Patent Publication Number: US-2023139234-A1

Title: Readout architectures for binned indirect time-of-flight sensors

Description:
BACKGROUND INFORMATION 
     Field of the Disclosure 
     This disclosure relates generally to image sensors, and in particular but not exclusively, relates to time-of-flight sensors. 
     Background 
     Interest in three dimensional (3D) cameras is increasing as the popularity of 3D applications continues to grow in areas such as imaging, movies, games, computers, user interfaces, facial recognition, object recognition, augmented reality, and the like. A typical passive way to create 3D images is to use multiple cameras to capture stereo or multiple images. Using the stereo images, objects in the images can be triangulated to create the 3D image. One disadvantage with this triangulation technique is that it is difficult to create 3D images using small devices because there must be a minimum separation distance between each camera in order to create the 3D images. In addition, this technique is complex and therefore requires significant computer processing power in order to create the 3D images in real time. 
     For applications that require the acquisition of 3D images in real time, active depth imaging systems based on time-of-flight measurements are sometimes utilized. Time-of-flight cameras typically employ a light source that directs light at an object, a sensor that detects the light that is reflected from the object, and a processing unit that calculates the distance to the object based on the round-trip time it takes for the light to travel to and from the object. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. 
         FIG.  1    is a block diagram that shows one example of a time-of-flight light sensing system in accordance with the teachings of the present invention. 
         FIG.  2    is a timing diagram that shows an example of light pulses emitted from a light source relative to the receipt of the reflected light pulses and measurements using various phase shifts in an example time-of-flight sensing system accordance with the teachings of the present invention. 
         FIG.  3    is a schematic illustrating an example of a portion of a time-of-flight pixel circuit including one photodiode in accordance with the teachings of the present invention. 
         FIG.  4    is a schematic illustrating an example of a time-of-flight pixel array including examples of time-of-flight pixel circuits that include four photodiodes with a reconfigurable binning readout architecture in accordance with the teachings of the present invention. 
         FIGS.  5 A- 5 E  are timing diagrams illustrating signals in an example time-of-flight sensing system in various different example binning configurations in accordance with the teachings of the present invention. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. In addition, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. 
     DETAILED DESCRIPTION 
     Examples directed to various embodiments of a time-of-flight pixel array including time-of-flight pixel circuits that may be reconfigured in a various example binning arrangements are described herein. In the following description, numerous specific details are set forth to provide a thorough understanding of the examples. One skilled in the relevant art will recognize, however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail in order to avoid obscuring certain aspects. 
     Reference throughout this specification to “one example” or “one embodiment” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present invention. Thus, the appearances of the phrases “in one example” or “in one embodiment” in various places throughout this specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more examples. 
     Spatially relative terms, such as “beneath,” “below,” “over,” “under,” “above,” “upper,” “top,” “bottom,” “left,” “right,” “center,” “middle,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is rotated or turned over, elements described as “below” or “beneath” or “under” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary terms “below” and “under” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated ninety degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. In addition, it will also be understood that when an element is referred to as being “between” two other elements, it can be the only element between the two other elements, or one or more intervening elements may also be present. 
     Throughout this specification, several terms of art are used. These terms are to take on their ordinary meaning in the art from which they come, unless specifically defined herein or the context of their use would clearly suggest otherwise. It should be noted that element names and symbols may be used interchangeably through this document (e.g., Si vs. silicon); however, both have identical meaning. 
     As will be discussed, various examples of indirect time-of-flight (e.g., iTOF) sensing systems are disclosed in which modulated light is emitted from a light source to an object, which is then reflected from the object back to a time-of-flight pixel array included in the time-of-flight sensing system. The object distance is determined in response to the measured phase of the modulation sensed by the time-of-flight pixel circuits, which may be used to yield a 3D frame. 
     In various examples, each photodiode of each time-of-flight pixel circuit is coupled via a plurality of transfer transistors to a plurality of respective floating diffusions. In the various examples, each of the floating diffusions may be coupled to a first one of a plurality of memory nodes through a respective sample and hold transistor. In the various examples, each of the floating diffusions may also be configured to be coupled to a second one of the plurality of memory nodes through a binning transistor and through another sample and hold transistor. As such, in various examples, each of the plurality of memory nodes may be configured to sample and hold a portion of charge information from multiple photodiodes, which enables the binning of charge information from the multiple photodiodes in accordance with the teachings of the present invention. 
     In the various examples, the plurality of memory nodes can be read out through respective readout transistors that are coupled to output source follower transistors, which are coupled to respective bitlines. In various examples, two readout transistors are coupled to the output source follower transistor of each time-of-flight pixel circuit. As such, in various examples, both of the readout transistors that are coupled to the output source follower transistor may also be configured to be turned ON (e.g., activated) at the same time, which enables the binning of charge information that is sampled and held in the multiple memory nodes at the output source follower transistor from respective photodiodes in accordance with the teachings of the present invention. 
     In the various examples, the signals that are on the bitlines may also be configured to be combined, which enables the binning of the signals on that are carried on the respective bitlines. In various examples, the signals that are on the bitlines may be combined using a variety of techniques such as for example coupling multiple row select transistors in different rows of the pixel array to the same bitline to realize vertical binning, coupling together multiple bitlines from different columns or charge sharing of sampled signals on column level of the pixel array to realize horizontal binning, summation of the input signals of an analog to digital converter (ADC) or in digital domain, etc. 
     To illustrate,  FIG.  1    is a block diagram that shows one example of a time-of-flight light sensing system  100  in accordance with the teachings of the present invention. In the depicted example, time-of-flight light sensing system  100  is a 3D camera that calculates image depth information of a scene (e.g., object  106 ) based on indirect time-of-flight (e.g., iToF) measurements with an image sensor that includes pixel array  110 . In some examples, it is appreciated that although time-of-flight light sensing system  100  is capable of sensing 3D images, time-of-flight light system  100  may also be utilized to capture 2D images. In various examples, time-of-flight light sensing system  100  may also be utilized to capture high dynamic range (HDR) images. 
     As shown in the depicted example, time-of-flight light sensing system  100  includes light source  102  that is synchronized with a time-of-flight sensor that includes a pixel array  110 , which includes a plurality of pixel circuits  112 , and a control circuit  114  that is coupled to control and synchronize the pixel array  110  and light source  102 . 
     As illustrated, light source  102  is configured to emit light  104  to the object  106  over a distance L. The emitted light  104  is then reflected from the object  106  as reflected light  108  (e.g., reflected light waves/pulses), some of which propagates towards the pixel array  110  of time-of-flight light sensing system  100  over the distance L and is incident upon the pixel circuits  112  of pixel array  110  as image light. Each pixel circuit  112  included in the pixel array  110  includes a photodetector (e.g., one or more photodiodes, avalanche photodiodes, or single-photon avalanche diodes, or the like) to detect the reflected light  108  and convert the reflected light  108  into an electric signal (e.g., electrons, image charge, etc.). 
     It is noted that pixel array  110  and control circuit  114  are represented as separate components in  FIG.  1    for explanation purposes. However, it is appreciated that pixel array  110  and components of control circuit  114  may be integrated onto a same integrated circuit chip or wafer in a non-stacked standard planar sensor. In various examples, it as also appreciated that pixel array  110  may implemented in a stacked time-of-flight image sensor. 
     Continuing with the depicted example, each pixel circuit  112  of pixel array  110  determines depth information for a corresponding portion of object  106  such that a 3D image of object  106  can be generated. As will be discussed in greater detail below, depth information is determined by modulating the transfer gates of each pixel circuit  112  with 0°/180° and 180°/0° phase modulation signals as well as with opposing 90°/270° and 270°/90° phase modulation signals in multiple subframes to measure the delay/phase difference between emitted light  104  and the received reflected light  108  to indirectly determine a round-trip time for light to propagate from light source  102  to object  106  and back to the pixel array  110  of time-of-flight light sensing system  100 . In the various example, the 0°, 90°, 180°, and 270° phase modulation signals may also be modulated at multiple different frequencies in the multiple subframes. In various examples, each of a plurality of memory nodes included in each pixel circuit  112  is capable of capturing and storing a subframe of a phase portion of charge information from the photodiode included the pixel circuit  112  during or prior to a readout of another memory node storing another phase portion of charge information acquired in a previous subframe. Thus, the depth information may be based on electric signals generated by the photodiode included in each pixel circuit  112 , which are subsequently transferred and stored in the plurality of memory nodes in each pixel circuit  112 , which are then read out subsequently. 
     As shown in the depicted example, the round-trip time for emitted light  104  to propagate from light source  102  to object  106  and then be reflected back to pixel array  110  can be used to determine the distance L using the following relationships in Equations (1) and (2) below: 
     
       
         
           
             
               
                 
                   
                     T 
                     TOF 
                   
                   = 
                   
                     
                       2 
                       ⁢ 
                       L 
                     
                     c 
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
       
         
           
             
               
                 
                   L 
                   = 
                   
                     
                       
                         T 
                         TOF 
                       
                       · 
                       c 
                     
                     2 
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     where c is the speed of light, which is approximately equal to 3×10 8  m/s, and T TOF  corresponds to the round-trip time, which is the amount of time that it takes for the light to travel to and from the object  106  as shown in  FIG.  1   . Accordingly, once the round-trip time is known, the distance L may be calculated and subsequently used to determine depth information of object  106 . 
     As shown in the depicted example, control circuit  114  is coupled to pixel array  110  and light source  102 , and includes logic and memory that when executed causes time-of-flight light sensing system  100  to perform operations for determining the round-trip time. Determining the round-trip time may be based on, at least in part, timing signals generated by control circuit  114 . For indirect time-of-flight (indirect time-of-flight) measurements, the timing signals are representative of the delay/phase difference between the light waves/pulses of when the light source  102  emits light  104  and when the photodetectors or photodiodes in pixel circuits  112  detect the reflected light  108 . 
     In some examples, time-of-flight light sensing system  100  may be included in a device (e.g., a mobile phone, a tablet, a camera, etc.) that has size and power constraints determined, at least in part, based on the size of the device. Alternatively, or in addition, time-of-flight light sensing system  100  may have specific desired device parameters such as frame rate, depth resolution, lateral resolution, etc. 
       FIG.  2    is a timing diagram that illustrates the timing relationship between example light pulses emitted from a light source relative to the receipt of the reflected light pulses and measurements using various phase shifts in an example time-of-flight imaging system accordance with the teachings of the present invention. Specifically,  FIG.  2    shows emitted light  204 , which represents the modulated light pulses that are emitted from the light source  102  to the object  106 , and corresponding pulses reflected light  208 , which represents the reflected light pulses that are back-reflected from the object  106  and received by the pixel circuits  112  pixel array  110  of  FIG.  1   . 
     The example depicted in  FIG.  2    also illustrates measurement pulses of the phase modulation signals including a 0° phase modulation signal  214 A (e.g., a first phase modulation signal) and a 180° phase modulation signal  214 B (e.g., a second phase modulation signal), as well as measurement pulses including a 90° phase modulation signal  216 A (e.g., a third phase modulation signal) and a 270° phase modulation signal  216 B (e.g., a fourth phase modulation signal), which as shown are all phase-shifted relative to the phase of the pulses of emitted light  204 . In addition, it is appreciated that in the depicted example the 180° phase modulation signal  214 B is an inverted 0° phase modulation signal  214 A, that the 90° phase modulation signal  216 A is ninety degrees out of phase with the 0° phase modulation signal  214 A, and that the 270° phase modulation signal  216 B is an inverted 90° phase modulation signal  216 A. 
       FIG.  2    also shows that the 0° phase modulation signal  214 A and 180° phase modulation signal  214 B, as well as the 90° phase modulation signal  216 A and 270° phase modulation signal  216 B pulses are all modulated at the same frequency as the modulated emitted light  204  and reflected light  208  to realize homodyne detection of the reflected light  208  in accordance with the teachings of the present invention. In various examples, the modulation frequency of the phase modulation signals and the modulated emitted light may be varied across the multiple subframes in which the phase is measured. It is appreciated that the measurements at additional frequencies and/or phases can improve systematic errors, such as for example harmonic distortions and/or multipath artifacts. Utilizing the different phases for the example measurement pulses as shown allows reconstruction of the encoded distance in multiple subframes in accordance with the teachings of the present invention. 
     As will be discussed, the 0° phase modulation signal  214 A and 180° phase modulation signal  214 B, as well as the 90° phase modulation signal  216 A and 270° phase modulation signal  216 B pulses correspond to the switching or modulation of transfer transistors that are included in the pixel circuits  112  of pixel array  110 . In operation, the modulation of the transfer transistors in the pixel circuits  112  of pixel array  110  can be used to measure the charge that is photogenerated in the one or more photodiodes that are included the pixel circuits  112  in response to the reflected light  208  to measure the delay or phase difference φ between the pulses of emitted light  204  and the corresponding pulses of reflected light  208 . 
     For instance, the example illustrated in  FIG.  2    shows that a first phase portion of charge Q 1  is photogenerated by the pulses of 0° phase modulation signal  214 A and that a second phase portion of charge Q 2  is photogenerated by the pulses of 180° phase modulation signal  214 B in response to reflected light  208 . Similarly, a third phase portion of charge Q 3  is photogenerated by the pulses of 90° phase  216 A and a fourth phase portion of charge Q 4  is photogenerated by the pulses of 270° phase modulation signal  216 B in response to reflected light  208 . As will be discussed in greater detail below, the measurements of four phase portions of charge Q 1 , Q 2 , Q 3 , and Q 4  can then be used to determine the delay or phase difference φ between the emitted light  204  and the reflected light  208 , and therefore the time of flight T TOF  of light from the light source  102  to the object  106  and then back to the pixel array  110  in accordance with the teachings of the present invention. 
       FIG.  3    is a schematic illustrating one example of a portion of a time-of-flight pixel circuit  312  in accordance with the teachings of the present invention. It is appreciated that the pixel circuit  312  of  FIG.  3    may be an example of a portion of one of the pixel circuits  112  included in pixel array  110  shown in  FIG.  1   , and that similarly named and numbered elements described above are coupled and function similarly below. 
     As shown in the example portion depicted in  FIG.  3   , pixel circuit  312  includes a photodiode  318  configured to photogenerate charge in response to incident light. In one example, the light that is incident on photodiode  318  is the reflected modulated light  108  that is reflected from an object  106  as described in  FIG.  1   . A first floating diffusion FDA  322 A is configured to store a first portion of charge photogenerated in the photodiode  318 , and second floating diffusion FDB  322 B is configured to store a second portion of charge photogenerated in the photodiode  318 . As will be discussed in greater detail below, in various examples, first floating diffusion FDA  322 A and second floating diffusion FDB  322 B may be coupled to other respective floating diffusions via respective binning transistors to provide reconfigurable binning for pixel circuit  312  in accordance with the teachings of the present invention. 
     In one example, a first reset transistor  324 A is coupled between a supply rail and the first floating diffusion FDA  322 A. A second reset transistor  324 B is coupled between the supply rail and the second floating diffusion FDB  322 B. In the various examples, the first reset transistor  324 A is configured to reset the first floating diffusion FDA  322 A in response to a first reset signal DA and the second reset transistor  324 B is configured to reset the second floating diffusion FDB  322 B in response to a second reset signal DB. In various examples, the first reset signal DA and second reset signal DB may be the same signal or different signals. In one example, the first reset transistor  324 A and second reset transistor  324 B may also act as overflow transistors. In such examples, the first reset transistor  324 A and second reset transistor  324 B may be operated in such a way that excess carriers generated by photodiode  318  may be guided to the power supply by first reset transistor  324 A and/or the second reset transistor  324 B or in a way such that the photosensitivity of photodiode  318  is disabled. 
     A first transfer transistor  320 A is configured to transfer the first portion of charge from the photodiode  318  to the first floating diffusion FDA  322 A in response to a first modulation signal TXA. In one example, the first modulation signal TXA may be an example of one of the phase modulation signals described in  FIG.  2   . A second transfer transistor  320 B is configured to transfer the second portion of charge from the photodiode  318  to the second floating diffusion FDB  322 B in response to a second modulation signal TXB. In the example, the second modulation signal TXB may also be an example of one of the phase modulation signals described in  FIG.  2   . 
     As shown in the depicted example, pixel circuit  312  also includes a first capacitor  328 A 1 , which provides a first memory nodes C 1 A  334 A 1 . In the example, pixel circuit  312  also includes a second capacitor  328 B 1 , which provides a second memory node C 1 B  334 B 1 . In the example, a first sample and hold transistor  326 A 1  is coupled between the first floating diffusion FDA  322 A and the first memory nodes C 1 A  334 A 1  as shown. Similarly, a second sample and hold transistor  326 B 1  is coupled between the second floating diffusion FDB  322 B and the second memory node C 1 B  334 B 1  as shown. 
     As shown in the depicted example, pixel circuit  312  further includes a first source follower transistor  330 A and a second source follower transistor  330 B. In the depicted example, a first output reset transistor  338 A is coupled to the gate of first source follower transistor  330 A and a second output reset transistor  338 B is coupled to the gate of second source follower transistor  330 B. In operation, the first and second output reset transistors  338 A and  338 B may be activated in response to output reset signals RSTA and RSTB to reset or precharge the gates of the first and second source follower transistors  330 A and  330 B between readouts. In various examples, the output reset signals RSTA and RSTB may be the same signal or independent signals. 
     In the depicted example, a first readout transistor  336 A 1  is coupled between the first memory node C 1 A  334 A 1  and a gate of the first source follower transistor  330 A. A second readout transistor  336 B 1  is coupled between the second memory node C 1 B  334 B 1  and a gate of the second source follower transistor  330 A. As will be discussed in greater detail below, in various examples, the gate of the first source follower transistor  330 A and the gate of the second source follower transistor  330 B may be coupled to other respective readout transistors to provide reconfigurable binning for pixel circuit  312  in accordance with the teachings of the present invention. 
     A first row select transistor  332 A is coupled between the first readout transistor  336 A 1  and the first source follower transistor  330 A and a first bitline  342 A, and a second row select transistor  332 B is coupled between the second readout transistor  336 B 1  and the second source follower transistor  330 B and a second bitline  342 B. In one example, the output of the first row select transistor  332 A may be considered a first tap of the pixel circuit  312  from which the output VA from first source follower transistor  330 A may be read out through first bitline  342 A, and the output of the second row select transistors may be considered a second tap of the pixel circuit  312  from which the output VB from second source follower transistor  330 B may be read out through second bitline  342 B. 
     In operation, the first modulation signal TXA and second modulation signal TXB that are configured to modulate the first transfer transistor  320 A and the second transfer transistor  320 B are modulation signals that are 180° out of phase or inverted versions of each other. For instance, in one example, in a first subframe, the first modulation signal TXA may be the 0° phase modulation signal  214 A while the second modulation signal TXA is therefore the 180° phase modulation signal  214 B. In that example, in another subframe, the first modulation signal TXA and the second phase modulated signal TXB are inverted relative to their respective signals in the first subframe. In other words, in that example, in the other subframe, the first modulation signal TXA is the 180° phase modulation signal  216 B while the second modulation signal TXB is the 0° phase modulation signal  214 A. In the various examples, it is appreciated that the first and second transfer transistors  320 A and  320 B may also be modulated with 90°/270° phase modulation signals as well as with the opposing phases of 270°/90° phase modulation signals in multiple subframes. 
     By modulating the first transfer transistor  320 A and the second transfer transistor  320 B with the first modulation signal TXA and second modulation signal TXB with the opposing phases of the 0°/180° and 180°/0° phase modulations signals as well as with the opposing phases of the 90°/270° and 270°/90° phase modulation signals in the multiple subframes as described, offset errors as well as dark current errors in the time-of-flight pixel circuits are canceled or removed in accordance with the teachings of the present invention. 
     In the various examples, the first modulation signal TXA and second modulation signal TXB may also be modulated at different phases and/or frequencies in different subframes, which improves systematic errors, such as for example harmonic distortions or multipath artifacts in accordance with the teachings of the present invention. For instance, in one example, the first modulation signal TXA and second modulation signal TXB are configured to alternate between two different modulation frequencies f 1  and f 2  for each subframe. In other words, in one example, the first modulation signal TXA and second modulation signal TXB are configured to be modulated at a modulation frequency f 1  during a first subframe, and then a modulation frequency f 2  during a second subframe. Then, in a third subframe, the first modulation signal TXA and second modulation signal TXB are configured to be modulated at the modulation frequency f 1 , and then in a fourth subframe, the first modulation signal TXA and second modulation signal TXB are configured to be modulated at the modulation frequency f 2 , and so on. 
       FIG.  4    is a schematic illustrating an example of a time-of-flight pixel array  410  including examples of time-of-flight pixel circuits that include two photodiodes with a reconfigurable binning readout architecture in accordance with the teachings of the present invention. It is appreciated that the example of time-of-flight pixel circuits illustrated in the pixel array  410   FIG.  4    share many similarities with the portion of the time-of-flight pixel circuit  312  shown in  FIG.  3   , and/or may be an example of the time-of-flight pixel circuits  112  shown in  FIG.  1   , and that similarly named and numbered elements described above are coupled and function similarly below. 
     In the example depicted in  FIG.  4   , a pixel circuit on the left hand side includes an upper portion of a pixel circuit  412 - 1  and a lower portion of a pixel circuit  412 - 2  and a pixel circuit on the right hand side includes an upper portion of a pixel circuit  412 - 3  and a lower portion of a pixel circuit  412 - 4 . In the example, it is appreciated that each of the portions of pixel circuits  412 - 1 ,  412 - 2 ,  412 - 3 ,  412 - 4  are substantially similar to the portion of pixel circuit  312  illustrated in  FIG.  3   , and will therefore not be described in detail for the sake of brevity. One of the differences, however, between the example illustrated in  FIG.  4    and the example illustrated in  FIG.  3    is that the portions of pixel circuits  412 - 1  and  412 - 2  in  FIG.  4    share a first output reset transistor  438 A, a first output source follower transistor  430 A, and a first row select transistor  432 A at the output tap coupled to first bitline  442 A. In addition, pixel circuits  412 - 1  and  412 - 2  also share a second output reset transistor  438 B, a second output source follower transistor  430 B, and a second row select transistor  432 B at the output tap coupled to second bitline  442 B. Similarly, the portions of pixel circuits  412 - 3  and  412 - 4  also share a respective first output reset transistor  438 C, a first output source follower transistor  430 C, and a first row select transistor  432 C at the output tap coupled to a respective first bitline  442 C, and a respective second output reset transistor  438 D, a second output source follower transistor  430 D, and a second row select transistor  432 D at the output tap coupled to respective second bitline  442 D. 
     As such, it is appreciated that the photodiode  418 - 1  and the photodiode  418 - 2  of pixel circuit portions  412 - 1  and  412 - 2  form a 2×1 arrangement from which non-binned outputs may be read out individually in one configuration from each photodiode  418 - 1  and  418 - 2  through respective readout transistors  436 A 1 / 436 B 1 ,  436 A 2 / 436 B 2  of pixel circuit portions  412 - 1  and  412 - 2  and the respective output taps coupled to first and second bitlines  442 A and  442 B. Similarly, the photodiode  418 - 3  and the photodiode  418 - 4  of pixel circuit portions  412 - 3  and  412 - 4  also form a 2×1 arrangement from which non-binned outputs may be read out individually from each photodiode  418 - 3  and  418 - 4  through respective readout transistors  436 C 1 / 436 D 1 ,  436 C 2 / 436 D 2  of pixel circuit portions  412 - 3  and  412 - 4  of pixel circuit portions  412 - 3  and  412 - 4  and the respective output taps coupled to the respective first and second bitlines  442 C and  442 D. 
     The example depicted in  FIG.  4    also illustrates that a first binning transistor  440 A is coupled between the first floating diffusion FDA  422 A 1  of the upper portion of the pixel circuit  412 - 1  and the first floating diffusion FDA  422 A 2  of the lower portion of the pixel circuit  412 - 2 . A second binning transistor  440 B is coupled between the second floating diffusion FDB  422 B 1  of the upper portion of the pixel circuit  412 - 1  and the second floating diffusion FDB  422 B 2  of the lower portion of the pixel circuit  412 - 2 . Similarly, a respective first binning transistor  440 C is coupled between the first floating diffusion FDC  422 C 1  of the upper portion of the pixel circuit  412 - 3  and the first floating diffusion FDC  422 C 2  of the lower portion of the pixel circuit  412 - 4 . A respective second binning transistor  440 D is coupled between the second floating diffusion FDD  422 D 1  of the upper portion of the pixel circuit  412 - 3  and the second floating diffusion FDD  422 D 2  of the lower portion of the pixel circuit  412 - 4 . 
     Therefore, in another configuration, the first and second binning transistors  440 A/ 440 C and  440 B/ 440 D may be turned ON, which couple together the first floating diffusions FDA  422 A 1 / 422 A 2  and FDC  422 C 1 / 422 C 2  and second floating diffusions FDB  422 B 1 / 422 B 2  and FDD  422 D 1 / 422 D 2 . As such, the portions of charge that are transferred from the photodiodes  418 - 1  and  418 - 2 , as well as the portions of charge that are transferred from photodiodes  418 - 3  and  418 - 4  are combined or binned in-pixel in the respective first floating diffusions FDA  422 A 1 / 422 A 2  and FDC  422 C 1 / 422 C 2  and second floating diffusions FDB  422 B 1 / 422 B 2  and  422 D 1 / 422 D 2  in accordance with the teachings of the present invention. In the various examples, the binned signals may then be read out from the respective first floating diffusions FDA  422 A 1 / 422 A 2  and FDC  422 C 1 / 422 C 2  and second floating diffusions FDB  422 B 1 / 422 B 2  and  422 D 1 / 422 D 2  through any one of the respective memory nodes  434 A 1 / 434 A 2 ,  434 B 1 / 434 B 2  and  434 C 1 / 434 C 2 ,  434 D 1 / 434 D 2 , corresponding readout transistors  436 A 1 / 436 A 2 ,  436 B 1 / 436 B 2  and  436 C 1 / 436 C 2 ,  436 D 1 / 436 D 2 , and corresponding output tap. In this configuration, 2×1 binning of the signals from photodiodes  418 - 1 / 418 - 2  and/or  418 - 3 / 418 - 4  is realized in accordance with the teachings of the present invention. 
     In yet another configuration, the binning transistors may be turned OFF (e.g., deactivated), but both readout transistors  436 A/ 436 A 2 ,  436 B 1 / 436 B 2 ,  436 C 1 / 436 C 2 , or  436 D 1 / 436 D 2  per output tap may be turned ON simultaneously during a readout, which enables the binning of charge information that is sampled and held in the multiple memory nodes C 1 A/C 2 A, C 1 B/C 2 B, C 1 C/C 2 C, or C 1 D/C 2 D to be combined or binned in-pixel at the respective gate terminals of the respective output source follower transistors  430 A/ 430 B or  430 C/ 430 D in accordance with the teachings of the present invention. Thus, in this configuration, 2×1 binning of the signals from photodiodes  418 - 1 / 418 - 2  and/or  418 - 3 / 418 - 4  is also realized in accordance with the teachings of the present invention. 
     In still another configuration, the signals that are on the bitlines  442 A,  442 B,  442 C,  442 D may also be configured to be combined, which enables the binning of the signals on that are carried on the respective bitlines  442 A,  442 B,  442 C,  442 D. For instance, in an example in which pixel circuit portions  412 - 1 ,  412 - 2 ,  412 - 3 ,  412 - 4  are arranged in the same row of pixel array  410 , first bitlines  442 A and  442 C and second bitlines  442 B and  442 D may be combined or coupled together, as indicated with the dashed-line in  FIG.  4   , to combine or horizontally bin the signals that are on the bitlines  442 A,  442 B,  442 C,  442 D. In this configuration, if non-binned signals corresponding to photodiode  418 - 1  and  418 - 3 , or if non-binned signals corresponding to photodiode  418 - 2  and  418 - 4 , are being output to the bitlines  442 A,  442 B,  442 C,  442 D, then 1×2 binning of the signals from photodiodes  418 - 1 / 418 - 3  or  418 - 2 / 418 - 4  is also realized in accordance with the teachings of the present invention. Similarly, in this configuration, if binned signals corresponding to photodiode  418 - 1 / 418 - 2  and  418 - 3 / 418 - 4  are being output to the bitlines  442 A,  442 B,  442 C,  442 D, then 2×2 binning of the signals from photodiodes  418 - 1 / 418 - 3  or  418 - 2 / 418 - 4  is also realized in accordance with the teachings of the present invention. 
     In yet another configuration, in an example in which pixel circuit portions  412 - 1 ,  412 - 2 ,  412 - 3 ,  412 - 4  are arranged in the same column of pixel array  410 , first bitlines  442 A and  442 C are the same bitline, and second bitlines  442 B and  442 D are the same bitline, which may also be with the dashed-line in  FIG.  4   , to combine or average or vertically bin the signals that are received on the bitlines  442 A/ 442 C and  442 B/ 442 D. In this arrangement, if binned signals corresponding to photodiodes  418 - 1 / 418 - 2  and  418 - 3 / 418 - 4  are being output to the bitlines  442 A/ 442 C and  442 B/ 442 D, then 1×4 binning of the signals from photodiodes  418 - 1 / 418 - 2  and  418 - 3 / 418 - 4  is also realized in accordance with the teachings of the present invention. 
     Therefore, in various examples, the signals that are on the bitlines may be combined using a variety of techniques such as for example coupling multiple row select transistors in different rows of the pixel array to the same bitline to realize vertical binning, or coupling together multiple bitlines from different columns or charge sharing of sampled signals at the column level of the pixel array to realize horizontal binning, or summing together the signals as input signals to an analog to digital converter (ADC), or combining the signals in digital domain, etc. 
       FIGS.  5 A- 5 E  are timing diagrams illustrating signals in an example time-of-flight sensing system in various different example binning configurations in accordance with the teachings of the present invention. It is appreciated that the signals illustrated in  FIGS.  5 A- 5 E  may be examples of signals found in example time-of-flight pixel circuits (e.g.,  412 - 1 / 412 - 2 ) as shown in  FIG.  4    or in a time-of-flight sensing system  100  as shown in  FIG.  1   , and that similarly named and numbered elements described above are coupled and function similarly below. In the examples described below, some corresponding elements from  FIG.  4    may therefore be referred to for explanation purposes. 
     For instance, the timing diagram depicted in  FIG.  5 A  illustrates an example of a time-of-flight sensing system that is configured for binning and no pipelining of integration and readout operations. In the example, the binning signal B  540  is deactivated such that the binning transistors are deactivated. However, as shown at time T 0 , readout signals RA 1 / 2   536 A and RB 1 / 2   536 B are activated and sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B are deactivated. As such, with both readout transistors controlled by the readout signals RA 1 / 2   536 A and RB 1 / 2   536 B turned ON simultaneously, a binned readout period occurs during which the charges that are sampled and held in both memory nodes C 1 A/C 2 A and C 1 B/C 2 B are combined or binned in-pixel at the gate terminals of the respective output source follower transistors (e.g.,  430 A/ 430 B). As such, it is appreciated that the readout of the charges from the photodiodes (e.g.,  418 - 1 / 418 - 2  or  418 - 3 / 418 - 4 ) are binned. At the same time, the sample and hold transistors controlled with sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B are deactivated. Thus, the reset signals DAB  524  are activated to reset the floating diffusions FDA/FDB while the modulation signals TXA/B  520  are also deactivated. 
     With the floating diffusions FDA/FDB reset by reset signals DAB  524 , the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B are activated at time T 1 . At time T 2 , an integration period begins with the modulation signals TXA/B  520  activated, the reset signals DAB  524  deactivated, and the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B activated. During the integration period, the charges photogenerated in the photodiodes are sampled and held into the memory nodes C 1 A/C 2 A and C 1 B/C 2 B in response to the modulation signals TXA/B  520 . As mentioned, no pipelined operation occurs in the example depicted in  FIG.  5 A , and as such, the readout signals RA 1 / 2   536 A and RB 1 / 2   536 B are deactivated during the integration periods such that no readout operations occur during integration periods. In addition, the output reset signals RSTA/B  538  are also activated at time T 2  to reset or precharge the gate terminals of the output source follower transistors while no readout operation occurs. 
     At time T 3 , another readout period begins as the integration period ends. As such, the modulation signals TXA/B  520  are deactivated, the reset signals DAB  524  are activated, the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B are deactivated, the readout signals RA 1 / 2   536 A and RB 1 / 2   536 B are activated, and the output reset signals RSTA/B  538  are deactivated as shown. Similar to the readout operation that occurred at time T 0 , both readout signals RA 1 / 2   536 A and RB 1 / 2   536 B are activated simultaneously, such that a binned readout period occurs during which the charges that are sampled and held in both memory nodes C 1 A/C 2 A and C 1 B/C 2 B are combined or binned in-pixel at the gate terminals of the respective output source follower transistors (e.g.,  430 A/ 430 B). 
     With the floating diffusions FDA/FDB reset by reset signals DAB  524 , the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B are activated at time T 4 . At time T 5 , another integration period begins with the modulation signals TXA/B  520  activated, the reset signals DAB  524  deactivated, and the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B activated. During the integration period, the charges photogenerated in the photodiodes (e.g.,  418 ) are sampled and held into the memory nodes C 1 A/C 2 A and C 1 B/C 2 B in response to the modulation signals TXA/B  520 . The readout signals RA 1 / 2   536 A and RB 1 / 2   536 B are deactivated such that no readout operation occurs. In addition, the output reset signals RSTA/B  538  are also activated at time T 5  to reset or precharge the gate terminals of the output source follower transistors while no readout operation occurs. 
     At time T 6 , another readout period begins as the integration period ends. As such, the modulation signals TXA/B  520  are deactivated, the reset signals DAB  524  are activated, the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B are deactivated, the readout signals RA 1 / 2   536 A and RB 1 / 2   536 B are activated, and the output reset signals RSTA/B  538  are deactivated as shown. Similar to the readout operation that occurred at time T 0  and at time T 3 , both readout signals RA 1 / 2   536 A and RB 1 / 2   536 B are activated simultaneously, such that a binned readout period occurs during which the charges that are sampled and held in both memory nodes C 1 A/C 2 A and C 1 B/C 2 B are combined or binned in-pixel at the gate terminals of the respective output source follower transistors (e.g.,  430 A/ 430 B). 
     With the floating diffusions FDA/FDB reset by reset signals DAB  524 , the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B are activated at time T 7 . At time T 8 , another integration period begins and the readout period ends with the modulation signals TXA/B  520  activated, the reset signals DAB  524  deactivated, the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B activated, the readout signals RA 1 / 2   536 A and RB 1 / 2   536 B deactivated, and the output reset signals RSTA/B  538  activated. 
     The timing diagram depicted in  FIG.  5 B  illustrates an example of a time-of-flight sensing system that is configured for no binning and no pipelining of integration and readout operations. In the example, the binning signal B  540  is deactivated such that the binning transistors are deactivated. At time T 0 , the reset signals DAB  524  are activated to reset the floating diffusions FDA/FDB while the modulation signals TXA/B  520  are also deactivated. In addition, the readout signals RA 1   536 A 1 , RA 2   536 A 2 , RB 1   536 B 1 , RB 2   536 B 2  are deactivated to deactivate the readout transistors while the output reset signals RSTA  538 A and RSTB  538 B are activated to reset or precharge the gate terminals of the output source follower transistors while no readout operation occurs. At this time, the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B are all deactivated to deactivate all of the sample and hold transistors (e.g.,  426 A 1 / 426 A 2 / 426 B 1 / 426 B 2 ). 
     With the floating diffusions FDA/FDB reset by reset signals DAB  524 , the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B are activated at time T 1 . At time T 2 , an integration period begins with the modulation signals TXA/B  520  activated, the reset signals DAB  524  deactivated, and the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B activated. During the integration period, the charges photogenerated in the photodiodes are sampled and held into the memory nodes C 1 A/C 2 A and C 1 B/C 2 B in response to the modulation signals TXA/B  520 . As mentioned, no pipelined operation occurs in the example depicted in  FIG.  5 B , and as such, the readout signals RA 1   536 A 1 , RA 2   536 A 2 , RB 1   536 B 1 , RB 2   536 B 2  are deactivated during the integration periods such that no readout operations occur during integration periods. In addition, the output reset signals RSTA  538 A and RSTB  538 B are also activated at time T 2  to reset or precharge the gate terminals of the output source follower transistors while no readout operation occurs. 
     At time T 3 , the integration period ends, and thus, the modulation signals TXA/B  520  are deactivated and the reset signals DAB  524  are activated to reset the floating diffusions FDA/FDB while the modulation signals TXA/B  520  are also deactivated. At this time, a readout period begins for the charge from the photodiode (e.g.,  418 - 1 ) that is sampled and held into the memory node (e.g., C 1 A) that is coupled to the readout transistor (e.g.,  436 A 1 ) that is controlled in response to the readout signal RA 1   536 A 1 , which is turned ON at time T 3 . As mentioned, no binning occurs in the example depicted in  FIG.  5 B , and as such, the other readout transistor (e.g.,  436 A 2 ) that is coupled to the same output source follower (e.g.,  432 A) remains turned OFF in response to readout signal RA 2   536 A 2  in the depicted example. 
     Once the charge that is sampled and held in the memory node (e.g., C 1 A) is read out, the output reset signal RSTA  538 A is pulsed as shown before time T 4 , and at time T 4 , the readout period for the charge that is sampled and held into the memory node (e.g., C 1 A) ends and the next readout period begins for the charge from the photodiode (e.g.,  418 - 2 ) that is sampled and held into the next memory node (e.g., C 2 A). As such, at time T 4 , the readout signal RA 1   536 A 1  is deactivated and the readout signal RA 2   536 A 2  is activated. 
     Once the charge that is sampled and held in the memory node (e.g., C 2 A) is read out, the output reset signal RSTA  538 A is turned ON as shown before time T 5 , and at time T 5 , the readout period for the charge from the photodiode (e.g.,  412 - 2 ) that is sampled and held into the memory node (e.g., C 2 A) ends and the next readout period begins for the charge from the photodiode (e.g.,  418 - 1 ) that is sampled and held into the next memory node (e.g., C 1 B) begins. As such, at time T 5 , the readout signal RA 2   536 A 2  is deactivated, the readout signal RB 1   536 B 1  is activated, and the output reset signal RSTB  538 B is deactivated. 
     Once the charge that is sampled and held in the memory node (e.g., C 1 B) is read out, the output reset signal RSTB  538 B is pulsed as shown before time T 6 , and at time T 6 , the next readout period for the charge from the photodiode (e.g.,  418 - 1 ) that is sampled and held into the memory node (e.g., C 1 B) ends and the next readout period begins for the charge from the photodiode (e.g.,  418 - 2 ) that is sampled and held into the next memory node (e.g., C 2 B). As such, at time T 6 , the readout signal RB 1   536 B 1  is deactivated and the readout signal RB 2   536 B 2  is activated. 
     Once the charge from the photodiode (e.g.,  418 - 2 ) that is sampled and held in the memory node (e.g., C 2 B) is read out, the output reset signal RSTB  538 B is turned ON as shown before time T 7 , and at time T 7 , the readout period ends as readout signal RB 2   536 B 2  are deactivated and the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B are activated. 
     The next integration period begins at time T 8  with the modulation signals TXA/B  520  activated, the reset signals DAB  524  deactivated, and the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B activated. During the integration period, the charges photogenerated in the photodiodes are sampled and held into the memory nodes C 1 A/C 2 A and C 1 B/C 2 B in response to the modulation signals TXA/B  520 . The readout signals RA 1   536 A 1 , RA 2   536 A 2 , RB 1   536 B 1 , RB 2   536 B 2  are deactivated during the integration period such that no readout operations occur during integration period. In addition, the output reset signals RSTA  538 A and RSTB  538 B also remain activated at time T 8  to reset or precharge the gate terminals of the output source follower transistors while no readout operation occurs. 
     The timing diagram depicted in  FIG.  5 C  illustrates an example of a time-of-flight sensing system that is configured for no binning, but does include pipelined operations of readout operations that can occur from one tap while integration occurs to sample and hold charge into the memory nodes that are coupled to the other tap of the pixel circuits. In the example, the binning signal B  540  is deactivated such that the binning transistors are deactivated. At time T 0 , the reset signal DA  524 A is activated to reset the floating diffusions FDA. At this time, the output reset signals RSTA  538 A and RSTB  538 B are also activated to reset or precharge the gate terminals of the output source follower transistors (e.g.,  430 A/ 430 B). The readout transistors are turned OFF with readout signals RA 1   536 A 1 , RA 2   536 A 2 , RB 1   536 B 1 , RB 2   536 B 2  deactivated as shown while no readout operation occurs. At this time, the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B are all deactivated to deactivate all of the sample and hold transistors (e.g.,  426 A 1 / 426 A 2 / 426 B 1 / 426 B 2 ). 
     With the floating diffusion FDA reset by reset signal DA  524 A, the sample and hold signals SA 1 / 2   526 A are activated before time T 1  to activate the sample and hold transistors (e.g.,  426 A 1 / 426 A 2 ) that are coupled to the memory nodes C 1 A/C 2 A. At time T 1 , an integration period begins to sample and hold charge into the memory nodes C 1 A/C 2 A with the modulation signals TXA/B  520  activated, the reset signal DA  524 A deactivated, the reset signal DB  524 B activated, sample and hold signals SA 1 / 2   526 A activated, and sample and hold signals SB 1 / 2   526 B deactivated. During the integration period, the charges photogenerated in the photodiodes are sampled and held into the memory nodes C 1 A/C 2 A in response to the modulation signals TXA/B  520 . As mentioned, pipelined operation with no binning occurs in the example depicted in  FIG.  5 C , and as such, the readout signal RB 1   536 B 1  is activated while the readout signal RB 2   536 B 2  is deactivated. At this time, the readout signals RA 1   536 A 1  and RA 2   536 A 2  are also deactivated such that only the charge from photodiode  418 - 1  that is sampled and held in memory node C 1 B is read out while the charges in memory nodes C 2 B, C 1 A, and C 2 A are not read out. 
     Once the charge from photodiode  418 - 1  that is sampled and held in the memory node C 1 B is read out, the output reset signal RSTB  538 B is pulsed as shown before time T 2 , and at time T 2 , the readout period for the charge from photodiode  418 - 1  that is sampled and held into the memory node C 1 B ends and the next readout period begins for the charge from the photodiode  418 - 2  that is sampled and held into the next memory node C 2 B. As such, at time T 2 , the readout signal RB 1   536 B 1  is deactivated and the readout signal RB 2   536 B 2  is activated. 
     Once the charge that is sampled and held in the memory node C 2 B is read out, the output reset signal RSTB  538 B is turned ON as shown before time T 3 , and at time T 3 , the readout period for the charge from the photodiode  418 - 2  that is sampled and held into the memory node C 2 B ends and the readout signal RB 2   536 B 2  is deactivated. At this time, the integration period ends and the modulation signals TXA/B  520  are deactivated, the reset signal DA  524 A is activated, the reset signal DB  524 B remains activated, and the output reset signals RSTA  538 A and RSTB  538 B are activated to reset the floating diffusions FDA/FDB and reset the gate terminals of the output source follower transistors  430 A/ 430 B while the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B and the readout signals RA 1   536 A 1 , RA 2   536 A 2 , RB 1   536 B 1 , RB 2   536 B 2  are all deactivated. 
     With the floating diffusion FDB reset by reset signal DB  524 B, the sample and hold signals SB 1 / 2   526 B are activated before time T 4  to activate the sample and hold transistors (e.g.,  426 B 1 / 426 B 2 ) that are coupled to the memory nodes C 1 B/C 2 B. At time T 4 , the next integration period begins to sample and hold charge into the memory nodes C 1 B/C 2 B with the modulation signals TXA/B  520  activated, the reset signal DB  524 B deactivated, the reset signal DA  524 A activated, sample and hold signals SB 1 / 2   526 B activated, and sample and hold signals SA 1 / 2   526 A deactivated. During the integration period, the charges photogenerated in the photodiodes are sampled and held into the memory nodes C 1 B/C 2 B in response to the modulation signals TXA/B  520 . As mentioned, pipelined operation with no binning occurs in the example depicted in  FIG.  5 C , and as such, the readout signal RA 1   536 A 1  is activated while the readout signal RA 2   536 A 2  is deactivated. At this time, the readout signals RB 1   536 B 1  and RB 2   536 B 2  are also deactivated such that only the charge from photodiode  418 - 1  that is sampled and held in memory node C 1 A is read out while the charges in memory nodes C 2 A, C 1 B, and C 2 B are not read out. 
     Once the charge from photodiode  418 - 1  that is sampled and held in the memory node C 1 A is read out, the output reset signal RSTA  538 A is pulsed as shown before time T 5 , and at time T 5 , the readout period for the charge from photodiode  418 - 1  that is sampled and held into the memory node C 1 A ends and the next readout period begins for the charge from the photodiode  418 - 2  that is sampled and held into the next memory node C 2 A. As such, at time T 5 , the readout signal RA 1   536 A 1  is deactivated and the readout signal RA 2   536 A 2  is activated. 
     Once the charge that is sampled and held in the memory node C 2 A is read out, the output reset signal RSTA  538 A is turned ON as shown before time T 6 , and at time T 6 , the readout period for the charge from the photodiode  418 - 2  that is sampled and held into the memory node C 2 A ends and the readout signal RA 2   536 B 2  is deactivated. At this time, the integration period ends and the modulation signals TXA/B  520  are deactivated, the reset signal DA  524 A remains activated, the reset signal DB  524 B is activated, and the output reset signals RSTA  538 A and RSTB  538 B are activated to reset the floating diffusions FDA/FDB and reset the gate terminals of the output source follower transistors  430 A/ 430 B while the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B and the readout signals RA 1   536 A 1 , RA 2   536 A 2 , RB 1   536 B 1 , RB 2   536 B 2  are all deactivated. 
     With the floating diffusion FDA reset by reset signal DA  524 A, the sample and hold signals SA 1 / 2   526 A are activated before time T 7  to activate the sample and hold transistors (e.g.,  426 A 1 / 426 A 2 ) that are coupled to the memory nodes C 1 A/C 2 A. At time T 7 , the next integration period begins to sample and hold charge into the memory nodes C 1 A/C 2 A with the modulation signals TXA/B  520  activated, the reset signal DA  524 A deactivated, the reset signal DB  524 B activated, sample and hold signals SA 1 / 2   526 A activated, and sample and hold signals SB 1 / 2   526 B deactivated. During the integration period, the charges photogenerated in the photodiodes are sampled and held into the memory nodes C 1 A/C 2 A in response to the modulation signals TXA/B  520 . As mentioned, pipelined operation with no binning occurs in the example depicted in  FIG.  5 C , and as such, the readout signal RB 1   536 B 1  is activated while the readout signal RB 2   536 B 2  is deactivated. At this time, the readout signals RA 1   536 A 1  and RA 2   536 A 2  are also deactivated such that only the charge from photodiode  418 - 1  that is sampled and held in memory node C 1 B is read out while the charges in memory nodes C 2 B, C 1 A, and C 2 A are not read out. 
     Once the charge that is sampled and held in the memory node C 1 B is read out, the output reset signal RSTB  538 B is pulsed as shown before time T 8 , and at time T 8 , the readout period for the charge from the photodiode (e.g.,  412 - 1 ) that is sampled and held into the memory node C 1 B ends and the next readout period begins for the charge from the photodiode (e.g.,  418 - 2 ) that is sampled and held into the next memory node C 2 B begins. As such, at time T 8 , the readout signal RB 1   536 B 1  is deactivated, the readout signal RB 2   536 B 2  is activated, and the output reset signal RSTB  538 B is deactivated. 
     Once the charge that is sampled and held in the memory node C 2 B is read out, the output reset signal RSTB  538 B is turned ON as shown before time T 9 , and at time T 9 , the readout period for the charge from the photodiode  418 - 2  that is sampled and held into the memory node C 2 B ends and the readout signal RB 2   536 B 2  is deactivated. At this time, the integration period ends and the modulation signals TXA/B  520  are deactivated, the reset signal DA  524 A is activated, the reset signal DB  524 B remains activated, and the output reset signals RSTA  538 A and RSTB  538 B are activated to reset the floating diffusions FDA/FDB and reset the gate terminals of the output source follower transistors  430 A/ 430 B while the sample and hold signals SA 1 / 2   526 A and SB 1 / 2   526 B and the readout signals RA 1   536 A 1 , RA 2   536 A 2 , RB 1   536 B 1 , RB 2   536 B 2  are all deactivated. 
     The timing diagram depicted in  FIG.  5 D  illustrates an example of a time-of-flight sensing system that is configured for binning as well as pipelined operations of readout operations that can occur from one tap while integration occurs to sample and hold charge into the memory nodes that are coupled to the other tap of the pixel circuits. In the example, the binning signal B  540  is deactivated such that the binning transistors are deactivated. At time T 0 , the reset signal DA  524 A is activated to reset the floating diffusions FDA. At this time, the output reset signals RSTA  538 A and RSTB  538 B are also activated to reset or precharge the gate terminals of the output source follower transistors (e.g.,  430 A/ 430 B). The readout transistors are turned OFF with readout signals RA 1   536 A 1 , RA 2   536 A 2 , RB 1   536 B 1 , RB 2   536 B 2  deactivated as shown while no readout operation occurs. At this time, the sample and hold signals SA 1   526 A 1 , SA 2   526 A 2 , SB 1   526 B 1 , SB 2   526 B 2  are all deactivated to deactivate all of the sample and hold transistors (e.g.,  426 A 1 / 426 A 2 / 426 B 1 / 426 B 2 ). 
     With the floating diffusion FDA reset by reset signal DA  524 A, the sample and hold signals SA 1 / 2   526 A are activated before time T 1  to activate the sample and hold transistors (e.g.,  426 A 1 / 426 A 2 ) that are coupled to the memory nodes C 1 A/C 2 A. At time T 1 , an integration period begins to sample and hold charge into the memory nodes C 1 A/C 2 A with the modulation signals TXA/B  520  activated, the reset signal DA  524 A deactivated, the reset signal DB  524 B activated, sample and hold signals SA 1 / 2   526 A activated, and sample and hold signals SB 1 / 2   526 B deactivated. During the integration period, the charges photogenerated in the photodiodes are sampled and held into the memory nodes C 1 A/C 2 A in response to the modulation signals TXA/B  520 . As mentioned, pipelined operation with binning occurs in the example depicted in  FIG.  5 D , and as such, both readout signal RB 1   536 B 1  and readout signal RB 2   536 B 2  are activated simultaneously at time T 1  as shown. At this time, the output reset signal RSTB  538 B as well as both the readout signals RA 1   536 A 1  and RA 2   536 A 2  are all deactivated. As such, the charges from both photodiodes  418 - 1 / 418 - 2  that are sampled and held in the memory nodes C 1 B/C 2 B are combined or binned at the gate terminal of the output source follower transistor  430 B to provide in-pixel binning of the charges from photodiodes  418 - 1 / 418 - 2  at the output coupled to the output source follower transistor  430 B while integration occurs at memory nodes C 1 A/C 2 A. 
     At time T 2 , the readout of the charges that are sampled and held in memory nodes C 1 B/C 2 B ends as the readout signal RB 1   536 B 1  and readout signal RB 2   536 B 2  are deactivated and the output reset signal RSTB  538 B is reactivated. 
     At time T 3 , the integration period ends as the modulation signals TXA/B  520  and sample and hold signals SA 1 / 2   526 A are deactivated, and the reset signal DA  524 A is reactivated. 
     With the floating diffusion FDB reset by reset signal DB  524 B, the sample and hold signals SB 1 / 2   526 B are activated before time T 4  to activate the sample and hold transistors (e.g.,  426 B 1 / 426 B 2 ) that are coupled to the memory nodes C 1 B/C 2 B. At time T 4 , the next integration period begins to sample and hold charge into the memory nodes C 1 B/C 2 B with the modulation signals TXA/B  520  activated, the reset signal DA  524 A activated, the reset signal DB  524 B deactivated, sample and hold signals SA 1 / 2   526 A deactivated, and sample and hold signals SB 1 / 2   526 B activated. During the integration period, the charges photogenerated in the photodiodes are sampled and held into the memory nodes C 1 B/C 2 B in response to the modulation signals TXA/B  520 . As mentioned, pipelined operation with binning occurs in the example depicted in  FIG.  5 D , and as such, both readout signal RA 1   536 A 1  and readout signal RA 2   536 A 2  are activated simultaneously at time T 4  as shown. At this time, the output reset signal RSTA  538 A as well as both the readout signals RB 1   536 B 1  and RB 2   536 B 2  are all deactivated. As such, the charges from both photodiodes  418 - 1 / 418 - 2  that are sampled and held in the memory nodes C 1 A/C 2 A are combined or binned at the gate terminal of the output source follower transistor  430 A to provide in-pixel binning of the charges from photodiodes  418 - 1 / 418 - 2  at the output coupled to the output source follower transistor  430 A while integration occurs at memory nodes C 1 B/C 2 B. 
     At time T 5 , the readout of the charges that are sampled and held in memory nodes C 1 A/C 2 A ends as the readout signal RA 1   536 A 1  and readout signal RA 2   536 A 2  are deactivated and the output reset signal RSTA  538 A is reactivated. 
     At time T 6 , the integration period ends as the modulation signals TXA/B  520  and sample and hold signals SB 1 / 2   526 B are deactivated, and the reset signal DB  524 B is reactivated. 
     With the floating diffusion FDA reset by reset signal DA  524 A, the sample and hold signals SA 1 / 2   526 A are activated before time T 7  to activate the sample and hold transistors (e.g.,  426 A 1 / 426 A 2 ) that are coupled to the memory nodes C 1 A/C 2 A. At time T 7 , the next integration period begins to sample and hold charge into the memory nodes C 1 A/C 2 A with the modulation signals TXA/B  520  activated, the reset signal DA  524 A deactivated, the reset signal DB  524 B activated, sample and hold signals SA 1 / 2   526 A activated, and sample and hold signals SB 1 / 2   526 B deactivated. During the integration period, the charges photogenerated in the photodiodes are sampled and held into the memory nodes C 1 A/C 2 A in response to the modulation signals TXA/B  520 . As mentioned, pipelined operation with binning occurs in the example depicted in  FIG.  5 D , and as such, both readout signal RB 1   536 B 1  and readout signal RB 2   536 B 2  are activated simultaneously at time T 7  as shown. At this time, the output reset signal RSTB  538 B as well as both the readout signals RA 1   536 A 1  and RA 2   536 A 2  are all deactivated. As such, the charges from both photodiodes  418 - 1 / 418 - 2  that are sampled and held in the memory nodes C 1 B/C 2 B are combined or binned at the gate terminal of the output source follower transistor  430 B to provide in-pixel binning of the charges from photodiodes  418 - 1 / 418 - 2  at the output coupled to the output source follower transistor  430 B while integration occurs at memory nodes C 1 A/C 2 A. 
     At time T 8 , the readout of the charges that are sampled and held in memory nodes C 1 B/C 2 B ends as the readout signal RB 1   536 B 1  and readout signal RB 2   536 B 2  are deactivated and the output reset signal RSTB  538 B is reactivated. 
     At time T 9 , the integration period ends as the modulation signals TXA/B  520  and sample and hold signals SA 1 / 2   526 A are deactivated, and the reset signal DA  524 A is reactivated. 
     The timing diagram depicted in  FIG.  5 E  illustrates another example of a time-of-flight sensing system that is configured for binning as well as pipelined operations of readout operations that can occur from one tap while integration occurs to sample and hold charge into the memory nodes that are coupled to the other tap of the pixel circuits. In the example, the binning signal B  540  is activated such that the binning transistors are deactivated. As such, the floating diffusions FDA  422 A 1  and FDA  422 A 2  are coupled together through binning transistor  440 A. Similarly, the floating diffusions FDB  422 B 1  and FDB  422 B 2  are coupled together through binning transistor  440 B. 
     At time T 0 , the reset signals DA  524 A and DB  524 B are activated to reset the all of floating diffusions FDA and FDB and the output reset signals RSTA  538 A and RSTB  538 B are also activated to reset or precharge the gate terminals of the output source follower transistors (e.g.,  430 A/ 430 B). The readout transistors are turned OFF with readout signals RA 1   536 A 1 , RA 2   536 A 2 , RB 1   536 B 1 , RB 2   536 B 2  deactivated as shown while no readout operation occurs. At this time, the sample and hold signals SA 1   526 A 1 , SA 2   526 A 2 , SB 1   526 B 1 , SB 2   526 B 2  are all deactivated to deactivate all of the sample and hold transistors (e.g.,  426 A 1 / 426 A 2 / 426 B 1 / 426 B 2 ). 
     With the floating diffusions FDA and FDB reset by reset signal DA  524 A and reset signal DB  524 B, the sample and hold signals SA 1   526 A 1  and SB 1   526 B 1  are activated before time T 1  to activate the sample and hold transistors (e.g.,  426 A 1 / 426 B 1 ) that are coupled to the memory nodes C 1 A/C 1 B. At time T 1 , an integration period begins to sample and hold charge into the memory nodes C 1 A/C 1 B with the modulation signals TXA/B  520  activated, the reset signal DA  524 A deactivated, the reset signal DB  524 B deactivated, sample and hold signal SA 1   526 A 1  activated, sample and hold signal SA 2   526 A 2  deactivated, sample and hold signal SB 1   526 B 1  activated, and sample and hold signal SB 2   526 B 2  deactivated. During the integration period, the charges photogenerated in both photodiodes  418 - 1 / 418 - 2  are sampled and held into the memory nodes C 1 A/C 1 B in response to the modulation signals TXA/B  520 . As such, the charges from both photodiodes  418 - 1 / 418 - 2  are combined or binned with the binning transistors  440 A/ 440 B turned ON. The binned charges are sampled and held into the memory nodes C 1 A/C 1 B. As mentioned, pipelined operation with binning occurs in the example depicted in  FIG.  5 E , and as such, both readout signal RA 2   536 A 2  and readout signal RB 2   536 B 2  are activated simultaneously at time T 1  as shown. At this time, the output reset signal RSTA  538 A as well as output reset signal RSTB  538 B are deactivated. The binned charge that was previously sampled and held in memory node C 2 A from photodiodes  418 - 1 / 418 - 2  is read out through output source follower transistor  430 A and the binned charge that was previously sampled and held in memory node C 2 B from photodiodes  418 - 1 / 418 - 2  is read out through output source follower transistor  430 B at this time. 
     At time T 2 , the readout of the binned charges that are sampled and held in memory nodes C 2 A/C 2 B ends as the readout signal RA 2   536 A 2  and readout signal RB 2   536 B 2  are deactivated and the output reset signals RSTA  538 A and RSTB  538 B are reactivated. 
     At time T 3 , the integration period ends as the modulation signals TXA/B  520  and sample and hold signals SA 1   526 A 1  and SB 1   526 B 1  are deactivated, and the reset signals DA  524 A and DB  524 B are reactivated. 
     With the floating diffusions FDA and FDB reset by reset signal DA  524 A and reset signal DB  524 B, the sample and hold signals SA 2   526 A 2  and SB 2   526 B 2  are activated before time T 4  to activate the sample and hold transistors (e.g.,  426 A 2 / 426 B 2 ) that are coupled to the memory nodes C 2 A/C 2 B. At time T 4 , the next integration period begins to sample and hold charge into the memory nodes C 2 A/C 2 B with the modulation signals TXA/B  520  activated, the reset signal DA  524 A deactivated, the reset signal DB  524 B deactivated, sample and hold signal SA 1   526 A 1  deactivated, sample and hold signal SA 2   526 A 2  activated, sample and hold signal SB 1   526 B 1  deactivated, and sample and hold signals SB 2   526 B 2  activated. During the integration period, the charges photogenerated in both photodiodes  418 - 1 / 418 - 2  are sampled and held into the memory nodes C 2 A/C 2 B in response to the modulation signals TXA/B  520 . As such, the charges from both photodiodes  418 - 1 / 418 - 2  are combined or binned with the binning transistors  440 A/ 440 B turned ON. The binned charges are sampled and held into the memory nodes C 2 A/C 2 B. As mentioned, pipelined operation with binning occurs in the example depicted in  FIG.  5 E , and as such, both readout signal RA 1   536 A 1  and readout signal RB 1   536 B 1  are activated simultaneously at time T 4  as shown. At this time, the output reset signal RSTA  538 A as well as output reset signal RSTB  538 B are deactivated. The binned charge that was previously sampled and held in memory node C 1 A from photodiodes  418 - 1 / 418 - 2  is read out through output source follower transistor  430 A and the binned charge that was previously sampled and held in memory node C 1 B from photodiodes  418 - 1 / 418 - 2  is read out through output source follower transistor  430 B at this time. 
     At time T 5 , the readout of the binned charges that are sampled and held in memory nodes C 1 A/ 12 B ends as the readout signal RA 1   536 A 1  and readout signal RB 1   536 B 1  are deactivated and the output reset signals RSTA  538 A and RSTB  538 B are reactivated. 
     At time T 6 , the integration period ends as the modulation signals TXA/B  520  and sample and hold signals SA 2   526 A 2  and SB 2   526 B 2  are deactivated, and the reset signals DA  524 A and DB  524 B are reactivated. 
     With the floating diffusions FDA and FDB reset by reset signal DA  524 A and reset signal DB  524 B, the sample and hold signals SA 1   526 A 1  and SB 1   526 B 1  are activated before time T 7  to activate the sample and hold transistors (e.g.,  426 A 1 / 426 B 1 ) that are coupled to the memory nodes C 1 A/C 1 B. At time T 7 , the next integration period begins to sample and hold charge into the memory nodes C 1 A/C 1 B with the modulation signals TXA/B  520  activated, the reset signal DA  524 A deactivated, the reset signal DB  524 B deactivated, sample and hold signal SA 1   526 A 1  activated, sample and hold signal SA 2   526 A 2  deactivated, sample and hold signal SB 1   526 B 1  activated, and sample and hold signal SB 2   526 B 2  deactivated. During the integration period, the charges photogenerated in both photodiodes  418 - 1 / 418 - 2  are sampled and held into the memory nodes C 1 A/C 1 B in response to the modulation signals TXA/B  520 . As such, the charges from both photodiodes  418 - 1 / 418 - 2  are combined or binned with the binning transistors  440 A/ 440 B turned ON. The binned charges are sampled and held into the memory nodes C 1 A/C 1 B. As mentioned, pipelined operation with binning occurs in the example depicted in  FIG.  5 E , and as such, both readout signal RA 2   536 A 2  and readout signal RB 2   536 B 2  are activated simultaneously at time T 7  as shown. At this time, the output reset signal RSTA  538 A as well as output reset signal RSTB  538 B are deactivated. The binned charge that was previously sampled and held in memory node C 2 A from photodiodes  418 - 1 / 418 - 2  is read out through output source follower transistor  430 A and the binned charge that was previously sampled and held in memory node C 2 B from photodiodes  418 - 1 / 418 - 2  is read out through output source follower transistor  430 B at this time. 
     At time T 8 , the readout of the binned charges that are sampled and held in memory nodes C 2 A/C 2 B ends as the readout signal RA 2   536 A 2  and readout signal RB 2   536 B 2  are deactivated and the output reset signals RSTA  538 A and RSTB  538 B are reactivated. 
     At time T 9 , the integration period ends as the modulation signals TXA/B  520  and sample and hold signals SA 1   526 A 1  and SB 1   526 B 1  are deactivated, and the reset signals DA  524 A and DB  524 B are reactivated. 
     The above description of illustrated examples of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific examples of the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. 
     These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific examples disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.