Method for reducing pixel size of event-driven sensor

Abstract

In one embodiment, the event sensor includes: a plurality of pixels; an external readout line shared among the plurality of pixels; and an external processing circuit. Each pixel is configured to output pixel data indicative of the intensity of incident light. The external processing circuit is configured to output a stream of pixel events. Each corresponding pixel event is generated when a comparator of the external processing circuit obtains a sample of pixel data exceeding a threshold from a particular pixel via the external readout line.

Description

Technical Field

[0001] The present disclosure generally relates to the field of image processing, and more particularly to techniques for reducing the pixel size of event-driven sensors. Background Art

[0002] Event cameras may include image sensors known as dynamic vision sensors ("DVS"), silicon retinas, event-based sensors, or frameless sensors. Thus, event cameras generate (and transmit) data regarding changes in light intensity at each pixel sensor, as opposed to frame-based cameras that output data regarding the absolute light intensity at each pixel. In other words, when the illumination level of a scene set within the field of view remains stable, frame-based cameras will continue to generate (and transmit) data regarding the absolute light intensity at each pixel, while event cameras will suppress the generation or transmission of data until a change in the illumination level is detected.

[0003] Existing event sensors may include pixels that locally process data regarding changes in light intensity. Providing such pixel-level processing of data within each pixel of an event sensor can limit the use of the event sensor in some imaging applications. For example, pixel-level processing of the data involves various intra-pixel components, such as comparators and controllers located within each pixel that increase the overall physical size ("pixel size") of each pixel. The increase in pixel size can limit the resolution of the image data output by the event sensor. Thus, reducing the pixel size of event sensor pixels can facilitate the expanded use of event sensors in some imaging applications. Summary of the Invention

[0004] Various embodiments disclosed herein relate to techniques for reducing the pixel size of event-driven sensors. In one embodiment, an event sensor includes: a plurality of pixels; an external readout line shared among the plurality of pixels; and an external processing circuit. Each pixel is configured to output pixel data indicative of incident light intensity. The external processing circuit is configured to output a stream of pixel events. Each corresponding pixel event is generated when a comparator of the external processing circuit obtains a sample of pixel data exceeding a threshold from a particular pixel via the external readout line. In one embodiment, the external processing circuit may be shared among a subset of pixels, where multiple external processing units are used to serve the entire pixel array. In one embodiment, the external processing circuit may be located on a second layer or wafer of a stacked sensor, thereby occupying the area beneath the pixels.

[0005] In another specific implementation, a pixel includes a photodetector circuit, an output node, and a readout switch inserted between the photodetector circuit and the output node. The photodetector circuit is configured to generate pixel data indicating the intensity of incident light at a sample node. The output node is coupled to an external processing circuit through an external readout line shared among a plurality of pixels. The external processing circuit is configured to output a stream of pixel events, where each corresponding pixel event is generated when a comparator in the external processing circuit obtains a sample of pixel data exceeding a threshold from a specific pixel through the external readout line. The readout switch is configured to isolate the sample node from the output node until a selection signal is received from a controller in the external processing circuit.

[0006] In another specific implementation, an event sensor includes: an external readout line shared among a plurality of pixels; and an external processing circuit. Each pixel is configured to output pixel data indicating the intensity of incident light. The external processing circuit is configured to output a stream of pixel events. Each corresponding pixel event is generated when a comparator in the external processing circuit obtains a sample of pixel data exceeding a threshold from a specific pixel through the external readout line. In one specific implementation, differential operation is implemented in a column circuit outside the pixel array through digital subtraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Therefore, the present disclosure can be understood by those of ordinary skill in the art, and for a more detailed description, reference can be made to aspects of some exemplary specific implementations, some of which are shown in the drawings.

[0008] Figure 1 A block diagram of an event sensor having a plurality of pixels each providing pixel-level processing of pixel data within each pixel is shown.

[0009] Figure 2 A block diagram of an event sensor having an exemplary pixel configured to output pixel data to an external processing circuit through an external readout line shared among a plurality of pixels is shown.

[0010] Figure 3 is Figure 2 An example of a timing diagram of the operation of the event sensor shown in

[0011] Figure 4 is Figure 2 Another example of a timing diagram of the operation of the event sensor shown in

[0012] Figures 5 to 8 Circuit diagrams of other exemplary pixels each configured to output pixel data to an external processing circuit through an external readout line shared among a plurality of pixels are shown.

[0013] In accordance with common practice, the various feature portions shown in the drawings may not be drawn to scale. Accordingly, for clarity, the dimensions of the various feature portions may be arbitrarily enlarged or reduced. Additionally, some of the drawings may not depict all of the components of a given system, method, or apparatus. Finally, like reference numerals may be used throughout the specification and drawings to denote like feature portions. Detailed Description

[0014] Numerous details are described in order to provide a thorough understanding of the example embodiments shown in the drawings. However, the drawings merely illustrate some example aspects of the present disclosure and should not be considered limiting. Those of ordinary skill in the art will appreciate that other effective aspects or variations do not include all of the specific details described herein. Additionally, well-known systems, methods, components, apparatuses, and circuits have not been described in detail so as not to obscure more relevant aspects of the example embodiments described herein.

[0015] A functional block diagram of an exemplary event sensor 100 is shown by Figure 1 FIG. The event sensor 100 includes a plurality of pixels 105 coupled to an external processing circuit 180 configured to output a stream of pixel events. In Figure 1 FIG., the plurality of pixels 105 are arranged in a matrix 107 of rows and columns, and thus, each pixel of the plurality of pixels 105 is associated with a row value and a column value. Each pixel of the plurality of pixels 105 includes a photodetector circuit 110, a differencing circuit 140, a comparator 160, and a controller 170.

[0016] The photodetector circuit 110 is configured to generate a signal indicative of the intensity of light (“incident illumination”) incident on the corresponding pixel 105. To this end, the photodetector circuit 110 includes a photodiode 112 configured to generate a photocurrent proportional to the incident light intensity. The photocurrent generated by the photodiode 112 flows into a log amplifier 120 formed by transistors 121, 123, 125, and 127. The log amplifier 120 is configured to convert the photocurrent into a voltage at node A, the value of which is the logarithm of the photocurrent value. The voltage at node A is then amplified by a buffer amplifier 130 formed by transistors 131 and 133 before being applied to the input side of the differencing circuit 140.

[0017] In pixel 105, differential circuit 140 consists of an alternating current (“AC”) coupling capacitor 145 and a switched capacitor amplifier 150. Differential circuit 140 is configured to remove a direct current (“DC”) voltage component from the voltage at node A to generate pixel data at sampling node B. By removing the DC voltage component from the voltage at node A, the pixel data at sampling node B provides a differential value of the incident light intensity detected by photodiode 112. The gain provided by amplifier 151 corresponds to the ratio defined by the respective capacitance values of AC coupling capacitor 145 and capacitor 153. When a reset signal is received from controller 170, reset switch 155 is activated (i.e., transitions from an open state to a closed state). By activating reset switch 155, the operating point of amplifier 151 is reset to a reference voltage associated with the threshold of comparator 160.

[0018] Comparator 160 is configured to provide pixel-level processing of the pixel data received from sample node B. To this end, when the pixel data received from sample node B indicates a change in the incident light intensity detected by photodiode 112 that exceeds a threshold, comparator 160 outputs an electrical response (e.g., a voltage). Optionally, when the pixel data received from sample node B indicates that photodiode 112 has not detected a change in the incident light intensity that exceeds a threshold, comparator 160 suppresses the output of the electrical response. In a particular implementation, comparator 160 is implemented using multiple comparators including a first comparator configured to output an electrical response indicating a positive event (e.g., an event with a positive polarity) and a second comparator configured to output an electrical response indicating a negative event (e.g., an event with a negative polarity). In a particular implementation, the first comparator outputs an electrical response when the pixel data received from sample node B indicates a change in the incident light intensity detected by photodiode 112 that exceeds a positive threshold. In a particular implementation, the second comparator outputs an electrical response when the pixel data received from sample node B indicates a change in the incident light intensity detected by photodiode 112 that exceeds a negative threshold. Controller 170 is configured to cooperate with other components of event sensor 100 (e.g., controllers within other pixels) to transmit an event signal to event compiler 185 of external processing circuit 180 for each electrical response output by comparator 160. In a particular implementation, reset switch 155 receives a reset signal from controller 170 whenever comparator 160 obtains pixel data at sampling node B that exceeds a threshold.

[0019] The event compiler 185 receives event signals from each of a plurality of pixels each representing a change in incident light intensity that exceeds a threshold. In response to receiving an event signal from a particular pixel among the plurality of pixels 105, the event compiler 185 generates a pixel event. Additionally, the event compiler 185 populates the pixel event with information indicating an electrical response included in the event signal (e.g., the value and / or polarity of the electrical response). In one specific implementation, the event compiler 185 also populates the pixel event with one or more of the following: timestamp information corresponding to the time point at which the pixel event is generated and an address identifier corresponding to the particular pixel that sent the event signal triggering the pixel event. Then, a stream of pixel events including each pixel event generated by the event compiler 185 can be transmitted to an image or video processing circuitry (not shown) associated with the event camera 100 for further processing.

[0020] By way of example, the stream of pixel events generated by the event compiler 185 can be accumulated or otherwise combined to produce image data. In some specific implementations, the stream of pixel events is combined to provide an intensity reconstruction image. In this specific implementation, an intensity reconstruction image generator (not shown) can accumulate pixel events over time to reconstruct / estimate absolute intensity values. As additional events are accumulated, the intensity reconstruction image generator changes the corresponding values in the reconstructed image. In this way, it generates and maintains an updated image of values for all pixels of the image even if only some pixels may have recently received events.

[0021] In various specific implementations, reducing the pixel size of event sensor pixels is achieved by processing pixel data output by a plurality of pixels using external processing circuitry shared among the plurality of pixels. In other words, in various specific implementations, reducing the pixel size is achieved by providing external processing of pixel data generated by a plurality of pixels rather than providing pixel-level processing of the pixel data. Figure 2 and Figures 5 to 8 The circuit diagrams depicted in provide various specific implementations of pixels of an event sensor that facilitate such external processing of pixel data by external processing circuitry shared among a plurality of pixels.

[0022] By way of example, Figure 2 a block diagram depicting a plurality of pixel sensors 205 in an event sensor each transmitting pixel data representing incident light intensity to external processing circuitry 280 is shown. In Figure 2 the example, each of the plurality of pixels 205 transmits pixel data to the external processing circuitry 280 via an external readout line 270 shared among the plurality of pixels 205. In Figure 1Similar to pixel 105, pixel 205 further includes a photodetector circuit 110 configured to generate a voltage proportional to the incident light intensity detected by photodiode 112 at node A. The AC coupling capacitor 210 removes the DC voltage component from the voltage at node A to generate pixel data at sample node B that provides a differential value of the incident light intensity. Different from pixel 105, the pixel data generated by pixel 205 at sample node B is externally processed by comparator 281 of the external processing circuit 280.

[0023] In a specific implementation, comparator 281 is implemented using a plurality of comparators including a first comparator configured to output an electrical response indicating a positive event (e.g., an event with a positive polarity) and a second comparator configured to output an electrical response indicating a negative event (e.g., an event with a negative polarity). In a specific implementation, when the pixel data received from sample node B indicates a change in the incident light intensity detected by photodiode 112 that exceeds a positive threshold, the first comparator outputs an electrical response. In a specific implementation, when the pixel data received from sample node B indicates a change in the incident light intensity detected by photodiode 112 that exceeds a negative threshold, the second comparator outputs an electrical response.

[0024] To avoid conflicts between samples of comparator 281 for pixel data transmission from each of the multiple pixels 205 through the external readout line 270, the external processing circuit 280 includes a controller 283. The controller 283 is configured to arbitrate access to the external readout line 270 among the multiple pixels 205 by selectively activating the readout switch 250 located within each pixel 205 using a selection signal. For example, the controller 283 can transmit a first selection signal to the readout switch located within Pixel-1 at a first moment, and can transmit a second selection signal to the readout switch located within Pixel-2 at a second moment after the first moment. In this example, the readout switch located within Pixel-1 can transfer a sample of the pixel data from Pixel-1 to the external readout line 270 at the first moment, while the readout switch located within Pixel-2 can transfer a sample of the pixel data from Pixel-2 to the external readout line 270 at the second moment. In a specific implementation, each of the multiple pixels 205 receives selection signals of different phases from the controller 283.

[0025] In pixel 205, a readout switch 250 is inserted between a sample node B and an output node 260. From this position, the readout switch 250 can isolate the sample node B from the output node 260 until a select signal is received from the controller 283. When the select signal is received from the controller 283, the readout switch 250 is activated (i.e., transitions from a non-conductive state to a conductive state). In a specific implementation, the readout switch 250 is implemented as an n-channel metal oxide semiconductor (MOS) transistor. By activating the readout switch 250, pixel data on the sample node B is transferred to the output node 260 through the transistor 243 of the second buffer amplifier 240 formed by the transistors 241 and 243.

[0026] Go to Figure 3 The timing diagram of Figure 3 more specifically explains the operations performed by the event sensor 200 in generating pixel events according to a specific implementation. At time T1, the readout switch 250 and the select switch 220 are activated in response to receiving a select signal from the controller 283, thereby transferring a sample of the pixel data to the output node 260. The select switch 220 enables one pixel among the pixels in a group of 4 pixels to be reset. The sample of the pixel data transferred to the output node 260 at time T1 is applied to the input side of the comparator 281. Since the sample of the pixel data obtained by the comparator 281 at time T1 exceeds the threshold, the comparator 281 outputs an electrical response to the input side of the controller 283. When the electrical response is received from the comparator 281 at time T1, the controller 283 sends a reset signal to the reset switch 230. In response to receiving the reset signal from the controller 283, the reset switch 230 is activated, thereby resetting the voltage of the pixel data at the sample node B to the reference voltage V ref .

[0027] In addition to sending a reset signal to the reset switch 230, the controller 283 also forwards the electrical response received from the comparator 281 at time T1 together with the information characterizing the electrical response to the event compiler 285. In various specific implementations, the information characterizing the electrical response may include one or more of the following: the value of the electrical response, the polarity of the electrical response, timestamp information corresponding to the time point of generating the event response, or an address identifier corresponding to the corresponding pixel that triggers the generation of the pixel event. When the event response and the characterizing information are received from the comparator 281 at time T1, the event compiler 285 generates a pixel event.

[0028] Unlike at time T1, the value of the pixel data at sample node B at time T3 does not exceed the threshold. Instead, the value of the pixel data at sample node B exceeds the threshold after time T3. Thus, the sample of the pixel data obtained by comparator 281 at time T3 does not exceed the threshold, and thus comparator 281 does not generate an electrical response at time T3. Since controller 283 does not receive an electrical response from comparator 281 at time T3, controller 283 neither sends a reset signal to reset switch 230 nor forwards an electrical response to event compiler 285 at time T3. Accordingly, the voltage of the pixel data at sample node B is not reset to the reference voltage V ref , and the event compiler does not generate a pixel event at time T3.

[0029] Similar to time T1 or time T2, the value of the pixel data at sample node B at time T5 exceeds the threshold. Unlike time T1 or time T2, the value of the pixel data at sample node B at time T5 does not exceed the upper threshold V th . Instead, the value of the pixel data at sample node B at time T5 is less than the lower threshold -V th . In one particular implementation, the difference between the upper threshold V th and the reference voltage V ref is equal to or substantially equal to the difference between the lower threshold -V th and the reference voltage V ref . The pixel event generated by event compiler 285 at time T1 or time T2 may be referred to as a "positive" pixel event. In one particular implementation, a positive pixel event is a pixel event with a positive polarity having a net increase in magnitude representing the incident light intensity that exceeds the magnitude defined by the upper threshold V th . The pixel event generated by event compiler 285 at time T5 may be referred to as a "negative" pixel event. In one particular implementation, a negative pixel event is a pixel event with a negative polarity having a net decrease in magnitude representing the incident light intensity that exceeds the magnitude defined by the lower threshold -V th .

[0030] Figure 4 is a timing diagram of the operations performed by event sensor 200 in generating pixel events according to one particular implementation. In one particular implementation, pixel 205 may be implemented without selection switch 220. Optionally, the pixel may be implemented by activating selection switch 220 at the same time in all 4 pixels. Figure 3 and Figure 4 The comparison between shows that reset switch 230 facilitates the implementation of a global reset option, where the voltage of the pixel data at sample node B is reset to the reference voltage V ref. In a specific implementation, the controller 283 implements a global reset option by starting a delay timer when sending a selection signal to the readout switch 250 and the selection switch 220 and sending a reset signal to the reset switch 230 once the delay time has expired.

[0031] Figure 5 The circuit diagram of another exemplary pixel 505 configured to output pixel data to the external processing circuit 280 via the external readout line 270 is shown. Similar to Figure 2 the pixel 205, the pixel 505 includes a photodetector circuit 110 that outputs a voltage indicative of the intensity of incident light detected by the photodiode 112. The pixel 505 also includes a differential circuit 530 that couples the output of the photodetector circuit 110 to the readout switch 550, which is configured to isolate the sample node 540 from the output node 560 until a selection signal is received from the controller 283. As Figure 5 shown, the differential circuit 530 includes an AC coupling capacitor 510 and a switched-capacitor amplifier 520. Similar to Figure 1 the switched-capacitor amplifier 150, the gain provided by the amplifier 521 corresponds to the ratio defined by the respective capacitance values of the AC coupling capacitor 510 and the capacitor 523. Different from the switched-capacitor amplifier 150, the operating point of the amplifier 521 in the switched-capacitor amplifier 520 is reset to a reference voltage associated with the threshold of the comparator 281 by activating both the reset switch 525 and the selection switch 527. The reset switch 525 and the selection switch 527 are activated (i.e., transition from the open state to the closed state) when receiving a reset signal and a selection signal from the controller 283, respectively. In a specific implementation, the switched-capacitor amplifier 520 improves the signal-to-noise ratio associated with the pixel data generated at the sampling node 540.

[0032] Figure 6 The circuit diagram of another exemplary pixel 605 configured to output pixel data to the external processing circuit 280 via the external readout line 270 is shown. In a specific implementation, the external readout line 270 is shared among multiple pixels in the column forming the pixel array including the pixel 605. The pixel 605 includes an AC coupling capacitor 610 inserted between the output of the photodetector circuit 110 and the input side of a buffer amplifier 650 formed by transistors 651 and 653. The pixel 605 also includes a readout switch 660 configured to isolate the sample node 640 from the output node 660 until a selection signal is received from the controller 283. The reset switch 630 in the pixel 605 is configured to reset the voltage of the pixel data at the sample node 640 to a reference voltage associated with the threshold of the comparator 281 in response to receiving a reset signal from the controller 283.

[0033] In pixel 605, the gray-scale switch 620 is coupled in parallel with the AC coupling capacitor 610. When the gray-scale switch 620 is in the open state, the AC coupling capacitor 610 removes the DC voltage component from the voltage at node A to generate pixel data providing a differential value of the incident light intensity detected by the photodiode 112 at the sample node 640. In response to receiving a gray-scale signal from the controller 283, the gray-scale switch 620 transitions from the open state to the closed state, thereby bypassing the AC coupling capacitor 610. When the gray-scale switch 620 is in the closed state, the pixel data at the sample node 640 provides the absolute value of the incident light intensity detected by the photodiode 112. In a specific implementation, when the gray-scale switch 620 is in the closed state, a ramp voltage signal is compared with a sample of the pixel data obtained from the pixel 605 at the input side of the comparator 281 to generate gray-scale image data at the output side of the comparator 281.

[0034] Figure 7 A circuit diagram of another exemplary pixel 705 configured to output pixel data to an external processing circuit 280 via an external readout line 270 is shown. In a specific implementation, the external readout line 270 is shared among a plurality of pixels in a column forming a pixel array including the pixel 705. The pixel 705 includes a differential circuit 730 that couples the output of the photodetector circuit 110 to a readout switch 750, which is configured to isolate the sample node 740 from the output node 760 until a selection signal is received from the controller 283. As Figure 7 shown, the differential circuit 730 includes an AC coupling capacitor 710 and a switched-capacitor amplifier 720. Similar to Figure 1 the switched-capacitor amplifier 150, the gain provided by the amplifier 721 in the switched-capacitor amplifier 720 corresponds to a ratio defined by the respective capacitance values of the AC coupling capacitor 710 and the capacitor 723. Also similar to the switched-capacitor amplifier 150, the operating point of the amplifier 721 is reset to a reference voltage associated with the threshold of the comparator 281 by activating the reset switch 725. When a reset signal is received from the controller 283, the reset switch 725 is activated (i.e., transitions from the open state to the closed state). In a specific implementation, a ramp voltage signal is compared with a sample of the pixel data obtained from the pixel 705 at the input side of the comparator 281 to obtain information defining the magnitude of the change in the incident light intensity detected by the photodiode 112 at the output side of the comparator 281.

[0035] Figure 8A circuit diagram of another exemplary pixel 805 configured to output pixel data to an external processing circuit 850 via an external readout line 840 is shown. In a specific implementation, the external readout line 840 is shared among a plurality of pixels in a column forming a pixel array including the pixel 805. The pixel 805 includes a photodetector circuit 110 and a readout switch 820 configured to isolate a sample node 810 from an output node 830 until a selection signal is received from a controller (not shown) of the external processing circuit 850. In response to receiving the selection signal from the controller, the readout switch 820 is activated (i.e., transitions from an open state to a closed state), and samples of the pixel data at the sample node 810 are transferred to the external processing circuit 850 in the analog domain.

[0036] The external processing circuit 850 includes a differential circuit 860, a digitization circuit 880, and a comparator 890. As Figure 8 shown, the differential circuit 860 includes an AC coupling capacitor 865 and a switched-capacitor amplifier 870. Similar to Figure 1 the switched-capacitor amplifier 150, the gain provided by the amplifier 871 in the switched-capacitor amplifier 870 corresponds to a ratio defined by the respective capacitance values of the AC coupling capacitor 865 and the capacitor 873. Also similar to the switched-capacitor amplifier 150, the operating point of the amplifier 871 is reset to a reference voltage associated with the threshold of the digital comparator 890 by activating a reset switch 875. When a reset signal is received from the controller, the reset switch 875 is activated (i.e., transitions from an open state to a closed state).

[0037] In Figure 8 it, the digitization circuit 880 includes a sample comparator 881, a counter 883, and a frame memory 885. The digitization circuit 880 is configured to convert samples of the pixel data obtained from the pixel 805 in the analog domain into digital samples of the pixel data in the digital domain for further processing by the digital comparator 890. A ramp voltage signal is compared with a sample of the pixel data obtained from the pixel 805 at the input side of the sample comparator 881 at a first moment to generate a digital sample of the pixel data at the output side of the sample comparator 881. This digital sample provides the absolute value of the incident light intensity detected by the photodiode 112 at the first moment. In response to receiving the digital sample of the pixel data corresponding to the first moment from the output side of the sample comparator 881, the counter 883 increments the digital sample and writes it to the frame memory 885. In a specific implementation, the counter 883 forwards the digital sample corresponding to the first moment to an image processing circuit system as grayscale image data.

[0038] At a second moment after the first moment, the ramp voltage signal is compared with a sample of the pixel data obtained from the input side of the sampling comparator 881 from the pixel 805 to generate another digital sample of the pixel data at the output side of the sampling comparator 881. In response to receiving, at the output side of the sampling comparator 881, the digital sample of the pixel data corresponding to the second moment, the counter 883 is incremented and a digital sample corresponding to the first moment is retrieved from the frame memory 885. The comparison between these digital samples is used to determine the change in the incident light intensity detected by the photodiode 112 between the first moment and the second moment. The result of this comparison is forwarded to the input side of the digital comparator 890 for comparison with a threshold. If the change in the incident light intensity detected by the photodiode 112 exceeds the threshold, the digital comparator 890 outputs a pixel event.

[0039] The use herein of "configured to" or "adapted to" means open and inclusive language that does not exclude devices that are adapted to or configured to perform additional tasks or steps. Additionally, the use of "based on" is open and inclusive because a process, step, calculation, or other action that is "based on" one or more of the stated conditions or values may in practice be based on additional conditions or values beyond those stated. The headings, lists, and numbering included herein are for ease of explanation only and are not intended to be restrictive.

[0040] It will also be understood that although terms such as "first," "second," etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first node may be referred to as a second node, and similarly, a second node may be referred to as a first node, which changes the meaning of the description, provided that all occurrences of "first node" are consistently renamed and all occurrences of "second node" are consistently renamed. The first node and the second node are both nodes, but they are not the same node.

[0041] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the claims. As used in the description of the present embodiments and the appended claims, the singular forms "a" and "the" are intended to also include the plural forms, unless the context clearly indicates otherwise. It will also be understood that the term "or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will also be understood that the term "comprising," as used in this specification, specifies the presence of the stated features, integers, steps, operations, elements, or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or groups thereof.

[0042] As used herein, the term "if" can be construed to mean "when the precondition is true" or "while the precondition is true" or "in response to determining" or "in accordance with determining" or "in response to detecting" the precondition is true, depending on the context. Similarly, the phrase "if it is determined [that the precondition is true]" or "if [the precondition is true]" or "when [the precondition is true]" is construed to mean "upon determining that the precondition is true" or "in response to determining" or "in accordance with determining" the precondition is true or "when detecting that the precondition is true" or "in response to detecting" the precondition is true, depending on the context.

[0043] The foregoing description and summary of the invention should be understood to be illustrative and exemplary in every respect and not restrictive, and the scope of the invention disclosed herein is determined not only by the detailed description of the illustrative embodiments, but by the full breadth permitted by patent law. It should be understood that the specific embodiments shown and described herein are merely illustrative of the principles of the invention and that various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Claims

1. An event sensor, comprising: A plurality of pixels, each pixel being configured to output pixel data and including a gray-scale switch, wherein when the gray-scale switch is in an open state, the pixel data provides a differential value of the incident light intensity, and when the gray-scale switch is in a closed state, the pixel data provides an absolute value of the incident light intensity; An external readout line, the external readout line being shared among the plurality of pixels; and An external processing circuit, the external processing circuit being configured to output a stream of pixel events, each corresponding pixel event being generated when a comparator of the external processing circuit obtains a sample of pixel data exceeding a threshold from a specific pixel via the external readout line.

2. The event sensor according to claim 1, wherein the external processing circuit includes: A controller, the controller being configured to arbitrate access to the external readout line among the plurality of pixels by selectively activating a readout switch located within each pixel using a selection signal.

3. The event sensor according to claim 1, wherein samples of pixel data transferred from the output of each pixel in the analog domain to the external processing circuit are converted to the digital domain before reaching the input terminals of the comparator.

4. The event sensor according to claim 1, wherein the external processing circuit is further configured to output gray-scale image data defining the absolute value of the incident light intensity at each pixel.

5. The event sensor according to claim 1, wherein the external readout line is capacitively coupled to the external processing circuit.

6. The event sensor according to claim 1, wherein the plurality of pixels form columns of a pixel array.

7. A pixel circuit, comprising: A photodetector circuit, the photodetector circuit including a gray-scale switch and being configured to generate pixel data at a sample node, wherein when the gray-scale switch is in an open state, the pixel data provides a differential value of the incident light intensity, and when the gray-scale switch is in a closed state, the pixel data provides an absolute value of the incident light intensity; An output node, the output node being coupled to an external processing circuit via an external readout line shared among a plurality of pixels, the external processing circuit being configured to output a stream of pixel events, each corresponding pixel event being generated when a comparator of the external processing circuit obtains a sample of pixel data exceeding a threshold from a specific pixel via the external readout line; and A readout switch, the readout switch being interposed between the photodetector circuit and the output node and being configured to isolate the sample node from the output node until a selection signal is received from a controller of the external processing circuit.

8. The pixel circuit according to claim 7, wherein the photodetector circuit includes a logarithmic amplifier, the logarithmic amplifier being configured to convert a photocurrent proportional to the incident light intensity into a voltage.

9. The pixel circuit according to claim 7, wherein the photodetector circuit includes a photodiode coupled to the sample node via a buffer amplifier.

10. The pixel circuit according to claim 7, wherein the pixel further comprises: A capacitor, the capacitor being interposed between the photodetector circuit and the readout switch.

11. The pixel circuit according to claim 10, further comprising: A gray-scale switch, the gray-scale switch being coupled in parallel with the capacitor, the gray-scale switch being configured to transition to a closed state in response to receiving a gray-scale signal from the controller, wherein when the gray-scale switch is in the closed state, the pixel data provides the absolute value of the incident light intensity.

12. The pixel circuit according to claim 7, further comprising: A switched-capacitor amplifier, the switched-capacitor amplifier being interposed between the photodetector circuit and the switch.

13. The pixel circuit according to claim 12, wherein the operating point of the switched-capacitor amplifier is reset in response to receiving a reset signal from the controller.

14. The pixel circuit according to claim 12, wherein the operating point of the switched-capacitor amplifier is reset in response to receiving the selection signal and the reset signal from the controller.

15. The pixel circuit according to claim 7, wherein in response to receiving a reset signal at the pixel, the voltage of the pixel data at the sample node is set to a reference voltage associated with the threshold.

16. An event sensor, comprising: An external readout line, the external readout line being shared among a plurality of pixels, each pixel being configured to output pixel data and comprising a gray-scale switch, wherein when the gray-scale switch is in an open state, the pixel data provides a differential value of the incident light intensity, and when the gray-scale switch is in a closed state, the pixel data provides the absolute value of the incident light intensity; and An external processing circuit, the external processing circuit being configured to output a stream of pixel events, each corresponding pixel event being generated when the comparator of the external processing circuit obtains a sample of pixel data exceeding a threshold via the external readout line from a specific pixel.

17. The event sensor according to claim 16, wherein each pixel comprises a sampling node coupled to the external readout line via a readout switch, and wherein the external processing circuit comprises a controller configured to reset the voltage appearing at the sampling node whenever the readout switch is activated.

18. The event sensor according to claim 16, wherein the external processing circuit comprises a differential circuit configured to remove a DC voltage component from the samples of pixel data provided to the comparator.

19. The event sensor according to claim 16, wherein the external processing circuit is further configured to output data defining the absolute value of the incident light intensity at each pixel.

20. The event sensor according to claim 16, wherein each corresponding pixel event comprises address information for the specific pixel that produced the sample of pixel data exceeding the threshold, the address information being determined based on the time at which the comparator obtained the sample.

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