Readout architecture for indirect time-of-flight sensing

Abstract

The present application relates to a readout architecture for indirect time-of-flight sensing. A time-of-flight sensor includes a pixel array of pixel circuits. A first subset of the pixel circuits is illuminated by reflected modulated light from a portion of an object. A second subset of the pixel circuits is not illuminated by the reflected modulated light. Each pixel circuit includes a floating diffusion that stores a portion of charge photogenerated in a photodiode in response to the reflected modulated light. A transfer transistor transfers the portion of charge from the photodiode to the floating diffusion in response to modulation by a phase modulation signal. A modulation driver block generates the phase modulation signal and is coupled to a light source that emits the modulated light toward the portion of the object. The modulation driver block synchronizes scanning of the modulated light emitted by the light source across the object with scanning of the first subset of the pixel circuits across the pixel array.

Description

Technical Field

[0001] The present disclosure relates generally to image sensors, and particularly, but not exclusively, to time-of-flight sensors. Background Art

[0002] As the popularity of three-dimensional (3D) applications continues to grow in areas such as imaging, movies, games, computers, user interfaces, facial recognition, object recognition, augmented reality and the like, interest in 3D cameras is increasing. A typical passive way to create a 3D image is to use multiple cameras to capture a stereoscopic or multiple images. Using stereoscopic images, objects in the image can be triangulated to create a 3D image. A shortcoming of this triangulation technique is that it is difficult to create a 3D image using a small device because a minimum separation distance must exist between each camera in order to create a 3D image. In addition, this technology is complex and therefore requires powerful computer processing capabilities to create a 3D image in real time.

[0003] For applications that require real-time 3D image acquisition, active depth imaging systems based on time-of-flight measurements are sometimes used. A time-of-flight camera typically uses a light source to direct light at an object, a sensor to detect the light reflected from the object, and a processing unit to calculate the distance to the object based on the round-trip time it takes for the light to reach and return from the object. Summary of the Invention

[0004] One aspect of the present disclosure provides a time-of-flight sensor comprising: a time-of-flight pixel array including a plurality of time-of-flight pixel circuits, wherein a first subset of the plurality of time-of-flight pixel circuits is configured to be illuminated by reflected modulated light from a portion of an object, and a second subset of the plurality of time-of-flight pixel circuits is configured not to be illuminated by the reflected modulated light from the portion of the object, wherein each of the time-of-flight pixel circuits comprises: a photodiode configured to photogenerate charge in response to the reflected modulated light incident on the photodiode; a first floating diffusion configured to store a first portion of the photogenerated charge in the photodiode; and a first transfer transistor configured to transfer the first portion of the charge from the photodiode to the first floating diffusion in response to modulation by a first phase modulation signal; and a modulation driver block configured to generate the first phase modulation signal, wherein the modulation driver block is coupled to a light source configured to emit the modulated light to the portion of the object, wherein the modulation driver block is configured to synchronize scanning of the modulated light emitted by the light source across the object with scanning of the first subset of the plurality of time-of-flight pixel circuits across the time-of-flight pixel array.

[0005] Another aspect of the present disclosure provides a time-of-flight sensing system comprising: a light source configured to emit modulated light toward a portion of an object; and a time-of-flight sensor configured to sense reflected modulated light from the object, wherein the time-of-flight sensor comprises: a time-of-flight pixel array comprising a plurality of time-of-flight pixel circuits, wherein a first subset of the plurality of time-of-flight pixel circuits is configured to be illuminated by the reflected modulated light from the object, and a second subset of the plurality of time-of-flight pixel circuits is configured not to be illuminated by the reflected modulated light from the object, wherein each of the time-of-flight pixel circuits comprises: a photodiode configured to respond to the reflected modulated light incident on the photodiode; photogenerated charge; a first floating diffusion configured to store a first portion of the charge generated by the photodiode; and a first transfer transistor configured to transfer the first portion of the charge from the photodiode to the first floating diffusion in response to modulation by a first phase modulation signal; and a modulation driver block configured to generate the first phase modulation signal, wherein the modulation driver block is configured to synchronize scanning of the modulated light across the object with scanning of the first subset of the plurality of time-of-flight pixel circuits across the time-of-flight pixel array, the first subset of the plurality of time-of-flight pixel circuits being configured to be illuminated by the reflected modulated light from the portion of the object. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] 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.

[0007] Figure 1 is a block diagram showing one example of a time-of-flight optical sensing system in accordance with the teachings of the present invention.

[0008] Figure 2 is a timing diagram showing an example of light pulses emitted from a light source relative to receipt of reflected light pulses and measurements made using various phase shifts in an example time-of-flight sensing system in accordance with the teachings of the present invention.

[0009] Figures 3A to 3F are diagrams of various instances of a time-of-flight pixel array of a time-of-flight sensor in accordance with the teachings of the present invention, on which the field of view for a given exposure is altered or programmed to include one or more fractional portions of the time-of-flight pixel array, the one or more fractional portions of the time-of-flight pixel array being scanned by an example time-of-flight light sensing system.

[0010] Figure 4is a schematic diagram illustrating one example of a time-of-flight pixel circuit included in a time-of-flight pixel array of a time-of-flight sensing system in accordance with the teachings of the present invention.

[0011] Figure 5A is a schematic diagram showing one example of a time-of-flight optical sensing system according to the teachings of the present invention.

[0012] Figure 5B is a schematic diagram showing another example of a time-of-flight optical sensing system according to the teachings of the present invention.

[0013] Figure 6 is a timing diagram showing one example of signals during integration and readout of one example of a time-of-flight optical sensing system in accordance with the teachings of the present invention.

[0014] Figure 7 is a schematic diagram illustrating another example of a time-of-flight pixel circuit included in a time-of-flight pixel array of a time-of-flight sensing system according to the teachings of the present invention.

[0015] Figure 8 is a schematic diagram showing yet another example of a time-of-flight optical sensing system according to the teachings of the present invention.

[0016] Throughout the several views of the drawings, corresponding reference symbols indicate corresponding components. Those skilled in the art will appreciate that the elements in the drawings are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some elements in the drawings may be exaggerated relative to other elements to help improve understanding of the various embodiments of the present invention. Additionally, common but well-understood elements that are useful or necessary in commercially feasible embodiments are generally not depicted to facilitate a more intuitive understanding of these various embodiments of the present invention. DETAILED DESCRIPTION

[0017] Examples of various embodiments of a time-of-flight sensing system with an indirect time-of-flight solution for a portion of a field of view are described herein. In the following description, numerous specific details are set forth to provide a thorough understanding of the examples. However, one skilled in the relevant art will recognize that the technology 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 to avoid obscuring certain aspects.

[0018] 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 multiple 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.

[0019] For ease of description, spatially relative terms (e.g., "below," "beneath," "above," "down," "above," "up," "top," "bottom," "left," "right," "center," "middle," and the like) may be used herein to describe the relationship of one element or feature relative to another element or feature, as illustrated in the figures. It should be understood that spatially relative terms are intended to encompass different orientations of the device in use or operation other than the orientation depicted in the figures. For example, if the device in the figures is rotated or flipped, an element described as being "below," "beneath," or "beneath" another element or feature would be oriented "above" the other element or feature. Thus, the exemplary terms "below" and "beneath" may encompass both above and below orientations. The device may be oriented in other ways (rotated ninety degrees or in other orientations), and the spatially relative descriptors used herein may be interpreted accordingly. Additionally, it should be understood that when an element is referred to as being "between" two other elements, it may be the only element between the two other elements, or one or more intervening elements may also be present.

[0020] Throughout this specification, several terms of the art are used. These terms are to have their ordinary meanings in the art, unless specifically defined herein or the context of their use clearly implies otherwise. It should be noted that element names and symbols are used interchangeably throughout this document (e.g., Si versus silicon); however, both have the same meaning.

[0021] As will be discussed, various examples of indirect time-of-flight sensing systems include a light source configured to emit modulated light toward an object. The modulated light is then reflected from the object back to a time-of-flight sensor, which includes a time-of-flight pixel array comprising a plurality of time-of-flight pixel circuits. In various examples, the time-of-flight sensor includes a modulation driver block that synchronizes the modulated light emitted from the light source with the time-of-flight pixel circuits included in the time-of-flight pixel array, which are configured to be illuminated by and read out from the reflected modulated light from the object.

[0022] In various instances, a first subset of time-of-flight pixel circuits included in a time-of-flight pixel array is configured to be enabled, while a second subset of time-of-flight pixel circuits included in the time-of-flight pixel array is configured to be disabled when sensing reflected modulated light from an object. In various instances, a first subset of time-of-flight pixel circuits included in the time-of-flight pixel array is configured to be illuminated by reflected modulated light from an object, while a second subset of time-of-flight pixel circuits included in the time-of-flight pixel array is configured not to be illuminated by reflected modulated light from an object. In various instances, the first subset of time-of-flight pixel circuits included in the time-of-flight pixel array that are configured to be illuminated by reflected modulated light from an object may be scanned across the time-of-flight pixel array until the entire frame is captured by the time-of-flight pixel array. In other instances, the first subset of time-of-flight pixel circuits included in the time-of-flight pixel array that are configured to be illuminated by reflected modulated light from an object may be randomly addressed and accessed to monitor or track an object and adjust an area of ​​interest in the time-of-flight pixel array.

[0023] As will be discussed, in various instances, the first subset of pixel circuits may include one or more linear regions of a pixel array included in a time-of-flight sensor (e.g., row(s) or column(s) in a time-of-flight pixel array), one or more point regions (e.g., randomly addressable contiguous regions of pixel circuits in a time-of-flight pixel array), and / or one or more non-contiguous regions (e.g., non-adjacent clusters of pixel circuits in a time-of-flight pixel array).

[0024] In operation, modulated light is reflected from a portion of an object and illuminates pixel circuits included in a first subset of pixel circuits included in a time-of-flight pixel array. Pixel circuits that are not illuminated by the reflected modulated light or that are not illuminated by the reflected modulated light may be included in a second subset of pixel circuits. Pixel circuits included in the second subset of pixel circuits may be deactivated, which reduces readout speed requirements and helps save power consumption and cost.

[0025] The object distance is determined in response to the measured phase of the modulation, which can be used to generate a 3D frame. As will be described in various examples, the demodulating pixel front end downconverts and / or mixes this waveform with a differential phase modulation signal that is applied to the transfer gates or transfer transistors of a fraction or subset of the indirect time-of-flight pixel circuits included in the time-of-flight pixel array for a given exposure.

[0026] In various examples, the differential phase modulated signal has the same frequency as the modulated light to enable homodyne detection by an indirect time-of-flight sensor. Using different phases in the differential phase modulated signal allows reconstruction of the encoded distance. In various examples, at least three independent measurements (e.g., subframes) are used to decode three unknowns: range / phase, reflectivity, and ambient light. Four phases are typically used (e.g., 0° / 180° and 90° / 270°).

[0027] It should be noted that phases that are 360° apart cannot be distinguished, which leads to ambiguity in the measurement. Therefore, the modulation frequency of the differential phase modulation signal is selected not to exceed the maximum modulation frequency in order to accommodate the desired depth range. However, a trade-off is that increasing the modulation frequency improves accuracy. Therefore, multiple frequencies are typically incorporated to resolve the ambiguity and still produce good accuracy. At each frequency, all ¾ phases need to be acquired.

[0028] To illustrate, Figure 1 is a block diagram showing one example of a time-of-flight light sensing system 100 in accordance with the teachings of the present invention. As shown in the depicted example, time-of-flight light sensing system 100 includes a light source 102 synchronized with a time-of-flight sensor including a pixel array 110 including a plurality of pixel circuits 112, and a control circuit 114 coupled to pixel array 110 and light source 102.

[0029] As shown in the example, light source 102 and pixel array 110 are positioned at a distance L from object 106. Light source 102 is configured to emit light 104 toward object 106. Reflected light 108 is directed from object 106 back to pixel array 110, as shown. Note that for explanation purposes, pixel array 110 and control circuitry 114 are not shown in FIG. Figure 1 However, it should be understood that the components of pixel array 110 and control circuitry 114 may be integrated onto the same integrated circuit chip or wafer in a non-stacked standard planar sensor.

[0030] As shown in the depicted example, light source 102 is configured to illuminate only portion 107 of object 106 at a time, such that portion 109 of object 106 is not illuminated by emitted light 104 from light source 102. In various examples, illuminated portion 107 can have various shapes (e.g., one or more line-shaped regions, one or more point-shaped regions, etc.) at a time for a given exposure. Thus, in accordance with the teachings of the present invention, reflected light 108 from object 106 illuminates only a corresponding subset 113 of pixel circuits 112 of pixel array 110, such that another subset 115 of pixel array 110 is not illuminated by reflected light 108 from object 106. In various examples, in accordance with the teachings of the present invention, illuminated portion 107 of object 106 can be scanned across object 106 such that the illuminated subset of pixel circuits 113 of pixel array 110 is correspondingly scanned across pixel array 110 in time-of-flight optical sensing system 100.

[0031] In the depicted example, the 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 made with an image sensor including a pixel array 110. In some examples, it should be understood that while the time-of-flight light sensing system 100 is capable of sensing 3D images, the time-of-flight light sensing system 100 can also be used to capture 2D images. In various examples, the time-of-flight light sensing system 100 can also be used to capture high dynamic range (HDR) images.

[0032] Continuing with the depicted example, each pixel circuit 112 of the pixel array 110 determines depth information for a corresponding portion of the object 106 so that a 3D image of the object 106 can be generated. As will be discussed, the depth information is determined by driving the transfer gate of each pixel circuit 112 with a differential phase modulated signal to measure the delay / phase difference between the emitted light 104 and the received reflected light 108 to indirectly determine the round-trip time for the light to propagate from the light source 102 to the object 106 and back to the pixel array 110 of the time-of-flight light sensing system 100. The depth information may be based on an electrical signal or charge photogenerated by a photodiode included in each pixel circuit 112, which is then transferred to a storage node and read out.

[0033] As illustrated, light source 102 is configured to emit light 104 toward object 106 within a distance L. Emitted light 104 then reflects from object 106 as reflected light 108 (e.g., reflected light waves / pulses), some of which propagates within distance L toward pixel array 110 of time-of-flight optical sensing system 100 and is incident as image light on pixel circuitry 112 of pixel array 110. Each pixel circuitry 112 included in pixel array 110 includes a photodetector (e.g., one or more photodiodes, avalanche photodiodes, or single-photon avalanche diodes, or the like) to detect reflected light 108 and convert the reflected light 108 into an electrical signal (e.g., electrons, image charge, etc.).

[0034] As shown in the depicted example, the round-trip time for emitted light 104 to travel from light source 102 to object 106 and then reflect back to pixel array 110 can be used to determine distance L using the following relationship in equations (1) and (2) below:

[0035]

[0036]

[0037] 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 it takes for light to travel to and from the object 106, as Figure 1 Thus, once the round trip time is known, the distance L can be calculated and then used to determine the depth information of the object 106.

[0038] As shown in the depicted example, control circuitry 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 a round-trip time. Determining the round-trip time can be based, at least in part, on a timing signal generated by control circuitry 114. For indirect time-of-flight (iTOF) measurements, the timing signal represents a delay / phase difference between a light wave / pulse when light source 102 emits light 104 and a light wave / pulse when a photodetector in pixel circuitry 112 detects reflected light 108.

[0039] In some examples, the time-of-flight optical sensing system 100 can be included in a device (e.g., a mobile phone, a tablet computer, a camera, etc.) having size and power constraints determined at least in part by the size of the device. Alternatively or additionally, the time-of-flight optical sensing system 100 can have specific desired device parameters, such as frame rate, depth resolution, lateral resolution, etc.

[0040] Figure 2is a timing diagram illustrating the timing relationship between example light pulses emitted from a light source relative to the receipt of reflected light pulses and measurements made using various phase shifts in an example time-of-flight imaging system according to the teachings of the present invention. Specifically, Figure 2 106 and 106. Emitted light 204, which represents light emitted from light source 102 to illuminate one or more portions 107 of object 106, and corresponding pulsed reflected light 208, which represents light reflected from the illuminated one or more portions 107 of object 106 and reflected by Figure 1 The reflected light pulses received by the corresponding one or more parts 113 of the pixel circuit 112 of the pixel array 110).

[0041] Figure 2 The example depicted in also illustrates a measurement pulse of a differential phase modulation signal comprising a 0° phase modulation signal 214A and a 180° phase modulation signal 214B, and a measurement pulse comprising a 90° phase modulation signal 216A and a 270° phase modulation signal 216B, all of which are phase shifted relative to the phase of the pulse of emitted light 204, as shown. Additionally, Figure 2 As shown, in accordance with the teachings of the present invention, the 0° phase signal 214A and the 180° phase modulation signal 214B, as well as the 90° phase modulation signal 216A and the 270° phase modulation signal 216B pulses are all modulated at the same frequency as the modulated emitted light 204 and reflected light 208 to achieve homodyne detection of the reflected light 208. Utilizing different phases for the example measurement pulses shown allows reconstruction of the encoded distance. In each example, at least three independent measurements (e.g., subframes) are used to decode three unknowns: range / phase, reflectivity, and environment. In the examples described herein, four phases (e.g., 0°, 180°, 90°, and 270°) are utilized.

[0042] As will be discussed, the 0° phase modulation signal 214A and the 180° phase modulation signal 214B, as well as the 90° phase modulation signal 216A and the 270° phase modulation signal 216B pulses correspond to the switching of transfer transistors included in the pixel circuits 112 of the pixel array 110. In operation, the switching of the transfer transistors in the pixel circuits 112 of the pixel array 110 can be used to measure the charge photogenerated in one or more photodiodes included in the pixel circuits 112 in response to the reflected light 208 to determine a delay or phase difference between a pulse of emitted light 204 and a corresponding pulse of reflected light 208.

[0043] For example, Figure 2The example illustrated in FIG2 shows that, in response to reflected light 208, charge Q1 is generated by a pulse of 0° phase modulation signal 214A and charge Q2 is generated by a pulse of 180° phase modulation signal 214B. Similarly, in response to reflected light 208, charge Q3 is generated by a pulse of 90° phase modulation signal 216A and charge Q4 is generated by a pulse of 270° phase modulation signal 216B. In various examples, the measurement of charges Q1, Q2, Q3, and Q4 can then be used to determine the delay or phase difference between emitted light 204 and reflected light 208 in accordance with the teachings of the present invention. And thus determine the flight time T of light from light source 102 to object 106 and then back to pixel array 110 TOF .

[0044] Figures 3A to 3F 310A-310F of a time-of-flight sensor on which the field of view for a given exposure is altered or programmed to include one or more fractional portions of the time-of-flight pixel array that are scanned by an example time-of-flight light sensing system in accordance with the teachings of the present invention. It should be understood that Figures 3A to 3F The example pixel arrays 310A to 310F illustrated in FIG. 3 may be Figure 1 , and similarly named and numbered elements described above are similarly coupled and function below.

[0045] Specifically, Figure 3A An example is shown where the illuminated field of view includes the entire pixel array 310A. In flash LiDAR (light detection and ranging), the entire field of view is illuminated by light reflected from objects illuminated by the illumination source. Thus, the illuminated portion 313 of the pixel array 310A is illuminated in Figure 3A As shown in FIG. 310A, the entire pixel array 310A is covered. Figure 3A In the example depicted in , the illumination source is typically operated at the strongest intensity that can tolerate peak power, electromagnetic interference (EMI), thermal management, etc. The illumination time is limited by motion blur or safety requirements. Typically, long exposure times (~ms) are generated. During these long exposure times, a significant amount of unwanted background signal from ambient light and dark current is accumulated. This is also a huge challenge for outdoor operation and non-silicon devices (SiGe, Ge, InGaAs, InP, GaAs, etc.) that exhibit significantly higher dark current. Another challenge associated with long exposure times is demodulation signaling, which is one of the main power contributors to indirect time-of-flight sensing and must operate for the entire duration across the entire pixel array 310A.

[0046] In contrast, Figure 3BAn example pixel array 310B is shown in accordance with the teachings of the present invention in which only a fraction or subset 313 of the pixel circuits of the pixel array 310B are illuminated by light reflected from an object illuminated by an illumination source. Thus, another subset 315 of the pixel circuits of the pixel array 310B are not illuminated by light reflected from the object. Figure 3B In the example shown in FIG, a horizontal linear portion or subset 313 of one or more rows of pixel array 310B is illuminated by reflected light. In various examples, the subset 313 of pixel circuits of pixel array 310B illuminated by reflected light can be scanned across pixel array 310B until the entire frame is captured.

[0047] Figure 3C Another example pixel array 310C is shown in which only a fraction or subset 313 of the pixel circuits of the pixel array 310C are illuminated by light reflected from an object illuminated by an illumination source. Thus, another subset 315 of the pixel circuits of the pixel array 310C are not illuminated by light reflected from the object. Figure 3C In the example shown in , a vertical linear portion or subset 313 of one or more columns of pixel array 310C is illuminated by reflected light. In various examples, the subset 313 of pixel circuits of pixel array 310C illuminated by reflected light can be scanned across pixel array 310C until the entire frame is captured.

[0048] Figure 3D Yet another example pixel array 310D is shown in which only a fraction or subset 313 of the pixel circuits of the pixel array 310D are illuminated by light reflected from an object illuminated by an illumination source. Thus, another subset 315 of the pixel circuits of the pixel array 310D are not illuminated by light reflected from the object. Figure 3D In the example shown in FIG, a horizontal linear portion or subset 313 of one or more rows of pixel array 310D is illuminated by reflected light. Figure 3D The examples depicted in show that the illuminated portion or subset 313 can be a non-contiguous portion of the pixel array 310D. In various examples, the portion of the pixel array 310D illuminated by reflected light can be scanned across the pixel array 310D until the entire frame is captured.

[0049] Figure 3E Yet another example pixel array 310E is shown in which only a fraction or subset 313 of the pixel circuits of the pixel array 310E are illuminated by light reflected from an object illuminated by an illumination source. Thus, another subset 315 of the pixel circuits of the pixel array 310E are not illuminated by light reflected from the object. Figure 3E In the example shown in FIG, vertical linear portions of one or more columns of pixel array 310E are illuminated by reflected light. Figure 3EThe examples depicted in show that the illuminated portion or subset 313 can be a non-contiguous portion of the pixel array 310E. In various examples, the portion of the pixel array 310E illuminated by reflected light can be scanned across the pixel array 310E until the entire frame is captured.

[0050] Figure 3F Yet another example pixel array 310F is shown in which only a fraction or subset 313 of the pixel circuits of the pixel array 310F are illuminated by light reflected from an object illuminated by an illumination source. Thus, another subset 315 of the pixel circuits of the pixel array 310F are not illuminated by light reflected from the object. Figure 3F In the example shown in FIG, a dot-shaped portion of one or more pixel circuits of pixel array 310F is illuminated by reflected light. In various examples, a subset 313 of the pixel circuits of pixel array 310F illuminated by reflected light can be randomly accessed or addressed. Thus, by providing random access illumination / exposure, a region of interest (ROI) can be monitored by a time-of-flight sensing system. In various examples, the ROI can be quickly updated by the host based on observed changes in the data stream / landscape. In various examples, the host can track an object and adjust the ROI accordingly according to the teachings of the present invention.

[0051] Therefore, about Figures 3B to 3F In all the examples depicted in FIG, instead of the corresponding exposure T for a given INT Instead of distributing a specific radiant flux Φ over a given solid angle Ω across the entire defined field of view (FOV), the entire radiant flux Φ may be focused into an angle ΔΩ = Ω / N, which illuminates only a 1 / N portion of the object rather than the entire object. Thus, in accordance with the teachings of the present invention, there are one or more portions of the object in the field of view that are not illuminated by the modulated light emitted by the light source. Consequently, reflected modulated light from the object illuminates only a subset 313 of the time-of-flight pixel circuits in pixel arrays 310B to 310F, as shown in FIG. Figures 3B to 3F Therefore, Figures 3B to 3F Another subset 315 of the time-of-flight pixel circuits in the pixel arrays 310B to 310F shown in FIG. 3 is not illuminated. This increases the irradiance to E×N, which reduces the exposure to T INT / N, resulting in the same signal carrier count. However, since the exposure is reduced to T INT / N, so the background signal generated by parasitics is also reduced.

[0052] In operation, the first ΔΩ1 of the lighting reaches T INTAfter ΔΩ 1 , ΔΩ 2 , ... ΔΩ N are scanned across the object, and after the corresponding subset of pixel circuits of the pixel array are read out, the emitted modulated light from the light source can then be scanned across the object, which in turn causes the reflected modulated light from the object to be scanned across the pixel arrays 310B through 310F, as shown. In other words, the radiant flux Φ can then be scanned or focused on ΔΩ 1 , ΔΩ 2 , ... ΔΩ N for a given exposure until the entire frame is at the same total exposure T according to the teachings of the present invention. INT It will therefore be appreciated that the example time-of-flight sensing system in which only a fraction of an object is illuminated at a time and thus the corresponding illuminated fraction of pixel arrays 310B-310F is scanned has the following advantages in accordance with the teachings of the present invention: efficient utilization of modulation power, with power consumption reduced by a factor of N.

[0053] Figure 4 FIG. 4 is a schematic diagram illustrating an example of a time-of-flight pixel circuit 412 included in a pixel array of a time-of-flight sensor according to the teachings of the present invention. Figure 4 The pixel circuit 412 may be Figure 1 An example of one of the pixel circuits 112 included in the pixel array 110 is shown in FIG. 1 , and similarly named and numbered elements described above are similarly coupled and function below.

[0054] like Figure 4 , pixel circuit 412 includes a photodiode 418 configured to photogenerate charge in response to incident light. In one example, the light incident on photodiode 418 is reflective modulated light 108 reflected from object 106, such as Figure 1 The first floating diffusion FD 422A is configured to store a first portion of the charge generated by light in the photodiode 418, such as (for example) Figure 2 The second floating diffusion FD 422B is configured to store a second portion of the charge generated by the photodiode 418, such as (for example) Figure 2 The charge Q2 or Q4 described in.

[0055] The first transfer transistor 420A is configured to transfer a first portion of the charge from the photodiode 418 to the first floating diffusion FD 422A in response to the first phase modulation signal TXA. In one example, the first phase modulation signal TXA may be Figure 2 4. The second transfer transistor 420B is configured to transfer a second portion of the charge from the photodiode 418 to the second floating diffusion FD 422B in response to the second phase modulation signal TXB. In one example, the second phase modulation signal TXB may be Figure 2 4. A first phase modulated signal TXA and a second phase modulated signal TXB are each configured to store a first portion of the charge from the first floating diffusion FD 422A via a first sample and hold transistor 426A, and a second storage node MEM 434B is configured to store a second portion of the charge from the second floating diffusion FD 422B via a second sample and hold transistor 426B. In each example, the first and second sample and hold transistors 426A and 426B are coupled to respond to a sample and hold signal SH.

[0056] continue Figure 4 , a first storage node MEM 434A is coupled to a first capacitor 428A and a gate of a first source follower transistor 430A. A first row select transistor 432A is coupled to the source of the first source follower transistor 430A. In various examples, the first row select transistor 432A is also coupled to a first bit line BL1, through which first output signal information can be read out from the pixel circuit 412. Similarly, a second storage node MEM 434B is coupled to a second capacitor 428B and a gate of a second source follower transistor 430B. A second row select transistor 432B is coupled to the source of the second source follower transistor 430B. In various examples, the second row select transistor 432B is also coupled to a second bit line BL2, through which second output signal information can be read out from the pixel circuit 412. In various examples, the first and second row select transistors 432A and 432B are coupled to respond to a row select signal RS.

[0057] In various examples, the pixel circuit 412 also includes a first reset transistor 424A coupled between a power rail and the first floating diffusion FD 422A. In various examples, the first reset transistor 424A is configured to reset the first floating diffusion FD 422A and the first storage node MEM 434A in response to a reset signal RST. Figure 4 , the first reset transistor 424A is configured to reset the first storage node MEM 434A via the first sample and hold transistor 426A. In various examples, it should be understood that the first reset transistor 424A can be operated in a manner such that excess carriers generated by the photodiode 418 can be directed to the power supply by the first reset transistor 424A or in a manner such that the photosensitivity of the photodiode 418 is disabled.

[0058] Similarly, the pixel circuit 412 also includes a second reset transistor 424B coupled between the power rail and the second floating diffusion FD 422B. In various examples, the second reset transistor 424B is configured to reset the second floating diffusion FD 422B and the second storage node MEM 434B in response to a reset signal RST. Figure 4 , the second reset transistor 424B is configured to reset the second storage node MEM 434B via the second sample and hold transistor 426B. In various examples, it should be understood that the second reset transistor 424B can be operated in a manner such that excess carriers generated by the photodiode 418 can be directed by the second reset transistor 424B to the power supply or in a manner such that the photosensitivity of the photodiode 418 is disabled.

[0059] Figure 5A is a schematic diagram showing an example of a time-of-flight optical sensing system 500A according to the teachings of the present invention. It should be understood that Figure 5A The time-of-flight optical sensing system 500A can be Figure 1 , and similarly named and numbered elements described above are similarly coupled and function below.

[0060] As shown in the depicted example, time-of-flight light sensing system 500A includes a light source 502 synchronized with a time-of-flight sensor including a pixel array 510. In various examples, light source 502 is configured to emit modulated light at only a portion of an object at a time, such as, for example, portion 107 of object 106, as shown in FIG. Figure 1 . In various examples, a laser can be used as the light source 502, and the field of view of the laser can be controlled by various examples of a scanning mechanism. For example, in various examples, the light source 502 can be implemented electronically (e.g., via an addressable laser array), mechanically (e.g., via a body or MEMS mirror), optically / electro-optically (e.g., via a phased array, liquid crystal, etc.), or with any other suitable type of light source or technology to emit modulated light toward an object in accordance with the teachings of the present invention.

[0061] In the depicted example, the time of flight sensor also includes a modulation driver block 534 that is coupled to the light source 502 and the pixel array 510. In operation, control and readout of enabled and disabled time of flight pixel circuits included in the time of flight pixel array 510 are synchronized with the modulated light emitted by the light source 502 toward the object. As shown in the depicted example, the time of flight pixel array 510 includes a plurality of time of flight pixel circuits 512A-512I. In the example, it should be noted that each of the time of flight pixel circuits 512A-512I can be Figure 44. Thus, it should be appreciated that for simplicity, each of the time-of-flight pixel circuits 512A-512I is described in detail in FIG. Figure 5A No more detailed description is given in the.

[0062] exist Figure 5A , time-of-flight pixel circuits 512A-512I are arranged in rows and columns in a time-of-flight pixel array 510. It should be noted that for purposes of explanation, the time-of-flight pixel array 510 is illustrated having time-of-flight pixel circuits 512A-512I arranged in three rows and three columns. In other examples, it should of course be understood that the time-of-flight pixel array 510 may include a greater or fewer number of rows and / or a greater or fewer number of columns.

[0063] Figure 5A Depicted is an example in which reflected modulated light from an object is configured to illuminate one or more rows of time-of-flight pixel array 510, rather than all rows of time-of-flight pixel array 510 at once. For example, a first subset of the plurality of time-of-flight pixel circuits (e.g., the rows including time-of-flight pixel circuits 512A-512C) is configured to be illuminated by reflected modulated light from the object, while a second subset of the plurality of time-of-flight pixel circuits (e.g., the rows including time-of-flight pixel circuits 512D-512I) is configured not to be illuminated by reflected modulated light from the object.

[0064] As shown in the depicted example, modulation driver block 534 includes a phase-locked loop circuit 540 configured to generate first and second phase modulation signals TXA and TXB. Figure 4 As described in the example of FIG, first and second phase modulation signals TXA and TXB are coupled to be received by transfer transistors of time-of-flight pixel circuits 512A to 512I. Light source driver 544 is coupled between light source 502 and phase-locked loop circuit 540. In operation, light source driver circuit 544 is configured to synchronize modulated light emitted from light source 502 to an object with first and second phase modulation signals TXA and TXB in response to phase-locked loop circuit 540.

[0065] Continuing with the depicted example, a plurality of driver circuits 536A-536F are coupled to phase-locked loop circuit 540. In the example, driver circuit 536A is configured to generate a first phase-modulated signal TXA, and driver circuit 536B is configured to generate a second phase-modulated signal TXB for a row of time-of-flight pixel array 510 including time-of-flight pixels 512A-512C. Driver circuit 536C is configured to generate a first phase-modulated signal TXA, and driver circuit 536D is configured to generate a second phase-modulated signal TXB for a row of time-of-flight pixel array 510 including time-of-flight pixels 512D-512F. Driver circuit 536E is configured to generate a first phase-modulated signal TXA, and driver circuit 536F is configured to generate a second phase-modulated signal TXB for a row of time-of-flight pixel array 510 including time-of-flight pixels 512G-512I.

[0066] In the example, the modulation driver block 534 also includes a plurality of driver switches 538A to 538F. Each of the plurality of driver switches 538A to 538F is coupled to the output of a respective one of the plurality of driver circuits 536A to 536F, as shown in FIG. Figure 5A Thus, driver switch 538A is coupled to the output of driver circuit 536A, driver switch 538B is coupled to the output of driver circuit 536B, driver switch 538C is coupled to the output of driver circuit 536C, driver switch 538D is coupled to the output of driver circuit 536D, driver switch 538E is coupled to the output of driver circuit 536E, and driver switch 538F is coupled to the output of driver circuit 536F.

[0067] As shown in the example, the modulation driver block 534 also includes a modulation control circuit 535 coupled to a plurality of driver switches 538A through 538F. In operation, the modulation control circuit 535 is configured to turn off or disable driver switches coupled to time-of-flight pixel circuits that are not illuminated, while the modulation control circuit 535 is configured to turn on or enable driver switches coupled to time-of-flight pixel circuits that are not illuminated.

[0068] To illustrate, in the above example where a first subset of the plurality of time-of-flight pixel circuits (e.g., a row including time-of-flight pixel circuits 512A-512C) is configured to be illuminated by reflected modulated light from an object, while a second subset of the plurality of time-of-flight pixel circuits (e.g., a row including time-of-flight pixel circuits 512D-512I) is configured not to be illuminated by reflected modulated light from an object, the modulation control circuit 535 is configured to turn on or enable driver switches 538A and 538B and to turn off or disable driver switches 536C-536F. Thus, the transfer transistors of the illuminated, and therefore enabled, time-of-flight pixel circuits 512A-512C are coupled to receive and respond to the first and second phase modulation signals TXA and TXB, while the transfer transistors of the non-illuminated, and therefore disabled, time-of-flight pixel circuits 512D-512F are not coupled to receive and therefore do not respond to the first and second phase modulation signals TXA and TXB.

[0069] Continuing with the depicted example, the modulation driver block 534 further includes a scan synchronization circuit 542 coupled to the modulation control circuit 535, as shown. In operation, the scan synchronization circuit 542 is configured to synchronize scanning of modulated light emitted by the light source across an object with scanning of a first subset of a plurality of time-of-flight pixel circuits illuminated by reflected modulated light across the time-of-flight pixel array 510. In other words, in accordance with the teachings of the present invention, the scan synchronization circuit 542 is configured to synchronize scanning of modulated light emitted by the light source 502 across an object with activation of appropriate driver switches 538A-538F coupled to corresponding time-of-flight pixel circuits 512A-512I illuminated by modulated light reflected from the object.

[0070] As shown in the depicted example, row control circuitry 548 is coupled to a plurality of time-of-flight pixel circuits 512A-512I of the time-of-flight pixel array 510. In the example, the row control circuitry 548 is configured to generate a reset signal RST, which is coupled to control a first reset transistor and a second reset transistor of each of the plurality of time-of-flight pixel circuits 512A-512I, as shown. In the example, the row control circuitry 548 is further configured to generate a sample-and-hold signal SH, which is coupled to control a first sample-and-hold transistor and a second sample-and-hold transistor of each of the plurality of time-of-flight pixel circuits 512A-512I, as shown. In the example, the row control circuitry 548 is further configured to generate a row select signal RS, which is coupled to control a first row select transistor and a second row select transistor of each of the plurality of time-of-flight pixel circuits 512A-512I, as shown. In the depicted example, column readout circuitry 550 is coupled to first and second bit lines BL1 and BL2 of each of a plurality of time-of-flight pixel circuits 512A- 512I to read out each of a plurality of time-of-flight pixel circuits 512A- 512I of time-of-flight pixel array 510 as shown.

[0071] Figure 5B is a schematic diagram showing another example of a time-of-flight optical sensing system 500B according to the teachings of the present invention. It should be understood that Figure 5B An example of a time-of-flight optical sensing system 500B may be Figure 5A Another example of a time-of-flight optical sensing system 500A or Figure 1 Another example of a time-of-flight optical sensing system 100 is shown in FIG, and similarly named and numbered elements described above are similarly coupled and function below. It should also be understood that Figure 5B An example of a time-of-flight optical sensing system 500B with Figure 5A The example time-of-flight optical sensing system 500A shares many similarities.

[0072] For example, Figure 5B , the time-of-flight light sensing system 500B also includes a light source 502 synchronized with the time-of-flight sensor including the pixel array 510. In various examples, the light source 502 is configured to emit modulated light at only a portion of an object at a time, such as, for example, portion 107 of the object 106, as shown in FIG. Figure 1. In various examples, a laser can be used as the light source 502, and the field of view of the laser can be controlled by various examples of a scanning mechanism. For example, in various examples, the light source 502 can also be implemented electronically (e.g., via an addressable laser array), mechanically (e.g., via a body or MEMS mirror), optically / electro-optically (e.g., via a phased array, liquid crystal, etc.), or with any other suitable type of light source or technology to emit modulated light toward an object in accordance with the teachings of the present invention.

[0073] In the depicted example, the time of flight sensor also includes a modulation driver block 534 that is coupled to the light source 502 and the pixel array 510. In operation, control and readout of enabled and disabled time of flight pixel circuits included in the time of flight pixel array 510 are synchronized with the modulated light emitted by the light source 502 toward the object. As shown in the depicted example, the time of flight pixel array 510 also includes a plurality of time of flight pixel circuits 512A-512I. In the example, it should be noted that each of the time of flight pixel circuits 512A-512I may also be Figure 4 4. Thus, it should be appreciated that for simplicity, each of the time-of-flight pixel circuits 512A-512I is described in detail in FIG. Figure 5B No more detailed description is given in the text.

[0074] exist Figure 5B , time-of-flight pixel circuits 512A-512I are arranged in rows and columns in a time-of-flight pixel array 510. It should be noted that for purposes of explanation, the time-of-flight pixel array 510 is illustrated having time-of-flight pixel circuits 512A-512I arranged in three rows and three columns. In other examples, it should of course be understood that the time-of-flight pixel array 510 may include a greater or fewer number of rows and / or a greater or fewer number of columns.

[0075] Figure 5B Depicted is an example in which reflected modulated light from an object is configured to illuminate one or more rows of time-of-flight pixel array 510, rather than all rows of time-of-flight pixel array 510 at once. For example, a first subset of the plurality of time-of-flight pixel circuits (e.g., the rows including time-of-flight pixel circuits 512A-512C) is configured to be illuminated by reflected modulated light from the object, while a second subset of the plurality of time-of-flight pixel circuits (e.g., the rows including time-of-flight pixel circuits 512D-512I) is configured not to be illuminated by reflected modulated light from the object.

[0076] As shown in the depicted example, modulation driver block 534 also includes a phase-locked loop (PLL) circuit 540 that is configured to generate first and second phase modulation signals TXA and TXB. Figure 5BThe time-of-flight pixel light sensing system 500B and Figure 5A One of the differences between the time-of-flight pixel light sensing system 500A is Figure 5B The time-of-flight pixel light-sensing system 500B also includes delay-locked loop (DLL) circuits 541A, 541B, ..., 541C, which are serially coupled to the output of the phase-locked loop circuit 540. In an example, each of the delay-locked loop circuits 541A, 541B, ..., 541C is configured to generate first and second phase-modulated signals TXA and TXB having respective phase shifts or delays for rows or groups of rows of the time-of-flight pixel array 510 coupled to the respective delay-locked loop circuits 541A, 541B, ..., 541C. It should be understood that, in another example, the delay-locked loop circuits 541A, 541B, ..., 541C can also be implemented to introduce phase delays between rows or groups of columns of the time-of-flight pixel array, depending on the configuration. Thus, it should be appreciated that adding intentional phase shifts with delay-locked loop circuits 541A, 541B, ..., 541C, in accordance with the teachings of the present invention, spreads out peak currents and, therefore, improves first and second phase-modulated signals TXA and TXB and reduces electromagnetic interference (EMI) by avoiding excessive current or power spikes when modulating transfer transistors included in time-of-flight pixel circuits 512A-512I of time-of-flight pixel array 510. As shown in the depicted example, first and second phase-modulated signals TXA and TXB generated by phase-locked loop (PLL) circuit 540 are generated by respective series-coupled delay-locked loop (DLL) circuits 541A, 541B, ..., 541C having corresponding phase shifts.

[0077] Figure 5B The time-of-flight pixel light sensing system 500B and Figure 5A Another difference between the time-of-flight pixel light sensing system 500A is that Figure 5BIn the time-of-flight pixel light sensing system 500B of FIG. 1 , each of the first and second phase-modulated signals TXA and TXB generated by respective delay-locked loop (DLL) circuits 541A, 541B, ..., 541C is received at a second input (e.g., bottom input) of respective logic circuits 537A, 537B, 537C, 537D, ..., 537E, 537F, as shown. In the depicted example, the logic circuits 537A, 537B, 537C, 537D, ..., 537E, 537F are illustrated as logic AND gates configured to gate the first and second phase-modulated signals TXA and TXB in response to respective enable signals received at a first input (e.g., top input) of each of the logic circuits 537A, 537B, 537C, 537D, ..., 537E, 537F. In other examples, it should be understood that other suitable types of logic circuits or combinations of logic circuits may be utilized, such as, for example, NAND / OR / NOR gates, etc., depending on the polarity of the signals included in the time-of-flight light sensing system 500B. In the example, the modulation control circuit 535 included in the modulation driver block 534 is configured to generate an enable signal received at a first input of each of the logic circuits 537A, 537B, 537C, 537D, ..., 537E, 537F. In operation, the modulation control circuit 535 is thus configured to disable the corresponding logic circuits 537A, 537B, 537C, 537D, ..., 537E, 537F coupled to the time-of-flight pixel circuits that are not illuminated, while the modulation control circuit 535 is configured to enable the corresponding logic circuits 537A, 537B, 537C, 537D, ..., 537E, 537F coupled to the illuminated time-of-flight pixel circuits. Thus, when corresponding enable signals are received from the modulation control circuit 535, first and second phase modulated signals TXA and TXB are thus produced at the respective output of each of the logic circuits 537A, 537B, 537C, 537D, ..., 537E, 537F.

[0078] continue Figure 5B, first and second phase modulation signals TXA and TXB from logic circuits 537A, 537B, 537C, 537D, ..., 537E, 537F are coupled to be received by transfer transistors of time-of-flight pixel circuits 512A through 512I. For example, in the depicted example, logic circuit 537A is configured to generate a first phase modulation signal TXA, and logic circuit 537B is configured to generate a second phase modulation signal TXB for a row of time-of-flight pixel array 510 including time-of-flight pixels 512A through 512C. Logic circuit 537C is configured to generate a first phase modulation signal TXA, and logic circuit 537D is configured to generate a second phase modulation signal TXB for a row of time-of-flight pixel array 510 including time-of-flight pixels 512D through 512F. Logic circuit 537E is configured to generate a first phase modulation signal TXA, and logic circuit 537F is configured to generate a second phase modulation signal TXB for a row of time-of-flight pixel array 510 including time-of-flight pixels 512G- 512I.

[0079] In operation, a first subset of the plurality of time-of-flight pixel circuits (e.g., a row including time-of-flight pixel circuits 512A to 512C) is configured to be illuminated by reflected modulated light from an object, while a second subset of the plurality of time-of-flight pixel circuits (e.g., a row including time-of-flight pixel circuits 512D to 512I) is configured not to be illuminated by reflected modulated light from the object. Thus, modulation control circuit 535 is configured to enable logic circuits 537A and 537B and disable logic circuits 537C to 537F. Thus, the transfer transistors of the illuminated and therefore enabled time-of-flight pixel circuits 512A to 512C are coupled to receive and respond to the first and second phase modulation signals TXA and TXB, while the transfer transistors of the unilluminated and therefore disabled time-of-flight pixel circuits 512D to 512F are not coupled to receive and therefore do not respond to the first and second phase modulation signals TXA and TXB. Operation is similar when the modulation control circuit 535 is configured to enable logic circuits 537C and 537D and disable logic circuits 537A-537B and 537E-537F, or when the modulation control circuit 535 is configured to enable logic circuits 537E and 537F and disable logic circuits 537A-537D, and so on.

[0080] Light source driver 544 is coupled between light source 502 and phase-locked loop circuit 540. In operation, light source driver circuit 544 is configured to synchronize modulated light emitted from light source 502 to an object with first and second phase modulation signals TXA and TXB in response to phase-locked loop circuit 540.

[0081] Continuing with the depicted example, the modulation driver block 534 further includes a scan synchronization circuit 542 coupled to the modulation control circuit 535, as shown. In operation, the scan synchronization circuit 542 is configured to synchronize scanning of modulated light emitted by the light source across an object with scanning of a first subset of a plurality of time-of-flight pixel circuits illuminated by reflected modulated light across the time-of-flight pixel array 510. In other words, in accordance with the teachings of the present invention, the scan synchronization circuit 542 is configured to synchronize scanning of modulated light emitted by the light source 502 across an object with the enabling of appropriate logic circuits 537A-537F coupled to corresponding time-of-flight pixel circuits 512A-512I illuminated by modulated light reflected from the object.

[0082] As shown in the depicted example, row control circuitry 548 is coupled to a plurality of time-of-flight pixel circuits 512A-512I of the time-of-flight pixel array 510. In the example, the row control circuitry 548 is configured to generate a reset signal RST, which is coupled to control a first reset transistor and a second reset transistor of each of the plurality of time-of-flight pixel circuits 512A-512I, as shown. In the example, the row control circuitry 548 is further configured to generate a sample-and-hold signal SH, which is coupled to control a first sample-and-hold transistor and a second sample-and-hold transistor of each of the plurality of time-of-flight pixel circuits 512A-512I, as shown. In the example, the row control circuitry 548 is further configured to generate a row select signal RS, which is coupled to control a first row select transistor and a second row select transistor of each of the plurality of time-of-flight pixel circuits 512A-512I, as shown. In the depicted example, column readout circuitry 550 is coupled to first and second bit lines BL1 and BL2 of each of a plurality of time-of-flight pixel circuits 512A- 512I to read out each of a plurality of time-of-flight pixel circuits 512A- 512I of time-of-flight pixel array 510 as shown.

[0083] Figure 6 is a timing diagram showing one example of signals during integration and readout of one example of a time-of-flight optical sensing system according to the teachings of the present invention. It should be understood that Figure 6 The signals described in the timing diagram can be Figure 5A Examples of signals found during operation of the time-of-flight sensing system 500A are described in and / or in Figure 4 Examples of signals found during operation of the time-of-flight pixel circuit 412 are described in and / or in Figure 1 Examples of signals found during operation of the time-of-flight sensing system 100 are illustrated in FIG. 1 , and similarly named and numbered elements described above are similarly coupled and function below.

[0084] exist Figure 6 In the example depicted in FIG, it is assumed for illustration purposes that the time-of-flight sensing system includes a time-of-flight pixel array having 480 rows of time-of-flight pixel circuits. As shown in the depicted example, at time T0, reset signals RST<1:48> 624A (coupled to the rows including a subset of the time-of-flight pixel circuits included in rows 1-48), reset signals RST<49:96> 624B (coupled to the rows including a subset of the time-of-flight pixel circuits included in rows 49-96), ..., and reset signals RST<433:480> 624C (coupled to the rows including a subset of the time-of-flight pixel circuits included in rows 433-480) are all activated, which turns on the first and second reset transistors in the respective time-of-flight pixel circuits to initialize or reset the respective time-of-flight pixel circuits, respectively.

[0085] At time T1, reset signal RST<1:48> 624A (which is coupled to the row including the subset of time-of-flight pixel circuits included in rows 1 to 48) is deactivated, and first phase modulation signal TXA<1:48> 620A and second phase modulation signal TXB<1:48> 621A are modulated to modulate corresponding transfer transistors (e.g., 420A and 420B). Thus, integration of reflected modulated light incident on the illuminated subset of time-of-flight pixel circuits included in rows 1 to 48 of the time-of-flight pixel array occurs between times T1 and T2. In this example, it is assumed that the subset of time-of-flight pixel circuits included in the remaining rows 49 to 480 are not illuminated and therefore remain deactivated between times T1 and T2.

[0086] At time T2, rows 1-48 are no longer illuminated and reset signal RST<1:48> 624A is deactivated, and sample and hold signal SH<1:48> 626A coupled to the rows included in the now non-illuminated subset of the time-of-flight pixel circuits included in rows 1-48 is deactivated. Additionally, row select signal RS<1:48> 632A is now activated. Consequently, the corresponding charge sampled into the memory nodes (e.g., 434A and 434B) of the corresponding time-of-flight pixel circuits during the time interval between T1 and T2 is now retained during the time interval between T2 and T3. Consequently, the retained charge in the memory nodes in the previously illuminated, but now non-illuminated, subset of the time-of-flight pixel circuits included in rows 1-48 is now read out through the corresponding row select transistors (e.g., 432A and 432B) during the time interval between T2 and T3, as indicated by the assertion of row select signal RS<1:48> 632A.

[0087] Additionally, it should be appreciated that at time T2, the subset of time-of-flight pixel circuits included in rows 49 through 96 that was previously unilluminated during the time interval between times T1 and T2 is now illuminated during the time interval between times T2 and T3. Thus, at time T2, reset signal RST<49:96> 624B coupled to the subset of time-of-flight pixel circuits included in rows 49 through 96 is now deactivated, and first phase modulation signal TXA<49:96> 620B and second phase modulation signal TXB<49:96> 621B are modulated to modulate the respective transfer transistors (e.g., 420A and 420B) of the time-of-flight pixel circuits included in the now illuminated subset of time-of-flight pixel circuits included in rows 49 through 96 during the time interval between times T2 and T3. Thus, integration of reflected modulated light incident on the now illuminated subset of time-of-flight pixel circuits included in rows 49 through 96 of the time-of-flight pixel array occurs between times T2 and T3. In the example, assume that the subset of time-of-flight pixel circuits included in the remaining rows 1-48 and 97-480 are not illuminated and therefore remain deactivated between times T2 and T3.

[0088] 432B) are configured to be simultaneously read out through respective row select transistors (e.g., first and second row select transistors 432A and 432B) of one of the plurality of time-of-flight pixel circuits included in the second subset (e.g., rows 1-48 that are not illuminated during the time interval between T2 and T3), such that the first and second transfer transistors (e.g., first and second transfer transistors 420A and 420B) of one of the plurality of time-of-flight pixel circuits included in the first subset (e.g., rows 49-96 that are illuminated during the time interval between T2 and T3) are configured to be modulated in response to the first and second phase modulation signals 620B, 621B.

[0089] In the next period after time T3, when the subset of time-of-flight pixel circuits included in rows 48 to 96 is no longer illuminated, the retained charge in the memory nodes in the subset of time-of-flight pixel circuits included in rows 48 to 96 is read out, as indicated by the assertion of row select signal RS<48:96> 632B and the deactivation of sample and hold signal SH<49-96> 626B at time T3. Furthermore, in accordance with the teachings of the present invention, integration of subsequently illuminated rows after rows 48 to 96 are no longer illuminated can now occur while the retained charge in the memory nodes in the now non-illuminated subset of time-of-flight pixel circuits included in rows 48 to 96 is read out to continue pipelined integration and readout operations in the time-of-flight pixel array.

[0090] The pipelined integration and readout operation described above scans across the time-of-flight pixel array and continues through the rows of the time-of-flight pixel array. Thus, at a time period just before time TN, the reset signal RST<433:480>624C is deactivated, and the first phase modulation signal TXA<433:480>620C and the second phase modulation signal TXB<433:480>621C are modulated to modulate the corresponding transfer transistors (e.g., 420A and 420B). Thus, the integration of the reflected modulated light incident on the subset of the time-of-flight pixel circuits included in rows 433 to 480 of the time-of-flight pixel array occurs in the time period just before time TN. In this example, it is assumed that the subset of the time-of-flight pixel circuits included in the remaining rows 1 to 432 are not illuminated and therefore remain deactivated in the time period just before time TN.

[0091] At time TN, reset signal RST<433:480> 624C is reactivated and sample and hold signals SH<433:480> 626C coupled to the row containing the subset of time-of-flight pixel circuits included in rows 433 to 480 are deactivated. Consequently, the respective charges sampled into the memory nodes (e.g., 434A and 434B) of the respective time-of-flight pixel circuits are retained between times TN and TN+1. Consequently, the retained charges in the memory nodes in the subset of time-of-flight pixel circuits included in rows 433 to 480 are read out between times TN and TN+1. Consequently, the retained charges in the memory nodes in the subset of time-of-flight pixel circuits included in rows 433 to 480 are read out between times TN and TN+1, as indicated by the assertion of row select signal RS<433:480> 632C.

[0092] As shown in the example, the pipelined integration and readout operations of the time-of-flight pixel array then repeat and loop back to the subset of time-of-flight pixel circuits included in rows 1 to 48 of the time-of-flight pixel array. Specifically, at time TN, as at time T1, the reset signal RST<1:48> 624A (which is coupled to the row including the subset of time-of-flight pixel circuits included in rows 1 to 48) is deactivated, and the first phase modulation signal TXA<1:48> 620A and the second phase modulation signal TXB<1:48> 621A are modulated to modulate the corresponding transfer transistors (e.g., 420A and 420B). Thus, the integration of the reflected modulated light incident on the subset of time-of-flight pixel circuits included in rows 1 to 48 of the time-of-flight pixel array occurs between times TN and TN+1, just as it did during the period between times T1 and T2. Similarly, the processing performed at time TN+1 corresponds to the process occurring at time T2, and so on.

[0093] Figure 7 FIG. 7 is a schematic diagram illustrating another example of a time-of-flight pixel circuit 712 included in a time-of-flight pixel array of a time-of-flight sensing system according to the teachings of the present invention. Figure 7 The pixel circuit 712 may be Figure 4 Another example of the pixel circuit 412 in Figure 1 1 and 2. FIG. 1 is another example of one of the pixel circuits 112 included in the pixel array 110 shown in FIG. 1 , and similarly named and numbered elements described above are similarly coupled and function below. It should also be understood that Figure 7 An example pixel circuit 712 with Figure 4 The example pixel circuit 412 shares many similarities.

[0094] For example, Figure 7 , pixel circuit 712 includes a photodiode 718 configured to photogenerate charge in response to incident light. In one example, the light incident on photodiode 718 is reflective modulated light 108 reflected from object 106, such as Figure 1 The first floating diffusion FD 722A is configured to store a first portion of the charge generated by light in the photodiode 718, such as (for example) storing Figure 2 The second floating diffusion FD722B is configured to store a second portion of the charge generated by light in the photodiode 718, such as (for example) storing Figure 2 The charge Q2 or Q4 described in.

[0095] The first transfer transistor 720A is configured to transfer a first portion of the charge from the photodiode 718 to the first floating diffusion FD 722A in response to a first phase modulation signal TXA. In one example, the first phase modulation signal TXA may be Figure 2 , such as, for example, the 0° phase modulation signal 214A or the 90° phase modulation signal 214C. The second transfer transistor 720B is configured to transfer a second portion of the charge from the photodiode 718 to the second floating diffusion FD 722B in response to the second phase modulation signal TXB. In one example, the second phase modulation signal TXB may be Figure 2 , such as, for example, the 180° phase modulated signal 214B or the 270° phase modulated signal 214D. In each example, the first phase modulated signal TXA and the second phase modulated signal TXB are out of phase with each other, such as, for example, 180° out of phase with each other.

[0096] Similar to Figure 4 An example pixel circuit 412, Figure 7 The pixel circuit 712 also includes a first storage node MEM 734A (which is configured to store a first portion of the charge from the first floating diffusion portion FD 722A through the first sample and hold transistor 726A) and a second storage node MEM 734B (which is configured to store a second portion of the charge from the second floating diffusion portion FD 722B through the second sample and hold transistor 726B).

[0097] Figure 7 The pixel circuit 712 and Figure 4 One of the differences between the pixel circuits 412 is that Figure 7 The pixel circuit 712 also includes a first column sample and hold control transistor 744A coupled to the gate of the first sample and hold transistor 726A. In this example, the first column sample and hold control transistor 744A is coupled to respond to the first column sample and hold control signal CSH. CTRL Additionally, a first row sample and hold control transistor 742A is coupled to a first column sample and hold control transistor 744A, as shown. The first row sample and hold control transistor 742A is coupled to respond to a row sample and hold control signal RSH. CTRL Additionally, a first sample and hold enable / disable transistor 746A is also coupled to the gate of the first sample and hold transistor 726A. The first sample and hold enable / disable transistor 746A is coupled to be responsive to a sample and hold enable / disable control signal B1.

[0098] Similarly, Figure 7The pixel circuit 712 also includes a second column sample and hold control transistor 744B coupled to the gate of the second sample and hold transistor 726B. The second column sample and hold control transistor 744B is coupled to respond to the second column sample and hold control signal CSH. CTRL In one embodiment, the first and second column sampling and holding control signals CSH CTRL In addition, the second row sample and hold control transistor 742B is coupled to the second column sample and hold control transistor 744B, as shown. The second row sample and hold control transistor 742B is coupled to respond to the row sample and hold control signal RSH. CTRL Additionally, a second sample and hold enable / disable transistor 746B is coupled to the gate of the second sample and hold transistor 726B. The second sample and hold enable / disable transistor 746B is coupled to be responsive to the sample and hold enable / disable control signal B1.

[0099] Thus, in various instances, the first sample and hold transistor 726A is coupled to respond to the first column sample and hold control signal CSH. CTRL , row sampling and holding control signal RSH CTRL Similarly, the second sample and hold transistor 726B is coupled to respond to the second column sample and hold control signal CSH. CTRL , row sampling and holding control signal RSH CTRL and the sampling and holding enable / disable control signal B1. In each instance, the first and second column sampling and holding control signals CSH CTRL Can be the same signal.

[0100] continue Figure 7 , a first storage node MEM 734A is coupled to a first capacitor 728A and a gate of a first source follower transistor 730A. A first row select transistor 732A is coupled to the source of the first source follower transistor 730A. In various examples, the first row select transistor 732A is also coupled to a first bit line BL1, through which first output signal information can be read out from the pixel circuit 712. Similarly, a second storage node MEM 734B is coupled to a second capacitor 728B and a gate of a second source follower transistor 730B. A second row select transistor 732B is coupled to the source of the second source follower transistor 730B. In various examples, the second row select transistor 732B is also coupled to a second bit line BL2, through which second output signal information can be read out from the pixel circuit 712. In various examples, the first and second row select transistors 732A and 732B are coupled to respond to a row select signal RS.

[0101] Similar to Figure 4 An example pixel circuit 412, Figure 7 The pixel circuit 712 also includes a first reset transistor 724A coupled between the power rail and the first floating diffusion FD 722A and a second reset transistor 724B coupled between the power rail and the second floating diffusion FD 722B.

[0102] Figure 7 The pixel circuit 712 and Figure 4 Another difference between the pixel circuits 412 is that Figure 7 The pixel circuit 712 further includes a column reset control transistor 738 coupled to the gate of the first reset transistor 724A and the gate of the second reset transistor 724B. The column reset control transistor is coupled to respond to the column reset control signal CRST. CTRL In addition, a row reset control transistor 740 is coupled to the column reset control transistor 738. The row reset control transistor 740 is coupled to respond to the row reset control signal RRST. CTRL Additionally, a reset enable / disable transistor 736 is also coupled to the gate of the first reset transistor 724A and the gate of the second reset transistor 724B, as shown. The reset enable / disable transistors are coupled to be responsive to a reset enable / disable control signal B2.

[0103] Thus, in various instances, the first and second reset transistors 724A and 724B are coupled to be responsive to the column reset control signal CRST. CTRL , row reset control signal RRST CTRL and reset enable / disable control signal B2.

[0104] In various examples, the first reset transistor 724A is configured to reset the first floating diffusion FD 722A and the first storage node MEM 734A. Figure 7 In the example depicted in FIG, the first reset transistor 724A is configured to reset the first storage node MEM 734A via the first sample and hold transistor 726A. In various examples, it should be understood that the first reset transistor 724A can be operated in a manner such that excess carriers generated by the photodiode 718 can be directed to the power supply by the first reset transistor 724A or in a manner such that the photosensitivity of the photodiode 718 is disabled. Similarly, the second reset transistor 724B is configured to reset the second floating diffusion FD 722B and the second storage node MEM 734B. Figure 7, the second reset transistor 724B is configured to reset the second storage node MEM 734B via the second sample and hold transistor 726B. In various examples, it should be understood that the second reset transistor 724B can be operated in a manner such that excess carriers generated by the photodiode 718 can be directed by the second reset transistor 724B to the power supply or in a manner such that the photosensitivity of the photodiode 718 is disabled.

[0105] Figure 8 is a schematic diagram showing another example of a time-of-flight optical sensing system 800 according to the teachings of the present invention. It should be understood that Figure 8 An example of a time-of-flight optical sensing system 800 may be Figure 5A Another example of a time-of-flight optical sensing system 500A or Figure 1 Another example of a time-of-flight optical sensing system 100 is shown in FIG, and similarly named and numbered elements described above are similarly coupled and function below. It should also be understood that Figure 8 An example of a time-of-flight optical sensing system 800 with Figure 5A The example time-of-flight optical sensing system 500A shares many similarities.

[0106] For example, Figure 8 , an example time-of-flight light sensing system 800 includes a light source 802 synchronized with a time-of-flight sensor including a pixel array 810. In various examples, the light source 802 is configured to emit modulated light at only a portion of an object at a time, such as, for example, portion 107 of object 106, as shown in FIG. Figure 1 . In various examples, a laser can be used as light source 802, and the field of view of the laser can be controlled by various examples of a scanning mechanism. For example, in various examples, light source 802 can be implemented electronically (e.g., via an addressable laser array), mechanically (e.g., via a body or MEMS mirror), optically / electro-optically (e.g., via a phased array, liquid crystal, etc.), or with any other suitable type of light source or technology to emit modulated light toward an object in accordance with the teachings of the present invention.

[0107] In the depicted example, the time-of-flight sensor also includes a modulation driver block 834 that is coupled to the light source 802 and the pixel array 810. In operation, control and readout of enabled and disabled time-of-flight pixel circuits included in the time-of-flight pixel array 810 are synchronized with the modulated light emitted by the light source 802 toward the object. As shown in the depicted example, the time-of-flight pixel array 810 includes a plurality of time-of-flight pixel circuits 812A-812I. In the example, it should be noted that each of the time-of-flight pixel circuits 812A-812I can be Figure 7. Therefore, it should be understood that for the sake of brevity, each of the time-of-flight pixel circuits 812A to 812I is described in detail in FIG. Figure 8 No more detailed description is given in the.

[0108] exist Figure 8 , time-of-flight pixel circuits 812A-812I are arranged in rows and columns in a time-of-flight pixel array 810. It should be noted that for purposes of explanation, the time-of-flight pixel array 810 is illustrated having time-of-flight pixel circuits 812A-812I arranged in three rows and three columns. In other examples, it should of course be understood that the time-of-flight pixel array 810 may include a greater or fewer number of rows and / or a greater or fewer number of columns.

[0109] Figure 8 Depicted is an example in which reflected modulated light from an object is configured to illuminate one or more rows of time-of-flight pixel array 810, rather than all rows of time-of-flight pixel array 810 at once. For example, a first subset of the plurality of time-of-flight pixel circuits (e.g., the rows including time-of-flight pixel circuits 812A-812C) is configured to be illuminated by reflected modulated light from the object, while a second subset of the plurality of time-of-flight pixel circuits (e.g., the rows including time-of-flight pixel circuits 812D-812I) is configured not to be illuminated by reflected modulated light from the object.

[0110] As shown in the depicted example, modulation driver block 834 includes a phase-locked loop circuit 840 configured to generate first and second phase modulation signals TXA and TXB. Figure 8 As described in the example of FIG, first and second phase modulation signals TXA and TXB are coupled to be received by transfer transistors of time-of-flight pixel circuits 812A to 812I. Light source driver 844 is coupled between light source 802 and phase-locked loop circuit 840. In operation, light source driver circuit 844 is configured to synchronize modulated light emitted from light source 802 to an object with first and second phase modulation signals TXA and TXB in response to phase-locked loop circuit 840.

[0111] Continuing with the depicted example, a plurality of driver circuits 836A through 836F are coupled to phase-locked loop circuit 840. In the example, driver circuit 836A is configured to generate a first phase-modulated signal TXA, and driver circuit 836B is configured to generate a second phase-modulated signal TXB for rows of time-of-flight pixel array 810 including time-of-flight pixels 812A through 812C. Driver circuit 836C is configured to generate a first phase-modulated signal TXA, and driver circuit 836D is configured to generate a second phase-modulated signal TXB for rows of time-of-flight pixel array 810 including time-of-flight pixels 812D through 812F. Driver circuit 836E is configured to generate a first phase-modulated signal TXA, and driver circuit 836F is configured to generate a second phase-modulated signal TXB for rows of time-of-flight pixel array 810 including time-of-flight pixels 812G through 812I.

[0112] In the example, the modulation driver block 834 also includes a plurality of driver switches 838A to 838F. Each of the plurality of driver switches 838A to 838F is coupled to the output of a respective one of the plurality of driver circuits 836A to 836F, as shown in FIG. Figure 8 Thus, driver switch 838A is coupled to the output of driver circuit 836A, driver switch 838B is coupled to the output of driver circuit 836B, driver switch 838C is coupled to the output of driver circuit 836C, driver switch 838D is coupled to the output of driver circuit 836D, driver switch 838E is coupled to the output of driver circuit 836E, and driver switch 838F is coupled to the output of driver circuit 836F.

[0113] As shown in the example, the modulation driver block 834 also includes a modulation control circuit 835 coupled to a plurality of driver switches 838A through 838F. In operation, the modulation control circuit 835 is configured to turn off or disable driver switches coupled to time-of-flight pixel circuits that are not illuminated, while the modulation control circuit 835 is configured to turn on or enable driver switches coupled to time-of-flight pixel circuits that are illuminated.

[0114] To illustrate, in the above example where a first subset of the plurality of time-of-flight pixel circuits (e.g., a row including time-of-flight pixel circuits 812A-812C) is configured to be illuminated by reflected modulated light from an object, while a second subset of the plurality of time-of-flight pixel circuits (e.g., a row including time-of-flight pixel circuits 812D-812I) is configured not to be illuminated by reflected modulated light from an object, the modulation control circuit 835 is configured to turn on or enable driver switches 838A and 838B and to turn off or disable driver switches 836C-836F. Thus, the transfer transistors of the illuminated, and therefore enabled, time-of-flight pixel circuits 812A-812C are coupled to receive and respond to the first and second phase modulation signals TXA and TXB, while the transfer transistors of the non-illuminated, and therefore disabled, time-of-flight pixel circuits 812D-812F are not coupled to receive and therefore do not respond to the first and second phase modulation signals TXA and TXB.

[0115] Continuing with the depicted example, the modulation driver block 834 further includes a scan synchronization circuit 842 coupled to the modulation control circuit 835, as shown. In operation, the scan synchronization circuit 842 is configured to synchronize scanning of modulated light emitted by the light source across an object with scanning of a first subset of a plurality of time-of-flight pixel circuits illuminated by reflected modulated light across the time-of-flight pixel array 810. In other words, in accordance with the teachings of the present invention, the scan synchronization circuit 842 is configured to synchronize scanning of modulated light emitted by the light source 802 across an object with activation of appropriate driver switches 838A-838F coupled to corresponding time-of-flight pixel circuits 812A-812I illuminated by modulated light reflected from the object.

[0116] Figure 8 An example of a time-of-flight optical sensing system 800 with Figure 5A One of the differences between the example time-of-flight optical sensing system 500A is that Figure 8 The time-of-flight optical sensing system 800 includes a column control circuit 852 and a row control circuit 848. In the depicted example, the column control circuit 852 is configured to generate a column reset control signal (see, for example, Figure 7 CRST CTRL ), the column reset control signal is coupled to control the column reset control transistor of each of the time-of-flight pixel circuits 812A-812I (see, e.g., Figure 7 738 in FIG. 738). The column control circuit 852 is further configured to generate a first column sample and hold control signal (see, for example, Figure 7 CSH CTRL ), the hold control signal is coupled to control a first column sample and hold control transistor of each of the time-of-flight pixel circuits 812A-812I (see, e.g., Figure 7744A in FIG. 744B). Column control circuit 852 is also configured to generate a second column sample and hold control signal (see, for example, Figure 7 CSH CTRL ), the second column sample and hold control signal is coupled to control the second column sample and hold control transistor of each of the time-of-flight pixel circuits 812A to 812I (see, e.g., Figure 7 744B in the ).

[0117] Continuing with the depicted example, row control circuit 848 is configured to generate a row reset control signal (see, e.g., Figure 7 RRST CTRL ), the row reset control signal is coupled to control the row reset control transistor of each of the time-of-flight pixel circuits 812A-812I (see, e.g., Figure 7 740 in FIG. 740). In addition, the row control circuit 848 is further configured to generate a row sample and hold control signal (see, for example, Figure 7 RSH CTRL ), the sample and hold control signal is coupled to control the first column sample and hold control transistor and the second row sample and hold control transistor of each of the time-of-flight pixel circuits 812A-812I (see, e.g., Figure 7 742A and 742B in FIG. 7 ). In addition, the row control circuit 848 is also configured to generate a row select signal RS that is coupled to control the first row select transistor and the second row select transistor of each of the time-of-flight pixel circuits 812A to 812I (see, e.g., FIG. 7 ). Figure 7 732A and 732B), as shown.

[0118] In the depicted example, column readout circuitry 850 is coupled to first and second bit lines BL1 and BL2 of each of a plurality of time-of-flight pixel circuits 812A- 812I to read out each of the plurality of time-of-flight pixel circuits 812A- 812I of time-of-flight pixel array 810 as shown.

[0119] In operation, it should be understood that according to the teachings of the present invention, the use of Figure 8 The column reset control signal CRST supported by the time-of-flight optical sensing system 800 shown in FIG. CTRL , row reset control signal RRST CTRL , reset enable / disable control signal B2, column sample and hold control signal CSH CTRL , row sampling and holding signal RSH CTRLand sampling and holding enable / disable control signal B1, individual time-of-flight pixel circuits 812A to 812I can be randomly addressed and accessed so that the light spot-shaped portion of the time-of-flight light sensing system 800 can be illuminated and read out, as described above, for example Figure 3F In display.

[0120] The above description of the illustrated embodiments of the present invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Although specific embodiments of the present invention are described herein for illustrative purposes, as those skilled in the relevant art will recognize, various modifications are possible within the scope of the invention.

[0121] These modifications may be made to examples of the present 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 appended claims, which are to be construed in accordance with established doctrines of claim interpretation.

Claims

1. A time-of-flight sensor, comprising: A time-of-flight pixel array comprising a plurality of time-of-flight pixel circuits, wherein a first subset of the plurality of time-of-flight pixel circuits is configured to be illuminated by reflected modulated light from a portion of an object and a second subset of the plurality of time-of-flight pixel circuits is configured not to be illuminated by the reflected modulated light from the portion of the object, wherein each of the time-of-flight pixel circuits comprises: a photodiode configured to photogenerate charge in response to the reflected modulated light incident on the photodiode; a first floating diffusion configured to store a first portion of charge photogenerated in the photodiode; and a first transfer transistor configured to transfer the first portion of charge from the photodiode to the first floating diffusion in response to modulation by a first phase-modulated signal; and a first sample and hold transistor coupled between a first storage node and the first floating diffusion, wherein the first storage node is configured to store the first portion of the charge from the first floating diffusion through the first sample and hold transistor; and a modulation driver block configured to generate the first phase modulation signal, wherein the modulation driver block is coupled to a light source configured to emit the modulated light to the portion of the object, wherein the modulation driver block is configured to synchronize scanning of the modulated light emitted by the light source across the object with scanning of the first subset of the plurality of time-of-flight pixel circuits across the time-of-flight pixel array.

2. A time-of-flight sensor according to claim 1, wherein the modulation driver block is configured to enable the time-of-flight pixel circuits included in the first subset of the multiple time-of-flight pixel circuits to respond to the first phase modulation signal, and wherein the modulation driver block is configured to enable the time-of-flight pixel circuits included in the second subset of the multiple time-of-flight pixel circuits to be unable to respond to the first phase modulation signal. 3 . The time-of-flight sensor of claim 1 , wherein the first subset of the plurality of time-of-flight pixel circuits comprises one or more rows of time-of-flight pixel circuits of the time-of-flight pixel array. 4 . The time-of-flight sensor of claim 1 , wherein the first subset of the plurality of time-of-flight pixel circuits comprises one or more columns of time-of-flight pixel circuits of the time-of-flight pixel array. 5 . The time-of-flight sensor of claim 1 , wherein the first subset of the plurality of time-of-flight pixel circuits comprises a contiguous region of time-of-flight pixel circuits of the time-of-flight pixel array. 6 . The time-of-flight sensor of claim 1 , wherein the first subset of the plurality of time-of-flight pixel circuits comprises a plurality of non-contiguous regions of time-of-flight pixel circuits of the time-of-flight pixel array.

7. The time-of-flight sensor of claim 1 , wherein each of the time-of-flight pixel circuits further comprises: a second floating diffusion configured to store a second portion of the photogenerated charge in the photodiode; and a second transfer transistor configured to transfer the second portion of charge from the photodiode to the second floating diffusion in response to modulation by a second phase-modulated signal generated by the modulation driver, wherein the second phase-modulated signal is out of phase with the first phase-modulated signal, wherein the modulation driver block is further configured to generate the second phase-modulated signal.

8. The time-of-flight sensor of claim 7 , wherein each of the time-of-flight pixel circuits further comprises: a first reset transistor coupled between a first power rail and the first floating diffusion, wherein the first reset transistor is configured to reset the first floating diffusion; and A second reset transistor is coupled between the first power rail and the second floating diffusion, wherein the second reset transistor is configured to reset the second floating diffusion.

9. The time-of-flight sensor of claim 8, wherein each of the time-of-flight pixel circuits further comprises: A second sample and hold transistor is coupled between a second storage node and the second floating diffusion, wherein the second storage node is configured to store the second portion of the charge from the second floating diffusion through the second sample and hold transistor.

10. The time-of-flight sensor of claim 9, wherein each of the time-of-flight pixel circuits further comprises: a first source follower transistor having a gate coupled to the first storage node; a first row select transistor coupled between a source of the first source follower transistor and a first bit line; a second source follower transistor having a gate coupled to the second storage node; and A second row select transistor is coupled between the source of the second source follower transistor and a second bit line.

11. A time-of-flight sensor according to claim 10, wherein the first and second storage nodes of one of the multiple time-of-flight pixel circuits included in the second subset of the multiple time-of-flight pixel circuits are configured to be read out simultaneously, so that the first and second transfer transistors of one of the multiple time-of-flight pixel circuits included in the first subset of the multiple time-of-flight pixel circuits are configured to be modulated in response to the first and second phase modulation signals.

12. The time-of-flight sensor of claim 10 , wherein each of the time-of-flight pixel circuits further comprises: a column reset control transistor coupled to a gate of the first reset transistor and a gate of the second reset transistor, wherein the column reset control transistor is coupled to be responsive to a column reset control signal; a row reset control transistor coupled to the column reset control transistor, wherein the row reset control transistor is coupled to be responsive to a row reset control signal; and A reset enable / disable transistor is coupled to the gate of the first reset transistor and the gate of the second reset transistor, wherein the reset enable / disable transistor is coupled to be responsive to a reset enable / disable control signal.

13. The time-of-flight sensor of claim 12 , wherein each of the time-of-flight pixel circuits further comprises: a first column sample and hold control transistor coupled to a gate of the first sample and hold transistor, wherein the first column sample and hold control transistor is coupled to be responsive to a first column sample and hold control signal; a first row sample and hold control transistor coupled to the first column sample and hold control transistor, wherein the first row sample and hold control transistor is coupled to be responsive to a row sample and hold control signal; a first sample and hold enable / disable transistor coupled to the gate of the first sample and hold transistor, wherein the first sample and hold enable / disable transistor is coupled to be responsive to a sample and hold enable / disable control signal; a second column sample and hold control transistor coupled to a gate of the second sample and hold transistor, wherein the second column sample and hold control transistor is coupled to be responsive to a second column sample and hold control signal; a second row sample and hold control transistor coupled to the second column sample and hold control transistor, wherein the second row sample and hold control transistor is coupled to be responsive to the row sample and hold control signal; and A second sample and hold enable / disable transistor is coupled to the gate of the second sample and hold transistor, wherein the second sample and hold enable / disable transistor is coupled to be responsive to the sample and hold enable / disable control signal.

14. The time-of-flight sensor of claim 10 , wherein the modulation driver block comprises: a phase-locked loop circuit configured to generate the first and second phase-modulated signals; and A light source driver circuit is coupled between the light source and the phase-locked loop circuit, wherein the light source driver circuit is configured to synchronize the modulated light emitted from the light source to the portion of the object with the first and second phase-modulated signals in response to the phase-locked loop circuit.

15. A time-of-flight sensor according to claim 14, wherein the modulation driver block further includes a plurality of driver circuits coupled to the phase-locked loop circuit, wherein a first of the plurality of driver circuits is configured to generate the first phase modulation signal for the first subset of time-of-flight pixel circuits, wherein a second of the plurality of driver circuits is configured to generate the second phase modulation signal for the first subset of time-of-flight pixel circuits, wherein a third of the plurality of driver circuits is configured to generate the first phase modulation signal for the second subset of time-of-flight pixel circuits, and wherein a fourth of the plurality of driver circuits is configured to generate the second phase modulation signal for the second subset of time-of-flight pixel circuits.

16. The time-of-flight sensor of claim 15, wherein the modulation driver block further comprises: a plurality of driver switches, wherein each of the plurality of driver switches is coupled to an output of a corresponding one of the plurality of driver circuits, wherein a first one of the plurality of driver switches is coupled to an output of the first one of the plurality of driver circuits, wherein a second one of the plurality of driver switches is coupled to an output of the second one of the plurality of driver circuits, wherein a third one of the plurality of driver switches is coupled to an output of the third one of the plurality of driver circuits, and wherein a fourth one of the plurality of driver switches is coupled to an output of the fourth one of the plurality of driver circuits; and A modulation control circuit is coupled to the plurality of driver switches, wherein the modulation control circuit is configured to turn off the third of the plurality of driver switches and the fourth of the plurality of driver switches, while the modulation control circuit is configured to turn on the first of the plurality of driver switches and the second of the plurality of driver switches.

17. A time-of-flight sensor according to claim 16, wherein the modulation driver block further includes a scan synchronization circuit coupled to the modulation control circuit, wherein the scan synchronization circuit is configured to synchronize the scanning of the modulated light emitted by the light source across the object with the scanning of the first subset of the multiple time-of-flight pixel circuits across the time-of-flight pixel array.

18. The time-of-flight sensor of claim 14, further comprising: a plurality of delay locked loop circuits coupled in series to the phase locked loop circuit, wherein each of the plurality of delay locked loop circuits is configured to generate the first and second phase modulated signals having a respective phase shift; and A plurality of logic circuits coupled to the plurality of delay-locked loop circuits, wherein a first of the plurality of logic circuits is configured to generate the first phase-modulated signal having a first phase shift for the first subset of time-of-flight pixel circuits, wherein a second of the plurality of logic circuits is configured to generate the second phase-modulated signal having the first phase shift for the first subset of time-of-flight pixel circuits, wherein a third of the plurality of logic circuits is configured to generate the first phase-modulated signal having a second phase shift for the second subset of time-of-flight pixel circuits, and wherein a fourth of the plurality of logic circuits is configured to generate the second phase-modulated signal having the second phase shift for the second subset of time-of-flight pixel circuits.

19. The time-of-flight sensor of claim 18 , wherein the modulation driver block further comprises a modulation control circuit coupled to the plurality of logic circuits, wherein the modulation control circuit is configured to disable the third of the plurality of logic circuits and the fourth of the plurality of logic circuits while the modulation control circuit is configured to enable the first of the plurality of logic circuits and the second of the plurality of logic circuits.

20. A time-of-flight sensor according to claim 19, wherein the modulation driver block further includes a scan synchronization circuit coupled to the modulation control circuit, wherein the scan synchronization circuit is configured to synchronize the scanning of the modulated light emitted by the light source across the object with the scanning of the first subset of the multiple time-of-flight pixel circuits across the time-of-flight pixel array.

21. The time-of-flight sensor of claim 10, wherein the time-of-flight sensor further comprises: a row control circuit configured to generate a reset signal coupled to control the first reset transistor and the second reset transistor, wherein the row control circuit is further configured to generate a sample and hold signal coupled to control the first sample and hold transistor and the second sample and hold transistor, wherein the row control circuit is further configured to generate a row select signal coupled to control the first row select transistor and the second row select transistor; and Column readout circuitry is coupled to the first bit line and the second bit line to read out each of the time-of-flight pixel circuits.

22. The time-of-flight sensor of claim 13, wherein the time-of-flight sensor further comprises a column control circuit configured to generate the column reset control signal coupled to control the column reset control transistor, wherein the column control circuit is further configured to generate the first column sample and hold control signal coupled to control the first column sample and hold control transistor, wherein the column control circuit is further configured to generate the second column sample and hold control signal coupled to control the second column sample and hold control transistor; a row control circuit configured to generate the row reset control signal coupled to control the row reset control transistor, wherein the row control circuit is further configured to generate the row sample and hold control signal coupled to control the first row sample and hold control transistor and the second row sample and hold control transistor, wherein the row control circuit is further configured to generate a row select signal coupled to control the first row select transistor and the second row select transistor; and Column readout circuitry is coupled to the first bit line and the second bit line to read out each of the time-of-flight pixel circuits.

23. A time-of-flight sensing system comprising: a light source configured to emit modulated light toward a portion of the object; and a time-of-flight sensor configured to sense reflected modulated light from the object, wherein the time-of-flight sensor comprises: A time-of-flight pixel array comprising a plurality of time-of-flight pixel circuits, wherein a first subset of the plurality of time-of-flight pixel circuits is configured to be illuminated by the reflected modulated light from the object and a second subset of the plurality of time-of-flight pixel circuits is configured not to be illuminated by the reflected modulated light from the object, wherein each of the time-of-flight pixel circuits comprises: a photodiode configured to photogenerate charge in response to the reflected modulated light incident on the photodiode; a first floating diffusion configured to store a first portion of charge photogenerated in the photodiode; a first transfer transistor configured to transfer the first portion of charge from the photodiode to the first floating diffusion in response to modulation by a first phase modulation signal; and a first sample and hold transistor coupled between a first storage node and the first floating diffusion, wherein the first storage node is configured to store the first portion of the charge from the first floating diffusion through the first sample and hold transistor; and a modulation driver block configured to generate the first phase modulation signal, wherein the modulation driver block is configured to synchronize scanning of the modulated light across the object with scanning of the first subset of the plurality of time-of-flight pixel circuits across the time-of-flight pixel array, the first subset of the plurality of time-of-flight pixel circuits being configured to be illuminated by the reflected modulated light from the portion of the object.

24. A time-of-flight sensing system according to claim 23, wherein the modulation driver block is configured to enable the time-of-flight pixel circuits included in the first subset of the multiple time-of-flight pixel circuits to respond to the first phase modulation signal, and wherein the modulation driver block is configured to enable the time-of-flight pixel circuits included in the second subset of the multiple time-of-flight pixel circuits to be unable to respond to the first phase modulation signal.

25. The time-of-flight sensing system of claim 23, wherein the first subset of the plurality of time-of-flight pixel circuits comprises one or more rows of time-of-flight pixel circuits of the time-of-flight pixel array.

26. The time-of-flight sensing system of claim 23, wherein the first subset of the plurality of time-of-flight pixel circuits comprises one or more columns of time-of-flight pixel circuits of the time-of-flight pixel array.

27. The time-of-flight sensing system of claim 23, wherein the first subset of the plurality of time-of-flight pixel circuits comprises a contiguous region of time-of-flight pixel circuits of the time-of-flight pixel array.

28. The time-of-flight sensing system of claim 23, wherein the first subset of the plurality of time-of-flight pixel circuits comprises a plurality of non-contiguous regions of time-of-flight pixel circuits of the time-of-flight pixel array.

29. The time-of-flight sensing system of claim 23, wherein each of the time-of-flight pixel circuits further comprises: a second floating diffusion configured to store a second portion of the photogenerated charge in the photodiode; and a second transfer transistor configured to transfer the second portion of charge from the photodiode to the second floating diffusion in response to modulation by a second phase-modulated signal generated by the modulation driver, wherein the second phase-modulated signal is out of phase with the first phase-modulated signal, wherein the modulation driver block is further configured to generate the second phase-modulated signal.

30. The time-of-flight sensing system of claim 29, wherein each of the time-of-flight pixel circuits further comprises: a first reset transistor coupled between a first power rail and the first floating diffusion, wherein the first reset transistor is configured to reset the first floating diffusion; and A second reset transistor is coupled between the first power rail and the second floating diffusion, wherein the second reset transistor is configured to reset the second floating diffusion.

31. The time-of-flight sensing system of claim 30, wherein each of the time-of-flight pixel circuits further comprises: A second sample and hold transistor is coupled between a second storage node and the second floating diffusion, wherein the second storage node is configured to store the second portion of the charge from the second floating diffusion through the second sample and hold transistor.

32. The time-of-flight sensing system of claim 31 , wherein each of the time-of-flight pixel circuits further comprises: a first source follower transistor having a gate coupled to the first storage node; a first row select transistor coupled between a source of the first source follower transistor and a first bit line; a second source follower transistor having a gate coupled to the second storage node; and A second row select transistor is coupled between the source of the second source follower transistor and a second bit line.

33. A time-of-flight sensing system according to claim 32, wherein the first and second storage nodes of one of the multiple time-of-flight pixel circuits included in the second subset of the multiple time-of-flight pixel circuits are configured to be read out simultaneously, so that the first and second transfer transistors of one of the multiple time-of-flight pixel circuits included in the first subset of the multiple time-of-flight pixel circuits are configured to be modulated in response to the first and second phase modulation signals.

34. The time-of-flight sensing system of claim 32, wherein each of the time-of-flight pixel circuits further comprises: a column reset control transistor coupled to a gate of the first reset transistor and a gate of the second reset transistor, wherein the column reset control transistor is coupled to be responsive to a column reset control signal; a row reset control transistor coupled to the column reset control transistor, wherein the row reset control transistor is coupled to be responsive to a row reset control signal; and A reset enable / disable transistor is coupled to the gate of the first reset transistor and the gate of the second reset transistor, wherein the reset enable / disable transistor is coupled to be responsive to a reset enable / disable control signal.

35. The time-of-flight sensing system of claim 34, wherein each of the time-of-flight pixel circuits further comprises: a first column sample and hold control transistor coupled to a gate of the first sample and hold transistor, wherein the first column sample and hold control transistor is coupled to be responsive to a first column sample and hold control signal; a first row sample and hold control transistor coupled to the first column sample and hold control transistor, wherein the first row sample and hold control transistor is coupled to be responsive to a row sample and hold control signal; a first sample and hold enable / disable transistor coupled to the gate of the first sample and hold transistor, wherein the first sample and hold enable / disable transistor is coupled to be responsive to a sample and hold enable / disable control signal; a second column sample and hold control transistor coupled to a gate of the second sample and hold transistor, wherein the second column sample and hold control transistor is coupled to be responsive to a second column sample and hold control signal; a second row sample and hold control transistor coupled to the second column sample and hold control transistor, wherein the second row sample and hold control transistor is coupled to be responsive to the row sample and hold control signal; and A second sample and hold enable / disable transistor is coupled to the gate of the second sample and hold transistor, wherein the second sample and hold enable / disable transistor is coupled to be responsive to the sample and hold enable / disable control signal.

36. The time-of-flight sensing system of claim 32, wherein the modulation driver block comprises: a phase-locked loop circuit configured to generate the first and second phase-modulated signals; and A light source driver circuit is coupled between the light source and the phase-locked loop circuit, wherein the light source driver circuit is configured to synchronize the modulated light emitted from the light source to the portion of the object with the first and second phase-modulated signals in response to the phase-locked loop circuit.

37. A time-of-flight sensing system according to claim 36, wherein the modulation driver block further includes a plurality of driver circuits coupled to the phase-locked loop circuit, wherein a first of the plurality of driver circuits is configured to generate the first phase modulation signal for the first subset of time-of-flight pixel circuits, wherein a second of the plurality of driver circuits is configured to generate the second phase modulation signal for the first subset of time-of-flight pixel circuits, wherein a third of the plurality of driver circuits is configured to generate the first phase modulation signal for the second subset of time-of-flight pixel circuits, and wherein a fourth of the plurality of driver circuits is configured to generate the second phase modulation signal for the second subset of time-of-flight pixel circuits.

38. The time-of-flight sensing system of claim 37, wherein the modulation driver block further comprises: a plurality of driver switches, wherein each of the plurality of driver switches is coupled to an output of a corresponding one of the plurality of driver circuits, wherein a first one of the plurality of driver switches is coupled to an output of the first one of the plurality of driver circuits, wherein a second one of the plurality of driver switches is coupled to an output of the second one of the plurality of driver circuits, wherein a third one of the plurality of driver switches is coupled to an output of the third one of the plurality of driver circuits, and wherein a fourth one of the plurality of driver switches is coupled to an output of the fourth one of the plurality of driver circuits; and A modulation control circuit is coupled to the plurality of driver switches, wherein the modulation control circuit is configured to turn off the third of the plurality of driver switches and the fourth of the plurality of driver switches, while the modulation control circuit is configured to turn on the first of the plurality of driver switches and the second of the plurality of driver switches.

39. A time-of-flight sensing system according to claim 38, wherein the modulation driver block further includes a scan synchronization circuit coupled to the modulation control circuit, wherein the scan synchronization circuit is configured to synchronize the scanning of the modulated light emitted by the light source across the object with the scanning of the first subset of the multiple time-of-flight pixel circuits across the time-of-flight pixel array.

40. The time-of-flight sensing system of claim 36, wherein the modulation driver block comprises: a plurality of delay locked loop circuits coupled in series to the phase locked loop circuit, wherein each of the plurality of delay locked loop circuits is configured to generate the first and second phase modulated signals having a respective phase shift; and A plurality of logic circuits coupled to the plurality of delay-locked loop circuits, wherein a first of the plurality of logic circuits is configured to generate the first phase-modulated signal having a first phase shift for the first subset of time-of-flight pixel circuits, wherein a second of the plurality of logic circuits is configured to generate the second phase-modulated signal having the first phase shift for the first subset of time-of-flight pixel circuits, wherein a third of the plurality of logic circuits is configured to generate the first phase-modulated signal having a second phase shift for the second subset of time-of-flight pixel circuits, and wherein a fourth of the plurality of logic circuits is configured to generate the second phase-modulated signal having the second phase shift for the second subset of time-of-flight pixel circuits.

41. A time-of-flight sensing system according to claim 40, wherein the modulation driver block further includes a modulation control circuit, which couples the multiple logic circuits, wherein the modulation control circuit is configured to disable the third of the multiple logic circuits and the fourth of the multiple logic circuits, and at the same time the modulation control circuit is configured to enable the first of the multiple logic circuits and the second of the multiple logic circuits.

42. A time-of-flight sensing system according to claim 41, wherein the modulation driver block further includes a scan synchronization circuit coupled to the modulation control circuit, wherein the scan synchronization circuit is configured to synchronize the scanning of the modulated light emitted by the light source across the object with the scanning of the first subset of the multiple time-of-flight pixel circuits across the time-of-flight pixel array.

43. The time-of-flight sensing system of claim 32, wherein the time-of-flight sensor further comprises: a row control circuit configured to generate a reset signal coupled to control the first reset transistor and the second reset transistor, wherein the row control circuit is further configured to generate a sample and hold signal coupled to control the first sample and hold transistor and the second sample and hold transistor, wherein the row control circuit is further configured to generate a row select signal coupled to control the first row select transistor and the second row select transistor; and Column readout circuitry is coupled to the first bit line and the second bit line to read out each of the time-of-flight pixel circuits.

44. The time-of-flight sensing system of claim 35, wherein the time-of-flight sensor further comprises a column control circuit configured to generate the column reset control signal coupled to control the column reset control transistor, wherein the column control circuit is further configured to generate the first column sample and hold control signal coupled to control the first column sample and hold control transistor, wherein the column control circuit is further configured to generate the second column sample and hold control signal coupled to control the second column sample and hold control transistor; a row control circuit configured to generate the row reset control signal coupled to control the row reset control transistor, wherein the row control circuit is further configured to generate the row sample and hold control signal coupled to control the first row sample and hold control transistor and the second row sample and hold control transistor, wherein the row control circuit is further configured to generate a row select signal coupled to control the first row select transistor and the second row select transistor; and Column readout circuitry is coupled to the first bit line and the second bit line to read out each of the time-of-flight pixel circuits.

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