Ambient light adaptive correction system based on feedback control

Abstract

The invention discloses an ambient light adaptive correction system based on feedback control, which comprises a photodiode, a TIA module, a TIA DC compensation module, an analog-to-digital conversion module, a feedback control module and a data register, and is characterized in that the photodiode is used for converting an optical signal into a light current, and the light current is transmitted to the analog-to-digital conversion module after being processed by the TIA module and the TIA DC compensation module; the analog-to-digital conversion module converts the optical current into a digital signal and transmits the digital signal to the feedback control module; the feedback control module is electrically connected with the TIA direct current compensation module and the data register; wherein the feedback control module is used for realizing an ambient light self-adaptive correction method based on feedback control, and the self-adaptive correction method feeds back and adjusts TIA bias current in real time according to light current, ensures the working consistency of the TIA, ensures that the current sampled by the ADC is within a certain range, and calibrates the proportion of the sampled current, so that the current measurement precision of the ADC is improved; and adaptive calibration under chip distance measurement is realized.

Description

Technical Field

[0001] The present application relates to the field of optical sensing technology, and in particular to an ambient light adaptive correction system based on feedback control. Background Art

[0002] A TOF chip (Time of Flight) is a sensor that calculates distance by measuring the time it takes for a light signal to be emitted and reflected. It is primarily used for precise depth measurement and is widely used in 3D imaging, object detection, autonomous driving, and gesture recognition. A TOF chip works by emitting light (usually laser or infrared light) and then calculating the time it takes for that light to reflect off an object's surface to infer its distance from the sensor.

[0003] However, the use of TOF chips introduces ambient light, which (sunlight, lamplight) can interfere with the signal receiver. Strong ambient light can cause TIA signal saturation and ranging failure, and randomly fluctuating ambient light can also interfere with signal phase detection. To improve the measurement accuracy of ranging chips and suppress ambient light interference, current methods for combating ambient light interference include: using narrowband filters to allow only set wavelengths to pass, thereby filtering out other interfering light in the environment; employing high-precision SPAD arrays to directly suppress ambient light at the receiver; obtaining measurements based on different illumination angles and performing manual calibration to reduce the impact of ambient light; or measuring ambient light current through an ADC and recalibrating the ranging formula using an internal algorithm.

[0004] However, the aforementioned methods for suppressing ambient light rely primarily on static calibration, are highly dependent on the receiving device, and lack real-time performance. Consequently, TOF chips struggle to maintain high measurement accuracy in scenarios with sudden changes in illumination. Furthermore, due to the wide range of ambient light variations, direct current measurement using an ADC requires the use of a current mirror to reduce the measured current. This can lead to current matching issues, impacting the ADC's sampling accuracy. Summary of the Invention

[0005] To this end, the present application provides an ambient light adaptive correction system based on feedback control to solve the problem that the ambient light suppression method in the prior art mainly relies on static calibration, lacks real-time performance, and leads to low measurement accuracy.

[0006] In order to achieve the above objectives, this application provides the following technical solutions:

[0007] A feedback-controlled ambient light adaptive correction system includes a photodiode, a TIA module, a TIA DC compensation module, an analog-to-digital conversion module, a feedback control module, and a data register. The photodiode is used to convert a light signal into a photocurrent, which is processed by the TIA module and the TIA DC compensation module and then transmitted to the analog-to-digital conversion module. The analog-to-digital conversion module converts the photocurrent into a digital signal and transmits it to the feedback control module. The feedback control module is electrically connected to the TIA DC compensation module and the data register.

[0008] The feedback control module is used to implement an ambient light adaptive correction method based on feedback control, including:

[0009] Step 1: Determine whether the reading of the analog-to-digital conversion module is within a specified range;

[0010] Step 2: If the analog-to-digital conversion module reading is within the specified range, directly convert the analog-to-digital conversion module reading into a current coefficient for subsequent ranging correction;

[0011] Step 3: If the analog-to-digital conversion module reading is not within the specified range, determine whether the TIA bias current digital range has reached the boundary;

[0012] Step 4: If the digital range of the TIA bias current reaches the limit, wait again for the analog-to-digital conversion module to read the reading;

[0013] Step 5: If the TIA bias current digital range does not reach the boundary, the difference between the analog-to-digital conversion module reading and the specified range is calculated, the adjustment step is calculated based on the difference, and the TIA bias current digital range is adjusted according to the adjustment step, and the adjusted TIA bias current digital range is written into the data register.

[0014] Preferably, in step 1, the specified range of the reading of the analog-to-digital conversion module is determined according to the working saturation state of the TIA module.

[0015] Preferably, in step 4, if the digital value of the TIA bias current has reached the minimum limit, but the reading of the analog-to-digital conversion module still reaches the full-scale value, the feedback control module is automatically turned off.

[0016] Preferably, the full-scale value of the analog-to-digital conversion module is 256.

[0017] Preferably, in step 5, the analog-to-digital conversion module is reset while calculating the difference between the reading of the analog-to-digital conversion module and the specified range.

[0018] Preferably, a current mirror is further included, wherein the input end of the current mirror is electrically connected to the output end of the TIA DC compensation module, and the output end of the current mirror is electrically connected to the input end of the analog-to-digital conversion module.

[0019] Preferably, the feedback control module needs to calibrate the matching coefficient of the current mirror before implementing the ambient light adaptive correction method based on feedback control, specifically including: measuring the analog-to-digital conversion module readings under two or more different TIA bias current digital ranges under the same ambient light conditions or under no ambient light conditions, and calculating and fitting the designed current mirror scaling factor, and adjusting the multiple reserved for the data register according to the calculated current mirror scaling factor.

[0020] Preferably, it also includes a ranging correction module, which is used to obtain a ranging correction coefficient calculation formula based on the pre-fitted phase in the ranging algorithm and the nonlinear equation of the analog-to-digital conversion module reading, and calculate the correction coefficient according to the correction coefficient calculation formula, and perform ranging correction according to the correction coefficient.

[0021] Preferably, the correction coefficient calculation formula is:

[0022]

[0023] in, represents the correction coefficient, a and b represent the pre-fitted phase fitting coefficients, Indicates the analog-to-digital conversion module reading, Indicates the expected reading of the analog-to-digital conversion module.

[0024] Preferably, two photodiodes are provided.

[0025] Compared with the prior art, this application has at least the following beneficial effects:

[0026] The present application provides an ambient light adaptive correction system based on feedback control, comprising a photodiode, a TIA module, a TIA DC compensation module, an analog-to-digital conversion module, a feedback control module, and a data register. The photodiode is used to convert a light signal into a photocurrent, which is processed by the TIA module and the TIA DC compensation module and then transmitted to the analog-to-digital conversion module. The analog-to-digital conversion module converts the photocurrent into a digital signal and transmits it to the feedback control module. The feedback control module is electrically connected to the TIA DC compensation module and the data register. The feedback control module is used to implement an ambient light adaptive correction method based on feedback control. The adaptive correction method adjusts the TIA bias current based on real-time feedback of the photocurrent to ensure consistency of the TIA operation, avoid signal overload and distortion, and ensure that the current sampled by the ADC is within a certain range. A register is reserved for calibrating the sampling current ratio, thereby improving the ADC measurement current accuracy, realizing adaptive calibration under chip ranging, and improving the ranging accuracy of TOF at long and short distances. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To more intuitively illustrate the prior art and the present application, exemplary drawings are provided below. It should be understood that the specific shapes and structures shown in the drawings should not generally be considered as limiting conditions for implementing the present application. For example, based on the technical concepts disclosed in this application and the exemplary drawings, those skilled in the art are capable of easily making routine adjustments or further optimizations to the addition / reduction / attribution division of certain units (components), the specific shapes, positional relationships, connection methods, and dimensional ratios.

[0028] Figure 1 This is a schematic diagram of the structure of an ambient light adaptive correction system based on feedback control provided by this application;

[0029] Figure 2 A flow chart of an ambient light adaptive correction method based on feedback control provided by this application;

[0030] Figure 3 Ambient light measurement and calibration flow chart provided for this application;

[0031] Figure 4 A feedback control timing simulation diagram is provided for this application.

[0032] Description of reference numerals:

[0033] 1. Photodiode; 2. TIA module; 3. TIA DC compensation module; 4. Analog-to-digital conversion module; 5. Feedback control module; 6. Data register. DETAILED DESCRIPTION

[0034] The present application will be further described below in detail through specific embodiments in conjunction with the accompanying drawings.

[0035] In the description of this application: unless otherwise specified, "plurality" means two or more. The terms "first," "second," "third," etc. in this application are intended to distinguish the objects referred to and do not have any special technical connotations (for example, they should not be understood as emphasizing importance or order). Expressions such as "including," "comprising," and "having" also mean "not limited to" (certain units, components, materials, steps, etc.).

[0036] The terms such as "upper", "lower", "left", "right", "middle", etc. cited in this application are usually used to indicate the general relative position relationship for the convenience of intuitive understanding by referring to the drawings, and are not absolute limitations on the position relationship in the actual product.

[0037] See also Figure 1 The present application provides an ambient light adaptive correction system based on feedback control, comprising a photoelectric conversion module, an analog-to-digital conversion module 4, a feedback control module 5, and a data register 6. The photoelectric conversion module comprises two photodiodes 1, a TIA module 2, and a TIA DC compensation module 3. The photodiode 1 is used to convert a light signal into a photocurrent, which is processed by the TIA module 2 and the TIA DC compensation module 3 and then transmitted to the analog-to-digital conversion module (ADC) 4. The analog-to-digital conversion module 4 converts the photocurrent into a digital signal and transmits it to the feedback control module 5. The feedback control module 5 is electrically connected to the TIA DC compensation module 3 and the data register 6. The ambient light collected by the ambient light adaptive correction system based on feedback control provided by the present application is processed by the TIA module 2, the TIA DC compensation module 3, and the analog-to-digital conversion module 4 and then directly enters the feedback control module 5, thereby feedback-adjusting the TIA DC compensation module 3 to adapt to the ranging influence caused by the dynamic changes in ambient light.

[0038] The present application provides an ambient light adaptive correction system based on feedback control, which can adjust the TIA bias current according to the real-time feedback of the photocurrent, ensure the consistency of the TIA operation, avoid signal overload and distortion, and at the same time ensure that the current sampled by the ADC is within a certain range. A design register is reserved to calibrate the sampling current ratio, thereby improving the ADC measurement current accuracy and realizing adaptive calibration under chip ranging.

[0039] See also Figure 2 In this application, the feedback control module 5 is used to implement an ambient light adaptive correction method based on feedback control (i.e., dynamically adjusting the TIA bias current according to changes in ambient light) to ensure that the output signal of the TIA module 2 remains within an appropriate range, thereby improving ranging accuracy. The ambient light adaptive correction method based on feedback control includes:

[0040] S1: Determine whether the reading of the analog-to-digital conversion module 4 is within the specified range;

[0041] Specifically, the TIA bias current digital range (TIA_trim) is written to data register 6 by default. The ADC reading includes the ambient light current, the TIA bias current (TIA_tirm<0:2> + 1, Ibias), and the ADC current (Iamb). To ensure consistent TIA operation under varying ambient light conditions, the total current (ambient light current + Ibias) must be within the range of Imin to Imax. This current range translates to the ADC reading (Ambient) of Hmin to Hmax. The upper and lower limits (Hmin to Hmax) are determined primarily based on the saturation state of the designed TIA module 2.

[0042] S2: If the reading of the analog-to-digital conversion module 4 is within the specified range, the reading of the analog-to-digital conversion module 4 is directly converted into a current coefficient for subsequent distance measurement correction;

[0043] Specifically, the initial current measurement is first performed to determine the range. If it is within the range, the ADC reading is directly converted into a current coefficient for subsequent ranging correction. If it is outside the range, proceed to the next step.

[0044] S3: If the reading of the analog-to-digital conversion module 4 is not within the specified range, it is determined whether the digital range of the TIA bias current has reached the boundary;

[0045] Specifically, when the ADC reading exceeds the range, it is determined whether the current TIA bias current digital range (TIA_trim) has reached the boundary, which is manifested by introducing the maximum and minimum values of the TIA bias current.

[0046] S4: If the digital range of the TIA bias current reaches the limit, wait for the reading of the analog-to-digital conversion module 4 again;

[0047] Specifically, if it is determined that the boundary is reached, no dynamic adjustment is performed, and the ADC reading is read again, and then the range judgment of step S1 is entered; if TIA_trim does not reach the boundary range, the next step is entered to perform difference calculation.

[0048] When determining whether the TIA bias current digital range has reached its limit, if the TIA bias current digital value has reached the minimum limit but the analog-to-digital conversion module 4 still reads the full-scale value, the feedback control module 5 is automatically disabled. Specifically, the ADC's range is limited, and the range of its output digital values is fixed. For example, an ADC output value of 256 indicates that the input signal has reached the ADC's maximum measurement range (i.e., full-scale). If the ADC reading still reaches the full-scale value of 256 even though the TIA bias current digital range (TIA_trim<0:2>) has been adjusted to its minimum value, this indicates that the ambient light intensity is too high, exceeding the system's measurement capabilities. In this case, to prevent the system from continuing to operate outside the measurement range, which could lead to erroneous measurement results or system instability, the system automatically disables the adaptive control module to protect the system and prevent further errors.

[0049] S5: If the TIA bias current digital range does not reach the boundary, the difference between the reading of the analog-to-digital conversion module 4 and the specified range is calculated, the adjustment step is calculated based on the difference, and the TIA bias current digital range is adjusted according to the adjustment step. The adjusted TIA bias current digital range is written into the data register 6.

[0050] Specifically, if TIA_trim does not reach the boundary, the ADC resets and synchronously enters the difference calculation. Specifically, based on the number of bits between the ADC reading range specified in step S1 and the ADC reading read in step S1, the number of steps required to adjust TIA_trim to the specified range is calculated, and TIA_trim is directly adjusted. This allows feedback adjustment to be completed only once, eliminating the need for repeated TIA_trim addition and subtraction feedback adjustments, resulting in a shorter overall time period. The difference calculation between the specified range and the actual ADC reading is based on the ambient light calculation formula: the TIA_trim step size has a clear linear relationship with the ADC reading. Each additional step size increases the ADC reading by n. Based on the difference and the multiple of n, the number of steps required to adjust TIA_trim can be directly calculated. TIA_trim is then readjusted, and the ADC reading is readjusted before repeating the judgment in step S1.

[0051] The present application provides an ambient light adaptive correction system based on feedback control, which also includes a current mirror, the input end of the current mirror is electrically connected to the output end of the TIA DC compensation module 3, and the output end of the current mirror is electrically connected to the input end of the analog-to-digital conversion module 4.

[0052] Specifically, the TIA DC compensation module 3 sets a certain linear compensation range, which is achieved by controlling TIA_trim<0:2> through data register 6. Since the ambient DC light that the TIA can convert is relatively large, the variation range of the ambient light received by the TIA DC compensation module 3 reaches 400uA. If it is measured directly, the power consumption and control time will increase. Therefore, before the photocurrent enters the charge balance ADC, it is necessary to use a current mirror to perform a multiple scaling of B1. The scaled photocurrent, i.e., the sampling current, enters the ADC. The current tested by the charge balance ADC is the sum of the ambient light Ic, the TIA bias current, and the ADC range current. The current is converted into a digital quantity by the ADC module, and the ADC reading Ambient (full value 256) is read to complete the measurement of the ambient photocurrent. The ambient light calculation formula is:

[0053]

[0054] Wherein, ADC represents the fixed current of the ADC module, Iref represents the charge balance ADC sampling reference current, and TIA_trim represents TIA_trim<0:2>.

[0055] In this application, the current sampled by the ADC passes through the TIA DC compensation module 3. In order to reduce the measurement range of the ADC, a current mirror structure with B1 times scaling is used. The current multiple scaling brings a larger test range while amplifying the error caused by the ADC accuracy, which is easy to affect the final ADC reading and cause measurement and judgment errors. Therefore, it is necessary to calibrate the current mirror matching coefficient in advance. It is mainly through pre-calibrating the ADC readings under two or more different TIA_trim<0:2> under the same ambient light or no ambient light, calculating and fitting the designed B1 value, and realizing the deviation value calibration by adjusting the reserved register. Finally, the actual calculation formula of the ambient light is recalibrated. It should be noted that the actual correction of the ambient light formula will only be implemented once, and will not be repeated with the feedback system.

[0056] This application adjusts the TIA bias current in real time based on the measured ADC readings through a dynamic adjustment module (i.e., feedback control module 5), mainly to ensure that the total current (ambient light + TIA bias current) is always within a stable range and to ensure the consistency of TIA operation. The current mirror coefficient of the TIA DC compensation module is calibrated before the entire dynamic adjustment to ensure the accuracy of the ambient light calculation.

[0057] See also Figure 3 The present application provides an ambient light adaptive correction system based on feedback control, which first calibrates the ambient light calculation formula, then starts dynamic adjustment of the ambient light, completes the adaptive process of the ambient light, and finally directly uses the ADC reading to calibrate the chip's ranging.

[0058] Therefore, the ambient light adaptive correction system based on feedback control provided by the present application also includes a ranging correction module, which is used to obtain a ranging correction coefficient calculation formula based on the pre-fitted phase in the ranging algorithm and the nonlinear equation of the reading of the analog-to-digital conversion module 4, and calculate the correction coefficient according to the correction coefficient calculation formula, and perform ranging correction according to the correction coefficient. The correction coefficient calculation formula is:

[0059]

[0060] in, represents the correction coefficient, a and b represent the pre-fitted phase fitting coefficients, Indicates the analog-to-digital conversion module reading, Indicates the expected reading of the analog-to-digital conversion module.

[0061] At this point, the entire dynamic control process of ambient light can be completed, such as Figure 4 The following is a simulation diagram of the main timing of the TIA dynamic control process under a certain ambient light condition in this application. CLK is the charge balancing ADC operating clock, the ADC integration time is 256CLK, and when the EOC signal reads 1, the ADC register reading Ambient 170 is read. According to steps S1-S3, the ADC reading is determined to be within the specified range, where the ideal specified range is set to 189-235. At this time, the TIA_trim reading is 4. According to step S5 of the control flow, it is determined that TIA_trim has not reached the limit. The ADC module is immediately reset and the difference calculation is performed. If the ratio of the difference to n is less than 1, TIA_trim is directly increased by 1. During the reset phase, TIA_trim is written to 5, and the ADC restarts the measurement calculation, waiting for the next EOC to read the ADC register reading 193. Steps S1-S5 are repeated. If the reading is within the specified range, the dynamic adjustment of the ambient light is completed, and the specific ambient light current is obtained according to the ambient light calculation formula.

[0062] The present application provides an ambient light adaptive correction system based on feedback control, which achieves consistency in signal saturation under different illumination currents by dynamically adjusting the TIA bias current. Furthermore, the accuracy of the sampled current calculation is improved through an adjustable current matching calibration coefficient, enabling measurement of a larger illumination range and higher measurement accuracy. This allows for high-precision, wide-range ambient light measurement data to be obtained, further improving the chip's distance measurement calibration for both long and short distances.

[0063] Compared with traditional ambient light suppression methods, this application mainly improves the current matching in the ambient light current detection circuit. By real-time detection of ambient light current intensity, the TIA bias current is dynamically adjusted to keep the total current received by the TIA within a certain range, ensuring the consistency of TIA operation, and adding an adjustable matching calibration coefficient to the TIA bias current measurement circuit, so that the measurement error caused by ambient light is directly corrected to the phase calculation, realizing full-link automatic calibration, which is more real-time and accurate.

[0064] The technical features of the above embodiments can be combined arbitrarily (as long as there is no contradiction in the combination of these technical features). In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described; these embodiments that are not explicitly written should also be considered to be within the scope of this specification.

Claims

1. An ambient light adaptive correction system based on feedback control, characterized in that: The device comprises a photodiode, a TIA module, a TIA DC compensation module, an analog-to-digital conversion module, a feedback control module, and a data register. The photodiode is used to convert an optical signal into a photocurrent, and after being processed by the TIA module and the TIA DC compensation module, the optical signal is transmitted to the analog-to-digital conversion module. The analog-to-digital conversion module converts the photocurrent into a digital signal and transmits it to the feedback control module. The feedback control module is electrically connected to the TIA DC compensation module and the data register. The feedback control module is used to implement an ambient light adaptive correction method based on feedback control, including: Step 1: Determine whether the reading of the analog-to-digital conversion module is within a specified range; Step 2: If the analog-to-digital conversion module reading is within the specified range, directly convert the analog-to-digital conversion module reading into a current coefficient for subsequent ranging correction; Step 3: If the analog-to-digital conversion module reading is not within the specified range, determine whether the TIA bias current digital range has reached the boundary; Step 4: If the digital range of the TIA bias current reaches the limit, wait again for the analog-to-digital conversion module to read the reading; Step 5: If the TIA bias current digital range does not reach the boundary, the difference between the analog-to-digital conversion module reading and the specified range is calculated, the adjustment step is calculated based on the difference, and the TIA bias current digital range is adjusted according to the adjustment step, and the adjusted TIA bias current digital range is written into the data register.

2. The ambient light adaptive correction system based on feedback control according to claim 1, characterized in that: In step 1, the prescribed range of the analog-to-digital conversion module reading is determined according to the operating saturation state of the TIA module.

3. The ambient light adaptive correction system based on feedback control according to claim 1, characterized in that: In step 4, if the digital value of the TIA bias current has reached the minimum limit, but the reading of the analog-to-digital conversion module still reaches the full-scale value, the feedback control module is automatically turned off.

4. The ambient light adaptive correction system based on feedback control according to claim 3, characterized in that: The full scale value of the analog-to-digital conversion module is 256.

5. The ambient light adaptive correction system based on feedback control according to claim 1, characterized in that: In step 5, the difference between the reading of the analog-to-digital conversion module and the specified range is calculated and the analog-to-digital conversion module is reset.

6. The ambient light adaptive correction system based on feedback control according to claim 1, characterized in that: It also includes a current mirror, the input end of the current mirror is electrically connected to the output end of the TIA DC compensation module, and the output end of the current mirror is electrically connected to the input end of the analog-to-digital conversion module.

7. The ambient light adaptive correction system based on feedback control according to claim 6, characterized in that: Before the feedback control module is used to implement the ambient light adaptive correction method based on feedback control, it is necessary to calibrate the matching coefficient of the current mirror, specifically including: measuring the analog-to-digital conversion module readings under two or more different TIA bias current digital ranges under the same ambient light conditions or under no ambient light conditions, and calculating and fitting the designed current mirror scaling factor, and adjusting the multiple reserved by the data register according to the calculated current mirror scaling factor.

8. The ambient light adaptive correction system based on feedback control according to claim 1, characterized in that: It also includes a ranging correction module, which is used to obtain a ranging correction coefficient calculation formula based on the pre-fitted phase in the ranging algorithm and the nonlinear equation of the analog-to-digital conversion module reading, calculate the correction coefficient according to the correction coefficient calculation formula, and perform ranging correction according to the correction coefficient.

9. The ambient light adaptive correction system based on feedback control according to claim 8, characterized in that: The correction coefficient calculation formula is: ； in, represents the correction coefficient, a and b represent the pre-fitted phase fitting coefficients, Indicates the analog-to-digital conversion module reading, Indicates the expected reading of the analog-to-digital conversion module.

10. The ambient light adaptive correction system based on feedback control according to claim 1, characterized in that: Two photodiodes are provided.

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