Driver circuit and light-emitting device

Abstract

The present disclosure relates to a driver circuit (200) including: an output terminal (202) configured to be coupled with a light emitting element (252); a current delivery circuit (204) operable to control a delivery of current to the output terminal (202) via an electrically conductive path (206) for controlling a light emission by the light emitting element (252); and a safety circuit (208) operable to cause a permanent disconnection of the electrically conductive path (206) for the delivery of current to the output terminal (202).

Description

DRIVER CIRCUIT AND LIGHT-EMITTING DEVICETechnical Field

[0001] The present disclosure relates generally to a driver circuit for driving light emission by a plurality of light-emitting elements, and to a light-emitting device including the driver circuit.Background

[0002] In general, lighting fixtures and display devices are present in a wide range of technical contexts and applications, e.g., for illuminating the road while driving, for illuminating an environment, for displaying images, and the like. In particular, pixelated light sources consist of multiple individual light-emitting elements (pixels), which may be individually and independently addressed to precisely adjust the properties of the emitted light and / or to emit complex light patterns. Pixelated light sources have various applications, such as for stage lighting, advertisement, information displays, and the like. A particularly relevant use case is the use of pixelated light sources for automotive applications, where the individual control of the light-emitting elements allows an adaptive headlamp system capable of adjusting the brightness dynamically based on driving conditions, thus enhancing the safety for the driver and for the other traffic participants. Improvements in light-emitting devices, and in particular in pixelated light sources, are thus relevant for the further advancements of several technologies.Brief Description of the Drawings

[0003] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various aspects of the invention are described with reference to the following drawings, in which:FIG. l shows a circuit of a pixel in a schematic representation, according to various aspects;FIG.2A and FIG.2B show driver circuit for driving light emission by one or more light-emitting elements in a schematic representation, according to various aspects;FIG.2C and FIG.2D show a light-emitting device including the driver circuit and one or more light-emitting elements coupled with the driver circuit in a schematic representation, according to various aspects;FIG.3 shows an exemplary configuration of a driver circuit in a schematic representation, according to various aspects;FIG.4A and FIG.4B show a safety circuit for use in the driver circuit in a schematic representation, according to various aspects;FIG.5A to FIG.5C show a current delivery circuit for use in the driver circuit in a schematic representation, according to various aspects; andFIG.6 shows a schematic flow diagram of a method of driving light emission by one or more light emitting elements, according to various aspects.Description

[0004] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and aspects in which the invention may be practiced. These aspects are described in sufficient detail to enable those skilled in the art to practice the invention. Other aspects may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the invention. The various aspects are not necessarily mutually exclusive, as some aspects may be combined with one or more other aspects to form new aspects. Various aspects are described in connection with methods and various aspects are described in connection with devices (e.g., a light-emitting device, a driver circuit). However, it is understood that aspects described in connection with methods may similarly apply to the devices, and vice versa.

[0005] In general, pixelated light sources, particularly those based on Light-Emitting Diodes (LEDs), have become increasingly popular in various applications due to their high efficiency, long lifespan, and design flexibility. These devices may include an array of individually controllable light emitters that may be precisely controlled to produce a wide range of colors, brightness levels, and patterns. As a relevant use case, pixelated light sources have been adopted for automotive applications (e.g., to provide headlamps), due to their ability to provide advanced light control that may be adapted to the driving conditions (e.g., to the presence of other vehicles, to variations in the ambient light, and the like).

[0006] However, pixelated emitters (e.g., pixelated LEDs) also present some challenges. In particular, in pixelated emitters that contain an integrated driver the phenomenon known as "permanently-ON" pixels may occur. This phenomenon occurs when a driver failure causes one or more pixels to remain constantly lit (illustratively, always on), as soon as the component is switched on. Illustratively, some of the emitters may emit light even without a corresponding control signal to drive their light emission, and even in case they should rather not emit lightduring that light emission period. This issue may have significant consequences in automotive headlight applications, where uncontrolled dazzling of oncoming traffic may pose a serious threat to eye safety. The phenomenon may also be known as “always-on”, “stuck pixel”, or “continuous-on”.

[0007] The problem is further exacerbated by the fact that permanently ON affected components are typically sorted out during production testing (e.g., at wafer-level integrated circuit test, at the final test of the device, etc.), but there is no reliable mechanism to detect and address such issues once the device is installed in a customer product (e.g., a headlight). Illustratively, in operation there is no further protective mechanism, so that as soon as permanent-ON pixels develop (e.g., due to degradation of the driver, or of components relevant for the pixel), such components may only be detected visually (e.g., by end customers, or customer service, or oncoming traffic).

[0008] Some pixelated LEDs also incorporate self-diagnosis capabilities that allow them to electrically recognize and report permanently-ON pixels to higher-level products. While this feature provides some level of awareness about the issue, it does not prevent further operation and only serves as a "workshop alarm", e.g., in a vehicle.

[0009] The "permanently-ON" phenomenon may be illustrated with reference to FIG.l, which shows an exemplary configuration of a pixel 100 of a pixelated light source. The pixel 100 may include a LED 102 and a current mirror defined by two transistors 104, 106 (e.g., a first N-MOS and a second N-MOS). The current mirror may deliver a replica of a current Ii (provided by a current source 108) at the input branch as output current at the output branch. The replicated output current may be the LED current that causes light emission by the LED. The pair of transistors 104, 106 may be designed to amplify the current by a scaling factor N.

[0010] The pixel 100, as well as the other pixels in a pixel matrix, may thus be controlled via the pair of transistors 104, 106, and further via a switch 110 operable to selectively activate or deactivate the light-emitting element 102. The switch 110 may be controlled using a duty-cycle signal (e.g., a pulse-width modulation, PWM, signal) that controls the ON-time and OFF-time of the pixel 100. Illustratively, the switch 110 may receive a control signal that controls the behavior of the switch 110 to allow the current mirror to replicate the current at the output branch, or to prevent the current mirror from replicating the current. The switch 110 may thus selectively allow the current mirror to conduct or prevent the current mirror from conducting.

[0011] The voltage VGS at the output transistor 106 (0 and N*Ii) may thus be modulated via the "PWM" switch 110 in combination with a suitable control signal, generating a current pulse sequence that is converted by the LED 102 into a modulated luminous flux. The ratio of theduty cycle of the "PWM" signal may be used to control the integral of the luminous flux, which is perceived by the human eye as a reduction in brightness if the clock frequency is sufficiently high (illustratively, the eye may act as a low-pass filter).

[0012] If a process error occurs, the pixel 100 may end up in a “permanently ON” state. This may happen, for example, if the output transistor 106 is brought into a self-conducting state, or if due to interrupted lines the "PWM" switch 110 can no longer be closed. Both lead to a continuously emitting pixel. Illustratively, in this faulty scenario the pixel 100 is no longer controllable to interrupt the flow of current to the LED 102, which is thus always emitting light as soon as the device is powered ON.

[0013] Aspects of the present disclosure are related to a driver circuit for a light-emitting device, adapted to identify the occurrence of “permanently-ON” pixels, and to react to the pixel failure by causing a permanent disconnection of the pixel from a power supply. The driver circuit may illustratively be configured to bring the faulty pixel into a “permanently OFF” state (also referred to as “always OFF” state), which is safer than the “permanently ON” case. The driver circuit may trigger a safety mechanism that prevents the faulty pixel from receiving power (e.g., current), thus allowing the light-emitting device to continue operating without the risks associated with pixels that continuously emit light.

[0014] The driver circuit may include, for each pixel, a safety circuit that is configured to enable the safety mechanism. The safety circuit may be operable to cause the permanent disconnection of the pixel from the power supply upon receiving a corresponding control signal. In particular, the safety circuit may be operable to irreversibly open an electrically conductive path for the delivery of driving current to the pixel, thus preventing the pixel from emitting light again even when the device is in operation. By way of illustration, the approach described herein may be understood as a “self-destructing pixel”. The driver circuit recognizes electrically that the pixel has developed into permanent ON and carries out an electrical self-destruction.

[0015] In the proposed configuration, the disconnection of the pixel may thus be implemented at the physical level, rather than at the logic level. The approach may be based on the realization that in case of component failures (e.g., in case of a transistor in self-conducting state, or in case of interrupted control lines) it is not sufficient to simply instruct a pixel not to emit light, but it is rather necessary to act at the component level and actively inhibit the further delivery of driving current to the pixel.

[0016] In some aspects, the driver circuit may further be configured to generate a warning message representative of the occurrence of the pixel failure. The warning message may include information indicative that one pixel has been permanently disconnected, and the driver circuitmay deliver the warning message to a host device into which the light-emitting device is installed. For example, considering automotive applications, the driver circuit may deliver the warning message to a central processing unit of the vehicle, which may then inform the owner and prompt maintenance. Turning the faulty pixels into a “permanently OFF” state allows the vehicle to continue driving without the risk of dazzling oncoming traffic, thus ensuring compliance with safety regulations.

[0017] According to various aspects, a driver circuit may include: an output terminal configured to be coupled with a light emitting element; a current delivery circuit configured to control a delivery of current to the output terminal via an electrically conductive path for controlling a light emission by the light emitting element; and a safety circuit operable to cause a permanent disconnection of the electrically conductive path for the delivery of current to the output terminal.

[0018] According to various aspects, a light-emitting device may include: a pixel matrix comprising a plurality of pixels, wherein each pixel comprises a respective light-emitting element; and a driver circuit for driving a light emission via a delivery of current to the plurality of pixels, wherein the driver circuit is configured to: detect a failure of a pixel of the plurality of pixels, and cause an irreversible disconnection of an electrically conductive path for the delivery of current to that pixel.

[0019] As mentioned, the approach proposed herein may be particularly relevant in the automotive context. Thus, in a preferred configuration the light-emitting device may be a headlamp for use in a vehicle, or may be configured as a headlamp for use in a vehicle. It is however understood that in principle the proposed approach may be applicable in any suitable scenario and in any suitable type of light-emitting device that may suffer from the occurrence of “permanently ON” light emitters. As other examples, the light-emitting device having a driver circuit adapted as proposed herein may be part of a display, a luminaire, a light-based sensor such as a time-of-flight sensor, a monitoring system, and the like.

[0020] Furthermore, the approach proposed herein may be particularly relevant for light-emitting devices including a plurality of light-emitting elements (in other words, a plurality of light emitters), because turning one faulty light-emitting element permanently OFF would allow the other light-emitting elements to continue operating as normal, thus providing an uninterrupted, yet safe operation of the device. It is however understood that the proposed approach may also be applicable to a scenario with a single light-emitting element that may be irreversibly disconnected from the power supply in case of failure.

[0021] FIG.2A and FIG.2B show a driver circuit 200 for use in a light-emitting device, in a schematic representation according to various aspects. The driver circuit 200 may generally be configured to control (illustratively, to drive) light emission by the light-emitting elements of the light-emitting device, and may further be adapted according to the approach proposed herein to bring light-emitting elements into a permanently OFF state in case a “permanently ON” phenomenon occurs. FIG.2A shows the configuration 200a in which the driver circuit 200 includes one output terminal 202 for coupling with one light-emitting element, and FIG.2B shows the configuration 200b in which the driver circuit 200 includes a plurality of output terminals 202 for coupling a plurality of light-emitting elements. It is understood that the aspects discussed in relation to the configuration 200a with a single output terminal 202 apply in a corresponding manner to the configuration 200b with multiple output terminals 202, and vice versa.

[0022] The general configuration and the general components of a driver circuit are known in the art. In this regard, it is understood that the representation in FIG.2A and FIG.2B (as well as FIG.2C and FIG.2D) is simplified to focus on the relevant aspects of the approach proposed herein, and that the driver circuit 200 may include additional components with respect to those shown. Further exemplary components of a driver circuit will be described in more detail in relation to FIG.3.

[0023] In general, the driver circuit 200 may be an integrated circuit. The term “integrated circuit” may be used herein as commonly understood in the art to describe a microelectronic device that includes one or more layers of semiconductor material (e.g., silicon, germanium, gallium arsenide, and the like), which are processed using various techniques (e.g., photolithography, etching, etc.). The layers of semiconductor material may be doped to form a complex pattern of conductive paths, insulating regions, and active devices. An integrated circuit may include one or more types of electronic components such as transistors, resistors, capacitors, diodes, and the like, which are interconnected via electrically conductive lines to enable various electrical functionalities. The electronic components and electrically conductive lines are integrated onto a single substrate, e.g., a single Printed Circuit Board (PCB).

[0024] With reference to the configuration in FIG.2A, the driver circuit 200 may include an output terminal 202 configured to be coupled with a light-emitting element. The output terminal 202 may be configured to enable coupling the driver circuit 200 with a light-emitting element, thus allowing the driver circuit 200 to drive light emission by the (coupled) light-emitting element. The output terminal 202 may thus be understood as a connection terminal or connection point configured to be electrically connected with the light-emitting element. Forexample, the output terminal 202 may be exposed towards the outside, to allow fixing a corresponding terminal of the light-emitting element thereto. An output terminal (e.g., the output terminal 202) may also be referred to herein as “connection terminal” or “driver terminal”. A “terminal” may also be referred to herein as “port” or “pin”.

[0025] The driver circuit 200 may further include a current delivery circuit 204 operable to control a delivery of current to the output terminal 202 via an electrically conductive path 206. The control of the delivery of current to the output terminal 202 may allow a corresponding control of a light emission by the light-emitting element coupled with the output terminal 202. Illustratively, the current delivery circuit 204 may be configured to allow a controlled delivery of current to the output terminal 202, thus allowing to regulate the timing of the delivery of current. Stated differently, the current delivery circuit 204 may be configured to enable the driver circuit 200 (e.g., a processing circuit 220 of the driver circuit 200) to control the amount of current provided at the output terminal 202 during a light emission period.

[0026] According to various aspects, the current delivery circuit 204 may be configured to receive (e.g., from the processing circuit 220) a control signal, and may be configured to regulate the flow of current to the output terminal 202 according to the control signal. Illustratively, the current delivery circuit 204 may be operable to selectively enable or disable flow of current through the electrically conductive path 206 according to the control signal, thus selectively enabling or disabling the delivery of current at the output terminal 202. In particular, the current delivery circuit 204 may be configured to receive a duty-cycle signal as control signal, and to regulate the flow of current to the output terminal 202 according to the duty-cycle signal.

[0027] In this regard, the term “duty-cycle signal” may be used herein to describe a signal that represents a duty cycle for driving light emission by a light-emitting element, and accordingly a signal that represents a duty cycle for regulating the current flow to an output terminal of a driver circuit (e.g., to the output terminal 202). As generally known in the art, the duty cycle is the ratio of on-time compared to the off-time. A “duty-cycle signal” may thus generally include a signal that during a certain time period (e.g., light emission period) is active for a portion of the time period and is inactive for another portion of the time period depending on the value of the duty cycle associated with the signal. A “duty-cycle signal” may thus generally include a modulated signal, in which at least one signal parameter varies over the time period according to the duty cycle that the signal should define. As an example, the duty cycle defined by a “duty-cycle signal” may be expressed as a percentage of “on-time”, illustratively a percentage of the time period during which the signal is active or “on”.

[0028] In this regard, the preferred modulation scheme for driving light emission may be based on pulse-width modulation. In a preferred configuration a “duty-cycle signal” may thus be a “PWM signal”, which defines the duty cycle via pulses having variable width. The width of the pulses may illustratively represent the duty cycle of the PWM cycle, such that a PWM signal having pulses with a width covering X % of the time period may define a X % duty cycle. PWM is widely employed for driving light emission since variable-width pulses may be generated in an accurate, reproducible, and relatively simple manner. Thus, in the present disclosure particular reference may be made to PWM and PWM signals for regulating current delivery and for driving light emission. It is however understood that in principle also other modulation schemes may be employed to define the duty cycle of a signal. Other examples include pulse frequency modulation (PFM) and pulse density modulation (PDM).

[0029] As an abridged overview, PWM may describe the use of a digital signal to obtain an analog result. The PWM signal may be a square wave switched between a high state (illustratively, an “on state”) and a low state (“off state”). The percentage of time in which the PWM signal is in the high state is the so-called duty cycle. By way of illustration, a PWM signal always on would have a 100% duty cycle, a PWM signal always off would have a 0% duty cycle, a PWM signal on for half of a period would have a 50% duty cycle, and so on. In addition to the duty cycle, another important parameter of a PWM signal is the frequency of the waveform, i.e. the inverse of the period, i.e. the inverse of the complete on-time and off-time of the PWM signal. By controlling the duty cycle of the PWM signal it is possible to control the electrical power perceived by a load. Illustratively, by varying the duty cycle (the relative on-time), the average voltage of the signal may vary accordingly.

[0030] Considering light emission, a relevant use case for the PWM technique is the control of the brightness of light emitted by a light-emitting element, the so-called “dimming”. With PWM, a light-emitting element is turned on and off with a duty cycle and frequency defined by the PWM signal. By varying the on-time, the brightness of the emitted light as perceived by the human eye may be varied accordingly. The PWM technique is based on switching the lightemitting element on and off at high frequency so that the power perceived by the light-emitting element varies in a range between 0 and the amount of power corresponding to the maximum output, thus regulating the brightness as a function of the ratio of the on-time to off-time.

[0031] Light emission based on a “duty cycle” (e.g., on PWM) may be the most relevant configuration for the approach proposed herein, due to its advantageous properties for controlling light emission. It is however understood that the driver circuit 200 and current delivery circuit 204 may be configured according to any suitable driving scheme and accordingto any suitable strategy to provide a controlled flow of current to the output terminal 202 and a corresponding controlled light emission by a coupled light-emitting element.

[0032] According to the adapted configuration proposed herein, the driver circuit 200 may further include a safety circuit 208. The safety circuit 208 may be operable to cause a permanent disconnection of the electrically conductive path 206 for the delivery of current to the output terminal 202. Illustratively, the safety circuit 208 may be configured to enable an irreversible interruption of the flow of current towards the output terminal 202. This configuration allows the driver circuit 200 to react to circuit failures in a simple, yet efficient manner, thus addressing the occurrence of “permanently ON” light emitting elements.

[0033] Possible configurations of the safety circuit 208 will be described in further detail in relation to FIG.4A and FIG.4B. As mentioned, the approach proposed herein may be implemented at the physical level. Thus, the safety circuit 208 may generally include one or more electrical components that are electrically controllable to cause the permanent disconnection of the electrically conductive path 206. Illustratively, the one or more electrical components may be operable to irreversibly open the electrically conductive path 206, thus preventing the output terminal 202 (and the light-emitting element coupled thereto) from further receiving current.

[0034] According to various aspects, the output terminal 202 may have a corresponding input terminal 212 associated therewith. The input terminal 212 may be configured to receive a supply voltage for generating the current to be delivered to the output terminal 202. Illustratively, an output terminal 202 and the corresponding current delivery circuit 204 and safety circuit 208 may constitute a light-emission unit 210 of the driver circuit 200, e.g., a set of components for driving light emission by a corresponding light-emitting element. For example, the light-emission unit 210 may be understood as a pixel unit of a light-emitting device. In this regard, the light-emission unit 210 may further include a corresponding input terminal 212 receive a supply voltage for powering the light emission.

[0035] The input terminal 212 may thus be configured to be coupled with a supply source (e.g., a voltage source), e.g., with a power supply. For example, the supply source may be internal to the driver circuit 200, and the input terminal 212 may be coupled with the internal supply source to receive the supply voltage therefrom.

[0036] In a preferred configuration, which provides a simpler design, the driver circuit 200 does not include an internal supply source. In this scenario, the driver circuit 200 may include a supply terminal 214 configured to be coupled with a supply source external to the driver circuit 200. For example, considering automotive applications, the supply terminal 214 may beconfigured to be coupled with the battery of a vehicle. As shown in FIG.2A, in this scenario the input terminal 212 may be coupled with the supply terminal 214, and may be configured to receive the supply voltage via the supply terminal 214.

[0037] It is understood that in principle also “mixed” configurations may be provided in which the driver circuit 200 includes a (small) internal supply source and further includes a supply terminal for coupling with an external supply source.

[0038] Considering the approach proposed herein, the electrically conductive path 206 may provide a direct electrical coupling between the output terminal 202 and the input terminal 212. Illustratively, the electrically conductive path 206 may provide a direct electrical coupling between the output terminal 202 and the supply voltage (e.g., with the supply source, or with the supply terminal 214).

[0039] In this regard, the safety circuit 208 may be operable to cause a permanent disconnection (in other words, an irreversible decoupling, e.g., an irreversible breakage) of the path to deliver supply voltage to the light-emission unit 210. Illustratively, the safety circuit 208 may be operable to cause an irreversible opening of the path between the output terminal 202 and the input terminal 212, and accordingly an irreversible disconnection of the output terminal 202 from the supply voltage. For example, the safety circuit 208 may be operable to permanently decouple the output terminal 202 from the supply source internal to the driver circuit 200. As another example, the safety circuit 208 may be operable to permanently decouple the output terminal 202 from the supply terminal 214.

[0040] As mentioned above, the driver circuit 200 may include a processing circuit 220 configured to control the overall behavior of the driver circuit 200. The processing circuit 220 may be a digital circuit configured to instruct the operation of the various components of the driver circuit 200 (see also FIG.3). In particular, the processing circuit 220 may be configured to instruct the behavior of the current delivery circuit 204, e.g., the processing circuit 220 may generate a control signal representative of the current delivery to be provided, and may provide the control signal to the current delivery circuit 204 for regulating the current flow accordingly. In the preferred configuration, the processing circuit 220 may generate a duty-cycle signal representative of the duty cycle to be provided for the current delivery (and accordingly for the light emission), and may provide the duty-cycle signal to the current delivery circuit 204.

[0041] According to the approach proposed herein, the processing circuit 220 may be further configured to implement a failure detection functionality. The processing circuit 220 may thus act as failure detection circuit. Alternatively, the driver circuit 200 may include a dedicated failure detection circuit for implementing the approach proposed herein. In this regard, theaspects discussed in relation to the failure detection carried out by the processing circuit 220 may apply in a corresponding manner to a separate dedicated failure detection circuit, and vice versa.

[0042] In various aspects, the processing circuit 220 may be configured to detect a failure of the current delivery circuit 204 and may be configured to trigger the safety mechanism that disconnects the electrically conductive path 206 upon detection of the failure. In particular, the failure of the current delivery circuit 204 may include a state of the current delivery circuit 204 for which current is constantly delivered to the output terminal 202, thus causing the corresponding light-emitting element to be permanently ON. Illustratively, the failure of the current delivery circuit 204 may include a current flow to the output terminal 202 even in absence of a corresponding control signal (e.g., duty-cycle signal). The failure of the current delivery circuit 204 may thus be a state of the current delivery circuit 204 that prevents the current delivery circuit 204 from responding to an instruction (e.g., a control signal) by the processing circuit 220 to interrupt the current flow to the output terminal 202.

[0043] As mentioned, the approach proposed herein may address the issue of “permanently ON” light emitters, and thus the above-described failure of the current delivery circuit 204 may be the most relevant case. It is however understood that in principle the safety mechanism proposed herein may also be implemented to address other types of failures for which causing a permanent disconnection of the electrically conductive path 206 may be beneficial.

[0044] If the processing circuit 220 detects the failure of the current delivery circuit 204, the processing circuit 220 may be configured to operate the safety circuit 208 to cause the permanent disconnection of the electrically conductive path 206. In this regard, various mechanisms may be provided, which will be described in further detail below. In general, upon detecting the occurrence of the failure (in other words, the malfunction) of the current delivery circuit 204, the processing circuit 220 may control the safety circuit 208 to trigger the irreversible decoupling of the output terminal 202 from the input terminal 212 (e.g., from the supply terminal 214).

[0045] The detection of the failure may be carried out in any suitable manner. In general, the processing circuit 220 may be configured to detect the failure based on one or more electrical parameters of the current delivery circuit 204 (see also FIG.5A to FIG.5C). Illustratively, the processing circuit 220 may be configured to evaluate the behavior of the current delivery circuit 204 based on one or more electrical parameters that characterize the operation of the current delivery circuit 204. The electrical parameters may include, as examples, a current flow through a component of the current delivery circuit 204, a voltage drop over a component of the currentdelivery circuit 204, a resistance value of a component of the current delivery circuit 204, and the like.

[0046] The processing circuit 220 may be configured to determine whether values associated with the one or more electrical parameters are within a predefined range, and to determine that a failure has occurred if at least one of the electrical parameters is outside the corresponding range (e.g., voltage range, current range, resistance range, etc.). For example, the processing circuit 220 may compare each electrical parameter with a corresponding reference value (e.g., a threshold value) and determine that a failure has occurred if the electrical parameter deviates from the reference value by more than a predefined acceptable deviation (e.g., more than 5%, more than 10%, more than 50%, as examples). As another example, the processing circuit 220 may determine that a failure has occurred if the electrical parameter is greater than the corresponding threshold value or smaller than the corresponding threshold value, depending on the type of comparison.

[0047] As an example, considering an exemplary realization of a current delivery circuit 204 including a transistor for selectively enabling or disabling the current flow to the output terminal 202, an electrical parameter may include a voltage drop across the transistor, e.g., a gate-source voltage of the transistor. The processing circuit 220 may compare the gate-source voltage with an expected value for the gate-source voltage, and determine whether a failure has occurred based on the comparison. For example, for a “permanently ON” scenario, the gate-source voltage may remain always above the threshold voltage of the transistor, thus maintaining a continuous flow of current to the output terminal 202.

[0048] According to various aspects, the processing circuit 220 (e.g., the failure detection circuit) may be further configured to report the occurrence of the failure, thus allowing a user to take corrective actions, e.g., maintenance or replacement of the faulty components. In this regard, the processing circuit 220 may be further configured to generate a warning message representative of the failure of the current delivery circuit 204. The warning message may include information that indicate that a failure has occurred, and further may include information that allows to identify which current delivery circuit 204 failed (in case of more than one current delivery circuit 204). For example, the warning message may allow determining which pixel was “permanently ON”. As an example, the warning message may include an address associated with the output terminal 202 (e.g., an address associated with the corresponding light emitting element). Illustratively, the warning message may include information representative of a position of the faulty current delivery circuit 204 within thedriver circuit 200, and / or information representative of a position of the faulty pixel in a lightemitting device.

[0049] The warning message may have any suitable form and configuration. For example, the warning message may be or include a warning signal encoded to contain the information representative of the failure. As another example, the warning message may be or include a human-perceptible signal (e.g., a visual signal or an audio signal) that a failure has occurred, etc.

[0050] According to various aspects, the driver circuit 200 may further include a communication interface 222 configured to enable a communicative coupling of the driver circuit 200 with further entities (e.g., devices and systems) external to the driver circuit 200. Illustratively, the communication interface 222 may be configured to enable a communication from and towards the outside of the driver circuit 200. For example, the driver circuit 200 may be coupled with the central processing unit of a vehicle via the communication interface 222. The communication interface 222 may thus include transmitter circuitry and / or receiver circuitry to transmit and / or receive information to / from the outside of the driver circuit 200. In various aspects, the processing circuit 220 may be configured to transmit the warning message via the communication interface 222.

[0051] The communication interface 222 may thus include any suitable component to enable the driver circuit 200 to transmit / receive data. The communication interface 222 may thus include one or more components that enable encoding / decoding of signals for transmission / reception over a physical medium.

[0052] In a preferred configuration, which provides a simpler implementation, the communication to / from the driver circuit 200 may be implemented in the context of wire-based communication. For example, the communication interface 222 may include one or more switches and one or more resistive elements to control a voltage level or current level at an electrically conductive connection between the driver circuit 200 and the entity to which the data should be transmitted (and / or from which data should be received). The control of the voltage level or current level may define a modulation that represents or encodes information in the output signal. For example, a first voltage level at the wired connection (e.g., a high voltage level) may be associated with a logic “1”, and a second voltage level at the wired connection (e.g., a low voltage level) may be associated with a logic “0”. It is however understood that the definition of logic “1” and logic “0” and of the type of signal modulation associated thereto may be arbitrary.

[0053] In this context, the driver circuit 200 may be configured to communicate according to any suitable wired communication protocol, such as the single-wire protocol, the Inter- Integrated Circuit bus (I2C) protocol, the Serial Peripheral Interface (SPI) protocol, the Controller Area Network (CAN) protocol, the Ethernet protocol, and / or the like.

[0054] It is however understood that in principle the communication to / from the driver circuit 200 may be implemented in the context of wireless communication. For example, the communication interface 222 may include a transceiver circuit configured to transmit / receive data according to a wireless communication standard. For example, the communication interface 222 may include an antenna or may be coupled to an antenna, and may transmit and / or receive radio frequency signals using the antenna. In this context, the driver circuit 200 may be configured to communicate according to any suitable wireless communication protocol, such as WiFi, Bluetooth, Near Field Communication (NFC), etc.

[0055] As discussed, the safety mechanism proposed herein may be particularly relevant in the context of multiple light emitters. In this regard, FIG.2B shows a configuration 200b in which the driver circuit 200 includes a plurality of output terminals 202, each configured to be coupled with a respective light-emitting element. Correspondingly, the driver circuit 200 may include a plurality of current delivery circuits 204, each operable to control a delivery of current to a respective output terminal 202 via a respective electrically conductive path 206 (illustratively, to control light emission by the respective light-emitting element), and a plurality of safety circuits 208, each operable to cause a permanent disconnection of a respective electrically conductive path 206 for the delivery of current to a respective output terminal 202. As shown in FIG.2B, the driver circuit 200 may include a plurality of input terminals 212, each associated with a respective output terminal 202 and configured to receive a supply voltage. For example, the plurality of input terminals 212 may be coupled with an internal supply source, or may be coupled with a supply terminal 214 of the driver circuit 200.

[0056] Illustratively, in the configuration 200b the driver circuit 200 may include a plurality of light-emission units 210, each configured to receive a respective light-emitting element at the output terminal 202, and each configured for allowing the driver circuit 200 to drive light emission by the light-emitting element. The driver circuit 200 may thus include a first lightemission unit 210-2 having a first output terminal 202, a first current delivery circuit 204, a first safety circuit 208, and a first input terminal 212; the driver circuit 200 may further include a second light-emission unit 210-1 having a second output terminal 202, a second current delivery circuit 204, a second safety circuit 208, and a second input terminal 212, etc., up to aN-th lightemission unit 210-N.

[0057] In general, the output terminals 202 may be arranged in any suitable manner, depending on the desired arrangement of the light-emitting elements in the end product, e.g., depending on the desired pixel arrangement. For example, the output terminals 202 may be arranged as a one-dimensional array, a two-dimensional array, with a non-symmetric distribution of output terminals 202, and the like. In a preferred configuration, the plurality of output terminals 202 may be organized in a two-dimensional array. Illustratively, the plurality of output terminals 202 may be disposed in a two-dimensional matrix having a number N of columns and a number M of rows, with N and M being integer numbers greater than 1. For example, the two-dimensional matrix may be a rectangular matrix or a square matrix. A 2D-matrix may represent the most relevant use case, e.g., for applications in headlights for vehicles.

[0058] The driver circuit 200 may include any suitable number of output terminals 202 (and correspondingly, any suitable number of light-emitting elements coupled thereto). Only as a numerical example, the plurality of output terminals 202 may include at least 10 output terminals 202, e.g., at least 100 output terminals 202, e.g., at least 1000 output terminals 202, e.g., at least 10000 output terminals 202. As another numerical example, the plurality of output terminals 202 may include a number of output terminals 202 in the range from 10 to 107, e.g., in the range from 103to 106, e.g., in the range from 104to 105.

[0059] In the configuration 200b, the approach proposed herein may allow the driver circuit 200 to continue operating in a safe manner even after the occurrence of a failure, by exploiting the fact that the faulty light-emission unit 210 is brought in a “permanently OFF” state. In various aspects, after one electrically conductive path 206 associated with a current delivery circuit 204 for which a failure was detected has been permanently disconnected (by operating the corresponding safety circuit 208), the processing circuit 220 may (still) transmit a control signal to another current delivery circuit 204 or to each other current delivery circuit 204 to control the current flow to the respective output terminal 202 (and prompt a light emission by the corresponding light-emitting element).

[0060] Illustratively, the processing circuit 220 may continue to instruct the current delivery circuits 204 to regulate the delivery of current at the respective output terminal 202 after the irreversible decoupling of another one of the output terminals 202 from the supply (or the decoupling of a subset of output terminals 202 from the supply). In a preferred configuration the processing circuit 220 may thus be configured to send a respective duty-cycle signal (e.g., a respective PWM signal) to the other (still connected) current delivery circuits 204 after one of the current delivery circuits 204 failed and the corresponding safety circuit 208 was operated to cause the permanent disconnection of the respective electrically conductive path 206.

[0061] In some aspects, the processing circuit 220 may be aware of which current delivery circuits 204 failed, and refrain from further instructing such current delivery circuits 204 for which the corresponding safety circuit 208 was operated to bring them in a permanently OFF state. Illustratively, the processing circuit 220 may be configured to transmit a control signal (e.g., a duty-cycle signal) to another current delivery circuit 204 or to each other current delivery circuit 204 to control the current flow to the respective output terminal 202, while refraining from transmitting the control signal to a current delivery circuit 204 for which a failure was detected and for which the corresponding electrically conductive path 206 has been permanently disconnected. This configuration may enable a resource-efficient operation of the driver circuit 200.

[0062] FIG.2C and FIG.2D show a light-emitting device 250 including the driver circuit 200 and light-emitting elements 252 coupled to the output terminals 202 of the driver circuit 200. In the configuration 250c in FIG.2C the light-emitting device 250 includes a single lightemitting element 252, and in the configuration 250d in FIG.2D the light-emitting device 250 includes a plurality of light-emitting elements 252 each coupled to a respective output terminal 202. In this scenario, the control delivery circuits 204 may regulate the current flow to the respective output terminal 202 to correspondingly control the light emission by the respective light-emitting element 252, as discussed above.

[0063] The driver circuit 200 may be used with any suitable type of light-emitting elements 252. In a preferred configuration, at least one light-emitting element 252 (e.g., each lightemitting element 252) may be a light emitting diode. LEDs may be a preferred type of lightemitting element 252 in view of their properties such as energy efficiency, long lifespan, flexible design, etc. In particular, a LED may have a certain forward voltage, e.g., in the range from 1.8 V to 3.8 V depending on the color of the LED, but a LED may operate without suffering catastrophic damages even at higher voltages, thus allowing a safe operation. It is however understood that a light-emitting element 252 may alternatively be of a different type, e.g., the light-emitting element 252 may be a laser diode, e.g., an edge emitting laser diode or a vertical cavity surface emitting laser diode. As other examples, a light-emitting element 252 may be an organic LED, a micro-LED, a Photonic Crystal Surface-emitting Lasers (PCSEL), and the like. Considering the scenario in which a light-emitting device 250 includes more than one light-emitting element 252, the light-emitting elements may be of the same type.

[0064] A light-emitting element 252 may be configured to emit light having a predefined wavelength, for example in the visible range (e.g., from about 380 nm to about 700 nm), infrared and / or near-infrared range (e.g., in the range from about 700 nm to about 5000 nm), orultraviolet range (e.g., from about 100 nm to about 400 nm). Considering the relevant applications of the proposed driving scheme, light emission in the visible range may be the preferred configuration.

[0065] A light-emitting element 252 may be coupled to the respective output terminal 202 in any suitable manner. In general, a light-emitting element 252 may be fixedly coupled to the output terminal 202, but in principle also a removable coupling may be provided. Illustratively, the driver circuit 200 and the light-emitting elements 252 may be assembled together to be part of the same component. As mentioned, the driver circuit 200 may be an integrated circuit, and the light-emitting elements 252 may be coupled (e.g., attached) to the IC via any suitable technique known in the art, such as soldering, adhesive bonding (e.g., using glue, epoxy, etc.), and the like. Illustratively, any suitable die-attach process may be used to permanently bond the light-emitting elements 252 to the driver circuit 200.

[0066] In a preferred configuration, the light-emitting device 250 may be configured as a pixelated light source. In this scenario, each light-emitting element 252 may correspond to a pixel of the light source. As discussed in relation to the output terminals 202, the pixels may be arranged in any suitable manner, e.g., as a one-dimensional array, two-dimensional array, with a non-symmetric distribution, etc. In a preferred configuration, the pixels may be arranged in a two-dimensional pixel matrix (e.g., a rectangular matrix).

[0067] By way of illustration, in some aspects the light-emitting device 250 may be understood as a pixelated light source including a plurality of pixels (e.g., arranged in a pixel matrix), each including a respective light-emitting element 252 (e.g., a LED). The driver circuit 200 may be configured to drive light emission by the pixels by controlling a delivery of current to the plurality of pixels (e.g., using duty-cycle signals, such as PWM signals), and the driver circuit 200 may be further configured to detect a failure of a pixel and cause an irreversible disconnection of an electrically conductive path for the delivery of current to that pixel. Illustratively, the driver circuit 200 may be configured to determine that a pixel is malfunctioning (e.g., that the pixel is permanently ON), and in response to determining the failure cause a permanent deactivation of that pixel (by operating the respective safety circuit 208). The driver circuit 200 may thus bring the malfunctioning pixel in a permanently OFF state, and continue to operate the other pixels in a safe manner.

[0068] In a preferred configuration, the light-emitting device 250 may be a headlamp for use in a vehicle, or may be part of a headlamp for use in a vehicle. Modem vehicles may be equipped with the possibility of emitting complex light patterns, e.g., to adapt the illumination in a dynamic manner in response to variations in the environment. In this context, modemheadlamps may be provided with dense pixel matrices, to allow projecting a variety of light patterns. It is however understood that the light-emitting device 250 may be in principle for use in any suitable type of device for which the proposed driving scheme may be advantageous. As other examples, the light-emitting device 250 may be (part of) a display device, a light projector, a light-based measurement system, a light-based communication system, and the like.

[0069] It is understood that the representation of the driver circuit 200 in FIG.2A to FIG.2D may be simplified, and the driver circuit 200 may include additional elements with respect to those shown. In this regard, FIG.3 shows an exemplary configuration of a driver circuit 300. The driver circuit 300 may be configured to implement the functionalities discussed in relation to FIG.2A to FIG.2D, and may illustrate possible exemplary components to implement further functionalities. It is understood that the configuration of the driver circuit 300 is exemplary, and the driver circuit 300 may include additional, fewer, or alternative components with respect to those shown.

[0070] In general, the driver circuit 300 may include a supply terminal 302 to receive a supply voltage as input voltage for powering an operation of the driver circuit 300. In addition to the supply terminal 302, the driver circuit 300 may include various further terminal for coupling with external circuit and components. For example, the driver circuit 300 may include one or more data terminals 304 for data transmission and reception. The data terminals 340 may include, for example, a chip select terminal, CS, to receive a chip select signal; a clock terminal, SCLK, to receive a clock signal, a multiple input single output, MISO, to receive data, and a multiple output single input, MO SI, to output data. As another example, the driver circuit 300 may include one or more test terminals 306 at which test signals may be provided to carry out a testing of the driver circuit 300, e.g., a testing of one or more components of the driver circuit 306. The driver circuit 300 may be coupled with a reference terminal 308.

[0071] The driver circuit 300 may further include a digital processing circuit 310 (a digital core) coupled with the data terminals 304 and configured to carry out digital processing. For example, the digital processing circuit 310 may be coupled with a memory 312 configured to store instructions for the digital processing circuit 310. For example, the memory 312 may store data and parameters for an operation of the driving circuit 300. As an exemplary implementation, the memory 312 may be a one-time programmable (OTP) memory. For example, the digital processing circuit 310 may be configured to carry out the functionality of the processing circuit 220 described in relation to FIG.2A to FIG.2D.

[0072] The driver circuit 300 may further include a reversal protection circuit 316 configured to protect the driver circuit 300 from reverse input voltage. Illustratively, the reversal protectioncircuit 316 may be configured to block a negative portion of the input voltage at the supply terminal 302. In this regard the term “negative” may refer to the absolute polarity of the input voltage. The driver circuit 300 may further include an overvoltage detection circuit 318 configured to monitor the input voltage (e.g., as output by the reversal protection circuit 316) and trigger a shutdown of the driver circuit 300 in case of overvoltage. The operation of the driver circuit 300 may be resumed as soon as the input (supply) voltage returns below a predefined threshold.

[0073] The driver circuit 300 may further include a power management circuit 320 coupled with the reversal protection circuit 316 and the overvoltage detection circuit 318 and configured to control their operation, e.g., to adjust one or more operating parameters of such circuits. For example, the power management circuit 320 may be an internal low-dropout regulator to generate a fixed voltage independently of the input voltage, thus providing a controlled voltage value for powering the components that require a small supply voltage, or in general a smaller supply voltage than other components of the driver circuit 300.

[0074] Regarding temperature protection, the driver circuit 300 may include a temperature sensor 322 and a thermal shutdown circuit 324. The temperature sensor 322 may be configured to sense a temperature of the driver circuit 300, and the thermal shutdown circuit 324 may be a hardwired circuit configured to force a shutdown of the driver circuit 300 if the sensed temperature indicates an over-temperature condition, e.g., if the sensed temperature is greater than a threshold temperature. The operation of the driver circuit 300 may be resumed as soon as the temperature returns below the predefined threshold temperature.

[0075] The driver circuit 300 may further include a plurality of output terminals 326 configured to be coupled with elements to be driven by the driver circuit 300. For example, the plurality of output terminals 326 may be coupled with the light-emitting elements of a light-emitting device. The driver circuit 300 may further include a control circuit 330 configured to control a behavior of the light-emitting elements coupled with the output terminals 326. For example, the control circuit 330 may be configured to control a plurality of switchable elements 328 (e.g., a plurality of transistors) to selectively enable a current flow through a light-emitting element (e.g., of current drawn by a current source 332) or disable the current flow through a light-emitting element, e.g., by bypassing the light-emitting element. The control circuit 330 and the digital processing circuit 310 are shown as separate elements. In some aspects, the driver circuit 300 may include a single component implementing the functionalities of the control circuit 330 and digital processing circuit 310. For example, the processing circuit 220 in FIG.2A to 2D may implement the functionalities of the control circuit 330.

[0076] FIG.4A and FIG.4B show a configuration of a safety circuit 400 in a schematic representation, according to various aspects. In general, the safety circuit 208 may be realized in any suitable manner that enables the controlled disconnection of the electrically conductive path. The safety circuit 400 is a preferred realization of the safety circuit 208, which has been found to provide a simple, yet reliable and efficient implementation of the safety mechanism proposed herein. It is understood that FIG.4A and FIG.4B show a scenario with a single lightemission unit 210, but the aspects discussed in relation to the safety circuit 400 may apply to each light-emission unit 210 of the driver circuit 200.

[0077] According to various aspects, the safety circuit 400 may include (or consists of) a fuse element 402 disposed along the electrically conductive path 206. Illustratively, the driver circuit 200 may include, as safety circuit 400, a fuse element 402 operable to cause the permanent disconnection of the electrically conductive path 206. As generally known, a “fuse element” is an electrically conductive component configured to intentionally fail or break upon receiving current (or voltage) above a certain threshold. The breakage of the fuse element interrupts the electrical circuit. The safety circuit 400 being operable to cause the permanent disconnection of the electrically conductive path 206 may thus include the fuse element 402 being operable to cause a permanent breakage of the fuse element 402, thereby causing the permanent disconnection of the electrically conductive path 206. A “fuse element” may also be referred to herein simply as fuse.

[0078] If failure of the current delivery circuit 204 is detected, the processing circuit 220 may be configured to cause a permanent breakage of the fuse element 402. For example, the processing circuit 220 may cause a current flow through the fuse element 402, the current flow being greater than a predefined current threshold to cause a permanent breakage of the fuse element 402. As another example, the processing circuit 220 may cause a voltage drop across the fuse element 402, the voltage drop being greater than a predefined voltage threshold to cause the permanent breakage of the fuse element 402.

[0079] The fuse element 402 may have any suitable configuration known in the art. For example, the fuse element 402 may include or consist of any suitable material, such as metal alloys (e.g., copper-zinc alloy), ceramic-based composites, carbon-based materials, and the like. In a preferred configuration the fuse element 402 may include or consist of polysilicon. Poly silicon may be advantageous as the breakage of the fuse element 402 occurs via the effect of migration at a corresponding current density. Exploiting electromigration rather than thermal fusing ensures a more localized breakage, thus reducing the risk of undesired damages to other components of the driver circuit 200.

[0080] In a corresponding manner, the fuse element 402 may have any suitable shape. For example, the fuse element 402 may be or include a thin-film structure. As another example, the fuse element 402 may be or include a three-dimensional structure. In a preferred configuration, as shown in FIG.4B, the fuse element 402b may have a tapered shape. Illustratively, the fuse element 402b may have a dimension or cross-sectional area that gradually decrease along its length or axis. The size of the fuse element 402 may gradually vary along its longitudinal axis. For example, as shown in FIG.4B, the fuse element 402b may have a dimension that gradually decreases from a first value at a first end of the fuse element 402b to a smaller second value at the center of the fuse element 402b, and then gradually increases back to the first value at a second end of the fuse element 402b. It is however understood that the fuse element 402b may have any suitable tapered shape, and that the smallest cross-section may be at any suitable location along the axis of the fuse. The tapered shape of the fuse element 402b may facilitate the breakage of the fuse at its smallest point, thus providing a reliable and resource-efficient safety mechanism.

[0081] In the preferred configuration the fuse element 402b may thus include polysilicon and further may have a tapered shape, such that the current flow (or voltage drop) may induce electromigration towards the tapered portion thereby causing the permanent breakage of the fuse element 402b at the tapered portion.

[0082] Various options exist for the driver circuit 200 to cause the breakage of the fuse element 402b. For example, the driver circuit 200 may include a dedicated current source configured to generate a current greater than the current threshold for breaking the fuse element 402b, or a dedicated voltage source configured to generate a voltage greater than the voltage threshold for breaking the fuse element 402b. The processing circuit 220 may control the current source or voltage source to deliver the current or voltage at the fuse element 402 in case of failure of the current delivery circuit 204. The dedicated current source or voltage source may be common to all the light-emission units 210 of the driver circuit 200. As an alternative configuration, each light-emission unit 210 may include a dedicated current source or voltage source to enable breaking the fuse element 402 of that light-emission unit 210.

[0083] In case the driver circuit 200 includes a plurality of light-emission units 210, as shown in FIG.2B, the driver circuit 200 may include a reference current source common to all the light-emission units 210 (or at least common to a subset of light-emission units 210). The reference current source may generate a reference current for the delivery of current at the output terminals 202 (illustratively, a reference current for the light emission). In this scenario, each current delivery circuit 204 may receive the common reference current and use thereference current for the delivery of current to the respective output terminal 202. In case of failure of a current delivery circuit 204, the processing circuit 220 may be configured to transmit a control signal to each current delivery circuit 204 to cause the current delivery circuit 204 to refrain from delivering current to the respective output terminal 202, and may control the reference current source to increase the reference current above a predefined current threshold for the breaking of the fuse elements 402.

[0084] Illustratively, the processing circuit 220 may instruct the current delivery circuits 204 not to deliver current at the respective output terminal. However, the malfunctioning current delivery circuit 204 in the “permanently ON” state would not respond to the instruction due to the failure, and thus the increased reference current would still flow through the respective electrically conductive path 206, thereby causing the breakage of the fuse element 402, 402b disposed along the path 206. The reference current being above the predefined current threshold causes the breakage of the fuse element 402 of the safety circuit 208 associated with the current delivery circuit 204 for which the failure was detected, while not affecting the other circuits thanks to the instruction by the processing circuit 220. This approach allows implementing the safety mechanism without the need for additional components, but rather exploiting the reference current source already present in the driver circuit 200.

[0085] FIG.5A to FIG.5C show a configuration of a current delivery circuit 500 in a schematic representation, according to various aspects. In general, the current delivery circuit 204 may be realized in any suitable manner that enables the controlled delivery of current to the output terminal 202, and corresponding regulated light emission. The current delivery circuit 500 is a preferred realization of the current delivery circuit 204, which has been found to provide a simple, yet reliable and efficient implementation of the safety mechanism proposed herein, e.g., in combination with fuse elements 402. It is understood that FIG.5 A to FIG.5C show a scenario with a single light-emission unit 210, but the aspects discussed in relation to the current delivery circuit 500 may apply to each light-emission unit 210 of the driver circuit 200.

[0086] In some aspects, the current delivery circuit 500 may include a switchable element 502 configured to selectively enable or disable the current flow towards the output terminal 202. Illustratively, the switchable element 502 may be operable to selectively allow or prevent delivering current to the output terminal 202, thereby selectively allowing or preventing light emission by the corresponding light-emitting element. In some aspects, the current delivery circuit 500 may include a plurality of switchable elements 502 operable, in combination, to selectively enable or disable the flow of current towards the output terminal 202.

[0087] The switchable element(s) 502 may have any suitable configuration to implement the selective delivery of current to the output terminal 202. In general, a switchable element 502 may be configured to receive a control signal (e.g., a duty-cycle signal), and to selectively allow or prevent delivery of the current to the output terminal 202 according to the received control signal. In particular, the switchable element(s) 502 may be operable to selectively allow or prevent a current flow to the output terminal 202 according to the duty cycle defined by a received duty-cycle signal.

[0088] As an exemplary realization, a switchable element 502 may be or include a transistor, for example a field-effect transistor (FET), a metal-oxide semiconductor field-effect transistor (MOSFET), a bipolar junction transistor (BJT), and the like. For example, the switchable element 502 may be or include a N-MOS or P-MOS transistor. As known in the art, transistors provide a compact and efficient realization of switchable elements. It is however understood that in principle the switchable element 502 may be realized in any suitable manner, e.g., with any suitable element or any suitable combination of multiple elements to implement the switching functionality. Considering the configuration in which the switchable element 502 is a transistor, the control signal may be delivered to a control terminal of the transistor, e.g., its gate or its base. The control signal may thus enable or disable current flow between the source and drain terminals, or between the emitter and collector terminals of the transistor.

[0089] The control signal may have, for example, a first state (e.g., a high state, for example a logic 1) that causes the switchable element 502 to allow delivery of current to the output terminal 202, and a second state (e.g., a low state, for example a logic 0) that causes the switchable element 502 to prevent delivery of current to the output terminal 202. In case of a duty-cycle signal, the control signal may be in the first state for a certain portion of a light emission period, and may be in the second state for a complementary portion of the light emission period.

[0090] In this scenario, the failure of the current delivery circuit 500 leading to a permanently ON state may include a failure of the switchable element(s) 502. Illustratively, the failure of the current delivery circuit 500 may include a state of one switchable element 502 (or more than one switchable element 502) in which the delivery of current to the output terminal 202 is permanently enabled. Stated differently, the failure of the current delivery circuit 500 may include a state of one switchable element 502 that inhibits or prevents selecting the disablement of the current flow to the output terminal 202. In this case, the switchable element 502 may behave as a short circuit, constantly delivering current to the output terminal 202.

[0091] As mentioned in relation to FIG.2A to FIG.2D, the processing circuit 220 of the driver circuit 200 may determine the occurrence of the failure based on electrical parameters of the current delivery circuit 500, in particular the processing circuit 220 may determine that a failure has occurred based on one or more electrical parameters associated with the switchable element 502 (e.g., of the transistors). For example, the processing circuit 220 may determine whether a failure has occurred based on a voltage drop across the switchable element 502 (e.g., a gatesource voltage of the transistor). As another example, the processing circuit 220 may determine whether a failure has occurred based on a resistance provided by the switchable element 502.

[0092] FIG.5B shows a preferred configuration in which the safety circuit 208 is realized by a fuse element 402 along the electrically conductive path 402, and in which the current delivery circuit 500 includes a plurality of current sources. In this scenario, the current delivery circuit 500 may include a first current source 504 configured to provide (e.g., generate) a first current, and a second current source 506 configured to provide (e.g., generate) a second current. Optionally the current delivery circuit 500 may include additional current sources, e.g., a third current source providing a third current, etc.

[0093] The first current may be different from the second current. In particular, the first current may be less than the predefined threshold current for causing the breakage of the fuse element 402, whereas the second current may be greater than the predefined threshold current for causing the breakage of the fuse element 402. The first current source 504 may thus be dedicated to the normal non-faulty operation of the current delivery circuit 500 to regulate the flow at the output terminal 202 for light emission. The second current source 506 may instead be dedicated to implementing the safety mechanism.

[0094] The first current source 504 may be operable to deliver the first current at the output terminal 202 according to the control signal received by the switchable element 502. The second current source 506 may be operable to cause a flow of the second current through the fuse element 402 in case of a failure of the current delivery circuit 500. The processing circuit 220 may thus control the second current source to cause the flow of the second current through the fuse element 402 in case of a failure of the current delivery circuit 500. For example, the current delivery circuit 500 may include a second switchable element 508 (e.g., a second transistor) configured to selectively enable or disable the flow of the second current through the fuse element 402. In case of failure, the processing circuit 220 may transmit a control signal to the second switchable element 508 to allow the second current to flow through the fuse element 402, thereby causing its breakage and disconnecting the electrically conductive path 206. The second switchable element 508 may be referred to herein as “fuse switch”.

[0095] The use of a dedicated individual current source allows a tailored adaptation of the current to the properties of the fuse element 402, thus enhancing the reliability and efficiency of the safety mechanism. The second current source 506 and second switchable element 508 are described in relation to the current delivery circuit 500, but may also be understood to be part of the safety circuit 208, 400.

[0096] As mentioned above, the current delivery circuit 500 may have any suitable configuration. In a relevant use case, the current delivery circuit 500 may include a current mirror, which may provide a simple and efficient configuration to provide amplification of an input current for driving light emission. Current mirrors are well known in the art. As an abridged overview, a current mirror may include an input branch (or master branch), and an output branch (a follower branch), and optionally one or more intermediate branches (e.g., for biasing). The current mirror may be configured to provide, as output current at the output branch, a replica (e.g., a magnified replica) of an input current received at the input branch.

[0097] Considering the configuration of the present disclosure, the output branch of the current mirror may be coupled with the output terminal 202, to allow delivering thereto the (amplified) replica of the reference current. Illustratively, the electrically conductive path 206 may be part of the output branch of the current mirror.

[0098] In this configuration, according to various aspects, the safety circuit may include a fuse element 402 disposed at the output branch of the current mirror. Additionally, the safety circuit may include a further fuse element disposed at the input branch of the current mirror. The further fuse element may be optional, but may be provided to ensure a correct dimensioning of the current mirror, e.g., to achieve a desired magnification factor for the replicated current. The further fuse element may thus be identical to the fuse element at the output branch. Upon detection of a failure, the further fuse element may be left intact, or may be broken as the fuse element at the output branch.

[0099] The specific implementation and architecture of a current mirror may be adapted depending on various considerations and desired properties, such as gain, bandwidth, noise, and the like. Current mirrors can be realized using various devices, including bipolar junction transistors (BJTs), field-effect transistors (FETs), operational amplifiers, and the like.

[0100] In this regard, FIG.5C shows an exemplary realization of a current delivery circuit and safety circuit, in which a current mirror and multiple fuse elements are provided. The configuration in FIG.5C may represent a preferred implementation of the scheme proposed herein, as it combines a convenient realization of the current delivery circuit with an efficientrealization of the safety mechanism. Illustratively, FIG.5C shows a light-emission unit 510 that may be a preferred realization of the light-emission unit 210 of the driver circuit 200a, 200b.

[0101] As shown in FIG.5C, the light-emission unit 510 may include a current mirror defined by two transistors 512, 514 (e.g., a first N-MOS and a second N-MOS). The current mirror may deliver a replica of a current Ii (provided by a first current source 516) at the input branch as output current at the output branch. The replicated output current may be the current for driving light emission by a light-emitting element 522 coupled at the output terminal 520. For example, the light-emitting element 522 may be a LED, or any other suitable type of light-emitting element as discussed above. In a preferred configuration, the transistors 512, 514 may be configured to magnify the current by a scaling factor N.

[0102] The light-emission unit 510 may further include a (first) switchable element 518, e.g., a further transistor, configured to selectively enable or disable the transfer of current from the input branch of the current mirror to the output branch of the current mirror, and correspondingly allow or prevent the delivery of current to the output terminal. As mentioned, the switchable element 518 may be controlled via a suitable control signal, e.g., a duty-cycle signal. The light-emission unit 510 may further include one or more input terminals 524 at which the light-emission unit 510 may receive a supply voltage, VDD.

[0103] Turning to the implementation of the safety mechanism, the light-emission unit 510 may include, as safety circuit, a first fuse element 526 at the input branch of the current mirror and a second fuse element 528 at the output branch of the current mirror. Furthermore, the lightemission unit 510 may include a dedicated (second) current source 530 configured to generate a (second) current greater than the threshold current for breaking the fuses (or at least for breaking the second fuse element 528), and a switchable element 532 (a fuse switch, e.g., a further transistor) to cause a flow of the second current through the fuse elements 526, 528 in case of failure. The second switchable element 532 may be operated in combination with the first switchable element 518, illustratively by controlling the first switchable element 518 to allow the transfer of current to the output branch, and controlling the second switchable element 532 to deliver the second (greater) current.

[0104] The second fuse element 528 at the output branch may be coupled between the input terminal 524 and the second transistor 514. In a preferred configuration, the second fuse element 528 may be coupled with the source terminal of the second transistor 514 (e.g., a NMOS), although also other types of coupling may be provided (e.g., with the drain).

[0105] Using the "fuse" switch 532 via an associated control signal, a selected pixel (via the "PWM" switch) may be selected and the fuse F2 may be triggered by the overcurrent. Thisdisconnects the pixel from the VDD supply voltage and transfers it from the permanent "ON" state to "Open", which is perceived as much less critical. In both error modes (self-conducting transistor and faulty "PWM" switch), the fuse F2 can be triggered.

[0106] As mentioned, the fuse elements 526, 528 may be tapered and / or may include polysilicon. In a CMOS process, a fuse may be designed as a polysilicon conductor track that is tapered at a defined position and provokes a dissolution of the tapered conductor track via the effect of migration at a corresponding current density.

[0107] FIG.6 shows a schematic flow diagram of a method 600 of operating a driver circuit, according to various aspects. Aspects described with respect to a configuration of the driver circuit 200 may also apply to the method 600 and vice versa.

[0108] The method 600 may include, in 610, detecting a failure of a current delivery circuit of the driver circuit, wherein the current delivery circuit is operable to control a delivery of current to an output terminal of the driver circuit via an electrically conductive path. For example, the method 600 may include detecting the failure based on one or more electrical parameters associated with the current delivery circuit.

[0109] The method 600 may further include, in 620, causing a permanent disconnection of the electrically conductive path in response to detecting the failure of the current delivery circuit. For example, the method 600 may include causing a breakage of a fuse element disposed along the electrically conductive path. For example, the method 600 may include causing a flow of current through the fuse element, wherein the current is greater than a threshold current to cause the breakage of the fuse element.

[0110] Considering a scenario with a light-emitting device including a plurality of lightemitting elements, e.g., a plurality of pixels, a corresponding method 600 may include: detecting a failure associated with a light-emitting element (e.g., a pixel), and causing a permanent deactivation of that light-emitting element in response to detecting the failure. For example, the method may include detecting that a light-emitting element is permanently emitting light, and causing the light-emitting element to go into a state in which the lightemitting element is permanently prevented from emitting light in response to detecting the failure.

[0111] In some aspects, a computer program product may be provided. The computer program product may include instructions which, when the program is executed by a computer (e.g., by a processing circuit), cause the computer to carry out the method 600.

[0112] The terms “processor”, “processing circuit”, or “control circuit” as used herein may be understood as any kind of technological entity that allows handling of data. The data may behandled according to one or more specific functions that the processor / processing circuit / control circuit may execute. Further, a processor / processing circuit / control circuit as used herein may be understood as any kind of circuit, e.g., any kind of analog or digital circuit. A processor / processing circuit / control circuit may thus be or include an analog circuit, digital circuit, mixed-signal circuit, logic circuit (e.g., a hard-wired logic circuit or a programmable logic circuit), microprocessor, Central Processing Unit (CPU), Graphics Processing Unit (GPU), Digital Signal Processor (DSP), Field Programmable Gate Array (FPGA), integrated circuit, Application Specific Integrated Circuit (ASIC), etc., or any combination thereof. It is understood that any two (or more) of the processors / processing circuits / control circuits detailed herein may be realized as a single entity with equivalent functionality or the like, and conversely that any single processor / processing circuit / control circuit detailed herein may be realized as two (or more) separate entities with equivalent functionality or the like.

[0113] The term “connected” may be used herein with respect to terminals, integrated circuit elements, devices, and the like, to mean electrically connected, which may include a direct connection or an indirect connection, wherein an indirect connection may only include additional structures in the current path that do not influence the substantial functioning of the described circuit or device. The term “electrically conductively connected” that is used herein to describe an electrical connection between one or more terminals, devices, regions, contacts, etc., may be understood as an electrically conductive connection with, for example, ohmic behavior, e.g. provided by a metal or degenerate semiconductor in absence of p-n junctions in the current path. The term “electrically conductively connected” may be also referred to as “galvanically connected”. The term “coupled” may be used herein in the same manner as the term “connected”.

[0114] The term “terminal” may be used herein to describe a location (e.g., a point) or structure of a device or of an element of the device at which a signal (e.g., an analog signal, for example a current or a voltage) may be provided and / or to which another device or element may be connected. Illustratively, a terminal may be a location or a structure that is electrically conductively connected with the device or the element. A terminal may also be referred to herein as port, pin, contact, or contact point.

[0115] The word “exemplary” is used herein to mean “serving as an example, instance, or illustration”. Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs.

[0116] The phrase “at least one” and “one or more” may be understood to include a numerical quantity greater than or equal to one (e.g., one, two, three, four, [...], etc.). The phrase “at leastone of’ with regard to a group of elements may be used herein to mean at least one element from the group consisting of the elements. For example, the phrase “at least one of’ with regard to a group of elements may be used herein to mean a selection of one of the listed elements, a plurality of one of the listed elements, a plurality of individual listed elements, or a plurality of a multiple of individual listed elements.

[0117] All acronyms defined in the above description additionally hold in all claims included herein.

[0118] While the invention has been particularly shown and described with reference to specific aspects, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes, which come within the meaning and range of equivalency of the claims, are therefore intended to be embraced.List of reference signs 320 Power management circuit322 Temperature sensor100 Pixel 324 Thermal shutdown circuit102 Light-emitting diode 326 Control terminals104 Transistor 328 Switchable elements106 Transistor 330 Control circuit108 Current source 332 Current source110 Switch 400 Safety circuit200 Driver circuit 402 Fuse element200a Configuration 402b Fuse element200b Configuration 500 Current delivery circuit202 Output terminal 502 Switchable element204 Current delivery circuit 504 First current source206 Electrically conductive path 506 Second current source208 Safety circuit 508 Second switchable element210 Light-emi ssion unit 510 Light-emission unit212 Input terminal 512 First transistor214 Supply terminal 514 Second transistor220 Processing circuit 516 First current source222 Communication interface 518 First switch250 Light-emitting device 520 Output terminal250c Configuration 522 Light-emitting element250d Configuration 524 Input terminal252 Light-emitting element 526 First fuse element300 Driver circuit 528 Second fuse element302 Supply terminal 530 Second current source304 Data terminals 532 Second switch306 Test terminals 600 Method308 Reference terminal 610 Method step310 Digital processing circuit 620 Method step312 Memory314 Control signal316 Reversal protection circuit318 Overvoltage detection circuit

Claims

Claims1. A driver circuit (200) comprising: an output terminal (202) configured to be coupled with a light emitting element (252); a current delivery circuit (204) operable to control a delivery of current to the output terminal (202) via an electrically conductive path (206) for controlling a light emission by the light emitting element (252); and a safety circuit (208) operable to cause a permanent disconnection of the electrically conductive path (206) for the delivery of current to the output terminal (202).

2. The driver circuit (200) according to claim 1, further comprising a processing circuit (220) configured to: detect a failure of the current delivery circuit (204); and operate the safety circuit (208) to cause the permanent disconnection of the electrically conductive path (206) if the failure of the current delivery circuit (204) is detected.

3. The driver circuit (200) according to claim 2, wherein the current delivery circuit (204, 500) comprises one or more switchable elements (502) to selectively enable or disable the delivery of current to the output terminal (202), and wherein the failure of the current delivery circuit (204, 500) comprises a state of the one or more switchable elements (502) in which the delivery of current to the output terminal (202) is permanently enabled.

4. The driver circuit (200) according to any one of claims 1 to 3, further comprising an input terminal supply terminal (212) configured to be coupled with a supply source,wherein the electrically conductive path (202) is an electrically conductive path between the supply terminal (212) and the output terminal (202).

5. The driver circuit (200) according to any one of claims 1 to 4, wherein the safety circuit (208, 400) comprises a fuse element (402) disposed along the electrically conductive path (206); and wherein the safety circuit (208, 400) being operable to cause the permanent disconnection of the electrically conductive path (206) comprises the fuse element (402) being operable to cause a permanent breakage of the fuse element (402), thereby causing the permanent disconnection of the electrically conductive path (206).

6. The driver circuit (200) according to claim 5, wherein the processing circuit (220) is configured to cause a current flow through the fuse element (402) upon detection of the failure of the current delivery circuit (204), wherein the current flow is greater than a predefined threshold current to cause a permanent breakage of the fuse element (402).

7. The driver circuit (200) according to claim 5 or 6, wherein the fuse element (402) has a tapered shape.

8. The driver circuit (200) according to claim 5 to 7, wherein the fuse element (402) comprises or consists of polysilicon.

9. The driver circuit (200) according to any one of claims 5 to 8, wherein the current delivery circuit (204, 500) comprises a first current source (504) configured to provide a first current at the electrically conductive path (206),wherein the current delivery circuit (204, 500) further comprises a second current source (506) configured to provide a second current at the electrically conductive path (206), wherein the first current is less than the predefined threshold current for causing the breakage of the fuse element (402), and wherein the second current is greater than the predefined threshold current for causing the breakage of the fuse element (402), and wherein the processing circuit (220) is configured to control the second current source (506) to cause a flow of the second current through the fuse element (402) upon detection of the failure of the current delivery circuit (204, 500).

10. The driver circuit (200) according to any one of claims 1 to 9, wherein the current delivery circuit (204, 500) comprises a current mirror having an input branch and an output branch, wherein the output branch of the current mirror is coupled with the output terminal (202) and the electrically conductive path (206) is at the output branch of the current mirror, wherein the current mirror is configured to receive an input current at the input branch and to provide, at the output branch, a replica of the input current as output current, wherein the safety circuit (204, 400) comprises a first fuse element (402) disposed at the input branch of the current mirror and a second fuse element (402) disposed at the output branch of the current mirror.

11. The driver circuit (200, 200b) according to any one of claims 1 to 10, further comprising: a plurality of output terminals (202) comprising the output terminal (202) and one or more further output terminals (202), wherein each output terminal (202) is configured to be coupled with a respective light emitting element (252);a plurality of current delivery circuits (204) comprising the current delivery circuit (204) and one or more further current delivery circuits (204), wherein each current delivery circuit (204) is configured to control a delivery of current to a respective output terminal (202) of the plurality of output terminals (202) via a respective electrically conductive path (206) for controlling a light emission by the respective light emitting element (252); and a plurality of safety circuits (208) comprising the safety circuit (208) and one or more further safety circuits (208), wherein each safety circuit (208) is operable to cause a permanent disconnection of a respective electrically conductive path (206) for the delivery of current to a respective output terminal (202) of the plurality of output terminals (202).

12. The driver circuit (200, 200b) according to claim 11, wherein each safety circuit (208, 400) comprises a fuse element (402) disposed along the respective electrically conductive path (206), wherein the driver circuit (200, 200b) comprises a reference current source configured to generate a reference current common to each current delivery circuit (204) of the plurality of current delivery circuits (204); and wherein the processing circuit (220) is further configured to: upon detection of a failure of one of the current delivery circuits (204), transmit a control signal to each current delivery circuit (204) to cause the current delivery circuits (204) to refrain from delivering current to the respective output terminal (202); and control the reference current to increase the reference current above the predefined threshold current, thereby causing a breakage of the fuse element (402) associated with the current delivery circuit (204) for which the failure was detected.

13. The driver circuit (200, 200b) according to claim 11 or 12, wherein the processing circuit (220) is further configured to transmit a control signal to the current delivery circuits (204) to instruct a control of the current flow to therespective output terminal (202), after one electrically conductive path (206) associated with one of the current delivery circuits (204) for which a failure was detected was permanently disconnected.

14. The driver circuit (200, 200b) according to claim 13, wherein the processing circuit (220) is further configured to refrain from transmitting the control signal to the current delivery circuit (204) for which the failure was detected and for which the associated electrically conductive path (206) was permanently disconnected.

15. A light-emitting device (250, 250d) comprising: a plurality of pixels, wherein each pixel comprises a respective light emitting element (252); and a driver circuit (200, 200b) for driving a light emission via a delivery of current to the plurality of pixels, wherein the driver circuit (200, 200b) is configured to: detect a failure of a pixel of the plurality of pixels, and cause an irreversible disconnection of an electrically conductive path (206) for the delivery of current to that pixel.

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