(19)
(11)EP 2 519 001 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
26.06.2019 Bulletin 2019/26

(21)Application number: 12165535.1

(22)Date of filing:  25.04.2012
(51)International Patent Classification (IPC): 
H04N 13/254(2018.01)
G01S 17/10(2006.01)
H04N 5/3745(2011.01)
H04N 13/296(2018.01)
G01S 17/89(2006.01)
H04N 5/235(2006.01)

(54)

Structured light imaging system

Strukturiertes Lichtabbildungssystem

Système d'imagerie à lumière structurée


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 26.04.2011 US 201161479029 P
19.01.2012 US 201213353593

(43)Date of publication of application:
31.10.2012 Bulletin 2012/44

(73)Proprietor: Aptina Imaging Corporation
KY1-9002 Grand Cayman (KY)

(72)Inventors:
  • Wan, Chung Chun
    Fremont, CA California 94568 (US)
  • Li, Xiangli
    San Jose, CA California 95131 (US)
  • Agranov, Gennadiy
    San Jose, CA California 95125 (US)

(74)Representative: Manitz Finsterwald Patent- und Rechtsanwaltspartnerschaft mbB 
Martin-Greif-Strasse 1
80336 München
80336 München (DE)


(56)References cited: : 
EP-A1- 2 296 368
US-B1- 6 369 899
US-A1- 2004 080 623
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    FIELD



    [0001] The present invention is directed to imaging systems and, more particularly, structured light imaging systems.

    BACKGROUND



    [0002] Structured light imaging systems are commonly used for three-dimensional (3D) imaging. A structured light imaging system has two main parts: an illumination source and a sensing device including an array of pixels. The illumination source projects one or more light patterns onto an object being imaged and the pixels within the sensing device detect light reflected by the object. The detected light is then processed by the sensing device to generate a representation of the object.

    [0003] FIG. 1 illustrates a typical four transistor (4T) pixel 50 utilized in a pixel array of an sensing device, such as a complementary metal-oxide-semiconductor (CMOS) sensing device. The pixel 50 includes a photosensor 52 (e.g., a photodiode), a storage node N configured as a floating diffusion (FD) region, transfer transistor 54, reset transistor 56, charge conversion transistor 58 configured as a source follower transistor, and row select transistor 60. The photosensor 52 is connected to the storage node N by the transfer transistor 54 when the transfer transistor 54 is activated by a transfer control signal TX. The reset transistor 56 is connected between the storage node N and an array pixel supply voltage VAA. A reset control signal RESET is used to activate the reset transistor 56, which resets the storage node N to a known state.

    [0004] The charge conversion transistor 58 has its gate connected to the storage node N and is connected between the array pixel supply voltage VAA and the row select transistor 60. The charge conversion transistor 58 converts the charge stored at the storage node N into an electrical output signal. The row select transistor 60 is controllable by a row select signal ROW for selectively outputting the output signal OUT from the-charge conversion transistor 58. For each pixel 50, two output signals are conventionally generated, one being a reset signal Vrst generated after the storage node N is reset, the other being an image or photo signal Vsig generated after charges are transferred from the photosensor 52 to the storage node N.

    [0005] FIG. 2 illustrates a sensing device 200 that includes an array 230 of pixels (such as the pixel 50 illustrated in FIG. 1) and a timing and control circuit 232. The timing and control circuit 232 provides timing and control signals for enabling the reading out of signals from pixels of the pixel array 230 in a manner commonly known to those skilled in the art. The pixel array 230 has dimensions of M rows by N columns of pixels, with the size of the pixel array 230 depending on its application.

    [0006] Signals from the sensing device 200 are typically read out a row at a time using a column parallel readout architecture. The timing and control circuit 232 selects a particular row of pixels in the pixel array 230 by controlling the operation of a row addressing circuit 234 and row drivers 240. Signals stored in the selected row of pixels are provided to a readout circuit 242 in the manner described above. The signals are read twice from each of the columns and then read out sequentially or in parallel using a column addressing circuit 244. The pixel signals (Vrst, Vsig) corresponding to the reset pixel signal and image pixel signal are provided as outputs of the readout circuit 242, and are typically subtracted by a differential amplifier 260 in a correlated double sampling operation and the result digitized by an analog to digital converter 264 to provide a digital pixel signal. The digital pixel signals represent an image captured by pixel array 230. The digital pixel signals are processed in an image processing circuit 268 to produce an output image.
    EP 2296368, US2004/080623 and US6369899 provide examples of prior arrangements with problems with regard to the structuring of lighting.

    SUMMARY OF THE INVENTION



    [0007] Aspects of the present invention are defined in the claims and particularly claim 1 and claim 9 below with other claims defining dependent features.

    BRIEF DESCRIPTION OF THE DRAWINGS



    [0008] The invention is best understood from the following detailed description when read in connection with the accompanying drawings, with like elements having the same reference numerals. When a plurality of similar elements are present, a single reference numeral may be assigned to the plurality of similar elements with a small letter designation referring to specific elements. When referring to the elements collectively or to a non-specific one or more of the elements, the small letter designation may be dropped. The letter "n" may represent a non-specific number of elements. Also, lines without arrows connecting components may represent a bidirectional exchange between these components. This emphasizes that according to common practice, the various features of the drawings are not drawn to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawings are the following figures:

    FIG. 1 is a circuit diagram illustrating a prior art four transistor pixel for use in a pixel array of an imaging device;

    FIG. 2 is a block diagram of a prior art imaging device;

    FIG. 3A is an illustration representing the generation, reflection, and capture of structured light in accordance with an aspect of the present invention;

    FIG. 3B is a block diagram of a multiple storage node pixel in accordance with an aspect of the present invention;

    FIG. 4A is an illustration partly in circuit diagram form of a two storage node pixel in accordance with an aspect of the present invention;

    FIG. 4B is an illustration partly in circuit diagram form of a four storage node pixel in accordance with an aspect of the present invention;

    FIG. 5 is a timing diagram illustrating exposure and readout for a four storage node pixel in accordance with an aspect of the present invention;

    FIG. 6 is an illustration partly in circuit diagram form of a N storage node pixel in accordance with an aspect of the present invention;

    FIG. 7A is a circuit diagram of a two storage node pixel in accordance with an aspect of the present invention;

    FIG. 7B is a semiconductor layer diagram and corresponding energy diagram for one storage node of a two storage node pixel in accordance with an aspect of the present invention;

    FIG. 7C is a circuit diagram of a two storage node pixel and readout circuitry in accordance with an aspect of the present invention;

    FIG. 8A is a circuit diagram of another two storage node pixel in accordance with an aspect of the present invention;

    FIG. 8B is a semiconductor layer diagram and corresponding energy diagram for one storage node of another two storage node pixel in accordance with an aspect of the present invention;

    FIG. 9A is a timing diagram for the circuit FIGs. 7A and 7C;

    FIG. 9B is a timing diagram for the circuit of FIG. 8A implemented using a readout structure such as illustrated in FIG. 7C; and

    FIG. 10 is a flow chart depicting the use of a two storage node register.


    DETAILED DESCRIPTION



    [0009] FIG. 3A depicts an imaging system 300 in accordance with an embodiment of the present invention. Systems in accordance with aspects of the present invention are able to capture depth information of a scene using an improved structured light approach. The depicted imaging system 300 includes an illumination source 302 and a sensing device 304 synchronized with the illumination source 302. The illustrated illumination source 302 is an infrared (IR) illumination source that generates structured light; however, other spectrums of light such as visible light may be employed. Suitable illumination sources for use with the present invention will be understood by one of skill in the art from the description herein.

    [0010] In accordance with one use, the imaging system 300 generates a 3D representation of an object/3D scene 306. The illumination source 302 generates pulsed structured light 303, which is directed toward the object 306. The object reflects portions of the pulsed structured light 303 as reflected structured light 307. The sensing device 304, which is in sync with the illumination source 302, captures the reflected light 307 and generates a 3D representation of the object. The illustrated sensing device 304 includes an array of pixels 308 and each pixel includes multiple storage elements, which are discussed in further detail below. Through the use of multiple storage elements, the present invention facilitates the capture and storage of rapidly changing scenes.

    [0011] FIG. 3B depicts a pixel 308 in accordance with an aspect of the present invention. The illustrated pixel 308 includes a photodiode 310 for converting light impinging on the photodiode to charge. The illustrated pixel308 also includes two storage elements, a first storage node 312 and a second storage note 314, for storing charge converted by the photodiode 310. In contrast to conventional structured light systems, the illumination source 302 illustrated in FIG. 3A emits pulses of structured light 303. As depicted in FIG. 3B, the pixels 308, being synchronized to the illumination source 302, are able to continuously capture reflected pulses of structured light 307- with the bright frames 307a (light pulses) stored in one storage element 312 while the background frames 307b (between light pulses) are stored in another storage element 314. Interleaving the bright and background frames in time strongly suppresses any degradation in depth resolution due to varying ambient lighting conditions. The time-interleaved frames acquired by the pixel 308 can be subtracted, e.g., either at the pixel or column level, upon read out in the analog domain to further improve performance. The charge stored in the storage elements 312/314 may be' combined in a floating diffusion region of a pixel output amplifier 316, which will be described in further detail below.

    [0012] FIG. 4A is a conceptual diagram depicted operation of a pixel 400 in accordance with an example of the present invention. The illustrated pixel400 includes a photodiode 402, a first switch 404 that selectively connects the photodiode 402 to a first storage element 406 (e.g., to store charge developed by the photodiode 402 during one or more light pulses), and a second switch 408 that selectively connects the photodiode 402 to a second storage element 410 (e.g., to store charge developed by the photodiode 402 between one or more light pulses). Being synchronized with the illumination source 302 (FIG. 3A), the two switches 404/408 of the pixel 400 are controlled to transfer photo-generated charges to the appropriate storage regions 406/410 where the new charges are added to the charges that were previously stored.

    [0013] In one embodiment, charge is accumulated in the photodiode 402 and then transferred to a storage element 406/410 (see, for example, FIGs. 7A and 7B and the related description below). In another embodiment, photo-generated charge is directly streamed and accumulated in a storage region 406/410 (see, for example, FIGs. 8A and 8B and the related description below). Pixel 400 may be synchronized and the switches 404/408 may be actuated under control of a conventional timing and control circuit such as timing and control circuit 232 depicted in FIG. 2. Suitable modifications to timing and control circuit 232 for use with pixel 400 and other pixels described herein will be understood by one of skill in the art from the description herein.

    [0014] FIG. 4B is a conceptual diagram depicting operation of another pixel 420 in accordance with an example of the present invention that enables projection and capture of multiple patterns, e.g., for more accurate depth measurement results. The illustrated pixel420 includes a photodiode 422 and four switches 424a-d that selectively connect the photodiode 422 to four respective storage elements 426a-d. By utilizing a pixel20 with four storage elements 426 as shown in FIG. 4B, three patterns projected by an illumination source and the background can all be captured in an exposure. In another embodiment, if one pattern is used, continuous acquisition can be performed in which readout and exposure are pipelined as shown in FIG. 5.

    [0015] FIG. 6 is a conceptual diagram depicting another pixel600 having a photodiode 602 and N storage elements 604a-N that can be selectively coupled to the photodiode 602 through N switches 606a-N. In accordance with this embodiment, N -1 projected patterns and the background can be captured. Further, since all the frames are interleaved in time, any degradation in depth resolution due to varying ambient lighting conditions is suppressed.

    [0016] FIG. 7A depicts a conceptual circuit diagram of a pixel 700 along with descriptive regions associated with semiconductor fabrication in accordance with aspects of the present invention. The pixel 700 includes a photodiode (PD) 702. The pixel 700 also includes a first storage device/element (SD1) 704 and a second storage device/element (SD2) 706. The first storage element 704 is selectively coupled to the photodiode 702 through a first storage gate (SG1) 708 and the second storage element 706 is selectively coupled to the photodiode 702 through a second storage gate (SG2) 710. Additionally, the first storage element 704 is selectively coupled to a first floating diffusion region (FD1) 712 through a first transfer switch (TX1) 714 and the second storage element 706 is selectively coupled to a second floating diffusion region (FD2) 716 through a second transfer switch (TX2) 718. The first and second floating diffusion regions 712/716 may be coupled together in one embodiment.

    [0017] FIG. 7B depicts an example of a semiconductor structure for implementing one storage element of a pixel 700 along with energy diagrams depicting the flow of electrons based on signals applied to the pixel 700, e.g., under the control of timing and control device 232 (FIG. 1). As depicted in FIG. 7B, the photodiode 702 may be fabricated as a p-n junction formed from a p+ region and an n- region within a semiconductor. The first storage element 704 may also be fabricated as a p-n junction formed from a p+ region and an n- region. A metal shield 720 is positioned over regions of the semiconductor other than the region including the photodiode 702 to prevent unwanted noise from being introduced. The first storage gate 708 and the first transfer switch 714 may be fabricated as poly-silicon or metal deposits on a dielectric layer on top of the semiconductor. The first floating diffusion region 712 may be fabricated as a n+ region.

    [0018] As indicated in the corresponding energy diagrams, applying a high signal level to the storage gate 708, signal SG, and a low signal level to the transfer switch, signal TX, allows charge to flow from the photodiode 702 to the storage element 704, but prevents the flow of charge to the floating diffusion region. Applying a low signal level to the storage gate 708 and a low signal level to the transfer switch isolates the charge stored in the storage element 704. Applying a low signal level to the storage gate 708 and a high signal level to the transfer switch allows charge to flow from the storage element to the floating diffusion region, but prevents the flow of charge from the photodiode 702 to the storage element 704.

    [0019] FIG. 7C depicts a circuit diagram 750 implementing the pixel 700 of FIG. 7A. In addition to the pixel components discussed above, pixel 700 includes a photodiode conditioning transistor 775, a reset transistor 780, and a charge conversion transistor 785 configured as a source follower transistor.

    [0020] The pixel 700 is coupled to conventional readout circuitry 752. The illustrated readout circuitry includes a row select transistor 790 and a voltage source, VM. The row select transistor 790 is controlled by a row signal, ROW, to produce an output signal, OUT, from a selected row.

    [0021] FIG. 9A depicts a timing diagram for controlling the operation of pixel 700. The pixel 700 is synchronized to structured light pulses produced by an illumination device (e.g., to illumination device signal, ID). The first storage gate signal, SG1, is in phase with the illumination device signal, ID, and is used to control the first storage gate 708. The second storage gate signal, SG2, is 180 degrees out of phase with the illumination device signal, ID, and is used to control the second storage gate 710. The first and second storage gate signals, SG1 and SG2, cycle a plurality of times (e.g., 10 times) to accumulate charge developed by the photodiode during the illumination device pulses in the first element 704 and to accumulate charge between the illumination device pulses in the second element 706. The appropriate number of cycles is dependent on the particular system and one of skill in the art will understand how to determine the appropriate number of cycles from the description herein.

    [0022] After the charge is accumulated in the first and second storage registers 704 and 706, the stored charge is read out of the storage registers and transferred to the floating diffusion regions 712/716 of the pixel during a Frame Valid period. In the illustrated embodiment, the charge is first read out of the first storage register 704 and, then, the charge is read out of the second storage register 706. Charge is read out of the first storage register by first applying a high row selection signal, ROW, to the row selection transistor 790 during the read out period, applying a reset signal, RST, pulse to the reset transistor 780 (which creates a Sample Reset pulse), and applying a transfer signal, TX1, pulse to the first transfer resistor 714. The readout circuitry 752 then reads the transferred charge during a Sample Signal period. A similar technique is applied to read out the charge stored in the second storage register.

    [0023] FIG. 8A depicts a conceptual circuit diagram of another pixel 800 along with descriptive regions associated with semiconductor fabrication in accordance with aspects of the present invention. The pixel 800 includes a photodiode (PD) 802. The pixel 800 also includes a first storage device/element (VB1) 804 and a second storage device/element (VB2) 806. The first storage element 804 is selectively coupled to the photodiode 802 through a first storage gate (SG1) 808 and the second storage element 806 is selectively coupled to the photodiode 802 through a second storage gate (SG2) 810. Additionally, the first storage element 804 is coupled to a first floating diffusion region (FD1) 812 through the structure of the first storage element 804 and the second storage element 806 is coupled to a second floating diffusion region (FD2) 816 through the structure of second storage element 806. The first and second floating diffusion regions 812/816 maybe coupled together in one embodiment.

    [0024] FIG. 8B depicts an example of a semiconductor structure for implementing one storage element of a pixel 800 along with energy diagrams depicting the flow of electrons based on signals applied to the pixel 800, e.g., under the control of timing and control device 232 (FIG. 1). As depicted in FIG. 8B, the photodiode 802 may be fabricated as a p-n junction formed from a p+ region and an n- region within a semiconductor. The first storage element 804 may be fabricated as an n- region. A metal shield 820 is positioned over regions of the semiconductor other than the region including the photodiode 802 to prevent unwanted noise from being introduced. The first storage gate 808 may be fabricated as poly-silicon or metal deposits on a dielectric layer on top of the semiconductor. The first floating diffusion region 812 may be fabricated as a n+ region.

    [0025] As indicated in the corresponding energy diagrams, applying a high signal level to the storage gate 808, signal SG, allows charge to flow from the photodiode 802 to the storage element 804, but prevents the flow of charge to the floating diffusion region. Applying a mid-level signal to the storage gate 808 isolates the charge stored in the storage element 804. Applying a low signal level to the storage gate 808 allows charge to flow from the storage element to the floating diffusion region, but prevents the flow of charge from the photodiode 802 to the storage element 804.

    [0026] The pixel 800 may be implemented using a circuit diagram such as the circuit diagram 750 and readout circuitry 752 described above with reference to FIG. 7A. Suitable modifications to circuit diagram 750 and readout circuitry 752 for use with pixel 800 will be understood by one of skill in the art from the description herein.

    [0027] FIG. 9B depicts a timing diagram for controlling the operation of pixel 800 implemented using a suitable modified circuit diagram 750 and readout circuitry 752. The pixel 800 is synchronized to structured light pulses produced by an illumination device (e.g., to illumination device signal, ID). The first storage gate signal, SG1, is in phase with the illumination device signal, ID, and is used to control the first storage gate 808. The second storage gate signal, SG2, is 180 degrees out of phase with the illumination device signal, ID, and is used to control the second storage gate 810. The first and second storage gate signals, SG1 and SG2, cycle a plurality of times (e.g., 10 times) to accumulate charge developed by the photodiode during the illumination device pulses in the first element 804 and to accumulate charge between the illumination device pulses in the second storage registers 806. The appropriate number of cycles is dependent on the particular system and one of skill in the art will understand how to determine the appropriate number of cycles from the description herein.

    [0028] After the charge is accumulated in the first and second storage registers 804 and 806, the stored charge is read out of the storage registers and transferred to the floating diffusion regions 812/816 of the pixel during a Frame Valid period. In the illustrated embodiment, the charge is first read out of the first storage register 804 and, then, the charge is read out of the second storage register 806. Charge is read out of the first storage register by first applying a high row selection signal, ROW, to the row selection transistor 790 during the read out period, applying a reset signal, RST, pulse to the reset transistor 780 (which creates a Sample Reset pulse), and then applying a low pulse to the storage signal, SG1. The readout circuitry 752 then reads the transferred charge during a Sample Signal period. A similar technique is applied to read out the charge stored in the second storage register.

    [0029] FIG. 10 is a flow chart 1000 depicting steps for storing charge in accordance with one embodiment of an imaging system.

    [0030] At step 1020, a stream of light pulses is generated. In one embodiment, the stream of light pulses is generated by an illumination source that generates a periodic stream of light pulses. The periodic stream of light pulses may have a rate of 5 kilo-Hertz. The stream of light pulses may be directed toward an object that is being imaged. In one embodiment, the stream of light pulses includes a single pattern of light. In other embodiments, the stream of light pulses include two or more distinct patterns. The patterns of light may include a pattern of random points or a zebra-stripe like pattern.

    [0031] At step 1040, the source of the light pulses and an image sensor are synchronized. In one embodiment, the image sensor is synchronized to the illumination source using conventional techniques that will be understood by one of skill in the art from the description herein.

    [0032] At step 1060, a reflection of the stream of light pulses is converted to charge. In one embodiment the stream of light pulses is reflected by an object that is being images/scanned and the reflected light is converted to charge by photodiodes within an array of pixels of the image sensor.

    [0033] At step 1080, the converted charge is routed to storage elements. If the converted charge corresponds to a light pulse, processing proceeds at block 1090. If the converted charge corresponds to a period of time between light pulses, processing proceeds at block 1100. In one embodiment, the photodiode is coupled to the first storage element to transfer accumulated charge converted during the one or more pulses of light and is coupled to the second storage element to transfer accumulated charge converted between the two or more pulses of light. In another embodiment, the charge converted by the photodiode is streamed to the first storage element during conversion of the one or more pulses of light and streamed by the photodiode to the second storage element between conversion of the two or more pulses of light.

    [0034] At step 1090, the converted charge corresponding to charge converted during one or more light pulses is stored in a first storage element of a pixel. At step 1100, the converted charge corresponding to charge converted between two or more light pulses is stored in a second storage element of a pixel. For example, charge converted from a first pulse may be stored to the first storage element, charge converted between the first pulse and a second pulse may be stored in a second storage element, charge converted from the second pulse may be stored to a third storage element, and charge converted between the second pulse and a third pulse may be stored to a fourth storage element.

    [0035] In embodiments where each pixel includes more than two storage element, charge may be stored in different storage elements based on the pattern of the structured light and/or to enable simultaneous conversion and readout of previously converted/stored charge. For example, where the stream of light pulses includes pulse streams having different patterns (e.g., a pulse having a first pattern, another pulse having a second pattern, and another pulse having a third pattern), the storing step during the one or more pulses of light may include storing charge converted from at least one pulse having the first pattern to the first storage element, storing charge converted from at least one pulse having the second pattern to a third storage element, and storing charge converted from at least one pulse having the third pattern to a fourth storage element.

    [0036] At step 1110, the system checks if additional cycles of the pulsed light are to be stored during an exposure period. If additional cycles are to be stored, processing proceeds at decision step 1080. If no more cycles are to be stored during the current exposure period, processing proceeds to step 1120.

    [0037] At step 1120, charge is processed and read out of the storage elements. In an embodiment including four storage elements, charge stored in the first and second storage elements may be read out during the storage of charge in the third and/or fourth storage elements. Charge converted between light pulses may be subtracted from charge converted during light pulses. For example, the charge stored in a second storage element may be subtracted from charge stored in a first storage element, e.g., either at the pixel or column level, upon read out in the analog domain to further improve performance. In embodiments where each pixel includes additional storage element, charge in one storage element (e.g., a storage element for storing charge between light pulses) may be subtracted from multiple storage elements (e.g., storage elements associated with pulses from different light patterns). For example, if there are four storage elements, charge stored in a second storage element may be subtracted from the charge stored in a first storage element, the charge stored in a third storage element, and the charge stored in a fourth storage element.

    [0038] Using conventional techniques that will be understood by one of skill in the art from the description herein, distance information may be obtained from the stored charge. In one example, the distortion of a projected pattern as imaged by the sensor can be used for an exact geometric reconstruction of the surface shape. By interleaving the captures of light and background frames and subtracting one from the other, the invention herein prevents degradation in depth resolution by rejecting the effects due to varying ambient illumination.

    [0039] In accordance with an embodiment, a structured light imaging system is provided, including an illumination source configured to generate a stream of light pulses and an image sensor having a photodiode that converts the stream after reflection by a scene to charge, a first storage element, a first switch coupled between the photodiode and the first storage element, a second storage element, a second switch coupled between the photodiode and the second storage element, and a controller coupled to the first and second switches, the controller configured to synchronize the image sensor to the illumination source, actuate the first switch to couple the first storage element to the photodiode to store charge converted during one or more of the light pulses, and actuate the second switch to couple the second storage element to the photodiode to store charge converted between one or more of the light pulses.

    [0040] In accordance with another embodiment, the image sensor further includes a readout circuit coupled to the controller wherein the controller is further configured to transfer charge stored in the first and second storage elements to the readout circuit.

    [0041] In accordance with another embodiment, the controller is further configured to subtract charge stored in the second storage element from charge stored in the first storage element.

    [0042] In accordance with another embodiment, the image sensor further includes a third storage element, a third switch coupled between the photodiode and the third storage element, a fourth storage element, and a fourth switch coupled between the photodiode and the fourth storage element, and the controller is further coupled to the third and fourth switches.

    [0043] In accordance with another embodiment, the stream of light pulses includes at least one pulse having a first pattern, at least one pulse having a second pattern, and at least one pulse having a third pattern, and the controller is further configured to actuate the first switch to couple the first storage element to the photodiode to store charge converted from the at least one pulse having the first pattern, actuate the third switch to couple the third storage element to the photodiode to store charge converted from the at least one pulse having the second pattern, and actuate the fourth switch to couple the fourth storage element to the photodiode to store charge converted from the at least one pulse having the third pattern.

    [0044] In accordance with another embodiment, the controller is further configured to subtract the charge stored in the second storage element from the charge stored in the first storage element, subtract the charge stored in the second storage element from the charge stored in the third storage element, and subtract the charge stored in the second storage element from the charge stored in the fourth storage element.

    [0045] In accordance with another embodiment, the stream includes a first pulse, a second pulse adjacent the first pulse, and a third pulse adjacent the second pulse and the controller is further configured to actuate the first switch to couple the photodiode to the first storage element to store charge converted from the first pulse, actuate the second switch to couple the photodiode to the second storage element to store charge converted between the first and second pulses, actuate the third switch to couple the photodiode to the third storage element to store charge converted from the second pulse, and actuate the fourth switch to couple the photodiode to the fourth storage element to store charge converted between the second and third pulses.

    [0046] In accordance with another embodiment, the system further includes a readout circuit coupled to the controller and the first, second, third, and fourth storage elements, where the controller is further configured to couple the readout circuit to the first and second storage elements when the photodiode is coupled to at least one of the third and fourth storage elements.

    [0047] In accordance with another embodiment, an imaging method is provided including generating a stream of light pulses; converting the stream after reflection by a scene to charge; storing charge converted during one or more of the light pulses to a first storage element; and storing charge converted between two or more of the light pulses to a second storage element.

    [0048] In accordance with another embodiment, the generating step is performed by an illumination source and the converting and storing steps are performed by an image sensor, the method further including synchronizing the image sensor to the illumination source.

    [0049] In accordance with another embodiment, the method further includes subtracting the charge stored in the second storage element from the charge stored in the first storage element.

    [0050] In accordance with another embodiment, the stream of light pulses includes at least one pulse having a first pattern, at least one pulse having a second pattern, and at least one pulse having a third pattern, the storing step during the one or more pulses of light including storing charge converted from at least one pulse having the first pattern to the first storage element; storing charge converted from at least one pulse having the second pattern to a third storage element; and storing charge converted from at least one pulse having the third pattern to a fourth storage element.

    [0051] In accordance with another embodiment, the method further includes subtracting the charge stored in the second storage element from the charge stored in the first storage element, subtracting the charge stored in the second storage element from the charge stored in the third storage element, subtracting the charge stored in the second storage element from the charge stored in the fourth storage element.

    [0052] In accordance with another embodiment, the stream includes a first pulse, a second pulse adjacent the first pulse, and a third pulse adjacent the second pulse, the storing steps including storing charge converted from the first pulse to the first storage element; storing charge converted between the first and second pulses to the second storage element; storing charge converted from the second pulse to a third storage element; and storing charge converted between the second and third pulses to a fourth storage element.

    [0053] In accordance with another embodiment, the converting step includes accumulating charge in a photodiode and the method further includes coupling the photodiode to the first storage element to transfer accumulated charge converted during the one or more pulses of light and coupling the photodiode to the second storage element to transfer accumulated charge converted between the two or more pulses of light.

    [0054] Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details without departing from the invention.


    Claims

    1. A structured light imaging system (300) comprising:
    an illumination source (302) configured to generate a plurality of light pulses (303) including first and second light pulses, wherein the first light pulse projects a first pattern of light onto a scene and wherein the second light pulse projects a second pattern of light onto the scene (306);
    and an image sensor comprising an array of pixels, each pixel comprising:

    a photodiode (310; 402; 422) that converts the light (307) reflected from the scene
    to a charge,

    a first storage element (312; 406; 426),

    a first switch (404; 424) coupled between the photodiode and the first storage element,

    a second storage element (314; 410; 426),

    a second switch (408; 424) coupled between the photodiode and the second storage element, the image sensor further comprising a controller coupled to the first and second switches, the controller configured to synchronize the image sensor to the illumination source, wherein, for each pixel, during an exposure period, the controller is configured to actuate the first switch to couple the first storage element to the photodiode to store charge converted during the first light pulse, and actuate the second switch to couple the second storage element to the photodiode to store charge converted between the first and second light pulses, each pixel further comprising:
    third and fourth storage elements (426), and third and fourth switches (424), wherein the third switch is coupled between the photodiode and the third storage element, wherein the fourth switch is coupled between the photodiode and the fourth storage element, wherein the controller is further coupled to the third and fourth switches, wherein the plurality of light pulses includes a third light pulse that projects a third pattern of light onto the scene, and wherein the controller is further configured to actuate the third switch to couple the third storage element to the photodiode to store charge converted during the second light pulse, actuate the fourth switch to couple the fourth storage element to the photodiode to store charge converted during the third light pulse, subtract the charge stored in the second storage element from the charge stored in the first storage element, subtract the charge stored in the second storage element from the charge stored in the third storage element, and subtract the charge stored in the second storage element from the charge stored in the fourth storage element.


     
    2. The system of claim 1, the image sensor further comprising:
    a readout circuit (242; 752) coupled to the controller;
    wherein the controller is further configured to transfer charge stored in the first and second storage elements to the readout circuit.
     
    3. The system of claim 1, further comprising:

    a readout circuit coupled to the controller and the first, second, third, and fourth storage elements,

    wherein the controller is further configured to couple the readout circuit to the first and second storage elements when the photodiode is coupled to at least one of the third and fourth storage elements.


     
    4. An imaging method comprising:

    with a light source (302), generating a plurality of light pulses (303), wherein the plurality of light pulses includes at least a first light pulse that projects a first pattern of light onto a scene (306) and a second light pulse that projects a second pattern of light onto the scene, wherein the first pattern is different than the second pattern;

    with a a photodiode in each pixel (308: 400; 420; 600) of an image sensor (310; 402; 422), converting (1090) reflected light from the scene to charge;

    synchronizing the image sensor to the illumination source;

    wherein, during an exposure period: coupling the photodiode to a first storage element in the pixel; storing (1100) charge converted during the first pulse to the first storage element in the pixel;

    coupling the photodiode to a second storage element in the pixel; storing (1100) charge converted between the first and second light pulses to the second storage element in the pixel, wherein the plurality of light pulses includes at least a third light pulse that projects a third pattern of light onto the scene;

    coupling the photodiode to a third storage element in the pixel; storing charge converted during the second light pulse to the third storage element in the pixel;

    coupling the photodiode to a fourth storage element in the pixel; storing charge converted during the third light pulse to the fourth storage element in the pixel;

    subtracting the charge stored in the second storage element from the charge stored in the first storage element;

    subtracting the charge stored in the second storage element from the charge stored in the third storage element; and

    subtracting the charge stored in the second storage element from the charge stored in the fourth storage element.


     


    Ansprüche

    1. Strukturiertes Lichtabbildungssystem (300), das umfasst:

    eine Beleuchtungsquelle (302), die ausgestaltet ist, um mehrere Lichtimpulse (303) zu erzeugen, welche erste und zweite Lichtimpulse beinhalten, wobei der erste Lichtimpuls ein erstes Lichtmuster auf eine Szene projiziert und wobei der zweite Lichtimpuls ein zweites Lichtmuster auf die Szene (306) projiziert;
    und

    einen Bildsensor, der eine Pixelmatrix umfasst, wobei jeder Pixel umfasst:

    eine Fotodiode (310; 402; 422), die das von der Szene reflektierte Licht (307) in eine Ladung umwandelt,

    ein erstes Speicherelement (312; 406; 426),

    einen ersten Schalter (404; 424), der zwischen die Fotodiode und das erste Speicherelement gekoppelt ist,

    ein zweites Speicherelement (314; 410; 426),

    einen zweiten Schalter (408; 424), der zwischen die Fotodiode und das zweite Speicherelement gekoppelt ist,
    wobei der Bildsensor ferner umfasst

    einen Controller, der mit dem ersten und zweiten Schalter gekoppelt ist, wobei der Controller ausgestaltet ist, um den Bildsensor mit der Beleuchtungsquelle zu synchronisieren, wobei der Controller während einer Belichtungsperiode ausgestaltet ist, um für jeden Pixel den ersten Schalter zu betätigen, um das erste Speicherelement mit der Fotodiode zum Speichern von Ladung zu koppeln, die während des ersten Lichtimpulses umgewandelt wurde, und um den zweiten Schalter zu betätigen, um das zweite Speicherelement mit der Fotodiode zu koppeln, um Ladung zu speichern, die zwischen dem ersten und zweiten Lichtimpuls umgewandelt wurde,

    wobei jeder Pixel ferner umfasst:

    dritte und vierte Speicherelemente (426), und

    dritte und vierte Schalter (424), wobei der dritte Schalter zwischen die Fotodiode und das dritte Speicherelement gekoppelt ist, wobei der vierte Schalter zwischen die Fotodiode und das vierte Speicherelement gekoppelt ist, wobei der Controller ferner mit dem dritten und vierten Schalter gekoppelt ist, wobei die mehreren Lichtimpulse einen dritten Lichtimpuls beinhalten, der ein drittes Lichtmuster auf die Szene projiziert, und wobei der Controller ferner ausgestaltet ist, um den dritten Schalter zu betätigen, um das dritte Speicherelement mit der Fotodiode zu koppeln, um Ladung zu speichern, die während des zweiten Lichtimpulses umgewandelt wurde, um den vierten Schalter zu betätigen, um das vierte Speicherelement mit der Fotodiode zu koppeln, um Ladung zu speichern, die während des dritten Lichtimpulses umgewandelt wurde, um die Ladung, die in dem zweiten Speicherelement gespeichert ist, von der Ladung zu subtrahieren, die in dem ersten Speicherelement gespeichert ist, um die Ladung, die in dem zweiten Speicherelement gespeichert ist, von der Ladung zu subtrahieren, die in dem dritten Speicherelement gespeichert ist, und um die Ladung, die in dem zweiten Speicherelement gespeichert ist, von der Ladung zu subtrahieren, die in dem vierten Speicherelement gespeichert ist.


     
    2. System nach Anspruch 1, wobei der Bildsensor ferner umfasst:

    eine Ausleseschaltung (242; 752), die mit dem Controller gekoppelt ist;

    wobei der Controller ferner ausgestaltet ist, um Ladung, die in dem ersten und zweiten Speicherelement gespeichert ist, an die Ausleseschaltung zu übertragen.


     
    3. System nach Anspruch 1, das ferner umfasst:

    eine Ausleseschaltung, die mit dem Controller und dem ersten, zweiten, dritten und vierten Speicherelement gekoppelt ist,

    wobei der Controller ferner ausgestaltet ist, um die Ausleseschaltung mit dem ersten und zweiten Speicherelement zu koppeln, wenn die Fotodiode mit dem dritten und/oder dem vierten Speicherelement gekoppelt ist.


     
    4. Abbildungsverfahren, das umfasst, dass:

    mit einer Lichtquelle (302) mehrere Lichtimpulse (303) erzeugt werden, wobei die mehreren Lichtimpulse mindestens einen ersten Lichtimpuls, der ein erstes Lichtmuster auf eine Szene (306) projiziert, und einen zweiten Lichtimpuls, der ein zweites Lichtmuster auf die Szene projiziert, beinhalten, wobei sich das erste Muster von dem zweiten Muster unterscheidet;

    mit einer Fotodiode in jedem Pixel (308; 400; 420; 600) eines Bildsensors (310; 402; 422) reflektiertes Licht von der Szene in Ladung umgewandelt wird (1090);

    der Bildsensor mit der Beleuchtungsquelle synchronisiert wird;

    wobei während einer Belichtungsperiode:

    die Fotodiode mit einem ersten Speicherelement in dem Pixel gekoppelt wird;

    Ladung, die während des ersten Lichtimpulses umgewandelt wird, in dem ersten Speicherelement in dem Pixel gespeichert wird (1100);

    die Fotodiode mit einem zweiten Speicherelement in dem Pixel gekoppelt wird;

    Ladung, die zwischen dem ersten und dem zweiten Lichtimpuls umgewandelt wird, in dem zweiten Speicherelement in dem Pixel gespeichert wird (1100), wobei die mehreren Lichtimpulse mindestens einen dritten Lichtimpuls beinhalten, der ein drittes Lichtmuster auf die Szene projiziert;

    die Fotodiode mit einem dritten Speicherelement in dem Pixel gekoppelt wird;

    Ladung, die während des zweiten Lichtimpulses umgewandelt wird, in dem dritten Speicherelement in dem Pixel gespeichert wird;

    die Fotodiode mit einem vierten Speicherelement in dem Pixel gekoppelt wird;

    Ladung, die während des dritten Lichtimpulses umgewandelt wird, in dem vierten Speicherelement in dem Pixel gespeichert wird;

    die Ladung, die in dem zweiten Speicherelement gespeichert ist, von der Ladung subtrahiert wird, die in dem ersten Speicherelement gespeichert ist;

    die Ladung, die in dem zweiten Speicherelement gespeichert ist, von der Ladung subtrahiert wird, die in dem dritten Speicherelement gespeichert ist; und

    die Ladung, die in dem zweiten Speicherelement gespeichert ist, von der Ladung subtrahiert wird, die in dem vierten Speicherelement gespeichert ist.


     


    Revendications

    1. Système d'imagerie à lumière structurée (300) comprenant :

    une source d'éclairage (302) configurée pour générer une pluralité d'impulsions lumineuses (303) incluant des première et deuxième impulsions lumineuses, la première impulsion lumineuse projetant un premier motif de lumière sur une scène et la deuxième impulsion lumineuse projetant un deuxième motif de lumière sur la scène (306) ; et

    un capteur d'image comprenant un réseau de pixels, chaque pixel comprenant :

    une photodiode (310 ; 402 ; 422) qui convertit la lumière (307) réfléchie par la scène en une charge,

    un premier élément de stockage (312 ; 406 ; 426),

    un premier commutateur (404 ; 424) couplé entre la photodiode et le premier élément de stockage,

    un deuxième élément de stockage (314 ; 410 ; 426),

    un deuxième commutateur (408 ; 424) couplé entre la photodiode et le deuxième élément de stockage,

    le capteur d'image comprenant en outre un dispositif de commande couplé aux premier et deuxième commutateurs, le dispositif de commande étant configuré pour synchroniser le capteur d'image avec la source d'éclairage, dans lequel, pour chaque pixel, pendant une période d'exposition, le dispositif de commande est configuré pour actionner le premier commutateur pour coupler le premier élément de stockage à la photodiode afin de stocker la charge convertie pendant la première impulsion lumineuse et actionner le deuxième commutateur pour coupler le deuxième élément de stockage à la photodiode afin de stocker la charge convertie entre les première et deuxième impulsions lumineuses,

    chaque pixel comprenant en outre :
    des troisième et quatrième éléments de stockage (426) et des troisième et quatrième commutateurs (424), le troisième commutateur étant couplé entre la photodiode et le troisième élément de stockage, le quatrième commutateur étant couplé entre la photodiode et le quatrième élément de stockage, le dispositif de commande étant en outre couplé aux troisième et quatrième commutateurs, la pluralité d'impulsions lumineuses incluant une troisième impulsion lumineuse qui projette un troisième motif de lumière sur la scène, et le dispositif de commande étant en outre configuré pour actionner le troisième commutateur pour coupler le troisième élément de stockage à la photodiode afin de stocker la charge convertie pendant la deuxième impulsion lumineuse, actionner le quatrième commutateur pour coupler le quatrième élément de stockage à la photodiode afin de stocker la charge convertie pendant la troisième impulsion lumineuse, soustraire la charge stockée dans le deuxième élément de stockage de la charge stockée dans le premier élément de stockage, soustraire la charge stockée dans le deuxième élément de stockage de la charge stockée dans le troisième élément de stockage et soustraire la charge stockée dans le deuxième élément de stockage de la charge stockée dans le quatrième élément de stockage.


     
    2. Système selon la revendication 1, le capteur d'image comprenant en outre :

    un circuit de lecture (242 ; 752) couplé au dispositif de commande ;

    le dispositif de commande étant en outre configuré pour transférer une charge stockée dans les premier et deuxième éléments de stockage au circuit de lecture.


     
    3. Système selon la revendication 1, comprenant en outre :

    un circuit de lecture couplé au dispositif de commande et aux premier, deuxième, troisième et quatrième éléments de stockage,

    le dispositif de commande étant en outre configuré pour coupler le circuit de lecture aux premier et deuxième éléments de stockage lorsque la photodiode est couplée à au moins l'un des troisième et quatrième éléments de stockage.


     
    4. Procédé d'imagerie comprenant les étapes consistant à :

    avec une source de lumière (302), générer une pluralité d'impulsions lumineuses (303), la pluralité d'impulsions lumineuses incluant au moins une première impulsion lumineuse qui projette un premier motif de lumière sur une scène (306) et une deuxième impulsion lumineuse qui projette un deuxième motif de lumière sur la scène, le premier motif étant différent du deuxième motif ;

    avec une photodiode dans chaque pixel (308 : 400 ; 420 ; 600) d'un capteur d'image (310 ; 402 ; 422), convertir (1090) la lumière réfléchie par la scène en une charge ;

    synchroniser le capteur d'image avec la source d'éclairage ;

    et, pendant une période d'exposition :

    coupler la photodiode à un premier élément de stockage du pixel ;

    stocker (1100) la charge convertie pendant la première impulsion dans le premier élément de stockage du pixel ;

    coupler la photodiode à un deuxième élément de stockage du pixel ;

    stocker (1100) la charge convertie entre les première et deuxième impulsions lumineuses dans le deuxième élément de stockage du pixel, la pluralité d'impulsions lumineuses incluant au moins une troisième impulsion lumineuse qui projette un troisième motif de lumière sur la scène ;

    coupler la photodiode à un troisième élément de stockage du pixel ;

    stocker la charge convertie pendant la deuxième impulsion lumineuse dans le troisième élément de stockage du pixel ;

    coupler la photodiode à un quatrième élément de stockage du pixel ;

    stocker la charge convertie pendant la troisième impulsion lumineuse dans le quatrième élément de stockage du pixel ;

    soustraire la charge stockée dans le deuxième élément de stockage de la charge stockée dans le premier élément de stockage ;

    soustraire la charge stockée dans le deuxième élément de stockage de la charge stockée dans le troisième élément de stockage ; et

    soustraire la charge stockée dans le deuxième élément de stockage de la charge stockée dans le quatrième élément de stockage.


     




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    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description