Method and apparatus for ambient light measurement

Abstract

Embodiments of the present disclosure relate to methods and devices for ambient light measurement. An embodiment method of measuring ambient light includes: generating a first signal by an ambient light sensor associated with a screen, the screen alternating between a first phase in which light is emitted and a second phase in which no light is emitted by the screen, the first signal representing an intensity of light received by the ambient light sensor during the first phase and the second phase; comparing the first signal to a threshold intensity value; and based on the comparison, controlling the timing of ambient light measurements performed by the light sensor.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of European application No. 20153603.4, filed on January 24, 2020, which is hereby incorporated by reference. Technical Field

[0003] The present disclosure relates generally to electronic systems and methods, and more particularly to electronic systems including ambient light sensors and methods of measuring ambient light using such systems. Background Art

[0004] It is known that electronic systems such as mobile phones or tablet computers include a screen that displays information and / or images intended for a user of the system.

[0005] In such a system, the optical power emitted by the screen may be adapted at least in part according to the ambient light level, which is measured by means of an ambient light sensor (ALS). For example, the ambient light measurement is used to adjust the optical power emitted by the screen according to the ambient light level to better perceive the image displayed on the screen by the human eye and to save energy; and thereby extend the life of the battery powering the screen.

[0006] In a known electronic system comprising a screen and an ambient light sensor for measuring the intensity of surrounding or ambient light, the sensor is arranged below a dedicated opening in the screen, below a protective glass covering the screen. It is desirable to position the sensor below the screen without a dedicated opening in the screen, the sensor capturing the weak transmission of light through the screen. However, it is difficult for the sensor to distinguish light emitted by the screen in the direction of the sensor from ambient light that reaches the sensor from outside through the screen. Summary of the invention

[0007] There is a need to address all or some of the disadvantages of known electronic systems comprising a screen and a light sensor for measuring the level of ambient light surrounding the system.

[0008] Thus, one embodiment addresses all or some of the disadvantages of known electronic systems that include a screen and a light sensor for measuring the level of ambient light surrounding the system.

[0009] In particular, one embodiment makes it possible to avoid that the ambient light level measured by the light sensor is distorted by the light emitted by the screen.

[0010] One embodiment provides a method for measuring ambient light, the method comprising: generating a first signal by an ambient light sensor associated with a screen, the screen alternating between a first stage and a second stage, in which light is emitted by the screen and a portion of the light is received by the ambient light sensor, and in which light is not emitted by the screen, the first signal representing an intensity of light received by the ambient light sensor during the first stage and the second stage; comparing the first signal to a threshold intensity value; and controlling the timing of ambient light measurements performed by the light sensor based on the comparison.

[0011] According to one embodiment, comparing the first signal to the threshold intensity value includes: generating a second signal, the second signal having a first state when the intensity of light received by the ambient light sensor is below the threshold intensity value, and having a second state when the intensity of light received by the ambient light sensor is above the threshold intensity value, and wherein the start of the measurement is triggered by at least one transition of the second signal to the first state, such that when the second signal is in the first state, the measurement starts, and the duration of the measurement is controlled based on at least one duration of the first state of the second signal.

[0012] According to one embodiment, the measurement starts after a first transition of the second signal to the first state.

[0013] According to one embodiment, the measurement starts with a time delay between 0.1 μs and 100 μs after the first transition.

[0014] According to one embodiment, the first transition triggers the start of the measurement and after the first transition the next transition of the second signal to the second state ends the measurement.

[0015] According to one embodiment, the duration of the measurement is controlled based on at least one previous duration of the first state of the second signal.

[0016] According to one embodiment, the duration of the measurement is controlled to be shorter than at least one previous duration of the first state of the second signal.

[0017] According to one embodiment, the measured duration is controlled based on an average of at least two consecutive previous durations of the first state of the second signal.

[0018] According to one embodiment, the at least one previous duration of the first state of the second signal comprises: a previous duration of the first state of the second signal immediately before the first state of the second signal at which the measurement starts.

[0019] According to one embodiment, the method comprises counting a number of clock cycles using a counter during at least one previous duration of the first state of the second signal, the duration of the measurement being controlled based on the counted number of clock cycles.

[0020] According to one embodiment, the measured duration is equal to the duration of a first number of consecutive clock cycles, the first number being lower than the counted number of clock cycles.

[0021] According to one embodiment, the first signal is generated based on an output signal of at least one pixel of a plurality of pixels of the ambient light sensor.

[0022] According to one embodiment, the threshold strength value is determined such that the second signal is in the first state during each second phase and in the second state during each first phase.

[0023] One embodiment provides an ambient light sensor configured to perform the method.

[0024] One embodiment provides an electronic device comprising: a screen; a screen driver configured to control the screen to alternate between a first stage in which light is emitted by the screen and a second stage in which no light is emitted by the screen; and the ambient light sensor defined above, configured so that a portion of the light emitted by the screen is received by the ambient light sensor.

[0025] According to one embodiment, the ambient light sensor is arranged at a first side of the screen, the first side being opposite to a second side of the screen from which light is emitted, and wherein, preferably, the transmittance of ambient light through the screen is in the range of 0.5% to 5% when no light is emitted by the screen. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above-mentioned features and advantages and other features and advantages will be described in detail in the following description of specific embodiments given by way of example and not limitation, in which:

[0027] Figure 1 One embodiment of an electronic device is illustrated in front view and in cross-sectional view;

[0028] Figure 2 Another embodiment of an electronic device is illustrated in front view and cross-sectional view;

[0029] Figure 3 The diagram is schematically shown in the form of a box. Figure 1 or Figure 2 The light sensor of the device;

[0030] Figure 4 is a diagram illustrating an embodiment of Figure 3 Timing diagram of the operating modes of the sensor;

[0031] Figure 5 is a diagram illustrating a method according to another embodiment Figure 3 Timing diagram of the operating modes of the sensor;

[0032] Figure 6 is a diagram illustrating a method according to yet another embodiment Figure 3 Timing diagram of the operating modes of the sensor;

[0033] Figure 7 schematically illustrates in block form a circuit according to an example embodiment; and

[0034] Figure 8 It's a picture. Figure 7 Timing diagram of the operating modes of the circuit. DETAILED DESCRIPTION

[0035] In the various drawings, the same features have been denoted by the same reference numerals. In particular, structural and / or functional features that are common between the various embodiments may have the same reference numerals and may be provided with the same structure, dimensions, and material properties.

[0036] For clarity, only operations and elements useful for understanding the embodiments described herein are illustrated and described in detail.

[0037] Unless otherwise specified, when referring to two elements being connected together, it means a direct connection without any intermediate elements other than conductors, and when referring to two elements being coupled together, it means the two elements may be connected or they may be coupled via one or more other elements.

[0038] In the following disclosure, unless otherwise stated, when referring to absolute position qualifiers such as terms "front", "back", "up", "down", "left", "right", etc., or relative position qualifiers such as terms "above", "below", "higher", "lower", etc., or orientation qualifiers such as "horizontal", "vertical", etc., reference is made to the orientation shown in the figure.

[0039] Unless otherwise indicated, the terms "about," "approximately," "substantially," and "on the order of" mean within 10%, preferably within 5%.

[0040] In the following disclosure, an electronic system is considered in which a screen is operated by alternating between phases in which the screen emits light and phases in which the screen is turned off (i.e., the screen does not emit light). In such a system, the average optical power emitted by the screen and perceived by the user is adapted by modifying the duty cycle and / or frequency of screen activation (e.g., by adjusting the duration of the light emission phase and / or the duration of the phase in which no light is emitted). With a sufficient switching frequency between phases in which the screen emits light and phases in which the screen is turned off, the user of the screen cannot perceive the transitions between these phases due to the visual persistence of the human eye. For example, the switching frequency is at least 25 Hz.

[0041] For example, the screen is controlled by a binary control signal, the first state of which causes a phase of light emission by the screen, and the second state of which causes a phase in which no light is emitted by the screen. The control signal is usually subjected to pulse width modulation (PWM) or pulse frequency modulation (PFM). The types of screens to which such control modes are applicable (e.g., LCD (liquid crystal display) or OLED (organic light emitting diode)) and the implementation of these control modes are not described in detail. The described embodiments are compatible with these known control modes and known screens to which these control modes are applicable.

[0042] Figure 1 Two views A and B of one embodiment of an electronic device 2000 are illustrated, which in this example is a mobile phone 2000, view A being a front view of the phone 2000 and view B being a cross-sectional view along the BB plane indicated in view A.

[0043] The device 2000 comprises an electronic system or circuit 1000. The electronic circuit 1000 comprises a screen 100 configured to display images and / or information destined for a user. The display screen or panel 100 comprises a matrix of light emitting pixels (not shown).

[0044] System 1000 further includes various electronic circuits including ambient light sensor 104. Figure 1 In the example shown, in view B, two further electronic circuits are illustrated, namely a processing unit 106 and a driver or control circuit 108 of the screen 100 .

[0045] Various electronic circuits of the system 1000 are mounted on, for example, a printed circuit board (PCB) 110, preferably a flexible printed circuit board, to be electrically coupled to each other via the board 110. Figure 1 A single board 110 is illustrated in the illustrated view B, but the system 1000 may include a plurality of boards 110 that may be electrically coupled to each other via ribbon cables.

[0046] For example, the display screen 100 may be of the OLED (organic light emitting diode) type. The screen 100 is therefore controlled, for example, by a binary control signal, which is generated, for example, by a driver 108. This control signal is selectively provided, for example, to each diode of the screen, thereby causing an alternation between a phase in which at least some of the diodes of the screen 100 emit light and a phase in which the diodes of the screen 100 do not emit light. The selection of the diodes of the screen 100 to receive or not receive the control signal is implemented, for example, by the driver 108. In some cases, for each diode, the driver 108 may adapt the voltage level of the binary signal corresponding to the light emission phase to adapt the light power emitted by the diode. Each pixel of the screen may consist of one or more diodes, which may be covered by an RGB (red, green, blue) color filter.

[0047] For example, the display screen 100 can also be of LCD (liquid crystal display) type. The screen 100 therefore includes, for example, a pixel matrix and an illumination board or illumination panel arranged below the pixel matrix, and each pixel includes a polarized liquid crystal filter. For example, the board is controlled by a binary control signal, and the binary control signal is generated, for example, by a driver 108, so that the board is operated by alternating between a light emission phase and a phase in which the board does not emit any light. In some cases, the driver 108 can further adapt the voltage level of the binary signal corresponding to the light emission phase to adapt the light power emitted by the board. The polarization filter of each pixel is controlled, for example, by the driver 108 of the screen 100 to allow or prevent the light emitted by the board from passing through the polarization filter toward the user. Each pixel of the screen can be covered by one or more RGB color filters.

[0048] In the example shown, the system 1000 also includes a touch screen or touchpad 112 above the display screen 100. The touch screen 112 completely covers the display screen 100, and the screens 100 and 112 have substantially the same surface area, preferably the same surface area.

[0049] Typically, device 2000 includes a protective glass pane 114 that covers screen 100, and more specifically, in this example, covers the assembly including the two screens 100 and 112. Glass pane 114 completely covers screen 100, and the surface area of ​​glass pane 114 is substantially equal to the surface area of ​​screen 100, preferably equal to the surface area of ​​screen 100.

[0050] Device 2000 includes a housing or casing 116 in which system 1000 is disposed, i.e., electronic circuits 104, 106, and 108 and one or more boards 110 are disposed. The assembly of screen 100, optional touch screen 112, and glass pane 114 is disposed on the surface of the system ( Figure 1 The upper surface in view B of Figure 1 The housing 116 is closed on one side of the surface visible in view A.

[0051] In this embodiment, phone 2000 is referred to as "borderless", i.e., screen 100, (and more specifically, the assembly of screen 100, optional touch screen 112, and glass pane 114) occupies substantially the entire surface of the device intended to be viewed by a user of the system, preferably the entire surface, i.e., Figure 1 The upper surface of the device 2000 in view B of FIG. The ambient light sensor 104 is therefore arranged below the screen 100, i.e. on the side of the screen 100 opposite to the surface of the screen 100 from which the screen emits light. The display screen 100, the optional touch screen 112 and the glass pane 114 are therefore at least partially transparent to the ambient light, which corresponds here for example to visible light and possibly to infrared and / or ultraviolet light. Therefore, the ambient light can pass through the components of the glass pane 114, the optional touch screen 112 and the display screen 100 and reach the sensor 104.

[0052] Figure 2 Two views A and B of another embodiment of an electronic device 3000 are illustrated, which in this example is a mobile phone 3000 , view A being a front view of the phone and view B being a cross-sectional view along the BB plane indicated in view A .

[0053] Figure 2 3000 devices with Figure 1 The device 2000 differs in that the display screen 100 and optional touch screen 112 are interrupted above the sensor 104 to allow ambient light to reach the sensor 104. More specifically, a window or recess 118 is provided through the screen 100 and optional touch screen 112, above the sensor 104. A glass pane 114 covers the window 118 to protect the electronic circuitry provided in the housing 116, and in particular, to protect the sensor 104.

[0054] For example, in devices 2000 and 3000, during phases when the screen is switched off and therefore no light is emitted by the screen, the transmittance of light through the components of glass pane 114, optional touch screen 114 and display screen 112 is in the range of 0.5% to 5%.

[0055] It should be noted that the devices 2000 and 3000 are illustrated in a very schematic manner and not all details of these devices are illustrated. Figure 1 and Figure 2 The exemplary device shown in the figure is applicable to all electronic devices including the electronic system 1000, such as tablet computers, connected watches, computer screens, mobile phones, multimedia devices equipped with, for example, flexible or foldable screens, etc. More specifically, the described embodiments are applicable to the electronic system 1000, which includes a display screen 100 and an ambient light sensor 104, which is arranged at a position such as Figure 1 As shown below the screen 100 or as Figure 2 The screen 100 is shown below a window or opening 118, wherein the screen 100 operates by alternating periods in which light is emitted and periods in which no light is emitted.

[0056] Figure 3 The diagram is schematically shown in the form of a box. Figure 1 or Figure 2 The light sensor 104 of the device.

[0057] The ambient light sensor 104 comprises, for example, a light-sensitive area 1041 comprising at least one pixel (not shown) receiving light. Preferably, the area 1041 comprises more than one pixel. Each pixel of the area 1041 provides an output signal 1045 .

[0058] For example, the output signal 1045 of the pixel is an analog signal, the value of which represents, for example, the value of the photocurrent generated by the photodiode of the pixel. Although not shown, the output signal of the pixel is provided, for example, by a transimpedance amplifier, a source follower transistor, or a charge integrator; the gate of the source follower transistor is coupled to a buffer capacitor, a voltage representing the photogenerated charge in the photodiode is stored in the buffer capacitor, and the charge integrator converts the photogenerated charge in the photodiode into a rising voltage. The output signal can also be provided by a readout circuit of the pixel, such as described in application US 9,927,291, the contents of which are incorporated herein by reference in their entirety.

[0059] The pixel's output signal 1045 may also be a binary signal having a pulse whenever a photon received by the pixel's single photon avalanche diode (SPAD) triggers an avalanche phenomenon, or a voltage having a value representing the number of pulses generated in a given time period.

[0060] The light sensor 104 comprises a read circuit 1043. The read circuit 1043 is configured to receive output signals 1045 of the pixels of the area 1041. In this embodiment, the read circuit 1043 is further configured to provide or generate an output signal OUT of the sensor 104 based on the signal 1045. The signal OUT (e.g., a digital signal comprising a plurality of bits) represents the amount of light received by the area 1041 during a given measurement phase, and thus represents the amount of light received by the sensor 104 during the given measurement phase.

[0061] For example, all pixels of sensor 104 are configured to receive light within the same and single wavelength range, and signal OUT represents the amount of light within the single wavelength range received during the measurement phase.

[0062] The pixels of the sensor 104 may also be divided into a plurality of pixel sets, such that in each pixel set, the pixels of the set are configured to receive only light within a given corresponding wavelength range that is different from the wavelength ranges of the other pixel sets, for example by associating each pixel in each pixel set with a corresponding filter suitable for the set wavelength range of the pixel. The signal OUT may thus represent the amount of light received during the measurement phase within each of the plurality of wavelength ranges corresponding to the plurality of pixel sets. Using such a signal OUT, the system 1000 ( Figure 1 or Figure 2 ) can be configured to determine the type of ambient light, for example, whether the light is natural, from a filament bulb, from a fluorescent lamp, whether the light is cold light or warm light, etc., based on the spectral redistribution of the light between each of the plurality of wavelength ranges. In addition, in the case where the screen 100 is a color screen of the OLED type, the processing unit 106 and / or the driver 108 ( Figure 1 or Figure 2 ) can thus be configured to control screen 100 so that, for each wavelength range that screen 100 can emit, screen 100 receives an indication of the average target power that screen 100 needs to emit for that wavelength range. In practice, in the case of an OLED color screen, circuit 108 is typically configured to control each pixel of the screen individually. As a result, system 1000 can thus adapt the type of light emitted by its screen 100 to the type of ambient light surrounding system 1000.

[0063] The reading circuit 1043 is also configured to provide or generate a signal L_int based on the signal 1045 from at least some pixels of the area 1041, the signal L_int being preferably an analog signal. The signal L_int represents the intensity of the light received by the sensor 104 (and more precisely by the area 1041 of the sensor 104) during the operation of the sensor 104. In other words, the value of the signal L_int changes when the intensity of the light received by the sensor 104 changes. For example, the value of the signal L_int is updated so that the time period between each two consecutive values ​​of the signal L_int is at least 10 times shorter, preferably 100 times shorter, than the minimum duration of the phase in which no light is emitted by the screen 100.

[0064] For example, in the case where each signal 1045 is a photocurrent generated by one of the photodiodes of the pixels of the area 1041 , the value of the signal L_int may correspond to an average of the values ​​of the signals 1045 .

[0065] For example, the value of the signal L_int may represent the number of pulses received by the read circuit 1043 within a given duration in consecutive periodic durations, where each signal 1045 presents a pulse for each avalanche phenomenon occurring in the SPAD of the pixel corresponding to the signal 1045. In such a case, the value of the signal 1045, and therefore the value of the signal L_int, is updated at the end of each of these consecutive periodic durations.

[0066] The reading circuit 1043 is under the control of the binary control signal MES, so that for each ambient light measurement phase, the start and end of the measurement phase and its duration are determined based on the signal MES. The circuit 1043 includes an input configured to receive the signal MES. Whenever the signal MES is in a first state (e.g., a high state), an ambient light measurement phase is performed by the sensor 104. The start of each ambient light measurement is triggered by the transition of the signal MES to its first state, and the end of the ambient light measurement is triggered by the next transition of the signal MES to its second state (e.g., a low state).

[0067] The sensor 104 further comprises a control circuit 1047. The control circuit 1047 comprises an input configured to receive a signal L_int and an output configured to provide a signal MES. The control circuit 1047 is configured to generate or provide a signal MES based on the signal L_int. Thus, the circuit 1047 controls the timing of each ambient light measurement phase, i.e., the start and end of an ambient light measurement phase, by means of the signal MES. The circuit 1047 is configured so that ambient light measurement occurs during a phase in which no light is emitted by the screen 100.

[0068] For example, the circuit 1047 is configured to compare the value of the signal L_int with a threshold intensity value th. The circuit 1047 is also configured to generate a binary signal COMP, which represents the comparison result of the signal L_int and the threshold intensity value th. The threshold intensity value th is selected so that the state of the signal COMP indicates whether the screen 100 emits light.

[0069] A first state (e.g., a high state) of the signal COMP indicates that the intensity value of the light received by the sensor 104 is lower than a threshold value determined based on the threshold intensity value th, and the signal COMP is in its first state when, for example, the signal L_int is lower than the threshold value th. A second state (e.g., a low state) of the signal COMP indicates that the intensity value of the light received by the sensor 104 is higher than a threshold value determined based on the threshold intensity value th, and the signal COMP is in its second state when, for example, the signal L_int is higher than the threshold value th. The threshold intensity value th is selected such that the first state of the signal COMP indicates that no light is emitted by the screen 100, and the second state of the signal COMP indicates that the screen 100 is emitting light and a portion of the emitted light is received by the sensor 104.

[0070] For example, the circuit 1047 includes a circuit or comparator 1049 configured to compare the signal L_int with the threshold intensity value th and generate a COMP signal accordingly. For example, the comparator 1049 includes: a first input configured to receive the signal L_int, for example, a negative input (-); a second input configured to receive the threshold intensity value th, for example, a positive input (+); and an output configured to generate the COMP signal.

[0071] The circuit 1047 is then configured to generate a signal MES based on the signal COMP so that an ambient light measurement is performed during corresponding phases in which no light is emitted by the screen 100. By doing so, during phases in which light is emitted by the screen 100, the value of the measured ambient light is not distorted by the light emitted by the screen 100 towards the sensor 104.

[0072] Figure 4 is a diagram illustrating an embodiment of Figure 3 A timing diagram of the operating modes of the sensor 104. Figure 4 In the embodiment of the present invention, the signal MES is the same as the signal COMP.

[0073] At the instant t0, the screen 100 is controlled to be in a phase ON in which light is emitted by the screen 100. The value of the signal L_int is greater than the threshold intensity value th, since a portion of the emitted light is received by the sensor 104. Therefore, the signals COMP and MES, which are identical here to each other, are in their second state, which in this example is a low state.

[0074] The screen 100 is in the ON phase until a moment t1 before the moment t0. At the moment t1, the screen 100 is switched to the OFF phase, in which no light is emitted by the screen 100. Since the sensor 104 does not receive the light emitted by the screen, the value of the signal L_int decreases and becomes lower than the threshold intensity value th. Therefore, the signals COMP and MES transition to their first state, which is a high state in this example.

[0075] The screen 100 is in the OFF phase until a moment t2 after the moment t1. At the moment t2, the screen is switched to the ON phase. The value of the signal L_int increases and becomes higher than the threshold intensity value th. Therefore, the signals COMP and MES transition to their second states.

[0076] The screen 100 is in the ON phase until a time t3 after the time t2. At the time t3, the screen is switched to the OFF phase, the signal L_int drops below the threshold intensity value th, and the signals COMP and MES transition to their first states.

[0077] The screen 100 is in the OFF phase until a time t4 after the time t3. At the time t4, the screen is switched to the ON phase, the signal L_int exceeds the threshold intensity value th, and the signals COMP and MES transition to their second states.

[0078] The screen 100 is in the ON phase until a time t5 after the time t4. At the time t5, the screen is switched to the OFF phase, the signal L_int drops below the threshold intensity value th, and the signals COMP and MES transition to their first states.

[0079] exist Figure 4 In the embodiment of the present invention, each transition of the signal MES to its first state triggers the start of a corresponding ambient light measurement phase (times t1, t3 and t5), and each transition of the signal MES to its second state ends a corresponding ambient light measurement phase (times t2 and t4). In other words, each ambient light measurement is performed starting from the transition of the signal COMP to its first state until the next transition or the next transition of the signal COMP to its second state.

[0080] Therefore, in Figure 4 In an embodiment of the invention, the duration of an ambient light measurement phase triggered by a given transition of the signal MES to its first state is determined by the corresponding duration of the first state of the signal MES (i.e. the duration of the first state of the signal MES after the given transition). In this way, each ambient light measurement phase is performed during a corresponding OFF phase.

[0081] Despite Figure 4 1 shows three consecutive ON phases alternating with three consecutive OFF phases, but the sensor 104 is configured to operate in the above-described manner regardless of the number of alternating ON and OFF phases.

[0082] Figure 5 is a diagram illustrating a method according to another embodiment Figure 3 A timing diagram of the operating modes of the sensor 104.

[0083] More specifically, in this embodiment, it is considered that when the screen 100 switches from the ON phase to the OFF phase, the intensity of the light emitted by the screen gradually decreases between a high value at the end of the ON phase and a zero value reached during the OFF phase due to the afterglow of the screen 100. Therefore, the transition of the signal COMP may occur even when the intensity of the light emitted by the screen is not yet zero.

[0084] In this embodiment, the ambient light measurement phase starts at a given time delay Ts after the signal COMP transitions to its first state, the time delay Ts being selected so that at the start of the ambient light measurement, the intensity of the light emitted by the screen 100 is zero. Thus, the time delay is determined based on the duration of the persistence of the screen. For example, the time delay Ts is in the range of 0.1 μs to 100 μs.

[0085] exist Figure 5 In Figure 4 As mentioned, at instant t0 , the screen 100 is in the ON phase, the signal L_int is therefore above the threshold intensity value th, and the signals COMP and MES are in their second state.

[0086] exist Figure 5 In Figure 4 As described, at time t1, the screen 100 is switched to the OFF phase. The intensity of the light emitted by the screen 100 then gradually decreases and reaches a zero value at time t1_2 after time t1. As a result, the signal L_int decreases from time t1 to time t1_2, and drops below the threshold intensity value th at time t1_1 between time t1 and t1_2. As a result, the signal COMP transitions to its first state at time t1_1, while the intensity of the light emitted by the screen 100 is not yet zero. However, at a time delay Ts after time t1_1, at time t1_3 after time t1_2 and equal to t1_1+Ts, the signal MES is transitioned to its first state by the circuit 1047. Therefore, when the ambient light measurement phase starts at time t1_3 due to the transition of the signal MES to its first state, the intensity of the light emitted by the screen is zero.

[0087] At time t2 after time t1_3, screen 100 is switched to the ON phase, signal L_int exceeds the threshold intensity value th, and signals COMP and MES transition to their second states.

[0088] At time t3 before time t2, screen 100 is switched to the OFF phase. Sensor 104 then operates at successive times t3_1, t3_2 and t3_3 in the same manner as described with respect to corresponding times t1_1, t1_2 and t1_3, time t3_3 thus being equal to t3_1+Ts.

[0089] At time t4 after time t3_3 , screen 100 is switched to the ON phase, signal L_int exceeds the threshold intensity value th, and signals COMP and MES transition to their second states.

[0090] At time t5 after time t4, screen 100 is switched to the OFF phase. Sensor 104 then operates in the same manner as described with respect to corresponding times t1_1, t1_2 and t1_3 at successive times t5_1, t5_2 and t5_3, time t5_3 thus being equal to t5_1+Ts.

[0091] Despite Figure 5 1 shows three consecutive ON phases alternating with three consecutive OFF phases, but the sensor 104 is configured to operate in the above-described manner regardless of the number of alternating ON and OFF phases.

[0092] exist Figure 4 and Figure 5 In an embodiment of the invention, each transition of the signal COMP to its first state (possibly after a time delay Ts) triggers a corresponding ambient light measurement, and the next transition of the signal COMP to its second state ends the measurement phase. Thus, the duration of the measurement phase is determined by the duration of the first state of the signal COMP after a transition of the signal COMP triggers the measurement phase.

[0093] In an alternative embodiment, each transition of the signal COMP to its first state triggers the start of a corresponding ambient light measurement phase, but the duration of this measurement phase is controlled based on at least one duration of the first state of the signal COMP occurring before this measurement phase. In other words, the duration of this measurement phase is controlled based on at least one duration of the first state of the signal COMP occurring before the transition of the signal COMP that triggered the measurement phase.

[0094] Figure 6 is a diagram illustrating a method according to another embodiment Figure 31 , wherein the duration of the ambient light measurement phase is determined based on at least one previous duration of a first state of the signal COMP, in this example by an immediately preceding duration of the first state of the signal COMP.

[0095] exist Figure 6 In Figure 4 and Figure 5 As shown, at time t0, the screen 100 is in the ON phase, the signal L_int is therefore higher than the threshold intensity value th, and the signals COMP and MES are in their second state. In addition, the duration T0 ( Figure 6 Information (not shown) has been stored by circuit 1047 in, for example, a memory of circuit 1047.

[0096] At time t1, the screen 100 is switched to the OFF stage, and the signal L_int gradually decreases to reach a zero value at time t1_2, and the signal L_int drops below the threshold intensity value th at time t1_1 between time t1 and t1_2.

[0097] Since the signal L_int falls below the threshold value th at the instant t1_1, the signal COMP changes to its first state at the instant t1_1. In this example, at the instant t1_3 separated by a time delay Ts from the instant t1_1, the change of the signal COMP to its first state causes the signal MES to change to its first state. Furthermore, the signal MES remains in its first state for a duration T0' which is lower than the duration T0, so that the signal MES changes to its second state while the screen 100 is still in the OFF phase. Therefore, during the OFF phase between the instants t1 and t2, the duration of the measurement phase performed is therefore T0'.

[0098] In this example, duration T0' is equal to T0-Ts-Te, Te being a given duration. Duration Te is selected so that at the end of duration T0', when signal MES changes to its second state at instant t1_4 ​​equal to t1_3+T0', screen 100 is still in the OFF phase.

[0099] Subtracting the duration Te from the previous duration T0 allows ensuring that, even if the signal COMP transitions to its second state with a delay compared to the moment when the signal L_int exceeds the threshold intensity value th, the ambient light measurement phase ends before the next ON phase of light emitted by the screen.

[0100] Furthermore, between times t1 and t2, circuit 1047 acquires or generates information representative of duration T1 of the first state of signal COMP between these times and stores this information.

[0101] At instant t3, the screen 100 is switched to the OFF phase and the signal L_int gradually decreases to a zero value at instant t3_2, the signal L_int falling below the threshold intensity value th at instant t3_1 between instants t3 and t3_2. Therefore, the signal COMP changes to its first state at instant t3_1 and the signal MES changes to its first state at instant t3_3 equal to t3_1+Ts in this example. The signal MES then remains in its first state for a duration T1' after the duration T1, at least before the duration Te, and more precisely, in this example, the duration T1' is equal to T1-Ts-Te. The signal MES changes to its second state at an instant t3_4 equal to t3_3+T1', while the screen 100 is still in the OFF phase, which ends at an instant t4 after the instant t3_4. Therefore, during the OFF phase between instants t3 and t4, the duration of the measurement phase performed is T1'.

[0102] Furthermore, information representative of the duration T2 of the first state of the signal COMP between the instants t3_1 and t4 is stored by the circuit 1047 .

[0103] At instant t5, the screen 100 is switched to the OFF phase and the signal L_int gradually decreases to a zero value at instant t5_2, the signal L_int falling below the threshold intensity value th at instant t5_1 between instants t5 and t5_2. Therefore, the signal COMP transitions to its first state at instant t5_1 and the signal MES transitions to its first state at instant t5_3, which is equal to t5_1+Ts in this example. The signal MES then remains in its first state for a duration T2' after the duration T2, at least before the duration Te, and more precisely, in this example, the duration T2' is equal to T2-Ts-Te. The signal MES transitions to its second state at an instant (not shown) equal to t5_3+T2', while the screen 100 is still in the OFF phase. Therefore, the duration of the measurement phase performed during the OFF phase starting at instant t5 is T2'.

[0104] Furthermore, information representative of the duration T3 of the first state of the signal COMP starting at the instant t5_1 is stored by the circuit 1047 .

[0105] Despite Figure 61 shows three consecutive ON phases alternating with three consecutive OFF phases, but the sensor 104 is configured to operate in the above-described manner regardless of the number of alternating ON and OFF phases.

[0106] In an alternative embodiment, after a given transition of the signal COMP to its first state, the duration of the ambient light measurement phase is determined based on several previous durations of the first state of the signal COMP. For example, after the signal COMP transitions to its first state at time t5, the duration T2' of the ambient light measurement phase is determined based on the durations T0, T1 and T2, the duration T2' being, for example, equal to Tmean-Te-Ts, where Tmean is the average of the durations T0, T1 and T2.

[0107] exist Figure 6 In an embodiment of the invention, the information representative of the duration of the first state of the signal COMP is output, for example, by a counter configured to count the number of periods of a periodic signal (e.g. a clock signal) while the signal COMP is in its first state. The period of the periodic signal is, for example, at least 10 times shorter than the minimum duration of the OFF phase, preferably at least 100 times shorter than the minimum duration of the OFF phase. The duration of the measurement phase may then correspond to the duration of a given number of consecutive periods of the periodic signal, for example a number of consecutive periods equal to the number of periods counted during the previous first state of the signal COMP, from which the number of periods corresponding to the duration Te and possibly the number of periods corresponding to the duration Ts have been subtracted. Thus, when the signal COMP switches to its first state, the signal MES is switched to its first state after a number of periods corresponding to the duration Te, the signal MES then being switched to its second state at the end of the duration of the measurement phase, the duration of the measurement phase being determined as described above.

[0108] exist Figure 6 In the embodiment of the invention, signal MES is generated, for example, by using at least one phase-locked loop of circuit 1047 .

[0109] For example, one phase-locked loop is locked when the signal COMP transitions to its first state, and one phase-locked loop is locked when the COMP signal transitions to its second state, and the output signals of the two phase-locked loops are used to generate the corresponding signal MES. In this case, the information representing the duration of the first state of the signal COMP corresponds to the phase difference between the two outputs of the phase-locked loops and is stored inside the circuit 1047 by the phase-locked loops themselves.

[0110] As another example, a single phase-locked loop is locked when the signal COMP transitions to its second state. For example, the phase-locked loop includes: a voltage-controlled oscillator, the output signal of which is delayed by a duration Te; and a phase detector, which outputs a signal representing the phase difference between the transition of the delayed signal to its second state and the transition of the COMP signal to its second state. The output signal of the phase detector can be used to control the voltage-controlled oscillator after being filtered by a low-pass filter, thereby controlling the phase and / or frequency of the output signal of the voltage-controlled oscillator. The transition of the signal COMP to its first state is preferably used to switch the signal MES to its first state after being delayed for a duration Ts, and the transition of the output signal of the voltage-controlled oscillator to its second state is used to switch the signal MES to its second state. For example, the delayed signal COMP is provided to the set input of an RS-type latch, the output signal of the voltage-controlled oscillator is provided to the reset input of the latch, and the signal MES is provided by the output of the latch.

[0111] Figure 7 A circuit configured to generate a signal MES based on a COMP signal using a single phase-locked loop according to an exemplary embodiment of the type described above is illustrated in block form.

[0112] The phase-locked loop PLL comprises a voltage-controlled oscillator VCO, a delay circuit eD, a phase-shift detector circuit PSD and, in this example, a low-pass filter LPF.

[0113] The oscillator VCO provides the MESe signal to the delay circuit eD.

[0114] The delay circuit eD applies a delay equal to the duration Te to the signal MESe, the resulting delayed signal MESed being provided by the circuit eD.

[0115] The circuit PSD receives the MESed signal and the COMP signal and provides a signal PSDo representing a phase shift between the signals MESed and COMP.

[0116] The circuit VCO is controlled based on the signal PSDo so that in stationary operation the switching of the signal MESed to its second state is synchronized with the switching of the COMP signal to its second state. More specifically, in this example, the signal PSDo is provided to the filter LPF and the resulting filtered signal fPSDo is the control signal of the circuit VCO.

[0117] Furthermore, the COMP signal is delayed for a duration Ts by a delay circuit sD which provides a delay signal MESs.

[0118] The signal MES is then generated based on the MESe and MESs signals. In this example, this is done using an RS-type latch RS, the output of which provides the MESe signal. The reset input of the latch RS receives the signal MESe inverted by the inverter circuit INV, and the set input of the latch RS receives the signal MESs.

[0119] Figure 8 It's a picture. Figure 7 Timing diagram of the operating modes of the circuit. Figure 8 The evolution of the signals COMP, MESs, MESe, MESed and MES is shown.

[0120] It can be seen that the signal MES switches to its first state when the signal MESs and therefore the signal COMP delayed by a duration Ts switches to its first state, and the signal MES switches to its second state when the signal MESe switches to its second state. Thus, the signal MES switches to its first state with a delay equal to the duration Te after the COMP signal switches to its first state correspondingly, and switches to its second state with a time advance equal to the duration Te before the signal COMP switches to its second state correspondingly.

[0121] In another alternative embodiment, a filter function is applied to the value of each duration of the first state of the signal COMP to remove values ​​that are relatively far from previous values, for example to remove values ​​that differ from at least one previous value by more than 10%. Figure 6 All embodiments described are compatible.

[0122] In another alternative embodiment, each transition of the signal COMP to its first state is not delayed for a duration Ts after a corresponding transition of the signal MES to its first state. Thus, in this case, the duration Ts is not subtracted from the previous duration of the first state of the signal COMP. This alternative embodiment is different from the one regarding Figure 6 All embodiments described are compatible.

[0123] In another alternative embodiment, the value representing the amount of light received by the sensor 104 during a given ambient light measurement phase is weighted by the duration of the measurement phase, for example by dividing this value by the duration of the measurement phase or by the number of periods of a periodic signal representing this duration. The signal OUT provided at the end of the measurement then represents the weighted value. This allows the ambient light to be measured without being sensitive to the fact that different ambient light measurement phases may have different durations. This alternative embodiment is similar to the one regarding Figure 4 , Figure 5 and Figure 6 All embodiments described are compatible.

[0124] In another alternative embodiment, circuit 1047 is further configured to detect when the current ambient light measurement phase ends during the ON phase of screen 100, for example by comparing the states of signals COMP and MES and detecting when signal MES is in its first state and signal COMP is in its second state. The result of this detection can be output by sensor 104, for example to make the output value of signal OUT valid or invalid. The generation of the output value of signal OUT can also be adjusted by the result of this detection to ensure that only the value of signal OUT corresponding to the ambient light measurement performed as a whole during the corresponding OFF phase is output. This alternative embodiment is similar to the one regarding Figure 6 All embodiments described are compatible.

[0125] As an example, in the above-described embodiment, the duration of each ON phase is between 1 ms and 10 ms, and the duration of each OFF phase is between 50 μs and 500 μs.

[0126] The above about Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 and Figure 8 The described embodiment allows synchronizing the ambient light measurement phases with the corresponding OFF phases of the screen, which alternates between OFF and ON phases. This synchronization is done without using a signal that controls the switching of the screen between OFF and ON phases or a signal derived from this control signal. Using such a signal would require an additional input pin for the sensor 104 compared to the above described embodiment and would cause problems due to unknown and uncontrolled time delays occurring in these signals.

[0127] It is particularly interesting to implement the above-described embodiments in an electronic device comprising an ambient light sensor 104, which is arranged below the screen 100 and without a notch or window above the light sensor 104. However, the embodiments described herein may also be implemented in the case where the screen 100 comprises such a notch or window above the sensor 104. Indeed, even with such a notch or window, the ambient light measurements performed at least partially during the ON phase of the screen will be distorted by the light emitted by the screen 100.

[0128] Various embodiments and variations have been described. Those skilled in the art will appreciate that certain features of these embodiments may be combined and that other variations will be readily apparent to those skilled in the art. Specifically, when it has been indicated that the first state or the second state of a binary signal corresponds to a high state or a low state of the signal, respectively, those skilled in the art are able to adapt the described embodiments to situations where the first state or the second state of the signal corresponds to a low state or a high state of the signal, respectively. Furthermore, although the value of the above-mentioned signal L_int increases or decreases, respectively, when the intensity of the light received by the sensor 104 increases or decreases, respectively, when the intensity of the light received by the sensor 104 decreases or increases, respectively, those skilled in the art are able to adapt the described embodiments to situations where the value of the above-mentioned signal L_int increases or decreases, respectively,

[0129] Finally, based on the functional description provided above, the actual implementation of the embodiments and variations described herein is within the capabilities of those skilled in the art. Specifically, based on the functional description provided above, the implementation of the read circuit 1043 and / or the implementation of the control circuit 1047 and / or the selection of the value Ts and / or the selection of the value Te are within the capabilities of those skilled in the art.

Claims

1. A method for measuring ambient light, include: generating, by an ambient light sensor associated with a screen, a first signal, the screen alternating between a first phase in which light is emitted by the screen and a portion of the light emitted by the screen is received by the ambient light sensor, and a second phase in which no light is emitted by the screen, the first signal representing an intensity of light received by the ambient light sensor during the first phase and the second phase; Comparing the first signal to a threshold intensity value, the comparing comprising: generating a second signal having a first state in response to the intensity of the light received by the ambient light sensor being below the threshold intensity value; and generating the second signal having a second state in response to the intensity of the light received by the ambient light sensor being above the threshold intensity value, and determining the threshold strength value so that the second signal is in the first state during each second phase and in the second state during each first phase; and Based on the comparison, the timing of ambient light measurements performed by the ambient light sensor is controlled, the start of the measurement being triggered by at least one transition of the second signal to the first state, such that the measurement starts when the second signal is in the first state, and the duration of the measurement is controlled based on at least one duration of the first state of the second signal. 2 . The method of claim 1 , wherein the measuring begins after a first transition of the second signal to the first state. 3 . The method of claim 2 , wherein the measurement starts at a time delay of between 0.1 μs and 100 μs after the first transition. 4 . The method of claim 2 , wherein the first transition triggers the start of the measurement, and a next transition of the second signal to the second state after the first transition ends the measurement. The method of claim 2 , wherein the duration of the measurement is controlled based on at least one previous duration of the first state of the second signal. The method of claim 5 , wherein the duration of the measurement is controlled to be shorter than the at least one previous duration of the first state of the second signal. 7 . The method of claim 5 , wherein the duration of the measurement is controlled based on an average of at least two consecutive previous durations of the first state of the second signal.

8. The method of claim 5, wherein the at least one previous duration of the first state of the second signal include: A previous duration of the first state of the second signal immediately preceding the first state of the second signal at which the measuring begins.

9. The method according to claim 5, further comprising: include: During the at least one previous duration of the first state of the second signal, a number of clock cycles is counted using a counter, the duration of the measurement being controlled based on the counted number of clock cycles.

10. The method of claim 9, wherein the duration of the measurement is equal to the duration of a first number of consecutive clock cycles, the first number being less than the counted number of clock cycles. 11 . The method of claim 1 , wherein the first signal is generated based on an output signal of at least one pixel of a plurality of pixels of the ambient light sensor.

12. An ambient light sensor associated with a screen, the screen alternating between a first phase in which light is emitted by the screen and a portion of the light emitted by the screen is received by the ambient light sensor, and a second phase in which no light is emitted by the screen and the ambient light sensor include: An electronic circuit device configured to: generating a first signal representing an intensity of light received by the ambient light sensor during the first stage and the second stage; comparing the first signal to a threshold strength value, the comparing comprising the electronic circuit arrangement being configured to: generating a second signal having a first state in response to the intensity of the light received by the ambient light sensor being below the threshold intensity value; and in response to the intensity of the light received by the ambient light sensor being above the threshold intensity value, generating the second signal having a second state, and determining the threshold strength value so that the second signal is in the first state during each second phase and in the second state during each first phase; as well as Based on the comparison, the timing of ambient light measurements performed by the ambient light sensor is controlled, wherein the start of the measurement is triggered by at least one transition of the second signal to the first state, such that the measurement starts when the second signal is in the first state, and the duration of the measurement is controlled based on at least one duration of the first state of the second signal.

13. The ambient light sensor of claim 12, wherein the electronic circuit arrangement is configured to start the measurement after a first transition of the second signal to the first state.

14. The ambient light sensor of claim 12, wherein the first signal is generated based on an output signal of at least one pixel of a plurality of pixels of the ambient light sensor.

15. The ambient light sensor of claim 12, wherein the measuring begins after a first transition of the second signal to the first state.

16. An electronic device, include: Screen; a screen driver configured to control the screen to alternate between a first phase in which light is emitted by the screen and a second phase in which no light is emitted by the screen; as well as an ambient light sensor, arranged so that a portion of the light emitted by the screen is received by the ambient light sensor, the ambient light sensor comprising: An electronic circuit device configured to: generating a first signal representing an intensity of light received by the ambient light sensor during the first stage and the second stage; comparing the first signal to a threshold strength value, the comparing comprising the electronic circuit arrangement being configured to: generating a second signal having a first state in response to the intensity of the light received by the ambient light sensor being below the threshold intensity value; and generating the second signal having a second state in response to the intensity of the light received by the ambient light sensor being above the threshold intensity value, and determining the threshold strength value so that the second signal is in the first state during each second phase and in the second state during each first phase; and Based on the comparison, the timing of ambient light measurements performed by the ambient light sensor is controlled, wherein the start of the measurement is triggered by at least one transition of the second signal to the first state, such that the measurement starts when the second signal is in the first state, and the duration of the measurement is controlled based on at least one duration of the first state of the second signal. 17 . The electronic device of claim 16 , wherein the ambient light sensor is disposed at a first side of the screen, the first side being opposite to a second side of the screen from which the light is emitted.

18. The electronic device of claim 17, wherein a transmittance of ambient light through the screen is in a range from 0.5% to 5% when no light is emitted by the screen.

19. The electronic device of claim 16, wherein the electronic circuit arrangement is configured to start the measurement after a first transition of the second signal to the first state.

20. The electronic device of claim 16, wherein the first signal is generated based on an output signal of at least one pixel of a plurality of pixels of the ambient light sensor.

21. The electronic device of claim 16, wherein the measuring begins after a first transition of the second signal to the first state.

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