as a sum of the duty cycles for the plurality of pixels in the immediately preceding display frame, and determine the total voltage based on the second total current.

[0056] In Example 6, Example 5 further includes: the controller is configured to multiply the second total current by the global bias current to generate a second bias current; determine a bias current difference between the first bias current and the second bias current; and determine the total voltage based on the bias current difference.

[0057] In Example 7, Example 6 further includes: the controller is configured to multiply the second bias current by the k factor value to generate an LED voltage adjustment; and determine the total voltage based on the LED voltage adjustment.

[0058] In Example 8, Example 7 further includes: the controller is configured to low-pass filter the second bias current to generate a low-pass filtered bias current before determining the bias current difference; and determine the bias current difference as a difference between the first bias current and the low-pass filtered bias current.

[0059] In Example 9, Example 8 further includes determining the total voltage as the sum of the average voltage, the 3 sigma value, the driver headroom value, the I*R loss, and the LED voltage adjustment.

[0060] Example 10 includes a method for performing the controller operations of one of Examples 1-9.

[0061] Example 11 includes a non-transitory machine-readable medium containing instructions that, when executed by a controller, cause the controller to perform the operations of one of the controllers of Examples 1-9.

[0062] Numerous modifications and other embodiments of the present invention will suggest themselves to one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. It is therefore understood that the present invention is not limited to the particular embodiments disclosed, but that modifications and embodiments are intended to be included within the scope of the appended claims. It is also understood that other embodiments of the present invention may be practiced without elements / steps not specifically disclosed herein. In software-controlled hardware-supported embodiments, the methods, procedures, and implementations described herein may be embodied in a computer program, software, or firmware embodied in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, read-only memory (ROM), random-access memory (RAM), registers, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks and digital versatile disks (DVDs).

Claims

1. a plurality of pixels, each pixel of the plurality of pixels including a pixel driver and a corresponding light emitting diode (LED); a memory storing voltage data, the voltage data including one or more of a 3 sigma value, a driver headroom value, or a k-factor value; a controller coupled to the memory and the pixel; sampling an anode voltage of each LED of the plurality of pixels to generate a sampled voltage; determining an average voltage based on the sampled voltages; determining a total voltage to provide to the pixel based on the average voltage and the voltage data; a controller configured to: and the 3 sigma value is three times the standard deviation of the forward voltages of the pixels, the driver headroom value indicates how much higher the driver voltage needs to be than the forward voltage for the pixel driver to operate the LED, and the k factor value indicates how much the total voltage can change to accommodate changes in content provided by the LED. Control system.

2. 2. The control system of claim 1, wherein the voltage data further comprises data indicative of a respective duty cycle for each of the plurality of pixels in a current display frame and an immediately preceding display frame.

3. the controller is configured to estimate a first total current in the current display frame as a sum of the duty cycles for the plurality of pixels in the current display frame; the total voltage is determined based on the first total current. The control system of claim 2 .

4. the voltage data further includes a resistance value and a global bias current, the resistance value being an estimate of an equivalent resistance used to determine I*R losses; the controller is configured to multiply the first total current by the global bias current to generate a first bias current, multiply the first bias current by the resistance value to generate the I*R loss, and determine the total voltage further based on the I*R loss. The control system of claim 3 .

5. 5. The control system of claim 4, wherein the controller is configured to estimate a second total current in the immediately preceding display frame as a sum of the duty cycles for the plurality of pixels in the immediately preceding display frame, and to determine the total voltage based on the second total current.

6. 6. The control system of claim 5, wherein the controller is configured to multiply the second total current by the global bias current to generate a second bias current, determine a bias current difference between the first bias current and the second bias current, and determine the total voltage based on the bias current difference.

7. 7. The control system of claim 6, wherein the controller is configured to multiply the second bias current by the k-factor value to generate an LED voltage adjustment, and determine the total voltage based on the LED voltage adjustment.

8. 8. The control system of claim 7, wherein the controller is configured to low-pass filter the second bias current to generate a low-pass filtered bias current before determining the bias current difference, and to determine the bias current difference as a difference between the first bias current and the low-pass filtered bias current.

9. The control system of claim 8 , wherein the total voltage is determined as the sum of the average voltage, the 3 sigma value, the driver headroom value, the I*R loss, and the LED voltage adjustment.

10. 1. A method performed by a light emitting diode (LED) matrix controller, comprising: Sampling the anode voltage of each LED of the plurality of pixels to generate a sampled voltage; determining an average voltage based on the sampled voltages; determining a total voltage to provide to the pixel based on the average voltage and voltage data from a memory coupled to the controller, the voltage data including one or more of a 3 sigma value, a driver headroom value, or a k-factor value; Having that, each of the plurality of pixels further comprising a pixel driver; the 3 sigma value is three times the standard deviation of the forward voltages of the pixels, the driver headroom value indicates how much higher the driver voltage needs to be than the forward voltage for the pixel driver to operate the LED, and the k factor value indicates how much the total voltage can change to accommodate changes in content provided by the LED. method.

11. 11. The method of claim 10, wherein the voltage data further comprises data indicative of a respective duty cycle for each of the plurality of pixels in a current display frame and an immediately preceding display frame.

12. estimating a first total current in the current display frame as a sum of the duty cycles for the plurality of pixels in the current display frame; determining the total voltage based on the first total current; 12. The method of claim 11, further comprising:

13. 13. The method of claim 12, wherein the voltage data further includes a resistance value and a global bias current, the resistance value being an estimate of an equivalent resistance used to determine I*R losses, the method further comprising multiplying the first total current by the global bias current to generate a first bias current, multiplying the first bias current by the resistance value to generate the I*R losses, and determining the total voltage further based on the I*R losses.

14. 14. The method of claim 13, further comprising: estimating a second total current in the immediately preceding display frame as a sum of the duty cycles for the plurality of pixels in the immediately preceding display frame; and determining the total voltage based on the second total current.

15. 15. The method of claim 14, further comprising: multiplying the second total current by the global bias current to generate a second bias current; determining a bias current difference between the first bias current and the second bias current; and determining the total voltage based on the bias current difference.

16. 16. The method of claim 15, further comprising: multiplying the second bias current by the k-factor value to generate an LED voltage adjustment; and determining the total voltage based on the LED voltage adjustment.

17. 17. The method of claim 16, further comprising: prior to determining the bias current difference, low-pass filtering the second bias current to produce a low-pass filtered bias current; and determining the bias current difference as a difference between the first bias current and the low-pass filtered bias current.

18. 18. The method of claim 17, wherein the total voltage is determined as the sum of the average voltage, the 3 sigma value, the driver headroom value, the I*R loss, and the LED voltage adjustment.

19. A tangible, machine-readable medium containing instructions that, when executed by a controller of a light emitting diode array, cause the controller to: Sampling the anode voltage of each LED of the plurality of pixels to generate a sampled voltage; determining an average voltage based on the sampled voltages; determining a total voltage to provide to the pixel based on the average voltage and voltage data from a memory coupled to the controller, the voltage data including one or more of a 3 sigma value, a driver headroom value, or a k-factor value; performing an operation comprising: each of the plurality of pixels further comprising a pixel driver; the 3 sigma value is three times the standard deviation of the forward voltages of the pixels, the driver headroom value indicates how much higher the driver voltage needs to be than the forward voltage for the pixel driver to operate the LED, and the k factor value indicates how much the total voltage can change to accommodate changes in content provided by the LED. Tangible machine-readable medium.

20. 20. The tangible, machine-readable medium of claim 19, wherein the voltage data further comprises data indicative of a respective duty cycle for each of the plurality of pixels in a current display frame and an immediately preceding display frame.

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