Light-emitting diode package and related method involving conversion and shifting of pulse-width modulated signals

Abstract

Disclosed are LED packages, more specifically LED packages and associated methods involving the conversion and shifting of pulse-width modulation (PWM) signals. Individual LED packages are arranged for cascaded communication. Each LED package contains one or more LED chips, and each LED package can independently receive communications from a data stream, control the operation of one or more LED chips, and perform conversion and shifting of the received PWM signal. The conversion may include compression and / or decompression of the received PWM signal by each LED package to expand the accessible dynamic range. After conversion, the LED package can shift the converted value to compensate for the turn-on delay of the LED chips, thereby mitigating the light falloff problem at low intensity levels.

Description

Technical Field

[0001]

[0001] This disclosure relates to light-emitting diode (LED) packages, and more particularly to LED packages and related methods involving the conversion and shift of pulse width modulation signals.

Background Art

[0002]

[0002] A light-emitting diode (LED) is a solid-state device that converts electrical energy into light and typically includes one or more active layers (or active regions) of semiconductor material disposed between oppositely doped n-type and p-type layers. When a bias is applied across the doped layers, holes and electrons are injected into one or more active layers where they recombine to generate light emission such as visible or ultraviolet light.

[0003]

[0003] LEDs are widely adopted in various lighting scenarios, such as backlights for liquid crystal display (LCD) systems (e.g., as an alternative to cold cathode fluorescent lamps) and direct-view LED displays. Applications that utilize LED arrays include vehicle headlamps, road lighting, light fixtures, and various indoor, outdoor, and special scenarios. Desirable characteristics of LED devices include high luminous efficiency and long lifespan.

[0004]

[0004] Large multi-color direct-view LED displays (including full-color LED video screens) generally consist of a number of individual LED panels, packages, and / or components that provide image resolution determined by the distance between adjacent pixels, i.e., the "pixel pitch". Direct-view LED displays generally include tricolor displays with arrangements of red, green, and blue (RGB) LEDs, and dyadic displays with arrangements of red and green (RG) LEDs. Other colors or color combinations may be used. For many LED display systems, it is desirable to form a group of LED colors per pixel, such as the primary colors red, green, and blue (RGB), which define the vertices of a triangle (or polygon) on a chromaticity diagram. This polygon defines the so-called color gamut of the display device, and its region describes all possible colors that the display device can produce. Driver printed circuit boards for controlling LED displays generally have a high density of electrical devices, including capacitors, field-effect transistors (FETs), decoders, microcontrollers, etc., for driving the pixels of the display. As the pixel pitch of high-resolution displays continues to decrease, the density of such electrical devices increases in proportion to the number of pixels per given panel area. This tends to increase the complexity and cost of LED panels for display applications.

[0005]

[0005] The technology continues to pursue improved LED array devices with smaller pixel pitches while overcoming the limitations associated with conventional devices and manufacturing methods. [Overview of the Initiative] [Means for solving the problem]

[0006]

[0006] This disclosure relates to a light-emitting diode (LED) package, and more specifically to an LED package and related methods involving the conversion and shifting of pulse-width modulation (PWM) signals. Individual LED packages are arranged for cascade communication. Each LED package contains one or more LED chips, and each LED package can independently receive communications from a data stream, control the operation of one or more LED chips, and perform conversion and shifting of the received data, thereby generating a modified PWM signal. The conversion may include compression and / or decompression of the received data by each LED package to expand the accessible dynamic range. After conversion, the LED package can shift the converted value to compensate for the turn-on delay of the LED chip, thereby mitigating the drop-off problem at low intensity levels.

[0007]

[0007] In one embodiment, a method for controlling the light output within an LED package comprises: converting a received input brightness value to provide a conversion result; applying a shift value to the conversion result to provide a pulse width modulation (PWM) value; and generating a PWM signal having a pulse width corresponding to the PWM value. The method may further comprise electrically activating an LED chip within the LED package using the PWM signal, wherein the shift value is configured such that, for all possible PWM values, the pulse width of the PWM signal is greater than the turn-on time of the LED chip. In certain embodiments, converting the received input brightness value comprises thermal compensation. In certain embodiments, converting the received input brightness value comprises data decompression. In certain embodiments, data decompression models a gamma function. In certain embodiments, converting the received input brightness value comprises multiplication by a calibration factor. In certain embodiments, generating a PWM signal having a pulse width corresponding to the PWM value comprises comparison with a PWM counter value, the PWM counter value is updated at a rate corresponding to the clock frequency. In certain embodiments, the clock frequency is determined by the local clock of the LED package. In certain embodiments, the clock frequency is determined by the communication speed of the digital signal received by the LED package. In certain embodiments, the clock frequency is determined by an external clock. In certain embodiments, applying a shift value to the conversion result comprises applying the shift value only if the conversion result is greater than zero. In certain embodiments, the shift value is applied so that the PWM value does not saturate and exceed the maximum value of the PWM period and does not roll over to a lower value.

[0008]

[0008] In another embodiment, an LED package configured to receive and transmit a digital communication signal comprises at least one LED chip, an LED driver configured to drive at least one LED chip at least partially by pulse width modulation (PWM), and a PWM processor configured to provide a conversion result based on at least one of multiplication or exponential transformation of a received input brightness value, the PWM processor further configured to provide a PWM value based on a shift of the conversion result. In a particular embodiment, the PWM processor is configured to generate a PWM signal to the LED driver based on the PWM value. In a particular embodiment, if the conversion result is zero, a portion of the PWM signal leaving the PWM processor is zero. In a particular embodiment, the PWM processor is configured to provide a PWM value as a final operation before the PWM signal is transmitted to the LED driver. In a particular embodiment, the PWM processor comprises a transformation element configured to provide a conversion result and a shifter element configured to provide a PWM value. In a particular embodiment, the PWM processor comprises a processing element configured to provide both a conversion result and a PWM value. In certain embodiments, the processing element is configured to perform multiple calculations at different times. In certain embodiments, the processing element is configured to perform multiple calculations under the control of a finite state machine. In certain embodiments, the processing element forms at least part of an arithmetic logic unit (ALU). In certain embodiments, the PWM processor is configured so that the PWM value does not exceed the maximum value of the PWM period and does not roll over to a lower value. In certain embodiments, the PWM processor is configured to provide a PWM signal to an LED driver with a pulse width corresponding to the PWM value, wherein the pulse width of the PWM signal is greater than the turn-on time of at least one LED chip for all levels of the PWM period of the PWM signal.

[0009]

[0009] In other embodiments, further advantages can be obtained by combining any of the embodiments described herein individually or together, and / or by combining various distinct embodiments and features described herein. Any of the various features and elements disclosed herein may be combined with one or more other disclosed features and elements unless otherwise indicated herein.

[0010]

[0010] Those skilled in the art will recognize the scope of the present disclosure and realize additional embodiments after reading the following detailed description of preferred embodiments in conjunction with the attached drawings.

[0011] The accompanying drawings incorporated herein and forming part thereof illustrate several aspects of this disclosure and, together with the description, are useful in illustrating the principles of this disclosure. [Brief explanation of the drawing]

[0011] [Figure 1]

[0012] This block diagram illustrates a system-level control scheme for lighting devices using cascaded communication for series-connected light-emitting diode (LED) packages. [Figure 2]

[0013] Figure 2A is a graph showing several pulse widths corresponding to low-level luminance input values ​​of a pulse-width modulation (PWM) signal.

[0014] Figure 2B is a graph showing the light output of the LEDs corresponding to various low-level brightness values ​​and associated pulse widths in Figure 2A. [Figure 3A]

[0015] This graph illustrates a comparison of a typical 16-bit input grayscale digital value, showing the difference between having and not having luminance output loss on a linear luminance scale. [Figure 3B]

[0016] To illustrate the human eye response more clearly, this is a graph of the same data as in Figure 3A, but with only a logarithmic luminance scale. [Figure 3C]

[0017] This graph illustrates low-level brightness roll-off caused by delayed LED turn-on time, showing the relationship between brightness intensity and PWM count. [Figure 4]

[0018] Figure 1 is a block diagram of an LED package that can convert and shift an input PWM signal according to the principles of this disclosure. [Figure 5]

[0019] This is a block diagram of a PWM processor that can represent any one or all of the PWM processors in Figure 4. [Modes for carrying out the invention]

[0012]

[0020] The embodiments described below provide the information necessary to enable those skilled in the art to realize the embodiments and illustrate the best mode for realizing the embodiments. By reading the following description with reference to the accompanying drawings, those skilled in the art will understand the concepts of this disclosure and recognize applications of these concepts not specifically addressed herein. It should be understood that these concepts and applications are included within the scope of this disclosure and the accompanying claims.

[0013]

[0021] In this specification, terms such as "first," "second," etc., may be used to describe various elements, but it will be understood that these elements should not be limited by these terms. These terms are used solely to distinguish one element from another. For example, without departing from the scope of this disclosure, a first element may be called a second element, and similarly, a second element may be called a first element. As used herein, the term "and / or" includes any and all combinations of one or more of the relevant list items.

[0014]

[0022] When an element such as a layer, region, or substrate is described as being "on top of" another element, or extending "upwards" of another element, it will be understood that the element may be directly on top of the other element, or may extend directly onto the other element, or there may be an intervening element. In contrast, when an element is described as being "directly on top of" another element, or extending "directly upwards" of another element, there is no intervening element. Similarly, when an element such as a layer, region, or substrate is described as being "above" another element, or extending "upwards," it will be understood that the element may be directly above another element, or may extend directly onto the other element, or there may be an intervening element. In contrast, when an element is described as being "immediately above" another element, or extending "immediately above" another element, there is no intervening element. Furthermore, when an element is said to be “connected” or “joined” to another element, it will be understood that the element may be directly connected or joined to the other element, or there may be an intermediary element. In contrast, when an element is said to be “directly connected” or “directly joined” to another element, there is no intermediary element.

[0015]

[0023] In this specification, relative terms such as “downward,” “upward,” “upper side,” “lower side,” “horizontal,” or “vertical” may be used to describe the relationship between one element, layer, or region and another, as illustrated in the figures. It is understood that these terms and the terms discussed above are intended to encompass various orientations of the device, in addition to the orientations shown in the figures.

[0016]

[0024] The terms used herein are for the sole purpose of describing specific embodiments and are not intended to limit the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural form unless the context clearly indicates otherwise. Furthermore, the terms “equipped,” “equipped,” “contains,” and / or “contains” as used herein identify the presence of a described feature, complete, step, action, element, and / or component, but are not intended to exclude the presence or addition of one or more other features, complete, step, action, element, component, and / or group thereof.

[0017]

[0025] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as those generally understood by those skilled in the art to the extent of this disclosure. Furthermore, terms used herein should be interpreted as having meanings consistent with their meanings in the context of this specification and related art, and it will be understood that they should not be interpreted in an idealized or overly formal sense unless expressly defined herein.

[0018]

[0026] In this specification, embodiments are described with reference to schematic diagrams of embodiments of the present disclosure. Therefore, the actual dimensions of layers and elements may vary, and for example, variations from the shape of the schematic diagrams are expected as a result of manufacturing techniques and / or tolerances. For example, regions exemplified or described as square or rectangular can have rounded or curved features, and regions illustrated as straight lines can have irregularities. Thus, the regions illustrated in the drawings are schematic and their shape is not intended to illustrate the exact shape of the regions of the device and is not intended to limit the scope of the disclosure. In addition, the size of a structure or region may be exaggerated compared to other structures or regions for illustrative purposes and is thus provided to illustrate the general structure of the subject matter and may or may not be drawn to scale. Common elements between the drawings may be illustrated with common element numbers in this specification and may not be described again later.

[0019]

[0027] The present disclosure relates to a light-emitting diode (LED) package, and more particularly to an LED package and related methods involving the conversion and shifting of data used to generate a pulse-width modulation (PWM) signal. Individual LED packages are arranged for cascade communication. Each LED package includes one or more LED chips, and each LED package can individually receive communication from a data stream, control the operation of the one or more LED chips, and perform the conversion and shifting of the received PWM signal. The conversion can include compression and / or decompression of the received data by each LED package to expand the accessible dynamic range. After conversion, the LED package can shift the converted value to correct the turn-on delay of the LED chip, thereby reducing the light drop problem at low intensity levels.

[0020]

[0028] In cascade digital communication, multiple electronic devices are arranged as repeaters and, for operation, continuously receive serial communication. In the case of a fine-pitch video display, multiple LED packages are arranged in series as LED pixels and receive cascade communication. The incoming signal to each LED pixel is generated by another element such as a master controller or a previous LED pixel, and the bit stream of the incoming signal is derived from the clock region of one or more preceding devices. It is difficult to appropriately distribute communication signals to thousands of LED pixels. To form the pixels of a high-resolution video display, a small size is required for the LED packages, and this size constraint creates further challenges.

[0021]

[0029] As used herein, the terms “data stream” and “communication channel” may be used interchangeably. However, “data stream” typically refers to a non-physical representation of data over time, flowing through a series of communication channels, as well as through internal wiring and storage registers within various elements such as controllers and active electrical elements. A data stream may also be referred to as digital communication between two elements, such as a controller element transmitting digital communication and a receiving element receiving digital communication. “Communication channel” typically refers to the physical medium through which a data stream is transmitted. For example, a communication channel may be a wire with associated electrical elements, an optical fiber, or even air, as in the case of radio, light, or sound waves. A given physical channel may also be divided by time or frequency to allow multiple “communication channels” simultaneously within a single medium, such as changes to different frequency bands. In certain embodiments, a communication channel may embody a serial digital communication channel. Certain embodiments relate to a binary communication channel, which is a single wire referenced to a common conductor such as ground, and can typically hold only one value at a time, either high or low voltage (e.g., digital "0" or "1"), controlled by the output register of a preceding device. While two-wire differential signaling methods are also conceivable, the preferred embodiments illustrated here refer to the single-wire approach primarily because providing more traces would increase complexity in fine-pitch displays.

[0022]

[0030] In certain embodiments, this disclosure relates to light-emitting devices including LEDs, LED packages, and associated LED displays, and more specifically, to the active control of LEDs in an LED display. An LED display may include rows and columns of LEDs that form an array of LED pixels. A particular LED pixel may include a cluster of LED chips of the same or multiple colors, and an exemplary LED pixel includes a red LED chip, a green LED chip, and a blue LED chip. In certain embodiments, an LED package includes a plurality of LED chips that form at least one LED pixel, and a plurality of such LED packages may be arranged to form an array of LED pixels for an LED display. Each LED package may include its own active electrical element configured to receive control signals and actively maintain an operating state, such as a brightness or gray level or color selection signal, of the LED chips of the LED device while other LED devices are being addressed. In certain embodiments, the active electrical element may include an active circuit configuration that includes one or more of the following: a driver device, a signal conditioning or conversion device, a memory device, a decoder device, an electrostatic discharge (ESD) protection device, a thermal management device, and a sensing device. The active electrical element further includes a circuit configuration that facilitates communication with multiple uncorrelated clock regions, including the original clock region from the controller and a local clock region derived within the active electrical element. In this regard, each LED pixel of the LED display may be configured to operate with active matrix addressing via mixed clock region communication. The active electrical element may be configured to receive one or more of the following: analog control signals, encoded analog control signals, digital control signals, and encoded digital control signals.In such an arrangement, a string of LED packages, each with its own active electrical element, can be arranged for serial communication, with each active electrical element receiving data from a data stream and transmitting the data to the next active electrical element in the string of LED packages.

[0023]

[0031] For active matrix addressing, each LED pixel is configured to actively maintain its operating state or control its drive state, such as brightness or gray level or color selection, while other LED pixels are being addressed. This allows each LED pixel to maintain or independently control its drive state, improving display and / or image recording using photographic equipment by mitigating or eliminating the effects caused by low-frequency pulse beats in the display light output from other asynchronous devices (e.g., light sources, other pulse displays, or image capture devices). Therefore, each LED pixel may be configured to maintain its operating state using a continuous drive signal, including pulse-width modulation (PWM), rather than the conventional method using a time-division multiplexed signal that scans between groups of pixels, often with a low-frequency component added to the drive signal associated with passive matrix addressing. In this regard, each LED pixel may include an active-electric chip or active-electric element that may include a memory device and a function to change the drive state of the LED pixel based on the state stored in the memory of the active-electric element. In certain embodiments, the continuous drive signal is a constant analog drive current, and the brightness level may be controlled by a pulse method such as PWM. In other embodiments, the continuous drive signal may refer to a PWM signal that is not interrupted by time-division multiplex scanning of other LED pixels in the array or sub-array. In certain embodiments, the active electrical element may include an active circuit configuration that includes one or more of the following: a driver device, a signal conditioning or conversion device, a memory device, a decoder device, an ESD protection device, a thermal management device, a sensing device, and a voltage and / or current sensing device, a command processing device, and a circuit configuration. In various embodiments, the active electrical element comprises an integrated circuit chip, an application-specific integrated circuit (ASIC), a microcontroller, or a field-programmable gate array (FPGA).In certain embodiments, the active electrical element may be configured to be programmable or reprogrammable after manufacturing through various memory elements and logic incorporated within the active electrical element.

[0024]

[0032] As used herein, the terms “active electrical chip,” “active electrical element,” or “active electrical component” include any chip or component that can change the driving state of an LED based on memory or other information which may be stored within the chip or component. As used herein, the terms “active LED pixel” and “smart LED pixel” may be used interchangeably and may refer to a device which includes one or more LED devices or chips forming a pixel and the active electrical element or chip described above. In certain embodiments, each LED pixel may comprise a single LED package configured as an active LED package which includes multiple LED chips and active electrical elements as described above. In this way, the number of separate electrical devices required for the LED display, such as separate electrical devices located on the back of the LED panel of the LED display as described above, may be reduced. In addition, the overall operating power required for the operation of the LED panel may also be reduced.

[0025]

[0033] LED display performance continues to improve. Previously, LED displays were better suited to static images such as LED signs than dynamic applications like video displays, due to a lack of many of the performance metrics expected for superior video image display. Various performance metrics required for LED considerations for high-quality video display include resolution, contrast, viewing angle, dynamic range, brightness, frame rate, and color gamut. Recent advancements in LED packaging, improved LED driver quality, and cost reductions have significantly increased resolution, among other requirements. As resolution increases, so has the packing density of LED packages, such as printed circuit boards (PCBs), and the complexity. Driving LEDs within an LED package to achieve high frame rates and refresh rates simultaneously with a high dynamic range remains challenging. This is because current driving techniques require remote drivers to be located on the opposite side of the PCB containing the LED array. Due to packing density constraints, drivers must be shared using time-division multiplexing techniques such as raster scanning. The recommended driving technique for LEDs utilizes PWM to set brightness, requiring even higher frequencies to achieve a high dynamic range. Therefore, the dynamic range is limited by the highest frequency pulse that can be transmitted, taking into account parasitic resistance, capacitance, and inductance. LED packages arranged as pixels for cascaded serial communication provide each LED package with a local driver, eliminating the need for a shared driver and significantly reducing parasitic resistance, capacitance, and inductance, thus improving the dynamic range.

[0026]

[0034] Figure 1 is a block diagram 10 illustrating a system-level control scheme for a lighting device using cascaded communication for series-connected LED packages 12. The lighting device may embody an LED display, and each LED package 12 may form an LED pixel of the display. For such applications, the terms LED package and LED pixel may be used interchangeably, although an LED package may be understood to consist of multiple LED pixels formed together in a single component. An exemplary LED string 14 arranged for serial communication is indicated by a dashed box in Figure 1. Only a single LED string 14 is provided in detail, but one or more other LED strings may be coupled to a controller 16. As illustrated, the controller 16 is arranged to control one or more LED strings 14. The controller 16 may comprise an integrated circuit such as one or more of the following: ASIC, microcontroller, programmable control element, and FPGA. In certain embodiments, the controller 16 may be referred to as the master controller for the LED strings 14. In other embodiments, the controller 16 may be a subcontroller to which a set of tasks relating to a larger system are delegated to another master controller (not shown). The data signal output (DOUT) of the controller 16 may be passed serially along the LED string 14, and the return data signal input (DIN) may be received again by the controller 16. This signal includes the original clock region provided by the controller 16 or another master controller as described above. In Figure 1, each LED package 12, i.e., LED pixel, is labeled such as "Px1,1", where the first number represents the row and the second number represents the column. Each LED package 12 contains its own active electrical element 18 registered and housed therein, and each LED package 12 has logic for responding to the received data signal.

[0027]

[0035] As shown in the arrangement of Figure 1, a key aspect involves the delivery of high-bit-depth data to an LED driver incorporated within each LED package 12, and the ability to effectively convert the data to energize the LED chip within each LED package 12, depending on the expected light output level in an extended dynamic range. In certain aspects, the LED package 12 and associated active electrical elements 18 can convert the received data by compression and / or decompression techniques such as a gamma function or correction. However, since this converted data is used for input to a PWM driver, at low values, the pulse width may be shorter than the time delay required to energize the LED chip, resulting in the LED chip not producing the expected response. This occurs across multiple lowest brightness levels, and as a result, the dynamic range can be significantly reduced. Disclosed herein are an LED package 12 and associated methods in which an integrated LED driver is controlled so that the dynamic range is well achieved as expected from the bit depth. As will be explained in more detail later, an LED package 12 is disclosed that expands the dynamic range by converting the received data and shifting the converted value sufficiently to compensate for the time delay required to power the LED chip. By applying a shift value to the converted data, pulse widths shorter than the turn-on time delay of the LED chip can be avoided. Therefore, if the shift value is appropriately selected, all data values ​​transmitted to the PWM driver will generate a light output from each LED chip.

[0028]

[0036] Figure 2A is a graph showing several pulse widths corresponding to low-level luminance input values ​​of a PWM signal. The y-axis represents the PWM signal that can be provided to the current driver or power driver inside the LED package 12 in Figure 1. In certain embodiments, the PWM signal can be the output of a PWM processor, as described later herein. The x-axis represents relative time illustrating the comparison of pulse widths. Pulse widths for luminance values ​​or levels 7, 10, 14, and 20 are exemplified, representing low luminance values ​​for any type of bit depth, such as 8-bit or 16-bit. For example, the values ​​7, 10, 14, and 20 may represent low luminance levels out of 255 levels for an 8-bit signal and out of 65,535 levels for a 16-bit signal. As exemplified, the pulse width increases as the luminance level increases.

[0029]

[0037] Figure 2B is a graph showing the light output of the LED corresponding to various low-level brightness values ​​and associated pulse widths in Figure 2A. The y-axis represents the light output, and the x-axis represents relative time on the same scale as in Figure 2A. For values ​​7, 10, 14, and 20, the delay time from when the LED turns on until it generates light output is the same. Factors influencing this delay include the amount of resistance and capacitance in the LED package's driver circuit, and the forward voltage of the LED chip at which the LED chip begins to emit light. This forward voltage required to generate light depends on the bandgap of the active region of the LED chip and therefore can also correspond to the color of the emitted light. This no-light output delay time is the time required for the driver to charge various capacitances such as the driver output, control line, and the capacitance of the LED itself, thereby raising the voltage from a low level to the forward voltage required to generate light. This delay time can be as short as 1 microsecond (μs), or even much shorter, but the PWM counter frequency required to generate a high dynamic range is much shorter. For example, a PWM counter or clock frequency of 10 megahertz (MHz) or higher may be required.

[0030]

[0038] Comparing the pulse width in Figure 2A with the optical output response in Figure 2B, the problem of little to no optical output for low brightness levels becomes apparent. As illustrated in Figure 2B, the delay time is very long, so when the value is 7 or less, there is little to no optical output from the LED before the end of the pulse width in Figure 2A. When the value is between 8 and 14, the amount of light gradually increases before the end of each pulse width, and when the value is greater than 14, the amount of optical output usually increases steadily because the LED turns on completely for most of the pulse width. At the end of each pulse width in Figure 2A, the capacitance discharges when the LED turns off, so the corresponding optical output in Figure 2B decreases rapidly, but not instantaneously. During turn-off, the voltage drops near the bandgap of the LED chip, and certain capacitances can keep the voltage level above zero, so the next PWM pulse can exhibit a shorter delay than the initial startup. Despite such short delays, when considering the integration of many pulses and many associated delays during PWM control, the problem of little to no optical output for low brightness levels becomes prominent.

[0031]

[0039] Figures 3A and 3B are illustrative graphs comparing the presence and absence of luminance output loss for exemplary 16-bit input grayscale digital values ​​used by an exemplary PWM driver. Such luminance output loss is described above in the context of Figures 2A and 2B, where, for ease of explanation, the first 16 values ​​are suddenly lost and the output is zero. In both Figures 3A and 3B, the x-axis represents the luminance input values ​​and the y-axis represents the luminance output in arbitrary units. In Figure 3A, the y-axis is provided as a linear axis, while in Figure 3B, a logarithmic y-axis is provided for the same data. With a 16-bit input, i.e., 65,535 levels, we obtain a dynamic range of approximately five orders of magnitude. The luminance output loss for the first 16 levels is provided as a solid line and compared to a dashed line without luminance output loss. In Figure 3A, the data line without luminance output loss and the data line with 16 levels of loss appear to overlap. In this regard, such luminance loss may not be noticeable if the response of the human eye is linear. However, the response of the human eye is better approximated by logarithmic behavior. Therefore, Figure 3B illustrates how the LED delay time that causes luminance loss in only the first 16 levels is inversely correlated with a loss that exceeds an order of magnitude of the overall dynamic range.

[0032]

[0040] Figure 3C is a graph of input PWM count and brightness intensity in arbitrary units, illustrating a low level of brightness rolloff due to a delayed LED turn-on time. In the example in Figure 3C, when the PWM count falls below approximately 10, the rolloff from the intended brightness begins, and the PWM value of "1" is completely lost. Thus, the pulse width associated with the PWM value of "1" is smaller than the delay time required to turn on the LED. In applications where the PWM frequency is increased to expand the dynamic range or improve the refresh rate, the rolloff and dropout of intensity become more pronounced and shift to the right to cover more PWM counts.

[0033]

[0041] According to embodiments disclosed herein, the aforementioned problem associated with delayed LED turn-on can be compensated for by shifting the converted input data so that each output PWM value corresponds to a pulse width greater than at least the delay time of the LED chip. In this way, appropriate brightness output can be provided across the entire dynamic range, including the lower levels described above. Each LED package arranged as an LED pixel in a display may include the ability to convert the input PWM signal to expand the dynamic range, and then shift the converted value to avoid pulse width reduction associated with brightness loss at low levels.

[0034]

[0042] Figure 4 is a block diagram of the LED package 12 of Figure 1, which can convert and shift an input PWM signal according to the principles of this disclosure. The active electrical element 18 may include a number of ports represented by a supply voltage (Vdd), ground (GND or Vss), and bidirectional communication ports or digital input / output ports (DIO1 and DIO2) according to embodiments disclosed herein. Having DIO1 and DIO2 ports configured as bidirectional ports, the active electrical element 18 may have the advantage of being able to detect an input signal from a communication channel and then assign one of the DIO1 and DIO2 ports as an input port and the other of the DIO1 and DIO2 ports as an output port. Such functionality can be provided by an input / output buffer and / or active switching network located within the active electrical element and electrically coupled to the DIO1 and DIO2 ports. This provides flexibility in the layout of displays in which multiple LED packages 12 are connected for cascaded communication. For example, multiple LED packages 12 may be arranged in multiple rows, where data cascades in a serpentine manner from package to package and from row to row along each row, as illustrated in Figure 1. In such an arrangement, bidirectional communication ports allow the LED packages 12 to be mounted in the same orientation, enabling the reception and transmission of digital communications from left to right or right to left, depending on the row position. In addition to the four ports Vdd, GND, DIO1, and DIO2 on the left side of the block diagram, the active electrical element 18 includes four ports on the right side, coupled to LEDs 20-1 to 20-3 of the LED package 12. In this regard, LEDs 20-1 to 20-3 are packaged together with the active electrical element 18 within a common LED package 12, forming individual pixels of a larger display. As used herein, LEDs 20-1 to 20-3 may also be referred to as LED chips.

[0035]

[0043] Specific elements of the active electrical element 18 will be described later. However, it is understood that the active electrical element 18 may include many other components, including memory elements, signal conditioning elements, thermal management elements, electrostatic discharge elements, clock elements, and oscillators. In Figure 4, the control logic 22 is arranged to receive input data, execute commands according to a command protocol, provide control signals for the operation of LEDs 20-1 to 20-3, report various voltage and / or temperature levels included with the output data, and transmit the output data to the next adjacent LED package via the DIO1 and DIO2 ports. The control logic 22 may operate in the digital domain and may include input / output buffers electrically coupled to the DIO1 and DIO2 ports, assigning input and output configurations to the bidirectional DIO1 and DIO2 ports.

[0036]

[0044] In certain embodiments, the active electrical element 18 may be configured to provide both forward-biased and reverse-biased states to LEDs 20-1 to 20-3. In this regard, the control logic 22 may include a reverse-biased control output signal configured to supply a voltage level of approximately Vdd or approximately GND to LEDs 20-1 to 20-3 using a suitable active element. The term "reverse bias" means that a reverse-biased state occurs when the output of the control logic 22 is at a high level, so the output signal can simply be coupled to an inverter 24 provided in the driver 26 of the active electrical element 18. Thus, LEDs 20-1 to 20-3 can be either forward-biased or reverse-biased depending on the specific operating state and / or command received by the control logic 22. The inverter 24, or inverter logic element, may have output characteristics sufficient to drive LEDs 20-1 to 20-3. The driver 26 may be a substantially analog interface of the active electrical element 18 that is electrically coupled to the control logic 22. The driver 26 may include controllable current sources 28-1 to 28-3, which can also be configured as LED sink drivers. By incorporating pull-up registers R1 to R3, a path to Vdd may be provided for each of the LEDs 20-1 to 20-3, which is useful for voltage measurement when configured in reverse bias. Each of the current sources 28-1 to 28-3 may be electrically coupled to digital output signals LED1 to LED3 of the control logic 22. The output signals LED1 to LED3 may be provided along multiple wires coupled to each of the current sources 28-1 to 28-3 for current selection purposes. The output signals LED1 to LED3 may embody PWM outputs of the control logic 22 for controlling the operation of LEDs 20-1 to 20-3. The driver 26 may also include a multiplexer 30 electrically coupled to the analog-to-digital (ADC) converter and ADC selector of the control logic 22. In addition, the driver 26 may include an on-chip temperature sensor provided through the multiplexer 30. In certain embodiments, the temperature sensor provides thermal compensation for LEDs 20-1 to 20-3 via a thermal compensation curve and / or thermal shutdown.

[0037]

[0045] The active electrical element 18 further includes a serial interface 32 that embodies a module having a circuit configuration configured to decode the incoming signals of a data stream and convert them into a bitstream in the local clock region, which can be further processed by control logic 22. Thus, the serial interface 32 may also be referred to as a digital communication receiving device. Digital communication can be received from a controller (e.g., 16 in Figure 1) and / or from another LED package in the serial string (e.g., 12 in Figure 1). The serial interface 32 is further configured to retransmit the decoded and converted bitstream, along with the corrected data, to a communication channel to which another LED package or another external element is connected, in a manner compatible with the entire LED display system.

[0038]

[0046] In certain embodiments, the control logic 22 may include a circuit configuration in the form of one or more PWM processors 34-1 to 34-3 that provide output PWM signals to LED1 to LED3. A separate PWM processor 34-1 to 34-3 may be provided for each LED chip 20-1 to 20-3, or the PWM processors 34-1 to 34-3 may be combined as a single PWM processor for all of the LED chips 20-1 to 20-3. As will be described in more detail below with reference to Figure 5, one or more PWM processors 34-1 to 34-3 are configured to convert an input PWM signal, then shift the converted PWM value, and provide the LED chips 20-1 to 20-3 with a pulse width that compensates for the delayed turn-on time.

[0039]

[0047] Figure 5 is a block diagram of a PWM processor 34 that can represent any one or all of the PWM processors 34-1 to 34-3 of Figure 4. Hash marks across various conductor lines also indicate that multiple lines or signals can be provided. The PWM processor 34 is configured to receive additional inputs labeled as other settings and controls, shift values, and PWM counters, in addition to brightness input values ​​such as input data, from the other elements of the control logic 22 in Figure 4. The PWM processor 34 outputs the PWM signal as a series of pulses for the other elements, in particular the driver 26 in Figure 4. The PWM counter input can embody a PWM counter value that is updated at a rate corresponding to the clock frequency. In certain embodiments, the clock frequency is determined by the local oscillator of the clock of the active electrical element 18 in Figure 4. The clock frequency can also be determined by the communication speed of the received digital signal. In yet another embodiment, the clock frequency is determined by a clock outside the LED package 12 in Figure 4, such as the controller 16 in Figure 1.

[0040]

[0048] In Figure 5, the transformation element 36 can perform calculations in response to the input. Exemplary calculations include compression or decompression, providing an expanded dynamic range. The transformation result may include at least one of multiplication or exponential transformation of the received input luminance value. In one embodiment, the calculation is a gamma calculation. In a particular embodiment, the transformation element 36 is an equation Conversion output = CalFctr * f (luminance) * g (scaledTemp) Accordingly, a conversion output or conversion result can be provided, where CalFctr is the calibration coefficient, f is a transfer function that provides functions such as data decompression (e.g., gamma) for the luminance input value, and g is another transfer function that provides a temperature compensation function along with the scaledTemp value received by the temperature sensor. The scaledTemp value is given by the formula scaledTemp=TempScale*(rawTemp-TempShift) Accordingly, it can be determined from the raw temperature sensor value, and rawTemp is the raw data value obtained from the temperature sensor.

[0041]

[0049] As illustrated in Figure 5, the conversion output of the conversion element 36 is received by the shifter element 38. Based on the received shift value input, the shifter element 38 is configured to shift the conversion output in a manner that compensates for the LED turn-on delay. The shift value input may be a value hard-set on the active electrical element 18 in Figure 4, or the shift value may be user-selectable. In certain embodiments, the shift value can be determined by an initial calibration that identifies the lowest PWM level that still provides a useful light output. Alternatively, the shift value may be the result of a previous calibration for a similar system and / or based on the known electrical characteristics of the selected LED chip. Useful light output varies by application but generally refers to a level of light output that the user notices. In another scheme, the lowest PWM level that continues to provide useful light can be characterized when the corresponding pulse width is greater than the time delay for turning on the LED chip. Once the lowest useful PWM level is determined, the shift value can then be set to the lowest useful PWM level or a higher level to ensure light output across the entire dynamic range. The shift value can then be user-selectable via a communication system to the PWM processor 34, or it can be hard-set or coded based on the system design. In certain embodiments, the shifter element 38 may comprise a logic set of gates such as AND gates, OR gates, or other logic. The shifter element 38 can embody a processor element that executes a program residing within the PWM processor 34. In certain embodiments, the logic associated with the shifter element 38 can be shared with other elements of the active electrical element 18. In certain embodiments, the shifter element 38 may also be referred to as an adder.

[0042]

[0050] As illustrated in Figure 5, the PWM processor 34 is configured to apply a shift after the input data (e.g., a brightness input value) has been transformed by the transformation element 36. The transformed and shifted signal is then provided as a PWM value 40, which is the result of at least two processing elements (i.e., the transformation element 36 and the shifter element 38). The output PWM signal of the PWM processor 34 is then generated as a result of a digital comparator 42, which outputs an "LED on" signal if the PWM counter input is less than the PWM value 40, and an "LED off" signal otherwise. Thus, the PWM value 40 can be referred to as the shifted value before the output PWM signal is provided to the driver 26 in Figure 4.

[0043]

[0051] If no shift is provided by the shifter element 38, the converted output from the conversion element 36 is provided to the digital comparator 42 for comparison with a PWM counter. Since the converted output is intended to increase resolution at lower PWM levels, such an arrangement will output a range of PWM levels below the LED turn-on threshold. Alternatively, if a shift is performed before conversion at the conversion element 36, such as when a shift already exists in the input brightness value received by the controller 16 in Figure 1, the multiplication coefficient during conversion may still result in PWM levels with pulse widths lower than the LED turn-on time. A shift should be applied after conversion to provide calibration, thermal compensation, and / or data decompression functions, while also correcting for the LED turn-on time. This ensures that the pulse width of all converted values ​​exceeds the LED turn-on time. Thus, the PWM value 40 in Figure 5 is given by equation PWM value = converted output + shift value This can be determined according to the following formula, and this formula can also be expressed according to the following formula, taking into account the calculation of the above conversion output.

[0044] PWM value = CalFctr * f (luminance) * g (scaledTemp) + shift value Therefore, the PWM value 40 in Figure 5 can be the result of a first transformation which may include a series of multiplications followed by the addition of a shift value.

[0045]

[0052] For example, in the case of a 16-bit signal with levels from 0 to 65,535, it can be determined that a shift value of 10 is needed to compensate for the LED turn-on delay. Therefore, the converted output value from the conversion element 36 is shifted by 10 levels by the shifter element 38, and the converted value "1" is shifted to the value "11" to ensure a useful light output. In certain embodiments, the logic within the PWM processor 34 can be implemented so that the shifted value does not exceed the maximum PWM value for the PWM period indicated by the PWM counter. In the 16-bit example above, such logic shifts the value by 10 levels from 1 to 65,525, and a reduction shift is applied so that all values ​​above 65,525 saturate and equal the maximum value of 65,535, and do not roll over to lower values. This is necessary because low-level logic designs may not be able to handle large values, and higher values ​​roll over to lower values ​​instead. Referring to the logarithmic eye response illustrated in Figure 3B, level 10 appears 10 times brighter than level 1, so the difference between levels 65,525 and 65,535 is far less detectable than the lower level differences between level 1 and level 10. In further embodiments, the logic within the PWM processor 34 can also be implemented to suppress shifts when the converted output value is "0", ensuring that there is no intended light output when the value is zero. With such logic implemented, the PWM value 40 in Figure 5 is given by equation

[0046]

number

[0047] The determination can be made accordingly, and a value of "0" remains "0", and the PWM value 40 does not exceed the maximum PWM value specified by the PWM counter. In this regard, the shifter element 38 operates only when the converted output > 0, and when the final carry signal is detected, the PWM Max It can be configured as a set of adders that generate [the specified value].

[0048]

[0053] The above description may suggest various aspects of the present disclosure by various embodiments. Many other adaptations are considered. For example, each LED chip in the package may be provided with a separate PWM processor 34, or the functions of the separate PWM processors 34 may be provided to a single PWM processor 34 that provides various calculations at different times. The conversion element 36 and the shifter element 38 may form separate processing elements within the PWM processor 34, or they may be integrated as a single processing element. One or more such processing elements within the PWM processor 34 may be implemented according to the instructions of a finite state machine (FSM). A further example is one or more processing elements that form at least part of an arithmetic logic unit (ALU) that provides all mathematical functions controlled by the FSM. Given the above, the block diagram of Figure 5 may provide one implementation and / or arrangement of physical hardware and connections. Alternatively, the block diagram of Figure 5 may conceptually provide a way in which physical hardware routes signals over time, but in various embodiments it does not necessarily provide a way in which the physical hardware is specifically arranged and physically connected together.

[0049]

[0054] Any of the embodiments described herein, and / or any of the various distinct embodiments and features described herein, may be combined for further advantages. Any of the various embodiments disclosed herein may be combined with one or more other disclosed embodiments unless otherwise indicated herein.

[0050]

[0055] Those skilled in the art will recognize improvements and modifications to preferred embodiments of this disclosure. All such improvements and modifications are deemed to fall within the scope of the concepts disclosed herein and the following claims.

Claims

1. A method for controlling the light output within a light-emitting diode (LED) package, The steps include: converting the received input brightness value and providing the conversion result; The steps include applying a shift value to the conversion result to provide a pulse width modulation (PWM) value, The steps include generating a PWM signal having a pulse width corresponding to the PWM value, and A method that includes [a certain feature].

2. A method according to claim 1, further comprising the step of electrically activating an LED chip in the LED package using the PWM signal, wherein the shift value is configured such that, for all possible PWM values, the pulse width of the PWM signal is greater than the turn-on time of the LED chip.

3. A method according to claim 1, wherein the step of converting the received input luminance value comprises thermal compensation.

4. A method according to claim 1, wherein the step of converting the received input brightness value comprises data decompression.

5. A method according to claim 4, wherein the data decompression is a method for modeling a gamma function.

6. A method according to claim 1, wherein the step of converting the received input luminance value comprises multiplication by a calibration coefficient.

7. A method according to claim 1, wherein the step of generating the PWM signal having the pulse width corresponding to the PWM value comprises a comparison with a PWM counter value, the PWM counter value being updated at a rate corresponding to a clock frequency.

8. A method according to claim 7, wherein the clock frequency is determined by the local clock of the LED package.

9. A method according to claim 7, wherein the clock frequency is determined by the communication speed of the digital signal received by the LED package.

10. A method according to claim 7, wherein the clock frequency is determined by an external clock.

11. A method according to claim 1, wherein the step of applying the shift value to the conversion result comprises the step of applying the shift value only if the conversion result is greater than zero.

12. A method according to claim 11, wherein the shift value is applied such that the PWM value saturates and does not exceed the maximum value of the PWM period and does not roll over to a lower value.

13. A light-emitting diode (LED) package configured to receive and transmit digital communication signals, At least one LED chip, An LED driver configured to drive at least one of the aforementioned LED chips at least partially by pulse width modulation (PWM), An LED package comprising a PWM processor configured to provide a conversion result based on at least one of multiplication or exponential conversion of a received input brightness value, wherein the PWM processor is further configured to provide a PWM value based on a shift of the conversion result.

14. An LED package according to claim 13, wherein the PWM processor is configured to generate a PWM signal to the LED driver based on the PWM value.

15. An LED package according to claim 14, wherein if the conversion result is zero, a portion of the PWM signal leaving the PWM processor is zero.

16. An LED package according to claim 14, wherein the PWM processor is configured to provide the PWM value as a final operation before transmitting the PWM signal to the LED driver.

17. The LED package according to claim 13, wherein the PWM processor comprises a conversion element configured to provide the conversion result and a shifter element configured to provide the PWM value.

18. An LED package according to claim 13, wherein the PWM processor comprises a processing element configured to provide both the conversion result and the PWM value.

19. An LED package according to claim 18, wherein the processing element is configured to perform a plurality of calculations at different times.

20. An LED package according to claim 19, wherein the processing element is configured to perform the plurality of calculations under the control of a finite state machine.

21. An LED package according to claim 19, wherein the processing element forms at least a part of an arithmetic logic unit (ALU).

22. An LED package according to claim 13, wherein the PWM processor is configured such that the PWM value does not exceed the maximum value of the PWM period and does not roll over to a lower value.

23. The LED package according to claim 13, wherein the PWM processor is configured to provide a PWM signal to the LED driver with a pulse width corresponding to the PWM value, An LED package wherein the pulse width of the PWM signal is greater than the turn-on time of at least one LED chip for all levels of the PWM period of the PWM signal.

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