PATENT DOCUMENT

Publication Number: US-11910109-B2
Application Number: US-202117376264-A
Country: US
Kind Code: B2

Title: Pixel size reduction method for event driven sensors

Abstract:
In one implementation, 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 an intensity of incident illumination. The external processing circuit is configured to output a stream of pixel events. Each respective pixel event is generated when a comparator of the external processing circuit obtains a sample of pixel data from a particular pixel via the external readout line that breaches a threshold value.

Claims:
What is claimed is: 
     
       1. An event sensor comprising:
 a plurality of pixels, each pixel configured to output pixel data, wherein, in a first state, the pixel data provides a differential value of the intensity of incident illumination and, in a second state, the pixel data provides an absolute value of the intensity of the incident illumination; 
 an external readout line shared among the plurality of pixels; and 
 an external processing circuit configured to output a stream of pixel events, each respective pixel event generated when a comparator of the external processing circuit obtains a sample of pixel data from a particular pixel via the external readout line that breaches a threshold value. 
 
     
     
       2. The event sensor of  claim 1 , wherein the external processing circuit comprises:
 a controller 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 of  claim 1 , wherein samples of pixel data transferred to the external processing circuit from an output of each pixel in an analog domain is converted into a digital domain prior to reaching an input terminal of the comparator. 
     
     
       4. The event sensor of  claim 1 , wherein the external processing circuit is further configured to output grayscale image data defining an absolute value of the intensity of incident illumination at each pixel. 
     
     
       5. The event sensor of  claim 1 , wherein the external readout line is capacitively coupled to the external processing circuit. 
     
     
       6. The event sensor of  claim 1 , wherein the plurality of pixels form a column of a pixel array. 
     
     
       7. A pixel comprising:
 a photodetector circuit configured to generate, at a sample node, pixel data, wherein, in a first state, the pixel data provides a differential value of the intensity of incident illumination and, in a second state, the pixel data provides an absolute value of the intensity of the incident illumination; 
 an output node coupled to an external processing circuit via an external readout line shared among a plurality of pixels, the external processing circuit configured to output a stream of pixel events, each respective pixel event generated when a comparator of the external processing circuit obtains a sample of pixel data from a particular pixel via the external readout line that breaches a threshold value; and 
 a readout switch intervening between the photodetector circuit and the output node that is 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 of  claim 7 , wherein the photodetector circuit includes a logarithmic amplifier configured to convert photocurrent that is proportional to the intensity of incident illumination into a voltage. 
     
     
       9. The pixel of  claim 7 , wherein the photodetector circuit includes a photodiode coupled to the sample node via a buffer amplifier. 
     
     
       10. The pixel of  claim 7 , further comprising:
 a capacitor intervening between the photodetector circuit and the switch. 
 
     
     
       11. The pixel of  claim 10 , further comprising:
 a grayscale switch coupled in parallel with the capacitor, the grayscale switch configured to transition to a closed state in response to receiving a grayscale signal from the controller, wherein the pixel data provides an absolute value of the intensity of incident illumination when the grayscale switch is in the closed state. 
 
     
     
       12. The pixel of  claim 7 , further comprising:
 a switched capacitor amplifier intervening between the photodetector circuit and the switch. 
 
     
     
       13. The pixel of  claim 12 , wherein an operating point of the switched capacitor amplifier is reset in response to receiving a reset signal from the controller. 
     
     
       14. The pixel of  claim 12 , wherein an operating point of the switched capacitor amplifier is reset in response to receiving the selection signal and a reset signal from the controller. 
     
     
       15. The pixel of  claim 7 , wherein a voltage of the pixel data at the sample node is set to a reference voltage associated with the threshold value in response to receiving a reset signal at the pixel. 
     
     
       16. An event sensor comprising:
 an external readout line shared among a plurality of pixels, each pixel configured to output pixel data, wherein, in a first state, the pixel data provides a differential value of the intensity of incident illumination and, in a second state, the pixel data provides an absolute value of the intensity of the incident illumination; and 
 an external processing circuit configured to output a stream of pixel events, each respective pixel event generated when a comparator of the external processing circuit obtains a sample of pixel data from a particular pixel via the external readout line that breaches a threshold value. 
 
     
     
       17. The event sensor of  claim 16 , wherein each pixel includes 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 a voltage appearing at the sampling node each time the readout switch is activated. 
     
     
       18. The event sensor of  claim 16 , wherein the external processing circuit includes a differencing circuit configured to remove a direct current voltage component from samples of pixel data provided to the comparator. 
     
     
       19. The event sensor of  claim 16 , wherein the external processing circuit is further configured to output data defining an absolute value of the intensity of incident illumination at each pixel. 
     
     
       20. The event sensor of  claim 16 , wherein each respective pixel event includes address information for the particular pixel producing the sample of pixel data that breaches the threshold value, the address information being determined based on a time that the comparator obtains the sample.

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to the field of image processing, and in particular, to techniques for reducing a pixel size of event driven sensors. 
     BACKGROUND 
     An event camera may include an image sensor that is referred to as a dynamic vision sensor (“DVS”), a silicon retina, an event-based sensor, or a frame-less sensor. Thus, the event camera generates (and transmits) data regarding changes in light intensity at each pixel sensor as opposed to data output by frame-based cameras regarding absolute light intensity at each pixel. Stated differently, while a frame-based camera will continue to generate (and transmit) data regarding absolute light intensity at each pixel when an illumination level of a scene disposed within its field of view remains static, an event camera will refrain from generating or transmitting data until a change in the illumination level is detected. 
     Existing event sensors may include pixels that locally process the data regarding changes in light intensity. Providing such pixel-level processing of the data within each pixel of the event sensor may limit event sensor usage in some imaging applications. For example, pixel-level processing of that data involves various in-pixel components, such as a comparator and a controller within each pixel that increase the overall physical dimensions (“pixel size”) of each pixel. That increase in pixel size may limit the resolution of image data output by the event sensor. Thus, reducing a pixel size of event sensor pixels may facilitate expanded usage of event sensors in some imaging applications. 
     SUMMARY 
     Various implementations disclosed herein relate to techniques for reducing a pixel size of event driven sensors. In one implementation, 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 an intensity of incident illumination. The external processing circuit is configured to output a stream of pixel events. Each respective pixel event is generated when a comparator of the external processing circuit obtains a sample of pixel data from a particular pixel via the external readout line that breaches a threshold value. In one implementation, the external processing circuit could be shared between a subset of pixels, where multiple external processing units are used to service the whole pixels array. In one implementation, an external processing circuit could be located on a second layer or wafer of a stacked sensor, occupying the area under the pixels. 
     In another implementation, a pixel includes a photodetector circuit, an output node, and a readout switch intervening between the photodetector circuit and the output node. The photodetector circuit is configured to generate pixel data indicative of an intensity of incident illumination at a sample node. The output node is coupled to an external processing circuit via an external readout line shared among a plurality of pixels. The external processing circuit is configured to output a stream of pixel events with each respective pixel event being generated when a comparator of the external processing circuit obtains a sample of pixel data from a particular pixel via the external readout line that breaches a threshold value. The readout switch is configured to isolate the sample node from the output node until a selection signal is received from a controller of the external processing circuit. 
     In another 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 indicative of an intensity of incident illumination. The external processing circuit is configured to output a stream of pixel events. Each respective pixel event is generated when a comparator of the external processing circuit obtains a sample of pixel data from a particular pixel via the external readout line that breaches a threshold value. In one implementation, a differencing operation is implemented in the column circuit outside of the pixel array by digital subtraction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the present disclosure can be understood by those of ordinary skill in the art, a more detailed description may be had by reference to aspects of some illustrative implementations, some of which are shown in the accompanying drawings. 
         FIG.  1    illustrates a block diagram of an event sensor with a plurality of pixels that each provide pixel-level processing of pixel data within each pixel. 
         FIG.  2    illustrates a block diagram of an event sensor with an example pixel that is configured to output pixel data to an external processing circuit via an external readout line shared among a plurality of pixels. 
         FIG.  3    is an example of a timing diagram for operations of the event sensor illustrated in  FIG.  2   . 
         FIG.  4    is another example of a timing diagram for operations of the event sensor illustrated in  FIG.  2   . 
         FIGS.  5 - 8    are circuit diagrams for other example pixels that are each configured to output pixel data to an external processing circuit via an external readout line shared among a plurality of pixels. 
     
    
    
     In accordance with common practice the various features illustrated in the drawings may not be drawn to scale. Accordingly, the dimensions of the various features may be arbitrarily expanded or reduced for clarity. In addition, some of the drawings may not depict all of the components of a given system, method or device. Finally, like reference numerals may be used to denote like features throughout the specification and figures. 
     DESCRIPTION 
     Numerous details are described in order to provide a thorough understanding of the example implementations shown in the drawings. However, the drawings merely show some example aspects of the present disclosure and are therefore not to be considered limiting. Those of ordinary skill in the art will appreciate that other effective aspects or variants do not include all of the specific details described herein. Moreover, well-known systems, methods, components, devices and circuits have not been described in exhaustive detail so as not to obscure more pertinent aspects of the example implementations described herein. 
     A functional block diagram of an example event sensor  100  is illustrated by  FIG.  1   . Event sensor  100  includes a plurality of pixels  105  coupled to an external processing circuit  180  that is configured to output a stream of pixel events. In  FIG.  1   , the plurality of pixels  105  are arranged in a matrix  107  of rows and columns and, thus, each of the plurality of pixels  105  is associated with a row value and a column value. Each of the plurality of pixels  105  include a photodetector circuit  110 , a differencing circuit  140 , a comparator  160 , and a controller  170 . 
     Photodetector circuit  110  is configured to generate signals indicative of an intensity of light incident on a respective pixel  105  (“incident illumination”). To that end, photodetector circuit  110  includes a photodiode  112  configured to generate a photocurrent that is proportional to an intensity of incident illumination. The photocurrent generated by photodiode  112  flows into a logarithmic amplifier  120  formed by transistors  121 ,  123 ,  125 , and  127 . Logarithmic amplifier  120  is configured to convert the photocurrent into a voltage at node A with a value that is a logarithm of a value of the photocurrent. The voltage at node A is then amplified by a buffer amplifier  130  formed by transistors  131  and  133  before being applied to an input side of a differential circuit  140 . 
     In pixel  105 , differencing circuit  140  is composed of alternating current (“AC”) coupling capacitor  145  and switched capacitor amplifier  150 . Differencing circuit  140  is configured to remove a direct current (“DC”) voltage component from the voltage at node A to produce 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 data provides a differential value of the intensity of incident illumination detected by photodiode  112 . A gain provided by amplifier  151  corresponds to a ratio defined by the respective capacitive values of AC coupling capacitor  145  to capacitor  153 . Reset switch  155  is activated (i.e., transitioned from an open state to a closed state) when a reset signal is received from controller  170 . By activating reset switch  155 , an operating point of amplifier  151  is reset to a reference voltage associated with a threshold value of comparator  160 . 
     Comparator  160  is configured to provide pixel-level processing of pixel data received from sample node B. To that end, comparator  160  outputs an electrical response (e.g., a voltage) when the pixel data received from sample node B indicates that photodiode  112  detected a change in an intensity of incident illumination that breaches a threshold value. Alternatively, comparator  160  refrains from outputting an electrical response when the pixel data received from sample node B indicates that photodiode  112  did not detect a change in the intensity of incident illumination that breaches the threshold value. In one implementation, comparator  160  is implemented using a plurality of comparators comprising a first comparator that is configured to output an electrical response indicative of positive events (e.g., events having a positive polarity) and a second comparator that is configured to output an electrical response indicative of negative events (e.g., events having a negative polarity). In one implementation, the first comparator outputs an electrical response when the pixel data received from sample node B indicates that photodiode  112  detected a change in the intensity of incident illumination that breaches a positive threshold value. In one implementation, the second comparator outputs an electrical response when the pixel data received from sample node B indicates that photodiode  112  detected a change in the intensity of incident illumination that breaches a negative threshold value. Controller  170  is configured to coordinate with other components of the event sensor  100  (e.g., controllers within other pixels) to communicate an event signal to an event compiler  185  of the external processing circuit  180  for each electrical response output by comparator  160 . In one implementation, reset switch  155  receives a reset signal from controller  170  each time comparator  160  obtains pixel data at sampling node B that breaches the threshold value. 
     Event compiler  185  receives events signals from each of the plurality of pixels that each represent a change in an intensity of incident illumination breaching the threshold value. In response to receiving an event signal from a particular pixel of the plurality of pixels  105 , event compiler  185  generates a pixel event. Furthermore, event compiler  185  populates the pixel event with information indicative of an electrical response (e.g., a value and/or polarity of the electrical response) included in the event signal. In one implementation, event compiler  185  also populates the pixel event with one or more of: timestamp information corresponding to a point in time at which the pixel event was generated and an address identifier corresponding to the particular pixel that sent the event signal which triggered the pixel event. A stream of pixel events including each pixel event generated by event compiler  185  may then be communicated to image or video processing circuitry (not shown) associated with event camera  100  for further processing. 
     By way of example, the stream of pixel events generated by event compiler  185  can be accumulated or otherwise combined to produce image data. In some implementations the stream of pixel events is combined to provide an intensity reconstruction image. In this implementation, an intensity reconstruction image generator (not shown) may 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 reconstruction image. In this way, it generates and maintains an updated image of values for all pixels of an image even though only some of the pixels may have received events recently. 
     In various implementations, reducing a pixel size of event sensor pixels is effectuated by processing pixel data output by a plurality of pixels with an external processing circuit shared among the plurality of pixels. Stated differently, pixel size reduction is effectuated in various implementations by providing external processing of pixel data generated by multiple pixels instead of providing pixel-level processing of pixel data. The circuit diagrams depicted in  FIGS.  2  and  5 - 8    provide various implementations of pixels for an event sensor that facilitate such external processing of pixel data by an external processing circuit shared among multiple pixels. 
     By way of example,  FIG.  2    depicts a block diagram of a plurality of pixel sensors  205  for an event sensor that each communicate pixel data representing an intensity of incident illumination to an external processing circuit  280 . In the example of  FIG.  2   , each of the plurality of pixels  205  communicates pixel data to external processing circuit  280  via an external readout line  270  shared among the plurality of pixels  205 . Similar to pixel  105  of  FIG.  1   , pixel  205  also includes photodetector circuit  110  configured to generate a voltage at node A proportional to an intensity of incident illumination detected by photodiode  112 . AC coupling capacitor  210  removes a DC voltage component from the voltage at node A to generate pixel data at sample node B that provides a differential value of the intensity of incident illumination. Unlike pixel  105 , the pixel data generated by pixel  205  at sample node B is processed external to pixel  205  by a comparator  281  of external processing circuit  280 . 
     In one implementation, comparator  281  is implemented using a plurality of comparators comprising a first comparator that is configured to output an electrical response indicative of positive events (e.g., events having a positive polarity) and a second comparator that is configured to output an electrical response indicative of negative events (e.g., events having a negative polarity). In one implementation, the first comparator outputs an electrical response when the pixel data received from sample node B indicates that photodiode  112  detected a change in the intensity of incident illumination that breaches a positive threshold value. In one implementation, the second comparator outputs an electrical response when the pixel data received from sample node B indicates that photodiode  112  detected a change in the intensity of incident illumination that breaches a negative threshold value. 
     To avoid collisions between samples of pixel data sent comparator  281  by each of the plurality of pixels  205  via external readout line  270 , external processing circuit  280  includes controller  283 . Controller  283  is configured to arbitrate access to external readout line  270  among the plurality of pixels  205  by selectively activating a readout switch  250  located within each pixel  205  using a selection signal. For example, controller  283  may communicate a first selection signal to a readout switch located within Pixel-1 at a first time and may communicate a second selection signal to a readout switch located within Pixel-2 at a second time subsequent to the first time. In this example, the readout switch located within Pixel-1 may transfer a sample of pixel data from Pixel-1 to external readout line  270  at the first time whereas the readout switch located within Pixel-2 may transfer a sample of pixel data from Pixel-2 to external readout line  270  at the second time. In one implementation, each pixel among the plurality of pixels  205  receives a different phase of a selection signal from controller  283 . 
     In pixel  205 , readout switch  250  intervenes between sample node B and output node  260 . From that position, readout switch  250  may isolate sample node B from output node  260  until a selection signal is received from controller  283 . When the selection signal is received from controller  283 , readout switch  250  is activated (i.e., transitioned from an non-conductive state to a conductive state). In one implementation, readout switch  250  is implemented as an n-channel MOS transistor. By activating readout switch  250 , pixel data on sample node B is transferred through transistor  243  of a second buffer amplifier  240  formed by transistors  241  and  243  to output node  260 . 
     Turning to the timing diagram of  FIG.  3   , the operations performed by event sensor  200  in generating pixel events are explained in greater detail in accordance with one implementation. At time T 1 , readout switch  250  and selection switch  220  activate in response to receiving a selection signal from controller  283  thereby transferring a sample of pixel data to output node  260 . Selection switch  220  enables reset for one of the pixels in the group of 4 pixels. The sample of pixel data transferred to output node  260  at time T 1  is applied to an input side of comparator  281 . Since that sample of pixel data obtained by comparator  281  at time T 1  breaches a threshold value, comparator  281  outputs an electrical response to an input side of controller  283 . Upon receiving the electrical response from comparator  281  at time T 1 , controller  283  sends a reset signal to reset switch  230 . In response to receiving the reset signal from controller  283 , reset switch  230  activates thereby causing a voltage of the pixel data at sample node B to reset to reference voltage V ref . 
     In addition to sending the reset signal to reset switch  230 , controller  283  forwards the electrical response received from comparator  281  at time T 1  along with information characterizing the electrical response to event compiler  285 . In various implementations, the information characterizing an electrical response may include one or more of: a value of the electrical response, a polarity of the electrical response, timestamp information corresponding to a point in time at which the event response was generated, or an address identifier corresponding to the respective pixel that triggered the generation of the pixel event. Upon receiving the event response and characterizing information from comparator  281  at time T 1 , event compiler  285  generates a pixel event. 
     Unlike time T 1 , a value of the pixel data at sample node B does not breach the threshold value at time T 3 . Rather, the value of the pixel data at sample node B breaches the threshold value subsequent to time T 3 . As such, the sample of the pixel data that comparator  281  obtains at time T 3  does not breach the threshold value, and consequently comparator  281  does not generate an electrical response at time T 3 . Because controller  283  does not receive an electrical response from comparator  281  at time T 3 , controller  283  neither sends a reset signal to reset switch  230  nor forwards an electrical response to event compiler  285  at time T 3 . Consequently, a voltage of the pixel data at sample node B is not reset to reference voltage V ref  by activation of reset switch  230  and event compiler does not generate a pixel event at time T 3 . 
     Similar to time T 1  or time T 2 , a value of the pixel data at sample node B breaches a threshold value at time T 5 . Unlike time T 1  or time T 2 , the value of the pixel data at sample node B does not exceed upper threshold value V th  at time T 5 . Instead, the value of the pixel data at sample node B is less than lower threshold value −V th  at time T 5 . In one implementation, a difference between upper threshold value V th  and reference voltage V ref  is equal or substantially equal to a difference between lower threshold value −V th  and reference voltage V ref . Pixel events generated by event compiler  285  at time T 1  or time T 2  may be referred to as “positive” pixel events. In one implementation, positive pixel events are pixel events with a positive polarity that represent net increases in the intensity of incident illumination that exceed a magnitude defined by the upper threshold value V th . The pixel event generated by event compiler  285  at time T 5  may be referred to as a “negative” pixel event. In one implementation, negative pixel events are pixel events with a negative polarity that represent net decreases in the intensity of incident illumination that exceed a magnitude defined by the lower threshold value −V th . 
       FIG.  4    is a timing diagram for operations performed by event sensor  200  in generating pixel events in accordance with one implementation. In one implementation, pixel  205  can be implemented without selection switch  220 . Alternatively it can be implemented by activating select switch  220  in all 4 pixels the same time. A comparison between  FIGS.  3  and  4    illustrates that reset switch  230  facilitates implementing a global reset option in which a voltage of the pixel data at sample node B is reset to reference voltage V ref  each time a sample of pixel data is transferred to output node  260 . In one implementation, controller  283  implements the global reset option by initiating a delay timer when a selection signal is sent to readout switch  250  and selection switch  220  and sending a reset signal to reset switch  230  once the delay time expires. 
       FIG.  5    illustrates a circuit diagram of another example pixel  505  that is configured to output pixel data to external processing circuit  280  via external readout line  270 . Similar to pixel  205  of  FIG.  2   , pixel  505  includes photodetector circuit  110  that outputs a voltage indicative of an intensity of incident illumination detected by photodiode  112 . Pixel  505  further includes a differencing circuit  530  that couples an output of photodetector circuit  110  to a readout switch  550  that is configured to isolate sample node  540  from output node  560  until a selection signal is received from controller  283 . As shown by  FIG.  5   , differencing circuit  530  includes AC coupling capacitor  510  and switched capacitor amplifier  520 . Similar to switched capacitor amplifier  150  of  FIG.  1   , a gain provided by amplifier  521  corresponds to a ratio defined by the respective capacitive values of AC coupling capacitor  510  to capacitor  523 . Unlike switch capacitor amplifier  150 , an operating point of amplifier  521  in switched capacitor amplifier  520  is reset to a reference voltage associated with a threshold value of comparator  281  by activating both reset switch  525  and selection switch  527 . Reset switch  525  and selection switch  527  are activated (i.e., transitioned from an open state to a closed state) when a reset signal and a selection signal, respectively, are received from controller  283 . In one implementation, switched capacitor amplifier  520  improves a signal-to-noise ratio associated with pixel data generated at sampling node  540 . 
       FIG.  6    illustrates a circuit diagram of another example pixel  605  that is configured to output pixel data to external processing circuit  280  via external readout line  270 . In one implementation, external readout line  270  is shared among a plurality of pixels including pixel  605  that form a column of a pixel array. Pixel  605  includes an AC coupling capacitor  610  intervening between an output of photodetector circuit  110  to an input side of buffer amplifier  650  formed by transistor  651  and transistor  653 . Pixel  605  further includes a readout switch  660  that is configured to isolate sample node  640  from output node  670  until a selection signal is received from controller  283 . A reset switch  630  in pixel  605  is configured to reset a voltage of the pixel data at sample node  640  to a reference voltage associated with a threshold value of comparator  281  in response to receiving a reset signal from controller  283 . 
     In pixel  605 , a grayscale switch  620  is coupled in parallel with AC coupling capacitor  610 . When grayscale switch  620  is in an open state, AC coupling capacitor  610  removes a DC voltage component from a voltage at node A to generate pixel data at sample node  640  that provides a differential value of the intensity of incident illumination detected by photodiode  112 . In response to receiving a grayscale signal from controller  283 , grayscale switch  620  transitions from the open state to a closed state thereby bypassing AC coupling capacitor  610 . When grayscale switch  620  is in the closed state, the pixel data at sample node  640  provides an absolute value of the intensity of incident illumination detected by photodiode  112 . In one implementation, a ramp voltage signal is compared with samples of pixel data obtained from pixel  605  on an input side of comparator  281  when grayscale switch  620  is in the closed state to generate grayscale image data on an output side of comparator  281 . 
       FIG.  7    illustrates a circuit diagram of another example pixel  705  that is configured to output pixel data to external processing circuit  280  via external readout line  270 . In one implementation, external readout line  270  is shared among a plurality of pixels including pixel  705  that form a column of a pixel array. Pixel  705  includes a differencing circuit  730  that couples an output of photodetector circuit  110  to a readout switch  750  that is configured to isolate sample node  740  from output node  760  until a selection signal is received from controller  283 . As shown by  FIG.  7   , differencing circuit  730  includes AC coupling capacitor  710  and switched capacitor amplifier  720 . Similar to switched capacitor amplifier  150  of  FIG.  1   , a gain provided by amplifier  721  in switched capacitor amplifier  720  corresponds to a ratio defined by the respective capacitive values of AC coupling capacitor  710  to capacitor  723 . Also similar to switch capacitor amplifier  150 , an operating point of amplifier  721  is reset to a reference voltage associated with a threshold value of comparator  281  by activating reset switch  725 . Reset switch  725  is activated (i.e., transitioned from an open state to a closed state) when a reset signal is received from controller  283 . In one implementation, a ramp voltage signal is compared with samples of pixel data obtained from pixel  705  on an input side of comparator  281  to obtain information defining an amplitude of change in the intensity of incident illumination detected by photodiode  112  on an output side of comparator  281 . 
       FIG.  8    illustrates a circuit diagram of another example pixel  805  that is configured to output pixel data to an external processing circuit  850  via an external readout line  840 . In one implementation, external readout line  840  is shared among a plurality of pixels including pixel  805  that form a column of a pixel array. Pixel  805  includes a photodetector circuit  110  and a readout switch  820  that is configured to isolate sample node  810  from output node  830  until a selection signal is received from a controller (not shown) of external processing circuit  850 . In response to receiving a selection signal from the controller, readout switch  820  activates (i.e., transitions from an open state to a closed state) and a sample of pixel data at sample node  810  is transferred to external processing circuit  850  in an analog domain. 
     External processing circuit  850  includes a differencing circuit  860 , a digitizing circuit  880 , and a comparator  890 . As shown by  FIG.  8   , differencing circuit  860  includes AC coupling capacitor  865  and switched capacitor amplifier  870 . Similar to switched capacitor amplifier  150  of  FIG.  1   , a gain provided by amplifier  871  in switched capacitor amplifier  870  corresponds to a ratio defined by the respective capacitive values of AC coupling capacitor  865  to capacitor  873 . Also similar to switch capacitor amplifier  150 , an operating point of amplifier  871  is reset to a reference voltage associated with a threshold value of digital comparator  890  by activating reset switch  875 . Reset switch  875  is activated (i.e., transitioned from an open state to a closed state) when a reset signal is received from the controller. 
     In  FIG.  8   , digitizing circuit  880  includes a sampling comparator  881 , a counter  883 , and a frame memory  885 . Digitizing circuit  880  is configured to convert samples of pixel data obtained from pixel  805  in the analog domain into digital samples of pixel data in a digital domain for further processing by digital comparator  890 . A ramp voltage signal is compared with a sample of pixel data obtained from pixel  805  at a first time on an input side of sampling comparator  881  to generate a digital sample of pixel data on an output side of sampling comparator  881 . That digital sample provides an absolute value of the intensity of incident illumination detected by photodiode  112  at the first time. In response to receiving the digital sample of pixel data from the output side of sampling comparator  881  corresponding to the first time, counter  883  increments and writes the digital sample to frame memory  885 . In one implementation, counter  883  forwards the digital sample corresponding to the first time to image processing circuitry as grayscale image data. 
     At a second time subsequent to the first time, the ramp voltage signal is compared with a sample of pixel data obtained from pixel  805  the input side of sampling comparator  881  to generate another digital sample of pixel data on the output side of sampling comparator  881 . In response to receiving the digital sample of pixel data from the output side of sampling comparator  881  corresponding to the second time, counter  883  decrements and the digital sample corresponding to the first time is retrieved from frame memory  885 . A comparison between those digital samples is used to determine a change in the intensity of incident illumination detected by photodiode  112  between the first time and the second time. The result of that comparison is forwarded to an input side of digital comparator  890  to compare with a threshold value. If that change in the intensity of incident illumination detected by photodiode  112  breaches the threshold value, digital comparator  890  outputs a pixel event. 
     The use of “adapted to” or “configured to” herein is meant as open and inclusive language that does not foreclose devices adapted to or configured to perform additional tasks or steps. Additionally, the use of “based on” is meant to be open and inclusive, in that a process, step, calculation, or other action “based on” one or more recited conditions or values may, in practice, be based on additional conditions or value beyond those recited. Headings, lists, and numbering included herein are for ease of explanation only and are not meant to be limiting. 
     It will also be understood that, although the terms “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 could be termed a second node, and, similarly, a second node could be termed a first node, which changing the meaning of the description, so long as all occurrences of the “first node” are renamed consistently and all occurrences of the “second node” are renamed consistently. The first node and the second node are both nodes, but they are not the same node. 
     The terminology used herein is for the purpose of describing particular implementations only and is not intended to be limiting of the claims. As used in the description of the implementations and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, 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 be further understood that the terms “comprises” or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or groups thereof. 
     As used herein, the term “if” may be construed to mean “when” or “upon” or “in response to determining” or “in accordance with a determination” or “in response to detecting,” that a stated condition precedent is true, depending on the context. Similarly, the phrase “if it is determined [that a stated condition precedent is true]” or “if [a stated condition precedent is true]” or “when [a stated condition precedent is true]” may be construed to mean “upon determining” or “in response to determining” or “in accordance with a determination” or “upon detecting” or “in response to detecting” that the stated condition precedent is true, depending on the context. 
     The foregoing description and summary of the invention are to be understood as being in every respect illustrative and exemplary, but not restrictive, and the scope of the invention disclosed herein is not to be determined only from the detailed description of illustrative implementations but according to the full breadth permitted by patent laws. It is to be understood that the implementations shown and described herein are only illustrative of the principles of the present invention and that various modification may be implemented by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20210715
Publication Date: 20240220
Grant Date: 20240220
Priority Date: 20190123
Inventors: BOCK, NIKOLAI E.
MANDELLI, EMANUELE
CLOCCHIATTI, Dario
Assignee: APPLE INC
CPC Classifications: [{"code": "H04N25/50", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N25/707", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N25/47", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N25/75", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N25/707", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N25/47", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N25/50", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04N25/75", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N25/77", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N25/77", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04N25/77", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04N25/50", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04N25/766", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N25/75", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N25/77", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 69740530