Global motion suppression in event-driven cameras

Abstract

Examples of global motion suppression in an event-driven camera are described herein. In some examples, global motion of the event-driven camera is detected based on multiple pixels of an event-driven image sensor detecting an event. In response to detecting the global motion, the global motion can be suppressed by the event-driven image sensor circuit.

Description

Background Art

[0001] Computing devices are used to perform a variety of tasks, including work activities, banking, research, transportation, and entertainment. In some examples, computing devices can be used to capture and process sensory data. For example, a camera can capture image data. In some examples, the camera can be an event-driven camera that detects changes in a scene. BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Various examples will be described below by referring to the following drawings.

[0003] Figure 1 is an example block diagram of an event-driven camera in which global motion suppression may be performed;

[0004] Figure 2 is an example flow chart illustrating a method for global motion suppression in an event-driven camera;

[0005] Figure 3 is an example of a four-pixel module for global motion suppression in event-driven cameras;

[0006] Figure 4 is an example of a 16-pixel array module for global motion suppression in event-driven cameras; and

[0007] Figure 5 is an example showing a reset signal and a global activation signal of a pixel array.

[0008] Throughout the drawings, the same reference numerals denote similar, but not necessarily identical, elements. The drawings are not necessarily drawn to scale, and the dimensions of some components may be exaggerated to more clearly illustrate the examples shown. In addition, the drawings provide examples and / or implementations consistent with the present description; however, the present description is not limited to the examples and / or implementations provided in the drawings. DETAILED DESCRIPTION

[0009] This article describes an example of global motion suppression in an event-driven camera. In some examples, an event-driven camera records motion that is not part of an object in the camera's field of view. This motion is global in nature and may be caused by the camera's own motion relative to the motion of the object. This global motion may be caused by panning, shaking, and other forms of camera motion. Reading and processing pixel data during global motion may be inefficient. This article describes an example of global motion suppression in an event-driven camera.

[0010] Figure 1is an example block diagram of an event-driven camera 102 in which global motion suppression may be performed. The event-driven camera 102 may be a standalone device or may be integrated into other electronic devices (e.g., desktop computers, laptop computers, tablet devices, smart phones, cellular phones, game consoles, server devices, cameras, and / or smart appliances, etc.). Examples of applications in which the event-driven camera 102 may be used include thermal imaging in 3D printers, print quality assessment, virtual reality, autonomous vehicle navigation, and robotics.

[0011] An emerging paradigm in computing is event-driven processing, which is one aspect within the larger scope of brain-inspired computing (also known as neuromorphic computing). Event-driven processing has similarities to spikes and spike propagation within the human brain. Because processing is triggered by events, the energy consumed by an event-driven camera 102 can be significantly less when compared to a non-event-driven system. For example, in a frame-based camera, an entire image frame is read out periodically, even when the changes between image frames are slight. For example, an entire image frame can be read out, and pixels within the image frame can be processed even when most pixels remain unchanged. In contrast, in an event-driven image sensor 104, instead of reading image frames periodically, individual pixels can be read when changes are detected. In the context of image data, energy efficiency in a camera can be beneficial for continuous sensing in edge conditions and when the camera can be powered by a battery.

[0012] While event-driven image sensors 104 can improve efficiency on the camera capture side, a similar event-driven approach can be implemented for image processing as well.By mimicking biology, and in particular the human brain, there is an opportunity to greatly improve these systems in terms of computational efficiency.

[0013] The event-driven camera 102 provides several benefits over frame-based cameras. The event-driven camera 102 is substantially more energy efficient, which results in an order of magnitude reduction in power consumption. Events are sparse results of storage, computation, and bandwidth efficiency. In addition, the event-driven camera 102 enables a significant increase in dynamic range, which enables detection of subtle image quality defects or facial and / or object recognition that may be challenged by difficult lighting conditions including object backlighting. However, the event-driven camera 102 may encounter scenarios that compromise energy storage, computation, and bandwidth efficiency as well as high dynamic range.

[0014] The event-driven camera 102 operates on the principle of capturing light in the presence of significant motion. In an event-driven camera 102, pixels 106 may report an event when the pixels 106 are triggered by motion. For example, when a person passes through the field of view (FOV), those pixels 106 on which motion is recorded may be read out for processing, while background pixels 106 without motion will not be processed.

[0015] The event-driven camera 102 can detect motion through the process of pixel integration. When light (e.g., photons) contacts a pixel 106, the pixel 106 stores electrons in a pixel well. The amount of electrons stored in the pixel well is proportional to the amount of light sensed by the pixel 106. As used herein, pixel integration is a measurement of the amount of light (e.g., photons) sensed by the pixel 106 over a period of time (e.g., exposure time). In other words, pixel integration is a measurement of the stored charge accumulated within the pixel 106 during a specified time interval. In some examples, the pixel 106 may output a pixel integration signal (referred to herein as a pixel integration output) indicating a pixel integration value.

[0016] During pixel integration, when the event threshold is reached, the pixel 106 that records the motion will do so. When high frequency motion is detected, the pixel 106 integrates quickly until it reaches the event threshold. This can be referred to as pixel firing. When the pixel 106 fires, the pixel output can be read out as an event. In one example, when the pixel integration reaches the event threshold, the pixel 106 can output a pixel firing signal. In other words, when the pixel well threshold (referred to as the event threshold) is reached, the pixel firing signal can be asserted.

[0017] These events can be processed within the event-driven image sensor 104 and by downstream processing (e.g., a spike neural network (SNN)). For example, downstream processing can be used to identify a person passing through the FOV. This is useful for applications such as pedestrian detection, object recognition, and various other applications. Event-based processing is also useful when the device powering the event-driven image sensor 104 has a small battery. In addition, event-based processing may be useful when the observed subject experiences a wide dynamic range, which may be beyond the capabilities of a frame-based camera sensor to detect.

[0018] While event-driven cameras 102 are very useful, there are common scenarios when their features may not provide the described benefits. These scenarios may occur when the event-driven camera 102 records motion that is not attributed to the object. This motion is global in nature because the motion is caused by the motion of the camera itself rather than the motion of the object. This global motion can be due to panning, shaking (e.g., hand shaking), jittering, and other forms of camera motion of the event-driven camera 102.

[0019] When such global motion occurs, all pixels 106 within the event-driven image sensor 104 record the motion. All pixels are then read out, processed, and stored. However, in this case, pixel readout, processing, and storage are unnecessary. In other words, pixel readout, processing, and storage during global motion events provide no benefit because no object motion is detected. When this happens, the event-driven camera 102 may become as inefficient as a frame-based camera.

[0020] Without suppressing global motion, the event-driven camera 102 may experience the following problems. Power consumption may increase dramatically. Since the power consumption due to global motion when processing pixels 106 is unnecessary, efficiency in an otherwise very efficient camera system is affected. This unnecessary pixel processing can also result in wasted power in other data paths, memory access, and processing networks downstream of the event-driven image sensor 104. In addition, wasted pixel processing may result in adversely affecting storage efficiency, compromising compression efficiency caused by the sparsity of events. In addition, pixels 106 have a maximum electron well (referred to as a pixel well) capacity. By integrating unnecessarily, the pixel well is more likely to saturate, which affects the benefits of high dynamic range.

[0021] In some approaches, post-processing can be performed to detect global motion at a later stage to aid the processing for event detection. However, with these approaches, the above-mentioned problems cannot be overcome. In fact, post-processing will lead to further power consumption.

[0022] Examples of event-driven cameras 102 are described herein that include circuitry within an event-driven image sensor 104 to detect and suppress global motion in a pixel array. This can free downstream stages of the event-driven camera 102 from having to carry, store, and process additional pixel data associated with global motion. This approach can also prevent premature saturation of pixel wells whenever global motion occurs.

[0023] The event-driven image sensor 104 includes a plurality of pixels 106. In one example, the pixels 106 are arranged in an array, wherein the plurality of pixels 106 form rows of pixels and the plurality of pixels 106 form columns of pixels.

[0024] It should be noted that the event-driven camera 102 can detect changes in the field of view of the event-driven image sensor 104. A given pixel 106 can output a pixel integration output signal and a pixel excitation signal. The pixel integration output signal is an output signal that is asserted when the pixel 106 is integrated. As used herein, the pixel integration output indicates the amount of light (e.g., photons) sensed by the pixel 106 over a period of time (e.g., exposure time). The pixel integration output can be used to detect low-frequency global motion.

[0025] The pixel fire signal is a signal that is asserted when the pixel well reaches the event threshold. The pixel fire signal can be used to detect high frequency events.

[0026] In some examples, pixel 106 may also receive a pixel reset signal. The pixel reset signal may be associated with pixel 106 such that whenever the reset signal is asserted, the pixel 106 is reset. The pixel reset signal may cause pixel 106 to discharge the pixel well, which results in a reset of the pixel integrated output.

[0027] The event-driven image sensor 104 may include a global motion detection circuit 108 to detect global motion of the event-driven camera 102 based on the detection of events by the plurality of pixels 106 of the event-driven image sensor 104. In some examples, the global motion may include panning or shaking of the event-driven camera 102.

[0028] Global motion may be detected when a predetermined percentage of pixels 106 detect an event. In some examples, global motion may be detected if a predetermined number or percentage of pixels 106 are active. For example, global motion may be detected when all pixels 106 are active. In another example, global motion may be detected when a predetermined percentage (e.g., less than 100%) of pixels 106 are active.

[0029] In other examples, a predetermined subset of pixels 106 may be used to detect global motion. For example, all edge pixels 106, every other pixel 106, every third pixel 106, etc. may be used to detect global motion. In this example, other pixels 106 may not be connected to the global motion detection circuit 108.

[0030] The global motion detection circuit 108 may receive a pixel integrated output from each of the plurality of pixels 106. The global motion detection circuit 108 may detect when the pixel integrated output of each of the plurality of pixels 106 reaches an event indication value. This may indicate that a low frequency event (e.g., global motion) has been detected by the pixel 106. The event indication value may be a value of the pixel integrated output that indicates that enough change has occurred in the pixel well to indicate a change in the field of view of the image sensor 104 driven by an event.

[0031] It should be noted that the event indication value can be less than the event threshold for asserting the pixel firing signal. For example, the pixel integrated output can be less than the event threshold that will trigger the pixel firing. However, the pixel integrated output can be used to detect low frequency motion (e.g., global motion) that might not otherwise trigger a high frequency event.

[0032] The global motion detection circuit 108 may also include a pixel integration delay component that delays when the pixel integration output reaches the event indication value. For example, the pixel integration delay component may have a first time constant that is a large time constant for detecting low-frequency global motion (e.g., panning). Because low-frequency global motion may be detectable over a longer period of time (compared to high-frequency events that would trigger a pixel excitation signal), the large time constant of the pixel integration delay component may be used to delay when global motion is detected by the pixel 106. This may ensure that global motion detection is not asserted prematurely.

[0033] In one example, the pixel integration delay component may be implemented as a capacitor coupled to the pixel integration output of pixel 106 . Figure 3 An example of this approach is described in .

[0034] The event-driven image sensor 104 may also include a global motion suppression circuit 110. The global motion suppression circuit 110 may suppress global motion in response to detecting global motion. Suppressing global motion by the global motion suppression circuit 110 may include generating a global activation signal that prevents storage and processing of data contained in multiple pixels 106. When all pixels 106 are triggered (e.g., pixels 106 detect an event based on pixel integration output), the global motion suppression circuit 110 may generate a global activation signal. When the global activation signal is output, this indicates that all pixels 106 have been activated. For example, when the event-driven camera 102 experiences global motion due to panning or shaking, the global activation signal may be asserted. In this case, the pixel value may be useless and may therefore cause additional power consumption.

[0035] In some examples, the global activation signal can be used as a selector for event-driven readout and processing of the pixel array within the image sensor 104. For example, when the global activation signal is asserted (e.g., ON), then global motion is detected and pixel data is not read out and / or processed. This will inhibit unnecessary and wasteful readout and processing of pixel data. When the global activation signal is de-asserted (e.g., OFF), then global motion is not detected and pixel data can be read out and / or processed.

[0036] In some examples, suppressing global motion can include resetting the plurality of pixels 106 in response to detecting global motion. For example, when the global activation signal is generated, a pixel reset signal can be sent to each of the plurality of pixels 106. When global motion occurs, the pixels 106 may integrate unnecessarily. Such global motion can cause the pixel wells to fill up faster and saturate the pixels 106 faster. Such a scenario can negatively impact the dynamic range of the event-driven image sensor 104.

[0037] To maintain the dynamic range, the global activation signal can be used to assert a reset signal that is fed back to all pixels 106 in the event-driven image sensor 104. The reset signal will cause the pixel 106 to empty the pixel well. In some embodiments, a delay element can be included on the reset signal assertion to prevent a race condition between pixel integration and pixel reset. The reset signal provides a mechanism by which all pixels 106 in the event-driven image sensor 104 can be reset whenever there is global motion. This can prevent premature saturation of the pixel 106, which improves the dynamic range of the event-driven image sensor 104.

[0038] The event-driven image sensor 104 may also include a pixel excitation detection circuit. As described above, a high-frequency event may cause the pixel 106 to excite. The high-frequency event may be caused by observable motion in the field of view of the event-driven image sensor 104. In other words, the high-frequency event may be meaningful information for the event-driven camera 102 to detect. When a high-frequency event is detected, the pixel 106 integrates quickly until it reaches an event threshold. When the pixel integration reaches the event threshold, the pixel 106 may output a pixel excitation signal. When the pixel 106 excites, this should be recorded. Any global motion suppression that is in progress may be interrupted.

[0039] The pixel fire detection circuitry may detect when the pixel fire signal of a given pixel 106 reaches an event threshold. The pixel fire detection circuitry may reset the pixel integration output of the given pixel 106, which disengages global motion suppression. In other words, once one of the plurality of pixels 106 no longer outputs a pixel integration output that is equal to or greater than the event indication value, the global motion suppression circuitry 110 may stop asserting the global activation signal. When the global activation signal is de-asserted (e.g., turned off), then global motion is not detected and the pixel data may be read out and / or processed.

[0040] In one example, the pixel excitation detection circuit may include a pixel excitation delay component having a second time constant that is less than a first time constant of a pixel integration delay component. As described above, the pixel integration delay component may have a large time constant to avoid prematurely asserting global motion detection. However, in order to avoid missing meaningful events, pixel excitation events may be detected quickly compared to global motion detection. In other words, high-frequency motion of the triggering event may be detected quickly to avoid missing the event. Therefore, the time constant of the pixel excitation delay component may be very small when compared to the first time constant of the pixel integration delay component. In one example, the pixel excitation delay component may be implemented as a capacitor coupled to the pixel excitation signal of pixel 106. Figure 3 An example of this approach is described in .

[0041] Some additional aspects of global motion suppression in event-driven cameras 102 are described herein. Figure 3 and Figure 4 Examples of circuits for detecting and suppressing global motion are described. Figure 5 One example of a global pixel reset signal asserted in response to detecting global motion is described.

[0042] Figure 2 is an example flow chart illustrating a method 200 for global motion suppression in an event-driven camera 102. The event-driven camera 102 may include an event-driven image sensor 104 having a plurality of pixels 106. The pixels 106 may each provide a pixel-integrated output.

[0043] The event-driven image sensor 104 may detect 202 a global motion of the event-driven camera 102 based on the detection of an event by a plurality of pixels 106 of the event-driven image sensor 104. For example, the event-driven image sensor 104 may include a global motion detection circuit 108 to detect when a predetermined percentage of pixel integrated outputs of the plurality of pixels 106 reaches an event indication value. In some implementations, the global motion detection circuit 108 may detect 202 a global motion when the pixel integrated outputs of all pixels 106 reach the event indication value.

[0044] In some examples, the global motion detection circuit 108 may also include a pixel integration delay component having a first time constant for each of the plurality of pixels 106. The first time constant of the pixel integration delay component may be a large time constant. When the pixel integration output reaches the event indication value, the pixel integration delay component may delay. The delay may enable the event-driven image sensor 104 to detect low-frequency global motion (e.g., panning and / or shake).

[0045] The event-driven image sensor 104 can suppress global motion in response to detecting global motion. For example, the event-driven image sensor 104 can include a global motion suppression circuit 110 to generate a global activation signal when the pixel integration output of each of the plurality of pixels 106 reaches an event indication value. The global activation signal can prevent the storage and processing of data contained in the plurality of pixels 106. The global motion suppression circuit 110 can also reset the plurality of pixels 106. For example, when global motion is detected, the global motion suppression circuit 110 can send a reset signal to the plurality of pixels 106.

[0046] Figure 3 is an example of a four-pixel module 311 for global motion suppression in an event-driven camera. The four-pixel module 311 is combined with Figure 1 An example of a global motion detection circuit and a global motion suppression circuit is described.

[0047] In this example, four pixels 306a-d are assembled into an array to form a four-pixel module 311. Each pixel 306 outputs a pixel integral output signal 312 that is asserted when the pixel 306 integrates. As described above, the pixel integral is a measure of the amount of light sensed by the pixel 306 over a period of time. Therefore, the pixel integral can be a measure of the stored charge accumulated within the pixel 306 during a specified time interval. The pixel integral output signals 312a-d can be referred to as pixel activation signals. In some examples, the pixel integral output signals 312a-d can include a voltage corresponding to the pixel integral value, wherein the voltage increases as the pixel integral value increases.

[0048] Pixels 306a-d also output pixel fire signals 318. Pixel 306 may output pixel fire signals when the pixel integration reaches an event threshold. In other words, pixel fire signals 318 may be asserted when a pixel well threshold (referred to as an event threshold) is reached.

[0049] Pixels 306a-d may receive a reset signal 330. Upon receiving the reset signal 330, pixels 306a-d may be reset. For example, the charge accumulated within the electron well may be discharged.

[0050] In the four-pixel module 311, the pixel integrated output signal 312 from each pixel 306 controls the gate input of a negative channel metal oxide (NMOS) transistor 314. Four NMOS transistors 314a-d are connected in series to form a NAND (non-AND) gate. In other words, the global motion detection circuit may include a NAND gate. The input of the NAND gate may be coupled to the pixel integrated outputs 312a-d of the plurality of pixels 306a-d.

[0051] When NMOS transistors 314a-d are not turned on, positive channel metal oxide (PMOS) transistors 326a-d can be used to pull up the line (i.e., four pixel activation signals 328). Therefore, the pixel integrated output signals 312a-d can be coupled to the gates of the parallel connected PMOS transistors 326a-d. In one example, the full circuit can constitute a complementary MOS (CMOS) NAND gate.

[0052] The inverted output from the gate can be a four-pixel activation signal 328. When the four-pixel activation signal 328 is asserted (e.g., turned on), this indicates that all inputs to the gates of the NMOS transistors 314a-d are turned on. In other words, when the four-pixel activation signal 328 is asserted, each of the event-driven pixels 306a-d has been activated. If the four-pixel activation signal 328 is off, then this means that (one or more) pixels 306 have not sensed an event. When all inputs to the NAND gate reach the event indication value, the inverted output of the NAND gate is turned on. When the inverted output of the NAND gate is turned on, the global motion suppression circuit generates a four-pixel activation signal 328.

[0053] In one example, NMOS transistors 314a-d are pull-down transistors connected to the pixel integrated output signals 312a-d of the four pixels 306a-d. The gates of NMOS transistors 314a-d are controlled by capacitors 316a-d. When the voltage across input capacitor 316 exceeds the threshold voltage of the corresponding NMOS transistor 314, the gate of NMOS transistor 314 is turned on.

[0054] Capacitors 316a-d may be trickle charge capacitors with large time constants. Capacitors 316a-d may be used to detect low frequency global motion (e.g., panning). These capacitors 316a-d are charged whenever their corresponding pixels 306a-d are integrated. For example, capacitors 316a-d may be charged based on a voltage associated with pixel integrated output signals 312a-d.

[0055] In some examples, the output four-pixel activation signal 328 of the four-pixel array may span a large distance and therefore may have higher parasitic effects. PMOS transistors 326a-d may be P-type pull-up transistors that ensure that the output state of the four-pixel activation signal 328 is maintained and is not susceptible to leakage caused by parasitic effects.

[0056] High frequency events can cause pixel 306 to excite. This occurs when pixel 306 integrates quickly until it reaches an event threshold. This is called pixel excitation. When the pixel 306 excites, this may be meaningful and should be recorded. Any global motion suppression that is in progress can be interrupted. In one example, this can be achieved by charging capacitors 320a-d coupled to pixel excitation signals 318a-d. When the voltage at the gate of NMOS transistors 322a-d reaches the threshold of NMOS transistors 322a-d, NMOS transistors 322a-d are turned on. This results in a path to ground to discharge the corresponding capacitors 316a-d on the pixel integration outputs 312a-d, thereby removing any charge accumulation caused by previous global motion events. Compared to global motion events, pixel excitation events can be detected quickly. Therefore, the time constant of pixel excitation capacitors 320a-d can be very small when compared to the time constant of pixel integration capacitors 316a-d.

[0057] When all four pixels 306a-d have detected global motion (i.e., when all four NMOS transistors 314a-d are turned on), this causes the 4-pixel global motion detection logic to turn on. In this case, the output signal capacitor 329 can be charged and the four-pixel activation signal 328 is asserted. In the case of a 4-pixel module, the four-pixel activation signal 328 is combined with Figure 1 An example of a global activation signal is described. Four-pixel activation signal 328 may also be referred to as a four-pixel activation output.

[0058] In some examples, the 4-pixel module may also include a reset signal 330. The value of the reset signal 330 may be stored in buffers 328a-b. The reset signal 330 may be coupled to the reset input of pixels 306a-d. When the reset signal 330 is asserted (e.g., turned on), the pixels 306a-d may be reset.

[0059] Reset signal 330 may also be coupled to the gates of NMOS transistors 324a-d. When the voltage at the gates of NMOS transistors 324a-d reaches the threshold of NMOS transistors 324a-d, NMOS transistors 324a-d turn on. This results in a path to ground to discharge the corresponding capacitors 316a-d on pixel integrated outputs 312a-d, thereby removing any charge accumulation due to the previous global motion event that reset the global motion detection.

[0060] It should be noted that even Figure 3A grouping of four pixels 306a-d is shown, and different group sizes may be selected according to design needs. For example, a pixel module may include 2 pixels, 3 pixels, 5 pixels, etc. This may be referred to as an n-pixel grouping, where "n" is a variable number of pixels 306.

[0061] Figure 4 4 is an example of a 16-pixel array module 432 for global motion suppression in an event-driven camera. As described above, n-pixel grouping can be used to construct macro-groupings of pixels. In this example, four four-pixel array modules 411a-d are grouped together to form a 16-pixel array module 432. Figure 4 The four-pixel array modules 411a-d can be implemented as Figure 3 The function of the 16-pixel array module 432 may be similar to that of the four-pixel array module 311a-d described in Figure 3 The four-pixel array module 311 described in .

[0062] In this example, each four-pixel array module 411 may include four pixels and circuitry to output a four-pixel activation signal 428. In this example, the four-pixel array modules 411a-d are assembled into an array to form a 16-pixel array. Each four-pixel array module 411 outputs a four-pixel activation signal 428 that is asserted when each pixel is integrated.

[0063] In this example, four pixel activation signals 428a-d from each four pixel array module 411 control the gate inputs of NMOS transistors 414a-d. Four NMOS transistors 414a-d are connected in series to form a NAND gate. PMOS transistors 426a-d can be used to pull up the line (i.e., 16 pixel activation signals 434) when NMOS transistors 414a-d are not turned on. Therefore, four pixel activation signals 428a-d can be coupled to the gates of PMOS transistors 426a-d connected in parallel.

[0064] The inverted output from the gates of the PMOS transistors 426a-d may be a 16-pixel activation signal 434. When the 16-pixel activation signal 434 is asserted (e.g., turned on), this indicates that all inputs to the gates of the NMOS transistors 414a-d are turned on. In other words, when the 16-pixel activation signal 434 is asserted, each of the 16 event-driven pixels within the 16-pixel array module 432 has been activated. If the 16-pixel activation signal 434 is off, this means that the pixel(s) have not sensed an event.

[0065] In one example, NMOS transistors 414a-d are pull-down transistors connected to the pixel integral output signals 412a-d of the four pixels 406a-d. The gates of NMOS transistors 414a-d are controlled by capacitors 416a-d. When the voltage across input capacitor 416 exceeds the threshold voltage of the corresponding NMOS transistor 414, the gate of NMOS transistor 414 is turned on. Capacitors 416a-d can be trickle charge capacitors with large time constants. Capacitors 416a-d can be used to detect low-frequency global motion (e.g., panning). Whenever the four-pixel activation signal 428 is asserted, these capacitors 416a-d are charged.

[0066] When each of the four pixel array modules 411a-d has detected global motion (i.e., when all four NMOS transistors 414a-d are on), this causes the 16-pixel global motion detection logic to turn on. In this case, the output signal capacitor 429 can be charged and the 16-pixel activation signal 434 is asserted.

[0067] In some examples, a 16-pixel array module 432 can be used to build a 64-pixel array module. A 64-pixel array module can be used to build a 256-pixel array module, etc. At each stage, when the N-pixel activation output is asserted, it means that all pixels within the module have sensed an event.

[0068] The output of a pixel in an event-driven camera will fire when activated. Using the pixel array modules described herein, each module can detect when all pixels within the module are activated. Using this hierarchical arrangement, activation at each module is propagated to larger modules. Thus, activation of the entire pixel array can be detected. The signal asserted when the entire pixel array is activated is the global activation signal.

[0069] Figure 5 5 is an example of a global activation signal 542 and a reset signal 530 of the pixel array 540. The pixel array 540 may include a combination of Figure 3 and Figure 4 When all pixels in the pixel array 540 detect an event, the pixel array 540 may output a global activation signal 542 .

[0070] In one example, the value of the global activation signal 542 may be stored in a buffer 544. The global activation signal 542 may be provided to an AND gate 552. An inverter 556 at the input of the AND gate 552 may invert the global activation signal 542. The AND gate 552 may also receive a read / process signal 550, which instructs the event-driven camera to read out and process pixel data.

[0071] When the global activation signal 542 is OFF (i.e., no global motion is detected), the AND gate 552 outputs a read / process signal 554 that matches the state of the input read / process signal 550. When the global activation signal 542 is ON (i.e., global motion is detected), the AND gate 552 outputs the read / process signal 554 as OFF even if the input read / process signal 550 is ON.

[0072] The global activation signal 542 may be used to activate the reset signal 530. In one example, the global activation signal 542 may be provided to a buffer 546 that stores the state of the global activation signal 542. The reset signal 530 may be fed back to all pixels in the pixel array 540. When the global activation signal 542 is asserted (e.g., turned on), the reset signal 530 may be asserted (e.g., turned on). The reset signal 530 may cause the pixel to clear its pixel well. This provides a mechanism by which all pixels in the pixel array 540 may be reset whenever there is global motion. This may prevent premature saturation of the pixel well, which may improve the dynamic range of the event-driven image sensor.

[0073] In some examples, reset signal 556 can be provided by other sources. For example, reset signal 556 can be asserted by other components of an event-driven image sensor or event-driven camera.

[0074] In some embodiments, a delay component 548 can be included on reset signal assertion. The delay component 548 can delay when the reset signal 530 is asserted. In other words, the delay component 548 can delay when the reset signal 530 is sent to the pixel array 540. This can prevent competition between pixel integration and pixel reset.

[0075] The reset can be maintained as long as there is global motion. When a non-global motion event is detected (e.g., when a pixel excitation occurs), the pixel(s) will de-assert the pixel activation signal (e.g., pixel integrated output signal 312), which propagates through the hierarchy of gates to de-assert the global activation signal 542. This allows further pixel reading / processing tasks. The de-assertion of the global activation signal 542 also de-asserts the reset signal 530, thereby allowing the pixel to accumulate charge.

Claims

1. A method comprising: The global motion of the event-driven camera is detected based on the detection of events by multiple pixels of the event-driven image sensor by the following operations: detecting pixel firing signals when a given signal of the plurality of pixels reaches an event threshold indicating an event within the field of view of the event-driven camera, and In response to detecting a pixel firing signal, reading out event pixel data for the given pixel; as well as The global motion is suppressed by the event-driven image sensor circuit by: In response to detecting global motion, generating a global activation signal, and In response to the global activation signal, pixel data of a plurality of pixels generated during the global motion is prevented from being processed.

2. The method according to claim 1, wherein: Suppressing the global motion by the event-driven image sensor circuit includes preventing storage of pixel data for the plurality of pixels in response to a global activation signal.

3. The method according to claim 2, wherein: The global activation signal is used as a selector for event-driven pixel array readout and processing within the image sensor.

4. The method according to claim 1, wherein: Suppressing the global motion by the event-driven image sensor circuit includes resetting the plurality of pixels in response to detecting the global motion.

5. The method according to claim 1, wherein: The global motion includes event-driven camera panning or shaking.

6. The method according to claim 1, wherein: Global motion is detected when a predetermined percentage of pixels detect an event.

7. The method according to claim 1, further comprising: detecting high frequency events while suppressing the global motion; as well as Interrupt global motion suppression.

8. An event-driven image sensor, comprising: A global motion detection circuit for detecting global motion of the event-driven camera based on a plurality of pixels of the event-driven image sensor detecting an event; as well as A global motion suppression circuit for suppressing the global motion in response to detecting the global motion, wherein in order to suppress the global motion in response to detecting the global motion, the global motion suppression circuit is configured to: When global motion is detected, a global activation signal is generated, and preventing storage and processing of a plurality of pixel data of the plurality of pixels; A readout operation of a pixel among a plurality of pixels of the event-driven image sensor is event-triggered based on a pixel integrated output indication event of the pixel among the plurality of pixels.

9. The event-driven image sensor according to claim 8, wherein: The global motion detection circuit includes circuitry for detecting when the pixel integrated outputs of all pixels in the event-driven image sensor reach an event indication value.

10. The event-driven image sensor according to claim 9, wherein: The global motion detection circuit also includes a pixel integration delay component having a first time constant for each pixel of the plurality of pixels to delay when a pixel integration output reaches an event indication value.

11. The event-driven image sensor according to claim 10, wherein: The event-driven image sensor further includes a pixel excitation detection circuit, which is used to: Detect when the pixel firing signal for a given pixel reaches an event threshold, and Resets the pixel integration output for a given pixel, thereby interrupting global motion suppression, Wherein, the pixel excitation detection circuit includes a pixel excitation delay component with a second time constant, and the second time constant is smaller than a first time constant of the pixel integration delay component.

12. The event-driven image sensor according to claim 9, wherein: The global motion suppression circuit includes circuitry for: When the pixel integrated outputs of a predetermined percentage of pixels reach an event indication value, a global activation signal is generated, and the plurality of pixels are reset.

13. An event-driven image sensor, comprising: a plurality of pixels, each pixel comprising a pixel integral output; a global motion detection circuit for detecting when a pixel integrated output of each of the plurality of pixels reaches an event indication value; as well as A global motion suppression circuit is used to generate a global activation signal when the pixel integration output of each of the multiple pixels reaches an event indication value, wherein the global activation signal prevents storage and processing of data contained in the multiple pixels, and is used to reset the multiple pixels.

14. The event-driven image sensor according to claim 13, wherein: The global motion detection circuit includes a NAND gate, wherein an input of the NAND gate is coupled to pixel integration outputs of the plurality of pixels.

15. The event-driven image sensor according to claim 14, wherein: When all inputs to the NAND gates reach event indication values, the inverting outputs of the NAND gates are on, and wherein the global motion suppression circuit generates a global activation signal when the inverting outputs of the NAND gates are on.

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