Apparatus and method for automatically controlling signal strength of direct time-of-flight sensor system

Abstract

The application discloses a device and a method for automatically controlling signal intensity of a direct time-of-flight 3D sensing system, the device comprising: a controller coupled with a transmitting device and a receiving device, and configured to adjust at least one of light intensity of the transmitting device, photosensitivity of the receiving device, and signal-to-noise ratio of a measurement result according to a signal histogram; the transmitting device coupled with the controller and configured to emit light; and the receiving device coupled with the controller and configured to receive light reflected by a measured object and generate a signal histogram.

Description

Technical Field

[0001] This invention relates to the field of 3D depth sensing, and more specifically to a sensing control device and method for a direct time-of-flight (DToF) sensor. Background Technology

[0002] Time-of-Flight (ToF) imaging technology has wide applications in various scenarios, such as Light-Detection-And-Ranging (LiDAR) systems, 3D imaging, depth mapping, and sensing devices based on Single-Photon Avalanche Diodes (SPADs). The principle of ToF imaging technology is to illuminate an object with light pulses and detect some of the pulses reflected from the object. The distance between the detector and the object can be directly measured by calculating the time of flight by the difference between the emission time of the emitted pulse and the arrival time of the radiation reflected from the corresponding point on the object; this is also known as Direct ToF (DToF).

[0003] A direct time-of-flight (DToF) sensor is an active optical sensor that consists of at least two main parts: a transmitter and a receiver. The transmitter emits a laser beam that illuminates the object being measured, and a portion of the laser beam is reflected and received by the receiver. Because the transmitter and receiver have a synchronization signal, the controller can record the time t it takes for the laser to travel back and forth in the air. Given the speed of light C, the distance to the object can be calculated as d = 1 / 2·C·t. Summary of the Invention

[0004] Technical problems to be solved

[0005] The intensity range of the light signal reflected back from the object being measured is very large, mainly affected by the detection distance, the material of the object's surface, its reflectivity, and the intensity of ambient light. However, the dynamic range of the receiving device is limited, often resulting in the following: near-range, highly reflective objects produce a strong signal, causing the receiving device's signal to saturate or accumulate, making distance measurement impossible or increasing the measurement error; far-range, low-reflective objects produce a weak signal, resulting in a low signal-to-noise ratio, making it difficult to find peaks in the signal histogram, and reducing the accuracy of distance measurement.

[0006] Technical solution

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system.

[0008] This invention provides a device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system, characterized in that it comprises: a controller coupled to a transmitting device and a receiving device, and the controller being configured to adjust at least one of the luminous intensity of the transmitting device, the photosensitivity of the receiving device, and the signal-to-noise ratio of the measurement result according to a signal histogram; a transmitting device coupled to the controller and configured to emit light; and a receiving device coupled to the controller and configured to receive light reflected by the object being measured and generate a signal histogram.

[0009] The present invention provides a device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system, characterized in that the receiving device includes a SPAD sensor.

[0010] The present invention provides a device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system, characterized in that the photosensitivity of the receiving device is adjusted by the bias voltage of the SPAD sensor.

[0011] This invention provides a device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system. The controller is further configured to check the shape and peak value of the signal histogram, and adjust the bias voltage of the SPAD sensor of the transmitting device according to the saturation level of the signal histogram. If the peak value of the signal histogram exceeds a first threshold, the bias voltage is actively reduced in the next frame; if the peak value of the signal histogram is within a preset range, the bias voltage is maintained; if the peak value of the signal histogram is less than a second threshold, the bias voltage is increased in the next frame.

[0012] The present invention provides a device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system, characterized in that the emitting device includes a laser, and the laser is configured to emit short-pulse laser.

[0013] The present invention provides a device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system, characterized in that the luminous intensity of the emitting device is adjusted by controlling the driving current of the laser.

[0014] This invention provides a device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system. The controller is further configured to check the shape and peak value of the signal histogram, and adjust the driving current of the laser in the transmitting device based on the saturation level of the signal histogram. If the peak value of the signal histogram exceeds a first threshold, the driving current is actively reduced in the next frame; if the peak value of the signal histogram is within a preset range, the driving current is maintained; if the peak value of the signal histogram is less than a second threshold, the driving current is increased in the next frame.

[0015] This invention provides a device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system. The controller is configured to check the shape and peak value of the signal histogram, and automatically increase / decrease the number of ranging operations to adjust the signal-to-noise ratio of the measurement results based on the saturation level of the signal histogram. If the peak value of the signal histogram exceeds a first threshold, the optical repetition test in the next frame is actively reduced; if the peak value of the signal histogram is within a preset range, the optical repetition test is maintained; if the peak value of the signal histogram is less than a second threshold, the optical repetition test in the next frame is increased, and the increased number of optical repetitions does not exceed a third maximum threshold.

[0016] The present invention provides a device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system, characterized in that the controller is configured such that the third maximum threshold for the number of light repetitions it adds is 10,000.

[0017] The present invention provides a device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system, characterized in that the controller is configured such that the first threshold of the signal histogram it checks is 90% of the maximum value that the receiving device can receive, the second threshold is 30% of the maximum value that the receiving device can receive, and the preset range is 30% to 90% of the maximum value that the receiving device can receive.

[0018] The present invention provides a method for automatically controlling the signal strength of a direct time-of-flight 3D sensing system, characterized in that it includes: using a controller to adjust at least one of the following according to a signal histogram: the light intensity of a transmitting device, the photosensitivity of a receiving device, and the signal-to-noise ratio of a measurement result; using the transmitting device to emit light; and using the receiving device to receive the light reflected by the object being measured and generate a signal histogram.

[0019] Beneficial effects

[0020] Compared with the prior art, the present invention provides a device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system. It has the following advantages: it can automatically adjust the received signal strength so that the final received signal strength is within the receiving range of the receiving device (e.g., between 30% and 90% of the maximum value), avoiding near-range signal saturation and distortion, and improving ranging accuracy. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of an apparatus for automatically controlling the signal strength of a direct time-of-flight 3D sensing system according to an embodiment of the present disclosure.

[0022] Figure 2 This is a schematic diagram of a SPAD sensor according to a disclosed embodiment.

[0023] Figure 3This is a schematic diagram of the round-trip time delay of a laser according to a disclosed embodiment.

[0024] Figure 4 It is a signal histogram according to a disclosed embodiment.

[0025] Figure 5 This is a graph showing the relationship between the photon detection probability (PDP) and the bias voltage (Vexc) of the SPAD photosensitive unit according to a disclosed embodiment.

[0026] Figure 6 This is a diagram showing the relationship between the excitation drive current and optical power of a vertical cavity surface-emitting laser (VCSEL) according to a disclosed embodiment.

[0027] Figure 7 This is a diagram illustrating how the controller 110 adjusts the number of short-pulse laser pulses in single-frame ranging according to a disclosed embodiment. Detailed Implementation

[0028] Before proceeding with the detailed description below, it may be advantageous to define certain words and phrases used throughout this patent document. The terms “coupled,” “connected,” and their derivatives refer to any direct or indirect communication or connection between two or more elements, regardless of whether those elements are physically in contact with each other. The terms “transmit,” “receive,” and “communicate,” and their derivatives cover both direct and indirect communication. The terms “comprise,” “include,” and their derivatives refer to, but are not limited to, those including, those including, those including, those including. The term “or” is inclusive, meaning and / or. The phrase “associated with,” and its derivatives refer to, including, being contained within, interconnected, containing, being included in, being connected or connected to, coupled or coupled to, communicating with, cooperating, intertwining, juxtaposed, proximate, bound or bound to, having, having attributes, having a relationship or being related to, etc. The term “controller” refers to any device, system, or part thereof that controls at least one operation. Such a controller may be implemented in hardware, or a combination of hardware and software and / or firmware. The functionality associated with any particular controller may be centralized or distributed, local or remote. The phrase "at least one" when used with a list of items means that different combinations of one or more of the listed items may be used, and that only one item from the list may be required. For example, "at least one of A, B, and C" includes any of the following combinations: A, B, C, A and B, A and C, B and C, A and B and C.

[0029] Definitions of other specific words and phrases are provided throughout this patent document. Those skilled in the art will understand that, in many, if not most, cases, such definitions apply to the prior and future use of the words and phrases thus defined.

[0030] In this patent document, the application combination of modules and the hierarchical division of sub-modules are for illustrative purposes only. Without departing from the scope of this disclosure, the application combination of modules and the hierarchical division of sub-modules can be in different ways.

[0031] Figure 1 This is a schematic diagram of an apparatus for automatically controlling the signal strength of a direct time-of-flight 3D sensing system according to an embodiment of the present disclosure.

[0032] like Figure 1 As shown, a device 100 for automatically controlling the signal strength of a direct time-of-flight 3D sensing system according to an embodiment of this disclosure can be a SPAD-based DToF ranging device. The SPAD-based DToF ranging device includes a controller 110, a transmitter 120, and a receiver 130.

[0033] The controller 110 is coupled to the transmitter 120 and the receiver 130. The controller 110 may include control circuitry. The controller 110 may be configured to control repeated ranging (controlling the transmitter 120 to transmit multiple times and controlling the receiver 130 to receive lasers multiple times) to improve the signal-to-noise ratio and record the time t that the laser travels back and forth in the air.

[0034] The transmitting device 120 is coupled to the controller 110. The transmitting device 120 may be an optical device including a laser such as a VCSEL 121. The VCSEL 121 is located inside the transmitting device 120. The transmitting device 120 may be configured to emit laser light (such as a short-pulse laser).

[0035] The receiving device 130 may include a SPAD sensor 131 and a lens 132. The SPAD sensor 131 is located inside the receiving device 130. The lens 132 is located in front of the SPAD sensor 131 for receiving reflected light. The receiving device 130 may be configured to receive laser light (such as short-pulse laser light) reflected by the object being measured.

[0036] Figure 2 This is a schematic diagram of a SPAD sensor according to a disclosed embodiment.

[0037] like Figure 2 The SPAD sensor 131 shown includes one or more SPAD photosensitive units arranged thereon in both the horizontal and vertical directions.

[0038] Figure 3 This is a schematic diagram of the round-trip time delay of a laser according to a disclosed embodiment.

[0039] Figure 4 It is a signal histogram according to a disclosed embodiment.

[0040] In use, the transmitting device 120 emits short-pulse laser light to illuminate the object being measured, and part of the short-pulse laser light is reflected and received by the receiving device 130. Since there is a synchronization signal between the transmitting device 120 and the receiving device 130, the controller 110 can record the time t that the short-pulse laser travels back and forth in the air. Figure 3 The time delay t1-t0 of the laser's round trip is shown. Given the speed of light C, the distance to the object can be calculated as d = 1 / 2·C·t. The intensity range of the reflected light signal is very large, depending on factors such as the detection distance, the material of the object's surface, its reflectivity, and the intensity of ambient light. However, the dynamic range of the receiving device 130 is limited. When the object being measured is close and has high reflectivity, the signal received by the receiving device 130 may exhibit characteristics such as... Figure 4 As shown in (a), the saturation or accumulation effect makes distance measurement impossible or increases the distance measurement error. When the object being measured is far away and has low reflectivity, the signal received by the receiving device 130 is weak, the signal-to-noise ratio is low, it is difficult to find peaks in the signal histogram, and the distance measurement accuracy is reduced. When the distance or reflectivity of the object being measured is moderate, the signal histogram is as shown in (a). Figure 4 As shown in (b) above, the signal strength is moderate.

[0041] Figure 5 This is a diagram showing the relationship between the PDP and the bias voltage of the SPAD photosensitive unit according to a disclosed embodiment.

[0042] According to one embodiment of this disclosure, the controller 110 can also be configured to check the signal histogram shape and peak value after each ranging operation, and adjust the bias voltage of one or more SPAD photosensitive units based on the saturation level of the signal histogram. Specifically, after a ranging operation is completed, the shape of the signal histogram is checked. If the peak value of the signal histogram exceeds a threshold (e.g., 90% of the maximum value that the receiving device can receive), the bias voltage is actively reduced in the next frame. If the peak value of the signal histogram is within a preset range (e.g., 30% to 90% of the maximum value that the receiving device can receive), the bias voltage is maintained. If the peak value of the signal histogram is less than a threshold (e.g., 30% of the maximum value that the receiving device can receive), the bias voltage in the next frame is increased, wherein the increased bias voltage does not exceed a maximum threshold, such as 5V. The specific value of the maximum threshold that the increased bias voltage does not exceed is exemplary and does not limit the invention to any particular implementation.

[0043] The receiving device 130 can also be configured such that its photosensitivity can be adjusted by the bias voltage of one or more SPAD photosensitive units arranged on the SPAD sensor 131. For example... Figure 5As shown, the SPAD photosensitive unit can be configured such that its PDP is positively correlated with the bias voltage. For example, when the bias voltage of the SPAD photosensitive unit decreases from V2 to V1, the PDP of the SPAD photosensitive unit decreases from PDP2 to PDP1.

[0044] In use, after a ranging operation is completed, the controller 110 checks the shape of the signal histogram. If the peak value of the signal histogram exceeds a threshold, the signal is considered too strong and sensitivity needs to be reduced. In the next frame, the controller 110 actively reduces the bias voltage. Since the PDP of one or more SPAD photosensitive units is positively correlated with the bias voltage, the PDP of one or more SPAD photosensitive units decreases accordingly, reducing the sensitivity of the receiver 130. Therefore, the peak value of the signal histogram in the next frame will be lower than that in the previous frame. If the peak value of the signal histogram is within a preset range in the next frame, the bias voltage is considered appropriate. The controller 110 maintains the bias voltage in subsequent ranging operations, and the PDP of one or more SPAD photosensitive units remains unchanged, as does the sensitivity of the receiver 130. If the peak value of the signal histogram is less than the threshold, the controller 110 increases the bias voltage in the next frame. The PDP of one or more SPAD photosensitive units increases accordingly, increasing the sensitivity of the receiver 130. Therefore, the peak value of the signal histogram in the next frame will be higher than that in the previous frame. The above steps are used throughout the entire distance measurement process.

[0045] Figure 6 This is a diagram showing the relationship between the laser drive current and optical power of a VCSEL according to a disclosed embodiment.

[0046] According to another embodiment of this disclosure, the controller 110 can also be configured to check the signal histogram shape and peak value after each ranging operation, and adjust the laser drive current of the VCSEL 121 of the transmitting device 120 according to the saturation level of the signal histogram. Specifically, after a ranging operation is completed, the shape of the signal histogram is checked. If the peak value of the signal histogram exceeds a threshold (e.g., 90% of the maximum value that the receiving device can receive), the laser drive current is actively reduced in the next frame. If the peak value of the signal histogram is within a preset range (e.g., 30% to 90% of the maximum value that the receiving device can receive), the laser drive current is maintained. If the peak value of the signal histogram is less than a threshold (e.g., 30% of the maximum value that the receiving device can receive), the laser drive current in the next frame is increased, wherein the increased laser drive current does not exceed a maximum threshold, such as 1A. The specific value of the maximum threshold that the increased laser drive current does not exceed is exemplary and does not limit the invention to any particular implementation.

[0047] The emitting device 120 can also be configured such that its luminous intensity can be adjusted by controlling the laser drive current of the VCSEL 121. For example, the VCSEL 121 can be configured such that its optical power is proportional to the laser drive current. Figure 6 The relationship is shown. When the laser drive current of VCSEL 121 decreases from I2 to I1, the optical power of VCSEL 121 decreases from P2 to P1.

[0048] In operation, after a ranging measurement is completed, the controller 110 checks the shape of the signal histogram. If the peak value of the signal histogram exceeds a threshold, the signal is considered too strong, and sensitivity needs to be reduced. In the next frame, the laser drive current is actively reduced, the optical power of the VCSEL 121 decreases accordingly, and the luminous intensity of the transmitting device 120 decreases. Therefore, the peak value of the signal histogram in the next frame will be lower than that in the previous frame. If the peak value of the signal histogram is within a preset range for the next frame, the laser drive current is considered appropriate, and the laser drive current is maintained in subsequent ranging measurements. The optical power of the VCSEL 121 and the luminous intensity of the transmitting device 120 remain unchanged. If the peak value of the signal histogram is lower than the threshold, the laser drive current in the next frame is increased, the optical power of the VCSEL 121 increases accordingly, and the luminous intensity of the transmitting device 120 increases. Therefore, the peak value of the signal histogram in the next frame will be higher than that in the previous frame. The above steps are used throughout the entire ranging process.

[0049] Figure 7 This is a diagram illustrating how the controller 110 adjusts the number of short-pulse laser pulses in single-frame ranging according to a disclosed embodiment.

[0050] According to another embodiment of this disclosure, the controller 110 can also be configured to check the signal histogram shape and peak value after each ranging operation, and automatically increase / decrease the number of ranging operations based on the saturation level of the signal histogram. Specifically, after a ranging operation is completed, the shape of the signal histogram is checked. If the peak value of the signal histogram exceeds a threshold (e.g., 90% of the maximum value that the receiving device can receive), the repetition of short-pulse laser pulses in a single frame is actively reduced in the next frame. If the peak value of the signal histogram is within a preset range (e.g., 30% to 90% of the maximum value that the receiving device can receive), the repetition of short-pulse laser pulses is maintained. If the peak value of the signal histogram is less than a threshold (e.g., 30% of the maximum value that the receiving device can receive), the repetition of short-pulse laser pulses in the next frame is increased, wherein the number of increased short-pulse laser pulse repetitions does not exceed a maximum threshold, such as 10,000 times. The specific value of the maximum threshold for the number of increased short-pulse laser pulse repetitions is exemplary and does not limit the invention to any particular implementation.

[0051] In use, after a ranging measurement is completed, the controller 110 checks the shape of the signal histogram. If the peak value of the signal histogram exceeds a threshold, the signal is considered too strong, and the sensitivity needs to be reduced. Therefore, in the next frame, the number of short laser pulses in a single frame is actively reduced for repeated testing, and the peak value of the signal histogram in the next frame will decrease compared to the previous frame (e.g., ...). Figure 7 The number of short-pulse laser pulses is reduced from N in Figure (a) to M in Figure (b). If the peak value of the signal histogram is within the preset range of the next frame, the number of short-pulse laser pulses is considered appropriate, and the number of short-pulse laser pulses is maintained in subsequent ranging operations. If the peak value of the signal histogram is less than the threshold, the number of short-pulse laser pulse repetitions in the next frame is increased, and the peak value of the signal histogram in the next frame will increase compared to the previous frame. The above steps are used throughout the ranging process.

[0052] Although this disclosure has been described with reference to exemplary embodiments, various combinations, changes, and modifications may be suggested to those skilled in the art. This disclosure is intended to cover such combinations, changes, and modifications that fall within the scope of the appended claims.

[0053] Any description in this invention should not be construed as implying that any particular element, step, or function is essential and must be included within the scope of the claims. The scope of the patent subject matter is defined only by the claims.

Claims

1. A device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system, characterized in that, include: A controller coupled to a transmitting device and a receiving device, and the controller is configured to adjust at least one of the following based on a signal histogram: the luminous intensity of the transmitting device, the photosensitivity of the receiving device, and the signal-to-noise ratio of the measurement results; A transmitting device, which is coupled to a controller and configured to emit light; A receiving device, coupled to a controller and configured to receive light transmitted by the transmitting device and reflected by a test object, and to generate a signal histogram, wherein the light reflected by the test object is affected by at least one of the following: detection distance, material of the object surface, and reflectivity. The controller is configured to check the shape and peak value of the signal histogram, and automatically increase / decrease the number of ranging operations based on the saturation level of the signal histogram to adjust the signal-to-noise ratio of the measurement results. If the peak value of the signal histogram exceeds the first threshold, the optical repetition test in a single frame is actively reduced in the next frame. If the peak value of the signal histogram is within the preset range, continue the optical repeat test; If the peak value of the signal histogram is less than the second threshold, the light repetition test is added to the next frame, and the number of light repetitions added does not exceed the third maximum threshold. The controller is configured such that the first threshold of the signal histogram it checks is 90% of the maximum value that the receiving device can receive, the second threshold is 30% of the maximum value that the receiving device can receive, and the preset range is 30% to 90% of the maximum value that the receiving device can receive.

2. The device for automatically controlling the signal strength of the direct time-of-flight 3D sensing system according to claim 1, characterized in that, The receiving device includes a SPAD sensor.

3. The device for automatically controlling the signal strength of the direct time-of-flight 3D sensing system according to claim 2, characterized in that, The photosensitivity of the receiving device is adjusted by the bias voltage of the SPAD sensor.

4. The device for automatically controlling the signal strength of the direct time-of-flight 3D sensing system according to claim 3, characterized in that, The controller is also configured to check the signal histogram shape and peak value, and adjust the bias voltage of the SPAD sensor of the transmitting device according to the saturation level of the signal histogram. If the peak value of the signal histogram exceeds the first threshold, the bias voltage is actively reduced in the next frame. If the peak value of the signal histogram is within the preset range, the bias voltage is maintained. If the peak value of the signal histogram is less than the second threshold, the bias voltage for the next frame is increased.

5. The device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system according to claim 1, characterized in that, The emitting device includes a laser, and the laser is configured to emit short-pulse laser light.

6. The device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system according to claim 1, characterized in that, The luminous intensity of the emitting device is adjusted by controlling the driving current of the laser.

7. The device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system according to claim 6, characterized in that, The controller is also configured to check the signal histogram shape and peak value, and adjust the drive current of the laser in the transmitting device according to the saturation level of the signal histogram. If the peak value of the signal histogram exceeds the first threshold, the drive current is actively reduced in the next frame. If the peak value of the signal histogram is within the preset range, the drive current is maintained; If the peak value of the signal histogram is less than the second threshold, the drive current for the next frame is increased.

8. The device for automatically controlling the signal strength of a direct time-of-flight 3D sensing system according to claim 1, characterized in that, The controller is configured such that the third maximum threshold for the number of light repetitions it adds is 10,000.

9. A method for automatically controlling the signal strength of a direct time-of-flight 3D sensing system, characterized in that, include: Use a transmitting device to emit light; The receiving device receives the light transmitted by the transmitting device and reflected by the object under test, and generates a signal histogram. The light intensity of the transmitting device, the photosensitivity of the receiving device, and the signal-to-noise ratio of the measurement result are adjusted according to the signal histogram. The light reflected by the object being measured is affected by at least one of the detection distance, the material of the object's surface, and the reflectivity. The controller is used to check the signal histogram shape and peak value, and automatically increases / decreases the number of ranging operations based on the saturation level of the signal histogram to adjust the signal-to-noise ratio of the measurement results. If the peak value of the signal histogram exceeds the first threshold, the optical repetition test in a single frame is actively reduced in the next frame. If the peak value of the signal histogram is within the preset range, continue the optical repeat test; If the peak value of the signal histogram is less than the second threshold, the light repetition test is added to the next frame, and the number of additional light repetitions does not exceed the third maximum threshold. The controller is configured such that the first threshold of the signal histogram it checks is 90% of the maximum value that the receiving device can receive, the second threshold is 30% of the maximum value that the receiving device can receive, and the preset range is 30% to 90% of the maximum value that the receiving device can receive.

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