Device and method for controlling display screen brightness

Abstract

The apparatus includes a display screen, an ambient light sensor disposed behind the display screen, and an electronic control unit. An integration time of the ambient light sensor is not synchronized with a frame rate of the display screen. The electronic control unit is operable to control the brightness of the display screen based on a duty cycle of a PWM blanking signal, wherein at least one off time of the PWM blanking signal occurs entirely within a first integration period of the ambient light sensor, and wherein at least one other integration period on time of the PWM blanking signal occurs entirely during an on time of the PWM blanking signal. The electronic control unit is further operable to acquire samples of the output of the ambient light sensor, identify a highest value and a lowest value from a group of consecutive samples, and estimate a magnitude of the ambient light signal based at least in part on the highest value and the lowest value.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 713,851, filed on August 2, 2018. The contents of this prior application are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to ambient light sensing systems. Background Art

[0004] A recent trend in smartphone industrial design is to maximize the screen area by reducing the bezel width and cleaning up the remaining bezel area by removing holes for optical sensors and other holes for microphones, speakers, and / or fingerprint reading devices. On the other hand, there is also a trend to increase the number of optical sensors for added functionality. For example, an ambient light sensor (ALS) may be provided to adjust the display brightness to the surrounding lighting environment so that the display looks clear and readable while also reducing the overall energy consumption of the display.

[0005] A further trend in the smartphone market is the adoption of organic light emitting displays (OLEDs). This trend creates the opportunity to move the ALS from the bezel of the smartphone to a location underneath the OLED. OLEDs are typically opaque, primarily due to a protective film on the back. This film can be removed in a very small area to allow ambient light to pass through the remaining layers of the OLED to the ALS. However, even with the film removed, OLEDs are not very light-transmissive, so very sensitive sensors are required for ambient light detection. There are further complications that make ambient light detection through OLEDs technically challenging. The ALS sensor detects not only ambient light that passes through the display (e.g. background light, daylight, etc.), but also light generated by the display itself. Therefore, driven by the ALS, the display brightness will fluctuate as the brightness of the pixels directly above the sensor changes. This fluctuation is undesirable. Summary of the invention

[0006] The present disclosure describes portable computing devices and other apparatuses that include ambient light sensor systems. The techniques described in the present disclosure are particularly advantageous when the ambient light sensor is disposed behind a display screen of a host device so that ambient light detected by the sensor passes through the illuminated display before being detected by the sensor.

[0007] For example, in one aspect, the present disclosure describes an apparatus including a display screen, an ambient light sensor disposed behind the display screen, and an electronic control unit. The integration time of the ambient light sensor is not synchronized with the frame rate of the display screen. The electronic control unit is operable to control the brightness of the display screen based on a duty cycle of a PWM blanking signal, wherein at least one OFF time of the PWM blanking signal occurs entirely within a first integration period of the ambient light sensor, and wherein at least one other integration period ON time of the PWM blanking signal occurs entirely during an ON time of the PWM blanking signal. The electronic control unit is further operable to acquire samples of the output of the ambient light sensor to identify a highest value and a lowest value from a group of consecutive samples, and to estimate the magnitude of the ambient light signal based at least in part on the highest value and the lowest value.

[0008] The present disclosure also describes a method that includes acquiring samples of an output of an ambient light sensor disposed behind a display screen, the display screen having a brightness that can be controlled by a duty cycle of a blanking PWM signal, wherein an integration time of the ambient light sensor is not synchronized with a frame rate of the display screen. The method also includes identifying a highest value and a lowest value from a group of consecutive samples in the samples, and estimating a magnitude of an ambient light signal based at least in part on the highest value and the lowest value.

[0009] Some embodiments include one or more of the following features. For example, in some cases, the PWM blanking waveform and the integration time are in the period P b In-phase and out-of-phase, so that P WTIME =P b / [(P b / P PWM )-1], where P WTIME is the sum of the integration time and the delay before the next integration time of the ambient light sensor begins, and where P PWM is the period of the PWM blanking signal.

[0010] In some embodiments, the electronic control unit is operable to estimate the magnitude of the ambient light signal further based on a duration of an integration period of the ambient light sensor and an off time of the PWM blanking signal. In some cases, the integration period of the ambient light sensor is less than or equal to a difference between an on time of the PWM blanking signal and a delay before a next integration time of the ambient light sensor begins. Further, in some cases, the integration time of the ambient light sensor is greater than a sum of an off time of the PWM blanking signal and a delay before a next integration time of the ambient light sensor begins.

[0011] The electronic control unit may adjust the brightness of the display screen based at least in part on the estimated magnitude of the ambient light signal.

[0012] For example, the present technique can be advantageous in asynchronous systems where the integration time of the ambient light sensor does not need to be synchronized with the frame rate of the display. In some cases, the sampling frequency may be slightly different from the display frame rate, allowing the sensor integration time to be in-phase and out-of-phase with the display PWM blanking time over a relatively short period. This feature, in turn, can increase the sampling time to nearly the entire display off time.

[0013] Other aspects, features, and advantages will become apparent from the following detailed description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Various features of a host device including an ambient light sensor behind a display screen are shown.

[0015] Figure 2 An example of a driving circuit for an organic light emitting display is shown.

[0016] Figure 3 An example of a PWM blanking signal is shown.

[0017] Figure 4 is a flow chart of a method for determining an ambient light signal.

[0018] Figure 5 is a block diagram of an example system.

[0019] Figure 6 An example of a calling sequence is shown. DETAILED DESCRIPTION

[0020] like Figure 1 As shown, a host device 10, such as a portable computing device (e.g., a smartphone, a personal digital assistant (PDA), a laptop computer, or a wearable), includes an OLED-type or other display screen 12, which may be disposed directly below a front glass 20. An ambient light sensor (ALS) 14 is disposed directly below a portion of the display screen 12 and is operable to sense ambient light (e.g., sunlight or other background light). The ALS 14 may also sense light generated by the display screen 12 itself. The ALS 14 may include one or more photodiodes or other light sensing elements, each of which is sensitive to a corresponding wavelength or wavelength range that may be different from one another. An electronic control unit (ECU) 16 is operable to receive, process, and analyze signals from the ALS 14 and control the brightness of the display screen 12. For example, the ECU 16 may be a processor for a sensor hub or some other processor in the portable computing device 10.

[0021] The overall brightness of the OLED can be controlled, for example, by applying PWM modulation to each pixel using a transistor in series with that pixel, or by adjusting the overall range of current that can drive each pixel. Figure 2 An example of an OLED driving circuit for a single OLED pixel is shown. Depending on the charge stored on capacitor C1, the current driving each pixel is controlled by the first transistor TFT1, thereby controlling the brightness of each pixel. Before each pixel is turned on, capacitor C1 is charged to an appropriate level V by setting voltage SCAN1 low. DATA Once the voltage SCAN2 goes high, the second transistor TFT2 turns on and allows current to flow through the OLED pixel modulated by the first transistor TFT1. The voltage SCAN2 is also used to apply PWM modulation to reduce the overall display brightness by applying a square wave at multiples of the periodic display frame rate (e.g., multiples of 60Hz). The duty cycle of the square wave sets the display brightness. The higher the duty cycle, the longer the PWM blanking signal is on (i.e., a digital high signal).

[0022] In principle, the ambient light signal can be determined by estimating the light contribution from the display screen and subtracting that value from the total measured light signal (i.e., a signal representing the sum of the ambient light and the display screen light). If the duty cycle of the PWM blanking signal is relatively low (e.g., less than 40% in some cases), the duty cycle off time of the PWM signal can be long enough to capture an entire sample during the duty cycle off time. However, when the duty cycle is relatively high (e.g., 40% or more in some cases), it becomes more difficult to sample the output from the ALS 14 during the duty cycle off time because the blanking off time of the PWM signal is relatively short. In addition, using a shorter integration time to capture output samples of the sensor tends to result in less reliable samples.

[0023] This disclosure describes asynchronous techniques and systems that facilitate decoupling of ambient light components from display screen brightness. In this context, asynchronous operation means that the integration time of the ALS sensor 14 does not need to be synchronized with the frame rate of the display screen. Figure 3 An example of a PWM blanking signal 100 having an off time 102 and an on time 104 is shown. Figure 3 Groups of sequential integration times 106 for ambient light sensors 14 are labeled 1 through 9 .

[0024] This disclosure describes techniques that use a sampling frequency that is slightly different from the display frame rate. This feature means that the integration time will be in-phase and out-of-phase with the display PWM blanking time for a relatively short period of time and allows the sampling time to be increased to almost the entire display off time. To help ensure that the PWM blanking waveform and integration time are within the period P b Internally in-phase and out-of-phase, the following relationship applies:

[0025] P WTIME =P b / [(P b / P PWM )–1](Equation 1)

[0026] Where P WTIME is the sum of the integration time of the sensor and the delay (e.g., waiting time) before the next integration time of the sensor begins, and where P PWM is the PWM blanking period. In some embodiments, the period P WTIME Stored and set by a register. For example, in some cases, the delay time from the end of one integration period to the beginning of the next integration period is 0.2777 milliseconds. For other embodiments, this value may be different.

[0027] In addition to the above constraints of Equation 1, at least one integration time 106 should occur entirely within the PWM on time 104. Therefore, the sensor's integration time 106 should be less than or equal to the difference between the PWM on time and the delay before the sensor's next integration time begins. The samples taken during this integration time measure the sum of the ambient light (A) and the display light (D). Further, at least one PWM off time 102 should occur entirely within another integration time 106. Therefore, the sensor's integration time 106 should be greater than the sum of the PWM off time and the delay before the sensor's next integration time begins. For example, assuming a PWM period of 4.167 milliseconds and a duty cycle of 90%, the PWM on time is approximately 3.75 milliseconds. Further assuming that the delay from the end of one integration time to the start of the sensor's next integration time is 0.2777 milliseconds, then an integration time of (3.75 milliseconds - 0.2777 milliseconds) = 3.472 milliseconds will satisfy the above two constraints.

[0028] The ECU 16 can calculate the ambient light level (A ambient ), for example using the following relationship:

[0029] A ambient =[VALUE_H / (integral time)]–[(VALUE_H–VALUE_L) / (blanking off time)]

[0030] For example, the integration time may be set by software driving the ALS sensor 14. For example, the blanking off time may be calculated as follows:

[0031] Blanking off time = (1-d)*(1 / f)

[0032] Where d is the duty cycle and f is the PWM frequency (i.e., P PWMThe ECU 16 may obtain the values ​​of d and f, for example, from a lookup table or by using a formula based on display brightness values ​​stored by an operating system of a host device (e.g., a smartphone) in which the sensor 14 is integrated. VALUE_H and VALUE_L are measured values, which will be further described below.

[0033] The ECU 16 is operable to read out the integrated signal from the ALS 14 and store the sampled signal, for example, in an array in a memory (e.g., RAM) 18. The ECU 16 is further operable to identify the highest stored value VALUE_H and the lowest stored value VALUE_L, respectively. The high value (VALUE_H) corresponds to a sample where the blanking PWM signal is on for the entire integration period. Thus, the value corresponds to the integration of the ALS signal only during the blanking on period (i.e., when the display is on). Thus, the highest value represents a combination of the ambient light signal and the display light. Conversely, the lowest value (VALUE_L) corresponds to a sample whose integration period covers the entire duty cycle off time of the blanking PWM signal (i.e., an integration period in which the blanking PWM signal is low for at least a portion of the integration period).

[0034] Using the values ​​of the integration time and blanking off time, along with the measured values ​​VALUE_H and VALUE_L, the ECU 16 can determine the total ambient light signal over one integration period 100. This value can be divided by the duration of the integration period 100 to obtain the magnitude of the ambient light signal (ie, lux).

[0035] ECU 16 can use the size of the ambient light signal to adjust the display brightness to make the display look clear and readable while also reducing the overall energy consumption of the display. Therefore, in some cases, the display brightness can be adjusted with high accuracy based on the surrounding lighting environment.

[0036] In some cases, the ECU 16 reads and stores N (e.g., 16) consecutive samples in an array in the memory 18, and then identifies the high and low values ​​(VALUE_H and VALUE_L) after the N samples are stored. The ECU 16 then repeats the process and appropriately adjusts the display brightness based on the calculated amount of ambient light. In other cases, the ECU 16 uses a sliding array in which the oldest samples are removed from the array and the most recent samples are added to the array. In this mode of operation, the ECU 16 can determine the high and low values ​​(VALUE_H and VALUE_L) as each new sample is measured and stored. The brightness of the display screen 12 can then be updated more frequently as appropriate under the control of the ECU 16.

[0037] Therefore, if Figure 4As shown, the present disclosure describes a method, the method includes acquiring samples of the output of an ambient light sensor in an asynchronous system, in which the integration time of the sensor does not need to be synchronized with the frame rate of the display screen, and wherein the sensor is disposed behind a display screen having a brightness that can be controlled by the duty cycle of a blanking PWM signal (150). The method includes identifying a highest value and a lowest value from a group of consecutive samples in the samples (152), and estimating a magnitude of an ambient light signal based at least in part on the highest value and the lowest value (154).

[0038] Figure 5 Further details according to some embodiments are shown. Figure 5 As shown, the sensor hub 200 includes a driver 204 that controls the ALS 14, which may be coupled to the driver 204 via a bus 206 (eg, a 400 kbit / sec bus). Lux information is calculated from within the sensor hub driver 204.

[0039] Various software stacks may be provided across the sensor hub 200 and the application processor 202, which in the illustrated example includes a kernel space 208 and a user space 210. The kernel space 208 may include a driver 212 and a display driver 214 that serve as a host for controlling the sensor hub 200. The user space 210 includes a hardware abstraction layer (HAL) 216, a framework layer 218 with a sensor manager, and an application layer 220.

[0040] Lux data may be sent from sensor hub 200 to HAL 216 on application processor 202 via driver 204 and sensor hub framework (ie, the software stack into which driver 204 is inserted). Application processor user space 210 includes display manager 222 operable to determine display brightness using lux readings.

[0041] In some embodiments, the sensor hub driver 204 implements interrupts or timers to handle hardware analog-to-digital (ADC) channel data. As described above, the sensor hub framework is operable to report lux and ADC channel data, integration time, and gain settings to the application processor. Preferably, the sensor hub driver 204 is capable of accepting configuration parameters during initialization to support system differences.

[0042] The display manager 222 should be operable to read lux data from the sensor manager in the framework layer 218. The display manager 222 should also be operable to obtain the current display brightness level, calculate lux to brightness (or implement an interface to access the lux to brightness algorithm), and set the brightness level of the display. Preferably, the lux to brightness algorithm can accept configuration parameters during initialization to support system differences.

[0043] Figure 6 Shown for Figure 5 200. An example of a call sequence using interrupts for a system. In this example, the sensor hub driver 204 is registered and executes its initialization sequence, which configures the ALS sensor hardware. When the hardware FIFO threshold is reached, the sensor hub driver 204 processes the converted digital channel data to produce a lux value. The sensor hub driver 204 then reports the lux value to the sensor hub framework 205, and if the reporting threshold is exceeded, the framework 205 publishes the lux calculation to the application processor 202. The display manager 222 periodically checks the lux reading and uses the lux reading and the current display brightness to calculate a new display brightness setting. To do this, the display manager 222 can access a lookup table or algorithm in the host device operating system.

[0044] Various aspects of the subject matter and functional operations described in this specification may be implemented in digital electronic circuits or in computer software, firmware or hardware (including the structures disclosed in this specification and their structural equivalents), or in a combination of one or more thereof. Therefore, various aspects of the subject matter described in this specification may be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer-readable medium, for execution by a data processing device or for controlling the operation of the data processing device. The computer-readable medium may be a machine-readable storage device, a machine-readable storage substrate, a memory device, a material combination that affects a machine-readable propagation signal, or a combination of one or more thereof. In addition to hardware, the device may include code that creates an execution environment for the computer program in question, for example, code that constitutes processor firmware.

[0045] A computer program (also referred to as a program, software, software application, script, or code) may be written in any form of programming language, including compiled or interpreted languages, and it may be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program may be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files storing one or more modules, subroutines, or portions of code). A computer program may be deployed to execute on one computer or on multiple computers located at one site or distributed across multiple sites and interconnected by a communications network.

[0046] The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and the apparatus can also be implemented as, special purpose logic circuitry, such as an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

[0047] For example, processors suitable for executing a computer program include general-purpose and special-purpose microprocessors, and any one or more processors of any type of digital computer. Typically, the processor will receive instructions and data from a read-only memory or a random access memory, or both. The essential elements of a computer are a processor for executing instructions and one or more memory devices for storing instructions and data. Computer-readable media suitable for storing computer program instructions and data include all forms of nonvolatile memory, media, and storage devices, including, for example, semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks, such as internal hard disks or removable disks; magneto-optical disks; and CD ROM and DVD-ROM disks. The processor and memory may be supplemented by or incorporated into special-purpose logic circuits.

[0048] Although this specification contains many details, these should not be interpreted as limitations on the scope of the present invention or the scope that may be claimed, but should be interpreted as descriptions of specific features of specific embodiments of the present invention. Certain features described in the context of separate embodiments in this specification may also be implemented in combination in a single embodiment. On the contrary, the various features described in the context of a single embodiment may also be implemented separately in multiple embodiments or in any suitable sub-combination. In addition, although features may be described above as working in certain combinations and even initially claimed as such, one or more features from the claimed combination may be removed from the combination in some cases, and the claimed combination may be directed to a sub-combination or a variant of the sub-combination.

[0049] Accordingly, other implementations are within the scope of the following claims.

Claims

1. A device for controlling the brightness of a display screen, comprising: Display screen; an ambient light sensor disposed behind the display screen, wherein an integration time of the ambient light sensor is not synchronized with a frame rate of the display screen; and an electronic control unit operable to control the brightness of the display screen based on a duty cycle of a PWM blanking signal, wherein at least one off-time of the PWM blanking signal occurs entirely within a first integration period of the ambient light sensor, and wherein at least one other integration period on-time of the PWM blanking signal occurs entirely during an on-time of the PWM blanking signal, wherein the electronic control unit is further operable to acquire samples of the output of the ambient light sensor to identify a highest value and a lowest value from a group of consecutive ones of the samples, and to estimate a magnitude of the ambient light signal based at least in part on the highest value and the lowest value, Among them, the PWM blanking waveform and the integration time are in the period P b In-phase and out-of-phase, so that: P WTIME =P b / [(P b / P PWM )–1], Among them, P WTIME is the sum of the integration time and the delay before the next integration time of the ambient light sensor begins, and where P PWM is the period of the PWM blanking signal.

2. The device according to claim 1, wherein: The electronic control unit is operable to estimate the magnitude of the ambient light signal further based on a duration of an integration period of the ambient light sensor.

3. The device as claimed in claim 2, wherein: The electronic control unit is operable to estimate the magnitude of the ambient light signal further based on an off time of the PWM blanking signal.

4. The device as claimed in claim 3, wherein: The integration period of the ambient light sensor is less than or equal to a difference between an on time of the PWM blanking signal and the delay before the next integration time of the ambient light sensor begins.

5. The device according to claim 3, wherein: The integration time of the ambient light sensor is greater than a sum of the off time of the PWM blanking signal and the delay before the next integration time of the ambient light sensor begins.

6. The device according to any one of claims 1 to 5, wherein: The electronic control unit is further operable to adjust a brightness of the display screen based at least in part on the estimated magnitude of the ambient light signal.

7. A method for controlling the brightness of a display screen, comprising: Acquire output samples of an ambient light sensor disposed behind a display screen, the display screen having a brightness controllable by a duty cycle of a blanking PWM signal, wherein an integration time of the ambient light sensor is not synchronized with a frame rate of the display screen; identifying a highest value and a lowest value from a group of consecutive samples in the sample; and estimating a magnitude of an ambient light signal based at least in part on the highest value and the lowest value, Among them, the PWM blanking waveform and the integration time are in the period P b In-phase and out-of-phase, so that: P WTIME =P b / [(P b / P PWM )–1], Among them, P WTIME is the sum of the integration time and the delay before the next integration time of the ambient light sensor begins, and where P PWM is the period of the PWM blanking signal.

8. The method of claim 7, wherein: Estimating the magnitude of the ambient light signal is also based on a duration of an integration period of the ambient light sensor.

9. The method of claim 8, wherein: Estimating the magnitude of the ambient light signal is also based on an off time of the PWM blanking signal.

10. The method of claim 9, wherein: The integration period of the ambient light sensor is less than or equal to a difference between an on time of the PWM blanking signal and the delay before the next integration time of the ambient light sensor begins.

11. The method of claim 9, wherein: The integration time of the ambient light sensor is greater than a sum of the off time of the PWM blanking signal and the delay before the next integration time of the ambient light sensor begins.

12. A method as claimed in any one of claims 7 to 11, comprising adjusting the brightness of the display screen based at least in part on the estimated magnitude of the ambient light signal.

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