Optical sensor capable of synchronizing with ambient light flickering

Abstract

An optical sensor including a photodiode, a waveform conversion circuit, a pixel array, and a processor. The photodiode detects ambient light flicker to generate a sine wave. The waveform conversion circuit converts the sine wave into a square wave. The processor is used to count the square wave using a sampling frequency, and determine whether the ambient light flicker is detected well based on the count value of each square wave and the change in the count values of multiple square waves within the counting period, and decide whether to adjust the acquisition phase of the image frame accordingly.

Description

Technical Field

[0001] The present invention relates to a photosensor, and more particularly to a photosensor capable of synchronizing the frame rate of the photosensor with the ambient light flicker frequency to eliminate the influence of ambient light. Background Art

[0002] An action detection device using a photosensor determines an object's action by calculating the change in light intensity in the image frames acquired by the photosensor. However, when such an action detection device operates indoors, since the indoor ambient light is sometimes provided by fluorescent lamps and has a flickering situation due to the alternating current nature of the power system, when the frame rate of the photosensor is not synchronized with the flicker frequency of the ambient light, the average brightness of the image frames acquired by the photosensor will also change between bright and dark, which may lead to misjudgment of the action. The flicker frequency of the ambient light is determined according to the alternating current frequency of the power system.

[0003] For example, referring to Figure 1 as shown, it shows a schematic diagram of a known photosensor acquiring image frames with respect to ambient light changes. When the photosensor acquires image frame 1 when the ambient light is the brightest, the average brightness of image frame 1 is the highest; when the photosensor acquires image frame 2 when the ambient light is the darkest, the average brightness of image frame 2 is the lowest; the average brightness of image frame 3 is between image frame 1 and image frame 2. The intensity changes of image frames 1 to 3 will lead to misjudgment of the object's action.

[0004] In view of this, the present invention further provides a photosensor that can synchronize the frame rate of the photosensor with the flicker frequency of the ambient light when the ambient light flicker is well detected. Summary of the Invention

[0005] The present invention provides a photosensor that includes an independently operating photodiode for detecting the flicker pulse of ambient light, and its digital backend determines whether the undulation of the ambient light is well detected based on the flicker pulse, and adjusts the frame rate of the image frame only when it is confirmed that the detection is good.

[0006] The present invention provides a photosensor including a photodiode, a waveform conversion circuit, a pixel array, and a digital backend. The photodiode is used to detect ambient light flicker to generate a sine wave signal. The waveform conversion circuit is used to convert the sine wave signal into a square wave signal. The pixel array is used to acquire image frames according to a frame signal. The digital backend is used to count the square wave signal using a sampling frequency, and generate an activation signal for adjusting the frame signal based on the count value of each square wave signal in the counting period and the consistency of the multiple count values of all square wave signals in the counting period.

[0007] The present invention also provides an optical sensor including a photodiode, a waveform conversion circuit, a pixel array, and a digital backend. The photodiode is configured to detect ambient light flicker to generate a sine wave signal. The waveform conversion circuit is configured to convert the sine wave signal into a square wave signal. The pixel array is configured to obtain an image frame according to a frame signal. The digital backend is configured to count the count value of each square wave signal in a counting period; when it is determined that the count value of each square wave signal is between two predetermined thresholds, and the difference between the maximum count value and the minimum count value among the multiple count values of all square wave signals in the counting period is within a preset range, synchronize the image frame with the ambient light flicker; and when it is determined that not all of the count values of each square wave signal in the counting period are between the two predetermined thresholds, or the difference between the maximum count value and the minimum count value of the multiple count values exceeds the preset range, do not synchronize the image frame with the ambient light flicker.

[0008] The present invention also provides an optical sensor including a photodiode, a waveform conversion circuit, a pixel array, and a digital backend. The photodiode is configured to detect ambient light flicker to generate a sine wave signal. The waveform conversion circuit is configured to convert the sine wave signal into a square wave signal having a square wave period. The pixel array is configured to obtain an image frame according to a frame period. The bit backend is configured to count the count value of each square wave signal in a counting period using a sampling frequency; when the frame period is equal to the square wave period and an activation signal is generated, adjust the acquisition phase of the second image frame in the next counting period of the counting period; and when the frame period is equal to a multiple of the square wave period and the activation signal is generated, adjust the acquisition phase of the first image frame in the next counting period of the counting period.

[0009] In order to make the above and other objects, features, and advantages of the present invention more obvious, the following will be described in detail with reference to the accompanying drawings. In addition, in the description of the present invention, the same components are denoted by the same reference numerals, which are hereby stated first. Description of the Drawings

[0010] Figure 1 It is a schematic diagram of a known optical sensor obtaining an image frame with respect to ambient light variation;

[0011] Figure 2 It is a block diagram of the optical sensor according to an embodiment of the present invention; and

[0012] Figures 3A to 3B It is a schematic diagram of the operation of the optical sensor according to some embodiments of the present invention.

[0013] Description of the Reference Numerals

[0014] 200 Optical sensor

[0015] 21 Photodiode

[0016] 23 Waveform conversion circuit

[0017] 25 Pixel array

[0018] 27 Digital backend

[0019] 271 Frequency generator Detailed implementation manners

[0020] The optical sensor of the present invention is suitable for operating under time-varying ambient light with a flicker frequency. When the ambient light flicker can be detected well, the image frame is synchronized with the flicker frequency to eliminate the situation of misjudgment actions. At the same time, in order to reduce unnecessary adjustments, when the ambient light flicker cannot be detected well, the synchronization mechanism is not performed. In the present invention, whether the ambient light flicker is detected well is judged according to the stability of the detected ambient light period change in a predetermined period.

[0021] Please refer to Figure 2 as shown, which is a block diagram of the optical sensor 200 according to an embodiment of the present invention. The optical sensor 200 can be built into various cameras or video cameras for motion detection or navigation. The optical sensor 200 includes a photodiode 21, a waveform conversion circuit 23, a pixel array 25, and a digital backend 27, wherein the digital backend 27 includes a frequency generator 271 for generating a frequency signal, for example, generating a frequency of 64 kHz, but not limited thereto, and its value depends on different applications.

[0022] The photodiode 21 is used to detect the ambient light flicker to generate and output a sine wave signal. It can be understood that when the ambient light does not flicker, the photodiode 21 does not output a sine wave signal. In one implementation manner, the photodiode 21 is an independent element located outside the pixel array 25. In another implementation manner, the photodiode 21 is at least one pixel of the pixel array 25, for example, at least one edge pixel of the pixel array 25, but not limited to edge pixels. When the photodiode 21 is composed of multiple pixels, its output is the sum or average of the output raw data of the multiple pixels, and the sum or average is calculated by the circuit of the pixel array 25, for example.

[0023] The waveform conversion circuit 23 is electrically connected to the photodiode 21 and is used to convert the sine wave signal into a square wave signal, which has a square wave period P FL , for example, refer to Figure 3A and Figure 3B . When the photodiode 21 detects the light change of the fluorescent lamp well, the square wave period P FLFor example, it is about 1 / 100 second or 1 / 120 second. The waveform conversion circuit 23 of the present invention can use a known sine-to-square waveform conversion circuit. For example, a commonly used sine-to-square conversion technique is to provide the waveform of an AC sine wave to a CMOS inverter or to one input terminal of a comparator, but it is not limited thereto. In the present invention, a square wave signal can be used to evaluate whether ambient light flicker is well detected during a counting period, for example Figure 3A showing a good counting period while Figure 3B showing both good and bad counting periods.

[0024] The pixel array 25 is, for example, the pixel array of a CMOS image sensor and includes a plurality of pixel circuits. The pixel array 25 is used to acquire an image frame according to a frame signal (frame tick), where the frame signal is used to determine the frame period for acquiring the image frame. For example, the pixel array 25 acquires one image frame relative to each frame signal, or acquires one image frame every multiple frame signals (for example, 10, but not limited thereto), depending on different applications.

[0025] The digital backend 27 is, for example, a digital signal processor (DSP), a microprocessing unit (MCU), or an application-specific integrated circuit (ASIC). The digital backend 27 counts the square wave signal output by the waveform conversion circuit 23 using a sampling frequency (for example, generated by the frequency generator 271), and generates an activation signal for adjusting the frame signal according to the count value of each square wave signal in a counting period and the consistency of the multiple count values of all square wave signals in the counting period. In the present invention, a counting period includes a plurality of square wave signals to evaluate whether ambient light flicker is well detected during a predetermined period (for example, the counting period). For example, when a counting period is configured as a square wave period P of 100 (relative to a 50 Hz AC power system) or 120 (relative to a 60 Hz AC power system) square wave signals FL the predetermined period is 1 second, but it is not limited thereto. The length of the square wave period can be manually selected, for example, determined by pressing a button or a human-machine interface menu; or measured according to the count value of each square wave signal, for example, the count value between the falling edge or rising edge of adjacent square wave pulses.

[0026] In the present invention, for the purpose of illustration, it is assumed that the AC frequency of the power system is 50 Hz, the frequency generator 271 generates a sampling frequency of 64 kHz, and the counting period is configured as 100 square wave periods, for example Figure 3A and Figure 3B as shown by N = 100, but it is not limited thereto. In other embodiments, N can be set to other values corresponding to the clock frequency of the frequency generator 271 and the AC frequency of the power system.

[0027] Please refer to Figure 3A and Figure 3B as shown, which shows a schematic diagram of the operation of the optical sensor 200 of some embodiments of the present invention. Among them, Figure 3A shows the operation after the start of synchronous operation. For example, the adjustment engine of the digital backend 27 (which is implemented by using hardware and / or firmware, for example) receives a signal to start operation (such as generated by pressing a button or executing an application software), for example, the display signal level is converted from a low level to a high level. After the start of synchronous operation, the photodiode 21 starts to output a sine wave signal to the waveform conversion circuit 23 to generate and output a square wave signal to the digital backend 27. The digital backend 27 uses the sampling frequency to count each square wave signal in the counting cycle to obtain a count value relative to each square wave signal. However, there is no specific limitation on whether the photodiode 21 outputs a sine wave signal before the start of synchronous operation.

[0028] Figure 3B shows the situation where a defective square wave signal is detected. For example, P FL _Failed shows an unstable square wave period.

[0029] First, the digital backend 27 first determines whether the ambient light flicker has good consistency in each counting cycle to confirm whether to perform frame rate adjustment.

[0030] When the digital backend 27 determines that the square wave signal in a counting cycle (such as Figure 3A the first counting cycle) has high consistency, an activation signal is generated in the next counting cycle (such as Figure 3A the second counting cycle) to adjust the phase of the frame signal (i.e., adjust the frame rate) in the next counting cycle so that the pixel array 25 acquires an image frame synchronized with the ambient light flicker. For example, Figure 3A shows that the ambient light flicker is well detected in each counting cycle, so activation signals are generated in the second and third counting cycles.

[0031] Figure 3A In, there is no counting result before the first counting cycle, so the digital backend 27 does not generate an activation signal nor perform synchronous adjustment therein, for example, it is shown as OFF. More specifically, the present invention does not directly start the synchronization mechanism when changing the signal level of the adjustment engine.

[0032] When the digital backend 27 determines that the square wave signal in a counting cycle has low consistency, no activation signal is generated in the next counting cycle of the counting cycle, nor is synchronization performed between the image frame and the ambient light flicker in the next counting cycle. For example, Figure 3BIt is shown that the ambient light flicker is not well detected in the second counting period, so the activation signal is not generated in the third counting period. In the present invention, the rising edge of the activation signal is configured to be in phase with the falling edge of the last square wave signal in the previous counting period. The activation signal can be used not only to control whether to synchronize the image frame with the ambient light flicker, but also as a basis for comparing the reference signal and the frame signal.

[0033] In the present invention, the digital backend 27 determines the high or low consistency of the square wave signals through two conditional judgments. The first condition is that the digital backend 27 determines whether the count values of each square wave signal in a counting period are all between two predetermined thresholds. As described above, when the digital backend 27 counts a 100 Hz square wave signal with a sampling signal of 64 kHz, ideally a square wave signal should contain 640 counts. In the present invention, the first threshold is configured to be 64 kHz / 90 Hz = 711, for example; and the second threshold is configured to be 64 kHz / 110 Hz = 581, for example. According to different sensitivity requirements, the first threshold and the second threshold can be set higher or lower, and the above values are only for illustration and not for limiting the present invention.

[0034] The second condition is that the digital backend 27 determines that the difference between the maximum count value and the minimum count value among all the count values (for example Figure 3A and Figure 3B shown as N = 100) in a counting period is within a preset range. For example, when the preset range is set to ±1% of 640, the preset range is 6 counts. Similarly, according to different sensitivity requirements, the preset range can be set wider or narrower.

[0035] In the present invention, when the digital backend 27 determines that the count values of each square wave signal in a counting period are all between two predetermined thresholds (such as the above 581 and 711), and the difference between the maximum count value and the minimum count value among all the count values in the counting period is within a preset range (such as 6 counts), it indicates high consistency and an activation signal is generated in the next counting period of the counting period to synchronize the image frame with the ambient light flicker. In another embodiment, when the digital backend 27 determines that only a predetermined number (such as 2, but not limited to) of the count values of the square wave signals in the counting period are not between the two predetermined thresholds, it is still determined that the counting period has high consistency.

[0036] In addition, when the digital backend 27 determines that not every count value of the square wave signal (or exceeding the predetermined number) in a counting period is between the two predetermined thresholds, or the difference between the maximum count value and the minimum count value of all count values in the counting period exceeds the preset range, it indicates low consistency, and the activation signal is not generated in the next counting period of the counting period, and the asynchronous image frame and the ambient light flicker.

[0037] For example, Figure 3A the second and third counting periods of Figure 3B and the first and second counting periods of Figure 3B perform a synchronization procedure (such as display ON), while

[0038] the third counting period of

[0039] does not perform a synchronization procedure (such as display OFF). Figure 3A and Figure 3B The digital backend 27 alternatively generates a reference signal in each counting period, Figure 3A and

[0040] displays that the rising edge of the reference signal is in phase with the rising edge of the first square wave signal in the same counting period. When the digital backend 27 determines that the square wave signal in a counting period has high consistency, it calculates the time offset |T1 - T2| between the reference signal and the first frame signal in the same counting period (i.e., the next counting period of the counting period), and adjusts the first period P1 between the second frame signal and the first frame signal in the next counting period according to the time offset |T1 - T2|. More specifically, the time offset |T1 - T2| represents the time difference between the frame signal and the square wave signal of the ambient light flicker, and the digital backend 27 adjusts the imaging phase of the pixel array 25 according to the time offset |T1 - T2|, for example Figure 3A displays that the imaging phase of the second frame signal in the second counting period is delayed to synchronize with the second square wave signal, i.e., N = 2.

[0040] In one implementation, the digital backend 27 calculates the first time difference T1 between the reference signal and the activation signal in the next counting period, the second time difference T2 between the first frame signal and the activation signal, and calculates the difference |T1 - T2| between the first time difference T1 and the second time difference T2 as the time offset. As Figure 3A shown in the second counting period of

[0041] More specifically, in the present invention, the digital backend 27 adjusts the period between the first frame signal and the second frame signal of the next counting period of the one counting period, that is, the first period P1, only when the square wave signal of one counting period has high consistency. Moreover, the subsequent period Ps of the frame signals after the second frame signal is configured to be equal to the square wave period. In addition, when the square wave signal of one counting period does not have high consistency, the first period P1 between the first frame signal and the second frame signal of the next counting period is configured to be equal to the subsequent period Ps, as Figure 3B the third counting period of.

[0042] As described above, the pixel array 25 can obtain an image frame relative to each frame signal or every multiple frame signals. Therefore, the frame period for the pixel array 25 to obtain an image frame can be equal to the square wave period of the square wave signal or equal to a multiple of the square wave period, where the multiple is, for example, a positive integer greater than 1, but not limited to an integer. As described above, since the digital backend 27 adjusts the second frame signal of the next counting period after the counted period. Therefore, when the frame period is equal to the square wave period and the activation signal is generated, the digital backend 27 adjusts the acquisition phase of the second image frame (corresponding to the 2nd frame signal) of the next counting period. However, when the frame period is equal to a multiple of the square wave period (e.g., 10 times) and the activation signal is generated, the digital backend 27 adjusts the acquisition phase of the first image frame (corresponding to the 10th frame signal) of the next counting period, that is, when the pulse time of the 2nd frame signal is adjusted, the subsequent other pulse times are also adjusted simultaneously.

[0043] In one embodiment, when the rising edge of the reference signal is in phase with the rising edge of the first square wave signal of the same counting period, the digital backend 27 can directly use the rising edge of the first square wave signal of the same counting period as the reference signal without generating the reference signal. In other embodiments, the reference signal is generated and corresponds to other phases of the first square wave signal of the same counting period or other square wave signals, as long as it has a fixed phase relationship with the square wave signal in each counting period.

[0044] The synchronization program of the present invention can be verified through the following steps: (1) Operate the optical sensor 200 of the embodiment of the present invention under a light source with a fixed flicker frequency (such as a fluorescent lamp tube) and check whether the frame rate of the pixel array 25 is stably synchronized with the fixed flicker frequency; (2) Intermittently cover and uncover the fluorescent lamp tube to create noise in the detection signal (such as the aforementioned square wave signal), and confirm whether the frame rate of the pixel array 25 remains stable; As described above, the present invention will only execute the synchronization program when ambient light flicker is well detected within a predetermined period. If the frame rate still changes in the presence of noise, it indicates that the synchronization program of the present invention is not executed properly; (3) Turn off the fluorescent lamp tube and confirm whether the frame rate of the pixel array 25 remains the same as before the fluorescent lamp tube was turned off; As described above, the frame rate of the pixel array 25 of the present invention should remain the same after the fluorescent lamp tube is turned off. If the frame rate changes after the fluorescent lamp tube is turned off, it indicates that the synchronization program of the present invention is not executed properly.

[0045] It can be understood that if the sampling frequency remains unchanged and the flicker frequency of the ambient light changes, for example, from 100 Hz to 120 Hz, the count value of each P FL and the length of Ps change accordingly. It can be understood that all the numerical values in the description of the present invention are only for illustration and not for limiting the present invention.

[0046] In summary, known motion sensors may be affected by ambient light flicker and may exhibit incorrect motion judgment. Therefore, the present invention further provides an optical sensor (refer to Figure 2 ) and its operation method (refer to Figures 3A to 3B ) which generate an activation signal to calculate and adjust the phase of the frame signal only when it is determined that ambient light flicker is well detected, so as to synchronize the image frame with the ambient light flicker.

[0047] Although the present invention has been disclosed through the foregoing examples, it is not intended to limit the present invention. Any person with ordinary knowledge and skills in the technical field to which the present invention pertains can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the appended claims.

Claims

1. An optical sensor, the optical sensor comprising: A photodiode for detecting ambient light flicker to generate a sine wave signal; A waveform conversion circuit for converting the sine wave signal into a square wave signal; A pixel array for obtaining an image frame according to a frame signal; and A digital backend for counting the square wave signal using a sampling frequency and generating an activation signal for adjusting the frame signal according to the count value of each square wave signal in a counting period and the consistency of multiple count values of all square wave signals in the counting period, wherein When the digital backend determines that the count value of each square wave signal is between two predetermined thresholds and the difference between the maximum count value and the minimum count value among the multiple count values is within a preset range, it indicates that all the square wave signals have high consistency and the activation signal is generated, and When the digital backend determines that not all the count values of each square wave signal are between the two predetermined thresholds, or the difference between the maximum count value and the minimum count value among the multiple count values exceeds the preset range, it indicates that all the square wave signals have low consistency and the activation signal is not generated.

2. The optical sensor according to claim 1, wherein the photodiode is separated from the pixel array.

3. The optical sensor according to claim 1, wherein the photodiode is at least one edge pixel of the pixel array.

4. The optical sensor according to claim 1, wherein the counting period comprises 100 or 120 square wave periods of the square wave signal.

5. The optical sensor according to claim 1, wherein the digital backend is further configured to: Calculate a first time difference between a reference signal and the activation signal, Calculate a second time difference between a first frame signal of the next counting period of the counting period and the activation signal, and Calculate a time offset between the first time difference and the second time difference to adjust a first period between a second frame signal of the next counting period and the first frame signal according to the time offset.

6. The sensor according to claim 5, wherein The rising edge of the reference signal is in phase with the rising edge of the first square wave signal of the next counting period; and The rising edge of the activation signal is in phase with the falling edge of the last square wave signal of the counting period.

7. The sensor according to claim 5, wherein the subsequent period of the frame signal after the second frame signal of the next counting period is configured as a square wave period of a square wave signal.

8. An optical sensor, the optical sensor comprising: A photodiode for detecting ambient light flicker to generate a sine wave signal; A waveform conversion circuit for converting the sine wave signal into a square wave signal; A pixel array for obtaining an image frame according to a frame signal; and A digital backend for: Counting the count value of each square wave signal in a counting period When it is determined that the count value of each of the square wave signals is between two predetermined thresholds, and the difference between the maximum count value and the minimum count value among the multiple count values of all the square wave signals in the counting period is within a preset range, synchronize the image frame with the ambient light flicker, and When it is determined that not all of the count values of the square wave signals in the counting period are between the two predetermined thresholds, or the difference between the maximum count value and the minimum count value of the multiple count values exceeds the preset range, do not synchronize the image frame with the ambient light flicker.

9. The optical sensor according to claim 8, wherein the photodiode is at least one edge pixel of the pixel array.

10. The optical sensor according to claim 8, wherein the counting period includes 100 or 120 square wave periods of the square wave signals.

11. The optical sensor according to claim 8, wherein the digital backend further generates an activation signal to control whether to perform synchronization of the image frame with the ambient light flicker.

12. The optical sensor according to claim 11, wherein the digital backend is further configured to: Calculate the time offset between the reference signal and the first frame signal of the next counting period of the counting period, and adjust the first period between the second frame signal and the first frame signal of the next counting period according to the time offset.

13. The optical sensor according to claim 12, wherein, The rising edge of the reference signal is in phase with the rising edge of the first square wave signal of the next counting period; and The rising edge of the activation signal is in phase with the falling edge of the last square wave signal of the counting period.

14. The optical sensor according to claim 12, wherein the subsequent period of the frame signals after the second frame signal of the next counting period is configured as one square wave period of the square wave signal.

15. An optical sensor, the optical sensor comprising: A photodiode for detecting ambient light flicker to generate a sine wave signal; A waveform conversion circuit for converting the sine wave signal into a square wave signal having a square wave period; A pixel array for obtaining an image frame according to a frame period; and A digital backend for: Counting the count value of each square wave signal using a sampling frequency in a counting period, Adjusting the acquisition phase of the second image frame of the next counting period of the counting period when the frame period is equal to the square wave period and an activation signal is generated, and Adjusting the acquisition phase of the first image frame of the next counting period of the counting period when the frame period is a multiple of the square wave period and the activation signal is generated, wherein when the digital backend determines that the count value of each square wave signal is between two predetermined thresholds, and the difference between the maximum count value and the minimum count value among the multiple count values of all the square wave signals in the counting period is within a preset range, the activation signal is generated.

16. The optical sensor according to claim 15, wherein the digital backend is further configured to: Generate a frame signal for determining the frame period, When the frame period is equal to the square wave period, control the pixel array to obtain one image frame relative to each of the frame signals. When the frame period is equal to a multiple of the square wave period, control the pixel array to obtain one image frame every multiple frame signals, and Calculate the time offset between the reference signal and the first frame signal of the next counting period of the counting period, so as to adjust the first period between the second frame signal and the first frame signal of the next counting period according to this time offset.

17. The optical sensor according to claim 16, wherein The rising edge of the reference signal is in phase with the rising edge of the first square wave signal of the next counting period; and The rising edge of the activation signal is in phase with the falling edge of the last square wave signal of the counting period.

18. The optical sensor according to claim 16, wherein the subsequent period of the frame signals after the second frame signal of the next counting period is configured as the square wave period of one square wave signal.

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