Display pixels comprising light-emitting diodes and display screens comprising such display pixels

Abstract

Display pixels comprising light-emitting diodes and display screen comprising such display pixels. This description relates to a display pixel (12i,j) comprising at least first and second light-emitting diodes (LEDs), a first controllable current source (CS_B) supplying said first light-emitting diode (LED) with a first current, a second controllable current source (CS_R) supplying said second light-emitting diode (LED) with a second current, and an electronic circuit (40) comprising a storage circuit (48) for storing at least the first and second color signals (R,B) and a control circuit (50) configured to control the first controllable current source (CS_B) to supply the first current by pulse-width modulation from the first color signal (B) and configured to control the second controllable current source (CS_R) to supply the second current by linear control from the second color signal (R). Figure for the abstract: 3,

Description

Title of the invention: Display pixels comprising light-emitting diodes and display screen comprising such display pixels Technical field

[0001] The present disclosure relates to a display pixel comprising light-emitting diodes and a display screen comprising such display pixels. Prior art

[0002] A pixel of an image corresponds to the unit element of the image displayed by a display screen. For the display of color images, the display screen generally comprises, for the display of each pixel of the image, at least three components, also called display sub-pixels, which each emit light radiation, called the color component of the image pixel, essentially in a single color (for example, red, green and blue). The superposition of the color components of the image pixel emitted by the three display sub-pixels provides the observer with the colored sensation corresponding to the pixel of the displayed image. In this case, the assembly formed by the three display sub-pixels used for the display of a pixel of an image is called a display pixel of the display screen. Each display sub-pixel may comprise a light source, in particular a light-emitting diode.

[0003] The display pixels may be distributed in a matrix, with each display pixel located at the intersection of a row (also referred to as a line) and a column of the matrix. Electrodes are provided along the rows and columns to connect each display pixel to control circuits. In general, each row of display pixels is successively selected by a signal transmitted along the row electrodes, and the display pixels in the selected row are programmed to display the desired image pixels by signals transmitted along the column electrodes.

[0004] It is known to control a light-emitting diode by pulse width modulation, also called PWM (English acronym for Pulse Width Modulation). This type of control consists of circulating successive current pulses of constant intensity in the light-emitting diode, the pulses being repeated cyclically, the duty cycle determining the light intensity emitted by the light-emitting diode. Such control advantageously makes it possible to operate the light-emitting diode at its optimal operating point where the efficiency of the light-emitting diode, equal to the duty cycle between the light output of the LED and the electrical power consumed by the LED, is maximum. In addition, a pulse width modulation control allows the current density flowing through the LED to be kept constant. This is advantageous because, for some types of LEDs, the central wavelength of the radiation emitted by the LED can vary with the current density flowing through the LED.

[0005] Some of the display subpixels of the display pixel may include a photoluminescent block covering the light emitting diode. The photoluminescent block includes phosphors capable, when excited by light emitted by the associated light emitting diode, of emitting light at a wavelength different from the wavelength of the light emitted by the associated light emitting diode. The light conversion performance of some types of phosphors, for example quantum dots, may decrease over time depending on the maximum luminous flux received by the quantum dots. Therefore, it may be desirable to control the light emitting diode covered by such a photoluminescent block so as to reduce the maximum luminous flux emitted by the light emitting diode. Summary of the invention

[0006] An object of an embodiment is to provide a display pixel comprising light emitting diodes and a display screen comprising such display pixels which overcome some or all of the disadvantages of existing display pixels comprising light emitting diodes and display screens comprising such display pixels.

[0007] One embodiment provides a display pixel comprising at least first and second light-emitting diodes, a first controllable current source supplying said first light-emitting diode with a first current, a second controllable current source supplying said second light-emitting diode with a second current, and an electronic circuit comprising a storage circuit for storing at least the first and second color signals and a driving circuit configured to control the first controllable current source to provide the first current by pulse width modulation from the first color signal and configured to control the second controllable current source to provide the second current by linear control from the second color signal.

[0008] Such a control advantageously makes it possible to operate the first light-emitting diode at its optimal operating point where the efficiency of the first light-emitting diode is maximum. In addition, pulse width modulation control allows the current density passing through the first light-emitting diode to be kept constant. This is advantageous because when the central wavelength of the radiation emitted by the first light-emitting diode can vary with the current density passing through the first light-emitting diode. In addition, linear control of the second light-emitting diode is advantageous because it allows the second light-emitting diode not to always emit radiation at the highest intensity, which could be harmful, particularly when the second light-emitting diode is covered with a photoluminescent block comprising quantum dots.

[0009] According to one embodiment, the display pixel further comprises a third light-emitting diode and a third controllable current source supplying said third light-emitting diode with a third current, the storage circuit being configured to store a third color signal and the driving circuit being configured to control the third controllable current source in order to provide the third current by a linear control based on the third color signal. The linear control of the third light-emitting diode is advantageous because it allows the third light-emitting diode not to always emit radiation at the highest intensity, which could be harmful in particular when the third light-emitting diode is covered with a photoluminescent block comprising quantum dots.

[0010] According to one embodiment, the first color signal is a digital signal and the storage circuit comprises first memory cells for storing the bits of the first color signal.

[0011] According to one embodiment, the second color signal is a digital signal and the storage circuit comprises second memory cells for storing the bits of the second color signal.

[0012] According to one embodiment, the driving circuit comprises a digital-to-analog converter configured to convert the second color signal stored in the second memory cells into an analog control signal for controlling the second current source.

[0013] According to one embodiment, the first color signal is an analog signal and the storage circuit comprises a first capacitor for storing the first color signal.

[0014] According to one embodiment, the second color signal is an analog signal and the storage circuit comprises a second capacitor for storing the second color signal.

[0015] According to one embodiment, each of the first and second light-emitting diodes nescents comprises several elementary light-emitting diodes each comprising an active zone covering a three-dimensional semiconductor element corresponding to a wire, conical, truncated cone or pyramidal element of the order of a nanometer or a micrometer. For such three-dimensional radial light-emitting diodes, the central wavelength of the radiation emitted by the light-emitting diode can vary significantly depending on the current density passing through the light-emitting diode. A pulse width modulation control makes it possible to keep the current density passing through the first light-emitting diode constant, which is advantageous when the first light-emitting diode is not covered by a photoluminescent block.

[0016] According to one embodiment, the second light-emitting diode is covered by a first photoluminescent block. According to one embodiment, the first light-emitting diode is configured to emit a first radiation at a first wavelength, the second light-emitting diode is configured to emit a second radiation at a second wavelength, and the first photoluminescent block is configured to convert the second radiation into a third radiation at a third wavelength, different from the second wavelength. The first photoluminescent block absorbs the second radiation emitted by the second light-emitting diode and emits the third radiation at a central wavelength different from the central wavelength of the second radiation emitted by the second light-emitting diode.The linear drive of the second light-emitting diode may cause the current density supplied to the second light-emitting diode to vary and, consequently, the center wavelength of the second radiation emitted by the second light-emitting diode to vary. However, the first photoluminescent unit may emit the third radiation with a fixed center wavelength even if the center wavelength of the second radiation emitted by the second light-emitting diode exhibits dispersion. Therefore, the center wavelength of the third radiation emitted by the first photoluminescent unit remains fixed even if the center wavelength of the second radiation emitted by the second light-emitting diode varies.

[0017] According to one embodiment, the first wavelength is equal to the second wavelength to within 10%. The first light-emitting diode and the second light-emitting diode may advantageously be light-emitting diodes manufactured using the same manufacturing method. The method for manufacturing the display pixel is therefore simpler.

[0018] According to one embodiment, the first photoluminescent block comprises first quantum dots. The light conversion performance of the first quantum dots tend to decrease over time depending on the maximum luminous flux received by the first quantum dots. Linear control of the second light-emitting diode advantageously limits the luminous flux on the first quantum dots compared to pulse width modulation control. Therefore, the first quantum dots do not always receive a second radiation from the second light-emitting diodes at the highest intensity. The durability of the light conversion performance of the first quantum dots is therefore increased.

[0019] According to one embodiment, the third light-emitting diode is covered by a second photoluminescent block. According to one embodiment, the third light-emitting diode is configured to emit a fourth radiation at a fourth wavelength, and the second photoluminescent block is configured to convert the fourth radiation into a fifth radiation at a fifth wavelength, different from the fourth wavelength. The second photoluminescent block absorbs the fourth radiation emitted by the third light-emitting diode and emits the fifth radiation at a central wavelength different from the central wavelength of the fourth radiation emitted by the third light-emitting diode.The linear drive of the third light-emitting diode can cause the current density supplied to the third light-emitting diode to vary and, consequently, the center wavelength of the fourth radiation emitted by the third light-emitting diode to vary. However, the second photoluminescent unit can emit the fifth radiation with a fixed center wavelength even if the center wavelength of the fourth radiation emitted by the third light-emitting diode exhibits dispersion. Therefore, the center wavelength of the fifth radiation emitted by the second photoluminescent unit remains fixed even if the center wavelength of the fourth radiation emitted by the third light-emitting diode varies.

[0020] According to one embodiment, the fourth wavelength is equal to the first wavelength to within 10%. The first light-emitting diode and the third light-emitting diode may advantageously be light-emitting diodes manufactured using the same manufacturing method. The method for manufacturing the display pixel is therefore simpler.

[0021] According to one embodiment, the second photoluminescent block comprises second quantum dots. The light conversion performance of the second quantum dots tends to decrease over time depending on the maximum luminous flux received by the second quantum dots. The linear control of the third light-emitting diode advantageously makes it possible to limit the luminous flux on the second quantum dots with respect to a pulse width modulation control. Therefore, the second quantum dots do not always receive radiation from the second light-emitting diodes at the highest intensity. The durability of the light conversion performance of the second quantum dots is therefore increased.

[0022] According to one embodiment, the display pixel comprises a first integrated circuit including the electronic circuit comprising said storage circuit and the driving circuit.

[0023] According to one embodiment, the display pixel comprises an optoelectronic circuit attached to the integrated circuit, the optoelectronic circuit comprising the first and second light-emitting diodes.

[0024] An embodiment also provides a display screen comprising: display pixels as defined above; first electrodes coupled to the display pixel drive circuits; a first circuit for providing a selection signal on each first electrode for selecting display pixels coupled to the first electrode; second electrodes coupled to the electronic circuits of the display pixels; and a second circuit for providing data signals on the second electrodes.

[0025] According to one embodiment, the second circuit is configured to provide the data signals on the second electrodes in the form of analog signals.

[0026] According to one embodiment, the second circuit is configured to provide the data signals on the second electrodes in the form of digital signals.

[0027] According to one embodiment, the second circuit is configured to provide the data signals on the second electrodes, comprising an alternation of digital signals and analog signals. Brief description of the drawings

[0028] The above-mentioned features and advantages, as well as others, will be described in detail in the following disclosure of specific embodiments given by way of illustration and not limitation with reference to the accompanying drawings, in which:

[0029] [Fig.l] partially and schematically represents an embodiment of a display screen;

[0030] [Fig.2] is a very simplified sectional view of one embodiment of a display pixel;

[0031] [Fig.3] represents a functional diagram of a display pixel of the screen of [Fig.l];

[0032] [Fig.4] represents a functional diagram of a light emitting circuit of the display pixel of [Fig.3];

[0033] [Fig.5] shows a block diagram of another embodiment of the light emitting circuit of the display pixel of [Fig.3];

[0034] [Fig.6] represents a functional diagram of a portion of the display pixel of [Fig.3];

[0035] [Fig.7] shows a functional diagram of another embodiment of a portion of the display pixel of [Fig.3];

[0036] [Fig.8] shows examples of signal timing diagrams of the display pixel of [Fig.7] according to one embodiment of a method of operating the display screen;

[0037] [Fig.9] shows a block diagram of another embodiment of a portion of the display pixel of [Fig.3];

[0038] [Fig. 10] shows examples of signal timing diagrams of the display pixel of [Fig.9] according to another embodiment of a method of operating the display screen;

[0039] [Fig.1 1] represents, partially and schematically, a more detailed embodiment of the display pixel represented in [Fig.2];

[0040] [Fig. 12] shows an embodiment of a three-dimensional light-emitting diode; and

[0041] [Fig. 13] shows another embodiment of a three-dimensional light-emitting diode. Description of the embodiments

[0042] Unless otherwise indicated, when reference is made to two elements connected together, this means a direct connection without any intermediate element other than conductors, and when reference is made to two elements coupled together, this means that these two elements can be connected or that they can be coupled through one or more other elements. Furthermore, a signal which alternates between a first constant state, for example a low logic state, denoted "0", and a second constant state, for example a high logic state, denoted "1", is called a "binary signal". The high and low states of the different binary signals of the same electronic circuit may be different. In practice, binary signals may correspond to voltages or currents which may not be perfectly constant in the high or low state.

[0043] Furthermore, unless otherwise indicated, when referring to a voltage at a conductive pad, the difference between the potential at said conductive pad and a reference potential, for example the earth, is considered to be equal to 0. V. When radiation has a spectrum of general "bell" shape, for example of Gaussian shape, having a maximum, the wavelength of the radiation, or central or principal wavelength of the radiation, is called the wavelength at which the maximum of the spectrum is reached.

[0044] Unless otherwise indicated, the expressions "about", "approximately", "substantially" and "of the order of" mean within 10%, and preferably within 5%. In addition, the expression "substantially constant" means that it varies by less than 10% over time compared to a reference value.

[0045] A light-emitting diode is said to be three-dimensional when it comprises a three-dimensional semiconductor element of micrometric or nanometric size extending in a preferred direction, for example a microwire or a nanowire, covered with an active zone. In particular, a three-dimensional light-emitting diode is said to be of the radial type when its active zone extends at least over the side walls of the three-dimensional semiconductor element.

[0046] [Fig. 1] partially and schematically represents a known example of a display screen 10. The display screen 10 comprises display pixels 12ij, for example, arranged in M ​​rows and N columns, M being an integer varying from 1 to 8000 and N being an integer varying from 1 to 16000, i being an integer varying from 1 to M, and j being an integer varying from 1 to N. For example, in [Fig.l], M and N are equal to 6. Each display pixel 12ij is coupled to a source of a low reference potential Gnd, for example ground, via an electrode 14; and to a source of a high reference potential Vcc via an electrode 16j. For example, the electrodes 14; are aligned along the rows of [Fig.l] and the electrodes 16j are aligned along the columns of [Fig.l], the reverse arrangement being possible.The supply voltage of the display screen corresponds to the voltage between the high reference potential Vcc and the low reference potential Gnd, and is denoted Vcc as the high reference potential. The supply voltage Vcc depends in particular on the arrangement of the light-emitting diodes and the technology by which the light-emitting diodes are manufactured. For example, the supply voltage Vcc can be in the order of 4 V to 5 V.

[0047] For each row, the display pixels 12;j of the row are coupled to a row electrode 18;. For each column, the display pixels 12;j of the column are coupled to a column electrode 20j. The display screen 10 includes a selection circuit 22 coupled to the row electrodes 18; and adapted to provide a selection signal Corn; on each row electrode 18;. The display screen 10 includes a data transmission circuit 24 coupled to the column electrodes 20j and adapted to transmit a data signal Dataj on each column electrode 20j. The selection circuit 22 and the control circuit 24 are controlled by a circuit 26, including for example a microprocessor.

[0048] [Fig. 2] is a very simplified sectional view of a known example of a display pixel 12^. Each display pixel 1¾ comprises a control circuit 30 covered by a display circuit 32. The display circuit 32 comprises light-emitting diodes, preferably at least three light-emitting diodes LED. The display pixel comprises a lower surface 34 and an upper surface 35 opposite the lower surface 34, the surfaces 34 and 35 preferably being planar and parallel. The control circuit 30 further comprises conductive pads P_Gnd, P_Vcc, P_Col, P_Row on the lower surface 34. The control circuit 30 may correspond to an integrated circuit comprising electronic components, in particular insulated gate field effect transistors, also called MOS transistors, or thin-film transistors, also called TFTs.Preferably, the display circuit 32 comprises only LEDs and the conductive elements of these LEDs, and the control circuit 30 comprises all the electronic components necessary for controlling the LEDs of the display circuit 32. Alternatively, the display circuit 32 may also comprise other electronic components in addition to the LEDs. According to one embodiment, each LED comprises several elementary three-dimensional LEDs. In [Fig. 2], the LEDs are shown as being connected to a common anode. However, it may be desirable to arrange the LEDs in another configuration. For example, the LEDs may be connected to a common cathode or be connected independently of each other.

[0049] Each conductive pad P_Gnd, P_Vcc, P_Col, P_Row is intended to be connected to one of the electrodes 14;, 16j, 18;, 20j shown schematically in [Fig.2]. The first conductive pad P_Gnd is coupled to the source of the low reference potential Gnd. The second conductive pad P_Vcc is coupled to the source of the high reference potential Vcc. The third conductive pad P_Row is coupled to the row electrode 18; and receives the selection signal Com;. The fourth conductive pad P_Col is coupled to the column electrode 20j and receives the data signal Dataj. The dimensions of the conductive pads P_Gnd, P_Vcc, P_Col, P_Row and the arrangement of the conductive pads P_Gnd, P_Vcc, P_Col, P_Row on the surface 34 are notably imposed by the design rules of the display pixel 12ij and by the method of assembling the display pixels 1¾ in the display screen 10.

[0050] According to one embodiment, the display pixel 1¾ comprises a first display sub-pixel emitting light at a first wavelength, a second display sub-pixel emitting light at a second wavelength and a third display sub-pixel emitting light at a third wavelength. According to one embodiment, the first wavelength corresponds to blue light and is between 430 nm and 490 nm. The first display sub-pixel is then called a blue display sub-pixel. According to one embodiment, the second wavelength corresponds to green light and is between 510 nm and 570 nm. The second display sub-pixel is then called a green display sub-pixel. According to one embodiment, the third wavelength corresponds to red light and is between 600 nm and 720 nm. The third display sub-pixel is then called a red display sub-pixel.

[0051] [Fig. 3] represents a functional diagram of an embodiment of display pixel 1¾ of the display screen 10. For a color display screen, the display pixel 1¾ comprises at least three display sub-pixels SPix_R, SPix_G, SPix_B emitting radiation of different colors. For example, the display sub-pixel SPix_B corresponds to the blue display sub-pixel defined previously, the display sub-pixel SPix_G corresponds to the green display sub-pixel defined previously, and the display sub-pixel SPix_R corresponds to the red display sub-pixel defined previously. Each sub-pixel SPix_R, SPix_G, SPix_B comprises at least one light-emitting diode LED. For each display subpixel SPix_R, SPix_G, SPix_B, the light-emitting diode LED is coupled in series to a controllable current source CS_R, CS_G, CS_B.In the present example, for each light-emitting diode LED, the anode of the light-emitting diode LED receives the high reference potential Vcc, received at the conductive pad P_Vcc of the display pixel 12^, and the cathode of the light-emitting diode LED is for example coupled to one terminal of the controllable current source CS_R, CS_G, CS_B, the other terminal of the controllable current source CS_R, CS_G, CS_B receiving the low reference potential Gnd, received at the conductive pad P_Gnd of the display pixel 1¾. Alternatively, the cathode of the light-emitting diode LED receives the low reference potential Gnd and the anode of the light-emitting diode LED is coupled to one terminal of the controllable current source CS_R, CS_G, CS_B, the other terminal of the controllable current source CS_R, CS_G, CS_B receiving the high reference potential Vcc. .

[0052] The display pixel 1¾ further comprises an electronic circuit 40 for controlling the controllable current source CS_R, CS_G, CS_B of each display sub-pixel SPix_R, SPix_G, SPix_B. The electronic circuit 40 may in particular comprise electronic components such as MOS transistors. It may be desirable to use a reduced supply voltage, less than 4 V, for example of the order of 1 V or 1.8 V, to power the electronic components of the circuit 40, this reduced supply voltage corresponding for example to the voltage sus capable of being applied between the power terminals of the MOS transistors. For this purpose, the display pixel 1¾ may comprise a circuit, not shown, making it possible to provide a reduced supply voltage Vdd, notably used for supplying the circuit 40, for example from the high reference potential Vcc or the selection signal Com; and the data signal Dataj.

[0053] The circuit 40 comprises an interface circuit 46 (Interface) coupled to the conductive pad P_Col receiving the data signal Dataj and coupled to the conductive pad P_Row receiving the selection signal Com; and configured to provide the data signals Data to a storage circuit 48 (Color Data Memory). The storage circuit 48 is configured to store analog or digital color signals R, G, B depending on the received data signals. The color signals R, G, B are representative of the color components of the pixels of the image to be displayed by each display sub-pixel SPix_R, SPix_G, SPix_B.

[0054] The circuit 40 further comprises a driving circuit 50 (LED driver) for controlling the controllable current source CS_R, CS_G, CS_B associated with each display sub-pixel SPix_R, SPix_G, SPix_B. The driving circuit 50 (LED driver) is configured to control the controllable current sources CS_R, CS_G, CS_B coupled to the light-emitting diodes LED with analog or digital signals I_red, I_green and I_blue, obtained from the color signals R, G, B. According to one embodiment, the control circuit 30 may correspond to a single integrated circuit comprising the circuit 40 for controlling the controllable current source CS_R, CS_G, CS_B of each display sub-pixel SPix_R, SPix_G, SPix_B. More generally, the circuit 40 may consist of several integrated circuits.

[0055] According to one embodiment, a pulse width modulation control is used to control the current source CS_B of the blue display sub-pixel SPix_B, while a linear control is used to control the current source CS_G of the green display sub-pixel SPix_G and to control the current source CS_R of the red display sub-pixel SPix_R. Therefore, the light-emitting diode LED of the blue sub-pixel SPix_B is powered by current pulses of constant intensity, the duration of the pulses depending on the stored color signal B, while the light-emitting diode LED of the green sub-pixel SPix_G is powered by a current whose intensity varies according to the stored color signal G and the light-emitting diode LED of the red sub-pixel SPix_R is powered by a current whose intensity varies according to the stored color signal R.

[0056] The fact that the intensity of the current passing through the light-emitting diode LED of the blue display sub-pixel SPix_B is constant is advantageous when it is important to obtain a reduced dispersion of the central wavelength of the emitted radiation by the LED light-emitting diode of the blue display sub-pixel SPix_B in operation. Indeed, the central wavelength of the radiation emitted by the light-emitting diode generally varies as a function of the current density passing through the light-emitting diode, this variation being significant for three-dimensional radial-type light-emitting diodes. In the present embodiment, the current density passing through each elementary light-emitting diode remaining constant regardless of the color signal B, the central wavelength of the radiation emitted by the elementary light-emitting diodes does not vary during operation.

[0057] According to one embodiment, each of the red and green display subpixels SPix_G and SPix_R comprises a photoluminescent block covering the light-emitting diode. The photoluminescent block absorbs radiation emitted by the light-emitting diode and emits radiation at a center wavelength different from the center wavelength of the radiation emitted by the light-emitting diode. The linear drive for the red and green display subpixels SPix_G and SPix_R may result in a variation in the current density supplied to the light-emitting diode LED of the red and green display subpixels SPix_G and SPix_R and, consequently, a variation in the center wavelength of the radiation emitted by the light-emitting diode LED of the red and green display subpixels SPix_G and SPix_R.However, a photoluminescent block can emit radiation with a fixed center wavelength even if the center wavelength of the radiation emitted by the light-emitting diode LED has dispersion. Therefore, the center wavelength of the radiation emitted by the photoluminescent block remains fixed even if the center wavelength of the radiation emitted by the light-emitting diode LED of the red and green display subpixels SPix_G and SPix_R varies due to the linear drive for the red and green display subpixels SPix_G and SPix_R.

[0058] The photoluminescent block may comprise quantum dots. The light conversion performance of quantum dots tends to decrease over time depending on the maximum luminous flux received by the quantum dots. Linear control for the red and green display subpixels SPix_G and SPix_R advantageously limits the luminous flux on the quantum dots compared to pulse width modulation control. Therefore, the quantum dots do not always receive radiation from the light emitting diodes LED at the highest intensity. The durability of the light conversion performance of the quantum dots is therefore increased.

[0059] According to one embodiment, the pulse width modulation control used to control the current sources CS_B of the blue display sub-pixel SPix_B is a digital pulse width modulation command. In this case, the I_blue signal is a binary signal and the color B signal is a digital signal.

[0060] [Fig.4] shows a functional diagram of an embodiment of the display subpixel SPix_B. The controllable current source CS_B comprises a switch SW in series with an adjustable current source VCS providing a current of controllable intensity. The switch SW is controlled by the signal I_blue. The adjustable current source VCS is controlled by a constant bias signal Bias.

[0061] [Fig.5] shows a functional diagram of an embodiment of the display subpixel SPix_R. The controllable current source CS_R comprises a MOS transistor. The signal I_red corresponds to an analog voltage applied to the gate of the transistor CS_R. The display subpixel SPix_G may have the same structure as the display subpixel SPix_R.

[0062] According to one embodiment, the data signal Dataj, received on the conductive pad P_Col of each display pixel 12ij, is a binary signal alternating between a low logic state "0" and a high logic state "1", the low logic state corresponding to the low reference potential Gnd and the high logic state "1" corresponding to a low voltage, for example, approximately 1 V, lower than the reduced supply voltage Vdd. In this embodiment, the stored color signals R, G and B are digital signals.

[0063] [Fig. 6] shows a functional diagram of an embodiment of the circuit 40 of the display pixel 1¾ of [Fig. 3] when the signal Dataj is a binary signal and the color signals R, G and B are digital signals. The storage circuit 48 comprises three registers RR, GR, BR. The bits of the digital color signal R are stored in the memory cells of the register RR, the bits of the digital color signal G are stored in the memory cells of the register RG, and the bits of the digital color signal B are stored in the memory cells of the register RB. The driving circuit 50 comprises a digital-to-analog converter DAC_R configured to receive the digital color signal R from the register RR and to convert the digital color signal R into an analog signal corresponding to the signal I_red.The driver circuit 50 also includes a digital-to-analog converter DAC_G configured to receive the digital color signal G from the register RG and to convert the digital color signal G into an analog signal corresponding to the signal I_green.

[0064] According to another embodiment, the stored R and G color signals are analog signals. The storage circuit 48 may include capacitors configured to store the analog R and G color signals. According to one embodiment embodiment, the circuit 48 is configured to convert the data bits relating to the color signal R into an analog voltage proportional to the data, the analog voltage being stored in a first capacitor. The voltage across the first capacitor may then correspond to the analog color signal R. The circuit 48 is configured to convert the data bits relating to the color signal G into an analog voltage proportional to the data, the analog voltage being stored across a second capacitor. The voltage across the first capacitor may then correspond to the analog color signal G.

[0065] According to one embodiment, the selection signal Com;, received at the conductive pad P_Row of each display pixel 12^, is a binary signal alternating between a low logic state "0" and a high logic state "1", the low logic state corresponding to the low reference potential Gnd and the high logic state "1" corresponding to a low voltage, for example, approximately 1 V, lower than the reduced supply voltage Vdd.

[0066] [Fig. 7] represents a functional diagram of another embodiment of the display pixel 1¾ of the display screen 10. The display pixel 1¾ shown in [Fig. 7] comprises all the elements of the display pixel 1¾ shown in [Fig. 6]. The interface circuit 46 is configured to provide a clock signal Clk from the selection signal Com; or the data signal Dataj and a data signal Data from the data signal Dataj to the storage circuit 48 in a first phase PI, also called the programming phase, and to provide a PWM modulation signal from the selection signal Com; to the driving circuit 50 for controlling the controllable current source CS_B of the display sub-pixel SPix_B in a second phase P2, also called the display phase. The PWM modulation signal may be equal to the selection signal Com; during each display phase P2.The clock signal Clk may be equal to the selection signal Com; during each PI programming phase when it is generated from the selection signal Com;. The storage circuit 48 is configured, when clocked by the clock signal Clk, to store the digital color signals R, G, B from the received digital data.

[0067] [Fig.8] shows a timing diagram of signals received by the display pixels 1¾ having the structure shown in [Fig.7] for one embodiment of a method of displaying an image on the display screen 10.

[0068] The potentials Vcc and Gnd are substantially constant. The pixels of a new image to be displayed are displayed successively from the row of rank 1 to the row of rank M. The duration of the frame T is the duration separating two successive selections of the same row of the display screen 10. The time diagrams of the signals Comi and Datai will be detailed for the row of rank 1, knowing that the diagrams of times of the Com signals; are similar to the timing diagram of the Comi signal, although shifted in time. The display of a new image pixel by a display pixel 12ij, with j varying from 1 to N, of the row of rank 1 comprises a first phase PI followed by a second phase P2. During the PI phase, the data signals Data, are transmitted to each display pixel 12ij of the row of rank 1, only the signal Datai being shown in [Fig.8]. During the second phase P2, the light-emitting diodes of each display pixel 12ij are controlled from the color signals R, G, B, determined from the data signals Data,.

[0069] During the first phase PI, the selection signal Comi is set to the state "1". Setting the signal Comi to the state "1" for a long time is detected by the interface circuit 46 of each display pixel 12i j of the row of rank 1 and thus makes it possible to select the display pixels 12ij of this row, while the display pixels of the other rows are not selected. During the first phase PI, the data signals Dataj are transmitted to the column electrodes 20j. For each display pixel 12ij, the interface circuit 46 determines a clock signal Clk and data Data from the pulses of the data signal Dataj. For example, each pulse of the signal Dataj may have a first duration or a second duration, longer than the first.The signal Clk may correspond to a sequence of pulses of the same duration whose rising edges coincide, with a possible constant offset, with the rising edges of the pulses of the data signal Dataj. The data Data may correspond to a binary signal in state "0" when the pulse of the signal Dataj has the first duration, and in state "1" when the pulse of the signal Dataj has the second duration. The interface circuit 46, selected by the signal Comi in state "1", delivers, at the rate of the clock signal Clk, the data Data which are stored in the circuit 48 in the form of digital signals R, G, B whose bits are provided by the successive values ​​of the signal Data. The end of the first PI period for a row corresponds to the beginning of the first PI period for the following row.

[0070] According to one embodiment, the light-emitting diodes of the display sub-pixel SPix_B are controlled by pulse width modulation or PWM. For this purpose, during the second phase P2, the selection signal Comi presents the repetition of a succession of pulses in the state "1" which are transmitted by the interface circuit 46 of each display pixel 12i j of the row of rank 1 to the circuit 50 (PWM signal) to regulate the operation of the circuit 50 for controlling the light-emitting diodes LED of the display sub-pixel SPix_B by pulse width modulation. The number of pulses in the succession corresponds to the number of bits of each digital signal B. For example, when the current source CS_B is as shown in [Fig.4], the switch SW is opened or closed, at the rate of the PWM pulses, depending on the value "0" or "1" of each bit of the color signal B, starting with the most significant bit, this transistor being kept on or off until the next pulse of the Comi signal. The time between two successive pulses of the Comi signal is divided by two each time, so that the total time during which the light-emitting diode is lit depends on the value of the color signal B. The succession of pulses of the Comi signal is repeated until the first next PI phase of the row of rank 1, a single repetition being illustrated as an example in [Fig.8].

[0071] According to another embodiment, the data signal Dataj, received on the conductive pad P_Col of each display pixel 12^, is an analog signal. The storage circuit 48 may comprise capacitors configured to store the analog color signals R, G, B.

[0072] [Fig.9] shows a functional diagram of another embodiment of the pixel display pixel 1¾ of the display screen 10. The display pixel 1¾ shown in [Fig.9] comprises all the elements of the display pixel 1¾ shown in [Fig.6]. According to one embodiment, the selection signal Com;, received on the conductive pads P_Row of each display pixel 12ij, is an analog signal. The interface circuit 46 is configured to receive the data signal Dataj and to provide the analog signal Data to the storage circuit 48 in the programming phase PI and to provide an analog reference signal REF suitable for executing a PWM command in the display phase P2. The storage circuit 48 comprises a capacitor CR for storing the analog color signal R. The analog color signal R may correspond to the voltage of the capacitor CR. The storage circuit 48 comprises a capacitor CG for storing the analog color signal G.The analog color signal G may correspond to the voltage across the capacitor CG. The storage circuit 48 includes a capacitor CB for storing the analog color signal B. The analog color signal B may correspond to the voltage across the capacitor CB. The driving circuit 50 is configured to control the controllable current sources CS_R, CS_G, CS_B coupled to the light-emitting diodes LED with control signals obtained from the analog control signals R, G, B and, for the current source CS_B of the display subpixel SPix_B, from the analog reference signal REF. .

[0073] In one embodiment, the signal Com; makes it possible both to select the display pixel 1¾ for the storage of a data signal Data and to provide the analog reference signal used for the PWM control of the light-emitting diodes of the display sub-pixel SPix_B.

[0074] [Fig. 10] shows timing diagrams of signals received by the display pixels 1¾ for one embodiment of a method of displaying an image on the display screen 10. For illustration purposes, in [Fig. 10], only signals associated with the row of rank 1 and the column of rank 1 of the display screen 10 have been represented.

[0075] In the present embodiment, the potentials Vcc and Gnd, not shown in [Fig. 10], are substantially constant during the operation of the display screen 10. The pixels of a new image to be displayed are displayed successively from the row of rank 1 to the row of rank M. The duration of the frame T is the duration separating two successive selections of the same row of the display screen 10. The display of a new image pixel by a display pixel 12ij, j varying from 1 to N, of the row of rank i comprises a first phase PI followed by a second phase P2. During the phase PI, analog data signals Dataj are transmitted to the display pixels 12ij of the row i, only the signal Datai being shown in [Fig. 10]. Each display pixel 1¾ stores a new value of the analog color signal R, G or B from the received analog data signal Dataj.According to one embodiment, the display pixel 1¾ can receive the data signals Dataj corresponding to the different colors successively during the phase PL. During the second phase P2, the light-emitting diodes of each display pixel 12ij are controlled from the stored R, G, B color signals.

[0076] During the first phase PI, the selection signal Com; is set to a high, substantially constant level, thus forming a voltage pulse. The pulse of the signal Com; is detected by the interface circuit 46 of each display pixel 1¾ of the row of rank i and thus makes it possible to select the display pixels 1¾ of this row, while the display pixels of the other rows are not selected. According to one embodiment, the duration of each pulse is less than the duration of the frame divided by the number of rows to be selected, preferably less than 100 ps. During the first phase PI, the data signals Dataj are transmitted to the column electrodes 20j. Each signal Dataj can correspond to an analog signal capable of taking a constant value ranging from a minimum value to a maximum value.The interface circuit 46 delivers the signal Dataj which is stored in the circuit 50 of the display pixel 12ij in the form of an R, G or B signal whose value depends on the signal Dataj, the signal R14 stored by the display pixel 12i4, and the current ILEDi flowing through the light-emitting diode of the display sub-pixel SPix_B of the display pixel 12i4 shown as an example in [Fig. 10]. The end of the first PI phase for a row may correspond to the start of the first PI phase for the next row.

[0077] According to one embodiment, the light-emitting diodes of the display sub-pixel SPix_B of the display pixel 12ij are controlled by pulse width modulation. To this end, during a first portion P2_ON of the second phase P2, the selection signal Com; varies periodically, presenting a succession of identical patterns which are detected by the interface circuit 46 of each display pixel 1¾ of the row of rank i. The interface circuit 46 transmits the succession of patterns to the circuit 50, as an analog reference signal REF for controlling the light-emitting diodes LED of the display sub-pixel SPix_B by pulse width modulation. For example, in [Fig. 10], each pattern comprises an ascending voltage ramp followed by a descending voltage ramp. According to another example, each pattern comprises only an ascending voltage ramp or only a descending voltage ramp. In general, each pattern comprises a determined voltage variation curve, for example an exponential growth curve, a sinusoidal curve, etc. The shape of the pattern may for example include compensations for eye sensitivity, in particular gamma correction.The pattern repetition frequency on each P2_OFF phase allows for between 1 and 1000 pattern cycles per P2_OFF phase.

[0078] The circuit 50 of the display pixel 1¾ controls the light-emitting diodes LED of the display sub-pixel SPix_B according to the comparison between the stored analog signal B and the analog reference signal REF. For example, the current source CS_B of the display sub-pixel SPix_B is deactivated when the stored analog signal B is greater than the analog reference signal REF, which results in a zero current L ,fb supplying the light-emitting diode, and the current source CS_B of the display sub-pixel SPix_B is activated when the stored analog signal B is less than the analog reference signal REF, which results in a current I, ,Pr>i , supplying the light-emitting diode at a constant non-zero value.

[0079] During a second part P2_OFF of the second phase P2, the selection signal Com; is maintained at a constant level, for example at a low level, so that the light-emitting diodes LED of the display subpixels SPix_B of the display pixels of the row are switched off. The duration of the second part P2_OFF can vary from 0 to 100% of the duration of the second phase P2. In particular, the second part P2_OFF can be absent. According to one embodiment, the duration of each phase P2 is equal to the duration of the frame Tframe reduced by the duration of the phase PL

[0080] During the display phase P2, the control circuit 50 controls the controllable current sources CS_R and CS_G coupled to the light-emitting diodes LED of the display sub-pixels SPix_R and SPix_B with the control signals I_green and I_red obtained which can correspond to the analog control signals R and G.

[0081] According to another embodiment, the data signal Dataj, received on the conductive pad P_Col of each display pixel 12ij, is a digital signal for the transmission of the color signal B and is an analog signal for the transmission color signals G and R. Therefore, the color signal B is a digital signal and the storage circuit 48 may include a register for storing the digital color signal B. Further, the color signals R and G are each an analog signal. The storage circuit 48 may include capacitors configured to store the analog color signals R and G.

[0082] [Fig. 11] is a simplified partial sectional view of an embodiment of the display pixel 1¾ comprising microwires or nanowires. The display pixel 12 ij comprises, from bottom to top in [Fig.l 1]: - a substrate 60 comprising opposite surfaces 62 and 64, the upper surface 62 preferably being planar at least at the level of the light-emitting diodes; - a germination layer 66 made of a material promoting the growth of the threads and arranged on the surface 62; - an insulating layer 68 covering the seed layer 66 and comprising openings 70 exposing parts of the seed layer 66; - LED light-emitting diodes (six LEDs are shown), each LED light-emitting diode being in contact with the seed layer 66 through one of the openings 70; - an insulating layer 74 extending over the side walls of a lower portion of the LED and extending over the insulating layer 68 between the LEDs; - a layer 76 forming an electrode covering each light-emitting diode LED and extending over the insulating layer 74 between the light-emitting diodes LED - a reflective conductive layer 78 extending over the insulating layer 68 between the light-emitting diodes LED; - a reflective conductive layer 78, extending over the layer 76 between the light-emitting diodes LED, the conductive layer 78 being alternatively interposed between the electrode layer 76 and the insulating layer 74 between the light-emitting diodes LED; - a dielectric protection layer 80 extending over layers 76 and 78; - photoluminescent blocks 82 covering the sets of light-emitting diodes of the display sub-pixels SPix_R and SPix_G; - blocks 84 transparent to the radiation emitted by the light-emitting diodes of the display sub-pixels SPix_B, these transparent blocks 84 being able to be omitted; - walls 88 between the blocks 82, 84, each wall 88 being opaque to the radiation emitted by the light-emitting diodes LED; and - one, two or three 90 color filters, for example a single yellow filter, two filters, the first being a yellow filter and the second a red filter, or three filters, the first being a red filter, the second a green filter and the third a blue filter, covering at least part of the blocks 82, 84, a single filter 90 covering two blocks being shown as an example.

[0083] According to one embodiment, each light-emitting diode may be a three-dimensional light-emitting diode. According to one embodiment, the light-emitting diodes LED comprise semiconductor layers made of III-V compounds, for example GaN, AIN, InN, InGaN, AlGaN or AlInGaN, or of II-VI compounds.

[0084] A three-dimensional light-emitting diode comprises a three-dimensional semiconductor element, for example a wire, a conical, frustoconical or pyramidal element, in particular a microwire or a nanowire, on which the active zone of the light-emitting diode extends. The term "microwire" or "nanowire" designates a three-dimensional structure of elongated shape in a preferred direction, of which at least two dimensions, called minor, are between 5 nm and 2.5 qm, preferably between 50 nm and 2.5 qm, the third dimension, called major, being at least equal to 1 time, preferably at least 2 times, the largest of the minor dimensions. In certain embodiments, the minor dimensions may be less than or equal to approximately 3 qm, preferably between 100 nm and 3 qm, more preferably between 1 qm and 1.5 qm.In some embodiments, the height of each microwire or nanowire may be greater than or equal to 500 nm, preferably between 1 qm and 50 qm.

[0085] [Fig. 12] is a partial and schematic sectional view of an embodiment of the LED light-emitting diodes of the display pixel 1¾. According to one embodiment, each LED light-emitting diode comprises a wire 90 in contact with the seed layer 66 through one of the openings 70 and an envelope 92 comprising a stack of semiconductor layers covering the side walls and the top of the wire 90. Such a configuration is called radial. The assembly formed by each wire 90 and the associated envelope 92 constitutes the LED light-emitting diode.

[0086] The envelope 92 may comprise a stack of several layers including in particular an active layer 94 and a bonding layer 96. The active layer 94 is the layer from which the majority, preferably all, of the radiation provided by the light-emitting diode LED originates. According to one example, the active layer 94 may comprise confinement means, such as a single quantum well or multiple quantum wells. The bonding layer 96 may comprise a stack of semiconductor layers of the same IILV material as the wire 90, but of a conductivity type opposite that of the wire 90.

[0087] [Fig. 13] is a partial and schematic sectional view of another embodiment of the light-emitting diode LED of the display pixel 1¾. The light-emitting diode LED shown in [Fig. 13] comprises all the elements of the diode LED electroluminescent light shown in [Fig. 12], with the difference that the envelope 92 is only present at the top of the wire 90. Such a configuration is called axial.

[0088] The formation of the light-emitting diodes LED as shown in Figures 12 and 13, i.e. the growth of the wires 90 in the openings 70, and the formation of the shells 92 covering the wires 90 can be carried out for example by metal-organic chemical vapor deposition (MOCVD) or by any other suitable method.

[0089] The substrate 60 may correspond to the control circuit 30 described previously.

[0090] The seed layer 66 is made of a material that promotes the growth of the wires. For example, the material forming the seed layer 66 may be a nitride, a carbide or a boride of a transition metal from column IV, V or VI of the periodic table of elements or a combination of these compounds. According to one embodiment, the seed layer 66 may be omitted. According to another embodiment, the seed layer 66 may be replaced by seed pads, for example, formed at the bottom of the openings 70.

[0091] Each insulating layer 68, 74, 80 may be made of a dielectric material, for example silicon oxide (SiO2), silicon nitride (SixNy, where x is approximately equal to 3 and y is approximately equal to 4, for example Si3N4), silicon oxynitride (in particular of general formula SiOxNy, for example Si2ON2), aluminum oxide (A12O3), hafnium oxide (HfO2), titanium dioxide (TiO2), or diamond. The insulating layer 68, 74, 80 may have a single-layer structure or correspond to a stack of two layers or more than two layers. When the insulating layer 68 corresponds to a stack of at least two layers, the upper layer of the stack is of the insulating type, for example made of a dielectric material.

[0092] The conductive layer 78 preferably corresponds to a metal layer, for example aluminum, silver, copper, gold or zinc. The thickness of the conductive layer 78 may be between 0.01 μm and 1000 μm.

[0093] The electrode layer 76 is capable of allowing the electromagnetic radiation emitted by the light-emitting diodes to pass through. The material forming the electrode layer 76 may be a transparent and conductive material such as indium-tin oxide (ITO), aluminum or gallium-zinc oxide, or graphene. The thickness of the electrode layer 76 may be between 0.01 μm and 10 μm.

[0094] According to one embodiment, each photoluminescent block 82 is located opposite one of the light-emitting diodes or a set of light-emitting diodes. Each photoluminescent block 82 comprises phosphors capable, when excited by the light emitted by the associated light-emitting diode LED, of emitting light at a wavelength different from the wavelength of the light emitted by the associated light-emitting diode LED. According to one embodiment, the display pixel 1¾ comprises at least two types of photoluminescent blocks 82. Each photoluminescent block 82 of the first type is capable of converting the radiation provided by the light-emitting diodes into a first radiation at a first wavelength, and each photoluminescent block 82 of the second type is capable of converting the radiation provided by the light-emitting diodes that it covers into a second radiation at a second wavelength.

[0095] According to one embodiment, the light-emitting diodes are capable of emitting blue light, i.e. radiation whose wavelength is between 430 nm and 480 nm. According to one embodiment, the first wavelength corresponds to green light and is between 510 nm and 570 nm. According to one embodiment, the second wavelength corresponds to red light and is between 600 nm and 720 nm.

[0096] The aspect ratio of the blocks 82, i.e. the ratio between the height and the maximum width of the block, may be between 0.01 and 10, preferably between 0.05 and 2.

[0097] According to one embodiment, each photoluminescent block 82 comprises particles of at least one photoluminescent material, for example in a transparent matrix. An example of a photoluminescent material is yttrium aluminum garnet (YAG) activated by trivalent cerium ion, also called YAG:Ce or YAG:Ce3+. The average particle size of conventional photoluminescent materials is generally greater than 5 pm.

[0098] According to one embodiment, each photoluminescent block 82 comprises a matrix in which nanometric-sized monocrystalline particles of a semiconductor material are dispersed, also called semiconductor nanocrystals or luminophore nanoparticles in the remainder of this document. The internal quantum efficiency QYint of a photoluminescent material is equal to the ratio between the number of photons emitted and the number of photons absorbed by the photoluminescent substance. The internal quantum efficiency QYint of the semiconductor nanocrystals is greater than 5%, preferably greater than 10%, more preferably greater than 20%.

[0099] According to one embodiment, the average size of the nanocrystals is between 0.5 nm and 1000 nm, preferably between 0.5 nm and 500 nm, more preferably between 1 nm and 100 nm, in particular between 2 nm and 30 nm. For dimensions less than 50 nm, the photoconversion properties of the semiconductor nanocrystals depend essentially on quantum confinement phenomena. The semiconductor nanocrystals then correspond to quantum dots.

[0100] According to one embodiment, the semiconductor material of the semiconductor crystals is chosen from the group comprising cadmium selenide (CdSe), indium phosphide (InP), cadmium sulfide (CdS), zinc sulfide (ZnS), zinc selenide (ZnSe), cadmium telluride (CdTe), zinc telluride (ZnTe), cadmium oxide (CdO), cadmium zinc oxide (ZnCdO), cadmium zinc sulfide (CdZnS), cadmium zinc selenide (CdZnSe), silver indium sulfide (AgInS2), perovskites of the PbScX3 type where X is a halogen atom, in particular iodine (I), bromine (Br), or chlorine (Cl), and a mixture of two or more of these compounds. According to one embodiment, the semiconductor material of the semiconductor nanocrystals is chosen from the materials mentioned in the publication of Le Blevenec et al. in Physica Status Solidi (RRL) - Rapid Research Letters Volume 8, No. 4, pages 349-352, April 2014.

[0101] According to one embodiment, the dimensions of the semiconductor nanocrystals are selected according to the desired wavelength of the radiation emitted by the semiconductor nanocrystals. For example, CdSe nanocrystals having an average size of the order of 3.6 nm are capable of converting blue light into red light and CdSe nanocrystals having an average size of the order of 1.3 nm are capable of converting blue light into green light. According to another embodiment, the composition of the semiconductor nanocrystals is chosen according to the desired wavelength of the radiation emitted by the semiconductor nanocrystals.

[0102] The matrix is ​​at least partially transparent to the radiation emitted by the photoluminescent particles and / or the LED light-emitting diodes, preferably more than 80%. The matrix is ​​for example made of silica. The matrix is ​​for example made of any at least partially transparent polymer, in particular silicone, acrylic resin or poly(methyl methacrylate) (PMMA) or polylactic acid (PLA). The matrix may in particular be made of an at least partially transparent polymer used with three-dimensional printers. The matrix may correspond to a photosensitive or non-photosensitive glass deposited by centrifugation (SOG, Spin-On Glass). According to one embodiment, the matrix contains from 2% to 90%, preferably from 10% by weight to 60% by weight, of nanocrystals, for example approximately 30% by weight of nanocrystals.

[0103] The thickness of the photoluminescent blocks 82 depends on the concentration of nanocrystals and the type of nanocrystals used. The height of the photoluminescent blocks 82 is preferably greater than the height of the wires 71 and less than or equal to the height of the walls 88. In top view, each photoluminescent block 82 may correspond to a square, a rectangle, an "L" shaped polygon, etc. having a surface area which may be equal to the surface area of ​​a square having a side length of 1 pm to 100 pm, preferably 3 pm to 15 pm.

[0104] According to one embodiment, the opaque walls 88 are reflective for the radiation emitted by the light-emitting diodes LED. The walls 88 are at least partially made of at least one reflective material. The reflective material may be a metallic material, including iron, copper, aluminum, tungsten, silver-plated titanium, hafnium, zirconium, or a combination of at least two of these compounds. Preferably, the walls 88 are made of a material compatible with the manufacturing processes implemented in microelectronics. Preferably, the walls 88 are made of aluminum or silver.

[0105] The height of the walls 88, measured along a direction perpendicular to the surface 62, is between 300 nm and 200 pm, preferably between 3 pm and 15 pm. The thickness of the walls 88, measured along a direction parallel to the surface 62, is between 100 nm and 50 pm, preferably between 0.5 pm and 10 pm.

[0106] According to one embodiment, the walls 88 may be made of a reflective material or covered with a coating reflecting the wavelength of the radiation emitted by the photoluminescent blocks 82 and / or the light-emitting diodes. Preferably, the walls 88 surround the photoluminescent blocks 82. The walls 88 then reduce the crosstalk between the adjacent photoluminescent blocks 82.

[0107] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations may be combined, and that other variations will occur to those skilled in the art.

[0108] Finally, the practical implementation of the described embodiments and their variants is within the reach of persons skilled in the art, on the basis of the functional indications given above.

Claims

Claims

1. A display pixel (1¾) comprising at least first and second light-emitting diodes (LEDs), a first controllable current source (CS_B) supplying said first light-emitting diode (LED) with a first current, a second controllable current source (CS_R) supplying said second light-emitting diode (LED) with a second current, and an electronic circuit (40) comprising a storage circuit (48) for storing at least first and second color signals (R, B) and a driving circuit (50) configured to control the first controllable current source (CS_B) to provide the first current by pulse width modulation from the first color signal (B) and configured to control the second controllable current source (CS_R) to provide the second current by linear control from the second color signal (R).

2. The display pixel of claim 1, further comprising a third light emitting diode (LED) and a third controllable current source (CS_G) supplying said third light emitting diode (LED) with a third current, the storage circuit (48) being configured to store a third color signal (G) and the driving circuit (50) being configured to control the third controllable current source (CS_G) to provide the third current by a linear control based on the third color signal (G).

3. A display pixel according to claim 1 or 2, wherein the first color signal (B) is a digital signal and the storage circuit (48) comprises first memory cells (RB) for storing the bits of the first color signal (B).

4. A display pixel according to any one of claims 1 to 3, wherein the second color signal (R) is a digital signal and the storage circuit (48) comprises second memory cells (RR) for storing the bits of the second color signal (R).

5. A display pixel according to claim 4, wherein the drive circuit (50) comprises a digital-to-analog converter (DAC_R) configured to convert the second color signal (R) stored in the second memory cells (RR) into an analog control signal (I_red) for controlling the second color source. current (CS_R).

6. A display pixel according to claim 1 or 2, wherein the first color signal (B) is an analog signal and the storage circuit (48) comprises a first capacitor (CB) for storing the first color signal (B).

7. A display pixel according to claim 1 or 2, wherein the second color signal (R) is an analog signal and the storage circuit (48) comprises a second capacitor (CR) for storing the second color signal (B).

8. A display pixel according to any one of claims 1 to 7, wherein each of the first and second light-emitting diodes (LEDs) comprises several elementary light-emitting diodes each comprising an active zone (94) covering a three-dimensional semiconductor element (90) corresponding to a wire, conical, truncated cone or pyramidal element of the order of a nanometer or a micrometer.

9. A display pixel according to any one of claims 1 to 8, wherein the second light-emitting diode (LED) is covered by a first photoluminescent block (82).

10. The display pixel of claim 9, wherein the first light-emitting diode (LED) is configured to emit first radiation at a first wavelength, wherein the second light-emitting diode (LED) is configured to emit second radiation at a second wavelength, and wherein the first photoluminescent block (82) is configured to convert the second radiation into third radiation at a third wavelength, different from the second wavelength.

11. The display pixel of claim 10, wherein the first wavelength is equal to the second wavelength within 10%.

12. A display pixel according to any one of claims 9 to 11, wherein the first photoluminescent block (82) comprises first quantum dots.

13. The display pixel of claim 2, wherein the third light emitting diode (LED) is covered by a second photoluminescent block (82).

14. The display pixel of claims 10 and 13, wherein the third light-emitting diode (LED) is configured to emit fourth radiation at a fourth wavelength, and in wherein the second photoluminescent block (82) is configured to convert the fourth radiation into a fifth radiation at a fifth wavelength, different from the fourth wavelength.

15. The display pixel of claim 14, wherein the fourth wavelength is equal to the first wavelength within 10%.

16. A display pixel according to any one of claims 13 to 15, wherein the second photoluminescent block (82) comprises second quantum dots.

17. A display pixel according to any one of claims 1 to 16, comprising a single integrated circuit (30) including said electronic circuit (40) comprising said storage circuit (48) and said drive circuit (50).

18. The display pixel of claim 17, comprising an optoelectronic circuit (32) attached to the integrated circuit (30), said optoelectronic circuit (32) comprising the first and second light emitting diodes (LEDs).

19. A display screen (10) comprising display pixels (1¾) according to any one of claims 1 to 18; first electrodes (180) coupled to the driving circuits (50) of the display pixels (1¾); a first circuit (22) for providing a selection signal (Com;) on each first electrode for selecting the display pixels (1¾) coupled to the first electrode; second electrodes (200) coupled to the electronic circuits (40) of the display pixels (1¾); and a second circuit (24) for providing data signals (Dataj) on the second electrodes.

20. A display screen according to claim 19, wherein the second circuit (24) is configured to provide the data signals (Dataj) on the second electrodes (20j) in the form of analog signals.

21. A display screen according to claim 19, wherein the second circuit (24) is configured to provide the data signals (Dataj) on the second electrodes (20j) in the form of digital signals.

22. A display screen according to claim 19, wherein the second circuit (24) is configured to provide the data signals (Dataj) on the second electrodes (20j) comprising an alternation of digital signals and analog signals.

Images