Method and apparatus for optical proximity sensing with reduced pixel distortion

Abstract

A method of operating an optical proximity sensor of a computer device having a display, wherein the optical proximity sensor is positioned below the display or otherwise positioned adjacent to the display. The method includes: obtaining a vertical synchronization signal from a display driver; and synchronizing periodic illumination of a light emitter of the optical proximity sensor with the vertical synchronization signal.

Description

Technical Field

[0001] The present invention relates to optical proximity sensing in a device having a display, where the proximity sensor is located behind the display or otherwise near the display. Background Art

[0002] Many smartphones use an optical proximity sensor to determine when to turn the display on or off. This is typically to save battery power (e.g., when the smartphone is placed in the user's pocket) or to prevent unwanted on-screen button selections when answering a call. The same may be true for other computer devices having a display, such as tablet computers and laptop computers, where it is desirable to turn off the display when the device is closed or otherwise covered. Optical proximity sensing typically relies on emitting near-infrared (NIR) light and measuring any light energy reflected back. Reflection above a certain threshold indicates that the display may be covered.

[0003] For this purpose, the NIR light emitter was previously located in the bezel of the smartphone or other device. However, in recent years, due to the pursuit of the screen-to-body ratio, the bezel that was previously used to house the proximity sensor has been eliminated from many devices. Many smartphones now use an organic light-emitting diode (OLED) display. The OLED display allows some light, including NIR light, to pass through the display. Thus, the proximity sensor can be located behind the OLED display.

[0004] However, the energy of the NIR light emitted through the display causes visible distortion on the display; for example, bright spots appear in the display above the location of the proximity sensor. These distortions can be visible under many conditions, such as even when the screen is displaying a black image. Summary of the Invention

[0005] According to a first aspect of the present invention, there is provided a method of operating an optical proximity sensor of a computer device having a display, where the optical proximity sensor is located below the display or otherwise adjacent to the display. The method includes: obtaining a vertical synchronization signal from a display driver; and synchronizing periodic illumination of a light emitter of the optical proximity sensor with the vertical synchronization signal.

[0006] The display may be an organic light-emitting diode display.

[0007] The optical proximity sensor may be an infrared optical proximity sensor, such as a near-infrared optical proximity sensor.

[0008] The synchronization step may include introducing a delay to the vertical synchronization signal and using the pulses of the delayed signal to trigger the periodic illumination. The delay may cause the illumination of the emitter to occur just before the blanking or dimming of the display area directly above the optical proximity sensor. Alternatively, the delay may cause the illumination of the emitter to coincide with the blanking or dimming portion of the display area directly above the optical proximity sensor.

[0009] The method may include illuminating the light emitter after each synchronization pulse of the vertical synchronization signal. Alternatively, the light emitter may be illuminated after each sequence of a plurality of synchronization pulses of the vertical synchronization signal.

[0010] According to a second aspect of the present invention, there is provided a computer device including a display and an optical proximity sensor located below the display or otherwise adjacent to the display and including a light emitter. The device further includes a display driver for generating a vertical synchronization signal and is configured to synchronize the periodic illumination of the light emitter with the vertical synchronization signal. The synchronization may be performed by a synchronization circuit (e.g.,) of the optical proximity sensor or by a processor.

[0011] The display may be an organic light emitting diode display.

[0012] The optical proximity sensor may be an infrared optical proximity sensor, such as a near-infrared optical proximity sensor.

[0013] The device may include a delay circuit for delaying the vertical synchronization signal, which is integrated into the optical proximity sensor or implemented as a component separate from the optical proximity sensor, and the delay circuit is coupled to the light emitter to trigger the illumination of the light emitter. The delay circuit may delay the vertical synchronization signal to cause the illumination of the emitter to occur just before the blanking or dimming of the display area directly above the optical proximity sensor. Alternatively, the delay circuit may delay the vertical synchronization signal to cause the illumination of the emitter to coincide with the blanking or dimming portion of the display area directly above the optical proximity sensor.

[0014] The device may be a smart phone, a tablet computer, or a laptop computer.

[0015] Embodiments of the present invention provide a way to reduce or eliminate pixel distortion in a display while continuing to allow the use of an NIR light source located behind the display for optical proximity sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematically shows a smart phone with a proximity sensor;

[0017] Figure 2is a flowchart depicting an optical proximity sensing method at a high level;

[0018] Figure 3 Schematically shows Figure 1 the operational interactions of components of a smart phone;

[0019] Figure 4 Depicts Figure 1 the timing scheme of a smart phone;

[0020] Figure 5 Shows an exemplary trajectory generated using Figure 4 the timing scheme;

[0021] Figure 6 Shows alternative exemplary trajectories within a number of display cycles;

[0022] Figure 7 Schematically shows alternative operational interactions of components of a smart phone;

[0023] Figure 8 is a flowchart depicting an alternative optical proximity sensing method at a high level;

[0024] Figure 9 Shows an exemplary trajectory generated using Figure 8 the method; Detailed Description

[0025] The problems caused by using a NIR proximity sensor under a display (such as an OLED display) have been discussed above. The solution to be discussed below stems from the recognition that distortion can be reduced by illuminating the proximity sensor only at the optimal time points relative to the operational state of the display pixels.

[0026] During operation of the display, the display is refreshed periodically at an image refresh rate. This rate can be, for example, 60 Hz, i.e., the display is updated 60 times per second. The start of a new frame is indicated by a vertical synchronization (VSYNC) pulse signal generated by the display driver of the device. The VSYNC signal synchronizes the frame rate of the processor with the refresh rate of the display, such that the frames per second (FPS) is limited by the refresh rate and no frames are skipped. The VSYNC pulse indicates the start of a new frame (image) on the display. The present invention uses the VSYNC pulse to synchronize the light emission from the proximity sensor with the display refresh rate. Specifically, the NIR optical emission is synchronized to start at a time point in the refresh cycle of the display, the result of which can reduce or eliminate distortion of the image. Depending on the particular OLED display present in the device, the optimal emission time can be just before or exactly during the time when the display pixels directly above the proximity sensor are inactive. The present invention allows continued use of the NIR proximity sensor under the display, while allowing for thinner or non-existent bezels, and without the need for more expensive solutions such as using far infrared (FIR) emitters or ultrasonic solutions.

[0027] Figure 1 Schematically illustrated is an exemplary smartphone 1, shown in a cross-section through a plane perpendicular to the plane of the display. The smartphone 1 includes an OLED display 2, an OLED display driver 3, and a NIR optical proximity sensor module 4 within the body of the smartphone and below the OLED display. The display driver 3 is typically implemented by a combination of hardware and software, where the hardware can include a graphics processing unit (GPU) and associated memory. The proximity sensor module 4 includes a NIR emitter 5 and a proximity detector 6, which have a clear line of sight to the underside of the display 2. Although not shown, the sensor module can include optical components such as lenses. The proximity sensor module 4 also has an integrated delay circuit 7 and can be configured through registers to optimize the timing of the light emission to reduce display pixel distortion. The exact configuration for a given display can be determined empirically, for example, during the prototyping stage of the product.

[0028] Figure 2 is shown at a high level Figure 1Flowchart of a process of optical proximity sensing with reduced pixel distortion in a smart phone. During operation of the smart phone, a VSYNC signal (S1.1) is periodically generated by the OLED display driver 3 for refreshing the display. Here, the VSYNC is additionally provided to the integrated delay circuit 7 of the optical proximity sensor module 4 (S1.2). When the delay circuit detects the timing (refresh) pulse of the VSYNC signal, it starts a delay timer (S1.3), and after the delay timer expires, triggers the emitter 5 to emit NIR light within a predetermined period (S1.4). The emitted light passes through the OLED display 2 to interact with any object that may be in front of the display. Any light reflected back through the OLED display is detected by the detector 6.

[0029] Figure 3 Schematically illustrated Figure 1 Relevant functional components of the smart phone 1. These include the OLED display driver 3 and the optical proximity sensor module 4, and the optical proximity sensor module 4 includes the integrated delay circuit 7. The VSYNC signal is shown as being transmitted from the driver 3 to the delay circuit 7 of the module 4.

[0030] Figure 4 Illustrates an exemplary timing scheme. The upper trace 8 shows the VSYNC signal generated by the OLED display driver 3, the middle trace 9 shows the display brightness at a position above the proximity sensor module 4, and the lower trace 10 shows the light emission from the emitter 5 of the proximity sensor module 4. At a given time t1 after the leading edge of the VSYNC pulse, the display brightness above the proximity sensor module 4 is temporarily reduced due to refreshing or "blanking" the corresponding pixel line. To take advantage of this state, after a time delay t2 from the leading edge of the VSYNC pulse, the delay circuit 7 generates an emitter drive pulse to drive the emitter 5 of the proximity sensor module 4. This drive pulse has a duration t3. The periods t2 and t3 are optimized to minimize the visual distortion in the display 2 caused by the NIR light pulse. For example, the timing can result in the generation of the NIR light pulse within a very short time before covering the display pixel blanking.

[0031] Figure 5 Shows the exemplary trace resulting from the Figure 2 Steps. The VSYNC pulse is shown by the peak 11 of the lower trace. Approximately 1.76 ms after the leading edge of the VSYNC pulse, the proximity sensor emits light (detected using an NIR sensor positioned above the display under test conditions), as shown by the peak 12. Approximately 1.15 ms after emitting the proximity sensing light, the pixels are blanked, as shown by the trough 13.

[0032] Different displays and (a number of) IR emitters may have different timing requirements to achieve minimal distortion. For example, the time t1 from the leading edge of the VSYNC pulse to the pixel line refresh will likely vary based on the specific display and the position of the sensor module beneath the display. The start time t2 and duration t3 will change accordingly.

[0033] It should be understood that the emitted optical power will be optimized to minimize pixel distortion as much as possible.

[0034] It should be understood that further modifications can be made to the timing scheme. For example, a long delay t2 (e.g., 10 ms or longer) can be introduced to cause some VSYNC pulses to be skipped. For example Figure 6 as shown in, the NIR light pulse 12 can be triggered only on every other VSYNC pulse 11. Alternatively, a counter can be used in combination with a short delay to trigger the proximity measurement emission only after a certain number of VSYNC pulses have occurred. When the display blanks more than once per VSYNC signal (which can occur, for example, when the display is operating at less than 100% brightness), pixel distortion can be optimized by synchronizing the proximity pulse to occur before the first blanking after the VSYNC signal. Additionally, the proximity pulse 12 can overlap with the blanking time 13.

[0035] Modifications can also be made to the Figure 1 and Figure 3 devices. For example Figure 7 as shown in, instead of integrating the delay function into the proximity sensor, it can be performed by a separate delay circuit (such as a microcontroller 14). The flowchart of Figure 8 shows the process implemented by the Figure 7 device at a high level. The VSYNC signal is sent from the OLED display driver 3 (S2.1) and received by an external delay circuit (such as a microcontroller 14) (S2.2). The microcontroller adds a delay to the VSYNC signal (S2.3), and passes this delayed VSYNC signal to the proximity sensor 15 via the GPIO interface (S2.4). The arrival of the GPIO pulse at the proximity sensor (S2.5) triggers the start of NIR light emission (S2.6). There may be a further delay inherent in the operation of the sensor between the time the GPIO pulse is received and the time the light is emitted.

[0036] Figure 9 as shown in can be by Figure 7 architecture and implementation Figure 8Exemplary trajectories resulting from the steps of. The transmitter drive signal (GPIO) pulse 16 is observed 0.650 ms after the leading edge of the VSYNC pulse 11. After a further delay of 1.11 ms after the leading edge of the GPIO pulse, the proximity sensor emits light, as shown by the peak 12. Again, the pixels are blanked 1.15 ms after the proximity sensing light is emitted, as shown by the trough 13.

[0037] The optical transmitter can be a NIR LED (e.g., emitting at 940 nm), a vertical cavity surface emitting laser (VCSEL) transmitter, or any other suitable optical transmitter that can produce unwanted pixel distortion.

Claims

1. A method of operating an optical proximity sensor of a computer device having a display, wherein the optical proximity sensor is positioned below the display or adjacent to the display, the method comprising: Obtain a vertical synchronization signal from a display driver; and Synchronize the periodic illumination of the light emitter of the optical proximity sensor with the vertical synchronization signal; wherein the synchronization step includes introducing a delay into the vertical synchronization signal and using the pulses of the delayed signal to trigger the periodic illumination, and wherein, Triggering the periodic illumination includes generating drive pulses for driving the light emitter before the display area of the display covering the illumination of the optical proximity sensor blanks, wherein the periodic illumination of the light emitter is synchronized to start at a time point in the refresh cycle of the display, with the result that distortion of the image on the display is reduced or eliminated, wherein the delay causes the illumination of the emitter to occur immediately before the blanking or dimming of the display area directly above the optical proximity sensor, or wherein the delay causes the illumination of the emitter to coincide with the blanking or dimming portion of the display area directly above the optical proximity sensor.

2. The method according to claim 1, wherein the display is an organic light emitting diode display.

3. The method according to claim 1 or 2, wherein the optical proximity sensor is an infrared optical proximity sensor.

4. The method according to claim 3, wherein the infrared optical proximity sensor is a near infrared optical proximity sensor.

5. The method according to claim 1 or 2, wherein the delay causes illumination of the emitter immediately before blanking or dimming of the display area directly above the optical proximity sensor.

6. The method according to claim 1 or 2, wherein the delay causes illumination of the emitter to coincide with the blanked or dimmed portion of the display area directly above the optical proximity sensor.

7. The method according to claim 1 or 2, comprising illuminating the light emitter after each synchronization pulse of the vertical synchronization signal.

8. The method according to claim 1 or 2, comprising illuminating the light emitter after each sequence of a plurality of synchronization pulses of the vertical synchronization signal.

9. A computer device, comprising: A display; An optical proximity sensor positioned below or adjacent to the display and including a light emitter; and A display driver for generating a vertical synchronization signal, The device is configured to synchronize the periodic illumination of the light emitter with the vertical synchronization signal; wherein the device further includes a delay circuit for delaying the vertical synchronization signal, the delay circuit being integrated into the optical proximity sensor or implemented as a component separate from the optical proximity sensor, the delay circuit being coupled to the light emitter to trigger the illumination of the light emitter, and wherein, Triggering the periodic illumination includes generating drive pulses for driving the light emitter before the display area of the display covering the illumination of the optical proximity sensor blanks, wherein the delay circuit is configured to synchronize the periodic illumination of the light emitter to start at a time point in the refresh cycle of the display, with the result that distortion of the image on the display is reduced or eliminated, wherein the delay causes the illumination of the emitter to occur immediately before the blanking or dimming of the display area directly above the optical proximity sensor, or wherein the delay causes the illumination of the emitter to coincide with the blanking or dimming portion of the display area directly above the optical proximity sensor.

10. The computer device according to claim 9, wherein the display is an organic light emitting diode display.

11. The computer device according to claim 10, wherein the optical proximity sensor is an infrared optical proximity sensor.

12. The computer device according to claim 11, wherein the infrared optical proximity sensor is a near-infrared optical proximity sensor.

13. The computer device according to claim 9 or 10, wherein the delay circuit delays the vertical synchronization signal to cause illumination of the emitter immediately before blanking or dimming of the display area directly above the optical proximity sensor.

14. The computer device according to claim 9 or 10, wherein the delay circuit delays the vertical synchronization signal to cause the illumination of the emitter to coincide with the blanked or dimmed portion of the display area directly above the optical proximity sensor.

15. The computer device according to claim 9 or 10, wherein the device is one of a smart phone, a tablet computer, or a laptop computer.

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