Driver circuit and methods thereof

Abstract

The present disclosure relates to a light-emitting device (400) including: a plurality of pixels (402), wherein the plurality of pixels (402) are organized in a plurality of pixel blocks (404), wherein each pixel block (404) includes a respective subset of pixels (402) of the plurality of pixels (402); and a driver circuit (407) configured to: determine a phase-shift table (412) common to the plurality of pixel blocks (404), wherein the phase shift table includes, for each pixel (402) of a pixel block (404) of the plurality of pixel blocks (404), a respective phase-shift value; and for each pixel block (404) of the plurality of pixel blocks (404): determine a respective block driving signal (414) for driving light emission by the pixel block (404), wherein the block driving signal (414) comprises, for each pixel (402) of the pixel block (404), a respective duty-cycle signal for driving light emission by the pixel (402), wherein the duty-cycle signal is phase shifted by the phase shift value defined by the phase-shift table (412) for that pixel (402).

Description

[P96042]DRIVER CIRCUIT AND METHODS THEREOFTechnical Field

[0001] The present disclosure relates generally to a driver circuit configured to implement an adapted driving scheme for driving light emission by a plurality of pixels, and to methods thereof (e.g., a method of driving light emission by a plurality of pixels).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. For driving individual pixels in a display or an ensemble there are high demands in terms of dynamic range and homogeneity. Two approaches are commonly used for driving the pixels. A first approach is based on modulation in time, preferably via pulse width modulation (PWM), where a driving current is maintained at a constant value, and the ratio between on-time and off-time is varied to create a different impression of brightness. A second approach is based on amplitude modulation, in which the current is varied for each brightness value. Combinations of the two approaches are also known, where discrete amplitude settings are combined with PWM, wherein the amplitude is controlled for the entire display rather than pixel-by-pixel. Modulation-based schemes may however suffer from current peaks and electromagnetic interference (EMI) which may result from the driving of adjacent pixels with different duty-cycles. For example, current peaks and EMI may occur when driving multiple light-emitting diodes (LEDs) with PWM modulation. There is thus a need for improvements in driving schemes for lighting fixtures and display devices, which may be of particular relevance for the further advancement 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.1A and FIG. IB show a light-emitting device in a schematic representation, according to various aspects;[P96042]FIG.1C shows an exemplary realization of the light-emitting device in a schematic representation, according to various aspects;FIG.2A shows a pixel for use in a light-emitting device in a schematic representation, according to various aspects;FIG.2B to FIG.2D show exemplary realizations of the pixel in a schematic representation, according to various aspects;FIG.3 shows an exemplary duty-cycle signal in a schematic representation, according to various aspects;FIG.4 shows a light-emitting device in a schematic representation, according to various aspects;FIG.5 A shows a phase-shift table in a schematic representation, according to various aspects;FIG.5B and FIG.5C show exemplary realizations of the phase-shift table in a schematic representation, according to various aspects; andFIG.6A and FIG.6B show various graphs associated with light emission driven according to the scheme proposed herein, 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., 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, a commonly used driving scheme for controlling the delivery of electrical energy (e.g., current or voltage) from a power supply to a load is the so-called pulse width modulation (PWM), which may be applied for controlling light-emitting elements (e.g., LEDs), motors, battery chargers, solar panels, and the like. The PWM technique is based on pulsing the power supply on and off at a certain frequency and with a certain pulse width, thus allowing to control the amount of electrical energy delivered to the load over a certain period of time,[P96042] illustratively the average power delivered to the load. In general, the PWM driving scheme is well known in the art. Some basic concepts are described herein to introduce aspects relevant for the present disclosure.

[0006] 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.

[0007] A relevant use case for the PWM technique is the control of the brightness of light emitted by a light-emitting diode (LED), the so-called “dimming”. With PWM, a LED 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 frequency of the PWM signal should be sufficiently high to avoid flickering, i.e. the on / off frequency should be faster than the perception of the human eye (the so-called Flicker Fusion Rate). For LED dimming, the frequency of a PWM signal may be for example around 100 Hz.

[0008] For example, with a 100% duty cycle, i.e. a LED always on during a frame, a maximum brightness (illustratively, 100%), is obtained. Conversely, by maintaining the LED on only for a fraction of the duration of a frame, the brightness may be reduced (illustratively, dimmed) accordingly. Illustratively, with a 25% duty cycle the LED may be on for 25% of the duration of a frame, and the 25% of the maximum achievable brightness may be obtained, with a 50% or 75% duty cycle, the LED may be on for 50% or 75% of the duration of a frame, and the 50% or 75% of the maximum achievable brightness may be obtained, etc.

[0009] A LED has an amount of power for which the LED produces a maximum output (e.g., light at maximum brightness). The PWM technique is based on switching the LED on and off at high frequency so that the power perceived by the LED 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. PWM thus provides an approach in which a[P96042] current is fixed and a LED is switched on and off for periods of time to obtain a change in brightness based on the length of the periods.

[0010] PWM may thus provide a relatively simple scheme for dimming the maximum light intensity emitted from the LED, without changing the current of the driver. However, in case of multiple LEDs (e.g., connected to the same power supply), it may happen that if all PWM modulations are synchronized big current peaks appear when all LED are switched on together. In a corresponding manner almost zero current consumption may be observed at the end of the PWM period when all LED are off. This behaviour may generate a big current ripple. A high EMI could be also produced when driving all LED “on” together.

[0011] Aspects of the present disclosure may be directed to a driving scheme for delivering electrical power to a plurality of light-emitting pixels, adapted to overcome at least some of the limitations of conventional driving methods (e.g., classic PWM). The driving scheme may be based on applying a phase-shift to the individual driving signals, thus imposing a time-delay on the on-time and off-time of neighboring pixels. The phase-shift may thus avoid that all the pixels (or in general, a large number of pixels) go on and / or off at the same time, thus preventing current ripples and EMI. In more detail, the present disclosure may be based on the realization that the plurality of pixels may be logically divided into blocks, and a phase-shift table defining the phase-shifts for the pixels may be defined for one block and then repeated across the plurality of blocks. The repetition of a common phase-shift table may enable a simple, yet efficient driving scheme, which prevents current ripples and EMI, and ensures a reproducible and uniform behavior of the pixels across the array.

[0012] According to the proposed driving scheme, a phase-shift table may be defined that includes, for each pixel position within a pixel block, a respective phase-shift to be imposed onto a duty-cycle signal for driving the light emission from that pixel. The “on-times” and “off-times” for the pixels within the pixel block may thus be shifted in time with respect to one another, thus ensuring a current consumption at the block that does not present excessively high current peaks. Furthermore, the use of a repeated phase-shift table, rather than defining the phase-shifts individually for all the pixels, provides a resource-efficient approach for implementing the driving scheme.

[0013] According to various aspects, a light-emitting device includes: a plurality of pixels, wherein the plurality of pixels are organized in a plurality of pixel blocks, wherein each pixel block includes a respective subset of pixels of the plurality of pixels; and a driver circuit configured to: determine a phase-shift table common to the plurality of pixel blocks, wherein the phase-shift table includes, for each pixel of a pixel block (illustratively, for each pixel[P96042] position within the block), a respective phase-shift value; and for each pixel block of the plurality of pixel blocks: determine a respective block driving signal for driving light emission by the pixel block, wherein the block driving signal includes, for each pixel of the pixel block, a respective duty-cycle signal for driving light emission by the pixel, wherein the duty-cycle signal is phase-shifted by the phase-shift value defined by the phase-shift table for that pixel.

[0014] According to various aspects, a method of driving light emission by a plurality of pixels is provided, wherein the plurality of pixels are organized in a plurality of pixel blocks, wherein each pixel block includes a respective subset of pixels of the plurality of pixels, wherein the method includes: determining a phase shift table common to the plurality of pixel blocks, wherein the phase shift table includes, for each pixel of a pixel block (illustratively, for each pixel position within the block), a respective phase shift value; and for each pixel block of the plurality of pixel blocks: determining a respective block driving signal for driving light emission by the pixel block, wherein the block driving signal includes, for each pixel of the pixel block, a respective duty-cycle signal for driving light emission by the pixel, wherein the duty-cycle signal is phase shifted by the phase shift value defined by the phase shift table for that pixel.

[0015] The approach proposed herein may thus be understood as an adapted driving of a pixel array (e.g., a LED array) using a duty-cycle-based scheme (e.g., PWM) and reducing the current peaks. The proposed scheme applies to the driver circuit that drives the light emission by the pixels, but also to the control logic used to drive the driver (e.g., the LED driver).

[0016] In general, for controlling a pixel (e.g., including a LED) to emit light it may be preferable to control the current delivered to the pixel rather than the voltage applied to the pixel, because small variations in the voltage may cause large variations in the current conducted through the pixel. It may thus be difficult to precisely control the behavior relying on the voltage. Thus, in the present disclosure, particular reference may be made to the duty-cycle-based delivery of current according to the proposed driving scheme. Illustratively, particular reference may be made to a configuration in which the current delivered to the individual pixels is delivered according to the respective phase-shifted duty-cycle signal. It is however understood that the aspects described herein in relation to a delivery of current may apply in a corresponding manner to a delivery of voltage according to phase-shifted duty-cycle signals, and vice versa. For example, a voltage-based driving may be used for driving cells of a Liquid Crystal Display (LCD) device.

[0017] The term “duty-cycle signal” is used herein to describe a signal that represents a duty cycle for driving light emission by a pixel (illustratively, light emission by a light-emitting[P96042] element of the pixel, e.g., by a LED). 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”.

[0018] 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 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).

[0019] FIG.1A shows a light-emitting device 100 in a schematic representation according to various aspects. FIG. IB shows a further configuration 100b of the light-emitting device 100 of FIG.1A. In general, the light-emitting device 100 may include a plurality of pixels 102, each including a corresponding light-emitting element, as discussed in further detail below (see also FIG.2A to FIG.2D). The pixels 102 may thus be light-emitting pixels configured to receive an electrical signal (e.g., a current or a voltage) and emit light according to the received electrical signal. The light-emitting device 100 may represent a scenario in which the adapted driving scheme proposed herein is implemented (see also FIG.4). It is understood that the representation in FIG.1A and FIG. IB is exemplary to illustrate the relevant aspects of a light-emitting device 100 in which the proposed driving scheme may be applied. In this regard, the light-emitting device 100 may include any suitable number of pixels 102, arranged and organized in any suitable manner, as discussed in further detail below. It is also understood that the light-emitting device 100 may include additional components with respect to those shown.[P96042]

[0020] In a preferred configuration, the light-emitting device 100 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, modem headlamps may be provided with dense pixel matrices, to allow projecting a variety of light patterns. The driving scheme proposed herein may thus be of particular relevance to avoid current ripples and EMI in such devices.

[0021] It is however understood that the light-emitting device 100 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 100 may be (part of) a display device, a light projector, a light-based measurement system, a light-based communication system, and the like.

[0022] The light-emitting device 100 may include any suitable number of pixels 102 (and correspondingly, any suitable number of light-emitting elements). Only as a numerical example, the plurality of pixels 102 may include at least 10 pixels, e.g., at least 100 pixels, e.g., at least 1000 pixels, e.g., at least 10000 pixels. As another numerical example, the plurality of pixels 102 may include a number of pixels in the range from 10 to 107pixels, e.g., in the range from 103to 106pixels, e.g., in the range from 104to 105pixels.

[0023] The pixels 102 may be organized in a plurality of pixels blocks 104. Illustratively, the pixels 102 may be logically (sub-)divided into a plurality of pixel blocks 104, wherein each pixel block 104 includes a respective subset of pixels 102. A pixel block 104 may thus be understood as a group of pixels 102 that are logically grouped together. For example, the pixels 102 belonging to a pixel block 104 may be adjacent pixels. Illustratively, the pixels 102 of a pixel block 104 may be located next to one another within the light-emitting device 100. Each pixel 102 may be uniquely associated with a corresponding pixel block 104, so that each pixel 102 logically belongs to a single pixel block 104 among the plurality of pixels blocks 104. A “pixel block” may also be referred to herein as “pixel group”.

[0024] In general, the pixel blocks 104 may include the same number of pixels 102. With reference to FIG.1 A, a first pixel block 104-1 may include a first number of pixels 102, a second pixel block 104-2 may include a second number of pixels 102, and the first number of pixels 102 may be equal to the second number of pixels 102 (and to a third number of pixels of a third pixel block, etc.). Thus, in a preferred configuration for implementing the driving scheme proposed herein in an efficient manner, each pixel block 104 of the plurality of pixel blocks 104 may include the same number of pixels 102.[P96042]

[0025] It is however understood that in principle a configuration may be provided in which different pixel blocks 104 include different numbers of pixels 102. For example, the first number of pixels 102 may be different from the second number of pixels 102 (and from a third number of pixels of a third pixel block, etc.). For example, at least two pixel blocks 104 of the plurality of pixel blocks 104 may have the same number of pixels 102 (which may then be equal to or different from the number of pixels of a third pixel block, etc.).

[0026] In principle, the plurality of pixels 102 may be organized in any suitable number of pixel blocks 104. In general, the light-emitting device 100 may include a number of pixel blocks 104 suitable to logically cover all the pixels 102. For example, considering the scenario in which the pixel blocks 104 include the same number of pixels 102, the number of pixel blocks 104 may correspond to the total number of pixels 102 divided by the number of pixels 102 to be included in a pixel block 104.

[0027] In general, the plurality of pixels 102 may be arranged in any suitable manner, e.g., as a one-dimensional array of pixels 102, a two-dimensional array of pixels 102, with a non-symmetric distribution of pixels 102, and the like. The pixel arrangement may be adapted depending on the intended use and application of the light-emitting device 100. In a preferred configuration, the plurality of pixels 102 may be organized in a two-dimensional array. Illustratively, the plurality of pixels 102 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. A 2D-matrix may represent the most relevant use case for the proposed driving scheme, e.g., for applications in headlights for vehicles.

[0028] In a corresponding manner, the pixels 102 of a pixel block 104 may be arranged in any suitable manner. Illustratively, the pixels 102 of a pixel block 104 may be arranged as a one-dimensional array of pixels 102, a two-dimensional array of pixels 102, with a non-symmetric distribution of pixels 102, and the like. In general, the arrangement of a pixel block 104 may reproduce the arrangement of the light-emitting device 100. In the preferred configuration in which the pixels 102 are arranged in a two-dimensional matrix, each pixel block 104 may corresponds to a sub-portion of the two-dimensional matrix. In this configuration, each pixel block 104 may thus include a respective number of rows N1 and a respective number of columns Ml, with N1 and Ml being integer numbers greater than 1 (and less than N and M, respectively). In a preferred configuration that facilitates the implementation of the proposed driving scheme, at least one pixel block 104 (e.g., each pixel block 104) may have a number of rows N1 equal to the number of columns Ml.[P96042]

[0029] The number of pixels 102 logically associated together in the same pixel block 104 may be freely selected depending on system considerations. In general, a pixel block 104 includes a plurality of pixels 102, in particular more than two pixels, e.g., more than five pixels, e.g., more than ten pixels, e.g., more than twenty pixels. In a preferred configuration, a pixel block 104 may include a number of pixels 102 that is equal to a number of values that may be represented using an integer number of bits, in particular a number of bits greater than one. In particular, a pixel block 104 may include 256 pixels, for example arranged in a 16x16 matrix. Sub-dividing the pixels into blocks of 256 enables an efficient driving scheme, because in this case the driving scheme proposed herein may be defined using 8 bits (1 byte). Illustratively, 8 bits allow to represent values from 0 to 255, and thus in a 256-pixel configuration each pixel may be addressed using a corresponding value (which defines a corresponding phase-shift, as discussed in further detail below). In this scenario, the proposed driving scheme may thus be implemented in a computationally efficient manner.

[0030] According to various aspects, the total number of pixels 102 may thus be an integer multiple of the number of values that may be represented using the integer number of bits. In particular, the total number of pixels 102 of the light-emitting device 100 may be an integer multiple of 256, e.g., an integer multiple of a 16x16 unit addressable using 8 bits. As mentioned above, however, the proposed driving scheme is not limited to such configuration, and may be applied to any suitable number of pixels 102 and pixel blocks 104.

[0031] According to various aspects, as shown in FIG. IB for a configuration 100b of the lightemitting device 100, in addition to the logic subdivision into blocks 104, the pixels 102 of the light-emitting device 100 may be subdivided into a plurality of segments 106. Each segment 106 may include one or more pixel blocks 104, e.g., a plurality of pixel blocks 104 (illustratively, a respective subset of pixel blocks 104 having more than one pixel block 104 but less than the total number of pixel blocks 104). A segment 106 may thus be understood as a group of pixel blocks 104. Each pixel block 104 may be uniquely associated with a corresponding segment 106, so that each pixel block 104 belongs to a single segment 106 among the plurality of segments 106 (and accordingly each pixel 102 belongs to a single segment 106 among the plurality of segments 106). A “segment” may also be referred to herein as “pixel segment”.

[0032] In general, the segments 106 may include the same number of pixel blocks 104. With reference to FIG. IB, a first segment 106-1 may include a first number of pixel blocks 104, a second segment 106-2 may include a second pixel blocks 104, and the first number of pixel blocks 104may be equal to the second number of pixel blocks 104 (and to a third number of[P96042] pixel blocks 104 of a third segment, etc.). Thus, in a preferred configuration for implementing the driving scheme proposed herein in an efficient manner, each segment 106 of the plurality of segments 106 may include the same number of pixel blocks 104 (e.g., each including the same number of pixels 102).

[0033] It is however understood that in principle a configuration may be provided in which different segments 106 include different numbers of pixel blocks 104. For example, the first number of pixel blocks 104 may be different from the second number of pixel blocks 104 (and from a third number of pixel blocks 104 of a third segment 106, etc.). For example, at least two segments 106 of the plurality of segments 106 may have the same number of pixel blocks 104 (which may then be equal or different from the number of pixel blocks 104 of a third segment 106, etc.).

[0034] In principle, the plurality of pixels 102 may be organized in any suitable number of segments 106. In general, the light-emitting device 100 may include a number of segments 106 suitable to cover all the pixel blocks 104. For example, considering the scenario in which the segments 106 include the same number of pixel blocks 104, the number of segments 106 may correspond to the total number of pixel blocks 104 divided by the number of pixel blocks 104 included in a segment 106. As an exemplary configuration, which has been found to provide an efficient implementation of the driving scheme proposed herein, each segment 106 may include 6400 pixels 102, e.g., organized in twenty-five pixel blocks 104 of 16x16 pixels.

[0035] According to various aspects, while the division into blocks 104 may be at a logical level, the division into segments 106 may be at the hardware level. For example, each segment 106 may include respective analog circuitry and respective digital circuitry which are separate from the analog circuitry and digital circuitry of the other segments 106. Illustratively, analog circuitry and digital circuitry for enabling / controlling light emission may be replicated multiple times to define the plurality of segments 106.

[0036] In some aspects, each segment 106 may be an independent chip, e.g., including its own registers and a bus to transfer the data. The configuration with independent chips may simplify the design, making it scalable and avoiding chips that have excessively large dimensions, which would cause difficulties to close the timing and synchronize the signals in the digital part. For example, even in case of independent chips, the segments 106 may be formed on the same substrate (e.g., the same silicon) together with a main driver circuit 120 of the light-emitting device 100 and together with any further suitable circuit component (e.g., communication interfaces, data busses, and the like).[P96042]

[0037] According to various aspects, as shown in FIG. IB, each segment 106 may include a respective segment driver 110. A segment driver 110 may be a local control circuit configured to control the operation of the pixels 102 of the blocks 104 that belong to the segment 106. For example, the segment driver 110 may include a first circuit configured to control the pixels 102 to cause the pixels 102 to emit light. The first circuit may be for example a duty-cycle circuit configured to receive a duty-cycle signal from the main driver circuit 120, and to cause the pixels 102 to emit light according to the received a duty-cycle signal.

[0038] Illustratively, the duty-cycle circuit may be configured to cause an activation / deactivation of the light emitting elements of the pixels 102 belonging to the segment according to the duty cycle that the duty-cycle signal specifies for each pixel 102. In a preferred configuration, the duty-cycle circuit may be a PWM circuit configured to control the light emission by the pixels 102 according to a PWM signal provided by the main driver circuit 120.

[0039] For example, each segment driver 110 may receive a respective control signal by the main driver circuit 120 of the light-emitting device 100. The control signal may include instructions representative of a light emission to be carried out via the pixels 102 of the segment 106, and the segment driver 110 may be configured to control the light emission of the pixels 102 of the segment according to the instructions contained in the control signal. For example, the duty-cycle circuit may cause the pixels 102 to emit light with a duty cycle as defined by the control signal (e.g., by the duty-cycle signal). The main driver circuit 120 may thus be configured to implement a coordinated control of the light emission by the plurality of pixels 102 of the device 100, by delivering suitable control signals to the segment drivers 110 to obtain desired properties for the emitted light (e.g., to emit a certain light pattern, to emit light with a certain intensity, and the like).

[0040] In some aspects, the segment driver 110 may include a memory (e.g., a register, not shown) configured to store data and instructions for controlling the operation of the pixels 102 of the segment 106. For example, the memory may be configured or used to store information associated with the pixels 102 of the segment 106, e.g., their address, nominal voltage, emitted color, and the like. As a further example, the memory may be configured or used to store further graphics data, such as frame rate, predefined light patterns, and the like. As an example, the memory may be or include a video random access memory (VRAM).

[0041] Although not shown in detail, it is understood that the light-emitting device 100 may include one or more communication buses, one or more supply lines, or in general any suitable component to enable an operative coupling of the various components of the device 100 with one another and / or with other circuits disposed externally to the light-emitting device 100. For[P96042] example, the segment drivers 110 may be coupled with the main driver circuit 120 via a communication bus 114. For example, the segment drivers 110 may be coupled with the communication bus 114 in parallel with one another, and the communication bus 114 may enable one-directional or bi-directional communication between the main driver circuit 120 and the segment drivers 110. In a corresponding manner, each segment driver 110 may be coupled to the pixels 102 of the respective segment 106 via an electrical connection 112, e.g., an electrically conductive trace to allow the delivery of control signals (e.g., duty-cycle signals) from the segment driver 110 to the pixels 102.

[0042] In some aspects, the light-emitting device 100 may include a reference current common to all the pixels 102 and used by the pixels 102 for the light emission. Illustratively, the lightemitting device 100 may include a source of reference current (or a plurality of current sources generating the same reference current) and the reference current may be delivered to all the pixels 102 to be used for the light emission. In such configuration, the proposed driving scheme outlined below may be of particular relevance to prevent current spikes when a large number of pixels should be on at the same time and go off at the same time. As another exemplary component, each pixel 102 may be coupled to a supply line via which the pixel 102 receives a supply voltage.

[0043] FIG.1C shows a light-emitting device 150 in a schematic representation, according to various aspects. The light-emitting device 150 may be an exemplary realization of the lightemitting device 100 and may include a plurality of segments 156, each including a plurality of pixels organized in a plurality of pixel blocks. For example, the light-emitting device 150 may include 14 segments 156, each including twenty-five pixel blocks having a 16x16 matrix of pixels. The 14 segments 156 may thus include 80x80 pixels organized in a 5x5 matrix of pixel blocks. The full array may thus be composed from 14 segments for a total of 560x160 pixels.

[0044] For each segment 156, the light-emitting device 150 may include a corresponding segment driver 160. The segment driver 160 may include a duty-cycle circuit 162 (e.g., a PWM circuit), and a memory 164 (e.g., a plurality of VRAMs) for controlling the light emission by the pixels of the respective segment 156.

[0045] The light-emitting device 150 may further include one or more buses for a communicative coupling of the various segments 156 (e.g., with a main driver circuit, not shown). For example, the light-emitting device 150 may include a control bus coupled to the segments 156 for delivering control signals thereto. As another example, the light-emitting device 150 may further include a diagnostic bus 174 via which the segments 156 may deliver diagnostic information to the main control circuit, e.g., to report a status of the pixels of the[P96042] segment 156, thus allowing the main control circuit to detect malfunctions, damaged pixels, and the like.

[0046] As mentioned above, the pixels 102 may be light-emitting pixels. In this regard, FIG.2A to FIG.2D show exemplary configurations of a pixel 200a, 200b, 200c, 200d for use in a lightemitting device. Illustratively, the pixel 200a, 200b, 200c, 200d may be an exemplary configuration of a pixel 102 of the light-emitting device 100. The aspects discussed in relation to the pixels 200a, 200b, 200c, 200d in FIG.2A to FIG.2D may thus apply to the pixels 102 of FIG.1A and FIG. IB, and vice versa. It is understood that the configurations illustrated in FIG.2A to FIG.2D and a pixel 102 may have any suitable configuration known in the art.

[0047] In general, with reference to FIG.2A, a pixel 200a may include a light-emitting element 202 and a switchable element 204. The light emitting element 202 may be configured to emit light upon receiving an electrical signal (e.g., a current), and the switchable element 204 may be configured to enable a selective delivery of the electrical signal to the light-emitting element 202. Illustratively, the switchable element 204 may be configured to selectively allow or prevent a flow of electrical current through the light-emitting element 202, thus selectively enabling or disabling light emission by the light emitting element 202. The configuration of FIG.2A may be the general configuration of each pixel 102 of the light-emitting device 100. Exemplary detailed realizations are shown in FIG.2B to FIG.2D.

[0048] In the configuration in FIG.2A to FIG.2D, a pixel 200a-200d is shown to include a single light emitting element 202. This may be the most common configuration for general applications of the light-emitting device 100. It is however understood that in principle a pixel 200a-200d may include more than one light emitting element 202. For example, a pixel 200a- 200d may include a plurality of light emitting elements 202 (e.g., a plurality of LEDs) connected in series with one another, such that the switchable element 204 may allow or prevent the flow of electrical current through the series of light emitting elements to enable or disable light emission by the plurality of light emitting elements. This configuration may be provided, for example, to obtain more complex colors via the combination of the individual colors emitted by the light emitting elements 202.

[0049] In principle, the light-emitting element 202 may be of any suitable type. Considering the context of integrated circuits, the light-emitting element 202 may be or include a lightemitting diode (LED), e.g., the plurality of pixels 102 may each include at least one lightemitting diode. LEDs may be a preferred type of light emitting element 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[P96042] 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 the light-emitting element 202 may alternatively be of a different type, e.g., the light-emitting element 202 may be a laser diode, e.g., an edge emitting laser diode or a vertical cavity surface emitting laser diode. Considering the scenario in which a pixel 200a-200d includes more than one light-emitting element 202, the light-emitting elements of the pixel may be of the same type.

[0050] The light-emitting element 202 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), or ultraviolet 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.

[0051] Turning back to the configuration in FIG.1A and FIG. IB, the pixels 102 of the lightemitting device 100 may all include light-emitting elements of the same type (e.g., LEDs), but the individual properties of the light-emitting elements may be freely adapted across the plurality of pixels 102 to tailor the properties of the light emission. For example, light-emitting elements belonging to different pixels may emit light having different wavelength, or may have a different forward voltage, or may have different size, etc. In some aspects, the light-emitting elements belonging to different pixels 102 may be configured to emit light in different wavelength ranges. For example, a first light-emitting element of a first pixel may be configured to emit light in a first wavelength range (e.g., a first color, for example blue), a second lightemitting element of a second pixel may be configured to emit light in a second wavelength range (e.g., a second color, for example red), and a third light-emitting element of a third pixel may be configured to emit light in a third wavelength range (e.g., a third color, for example green), etc.

[0052] The switchable element 204 may have any suitable configuration to implement the selective delivery of an electrical signal to the light-emitting element 202. In general, the switchable element 204 may be configured to receive a control signal 206 (e.g., a duty-cycle signal), and to selectively allow or prevent delivery of the electrical signal to the light-emitting element 202 according to the received control signal 206. In particular, the switchable element 204 may be configured to selectively allow or prevent a current flow through the light-emitting element 202 according to the duty cycle defined by a received duty-cycle signal.

[0053] As an exemplary realization, the switchable element 204 may be or include a transistor, for example a field-effect transistor (FET), a metal-oxide semiconductor field-effect transistor[P96042](MOSFET), a bipolar junction transistor (BJT), and the like. For example, the switchable element 204 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 204 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.

[0054] Considering the configuration in which the switchable element 204 is a transistor, the control signal 206 may be delivered to a control terminal of the transistor, e.g., its gate or its base. The control signal 206 may thus enable or disable current flow between the source and drain terminals, or between the emitter and collector terminals of the transistor.

[0055] The control signal 206 may have, for example, a first state (e.g., a high state, for example a logic 1) that causes the switchable element 204 to allow delivery of the electrical signal to the light emitting element 202, and a second state (e.g., a low state, for example a logic 0) that causes the switchable element 204 to prevent delivery of the electrical signal to the light emitting element 202. In case of a duty-cycle signal, the control signal 206 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 (see also FIG.3).

[0056] As shown in FIG.2A, a pixel 200a may further include an input terminal 208, at which the pixel 200a may receive the electrical signal for the light emission. For example, the input terminal 208 may be configured to receive a reference current common to all the pixels of the light emitting device, and the switchable element 204 may selectively enable or disable flow of the reference current through the light-emitting element 202. As another example, the input terminal 208 may be configured to receive a voltage, and the switchable element 204 may selectively enable or disable a voltage drop across the light-emitting element 202 (to cause or prevent a corresponding current flow through the light-emitting element 202).

[0057] There may be various options to implement the switchable activation of the light-emitting element 202 via the switchable element 204. Some examples are shown in FIG.2B to FIG.2D, but it is understood that in principle any suitable configuration may be provided. Broadly speaking, the switchable element 204 may be configured to selectively connect or disconnect an electrically conductive path to enable or disable the delivery of the electrical signal to the light-emitting element 202. The type of electrically conductive path, and the type of connection / disconnection may be adapted depending on system considerations.

[0058] For example, the electrically conductive path may be between the input terminal 208 and the light-emitting element 202, such that the switchable element 204 may connect (close)[P96042] the path to couple the input terminal 208 and the light-emitting element 202 with one another, or disconnect (open) the path to decouple the input terminal 208 and the light-emitting element 202 from one another.

[0059] As another example, the electrically conductive path may be a low-resistance path parallel to the path that couples the input terminal 208 and the light-emitting element 202 with one another. The low-resistance path may have a lower resistance compared to the lightemitting element 202, such that the switchable element 204 may connect (close) the low- resistance path to cause current flow therethrough bypassing the light-emitting element 202, or disconnect (open) the low-resistance path to cause current flow through the light-emitting element 202.

[0060] FIG.2B to FIG.2D show exemplary realizations of a pixel 200b-200d, according to various aspects. The configurations in FIG.2B to FIG.2D are realized with exemplary components (e.g., LED, N-MOS transistors, resistors, etc.), but it is understood that the aspects discussed in relation to the exemplary realizations of FIG.2B to FIG.2D may be applied in a corresponding manner to configurations based on different components (e.g., different types of light-emitting elements, different types of switchable elements, etc.). It is also understood that the configurations in FIG.2B to FIG.2D may be simplified for purpose of illustration, and a pixel 200b-200d may include additional components with respect to those shown (e.g., capacitors, resistors, diodes, etc.).

[0061] In the configuration in FIG.2B and FIG.2C, a pixel 200b, 200c may include a LED 222 as light-emitting element, and a N-MOS transistor 224 as switchable element. Furthermore, the pixel 200b, 200c may include a control terminal 226 configured to receive the control signal for the N-MOS transistor 224 (e.g., the control terminal 226 may be coupled with the gate of the N-MOS). The pixel 200b, 200c may further include an input terminal 228 configured to receive an electrical signal (e.g., a voltage or a current) for causing light emission by the LED 222.

[0062] In the exemplary configuration in FIG.2B and FIG.2C, the pixel 200b, 200c may further include a first resistive element 225 (e.g., a first resistor) disposed between the control terminal 226 and the N-MOS. In this scenario, the control signal at the control terminal 226 may for example include a current, and the first resistive element 225 may provide a corresponding voltage at the gate of the N-MOS as gate voltage. As a further exemplary component, the pixel 200b, 200c may include a second resistive element 227 (e.g., a second resistor) disposed between the input terminal 228 and the LED 222.[P96042]

[0063] In the configuration in FIG.2B, the N-MOS 224 may be coupled between the LED 222 and a reference terminal 229 (e.g., ground), and the control signal may control the N-MOS 224 to connect the path between the LED 222 and the reference terminal 229, thus enabling flow of current through the LED 222, or may control the N-MOS 224 to disconnect the path between the LED 222 and the reference terminal 229, thus opening the circuit and disabling the flow of current through the LED 222.

[0064] In the configuration in FIG.2C, the N-MOS 224 may define a bypass path in parallel to the LED 222. The control signal may control the N-MOS 224 to connect the bypass path, thus diverting the flow of current from the LED 222 to the path through the N-MOS 224 (and then to ground), or may control the N-MOS 224 to disconnect the bypass path thus maintaining the flow of current through the LED 222.

[0065] In the configuration in FIG.2D, a pixel 200d may include a LED 232 as light-emitting element, and may include a current mirror defined by two transistors 235, 237 (e.g., a first N- MOS and a second N-MOS). The current mirror may deliver a replica of a reference current (provided by a current source 233) 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. For example, the current mirror may be dimensioned such that the output current is a multiple of the reference current.

[0066] For example, the first N-MOS 235 may be coupled with a first input terminal 238-1, and the second N-MOS 237 may be coupled with a second input terminal 238-2. The current source 233 may be coupled between the first N-MOS 235 and a reference terminal 239, and the LED 232 may be coupled between the second N-MOS 237 and another reference terminal 239.

[0067] In the configuration in FIG.2D, the pixel 200d may further include a switchable element 234 (e.g., a further transistor, e.g., a further N-MOS) configured to selectively enable or disable the operation of the current mirror. Illustratively, the switchable element 234 may receive a control signal 236 that controls the behavior of the switchable element 234 to allow the current mirror to replicate the reference current at the output branch, or to prevent the current mirror from replicating the reference current. The switchable element 234 may thus selectively allow the current mirror to conduct or prevent the current mirror from conducting.

[0068] FIG.3 shows a graph 300 illustrating an exemplary duty-cycle signal 302, according to various aspects. The duty-cycle signal 302 may be an exemplary realization of a control signal for controlling the light emission by a pixel, e.g., for controlling the switchable element of the pixel to selectively cause or prevent light emission by the corresponding light emitting element. The graph 300 shows the behavior of the signal S(t) over time, t. It is understood that the signal[P96042]302 is exemplary, to illustrate general aspects of a duty-cycle signal, and that a duty-cycle signal described herein may have any suitable parameters for controlling the light emission (e.g., any suitable frequency, duty cycle, modulation, etc.). Furthermore, the duty-cycle signal 302 may be a PWM signal, but it is understood that the aspects discussed in relation to the signal 302 may apply in a corresponding manner to other types of modulation that define a duty cycle (e.g., PFM, PDM).

[0069] In general, a duty-cycle signal 302 may have a frequency, f, that defines the period, T (as 1 / f), of the signal. Illustratively, the frequency defines the amount of time over which the duty cycle of the signal 302 is defined. The duty cycle of the signal 302 may thus be expressed as the % of the period, T, for which the signal 302 is ON. As shown in FIG.3, the signal 302 may have, during the period T, an on-time, toN, and an off-time, toFF. During the on-time, the signal 302 may be at a signal level SI (e.g., a certain voltage) that corresponds to a logic 1, and that activates light emission by a pixel. The signal level SI may define a first state of the signal 302 for controlling a switchable element to enable delivery of the electrical signal to the corresponding light-emitting element. For example, the signal level SI may be a voltage causing a voltage drop greater than a threshold voltage of a transistor used as switchable element. Given the above definition, the duty cycle of the signal 302 may be expressed as the ratio of the on-time to the period, i.e., as tox / T (in %).

[0070] During the off-time, the signal 302 may be at another signal level SO (e.g., a certain voltage, e.g., 0 V) that corresponds to a logic 0, and that deactivates light emission by a pixel. The signal level SO may define a second state of the signal 302 for controlling a switchable element to disable delivery of the electrical signal to the corresponding light-emitting element. For example, the signal level SO may be a voltage causing a voltage drop less than the threshold voltage of a transistor used as switchable element.

[0071] The adapted approach to driving light emission by a plurality of pixels will now be described in further detail in relation to FIG.4 to FIG.6B. In this regard, particular reference will be made to the configuration of a light emitting device, pixel, signals, etc. discussed above in relation to FIG.1A to FIG.3. It is however understood that the proposed approach may be generally applicable to any suitable “light-emitting scenario”.

[0072] FIG.4 shows a light-emitting device 400 adapted according to the driving scheme proposed herein. The light-emitting device 400 may be configured as the light-emitting device 100 of FIG.1 A and FIG. IB, and include a plurality of pixels 402 organized in a plurality of pixel blocks 404 (and, in some aspects, in a plurality of segments). The aspects discussed in[P96042] relation to the light-emitting device 100, pixels 102, blocks 104, segments 106, etc. apply also to the light-emitting device 400, pixels 402, blocks 404, segments (not shown), and vice versa.

[0073] The light-emitting device 400 may include a driver circuit 407 coupled to a memory 409. The memory 409 may be configured to store instructions (e.g., software instructions) executed by the driver circuit 407. The instructions may cause the driver circuit 407 to perform an adapted method 410 of driving light emission by a plurality of pixels 402, which is described in further detail below. Aspects described with respect to a configuration of the driver circuit 407 may also apply to the method 410 and vice versa. In some aspects, the driver circuit 407 may be an integrated circuit to which the pixels 402 are coupled (e.g., the driver circuit 407 may be coupled with segment drivers of the light-emitting device 400). For example, the driver circuit 407 may include one or more processors configured to carry out the method 410. The driver circuit 407 may be an adapted configuration of the main driver circuit 120 discussed in relation to FIG. IB.

[0074] According to the adapted method 410, the driving circuit 407 may be configured to determine a phase-shift table 412 common to the plurality of pixel blocks 404. Illustratively, the driving circuit 407 may be configured to define (e.g., calculate, or retrieve from memory 409) a phase-shift table 412 to be used for each of the pixel blocks 404 that should emit light (e.g., for at least for a subset of the pixel blocks 404) for controlling the light emission by the respective pixels 402.

[0075] The phase-shift table 412 may include, for each pixel position within a pixel block 404, a respective phase-shift value. Illustratively, the phase-shift table 412 may specify, for each pixel 402 of a pixel block 404, a respective phase-shift to be used for phase-shifting a duty-cycle signal for driving the light emission by that pixel. The phase-shift table 412 may thus include a plurality of phase-shift values, one for each pixel 402 in a pixel block 404.

[0076] As mentioned, the phase-shift table 412 may be common to the pixel blocks 404, so that the driver circuit 407 may use the same phase-shift table 412 for the light emission of each of the pixel blocks 404 that should emit light during a certain light-emission period. The repeated use of a single phase-shift table 412 across a plurality of pixel blocks 404 enables a simple, yet accurate approach for driving light emission while preventing current ripple and EMI.

[0077] Based on the phase-shift table 412, the driver circuit 407 may determine a respective block driving signal 414 for each pixel block 404. Illustratively, the driver circuit 407 may use the phase-shift table 412 to define, for each pixel block 404, a block driving signal 414 for driving light emission by the pixels 402 of the pixel block 404. The block driving signal 414 associated with a pixel block 404 may include, for each pixel 402 of the pixel block 404, a[P96042] respective duty-cycle signal for driving light emission by that pixel 402. Based on the phaseshift table 412, the duty-cycle signal for a pixel 402 may be phase-shifted by the phase-shift value defined by the phase-shift table 412 for that pixel 402.

[0078] A block driving signal 414 may thus include a plurality of duty-cycle signals, each having a phase-shift imposed thereon according to the phase-shift value defined by the phaseshift table 412 for that pixel position within the pixel block 404. For example, at least one dutycycle signal (e.g., the one corresponding to a first pixel 402 in the block 404) may be nonshifted, e.g., may have a phase-shift of 0. The other duty-cycle signals may be phase-shifted with respect to the non-shifted duty-cycle signal (acting as reference signal), each by a corresponding phase shift.

[0079] In a preferred configuration, the phase-shift table 412 may include a plurality of unique values defining the phase-shifts for the duty-cycle signals. Illustratively, in this configuration each duty-cycle signal may be phase-shifted by a unique phase-shift among the plurality of duty-cycle signals. The phase-shift value associated with a pixel position within a pixel block 404 may thus be a unique phase-shift value in the phase shift table 412. This approach minimizes the current ripple and EMI. It is however understood that, in principle, some of the phase-shifts may be repeated across the phase-shift table 412, e.g., to simplify the overall processing steps. For example, in this other configuration, the phase-shift table 412 may include a predefined set of phase-shift values that are repeated across the phase-shift table 412.

[0080] The phase-shifting of the duty-cycle signals ensures that a time delay is introduced in the activation / deactivation of the pixels 402, such that it may be avoided that an excessively large number of pixels draw current or stop drawing current at the same time. In this regard, the phase-shift table 412 may also be understood as a time-delay table, defining for each pixel 402 in a pixel block 404 a respective time-delay to be imposed to the respective duty-cycle signal (e.g., a unique time-delay among the plurality of duty-cycle signals). By way of illustration, the phase-shift table 412 may define, for each pixel 402 of a pixel block 404, a respective start time for the start of the period of the duty-cycle signal that drives light emission by that pixel 402.

[0081] The specific duty-cycles for the light emission by the pixels 402 may be freely adapted depending on the emission to be obtained. Illustratively, the duty cycle to be used for each pixel 402 varies depending on the light to be emitted by the device 400 (e.g., according to the brightness of each pixel 402), so that the duty-cycle signals may define the duty cycles for the pixels 402 and in addition may be phase-shifted with respect to one another. As mentioned, in some aspects the light-emitting device 400 may have a reference current common to all the[P96042] pixels 402, and the duty-cycle signals may control the delivery of the reference current to the pixels 402.

[0082] The phase-shift table 412 may be configured in any suitable manner, taking into consideration the configuration of the pixel blocks 404. In general, the phase-shift table 412 may have the same dimensionality as the pixel blocks 404. In this regard, the phase-shift table 412 may include a one-dimensional array of values, a two-dimensional array of values, an array with a random distribution of values, and the like. In a preferred configuration, the phase-shift table 412 may be a two-dimensional matrix having the same number of rows and columns as two-dimensional pixel blocks 404. Further aspects related to the phase-shift table 412 will be discussed in relation to FIG.5 A to FIG.5C.

[0083] In general, the driver circuit 407 may determine a number of block driving signals 414 equal to the number of pixel blocks 404 of the device 400. As shown in FIG.4, the driver circuit 407 may determine a first block driving signal 414-1 for driving light emission by the pixels 402 of a first pixel block 404-1, a second block driving signal 414-2 for driving light emission by the pixels 402 of a second pixel block 404-2,. . ., and an N-th block driving signal 414-N for driving light emission by the pixels 402 of an N-th pixel block 404, thus covering all the pixel blocks 404 of the device 400.

[0084] In some aspects, however, the driver circuit 407 may determine a number of block driving signals 414 less than the number of pixel blocks 404 of the device 400. This may be the case, for example, if some of the pixel blocks 404 should not emit any light during a certain light emission period. In this scenario, the driver circuit 407 may refrain from determining the block driving signals 414 for these pixel blocks 404, while determining the block driving signals 414 for the other pixel blocks 404 that should emit light in the light emission period. Alternatively, the driver circuit 407 may determine a block driving signal 414 for each pixel block 404 also in this case, with the block driving signal 414 of a block 404 that should not emit light including duty-cycle signals that define a duty cycle of 0.

[0085] As mentioned in relation to FIG.1 A, in a preferred configuration all the pixel blocks 404 may include the same number of pixels 402. However, the proposed approach may also be applicable to a configuration in which the pixel blocks 404 have different numbers of pixels. In this scenario, the phase-shift table 412 may have the dimensionality of the greatest pixel block(s), so that the phase-shift table 412 includes a plurality of phase-shifts corresponding to the greatest number of pixels 402 among the pixel blocks 404. In this case, the phase-shift values that would correspond to pixel positions that are not present in a smaller pixel block 404 may be ignored when defining the duty-cycle signal for that block 404.[P96042]

[0086] According to various aspects, the driver circuit 407 may be further configured to drive the light emission by the pixel blocks 404 using the block driving signals 414. Illustratively, the driver circuit 407 may cause the pixels 402 of a pixel block 404 to emit light according to the respective phase-shifted duty-cycle signal. Considering the configuration of FIG.2A, the driver circuit 407 may control the switchable element of a pixel belonging to a certain pixel block according to the phase-shifted duty-cycle signal defined for that pixel by the block driving signal 414 for that block 404.

[0087] In some aspects, the driver circuit 407 may receive a light emission signal representative of a target light emission to be obtained by the light emission of the plurality of pixels 402. For example, the light emission signal may be a light emission pattern signal representative of a light emission pattern to be defined by the light emission of the plurality of pixels. In some aspects, the driver circuit 407 may receive such light emission signal from an entity external to the device 400, e.g., from a central control unit of a vehicle in which the light-emitting device 400 is installed. As another example, the driver circuit 407 may retrieve the light emission signal from the memory 409 and control the pixels 402 accordingly. For example, the driver circuit 407 may be configured to determine a target light emission suitable for a current environment in which the device 400 is located, and determine which light emission or light emission pattern should be provided in that environment.

[0088] The driver circuit 407 may thus determine the block driving signals 414 according to the target light emission (e.g., according to the light emission pattern to be projected using the pixels 402). In this regard, the driver circuit 407 may determine the duty cycles for the pixels 402 to obtain a light emission (pattern) that matches the target light emission (pattern), and may then impose phase-shifts to such duty cycles according to the common phase-shift table 412.

[0089] According to various aspects, the phase-shift table 412 may be predefined. Illustratively, in this configuration, the phase-shift table 412 may be determined in advance, prior to a light emission period in which the block driving signals 414 should be determined. For example, the phase-shift table 412 may be defined at a fabrication stage, or at a subsequent calibration stage of the device 400. The predefined phase-shift table 412 may for example be stored in the memory 409, and the driver circuit 407 may retrieve the predefined phase-shift table 412 from the memory 409 to define the block driving signals 414. This approach facilitates the implementation of the proposed strategy.

[0090] In other aspects, the driver circuit 407 may be configured to generate (e.g., calculate) the phase-shift table 412 at the beginning of a light emission period. Illustratively, the driver circuit 407 may determine, on the fly, which phase-shifts to use for driving the light emission,[P96042] for example taking into account historic data related to current spikes and EMI of the device 400. This approach may be more computationally intensive but provides a greater flexibility for implementing the proposed approach.

[0091] The proposed approach may be implemented in a static manner or in a dynamic manner. The static implementation may be simpler, whereas the dynamic implementation may enhance the flexibility of the control over the light emission. Illustratively, light emission by the pixels 402 may occur over a plurality of light emission periods (illustratively, a plurality of time periods in which the pixels 402 emit light). The light emission periods may for example correspond to consecutive PWM periods, illustratively PWM periods that are subsequent to one another in time and in which different PWM parameters may be applied. For example, considering a display device, the light emission periods may be frames. In the static approach, the same phase-shift table 412 may be used over a plurality of consecutive light emission periods. In the dynamic approach, the phase-shift table 412 may vary from one light emission period to the next.

[0092] Considering for example a plurality of light emission periods including at least a first light emission period and a second light emission period (and optionally a third light emission period, etc.), in the static approach the phase-shift table 412 may define the same phase shifts in the first light emission period and in the second light emission period (and optionally in the third light emission period, etc.).

[0093] In the dynamic approach, the phase-shift table 412 may define different phase shifts in the first light emission period with respect to the second light emission period (and optionally in the third light emission period, etc.). In this scenario, the driver circuit 407 may determine a first phase-shift table for use in the first light emission period, and may determine a second phase-shift table for use in the second light emission period (and a third phase-shift table for use in the third light emission period, etc.). For example, the driver circuit 407 may retrieve different predefined tables from the memory 409, or may generate different tables in different light emission periods.

[0094] In the dynamic approach, one or more phase shift values of the first phase-shift table are different from corresponding one or more phase-shift values of the second phase-shift table. Illustratively, for the same pixel or pixel position within the pixel block, the first phase-shift table may define a different phase-shift value compared to the value defined by the second phase-shift table.

[0095] The difference between the phase shift values defined by different phase-shift tables 412 may be freely selected according to system considerations. For example, a 90° phase-shift[P96042] may be provided between the phase shift values of the first phase-shift table and the corresponding phase-shift values of the second phase-shift table. A 90° phase-shift may ensure a “decorrelation” of the light emission happening in different (e.g., consecutive) time periods, thus further reducing the risk of current ripple and EMI. For example, the 90° phase difference may be provided between initial phase-shift values of the tables, and then the remaining phaseshifts may be derived from such initial phase-shift values

[0096] As another example, a pseudo-random phase difference may be provided between the phase shift values of the first phase-shift table and the corresponding phase-shift values of the second phase-shift table. For example, the pseudo-random phase difference may be provided between initial phase-shift values of the tables, and then the remaining phase-shifts may be derived from such initial phase-shift values. The use of pseudo-random phase differences may reduce the risk of systematic errors that could otherwise affect the light emission.

[0097] Further aspects related to the phase-shift table(s) 412 will now be described in further detail in relation to FIG.5 A to FIG.5C.

[0098] FIG .5A shows a phase-shift table 512 in a schematic representation, according to various aspects. The phase-shift table 512 may be an example of the phase-shift table 412, so that the aspects discussed in relation to the phase-shift table 512 may apply to the phase-shift table 412, and vice versa. The phase-shift table 512 is represented as a two-dimensional matrix, to exemplarily illustrate the most relevant scenario, but the aspects discussed for the phase-shift table 512 apply correspondingly to other structures (e.g., to a one-dimensional table).

[0099] As discussed in relation to FIG.4, the phase-shift table 512 may include a plurality of phase-shift values 502. In FIG.5A, the phase-shift table 512 includes N phase-shift values, e.g., a first phase-shift value 502-1, a second phase shift-value 502-2, a third phase-shift value 502-3,. . ., a N-th phase-shift value 502-N. However, the phase-shift table 512 may include any suitable number of phase-shift values 502, depending on the configuration of the blocks of the light-emitting device.

[0100] As mentioned, in some aspects each phase-shift value 502 may be unique. Illustratively, the first phase-shift value 502-1 may be different from each other phase-shift value 502 of the table 512. The second phase-shift value 502-2 may be different from each other phase-shift value 502 of the table 512, etc. For example, unique phase-shift values 502 may be provided by defining the phase-shift values 502 individually.

[0101] As a more computationally-efficient alternative, a predefined phase-shift delta (illustratively, a predefined phase difference) may be used across the table to distinguish (e.g., increment) the phase-shift values 502. Illustratively, each phase-shift value 502 in the[P96042] phase-shift table 512 may differ from another phase-shift value 502 by the predefined phaseshift delta, which is constant over the table 512. For example, the first phase-shift value 502-1 may differ from the second phase-shift value 502-2 by the predefined phase-shift delta. The second phase-shift value 502-2 may differ from the third phase-shift value 502-3 by the predefined phase-shift delta (and the third phase-shift value 502-3 may differ from the first phase-shift value 502-1 by twice the delta), etc.

[0102] For example, the phase-shift delta may define an increment of the phase-shift, such that the phase-shift values increase from an initial phase-shift value (e.g., corresponding to the first phase-shift value 502-1) to a final phase-shift value (e.g., corresponding to the N-th phaseshift value 502-N) in discrete steps defined by the phase-shift delta.

[0103] In a preferred configuration, the phase-shift delta may be configured such that a phase shift difference between the initial phase-shift value and the final phase-shift value of the phase-shift table is 360°. The phase-shift delta may thus be adapted depending on the number of pixels in a pixel block to obtain the full phase-shift over the table 512. It is however understood that also other configurations may be provided, defining different phase-shifts depending on the desired application.

[0104] Considering the preferred configuration discussed in relation to FIG.1A, the phaseshift table 512 may include a number of phase-shift values that is equal to a number of values that may be represented using an integer number of bits, in particular a number of bits greater than one. In particular, considering the configuration with 256 pixels (e.g., in a 16x16 matrix), the phase-shift table 512 may include 256 phase-shift values. In this scenario, using 8-bits it is possible to represent values from 0 to 255, each associated with a corresponding phase-shift to be imposed to the duty-cycle signal of the corresponding pixel. In this case, the phase may be increased by 1 least significant bit (1 LSB) from one phase-shift value to the next, thus covering the full 0-255 range over the table.

[0105] This configuration is shown in the exemplary phase-shift table 550b of FIG.5B, which covers the range 0-255 corresponding to a phase-shift range from 0° to 360°, by incrementing by 1 LSB across the table 550b. The 16x16 phase shift table has a value that is increased by +1 LSB on every adjacent value on the table, so that a full 360° phase (256 LSB on 8 bit) is covered from the 16x16 table.

[0106] In some aspects, adjacent (in other words, consecutive, or neighboring) phase-shift values in the phase-shift table 512 may define a phase shift having opposite sign with respect to one another. In this configuration, the phase-shift table 512 may include phase-shift values having alternating sign, e.g., such that a first phase-shift value may have a positive sign, a[P96042] second phase-shift value may have a negative sign, a third phase-shift value may have again a positive sign, and so on. For example, adjacent phase-shift values in the phase-shift table 512 alternately increase by a first predefined phase-shift delta starting from a first initial phase shift value or decrease by a second predefined phase shift delta starting from a second initial phase shift value. This configuration may further contribute to the elimination of current ripple, by ensuring that adjacent pixels 402 become active / inactive at different time points.

[0107] This configuration is shown in the exemplary phase-shift table 550c of FIG.5C, which covers the range 0-255 by alternating the phase sign across the table 550c. The phase flipping provides a better spread of the phases of the pixels, especially in case that light patterns with very tiny horizontal rows or vertical lines of pixels are activated with high brightness. As shown in the table 550c, the phase is flipped every 2 pixels, and also the values are flipped left to right.

[0108] The strategy proposed herein may thus include using a small table (e.g., a small matrix) of phase-shift values that is repeated many times, and that may be varied (dynamically) over time. The small matrix repeated many times allows a simplified hardware implementation. The variation over time of the matrix allows a reduction of the EMI of current peaks. Considering LED applications, the proposed approach allows applying a uniform phase shifting to the LEDs to minimize load variations, and resulting also in reduced output capacitance, improved efficiency and reduced EMI.

[0109] Considering the configuration with 25 segments, repeating the phase-shift pattern 25 times inside the 80x80 segment, and having 14 segments, gives very good results on the average current consumption, without big ripples with many light test patterns. Experimental results in this regard are illustrated in FIG.6 A and FIG.6B.

[0110] FIG.6A shows various graphs 600a-640a illustrating a test light pattern (graph 600a) emitted using an array of pixels controlled via PWM. The graphs 610a shows the current in the array when the approach proposed herein is not applied. The graphs 620a to 640a refer to a scenario in which the “phase-shift-based” approach proposed herein is applied. In particular, the graph 620a shows the current in a PWM cycle. The graph 630a shows the Fast Fourier Transform (FFT) of the current ripple considering a “static” phase-shift in different light emission periods, and the graph 640a shows the FFT of the current ripple considering a “dynamic” phase-shift in different light emission periods. Correspondingly, FIG.6B shows various graphs 600b-640b illustrating another test light pattern (graph 600b) emitted using an array of pixels controlled via PWM and applying the “phase-shift-based” approach proposed herein. The graph 620b shows the current in a PWM cycle. The graph 630b shows the FFT of the current ripple considering a “static” phase-shift in different light emission periods, and the[P96042] graph 640b shows the FFT of the current ripple considering a “dynamic” phase-shift in different light emission periods.

[0111] As may be observed by making an FFT on the current along PWM cycle, there are some frequencies that produce slightly higher peaks. It may be possible to decrease the EMI with an external capacitor, but to further improve this concept and decrease the average EMI, the (variable) phase-shift PWM may be applied. The graphs show the results for an increase by 30° (21 LSB) of the phase shift, then every new PWM iteration an increase of the phase shift by 90° (64 LSB). As visible, a reduction in the current peaks in the FFT may be observed, making an average on more PWM cycles and having a better EMI performance.

[0112] The current ripple is very low for the selected algorithm (both % and absolute value) with the algorithm proposed with the 16x16 table repeated many times. A plot of the current ripple and FFT of current ripple with and without phase shifting over time is reported to show the EMI improvement.

[0113] 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 be handled 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.

[0114] 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[P96042] 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”.

[0115] 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.

[0116] 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.

[0117] 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 least one 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.

[0118] All acronyms defined in the above description additionally hold in all claims included herein.

[0119] 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.[P96042]List of reference signs 228 Input terminal232 Light-emitting diode100 Light-emitting device 233 Current source102 Pixel 234 Switchable element104 Pixel block 235 N-MOS Transistor104-1 First pixel block 236 Control signal104-2 Second pixel block 237 N-MOS Transistor106 Segment 238-1 Input terminal106-1 First segment 238-2 Input terminal106-2 Second segment 239 Reference terminal110 Segment Driver 300 Graph112 Electrical connection 302 Duty-cycle Signal114 Communication bus 400 Light emitting device120 Main control circuit 402 Pixel150 Light emitting device 404 Pixel block156 Segment 404-1 First pixel block160 Segment driver 404-2 Second pixel block162 Duty-cycle circuit 407 Driver circuit164 Memory 409 Memory172 Control bus 410 Method174 Diagnostic bus 412 Phase-shift table200a Pixel 414 Block driving signals200b Pixel 414-1 First block driving signal200c Pixel 414-2 Second block driving Signal200d Pixel 414-N N-th block driving Signal202 Light-emitting element 502 Phase-shift values204 Switchable element 502-1 First phase-shift value206 Control Signal 502-2 Second phase-shift value208 Input terminal 502-3 Third phase-shift value222 Light-emitting diode 502-N N-th phase-shift value224 N-MOS Transistor 512 Phase-shift table225 Resistor 550b Phase-shift table226 Control terminal 550c Phase-shift table227 Resistor 600a Light pattern[P96042] b Light patterna Graph a Graph b Graph a Graph b Graph a Graph b Graph

Claims

[P96042]Claims1. A light-emitting device (400) comprising: a plurality of pixels (402), wherein the plurality of pixels (402) are organized in a plurality of pixel blocks (404), wherein each pixel block (404) comprises a respective subset of pixels (402) of the plurality of pixels (402); and a driver circuit (407) configured to: determine a phase-shift table (412) common to the plurality of pixel blocks (404), wherein the phase shift table comprises, for each pixel (402) of a pixel block (404) of the plurality of pixel blocks (404), a respective phase-shift value; and for each pixel block (404) of the plurality of pixel blocks (404): determine a respective block driving signal (414) for driving light emission by the pixel block (404), wherein the block driving signal (414) comprises, for each pixel (402) of the pixel block (404), a respective duty-cycle signal for driving light emission by the pixel (402), wherein the duty-cycle signal is phase shifted by the phase shift value defined by the phase-shift table (412) for that pixel (402).

2. The light-emitting device (400) according to claim 1, wherein the driver circuit (407) is further configured to drive the light emission by the plurality of pixels (402) using the determined block driving signals (414).

3. The light-emitting device (400) according to claim 1 or 2, wherein adjacent phase-shift values in the phase-shift table (412, 512) differ from one another by a predefined phase-shift delta that is constant over the phase shift table (412, 512).[P96042]4. The light-emitting device (400) according to claim 3, wherein the predefined phase-shift delta is configured such that a phase-shift difference between an initial phase-shift value (502-1) and a final phase shift value (502-N) of the phase-shift table (412, 512) is 360°.

5. The light-emitting device (400) according to claim 1 or 2, wherein adjacent phase-shift values in the phase-shift table (412, 512) define a phase shift having opposite sign with respect to one another.

6. The light-emitting device (400) according to any one of claims 1 to 5, wherein the phase-shift value associated with a pixel (402) of a pixel block (404) is a unique phase-shift value in the phase-shift table (412, 512).

7. The light-emitting device (400) according to any one of claims 1 to 6, wherein to determine the phase-shift table (412, 512) common to the plurality of pixel blocks (404), the driver circuit (407) is further configured to: determine a first phase-shift table common to the plurality of pixel blocks (404) for use during a first light emission period; and determine a second phase-shift table common to the plurality of pixel blocks (404) for use during a second light emission period, wherein one or more phase-shift values of the first phase-shift table are different from corresponding one or more phase shift values of the second phase-shift table.

8. The light-emitting device (400) according to claim 7, wherein a first initial phase shift value of the first phase-shift table and a second initial phase shift value of the second phase-shift table differ from one another by 90°.[P96042]9. The light-emitting device (400) according to claim 7, wherein a first initial phase-shift value of the first phase-shift table and a second initial phase-shift value of the second phase-shift table differ from one another by a pseudo random phase difference.

10. The light-emitting device (400) according to any one of claims 1 to 9, wherein the plurality of pixels (402) is organized in a two-dimensional matrix, and wherein each pixel block (404) corresponds to a sub-portion of the two- dimensional matrix.

11. The light-emitting device (400) according to claim 10, wherein at least one pixel block (404) has a number of rows equal to a number of columns.

12. The light-emitting device (400) according to any one of claims 1 to 11, wherein at least one pixel block (404) comprises a number of pixels (402) that is equal to a number of values that are representable using an integer number of bits.

13. The light-emitting device (400) according to claim 12, wherein at least one pixel block (404) comprises 256 pixels (402), wherein preferably the 256 pixels are arranged in a 16 by 16 matrix.

14. The light-emitting device (400) according to any one of claims 1 to 13, wherein each pixel (200a, 402) comprises: a corresponding light emitting element (202) configured to emit light upon receiving an electrical signal, and[P96042] a corresponding switchable element (204) configured to enable a selective delivery of the electrical signal to the light-emitting element (202), wherein the duty-cycle signal for a pixel (402) defines a duty cycle for an activation or deactivation of the corresponding switchable element (204).

15. A method of driving light emission by a plurality of pixels, wherein the plurality of pixels is organized in a plurality of pixel blocks, wherein each pixel block comprises a respective subset of pixels of the plurality of pixels, wherein the method comprises: determining a phase-shift table common to the plurality of pixel blocks, wherein the phase-shift table comprises, for each pixel of a pixel block, a respective phase-shift value; and for each pixel block of the plurality of pixel blocks, determining a respective block driving signal for driving light emission by the pixel block, wherein the block driving signal comprises, for each pixel of the pixel block, a respective duty-cycle signal for driving light emission by the pixel, wherein the duty-cycle signal is phase-shifted by the phase shift value defined by the phase-shift table for that pixel.

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