Current control of LED pixel arrays

Abstract

A light-emitting diode (LED) array includes an array of pixel components and a pulse width modulator. The pulse width modulator generates a pulse width modulation (PWM) signal to control the duty cycle of each pixel. Each pixel component includes an LED, a switching circuit, and a closed-loop circuit. The switching circuit receives the PWM signal and alternately turns the LED on and off based on the PWM signal. The closed-loop circuit regulates the LED current supplied by the switching circuit to the LED based on a feedback signal received from the switching circuit.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit and priority of U.S. Provisional Application No. 62 / 938479, filed November 21, 2019, the disclosure of which is incorporated herein by reference in its entirety for all purposes. Technical Field

[0003] This disclosure generally relates to LED pulse width modulation circuits that can be used in micro LED pixel arrays. More specifically, this disclosure describes a technique for reducing LED current variations and pixel-to-pixel crosstalk during pulse width modulation switching. Background Technology

[0004] Miniature light-emitting diode (micro-LED) arrays are currently under development for lighting and display applications. Micro-LED control systems can support arrays of thousands to millions of micro-LED pixels, which actively emit light and are individually controlled. Compared to backlight LED technology, micro-LED arrays can offer higher brightness and energy efficiency, making them attractive for a variety of applications such as televisions, automotive headlights, and mobile phones. To display images, the current levels of micro-LED pixels at different locations on the array can be individually adjusted according to a specific image, light intensity, or color profile.

[0005] A miniature LED lighting system can include an LED array matrix with n LED modules, each module having one or more LEDs connected in series or parallel. An LED control system with a constant input voltage power supply connected to the LED array matrix can use pulse width modulation (PWM) control for dimming and color adjustment. PWM control works by turning pixels on and off at a certain frequency; essentially, it adjusts the ratio between the on-time and the period or cycle time, also known as the duty cycle. The average DC current through the pixel is the product of the current amplitude and the duty cycle. Attached Figure Description

[0006] Figure 1 This is a block diagram of an example vehicle headlight system including micro LED components according to some embodiments of the present disclosure;

[0007] Figure 2 Example micro-LED assemblies according to some embodiments of the present disclosure are shown;

[0008] Figure 3 This is a block diagram of two exemplary pixel components according to some embodiments of the present disclosure;

[0009] Figure 4 A circuit diagram illustrating an example implementation of two pixel components according to some embodiments of this disclosure;

[0010] Figure 5 A circuit diagram of a second example embodiment of a switching circuit according to some embodiments of the present disclosure is shown; and

[0011] Figure 6 A circuit diagram is shown, illustrating another example implementation of a two-pixel assembly according to some embodiments of the present disclosure, wherein the LEDs are configured as a common cathode rather than a common anode. Detailed Implementation

[0012] Overview

[0013] The systems, methods, and apparatuses disclosed herein each have several innovative aspects, none of which alone is solely responsible for all the desirable properties disclosed herein. Details of one or more embodiments of the subject matter described herein are set forth in the following description and the accompanying drawings.

[0014] To illustrate the purpose of the LED pixel components described herein, it may be helpful to understand the phenomena that may function in miniature LED components with PWM control. The following basic information can be considered as the basis for a proper interpretation of this disclosure. This information is provided for illustrative purposes only and therefore should not be construed in any way as limiting the scope of this disclosure and its potential applications.

[0015] Existing microLED arrays using PWM control typically include a microLED, a PWM switch, and a transistor that serves as the current source for the microLED in each pixel. The transistor receives a current control signal at its gate; this signal sets the current amplitude of the microLED. The microLED, PWM switch, and transistor are connected in series, with the microLED receiving a fixed input voltage and the transistor's source grounded. In a microLED array, all or a subset of microLEDs receive the same current control signal, so multiple transistor gates are connected to the same control line. Furthermore, each source terminal is connected to a common ground.

[0016] These miniature LED arrays experience current variations due to non-zero parasitic resistance in the ground path. This parasitic resistance can include interconnect resistance in an integrated circuit (IC) having multiple transistors that support the activation of multiple LEDs in the array. In effect, the ground voltage is not zero due to the parasitic resistance associated with the conductive path. As a result, a voltage drop is formed between the source terminals of the transistors and ground. This voltage drop between the transistors and ground varies with the pixel location, where the parasitic resistance and total current value may differ. Since the gate voltage of all pixels is fixed, the gate-source voltage of the individual transistors differs between pixels, causing variations in the current input to the LEDs. This effect can compromise the consistency or uniformity of the current magnitude and brightness of the array matrix.

[0017] Another drawback associated with using conventional circuitry for PWM control of a miniature LED matrix is ​​crosstalk. PWM switching generates Miller capacitance between the gate and drain of each transistor during charging and discharging, affecting the shared gate voltage and current settings. Therefore, switching in one pixel causes crosstalk, which can affect the operation of other pixels in the array. Existing solutions to this problem typically require additional IC pins and expensive external capacitors.

[0018] Ground path resistance and crosstalk issues can be particularly critical for large matrix pixel arrays of micro-LEDs that already face power and data management challenges. In many applications, it may be necessary to control the individual light intensity of thousands of emitting pixels at refresh rates of 30-60 Hz, and fine-grained color and image control may also be required.

[0019] Embodiments of this disclosure provide an LED array that can decouple current control from PWM switching. Each pixel of the LED array includes a switching circuit that receives a PWM signal and turns the LED on and off, and a closed-loop circuit that controls the amplitude of the current through the LED based on the current control signal. The closed-loop circuit includes a transistor and an operational amplifier (op-amp). The transistor receives the current control signal and outputs a reference current to the operational amplifier. The output of the operational amplifier is coupled to the transistor in the switching circuit. The transistor in the switching circuit generates an LED current that drives the LED; the LED current is based on the output of the operational amplifier. The switching circuit also provides a feedback signal to the operational amplifier, and the operational amplifier controls the LED current based on the feedback signal. While the transistor in the switching circuit may experience Miller capacitance due to PWM switching, the transistor in the closed-loop circuit is largely unaffected because the operational amplifier decouples the two transistors, thereby minimizing crosstalk between pixels connected to the same current control line. The closed-loop circuit also includes two resistors, each connected to a corresponding input of the operational amplifier, and each resistor is connected to ground. The resistors can be selected to significantly reduce the differences between LEDs caused by parasitic resistance.

[0020] In one aspect, the LED array includes a pulse width modulator configured to generate multiple PWM signals and multiple pixel components. Each pixel component includes an LED, a switching circuit, and a closed-loop circuit. The switching circuit is configured to receive a corresponding one of the multiple PWM signals and alternately turn the LED on and off according to the received PWM signal. The closed-loop circuit is configured to regulate the LED current supplied to the LED by the switching circuit based on a feedback signal.

[0021] In another embodiment, the LED assembly includes an LED, a switching circuit coupled to the LED, and a closed-loop circuit. The switching circuit is configured to receive a PWM signal and alternately turn the input current to the LED on and off based on the PWM signal. The closed-loop circuit is configured to regulate the input current to the LED based on a current control signal and feedback from the switching circuit.

[0022] In another aspect, the LED control circuit includes a closed-loop circuit and a switching circuit. The closed-loop circuit is configured to receive a current control signal and output an LED current regulation signal based on the current control signal. The switching circuit is configured to output an LED current according to a PWM signal, the LED current having an amplitude regulated by the LED current regulation signal received from the closed-loop circuit, and the switching circuit is also configured to provide feedback to the closed-loop circuit to regulate the LED current.

[0023] As those skilled in the art will appreciate, aspects of this disclosure—particularly those of the miniature LED pixel array with improved current control described herein—can be embodied in various ways, for example, as a method, system, computer program product, or computer-readable storage medium. Therefore, aspects of this disclosure can take the form of a completely hardware embodiment, a completely software embodiment (including firmware, resident software, microcode, circuit design, etc.), or an embodiment combining software and hardware aspects, all of which can generally be referred to herein as a “circuit,” “module,” or “system.” The functionality described in this disclosure can be implemented as an algorithm executed by one or more hardware processing units (e.g., one or more microprocessors) of one or more computers. In various embodiments, different steps and step portions of each method described herein can be executed by different processing units. Furthermore, aspects of this disclosure can take the form of a computer program product embodied in one or more computer-readable media, preferably non-transitory, on which computer-readable program code is embodied (e.g., stored). In various embodiments, such a computer program can, for example, be downloaded (updated) to existing devices and systems, or stored during the manufacture of such devices and systems.

[0024] In the following detailed description, various aspects of the illustrative embodiments may be described using terminology commonly used by those skilled in the art to communicate the substance of their work to others skilled in the art. For example, the term “connection” refers to a direct electrical or magnetic connection between connected things without any intermediate devices, while the term “coupling” refers to a direct electrical or magnetic connection between connected things, or an indirect connection via one or more passive or active intermediate devices. The term “circuit” refers to one or more passive and / or active components arranged to cooperate with each other to provide a desired function. The terms “substantially,” “close to,” “approximately,” “near,” and “about” generally refer to the context of a specific value described herein or known in the art, within + / - 20% of the target value, preferably within + / - 10%. Similarly, terms indicating the orientation of various elements—e.g., “coplanar,” “perpendicular,” “orthogonal,” “parallel,” or any other angle between elements—generally refer to the context of a specific value described herein or known in the art, within + / - 5-20% of the target value.

[0025] The terms used herein, such as “above,” “below,” “between,” and “up,” refer to the relative position of a material layer or component with respect to other layers or components. For example, a layer disposed above or below another layer may be in direct contact with that other layer, or may have one or more intermediate layers. Furthermore, a layer disposed between two layers may be in direct contact with one or both of the two layers, or may have one or more intermediate layers. Conversely, a first layer described as being “on” a second layer refers to a layer in direct contact with that second layer. Similarly, unless explicitly stated otherwise, a feature disposed between two features may be in direct contact with the adjacent feature, or may have one or more intermediate layers.

[0026] For the purposes of this disclosure, the phrase "A and / or B" means (A), (B), or (A and B). For the purposes of this disclosure, the phrase "A, B, and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C). When referring to the use of measurement range, the term "between" includes both ends of the measurement range. As used herein, the symbol "A / B / C" means (A), (B), and / or (C).

[0027] This specification uses the phrases "in one embodiment" or "in an embodiment," each of which can refer to one or more of the same or different embodiments. Furthermore, the terms "comprising," "including," "having," etc., used with respect to embodiments of this disclosure are synonymous. This disclosure may use perspective-based descriptions, such as "above," "below," "top," "bottom," and "side"; such descriptions are used to facilitate discussion and are not intended to limit the application of the disclosed embodiments. Unless otherwise stated, the use of sequential adjectives such as "first," "second," and "third" to describe a common object merely indicates that different instances of similar objects are referenced and is not intended to mean that the objects so described must be in a given order in time, space, sequence, or any other way.

[0028] In the following detailed description, reference is made to the accompanying drawings, which form a part of the description, illustrating by way of example some embodiments that may be practiced. In the drawings, the same reference numerals refer to the same or similar elements / materials, such that, unless otherwise stated, the interpretation of elements / materials with given reference numerals provided in the context of one drawing is applicable to other drawings in which elements / materials with the same reference numerals may be shown. For convenience, if there exists a set of drawings designated with different letters, for example... Figure 2 A- Figure 2 C, in this article, may not use letters to refer to such a set (e.g., " Figure 2The accompanying drawings are not necessarily drawn to scale. Furthermore, it will be understood that some embodiments may include more elements than are shown in the drawings, some embodiments may include a subset of the elements shown in the drawings, and some embodiments may combine any suitable combination of features from two or more drawings.

[0029] Various operations can be described sequentially as multiple discrete actions or operations in a manner most conducive to understanding the claimed subject matter. However, the order of description should not be construed as implying that these operations are necessarily order-dependent. In particular, these operations may not be performed in the order presented. The described operations may be performed in a different order than in the described embodiments. In additional embodiments, various additional operations may be performed, and / or the described operations may be omitted.

[0030] In some of the examples provided herein, interactions may be described based on two, three, four, or more electrical components. However, this is done merely for clarity and illustrative purposes. It should be understood that the devices and systems described herein can be combined in any suitable manner. Along similar design alternatives, any of the components, modules, and elements shown in the accompanying figures can be combined in a variety of possible configurations, all of which are clearly within the broad scope of this disclosure. In some cases, it may be easier to describe one or more functions of a given set of processes by referring to only a limited number of electrical components.

[0031] The following detailed description illustrates various embodiments of certain specific examples. However, it should be understood that other embodiments may be utilized, and structural or logical changes may be made without departing from the scope of this disclosure. In general, the innovations described herein may be embodied in a variety of different ways, for example, as defined and covered by the claims and / or selected examples, and the following detailed description should not be considered limiting.

[0032] Example system of micro LED array

[0033] Micro-LED arrays enable applications that benefit from fine-grained intensity, spatial, and temporal control of light distribution. For example, a micro-LED array can provide precise spatial patterning of emitted light from a block of pixels or a single pixel. Depending on the application, the emitted light can be spectrally distinct, time-adaptive, and / or environmentally responsive. Micro-LED arrays can provide pre-programmed light distributions in various intensity, spatial, or temporal modes. The emitted light can be at least partially based on received sensor data. The associated optics can be distinct at the pixel, pixel block, or device level. An example micro-LED array includes a device with a central block of devices that share common control over high-intensity pixels and edge pixels, the high-intensity pixels having associated common optics, and the edge pixels having individual optics. Some applications supported by micro-LED arrays include video lighting, automotive headlights, architectural and area lighting, street lighting, and information displays.

[0034] Vehicle headlights, or front lights, are an example application of micro-LED arrays. Vehicle headlights, composed of micro-LEDs, include a large number of pixels and have a high data refresh rate. Automotive headlights that actively illuminate only selected portions of the road can be used to reduce problems associated with glare or blindness to oncoming drivers. For example, using an infrared camera as a sensor, a micro-LED array can activate only those pixels needed to illuminate the road, while deactivating pixels that might glare pedestrians or drivers of oncoming vehicles. As another example, micro-LED arrays can be used to selectively illuminate pedestrians, animals, or signs outside the road to improve driver environmental awareness. If the pixels of the micro-LED array are spectrally distinct, the color temperature of the light can be adjusted according to corresponding daytime, dusk, or nighttime conditions. Some pixels can be used for optical wireless vehicle-to-vehicle communication.

[0035] Figure 1 This is a block diagram of an example vehicle headlight system 100 including micro LED components. The vehicle headlight system 100 includes an electronic control unit (ECU) 110 and headlights 130. Although Figure 1 The image shows one headlight 130, but it should be understood that the vehicle includes two or more headlights similar to headlight 130; other headlights are similar to headlight 130 and operate in a similar manner. Furthermore, other lights (e.g., daytime running lights, fog lights, etc.) may be similar to... Figure 1 The headlight 130 is configured and operated in the manner depicted in the text.

[0036] ECU 110 is an embedded system within the vehicle that controls the vehicle's electrical systems or subsystems (including headlights 130). In addition to controlling the headlights, ECU 110 may include controls for, for example, engine components, powertrain components, doors, brakes, telematics, battery management, etc. ECU 110 may be located in or near the engine compartment. ECU 110 receives image data 105, for example, from memory accessible to ECU 110, which stores different headlight images used in different settings or applications. Vehicle microprocessor 115 of ECU 110 can generate or select images for headlights 130. For example, vehicle microprocessor 115 receives data from one or more environmental sensors, selects an image for headlights 130 based on the current environment, and retrieves image data 105 of the selected image. Vehicle microprocessor 115 generates control signals for headlights 130 based on the selected image and transmits the control signals to serializer 120. Serializer 120 serializes control signals and transmits them via a serial connection, such as unshielded twisted pair (UTP) or coaxial connection. Serializer 120 can convert control signals into low-voltage differential signal (LVDS) format. The selection of the physical connection and data format between ECU 110 and headlight 130 ensures reliable transmission of control signals through the vehicle, which may experience wide temperature variations, humidity, noise, and other adverse conditions.

[0037] The headlamp 130 includes a deserializer 135 that reformats control signals and transmits them to the micro-LED assembly 155. For example, the control signals provided to the micro-LED assembly 155 may include a vertical sync signal, a pixel clock, a pixel enable signal, and multiple pixel data lines. The micro-LED assembly 155 outputs an image based on the control signals. Figure 2 The micro LED assembly 155 is shown in more detail, and regarding... Figure 3-6 Example pixel components are shown and described.

[0038] The headlamp 130 also includes a headlamp microprocessor 140, a DC / DC converter 145, and a power supply 150. The deserializer 135 also provides control signals to the headlamp microprocessor 140 and can receive feedback (e.g., error messages) from the headlamp microprocessor 140 to return to the ECU 110. The headlamp microprocessor 140 controls the power supply 150, which supplies power to the DC / DC converter 145 via one output line and to the micro-LED assembly 155 via a second output line. The voltage supplied to the micro-LED assembly 155 by the power supply 150 is used to power the LED pixels. The voltage sent to the DC / DC converter is used to power the internal logic of the headlamp 130, such as the internal logic of the headlamp microprocessor 140 and the micro-LED assembly 155. The DC / DC converter 145 converts the direct current (DC) signals received from the power supply into different voltages to power the logic of the headlamp microprocessor 140 and the micro-LED assembly 155. The DC / DC converter 145 distributes the converted DC voltage to the headlamp microprocessor 140 and the microLED assembly 155. The headlamp microprocessor 140 also has an interface to the microLED assembly 155 for, for example, exchanging data, providing clock control, and receiving fault data from the microLED assembly 155 in case of a fault.

[0039] It should be understood that the vehicle headlight system 100 is merely one example application of micro-LED arrays. In another application, micro-LED components 155 are used in lighting fixtures to selectively and adaptively illuminate buildings or environments to improve visual display or reduce lighting costs. For example, in conjunction with tracking sensors and / or cameras, micro-LED arrays can be used to selectively illuminate areas around pedestrians. As another example application, micro-LED arrays are used to project onto media facades for decorative motion or video effects. Pixels with distinctly different spectra can be used to adjust the color temperature of the lighting, as well as to support garden lighting with specific wavelengths.

[0040] Street lighting is another example application that benefits from the use of micro-LED arrays. A single type of light-emitting array can be used to simulate various street light types, allowing switching between Type I linear streetlights and Type IV semi-circular streetlights, for example, by appropriately activating or deactivating selected LEDs. Street lighting costs can be reduced by adjusting the beam intensity or distribution according to environmental conditions or usage time. For example, when there are no pedestrians, the light intensity and distribution area can be reduced. If the pixels of the micro-LED array are spectrally distinct, the color temperature of the light can be adjusted according to the corresponding daytime, dusk, or nighttime conditions.

[0041] Miniature LED arrays are also well-suited for applications requiring direct display or projected display. For example, warnings, emergency signs, or information signs can be displayed or projected using miniature LED arrays. This allows for the projection of color-changing or flashing exit signs. If the miniature LED array consists of a large number of pixels, it can display text or numerical information. Directional arrows or similar indicators can also be provided.

[0042] Miniature LED arrays can be used alone or in combination with primary or secondary optics, including lenses or mirrors. To reduce overall data management requirements, some or all pixels in a miniature LED array can be restricted to on / off functionality or toggled between relatively few light intensity levels. Full pixel-level control of light intensity is not necessarily supported.

[0043] In operation, image data corresponding to pixels in the micro-LED array is used to define the response of the corresponding pixel in the micro-LED array, where the pixel intensity and spatial modulation are based on the image(s). To reduce data rate issues, in some embodiments, pixel groups (e.g., 5×5 blocks) can be controlled as a single block. High-speed and high-data-rate operation can be supported, with pixel values ​​from consecutive images being loaded as consecutive frames in an image sequence at rates, for example, between 30 Hz and 100 Hz (e.g., 60 Hz). Combined with a pulse width modulation module, each pixel in the pixel module can be operated to emit light at a mode and intensity at least in part depending on the image stored in the image frame buffer.

[0044] Example micro LED components

[0045] Figure 2 Examples of micro-LED components 155 according to some embodiments of this disclosure are shown. Micro-LED components 155 can be used in vehicle headlight applications, any other applications described above, or other potential applications of LED arrays. Micro-LED components 155 include a pulse width modulator 210, a digital-to-analog converter (DAC) 220, and a pixel array 230. The pixel array 230 includes pixel components 235 arranged in a matrix, such as pixel components 235a and 235b. Each pixel component 235 actively emits light and can be individually controlled. Although... Figure 2 The diagram shows 25 example pixel components, but pixel array 230 can include thousands to millions of micro-LED pixel components. To emit light in a pattern or sequence that results in an image display, the current levels of the micro-LEDs in pixel components 235 at different locations on the array are individually adjusted according to the specific image. This can be achieved using pulse width modulation (PWM), which turns the pixels on and off at a specific frequency. During PWM operation, the average DC current through the pixel is the product of the current amplitude and the PWM duty cycle, which is the ratio between the on-time and the period or cycle time.

[0046] Pulse width modulator 210 generates a PWM signal 215 output to pixel array 230 to control the PWM duty cycle of the pixels. In some embodiments, pulse width modulator 210 generates a separate PWM signal 215 for each pixel in pixel array 230. In other embodiments, one PWM signal can control multiple pixels, such as a specific subset of pixels in pixel array 230. (Regarding...) Figure 1 In the described vehicle headlight example, pulse width modulator 210 receives an image control signal from deserializer 135 and generates a PWM signal 215 based on the image control signal. In other embodiments, another control block within the microLED assembly 155 or in another system may generate image data that is fed to pulse width modulator 210.

[0047] DAC 220 generates a current control signal 225 provided to pixel array 230. Although each pixel component 235 receives a unique PWM signal 215, the entire pixel array 230 or a block of multiple pixel components 235 within the pixel array 230 can receive the same current control signal 225. DAC 220 receives control signals indicating the current level provided from deserializer 135 (in the vehicle headlight example) or another digital control interface (e.g., an internal integrated circuit (I2C) interface).

[0048] Example pixel component

[0049] Figure 3 This is a block diagram of two exemplary pixel components according to some embodiments of the present disclosure. Figure 3 The two pixel components 310a and 310b shown are Figure 2 Examples of pixel components 235a and 235b are shown. Additional pixel components in a micro-LED array can be configured similarly. Figures 3-6 In the diagram, nodes such as node 390 are used to illustrate electrical connections; intersections without node 390 are not electrically connected.

[0050] Each pixel component 310 includes an LED 320, a closed-loop circuit 330, and a switching circuit 340. The LED 320 may be a micro LED or another type of LED. In this example, the LED 320 is a common anode LED. In other embodiments, the LED 320 is a common cathode LED; Figure 6 An example pixel assembly with a common cathode LED is shown. Although Figure 3The diagram shows one LED 320, but in other embodiments, the pixel assembly 310 includes multiple LEDs 320 connected in series and / or parallel. The LEDs 320 are connected to an input voltage Vin 360, which is the input voltage that powers the pixel assembly 310. Figure 1 In the headlight example shown, Vin 360 is supplied by power supply 150. When LED current (e.g., I1 in pixel assembly 1310) passes through LED 320a, LED 320a emits light, as shown by... Figure 3 As indicated by the arrow in the image.

[0051] Switching circuit 340 receives a PWM signal 380 from a pulse width modulator, such as one of the PWM signals 215 provided by pulse width modulator 210. In this example, each switching circuit 340 receives a separate PWM signal 380; for example, switching circuit 1 340a receives PWM signal 1 380a, and switching circuit 2 340b receives PWM signal 2 380b. Switching circuit 340 alternately turns LED 320 on and off according to the received PWM signals 380. Specifically, switching circuit 340 provides LED current (e.g., I1 or I2) to LED 320 to turn it on, and does not provide LED current to LED 320 to turn it off.

[0052] When LED 320 is turned on, closed-loop circuit 330 regulates the LED current (controlled by PWM signal 380) supplied to LED 320 by switching circuit 340. Closed-loop circuit 330 receives current control signal 370 (e.g., current control signal 225 provided by DAC 220), which sets the current level driving LED 320. Closed-loop circuit 330 is coupled to switching circuit 340 via current regulation connection 350. Closed-loop circuit 330 receives feedback from switching circuit 340 from feedback connection 355. Closed-loop circuit 330 regulates LED current based on feedback. More specifically, closed-loop circuit 330 outputs a voltage to switching circuit 340 via current regulation connection 350, wherein this voltage is tuned by closed-loop circuit 330 such that switching circuit 340 drives LED 320 at the current level indicated by current control signal 370. Closed-loop circuit 330 adjusts its output voltage based on feedback from switching circuit 340.

[0053] The closed-loop circuit 330 is powered by the input voltage Vin 360. For example... Figure 1As shown, two lines are connected to Vin 360: a first power line is connected to closed-loop circuits 330a and 330b, and a second power line is connected to LEDs 320a and 320b. Splitting Vin 360 onto two separate lines spanning the pixel array or a portion of the pixel array prevents parasitic resistance on the power lines driving the closed-loop circuit 330 from affecting the power lines driving the LEDs 320.

[0054] Example pixel component circuit diagram

[0055] Figure 4 This is a circuit diagram of an example implementation of two pixel components according to some embodiments of this disclosure. Figure 4 Example circuit diagrams of two pixel components 410a and 410b are shown. These two pixel components are Figure 3 Examples of pixel components 310a and 310b are shown. Additional pixel components in a micro LED array can be configured similarly.

[0056] Each pixel assembly 410 includes an LED 420, similar to the LED 320 described above. Each pixel assembly 410 includes a closed-loop circuit 430 and a switching circuit 440, where the closed-loop circuit 430 is an example implementation of the closed-loop circuit 330, and the switching circuit 440 is an example implementation of the switching circuit 340. The pixel assembly 410 receives an input voltage Vin460 similar to the input voltage Vin 360, and like... Figure 3 The input voltage Vin 360 is the same as that provided on two power lines 462 and 464. Pixel component 410 also receives a current control signal 470 similar to the current control signal 370. Each pixel component 410 also receives a corresponding PWM signal ( Figure 4 (not shown in the image), the corresponding PWM signal is similar to Figure 3 The PWM signal 380 is shown in the figure.

[0057] The closed-loop circuit 430 includes a reference current transistor 432, an operational amplifier 434, a first resistor 436, and a second resistor 438. The operational amplifier 434 has two inputs: a non-inverting input (indicated by a + sign) and an inverting input (indicated by a - sign). The non-inverting input of the operational amplifier 434 is coupled to the reference current transistor 432. The reference current transistor 432 is a p-type metal-oxide-semiconductor (PMOS) transistor, with its gate connected to a current control signal 470, its source connected to an input voltage Vin 460, and its drain connected to the non-inverting input of the operational amplifier 434. The reference current transistor 432 generates a reference current for the pixel assembly 410 based on the current control signal 470.

[0058] The inverting input of operational amplifier 434 is coupled to switching circuit 440 to receive a feedback signal. Specifically, the inverting input of operational amplifier 434 is coupled to the source of switching transistor 444 included in switching circuit 440. The output of operational amplifier 434 is coupled to the input of switching circuit 440. In this example, the output of operational amplifier 434 is connected to the gate of switching transistor 444. The output of operational amplifier 434 sets the gate voltage of switching transistor 444.

[0059] The switching transistor 444 is an n-type metal-oxide-semiconductor (NMOS) transistor with its gate connected to operational amplifier 434, its source connected to a second resistor 438, and its drain coupled to LED 420. In this example, a PWM switch 442 is located between the drain of the switching transistor 444 and LED 420; the PWM switch 442 turns on and off according to a PWM signal. The switching transistor 444 generates an LED current to drive LED 420 based on the voltage output of operational amplifier 434.

[0060] A first resistor 436 is coupled to the non-inverting input of operational amplifier 434, and a second resistor 438 is coupled to the inverting input of operational amplifier 438. Each of resistors 436a, 436b, 438a, and 438b is also connected to common ground 490. Each of the first and second resistors 436 and 438 has corresponding resistances R1 and R2. The first resistor senses a reference current from reference current transistor 432. The second resistor 438 is connected in series with LED 420, PWM switch 442, and switching circuit transistor 444. The second resistor 438 senses the LED current generated by switching circuit transistor 444 and driving LED 420.

[0061] In operation, operational amplifier 434 amplifies the difference between the voltage drop across the first resistor 436 and the voltage drop across the second resistor 438 to adjust the gate voltage of switching transistor 444. Therefore, the LED current changes, causing the voltage drop across the second resistor 438 to become closer to the voltage drop across the first resistor 436. As a result of closed-loop operation, the voltage drops across the first and second resistors 436 and 438 become equal in steady state. The LED current generated by switching transistor 444 and driving LED 420 is determined by the following equation:

[0062]

[0063] Among them, I LED It is the LED current, I REF R1 is the reference current, R2 is the resistance of the first resistor 436, and R2 is the resistance of the second resistor 438.

[0064] During operation, the parasitic resistance of the conductive path is located in two tracks of power lines 462 and 464. Taking the first pixel assembly 410a as an example, the ground points of resistors 436a and 438a are located in the same pixel and can be considered identical, thus exhibiting almost no parasitic effect. However, the parasitic resistance at Vin 460 is distributed across the entire array, which affects the source voltage of the reference current transistor 432. Therefore, since the gate voltage at the reference current transistor 432 (i.e., the current control signal 470) is fixed, both the reference current and the LED current can vary. To address this issue, the path at Vin 460 is split into a first line 462 for LED 420 and a second line 464 for reference current transistor 432. According to the above I... LED The formula allows the reference current to be designed to be less than the LED current by selecting a large R1:R2 ratio. For example, the resistance of R1 can be 5 to 50 times that of R2. By selecting a large R1:R2 ratio, the voltage drop across the parasitic resistance at Vin line 464 is significantly reduced, and its impact on current variations is minimized. Therefore, using two power lines reduces or eliminates the effect of the higher parasitic voltage drop on power line 462 driving LED 420.

[0065] Due to the decoupling effect of the operational amplifier 434, Figure 4 The circuit shown offers further advantages in reducing crosstalk. Although the gate of the switching transistor 444 is still charged and discharged by the Miller capacitor during the switching of the PWM switch 442, the Miller capacitor has little effect on the reference current transistor 432 because the operational amplifier 434 separates the two transistors 432 and 444.

[0066] Figure 5 A circuit diagram of a second example embodiment of a switching circuit according to some embodiments of the present disclosure is shown. Figure 5 Example circuit diagrams of two pixel components 510a and 510b are shown. These two pixel components are Figure 3 Examples of pixel components 310a and 310b are shown. Additional pixel components in a micro LED array can be configured similarly.

[0067] Each pixel assembly 510 includes an LED 520, similar to the LED 320 described above. Each pixel assembly 510 includes a closed-loop circuit 530 and a switching circuit 540, where the closed-loop circuit 530 is an example of the closed-loop circuit 330, and the switching circuit 540 is an example of the switching circuit 340. Components of the closed-loop circuit 530 (i.e., the reference current transistor 532, the operational amplifier 534, and the first and second resistors 536 and 538) correspond to a reference... Figure 4The closed-loop circuit 430 is described with components 432-438, and the closed-loop circuit 530 has the same arrangement as the closed-loop circuit 430. Furthermore, the pixel assembly 510 receives an input voltage Vin 560 similar to input voltages 360 and 460, and like... Figure 3 and Figure 4 The input voltage is the same as that provided on two power lines 562 and 564. Pixel component 510 also receives a current control signal 570, similar to current control signals 370 and 470. Each pixel component 510 also receives a corresponding PWM signal ( Figure 5 (not shown in the image), the corresponding PWM signal is similar to Figure 3 The PWM signal 380 is shown in the figure.

[0068] exist Figure 5 In this circuit, the switching circuit 540 includes a PWM switch 542 and a switching circuit transistor 544. For example... Figure 4 In this configuration, the inverting input of operational amplifier 534 is coupled to the source of switching transistor 544. The output of operational amplifier 534 is coupled to the input of switching circuit 540. In this example, PWM switch 542 is located at the input of switching circuit 540 and is connected to the gate of switching transistor 544. When PWM switch 542 is closed, the output of operational amplifier 534 is coupled to switching transistor 544, setting the gate voltage of switching transistor 544. This arrangement can be more efficient than... Figure 4 The circuit arrangement shown is more efficient because the gate terminal of the switching transistor 544 consumes only a small current to charge and discharge the parasitic capacitance during PWM switching. Additional circuit characteristics and advantages are similar to those described above, for example, regarding... Figure 3 and Figure 4 The described features and advantages.

[0069] Figure 6 A circuit diagram is shown, illustrating another example implementation of a two-pixel assembly according to some embodiments of the present disclosure, wherein the LEDs are configured as a common cathode rather than a common anode. Figure 6 Example circuit diagrams of two pixel components 610a and 610b are shown. These two pixel components are Figure 2 Examples of pixel components 235a and 235b are shown. Additional pixel components in a micro LED array can be configured similarly.

[0070] exist Figure 6 In the example shown, LED 620 is configured as a common cathode, instead of as... Figures 3-5 The common anode is connected in the middle. This circuit is relative to... Figure 4 and Figure 5The circuit shown is reversed, such that LED 620 and reference current transistor 632 are connected to ground 690 instead of Vin 660. Furthermore, operational amplifier 634 and resistors 636 and 638 are connected to Vin 660 instead of ground 690. In this example, ground line 690 is split into two tracks, one line 694 connected to LED 620 and the other line 692 connected to reference current transistor 632. Switching circuit 640 may have… Figure 4 or Figure 5 The switching circuit design shown can be used, or another switching circuit configuration can be employed. The current control signal 670 is similar to the current control signals 370 and 470 described above. Figure 6 The operating characteristics and advantages of the circuit shown are similar to those mentioned above. Figures 3-5 Describe the characteristics and advantages.

[0071] Other implementation details, variations, and applications

[0072] It should be understood that not all objectives or advantages may be achieved according to any particular embodiment described herein. Therefore, for example, those skilled in the art will recognize that certain embodiments may be configured to operate in a manner that achieves or optimizes one or more advantages of the teachings herein, without necessarily achieving other objectives or advantages of the teachings or suggestions herein.

[0073] It should be understood that the circuits in the accompanying figures and their teachings are readily expandable and can accommodate a large number of components, as well as more complex / precise arrangements and configurations. Therefore, the examples provided should not limit the scope or inhibit the extensive teachings that can potentially be applied to countless other architectures.

[0074] In some embodiments, any number of the circuits shown in the accompanying drawings may be implemented on a board of the associated electronic device. The board may be a general-purpose circuit board that can house various components of the internal electronic system of the electronic device and further provide connectors for other peripheral devices. More specifically, the board may provide electrical connections through which other components of the system can communicate electrically. Any suitable processor (including digital signal processors, microprocessors, supporting chipsets, etc.), computer-readable non-transitory memory elements, etc., may be appropriately coupled to the board based on specific configuration needs, processing requirements, computer design, etc. Other components, such as external storage, additional sensors, controllers for audio / video displays, and peripheral devices, may be attached to the board via cables as insert cards or integrated into the board itself. In various embodiments, the functions described herein may be implemented in emulation form as software or firmware running within one or more configurable (e.g., programmable) elements arranged in a structure supporting these functions. The software or firmware providing this emulation may be provided on a non-transitory computer-readable storage medium including instructions that allow the processor to perform those functions.

[0075] In some embodiments, the circuitry in the accompanying drawings may be implemented as a stand-alone module (e.g., a device with associated components and circuitry configured to perform a particular application or function) or as a plug-in module in the dedicated hardware of an electronic device. Note that some embodiments of this disclosure can be readily included, in whole or in part, in a System-on-Chip (SOC) package. SOC stands for Integrated Circuit (IC), which integrates components of a computer or other electronic system onto a single chip. It can include digital, analog, mixed-signal, and generally radio frequency functions: all of which can be provided on a single chip substrate. Other embodiments may include a Multi-Chip Module (MCM), in which multiple individual ICs reside within a single electronic package and are configured to interact closely with each other via the electronic package.

[0076] Those skilled in the art will identify a variety of other changes, substitutions, variations, alterations, and modifications, and it is intended that this disclosure cover all such changes, substitutions, variations, alterations, and modifications falling within the scope of the appended claims. Note that all optional features of any device and system described herein may also be implemented with respect to the methods or processes described herein, and details in the examples may be used anywhere in one or more embodiments.

[0077] Selected Example

[0078] Example 1 provides an LED array including a pulse width modulator configured to generate a plurality of PWM signals and a plurality of pixel components. Each pixel component includes: an LED; a switching circuit configured to receive a corresponding one of the plurality of PWM signals and alternately turn the LED on and off according to the received PWM signal; and a closed-loop circuit configured to regulate the LED current supplied to the LED by the switching circuit based on a feedback signal.

[0079] Example 2 includes the LED array of Example 1, wherein the closed-loop circuit is configured to receive a feedback signal from the switching circuit and adjust the voltage applied to the switching circuit based on the feedback signal, and the LED current is based on the voltage applied to the switching circuit.

[0080] Example 3 includes the LED array of Example 1 or 2, wherein the closed-loop circuit includes an operational amplifier having a first input, a second input, and an output, the first input being coupled to a reference current transistor, the second input being coupled to a switching circuit to receive a feedback signal, and the output being coupled to the input of the switching circuit.

[0081] Example 4 includes the LED array of Example 3, wherein the closed-loop circuit further includes a first resistor coupled to a first input and a second resistor coupled to a second input, the first resistor having a first resistance and the second resistor having a second resistance.

[0082] Example 5 includes the LED array of Example 4, wherein the current supplied to the LED by the switching circuit is equal to the reference current from the reference current transistor multiplied by the ratio of the first resistor and the second resistor.

[0083] Example 6 includes the LED array of Example 4 or 5, wherein the reference current transistor is a PMOS transistor, with its source coupled to the input voltage, its gate coupled to the current control signal, and its drain coupled to the first input of the operational amplifier.

[0084] Example 7 includes an LED array of any one of Examples 3-6, wherein the switching circuit includes a switching circuit transistor whose gate voltage is set by the output of an operational amplifier.

[0085] Example 8 includes the LED array of Example 7, wherein the switching circuit transistor is an NMOS transistor, which further includes a source coupled to a second resistor and a drain coupled to the LED.

[0086] Example 9 provides an LED assembly including an LED, a switching circuit coupled to the LED, and a closed-loop circuit. The switching circuit is configured to receive a PWM signal and alternately turn the input current to the LED on and off based on the PWM signal. The closed-loop circuit is configured to regulate the input current to the LED based on a current control signal and feedback from the switching circuit.

[0087] Example 10 includes the LED assembly of Example 9, wherein the closed-loop circuit includes an operational amplifier having a first input, a second input, and an output, the first input being coupled to a reference current transistor, the second input being coupled to a switching circuit to receive feedback from the switching circuit, and the output being coupled to the input of the switching circuit.

[0088] Example 11 includes the LED assembly of Example 10, wherein the reference current transistor receives a current control signal and outputs a reference current based on the current control signal.

[0089] Example 12 includes the LED assembly of Example 11, wherein the closed-loop circuit further includes a first resistor coupled to a first input and a second resistor coupled to a second input, the first resistor having a first resistance and the second resistor having a second resistance.

[0090] Example 13 includes the LED assembly of Example 12, wherein the input current to the LED is equal to the reference current multiplied by the ratio of the first resistor and the second resistor.

[0091] Example 14 includes an LED assembly of any of Examples 11-13, wherein the reference current transistor is a PMOS transistor, the source of which is coupled to the input voltage, the gate of which is coupled to the current control signal, and the drain of which is coupled to the first input of the operational amplifier.

[0092] Example 15 includes an LED assembly of any of Examples 10-14, wherein the switching circuit includes a switching circuit transistor whose gate voltage is set by the output of an operational amplifier.

[0093] Example 16 includes the LED assembly of Example 15, wherein the switching circuit transistor is an NMOS transistor, which further includes a source coupled to a second resistor and a drain coupled to the LED.

[0094] Example 17 provides a control circuit for an LED, including a closed-loop circuit and a switching circuit. The closed-loop circuit is configured to receive a current control signal and output an LED current regulation signal based on the current control signal. The switching circuit is configured to output an LED current according to a PWM signal, the LED current having an amplitude regulated by the LED current regulation signal received from the closed-loop circuit, and the switching circuit is also configured to provide feedback to the closed-loop circuit to regulate the LED current.

[0095] Example 18 includes the control circuit of Example 17, wherein the closed-loop circuit includes an operational amplifier having a first input, a second input, and an output. The first input is coupled to a reference current transistor, the second input is coupled to a switching circuit to receive feedback from the switching circuit, and the output is coupled to the input of the switching circuit.

[0096] Example 19 includes the control circuitry of Example 18, wherein the reference current transistor receives a current control signal and outputs a reference current based on the current control signal.

[0097] Example 20 includes the control circuit of Example 19, wherein the closed-loop circuit further includes a first resistor coupled to a first input and a second resistor coupled to a second input, the first resistor having a first resistance and the second resistor having a second resistance, wherein the LED current is equal to a reference current multiplied by the ratio of the first resistance and the second resistance.

[0098] Example 21 provides an LED array including a plurality of LEDs, a pulse width modulator configured to provide PWM signals to the plurality of LEDs, and a plurality of control circuits, each control circuit being coupled to a corresponding LED among the plurality of LEDs. Each control circuit includes a transistor coupled to the LED and an operational amplifier coupled to the transistor and configured to control the current supplied to the LED by the transistor.

[0099] Example 22 includes the LED array of Example 21, wherein each of the plurality of control circuits includes a second transistor coupled to the input of the operational amplifier and configured to set a reference current for the LED.

[0100] Example 23 includes the LED array of Example 22, wherein the second transistor is a PMOS transistor.

[0101] Example 24 includes an LED array of any of Examples 21-23, wherein the transistors are NMOS transistors.

[0102] Example 25 includes an LED array of any of Examples 21-24, wherein each control circuitry further includes a PWM switch and a resistor, wherein the LED is connected in series with the PWM switch, the transistor, and the resistor, and the resistor is configured to sense the current supplied to the LED by the transistor.

[0103] Example 26 includes an LED array of any of Examples 21-25, wherein each of the plurality of LEDs is a common anode LED.

[0104] Example 27 includes an LED array of any of Examples 21-25, wherein each of the plurality of LEDs is a common cathode LED.

[0105] Example 28 includes an LED array of any of Examples 21-27, wherein each control circuit further includes a resistor and a PWM switch connected between a transistor and an operational amplifier, wherein the LED is connected in series with the transistor and the resistor, and the resistor is configured to sense the current supplied to the LED by the transistor.

[0106] Example 29 provides a pixel of a microLED array, comprising a microLED, a switching circuit coupled to the microLED, a transistor, and an operational amplifier. The switching circuit is configured to receive a PWM signal and control the activation of the microLED based on the PWM signal. The transistor is configured to set a reference current for the pixel. The operational amplifier has an input coupled to the transistor output and an output coupled to the switching circuit.

[0107] Example 30 includes the pixels of Example 29, wherein the transistor is a PMOS transistor.

[0108] Example 31 includes the pixel of Example 29 or 30, wherein the switching circuit includes an NMOS transistor.

[0109] Example 32 includes a pixel of any of Examples 29-31, wherein a microLED is connected in series with a PWM switch, a transistor, and a resistor configured to sense current through the microLED.

[0110] Example 33 includes the pixels of any of Examples 29-32, where the microLED is a pixel of the matrix pixel array.

[0111] Example 34 includes pixels from any of Examples 29-33, where the micro-LEDs are common anode LEDs.

[0112] Example 35 includes pixels from any of Examples 29-33, where the microLEDs are common cathode LEDs.

[0113] Example 36 includes a pixel of any of Examples 29-35, and also includes a PWM switch connected between a transistor and an operational amplifier, wherein a microLED is connected in series with a transistor and a resistor configured to sense current through the microLED.

[0114] Example 37 provides a method for controlling an LED array, comprising arranging a plurality of LEDs in a matrix pixel array, each of the plurality of LEDs being connected to a corresponding one of a plurality of transistors; providing a PWM signal to the plurality of light-emitting diodes; and using a plurality of corresponding operational amplifiers to control the current to each of the plurality of LEDs, each operational amplifier being coupled to a corresponding LED through a corresponding one of the plurality of transistors.

[0115] Example 38 includes the control method of Example 37, wherein a second plurality of transistors sets a reference current for a corresponding one of a plurality of light-emitting diodes, each of the second plurality of transistors being connected to the input of a corresponding one of a plurality of operational amplifiers.

[0116] Example 39 includes the control method of Example 38, wherein the first plurality of transistors are NMOS transistors and the second plurality of transistors are PMOS transistors.

[0117] Example 40 includes a control method of any of Examples 37-39, wherein each of the plurality of LEDs is connected in series to a PWM switch, a corresponding one of the plurality of transistors, and a resistor, the PWM switch being configured to receive one of the PWM signals, and the resistor sensing the current applied to the LED.

Claims

1. An LED array comprising: a pulse width modulator configured to generate a plurality of pulse width modulated signals; a first power line; a second power line; and a plurality of pixel assemblies, each pixel assembly comprising: - an LED coupled to the first power line; - a switching circuit configured to receive a respective different one of the plurality of pulse width modulated signals and alternately turn on and off the LED in accordance with the received pulse width modulated signal, the switching circuit comprising a switching circuit transistor; and - a closed loop circuit coupled to the second power line and configured to adjust an input current provided by the switching circuit to the LED based on a feedback signal, the closed loop circuit comprising: a reference current transistor arranged to output a reference current based on a current control signal, an operational amplifier having a first input coupled to the reference current transistor, a second input coupled to the switching circuit to receive the feedback signal, and an output coupled to an input of the switching circuit, a first resistor coupled to the first input and arranged to sense the reference current, and a second resistor coupled to the second input and arranged to sense an LED current, wherein the operational amplifier amplifies a difference between a voltage drop across the first resistor and a voltage drop across the second resistor to adjust a gate voltage of the switching circuit transistor.

2. The LED array of claim 1, wherein the closed loop circuit is configured to receive the feedback signal from the switching circuit and adjust a voltage applied to the switching circuit based on the feedback signal, wherein the input current to the LED is based on the voltage applied to the switching circuit.

3. The LED array of claim 1, wherein the first resistor has a first resistance, the second resistor has a second resistance, and a current provided by the switching circuit to the LED is equal to a reference current from the reference current transistor multiplied by a ratio of the first resistance and the second resistance.

4. The LED array of claim 1, wherein the reference current transistor is a p-type metal oxide semiconductor (PMOS) transistor, a source of the p-type metal oxide semiconductor transistor is coupled to an input voltage, a gate is coupled to a current control signal, and a drain is coupled to the first input of the operational amplifier.

5. The LED array of claim 1, wherein the switching circuit transistor is an n-type metal oxide semiconductor (NMOS) transistor, the n-type metal oxide semiconductor transistor further comprising a source coupled to the second resistor and a drain coupled to the LED.

6. An LED pixel assembly comprising: an LED configured to receive power from a first power line; a switching circuit coupled to the LED, the switching circuit configured to receive a pulse width modulated signal and alternately turn on and off an input current to the LED based on the pulse width modulated signal, the switching circuit comprising a switching circuit transistor; and and a closed loop circuit configured to receive power from a different, second power line and configured to regulate the input current to the LED based on a current control signal and feedback from the switching circuit, the closed loop circuit comprising: a reference current transistor arranged to output a reference current based on a current control signal, an operational amplifier having a first input coupled to the reference current transistor, a second input coupled to the switching circuit to receive feedback from the switching circuit, and an output coupled to an input of the switching circuit, a first resistor coupled to the first input and arranged to sense the reference current, and a second resistor coupled to the second input and arranged to sense the LED current, wherein the operational amplifier amplifies a difference between a voltage drop across the first resistor and a voltage drop across the second resistor to adjust a gate voltage of the switching circuit transistor.

7. The LED pixel assembly of claim 6, wherein the first resistor has a first resistance, the second resistor has a second resistance, and the input current to the LED is equal to the reference current multiplied by a ratio of the first resistance and the second resistance.

8. The LED pixel assembly of claim 6, wherein the reference current transistor is a p-type metal-oxide-semiconductor (PMOS) transistor having a source coupled to an input voltage, a gate coupled to the current control signal, and a drain coupled to the first input of the operational amplifier.

9. The LED pixel assembly of claim 6, wherein the switching circuit transistor is an n-type metal-oxide-semiconductor (NMOS) transistor further comprising a source coupled to the second resistor and a drain coupled to the LED.

10. A control circuit for an LED configured to receive power from a first power line, the control circuit comprising: a closed loop circuit configured to receive power from a different, second power line and configured to receive a current control signal and output an LED current regulation signal based on the current control signal; and a switching circuit configured to output an LED current according to a pulse width modulation signal, the LED current having an amplitude adjusted by the LED current regulation signal received from the closed loop circuit, the switching circuit further configured to provide feedback to the closed loop circuit to adjust the LED current, the switching circuit comprising a switching circuit transistor, wherein the closed loop circuit comprises: a reference current transistor arranged to output a reference current based on a current control signal, an operational amplifier having a first input coupled to the reference current transistor, a second input coupled to the switching circuit to receive feedback from the switching circuit, and an output coupled to an input of the switching circuit, a first resistor coupled to the first input and arranged to sense the reference current, and a second resistor coupled to the second input and arranged to sense the LED current, wherein the operational amplifier amplifies a difference between a voltage drop across the first resistor and a voltage drop across the second resistor to adjust a gate voltage of the switching circuit transistor. a first resistor coupled to the first input and arranged to sense a reference current, and a second resistor coupled to the second input and arranged to sense an LED current, wherein the operational amplifier amplifies a difference between a voltage drop across the first resistor and a voltage drop across the second resistor to adjust a gate voltage of the switching circuit transistor.

11. The control circuit of claim 10, wherein the first resistor has a first resistance and the second resistor has a second resistance, wherein the LED current is equal to the reference current multiplied by a ratio of the first resistance and the second resistance.

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