Built-in self-test for light emitting diodes

Abstract

In some examples, the device includes a built-in self-test for detecting whether there is a defect on a light-emitting diode (LED) or a driver for the LED. The device includes a pair of pads configured to be connected to the LED. The built-in self-test is configured to control the driver to turn on each pass switch connected to a pad of the pad pair. The built-in self-test is then configured to determine the voltage level at each pad of the pad pair. Based on the voltage level at each pad, the built-in self-test can determine whether there is a defect on the LED, across the first anode pad and the first cathode pad, or on the driver.

Description

Technology Field

[0001] The present disclosure relates to a circuit for driving a light source, such as a light-emitting device. Background Technology

[0002] A driver circuit can operate or drive one or more light sources, such as light-emitting diodes (LEDs). The driver circuit can control the light intensity output by the LED by changing the average amount of current flowing through the LED and / or changing the average forward voltage across the LED. For example, the driver circuit can increase the duty cycle of the current delivered to the LED to increase the light intensity generated by the LED. Similarly, the driver circuit can decrease the duty cycle of the current delivered to the LED to decrease the light intensity generated by the LED. At high switching frequencies, the human eye can perceive a change in the duty cycle of the current as a change in the brightness or intensity of the light produced by the LED.

[0003] Modern automotive LED headlights feature multi-pixelated light sources capable of controlling the individual brightness of activated pixels or groups of pixels. This control enables new lighting features such as glare-free high-beam systems, adaptive drive beams, and symbol projection. To provide these specific and other functions, the headlights can deliver high-resolution illumination across the driver's entire field of vision.

[0004] The headlight may include a matrix array of multiple LEDs (e.g., 16,000 or more LEDs) having a fine pixel-to-pixel pitch or fine display resolution. The headlight may be constructed using a chip-on-chip concept in which a second chip containing LEDs is mounted on a first chip containing a light source matrix and a driver using a hybridization process. While the first company manufactures the first chip, the second company may perform the hybridization process. The manufacturing and hybridization processes can introduce several potential points of failure in the finished product, particularly when performed by different companies.

[0005] The present disclosure describes a technique for testing drivers and / or light-emitting diodes (LEDs) using an embedded self-test. The embedded self-test may include a processing circuit configured to test drivers and / or LEDs one by one (or in a group). The embedded self-test may be configured to test for defects on the driver, across a pair of pads, or on each LED by turning on each pass device and measuring the forward voltage across the pass device or at each anode pad and each cathode pad.

[0006] Details of one or more examples are described in the attached drawings and the detailed description below. Other features, purposes, and benefits will become apparent from the detailed description, drawings, and claims. Brief explanation of the drawing

[0007] FIG. 1 is a conceptual block diagram of a device including a driver for controlling the operation of a light source according to the technology of the present disclosure. FIG. 2 is a circuit diagram of an amplifier for controlling a pass device connected in series with a light-emitting diode (LED) according to the technology of the present disclosure. FIG. 3 is a circuit diagram of three possible failure modes for a driver or LED according to the technology of the present disclosure. FIG. 4 is a circuit diagram for calibrating a sensing resistor according to the technology of the present disclosure. FIGS. 5 and FIGS. 6 are circuit diagrams for detecting defects according to the technology of the present disclosure. FIG. 7 is a flowchart illustrating an exemplary technique for detecting defects according to the technology of the present disclosure. FIG. 8 is a circuit diagram for measuring the cathode voltage for two LEDs according to the technology of the present disclosure. FIGS. 9a and 9b are diagrams of two exemplary test patterns that can be implemented by an embedded self-test according to the technology of the present disclosure. FIG. 10 is a circuit diagram of a device including a differential analog-to-digital converter for measuring the forward voltage across an LED according to the technology of the present disclosure. FIG. 11 is a flowchart illustrating an exemplary technique for detecting a defect between two LEDs according to the technology of the present disclosure. Specific details for implementing the invention

[0008] The present disclosure describes an apparatus, method, and technique for testing a light source using a built-in self-test (BIST). The BIST may be configured to detect defects in a light source, a pair of pads, and / or a driver configured to turn on the light source. The BIST may be configured to test the driver before and / or after the light source is connected to the driver (e.g., before hybridization). For example, the BIST may be configured to perform a front-end test of the function of each current source (e.g., each driver) before the hybridization process.

[0009] After the hybridization process is completed, all light-emitting diodes (LEDs) can be connected to a dedicated current source (e.g., soldered). Consequently, each cathode (for the low-side configuration) or each anode (for the high-side configuration) is no longer accessible, which may impede testability, field return analysis, and self-diagnostic capabilities. For example, the BIST of the present disclosure may be configured to verify the quality of the assembly and distinguish whether a defect occurred within the LED chip, within the current source driver chip, or across the pads for mounting the LED chip.

[0010] FIG. 1 is a conceptual block diagram of a device (100) including a driver (130) for controlling the operation of a light source (150) according to the technology of the present disclosure. In the example of FIG. 1, the device (100) includes a processing circuit (110), a BIST (120), a driver (130), a pass device (140), and pads (160, 170). An LED (150) and a power supply (180) are optional elements that may be part of the device (100) in some examples. Additionally or alternatively, the LED (150) and / or the power supply (180) may be external components that may be connected to, attached to, and / or mounted to the device (100). In some examples, the device (100) may be a vehicle, a building, and / or other system including a lighting device.

[0011] The processing circuit (110) may be configured to control the driver (130) to operate the LED (150). For example, the processing circuit (110) may be configured to cause one or more drivers (130) to turn on one or more respective pass devices (140) to turn on one or more LEDs (150). For example, the processing circuit (110) may transmit a low-power control signal to the driver (130), and the driver (130) may generate a high-power driver signal based on the control signal. The processing circuit (110) may also be configured to receive a detected signal indicating the forward voltage at both ends of one of the LEDs or at each pair of pads (160, 170).

[0012] The processing circuit (110) may include any suitable arrangement of hardware, software, firmware, or any combination thereof to perform the technology attributed to the processing circuit (110) in this specification. Examples of the processing circuit (110) include any one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuits, and any combination of these components. When the processing circuit (110) includes software or firmware, the processing circuit (110) further includes any hardware for storing and executing the software or firmware, such as one or more processors or processing units. In an example where the device (100) is mounted in a vehicle, the processing circuit (110) may be implemented by a headlight controller.

[0013] Generally, the processing unit may include one or more microprocessors, DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logic circuits, and any combination of these components. Although not illustrated in FIG. 1, the processing circuit (110) may include memory configured to store data. The memory may include any volatile or non-volatile medium, such as random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, etc. In some examples, the memory may be outside the processing circuit (110) (e.g., outside the package in which the processing circuit (110) is housed).

[0014] The driver (130) may be configured to drive a pass device (140) based on a signal received from the processing circuit (110). The driver (130) may include an amplifier and / or a level shifter for generating a relatively high-power signal based on a low-power signal received from the processing circuit (110). For example, the driver (130) may include a first driver configured to drive a first pass device and a second driver configured to drive a second pass device, wherein each pass device is configured to be connected to an LED. Details for additional examples of drivers for light-emitting diodes can be found in U.S. Patent No. 9,930,748, jointly assigned and issued on March 27, 2018, under the title "Synchronization for Light-Source Driver Circuitry," and U.S. Patent No. 10,297,190, jointly assigned and issued on May 21, 2019, under the title "Pixel Selection Method for a Light-Source Matrix Driver," the entire contents of which are incorporated herein by reference.

[0015] The pass device (140) can be operated as a switch that turns on and off. Additionally or alternatively, the pass device (140) can be operated as an analog device that can operate in linear mode. In some examples, the driver (130) may be configured to drive the pass device (140) to increase or decrease the current level processed by the pass device (140).

[0016] The LED (150) may include two or more light sources, such as light-emitting diodes (LEDs) or any other suitable light source. Although described in the context of LEDs, the technology of the present disclosure may also be applied to other light sources. The LED (150) may be arranged in a matrix or grid consisting of columns and rows, and each light source may be a pixel. In some examples, the LED (150) may include 16,384 light sources arranged in a grid of 128 light sources × 128 light sources. Alternatively, the LED (150) may include 1,024 light sources arranged in a grid of 32 light sources × 32 light sources.

[0017] Each LED (150) can be driven by each pass device (140). In some examples, each LED can be connected in series with each pass device between two power rails (e.g., power supply (180)). The LED (150) may be part of an external device that can be mounted on and electrically connected to pads (160, 170). Pad (160) can be connected to the cathode of the LED (150), and pad (170) can be connected to the anode of the LED (150). Alternatively, pad (160) can be connected to the anode of the LED (150), pad (170) can be connected to the cathode of the LED (150), and power supply (180) can be connected to the pass device (140). The LED (150) can be connected between the power supply (180) and the pass device (140) as shown in FIG. 1, or the arrangement of the pass device (140) and the LED (150) can be reversed so that the pass device (140) can be connected between the power supply (180) and the LED (150) (see FIG. 2, for example).

[0018] The power source (180) may be configured to supply power to the LED (150) through the pads (170, 182). The power source (180) may include a battery or other power storage device, a connection to mains power, and / or one or more power conversion circuits. In some examples, the power source (180) may be outside the device (100), but in other examples, the power source (180) may be part of the device (100). The device (100) may include one or more pads (182) so that the power source (180) can be mounted on the device (100) and electrically connected thereto.

[0019] An external device (192) can be connected to a diagnostic interface (190) to communicate with a processing circuit (110) and a BIST (120). For example, the processing circuit (110) may be configured to transmit data related to the operation of the device (100) to the external device (192). In some examples, the BIST (120) may receive a command signal (e.g., one or more bits) from the external device (192) and may be configured to perform an embedded self-test in response to the reception of this command signal. Additionally or alternatively, the BIST (120) may be configured to perform an embedded self-test at manufacturing time and / or at predefined time intervals. The BIST (120) may be configured to perform a self-test before or after the hybridization process is completed (e.g., front end or back end), after the combined device is soldered to a printed circuit board (PCB), and / or when the device is operating in an end-use system (e.g., a vehicle).

[0020] Testing for defects on the LED (150) or driver (130) can be difficult when the LED (150) is mounted on the driver (130). When the LED (150) is mounted on the driver (130), the nodes between the LED and each driver may be hidden or obscured by the LED chip. Because some nodes are inaccessible, the test probe may not be able to reach these nodes when measuring current or voltage.

[0021] Analog test equipment can be used to measure the forward voltage across each LED or a pair of pads, but for a matrix with thousands of LEDs, the measurement time is very long. As the number of LEDs in the matrix steadily increases, analog testing becomes incredibly time-consuming and costly.

[0022] It is important to verify the functionality of LEDs and drivers to ensure that the final LED device operates properly. Testing at various points in the manufacturing and assembly process allows for the rapid detection of defects. Testing at intermediate points enables the determination of the type and location of each defect, which can then be used to troubleshoot and optimize the manufacturing and assembly processes.

[0023] According to the technology of the present disclosure, the BIST (120) may be configured to detect defects on the driver (130), the pass device (140), and / or the LED (150) by testing each of the driver (130) or each of the LED (150) individually. To test the first driver or the first LED, the BIST (120) may be configured to turn on the first pass device configured to connect to the first LED by the first driver. Then, the BIST (120) may be configured to determine the voltage level at each pair of pads (160, 170) while the first pass device is active. The BIST (120) may be configured to test each of the LEDs (150) individually one by one after the LED (150) is connected to the pads (160, 170). Based on the voltage level, the BIST (120) may determine whether the first LED or the first driver is defective.

[0024] In some examples, the BIST (120) may also be configured to determine the voltage across each of the drivers (130) one by one. Based on the voltage across the drivers, the BIST (120) may be configured to determine whether the drivers are defective and / or whether each LED is defective. The BIST (120) may be configured to test each driver (130) individually one by one before and / or after the LED (150) is connected to the pads (160, 170).

[0025] While performing the built-in self-test, the BIST (120) may store a count of defects in memory (112). For example, the BIST (120) may be configured to increment a counter in response to determining each defect. There may be multiple counters to record different types of defects. The BIST (120) may store data in memory (112) indicating different categories of defects, such as short circuit defects, open circuit defects, LED defects, driver defects, etc. The BIST (120) may be configured to store the location and / or index of each defective LED or driver. The BIST (120) may also store data regarding the forward voltage measured by the processing circuit (110). The BIST (120) may be configured to output data regarding the built-in self-test to an external device (192).

[0026] The processing circuit (110) may be configured to perform corrective measures in response to defect detection. For example, the processing circuit (110) may be configured to set a bit indicating a defect to prevent the driver from turning on each pass device to activate each LED. The user may define the measures to be taken in response to one or more possible defects. The processing circuit (110) may store the option(s) selected by the user in memory (112), and accordingly, the processing circuit (110) may take the associated option.

[0027] BIST (120) can be configured to perform test routines in the digital domain, which can be faster than testing in the analog domain. For example, BIST (120) can be configured to test each LED within 10 to 20 microseconds. In comparison, an analog test routine may take about 5 to 10 milliseconds to test each LED. Therefore, the test routine implemented by BIST (120) can be much faster than other test methods, such as analog test methods.

[0028] Additionally, the test routine implemented by the BIST (120) includes voltage measurements at two points. One of the two measurement points can be a positive power supply or a negative power supply, which is more easily accessible than the node between the LED and the driver. The BIST (120) can be configured to access the node between the LED and the driver using a connection network, and thus there is no need to manually connect to the internal node.

[0029] FIG. 2 is a circuit diagram of an amplifier (230A-230C) for controlling a pass device (240A-240C) connected in series with an LED (250A-250C) according to the technology of the present disclosure. The device of the present disclosure may include a processing circuit (210), an amplifier (230A-230C), a pass device (240A-240C), a cathode pad (260A-260C), an anode pad (270A-270C), and a power supply pad (282). In some examples, the device may also include one or more power sources connected to the LED (250A-250C) and / or the cathode pad (260A-260C) and / or the power supply pad (282).

[0030] The processing circuit (210) may include digital logic configured to generate a low-power control signal and transmit it to the amplifiers (230A-230C). In some examples, each driver may include separate digital logic rather than a single centralized block of the processing circuit (210). Additionally or alternatively, the device may include multiple blocks of digital logic, each block generating a control signal for two or more drivers. The term "driver" as used in the description of FIG. 2 includes one of the amplifiers (230A-230C) and one of the pass devices (240A-240C). For example, the first driver may include the amplifier (230A) and the pass device (240A), the second driver may include the amplifier (230B) and the pass device (240B), and the third driver may include the amplifier (230C) and the pass device (240C). Alternatively, the term driver may include digital logic for generating a control signal.

[0031] The amplifier (230A-230C) may be configured to generate a high-power driver signal to drive the pass device (240A-240C) (e.g., by amplifying a low-power control signal). The amplifier (230A-230C) may deliver the driver signal to the control terminal (e.g., gate or base terminal) of the pass device (240A-240C). For example, the amplifier (230A) may activate the pass device (240A) by delivering the driver signal to the gate of the pass device (240A). The amplifier (230A-230C) may be configured to regulate the current flowing through the pass device (240A-240C) by operating the pass device (240A-240C) as an analog device rather than operating the pass device (240A-240C) as a digital device having only two states (on and off).

[0032] The pass device (240A-240C) may include, but is not limited to, any type of field-effect transistor (FET), bipolar junction transistor (BJT), insulated gate bipolar transistor (IGBT), high electron-mobility transistor (HEMT), and / or other elements that use voltage for control thereof. The pass device (240A-240C) may include n-type transistors and / or p-type transistors. The pass device (240A-240C) may include elements such as silicon, silicon carbide, and / or gallium nitride. In some examples, the pass device (240A-240C) includes a freewheeling diode connected in parallel with the transistor to prevent reverse breakdown of the transistor.

[0033] The LED (250A-250C) may be formed on a separate chip from the processing circuit (210), amplifier (230A-230C), and pass device (240A-240C). The chip for the LED (250A-250C) may be attached after the manufacture of the device including the processing circuit (210), amplifier (230A-230C), and pass device (240A-240C). The LED (250A-250C) may be attached to the pads (260A-260C and 270A-270C) during a hybridization process in which the LED (250A-250C) is mounted on the pads (260A-260C and 270A-270C) and electrically connected thereto. Another attachment process can be used to connect power to the pad (282), so that power can be delivered to the pass device (240A-240C).

[0034] In some examples, the ratio of LEDs to pass devices and amplifiers may be one-to-one. For example, an LED matrix may contain approximately 16,000 LEDs, where the LED matrix block may be mounted in a device having approximately 16,000 pass devices and approximately 16,000 amplifiers. As another example, an LED matrix may contain approximately 1,000 LEDs, where the LED matrix block may be mounted in a device having approximately 1 pass device and approximately 1 amplifier. Alternatively, there may be fewer pass devices and amplifiers than LEDs, and each pass device may be configured to control two or more LEDs.

[0035] The configuration illustrated in FIG. 2 is merely one example. The orientation of the LEDs (250A-250C) can be reversed so that the pass device (240A-240C) is connected to the cathode of the LEDs (250A-250C). Additionally, instead of multiple cathode pads (260A-260C), there may be only one cathode pad, where the cathodes of the LEDs (250A-250C) can be connected together within the LED chip. In the example with a single cathode pad, the "pad pair" refers to one of the anode pads (270A-270C) and the single cathode pad. In some examples, the LED (250A-250C) may be part of the same device as the amplifier (230A-230C) and the pass device (240A-240C), and accordingly, the pads (260A-260C and 270A-270C) become internal nodes rather than external pads.

[0036] One of the LEDs (250A-250C) may be defective. The defect may be a short circuit (no or low resistance) or an open circuit (high or infinite resistance) across the LED. The processing circuit (210) may be configured to detect a short circuit across the LED by determining that the voltage across the LED is below a minimum threshold voltage when the LED is activated. The processing circuit (210) may be configured to detect an open circuit across the LED by determining that the voltage across the LED is greater than a maximum threshold voltage when the LED is activated. The minimum and maximum threshold voltages may be limits of the voltage range allowed for the activated LED. In response to determining a defect on the LED, the processing circuit (210) may store the position or index of the LED and / or increment a counter.

[0037] A defect may exist in one of the amplifiers (230A-230C) or one of the pass devices (240A-240C). The defect may be a short circuit (no resistance or low resistance) or an open circuit (high resistance or infinite resistance) across the pass device, or other defects in the amplifier. The processing circuit (210) may be configured to detect a short circuit across the pass device by determining that the voltage across the pass device is greater than a first threshold voltage. The processing circuit (210) may be configured to detect an open circuit across the pass device by determining that the voltage across the pass device is less than a second threshold voltage.

[0038] The processing circuit (210) may be configured to detect the presence of a defect in the amplifier or pass device before the LED (250A-250C) is attached to the pads (260A-260C and 270A-270C). For example, a sensing resistor may be connected to the anode pad and the cathode pad, and the processing circuit (210) may detect the voltage across the sensing resistor. The processing circuit (210) may be configured to detect a short circuit across the pass device by determining that the voltage across the sensing resistor is greater than a first threshold voltage when the pass device is activated. The processing circuit (210) may be configured to detect an open circuit across the pass device by determining that the voltage across the LED is less than a second threshold voltage when the pass device is activated. The first and second threshold voltages may include an acceptable window for the voltage across the sensing resistor before the hybridization process, and a voltage outside the acceptable window indicates a defect in the pass device.

[0039] FIG. 3 is a circuit diagram of three possible fault modes for a driver (330A) or an LED (350A) according to the technology of the present disclosure. Segment (302) includes a driver (330A, 330B), wherein each driver includes one of a pass device (340A, 340B), an LED (350A, 350B), and a pad (360A, 360B, 370A, 370B). In some examples, the LED (350A, 350B) may be part of a device separate from the driver (330A, 330B).

[0040] Since turning on the pass device allows current to flow through each LED, the driver (330A, 330B) is described as a current source. Each driver (330A, 330B) may include an amplifier configured to drive the pass device as illustrated in FIG. 2. When the pass device is turned on, current can flow from the power supply (380) to the power supply (384) through the pass device and the LEDs. When the pass device is turned off, the current source (IALi) can sink or source current. The current source (IALi) may be part of the driver (330A), and the current source (IALj) may be part of the driver (330B).

[0041] A semiconductor die containing LEDs (350A, 350B) can be mounted on pads (360A, 360B, 370A, 370B) during the hybridization process. A single semiconductor die or semiconductor substrate may include all elements shown in FIG. 3 except for the LEDs (350A, 350B) and power supply (380, 384). In an example where there is a single anode pad instead of multiple pads (370A, 370B), the anode terminal of the LED (350A, 350B) can be connected to the single anode pad during the hybridization process. In an example where there is a single anode pad, each of the cathode pads (360A, 360B) can be paired with the single anode pad.

[0042] Resistors (322, 324, 326) indicate possible defects within the segment (302). Resistor (322) indicates a short circuit defect or an open circuit defect that may be present across the pads (360A, 370A) (before hybridization) or across the LED (350A) (after hybridization). An open circuit across the pads (360A, 370A) is expected before hybridization. The BIST may be configured to detect a short circuit defect across the pads (360A, 370A) or across the LED (350A) by determining that the forward voltage across the pads (360A, 370A) is less than the minimum threshold voltage. The BIST may be configured to detect an open circuit defect across the pads (360A, 370A) or across the LED (350A) by determining that the forward voltage across the pads (360A, 370A) is greater than the maximum threshold voltage.

[0043] The resistor (324) indicates a possible short-circuit or open-circuit fault between pads (360A, 360B) (before or after hybridization) or between the anodes of LEDs (350A, 350B) (after hybridization). The BIST can be configured to detect a fault between pads (360A, 360B) based on the forward voltage across LED (350A) and the forward voltage across LED (350B). As shown in FIG. 3, LEDs (350A, 350B) are adjacent LEDs, but in some examples, a fault may be detected between two non-adjacent LEDs.

[0044] The resistor (326) indicates a short circuit fault or an open circuit fault that may exist across the driver (330A) before or after the hybridization process occurs to attach the LEDs (350A, 350B). The BIST may be configured to detect a short circuit fault across the driver (330A) by determining that the voltage across the driver (330A) is less than a lower threshold voltage. The BIST may be configured to detect an open circuit fault across the driver (330A) by determining that the voltage across the driver (330A) is greater than an upper threshold voltage.

[0045] A short circuit is not necessarily zero resistance but can be defined as a resistance smaller than the minimum critical resistance. Therefore, the voltage of a short circuit can be zero or a small non-zero voltage. An open circuit is not necessarily infinite resistance but can be defined as a resistance larger than the maximum critical resistance. The voltage of an open circuit can be infinite or a large finite voltage.

[0046] The power supply (380, 384) may be part of another external device. For example, pads (382, 386) may be mounted on a PCB that includes connections to the power supply (380, 384). In some examples, each pad (382, 386) may include a number of individual pads for parallel connections, for example, to bond wires. The power supply (380, 384) may include power rails for positive and negative power, such as VDDP and reference ground power. The power supply (380, 384) may include connections to a power supply unit, such as a battery, or a main power supply.

[0047] FIG. 4 is a circuit diagram for calibrating a sensing resistor (424) according to the technology of the present disclosure. The logic (410) may be configured to calibrate the sensing resistor (424) for a front-end test (e.g., prior to hybridization) to reduce or eliminate the spread of resistance. Calibration of the sensing resistor (424) may provide a more accurate measurement of the absolute value of the current flowing through each LED in the segment (402). The logic (410) may be configured to calibrate the sensing resistor (424) by changing the resistance of a trimmable resistor (426).

[0048] The logic (410) may be configured to determine a trimming factor representing the resistance of a trimmable resistor (426). The logic (410) may store the trimming factor in a factor storage (412) which may include one-time programmable memory, flash, or electrically erasable programmable read-only memory. The logic (410) may be configured to use the trimming factor stored in the application field in addition to the front-end test. Trimming is optional, and alternatives include an external resistor or an untrimmed internal resistor. In some examples, the device may include an internal sense resistor with a pad for connecting an optional external sense resistor. Alternatively, the device may include a pad for an external resistor without any internal sense resistor. An external resistor may increase the number of components on the application board (e.g., PCB). Using an untrimmed internal resistor may cause the actual resistance value to spread out, potentially leading to inaccurate voltage sensing. Consequently, the resulting Gaussian distribution of the resistance may have an average value offset from the expected value.

[0049] The connection network (432) includes switches (S1, SN, SR) for selecting and detecting various nodes in the segment (402). To calibrate the detection resistor (424), the calibration routine (414) includes switches (S1-S NOpen ) and switch(S R It can be configured to close the sensing resistor (424) and the trimmable resistor (426) to connect to the test pad (438). The current source (436) can force an external current from the power supply (480) through the sensing resistor (424) and the trimmable resistor (426). A differential analog-to-digital converter (ADC) (422) can convert the voltage across the sensing resistor (424) into a digital number. The calibration routine (414) can be configured to perform the calibration routine by changing the equivalent resistance of the trimmable resistor (426). The calibration routine (414) can be configured to store the trimming factor in the factor storage (412). Further exemplary details regarding trimming can be found in U.S. Patent No. 10,069,399, jointly assigned and issued September 4, 2018, titled “Selecting an Aspect Ratio for Current Monitoring,” the entire contents of which are incorporated herein by reference.

[0050] Although FIGS. 4-6 and FIG. 10 illustrate a single ADC, in some examples, the device may include one or more ADCs to test LEDs in parallel. For example, the device may include four ADCs, each configured to test a subset (e.g., a quadrant) of LEDs in the device. A device with multiple ADCs may be configured to perform multiple test routines in parallel, with each test routine using one of the ADCs.

[0051] FIGS. 5 and FIGS. 6 are circuit diagrams for detecting defects according to the technology of the present disclosure. The test routine setup shown in FIG. 5 allows the logic (510) to read the forward voltage of each LED. The test routine shown in FIG. 5 can be used for front-end testing (e.g., prior to hybridization) as well as for back-end testing, final line testing, and application field testing. The logic (510) can be configured to evaluate whether the LEDs are connected through a pair of pads or, instead, whether an open circuit or a short circuit exists across the pair of pads.

[0052] To enable the routine, the finite state machine (FSM) (514) switches (S R The connection network (532) can be configured to control the ADC (522) to disconnect it from the sensing resistor (524) by opening ). The FSM (514) is a switch (S FSM By closing the ), the ADC (522) can be configured to connect to the test pad (538). The test pad (538) is shared by all LEDs of the segment (502), and the logic (510) can be configured to connect the LEDs to the test pad (538) one by one. The FSM (514) can turn on the LEDs by activating the drivers one by one, and the ADC (522) is connected to the switches (S1-S) connected to the ADC (522). N The forward voltage of the LEDs can be detected sequentially by controlling the FSM (514). Alternatively, the FSM (514) can turn on all LEDs in parallel, but this approach will result in higher power loss. The FSM (514) can also proceed to turn on a batch of LEDs at once and determine the forward voltage across each LED.

[0053] The ADC (522) can convert the forward voltage across the current source (530A) into a digital number. An internal logic calculator within the logic (510) can be configured to evaluate whether the digital number is greater than the maximum threshold voltage or less than the minimum threshold voltage. The current source (530A) is an example of a driver (e.g., an amplifier and pass device) for controlling an LED.

[0054] In response to a determination that the voltage across the current source (530A) is greater than the upper threshold voltage, the logic (510) may be configured to store the corresponding pixel index and report an open circuit state. In response to a determination that the voltage across the current source (530A) is less than the lower threshold voltage, the logic (510) may be configured to store the corresponding pixel index and report a short circuit state. The upper and lower threshold voltages may include an acceptable window for the voltage across the current source (530A). The logic (510) may be configured to store the number of each fault count in a register (512). The logic (510) may report the fault count and location of each fault to an external device via the diagnostic interface (590).

[0055] The logic (510) can be configured to execute a test routine in the application field by enabling the test routine at startup of the device (e.g., during normal operation). The logic (510) can be configured to perform the test routine regularly and / or at predefined intervals, and / or the logic (510) can be configured to perform the test routine in response to receiving a command signal from an external device, for example, through the diagnostic interface (590). The logic (510) can be configured to transmit the results of the test routine to an external device through the diagnostic interface (590) to notify the user of defective pixels and defect counts. Through the test results, the user can filter out defective parts and evaluate the results of the hybridization process.

[0056] FIG. 6 illustrates a test routine for measuring output current during the front end or back end. For the front end test (e.g., before the hybridization process), the logic (610) may be configured to verify the function of each current source in a reasonable time and with minimal effort for testing and data storage. The logic (610) may be configured to test each current source at the front end post-assembly or back end (e.g., after the hybridization process), evaluate the impact of the assembly process on the output current, and distinguish whether there is a defect in the LED attachment side or a defect in the current source side. The post-assembly test may be important for identifying the location of defects and also for field return analysis.

[0057] The sensing resistor (624) may include an internal resistor or an external resistor (e.g., untrimmed or previously trimmed). The logic (610) may be configured to control the connection network (632) so that current from the driver flows to the sensing resistor (624). The logic (610) may be configured to test the drivers one by one, such as connecting the sensing resistor (624) to a first driver, then connecting the sensing resistor to a second driver, and so on. The ADC (622) may be configured to detect the voltage across the sensing resistor (624) representing the voltage across the selected LED. The ADC (622) may convert the voltage across the sensing resistor (622) into a digital number. The positive input of the ADC (622) is configured to receive a first signal representing a voltage level at the first end of the sensing resistor (624) (e.g., the end connected to the power supply (680)). The negative input of the ADC (622) is configured to receive a second signal indicating a voltage level at the second end of the sensing resistor (624) (e.g., the end connected to the test pad (638)).

[0058] To enable automatic routines, the FSM (614) switches (S FSM By closing ) the ADC (622) is connected to the sensing resistor (624) and the switch (S R The ADC (622) can be configured to connect to the test pad (638) by closing the FSM (614). The FSM (614) can be configured to turn on each driver one by one (or all at once in parallel) and sequentially connect each current source to the sensing resistor (624). Current from the attached driver will flow through the sensing resistor (624), and the ADC (622) can convert the voltage across the sensing resistor (624). Based on Ohm's law and the known resistance of the sensing resistor (624), the logic (610) can determine the current being conducted by each driver. The logic (610) can be configured to determine whether a fault exists in the driver based on whether the determined current is within an acceptable range.

[0059] To determine whether the driver is defective, the logic (610) may be configured to evaluate whether the digital number output by the ADC (622) is outside an acceptable range, where the acceptable range is limited by a maximum threshold voltage and a minimum threshold voltage. For example, in response to a determination that the forward voltage across the LED (650A) is greater than the maximum threshold voltage, the logic (610) may be configured to determine that an open circuit exists across the pads (660A, 670A). In response to a determination that the forward voltage across the LED (650A) is less than the minimum threshold voltage, the logic (610) may be configured to determine that a short circuit exists across the pads (660A, 670A). The logic (610) may also be configured to determine whether the cathode terminal of the LED (650A) is properly connected to the cathode pad (670A) or whether the connection is missing or obstructed.

[0060] In response to a determination that a digital number is out of an acceptable range, the logic (610) may be configured to store a pixel index and / or an indication of the defect type. The logic (610) may also be configured to store data such as a defect count, minimum and maximum voltages (e.g., a digital number output by the ADC (622)) and / or average voltage in a count storage (612). The minimum, maximum, and average voltages may be based on all voltages detected by the ADC (622).

[0061] The logic (610) may be configured to store test parameters in a set of registers. The test parameters may include a bit to enable an output current measurement routine, a bit to enable a VLED forward voltage measurement routine, and a bit to enable a sense resistor calibration. The test parameters may also include a stabilization time between two consecutive current source selections, the number of iterative changes in the same current source, upper and lower limits (e.g., maximum and minimum threshold voltages), and maximum, minimum, and average threshold current and voltage values. The test parameters may also include one or more counters for maximum and minimum pixel coordinate values ​​for testing and the number of detected defects.

[0062] The logic (610) can be configured to report all stored data to an external device via the diagnostic interface (690). Using all data stored in the diagnostic register, the logic (610) can read the maximum, minimum, and average values ​​of digital numbers and evaluate the Gaussian distribution and process capability index (cpk) without needing to have statistical data of all current sources. The logic (610) can perform a test routine before or after the LED is mounted to the current source. For example, a sensing resistor (624) can be connected in parallel with the LED. By selecting an appropriate resistance value, the current can be partially or completely bypassed from the LED and current from the driver can be allowed to flow through the sensing resistor (624). By setting the resistance of the sensing resistor (624) sufficiently low, the logic (610) can measure the current conducted by the driver by measuring the voltage across the sensing resistor (624).

[0063] In an example where the logic (610) identifies a defect on the LED, the logic (610) may be configured to determine whether a defect exists in the LED and / or each driver by connecting a sensing resistor (624) in series with the driver. The logic (610) may distinguish between an LED defect and a driver defect using an output current measurement with the configuration shown in FIG. 6.

[0064] FIG. 7 is a flowchart illustrating an exemplary technique for detecting defects according to the technology of the present disclosure. The technology of FIG. 7 is described with reference to the circuit illustrated in FIG. 2, but other components may also illustrate similar technology.

[0065] In the example of FIG. 7, the processing circuit (210) causes the amplifier (230A) of the first driver to turn on the pass device (240A (700)). The processing circuit (210) can transmit a control signal to the amplifier (230A), and the amplifier (230A) can generate a high-power driver signal based on the control signal. In the example where the LED (250A) is mounted on the pads (260A, 270A), the processing circuit (210) can turn on the LED (250A) by controlling the amplifier (230A) to activate the pass device (240A).

[0066] In the example of FIG. 7, the processing circuit (210) determines the voltage level at the anode pad (270A) and the cathode pad (260A) (702). To detect the voltage level, the processing circuit (210) may be configured to control a network of switches to connect a sensing resistor across the pads (260A, 270A). A differential ADC may be configured to convert the voltage across the sensing resistor into a digital number representing the voltage across the pads (260A, 270A) (e.g., the voltage difference between the pads (260A, 270A)).

[0067] In the example of FIG. 7, the processing circuit (210) determines that there is a defect in the driver or LED (250A) based on the voltage level at the pads (260A, 270A) (704). In the example where the LED (250A) is not yet mounted on the pads (260A, 270A), the processing circuit (210) may be configured to determine whether there is a defect in the driver (e.g., amplifier (230A) or pass device (240A)) or whether there is a defect in the gap between the pads (260A, 270A) which must be an open circuit before connecting the LED (250A).

[0068] In an example where the LED (250A) is mounted on the pads (260A, 270A), the processing circuit (210) may first be configured to determine the voltage drop across the pass device (240A) while the LED (250A) is turned on. In response to detecting that the voltage drop across the pass device (240A) is outside the acceptable range, the processing circuit (210) may be configured to determine the voltage drop across the pads (260A, 270A) to determine whether a defect exists in the pass device (240A) and / or the LED (250A). In an example where the processing circuit (210) determines that two voltage levels are outside the acceptable range, the processing circuit (210) may be configured to store indications for two distinct defects.

[0069] FIG. 8 is a circuit diagram for measuring the cathode voltage for two LEDs (850A, 850B) according to the technology of the present disclosure. To detect a fault between the LEDs (850A, 850B), the logic (810) may be configured to control a connection network (832) to connect the cathode pads (860A, 860B) one by one to a test pad (838). When the cathode pad (860A) is connected to the test pad (838), for example, a current source (836) may sink current from the LED (850A).

[0070] The current sensor (834) is configured to measure the current conducted by the current source (836). The logic (810) can determine whether an LED-to-LED defect exists based on the current detected by the current sensor (834) while the cathode pad (860A) is connected to the test pad (838) and the cathode pad (860B) is connected to the test pad (838). For example, the logic (810) can be configured to force current through the LED (850A) (e.g., by activating the driver (830A)) and check whether current is present in the cathode pad (860B). Current from the LED (850A) should not be present in the cathode pad (860B) unless there is a relatively low resistance path between the cathode pads (860A, 860B).

[0071] FIGS. 9a and 9b are diagrams of two exemplary test patterns (900A, 900B) that can be implemented by BIST according to the technology of the present disclosure. BIST can be configured to automatically perform a low-power test routine using test patterns (900A, 900B). Test patterns (900A, 900B) use a complementary chessboard pattern. BIST can be configured to detect a specific failure mode, namely an LED-to-LED short circuit, using test patterns (900A, 900B).

[0072] Along with automatic measurement of internal parameters via a differential ADC, test patterns (900A, 900B) allow for fully automatic detection of LED-to-LED defects (e.g., for verifying channel-to-channel crosstalk). For each of test patterns (900A, 900B), BIST can generate a complementary chessboard pattern by setting the state of the i-th cell to 100% (enabled) and the state of the (i+1)-th cell to 0% (inactive). Cells can be sequentially numbered so that the first cell is adjacent to the second cell, the second cell is adjacent to the third cell, and so on, continuing along the row. If the 16th cell is at the end of the row, the 17th cell is at the beginning of the next row. Test pattern (900B) is the inverse of test pattern (900A).

[0073] For a test pattern (900A), the BIST may be configured to turn on a first subset of LEDs. The first subset may include a first LED, a third LED, a fifth LED, etc. For a test pattern (900A), the BIST may also be configured to turn off a second subset of LEDs. The second subset may include a second LED, a fourth LED, a sixth LED, etc. The first and second subsets of LEDs may form a chessboard or checkerboard pattern as illustrated in FIG. 9a and FIG. 9b. Other test patterns, such as ring patterns or stripe patterns, are also possible. For example, using a test pattern, defects between two LEDs placed diagonally (e.g., different rows and different columns) can be detected.

[0074] FIG. 10 is a circuit diagram of a device including a differential ADC (1022) for measuring the forward voltage across an LED according to the technology of the present disclosure. When applying a dedicated light pattern, the logic (1010) may be configured to perform an automatic routine including measuring the forward voltage across each LED of the entire matrix using the ADC (1022). To enable the automatic routine, the logic (1010) may be configured to control a connection network (1032) to connect the ADC (1022) to the power supply (1080) and to the cathode pad (1060A or 1060B) of the selected pixel using a switch labeled DIAG_SEL.

[0075] The logic (1010) may include an internal FSM that is automatically configured so that the ADC (1022) can convert the forward voltage of each LED into a digital number. The internal logic calculator may be configured to evaluate whether the forward voltage of an active LED pixel is within an acceptable range for the active LED. The internal logic calculator may also be configured to evaluate whether the forward voltage of a deactivated LED pixel is within an acceptable range for the deactivated LED. In the example depicted in FIG. 10, LED (1050A) is an active LED and LED (1050B) is a deactivated LED.

[0076] Each acceptable range may include an upper threshold and a lower threshold. The acceptable range for an activated LED may include a typical forward voltage for the LED, which may be between 1.7V and 3.3V depending on the type of LED. The upper threshold voltage for an activated LED may be in the range of 4 to 5V, such as 4.5V. In an example involving multiple LEDs connected in series, the typical voltage may be higher than 3.3 volts. The acceptable range for a deactivated LED may include 0 volts. Each acceptable range may be wider than the typical voltage; for example, the acceptable range for a deactivated LED may be from negative 0.3V to positive 0.6V. Accordingly, to determine whether a defect exists between the cathode pads (1060A, 1060B), the logic (1010) may be configured to determine whether the forward voltage of the LED (1050A) is less than the lower threshold voltage for the activated LED and whether the forward voltage of the LED (1050B) is greater than the upper threshold voltage for the deactivated LED.

[0077] In some examples, the expected forward voltage for the activated LED is about 3 volts higher than reference ground at the ground (GND) node, and the voltage level of VDDP is 4 volts higher than reference ground. Therefore, the expected voltage level at the cathode pad (1060A) is about 1 volt higher than reference ground. The logic (1010) may be configured to detect a short circuit from the cathode pad (1060A) to VDDP or some other fault in response to a determination that the voltage level at the cathode pad (1060A) is greater than an upper threshold voltage, such as 2 volts higher than reference ground. The logic (1010) may be configured to detect a short circuit from the cathode pad (1060A) to reference ground in response to a determination that the voltage level at the cathode pad (1060A) is less than a lower threshold voltage, such as 0.5 volts higher than reference ground.

[0078] The fact that the converted value for the forward voltage across the LEDs (1050A, 1050B) is outside their respective acceptable ranges implies that a dirty resistor is placed between adjacent pixels. For example, an open circuit (e.g., high resistance) between the cathode pads (1060A, 1060B) may be desirable. If the resistance decreases below an acceptable level, the voltage at the cathode pads (1060A, 1060B) measured by the ADC (1022) will not be within the acceptable voltage range.

[0079] The logic (1010) may be configured to store the number of detected defects and the location of each defect in memory. The logic (1010) may be further configured to report this data to an external device through a diagnostic interface. Defect testing between LEDs may occur at the backend, end line, or field. Backend testing may occur after the hybridization process is completed, end line testing may occur after the LED device is fully assembled, and field testing may occur after the device is installed and operated.

[0080] Test parameters for LED-to-LED testing may include stored values ​​for the type of chessboard pattern, values ​​for the settling time between two consecutive current source selections, the number of iterative changes for the same current source, upper and lower limits (e.g., maximum and minimum threshold voltages), and maximum, minimum, and average threshold current and voltage values. Test parameters may also include maximum and minimum pixel coordinate values ​​for the test and one or more counters for detected defects.

[0081] FIG. 11 is a flowchart illustrating an exemplary technique for detecting a defect between two LEDs according to the technology of the present disclosure. The technique of FIG. 11 is described with reference to the circuit illustrated in FIG. 10, but other components may also illustrate a similar technique.

[0082] In the example of FIG. 11, the logic (1010) enables the LED (1050A) (1000) and disables the LED (1050B) (1002). The logic (1010) can enable the LED (1050A) by causing the driver (1030A) to enable a pass device connected to the LED (1050A). When this pass device is enabled, current can flow through the LED (1050A). The logic (1010) can disable the LED (1050B) by causing the driver (1030B) to disable a pass device connected to the LED (1050AB). When this pass device is enabled, current flowing through the LED (1050B) is prevented or reduced.

[0083] In the example of FIG. 11, the logic (1010) determines the forward voltage across the LED (1050A) (1004) and the forward voltage across the LED (1050B) (1006). The logic (1010) can measure the forward voltage across the LED (1050A) by connecting an ADC (1022) across the pads (1060A, 1070A). The logic (1010) may be configured to control a connection network (1032) to disconnect the ADC (1022) from the pads (1060A, 1070A) and connect the ADC (1022) to the pads (1060B, 1070B), but in other examples, the anode pads of adjacent LEDs may not be directly connected. In the example of FIG. 10, the anode pad (1070A) is connected to the anode pad (1070B). The ADC (1022) can convert each forward voltage into a digital number stored in memory by the logic (1010).

[0084] In the example of FIG. 11, the logic (1010) determines whether a defect exists between the LEDs (1050A, 1050B) based on the forward voltage across the LEDs (1050A, 1050B) (1008). For example, the logic (1010) may be configured to determine whether each of the forward voltages is within an acceptable voltage range. The logic (1010) may also be configured to measure the voltage across the driver (1030A and / or 1030B) to determine whether the defect exists across a single LED or across a single driver. In response to the determination that a defect exists between the cathode pads (1070A, 1070B), the logic (1010) may be configured to increment a defect counter and store the position of the LEDs (1050A, 1050B).

[0085] The present disclosure has functions attributed to a processing circuit (110, 210), a BIST (120), and logic (410, 510, 610, 810, 1010). The processing circuit (110, 210), the BIST (120), and the logic (410, 510, 610, 810, 1010) may include one or more processors. The processing circuit (110, 210), the BIST (120), and the logic (410, 510, 610, 810, 1010) may include any combination of an integrated circuit, a discrete logic circuit, an analog circuit, for example, one or more microprocessors, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), and / or a field-programmable gate array (FPGA). In some examples, the processing circuit (110, 210), BIST (120), and logic (410, 510, 610, 810, 1010) may include a number of components, for example, one or more microprocessors, one or more DSPs, one or more ASICs, or one or more FPGAs, and any combination of other discrete or integrated logic circuits and / or analog circuits.

[0086] The technology described in the present disclosure may also be implemented or encoded in articles of manufacture comprising non-transient computer-readable storage media, such as processing circuits (110, 210), BIST (120), and logic (410, 510, 610, 810, 1010). Examples of non-transient computer-readable storage media may include RAM, ROM, programmable ROM (PROM), erasable programmable ROM (EPROM), electronically erasable programmable ROM (EEPROM), flash memory, hard disk, magnetic media, optical media, or any other computer-readable storage device or type of computer-readable media. The term “non-transient” may indicate that the storage medium is not implemented by a carrier or propagated signal. In certain examples, the non-transient storage medium may store data that may change over time (e.g., in RAM or cache).

[0087] The following numbered examples describe one or more aspects of the present disclosure.

[0088] Example 1. A method for an embedded self-test for detecting a defect comprises the step of causing a first driver among a set of drivers to turn on a first individual pass device, wherein each driver of the set of drivers comprises a pass device configured to be electrically connected to each pad of at least one anode pad or at least one cathode pad, and each driver of the set of drivers is configured to control whether each LED of an LED set is turned on or turned off. The method also comprises the step of determining a first voltage level at a first anode pad among at least one anode pad and the step of determining a first voltage level at a first cathode pad among at least one cathode pad. The method further comprises the step of determining whether a defect exists on the first driver, across the first anode pad and the first cathode pad, or on the first LED based on the first voltage level at the first anode pad and the first cathode pad.

[0089] Example 2. In the method of Example 1, the method further includes the step of determining a first voltage level at the first anode pad and the first cathode pad by determining the voltage drop across the sensing resistor while the sensing resistor is connected across the first anode pad and the first cathode pad.

[0090] Example 3. In the method of Example 1 or Example 2, the method further includes the step of individually testing each driver of a driver set one by one or each LED of an LED set one by one by determining a second voltage level at the second anode pad and the second cathode pad while the sensing resistor is connected across the second anode pad and the second cathode pad.

[0091] Example 4. In the method of Examples 1-3 or any combination thereof, the step of testing each driver or each LED individually one by one includes the step of turning on a second driver among the driver sets a second individual pass device.

[0092] Example 5. In the method of Examples 1-4 or any combination thereof, the step of testing each driver or each LED individually one by one includes the step of determining whether a defect exists in the second driver or the second LED based on the second voltage level at the second anode pad and the second cathode pad.

[0093] Example 6. In the method of Examples 1-5 or any combination thereof, the step of testing each driver or each LED individually one by one includes the step of controlling a connection network to connect a sensing resistor across the first anode pad and the first cathode pad before determining the first voltage level.

[0094] Example 7. In the method of Examples 1-6 or any combination thereof, the step of testing each driver or each LED individually one by one includes the step of controlling the connection network to disconnect the sensing resistor from the first anode pad and the first cathode pad before determining the second voltage level.

[0095] Example 8. In the method of Examples 1-7 or any combination thereof, the step of testing each driver or each LED individually one by one includes the step of controlling a connection network to connect a sensing resistor across the second anode pad and the second cathode pad before determining the second voltage level.

[0096] Example 9. In the method of Examples 1-8 or any combination thereof, the method further includes the step of outputting a digital number representing the voltage drop across a sensing resistor to a processing circuit by means of a differential ADC.

[0097] Example 10. In the method of Examples 1-9 or any combination thereof, determining whether a defect exists is based on digital numbers.

[0098] Example 11. In the method of Examples 1-10 or any combination thereof, the method further includes the step of causing a current source to deliver a test current to the sensing resistor while the sensing resistor is separated from at least one anode pad and at least one cathode pad.

[0099] Example 12. In the method of Examples 1-11 or any combination thereof, the method further includes the step of determining the voltage drop across the sensing resistor while the test current is delivered to the sensing resistor.

[0100] Example 13. In the method of Examples 1-12 or any combination thereof, the method further includes the step of changing the resistance of the sensing resistor based on the determined voltage drop across the sensing resistor.

[0101] Example 14. In the method of Examples 1-13 or any combination thereof, the step of changing the resistance of the sensing resistor using a trimming factor is further included.

[0102] Example 15. In the method of Examples 1-14 or any combination thereof, the step of storing the trimming coefficient in memory is further included.

[0103] Example 16. In the method of Examples 1-15 or any combination thereof, determining that a defect exists includes determining that the difference between the first voltage level at the first anode pad and the first voltage level at the first cathode pad is greater than an upper threshold value.

[0104] Example 17. In the method of Examples 1-16 or any combination thereof, determining that a fault exists includes determining that an open circuit exists across the first anode pad and the first cathode pad in response to determining that the difference between the first voltage levels is greater than an upper threshold value.

[0105] Example 18. In the method of Examples 1-17 or any combination thereof, determining that a defect exists includes determining that the difference between the first voltage level at the first anode pad and the first voltage level at the first cathode pad is smaller than a lower threshold value.

[0106] Example 19. In the method of Examples 1-18 or any combination thereof, determining that a fault exists includes determining that a short circuit exists across the first anode pad and the first cathode pad in response to determining that the difference between the first voltage levels is less than a lower threshold value.

[0107] Example 20. In the method of Examples 1-19 or any combination thereof, the step of storing a count of defects in memory is further included.

[0108] Example 21. In the method of Examples 1-20 or any combination thereof, the method further includes the step of storing a first count of detected open circuit faults in memory and storing a second count of detected short circuit faults in memory.

[0109] Example 22. In the method of Example 1-21 or any combination thereof, further include the step of outputting a count of faults to an external device through a diagnostic interface.

[0110] Example 23. In the method of Examples 1-22 or any combination thereof, the method further includes the step of determining whether the count of defects is greater than a threshold number and outputting the count of defects to an external device in response to determining that the count of defects is greater than the threshold number.

[0111] Example 24. In the method of Examples 1-23 or any combination thereof, the method further includes the step of determining the minimum value of the voltage difference across each individual anode pad of at least one anode pad and each individual cathode pad of at least one cathode pad.

[0112] Example 25. In the method of Examples 1-24 or any combination thereof, the method further includes the step of determining the maximum value of the voltage difference across each individual anode pad of at least one anode pad and each individual cathode pad of at least one cathode pad.

[0113] Example 26. In the method of Examples 1-25 or any combination thereof, the method further includes the step of determining the average value of the voltage difference across each individual anode pad of at least one anode pad and each individual cathode pad of at least one cathode pad.

[0114] Example 27. In the method of Examples 1-26 or any combination thereof, the step of storing the minimum value, maximum value, and average value in memory is further included.

[0115] Example 28. In the method of Examples 1-27 or any combination thereof, the method further includes the step of outputting the minimum value, maximum value, and average value to an external device through a diagnostic interface.

[0116] Example 29. In the method of Examples 1-28 or any combination thereof, the method further comprises the step of simultaneously testing a plurality of drivers of a driver set or a plurality of LEDs of an LED set as a group by causing at least a plurality of drivers to turn on each of a plurality of pass devices one by one, determining a plurality of voltage differences across each pad while a pass device among each of the plurality of pass devices is turned on, and determining whether any defect exists based on the plurality of voltage differences. The plurality of drivers comprises fewer than the total number of driver sets, and the plurality of LEDs comprises fewer than the total number of LED sets.

[0117] Example 30. In the method of Examples 1-29 or any combination thereof, the method further includes the step of receiving a signal from an external device through a diagnostic interface and determining whether a defect exists in response to receiving a signal from the external device.

[0118] Example 31. In the method of Examples 1-30 or any combination thereof, determining whether a defect exists occurs before or after the hybridization process.

[0119] Example 32. In the method of Examples 1-31 or any combination thereof, the method further includes the step of determining whether a defect exists in the first anode pad and the first cathode pad before the hybridization process.

[0120] Example 33. As a method of Example 1-32 or any combination thereof, determining whether a defect exists in the first LED occurs after the hybridization process.

[0121] Example 34. In the method of Examples 1-33 or any combination thereof, the hybridization process includes mounting a device in a structure including an LED set and electrically connecting a switch set to the LED set.

[0122] Example 35. The device includes a built-in self-test for detecting defects, and the device further includes at least one anode pad configured to be connected to the anode of an LED set and at least one cathode pad configured to be connected to the cathode of an LED set. The device further includes a driver set, and each driver of the driver set includes a pass device configured to be electrically connected to each pad of at least one anode pad or at least one cathode pad, and each driver of the driver set is configured to control whether each LED of the LED set is turned on or turned off. The device also includes a processing circuit configured to test each driver of a drive set one by one or each LED of an LED set one by one by causing a first driver of at least one driver of a driver set to turn on a first individual pass device, determine a first voltage level at a first anode pad among at least one anode pad, determine a first voltage level at a first cathode pad among at least one cathode pad, and determine that there is a defect on the first driver, across the first anode pad and the first cathode pad, or on the first LED based on the first voltage level at the first anode pad and the first cathode pad.

[0123] Example 36. The device of Example 35 further includes a sensing resistor configured to be connected to a first anode pad and a first cathode pad.

[0124] Example 37. The device of Example 35 or Example 36 further includes a differential ADC configured to measure the voltage across a sensing resistor.

[0125] Example 38. In the device of Examples 35-37 or any combination thereof, a connection network configured to connect to a first anode pad and a first cathode pad is further included.

[0126] Example 39. In the device of Examples 35-38 or any combination thereof, a memory configured to store a trimming factor for a sensing resistor is further included.

[0127] Example 40. In the device of Examples 35-39 or any combination thereof, further includes a memory configured to store the minimum, maximum, and average values ​​of the voltage difference across each LED, each pad pair, and / or each driver.

[0128] Example 41. In the device of Examples 35-40 or any combination thereof, the processing circuit includes a state machine configured to cause a driver set to turn on and turn off pass devices one by one as part of a self-test.

[0129] Example 42. In the device of Examples 35-41 or any combination thereof, the processing circuit is configured to perform the method of Example 1-34 or any combination thereof.

[0130] Example 43. The device includes a computer-readable medium storing executable instructions configured to be executable by a processing circuit to enable the processing circuit to perform the method of Example 1-34 or any combination thereof.

[0131] Example 44. The system includes means for performing the methods of Example 1-34 or any combination thereof.

[0132] Example 45. A method for an embedded self-test for detecting a defect between a first LED and a second LED of an LED set comprises the step of causing a first driver in a driver set to turn on a first individual pass device. Each driver in the driver set comprises a pass device configured to be electrically connected to each pad of at least one anode pad or at least one cathode pad, and each driver in the driver set is configured to control whether each LED of the LED set is turned on or turned off. The method also comprises the step of causing a second driver in the driver set to control a second individual pass device to turn off the second LED, determining a first forward voltage across the first LED, and determining a second forward voltage across the second LED. The method further comprises the step of determining that a defect exists between the first LED and the second LED of the LED set based on the first and second forward voltages.

[0133] Example 46. In the method of Example 45, the method further includes the step of determining whether the first forward voltage is outside the first allowable range for the activated LED.

[0134] Example 47. In the method of Example 45 or Example 46, the method further includes the step of determining whether the second forward voltage is outside the second allowable range for the deactivated LED.

[0135] Example 48. In the method of Examples 45-47 or any combination thereof, the step of determining that a defect exists includes determining that the first forward voltage is outside the first allowable range.

[0136] Example 49. In the method of Examples 45-48 or any combination thereof, the step of determining that a defect exists includes determining that the second forward voltage is outside the second allowable range.

[0137] Example 50. In the method of Examples 45-49 or any combination thereof, the step of determining whether the first forward voltage is outside the first allowable range includes determining that the first forward voltage is less than the first threshold level for the activated LED.

[0138] Example 51. In the method of Examples 45-50 or any combination thereof, the step of determining whether the second forward voltage is outside the second allowable range includes determining that the second forward voltage is greater than the second threshold level for the deactivated LED.

[0139] Example 52. In the method of Examples 45-51 or any combination thereof, the method further includes the step of outputting a digital number to a processing circuit that indicates a first forward voltage across the first LED or a second forward voltage across the second LED by means of a differential ADC.

[0140] Example 53. In the method of Examples 45-52 or any combination thereof, the method further includes the step of causing the first input of the differential ADC to receive a first signal indicating a voltage level at the anode pad of the first pad pair.

[0141] Example 54. In the method of Examples 45-53 or any combination thereof, the method further includes the step of causing the second input of the differential ADC to receive a second signal indicating a voltage level at the cathode pad of the first pad pair.

[0142] Example 55. In the method of Examples 45-54 or any combination thereof, the method further includes the step of causing the first input of the differential ADC to receive a third signal representing the voltage level at the anode pad of the second pad pair instead of receiving the first signal.

[0143] Example 56. In the method of Examples 45-55 or any combination thereof, the method further includes the step of causing the second input of the differential ADC to receive a fourth signal representing the voltage level at the cathode pad of the second pad pair instead of receiving the first signal.

[0144] Example 57. In the method of Examples 45-56 or any combination thereof, the method further includes the step of incrementing a counter in response to a determination that a defect exists between the first LED and the second LED.

[0145] Example 58. In the method of Examples 45-57 or any combination thereof, the step of outputting the value of the counter to an external device through a diagnostic interface is further included.

[0146] Example 59. In the method of Examples 45-58 or any combination thereof, the method further includes the step of storing the location of the first LED and the location of the second LED in memory in response to a determination that a defect exists between the first LED and the second LED.

[0147] Example 60. In the method of Examples 45-59 or any combination thereof, the method further includes the step of outputting the position of the first LED and the position of the second LED to an external device through a diagnostic interface.

[0148] Example 61. In the method of Examples 45-60 or any combination thereof, the method further includes the step of turning on a first subset of LED sets and turning off a second subset of LED sets.

[0149] Example 62. In the method of Examples 45-61 or any combination thereof, the first and second subsets form a chessboard pattern.

[0150] Example 63. In the method of Examples 45-62 or any combination thereof, the first and second subsets form a ring pattern or a stripe pattern.

[0151] Example 64. In the method of Examples 45-63 or any combination thereof, the method further includes the step of receiving a signal from an external device through a diagnostic interface.

[0152] Example 65. In the method of Examples 45-64 or any combination thereof, the method further includes the step of determining whether there is a defect between the first LED and the second LED in response to receiving a signal from an external device.

[0153] Example 66. In the method of Examples 45-65 or any combination thereof, the method further includes the step of performing a built-in self-test in response to receiving a signal from an external device.

[0154] Example 67. In the method of Examples 45-66 or any combination thereof, the method further includes a step of determining whether there is a defect between the first LED and the second LED during the startup phase of the device.

[0155] Example 68. In the method of Examples 45-67 or any combination thereof, the first LED is adjacent to the second LED.

[0156] Example 69. In the method of Examples 45-68 or any combination thereof, the first LED is arranged diagonally with respect to the second LED in the matrix.

[0157] Example 70. In the method of Examples 45-69 or any combination thereof, the step of determining that a defect exists includes determining that a short circuit exists between the cathode pad of the first pad pair and the cathode pad of the second pad pair.

[0158] Example 71. In the method of Examples 45-70 or any combination thereof, the method further includes the step of controlling a connection network to connect the ADC to the terminal of the first LED or the terminal of the second LED one at a time.

[0159] Example 72. The device includes a pad set comprising a first pad pair configured to be connected to the first LED and a second LED of an LED set, and a first pad pair configured to be connected to the second LED. The device also includes a driver set, each driver of the driver set including a pass device configured to be electrically connected to each pad of the pad set, and each driver of the driver set is configured to control whether each LED of the LED set is turned on or turned off. The device further includes a processing circuit configured to control the first driver of the driver set to turn on the first individual pass device and the second driver of the driver set to turn off the second individual pass device. The processing circuit is also configured to determine a first forward voltage across the first LED and a second forward voltage across the second LED, and to determine whether a defect exists between the first LED and the second LED of the LED set based on the first forward voltage and the second LED forward voltage.

[0160] Example 73. The device of Example 72 further includes a sensing resistor configured to be connected to a first anode pad and a first cathode pad.

[0161] Example 74. The device of Example 72 or Example 73 further includes a differential ADC configured to measure the voltage across the sensing resistor.

[0162] Example 75. In the device of Examples 72-74 or any combination thereof, a connection network configured to connect to a first anode pad and a first cathode pad is further included.

[0163] Example 76. In the device of Examples 72-75 or any combination thereof, a memory configured to store a trimming factor for a sensing resistor is further included.

[0164] Example 77. In the device of Examples 72-76 or any combination thereof, further includes a memory configured to store the minimum, maximum, and average values ​​of the voltage difference across each LED, each pad pair, and / or each driver.

[0165] Example 78. In the device of Examples 72-77 or any combination thereof, the processing circuit includes a state machine configured to cause a driver set to turn on and turn off pass devices one by one as part of a self-test.

[0166] Example 79. In the device of Examples 72-78 or any combination thereof, the processing circuit is configured to perform the method of Example 45-71 or any combination thereof.

[0167] Example 80. The device includes a computer-readable medium storing an executable instruction configured to be executable by a processing circuit to enable the processing circuit to perform the method of Example 45-71 or any combination thereof.

[0168] Example 81. The system includes means for performing the methods of Example 45-71 or any combination thereof.

[0169] Various examples of the present disclosure have been described. Any combination of the described systems, operations, or functions is considered. These and other examples are within the scope of the following claims.

Claims

Claim 1 A device comprising a built-in self-test for detecting defects, comprising: at least one anode pad configured to be connected to the anode of an LED set; at least one cathode pad configured to be connected to the cathode of the LED set; a driver set—each driver of the driver set comprises a pass device configured to be electrically connected to each pad of the at least one anode pad or the at least one cathode pad, and each driver of the driver set is configured to control whether each LED of the LED set is turned on or turned off—and a processing circuit, wherein the processing circuit comprises at least: causing a first driver of the driver set to turn on a first individual pass device, determining a first voltage level at a first anode pad among the at least one anode pad, determining a first voltage level at a first cathode pad among the at least one cathode pad, and based on the first voltage levels at the first anode pad and the first cathode pad, on the first driver, the first anode pad and the first cathode A device configured to test each driver of the driver set one by one or each LED of the LED set one by one individually by determining that there is a defect across the pad or on the first LED. Claim 2 The device according to claim 1, further comprising a sensing resistor configured to be connected to the first anode pad and the first cathode pad, wherein the processing circuit is configured to determine the first voltage level at the first anode pad and the first cathode pad by determining the voltage drop across the sensing resistor while the sensing resistor is connected across the first anode pad and the first cathode pad. Claim 3 In paragraph 2, the processing circuit is configured to test each driver of the driver set or each LED of the LED set individually by at least: causing the sensing resistor to be connected across the second anode pad of the at least one anode pad and the second cathode pad of the at least one cathode pad, causing the second driver of the driver set to turn on a second individual pass device, determining second voltage levels at the second anode pad and the second cathode pad while the sensing resistor is connected across the second anode pad and the second cathode pad, and determining that a defect exists on the second driver or the second LED based on the second voltage levels at the second anode pad and the second cathode pad. Claim 4 A device configured to test each driver of a driver set one by one or each LED of an LED set individually by controlling the connection network to connect the sensing resistor across the first anode pad and the first cathode pad before determining the first voltage levels, controlling the connection network to disconnect the sensing resistor from the first anode pad and the first cathode pad before determining the second voltage levels, and controlling the connection network to connect the sensing resistor across the second anode pad and the second cathode pad before determining the second voltage levels. Claim 5 A device according to claim 2, further comprising a differential analog-to-digital converter (ADC), wherein the differential ADC receives a first signal indicating a voltage level at a first terminal of the sensing resistor at a first input of the differential ADC, receives a second signal indicating a voltage level at a second terminal of the sensing resistor at a second input of the differential ADC, and is configured to output a digital number indicating a voltage drop across the sensing resistor to a processing circuit, and the processing circuit is configured to determine that the fault exists on the first driver or the first LED based on the digital number. Claim 6 In paragraph 2, the processing circuit is also configured to cause a current source to deliver a test current to the sensing resistor while the sensing resistor is separated from the at least one anode pad and the at least one cathode pad, to determine a voltage drop across the sensing resistor while the test current is delivered to the sensing resistor, and to change the resistance of the sensing resistor based on the determined voltage drop across the sensing resistor. Claim 7 A device according to claim 6, wherein the processing circuit is configured to change the resistance of the sensing resistor using a trimming coefficient, and the processing circuit is also configured to store the trimming coefficient in memory. Claim 8 A device according to claim 1, wherein the processing circuit is configured to determine that the defect exists by determining that the difference between the first voltage level at the first anode pad and the first voltage level at the first cathode pad is greater than an upper threshold value, and in response to the determination that the difference between the first voltage levels is greater than the upper threshold value, determining that an open circuit exists across the first anode pad and the first cathode pad. Claim 9 A device according to claim 1, wherein the processing circuit is configured to determine that the defect exists by determining that the difference between the first voltage level at the first anode pad and the first voltage level at the first cathode pad is less than a lower threshold value, and determining that a short circuit exists across the first anode pad and the first cathode pad in response to the determination that the difference between the first voltage levels is less than the lower threshold value. Claim 10 A device according to claim 1, further comprising a memory, wherein the processing circuit is further configured to store a count of defects in the memory. Claim 11 In claim 10, the device is further configured such that the processing circuit stores a first count of detected open circuit defects in the memory and stores a second count of detected short circuit defects in the memory, thereby storing the count of the defects in the memory. Claim 12 In claim 10, the device is further configured such that the processing circuit outputs a count of the defects to an external device through a diagnostic interface. Claim 13 In paragraph 12, the processing circuit is further configured to determine whether the count of the defects is greater than a threshold number, and the processing circuit is configured to output the count of the defects to the external device in response to the determination that the count of the defects is greater than the threshold number. Claim 14 A device according to claim 1, wherein the processing circuit is also configured to determine a voltage difference across each of the at least one anode pad and each of the at least one cathode pad, determine a minimum value of the voltage difference, determine a maximum value of the voltage difference, determine an average value of the voltage difference, and store the minimum value, the maximum value, and the average value in memory. Claim 15 In claim 14, the device is further configured such that the processing circuit outputs the minimum value, the maximum value, and the average value to an external device through a diagnostic interface. Claim 16 In claim 1, the processing circuit is configured to simultaneously test the plurality of drivers of the driver set or the plurality of LEDs of the LED set as a group by causing the plurality of drivers of the driver set to turn on each of the plurality of pass devices one by one, determining each of the plurality of voltage differences across each pad while the pass device of each of the plurality of pass devices is turned on, and determining whether any defect exists based on the plurality of voltage differences, wherein the plurality of drivers comprises fewer than the total number of the driver set, and the plurality of LEDs comprises fewer than the total number of the LED set. Claim 17 A device according to claim 1, wherein the processing circuit comprises a state machine configured to cause the driver set to turn on and turn off pass devices one by one as part of a self-test. Claim 18 A device according to claim 1, wherein the processing circuit is configured to receive a signal from an external device through a diagnostic interface, and the processing circuit is configured to determine whether the defect exists in response to receiving the signal from the external device. Claim 19 In claim 1, the processing circuit is configured to determine whether the defect exists in the first driver before and after a hybridization process, the processing circuit is configured to determine whether the defect exists across the first anode pad and the first cathode pad, the processing circuit is configured to determine whether the defect exists in the first LED after the hybridization process, and the hybridization process includes mounting the device on a structure including the LED set and electrically connecting a switch set to the LED set. Claim 20 A method for an embedded self-test for detecting defects, comprising the steps of: causing a first driver in a set of drivers to turn on a first individual pass device—each driver in the set of drivers includes a pass device configured to be electrically connected to each pad of at least one anode pad or at least one cathode pad, and each driver in the set of drivers is configured to control whether each LED of an LED set is turned on or turned off—; determining a first voltage level at a first anode pad in the set of at least one anode pad; determining a first voltage level at a first cathode pad in the set of at least one cathode pad; and determining that a defect exists on the first driver, across the first anode pad and the first cathode pad, or on the first LED based on the first voltage level at the first anode pad and the first cathode pad. Claim 21 A method for an embedded self-test, wherein, in paragraph 20, at least: controlling a connection network to connect a sensing resistor across the first anode pad and the first cathode pad before determining the first voltage levels, controlling the connection network to disconnect the sensing resistor from the first anode pad and the first cathode pad before determining the second voltage levels, and controlling the connection network to connect the sensing resistor across the second anode pad of the at least one anode pad and the second cathode pad of the at least one cathode pad before determining the second voltage levels, thereby further comprising the step of individually testing each driver of the driver set one by one or each LED of the LED set one by one. Claim 22 An embedded self-test device comprising a computer-readable medium storing an executable instruction configured to be executable by a processing circuit, wherein the executable instruction causes the processing circuit to turn on a first individual pass device of a driver set—each driver of the driver set includes a pass device configured to be electrically connected to each pad of at least one anode pad or at least one cathode pad, and each driver of the driver set is configured to control whether each LED of an LED set is turned on or turned off—determining a first voltage level at a first anode pad of the at least one anode pad and determining a first voltage level at a first cathode pad of the at least one cathode pad, and determining that a defect exists on the first driver, across the first anode pad and the first cathode pad, or on the first LED based on the first voltage levels at the first anode pad and the first cathode pad. Claim 23 An embedded self-test device, wherein the command is configured to enable the processing circuit to also: control a connection network to connect a sensing resistor across the first anode pad and the first cathode pad before determining the first voltage levels; control the connection network to disconnect the sensing resistor from the first anode pad and the first cathode pad before determining the second voltage levels; and control the connection network to connect the sensing resistor across the second anode pad of the at least one anode pad and the second cathode pad of the at least one cathode pad before determining the second voltage levels, thereby enabling the processing circuit to test each driver of the driver set one by one or each LED of the LED set one by one.

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