WO2001039491A1 - Retroaction de courant de masse de capteur d'image permettant de regler l'intensite de l'eclairage - Google Patents

Retroaction de courant de masse de capteur d'image permettant de regler l'intensite de l'eclairage Download PDF

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Publication number
WO2001039491A1
WO2001039491A1 PCT/US2000/041090 US0041090W WO0139491A1 WO 2001039491 A1 WO2001039491 A1 WO 2001039491A1 US 0041090 W US0041090 W US 0041090W WO 0139491 A1 WO0139491 A1 WO 0139491A1
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WO
WIPO (PCT)
Prior art keywords
bulk
image sensor
signal
scene
current
Prior art date
Application number
PCT/US2000/041090
Other languages
English (en)
Inventor
Randy R. Dunton
Lawrence A. Booth
Werner Metz
Original Assignee
Intel Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Intel Corporation filed Critical Intel Corporation
Priority to AU21127/01A priority Critical patent/AU2112701A/en
Publication of WO2001039491A1 publication Critical patent/WO2001039491A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/70—Circuitry for compensating brightness variation in the scene
    • H04N23/71—Circuitry for evaluating the brightness variation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/70—Circuitry for compensating brightness variation in the scene
    • H04N23/74—Circuitry for compensating brightness variation in the scene by influencing the scene brightness using illuminating means
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/70—SSIS architectures; Circuits associated therewith
    • H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors

Definitions

  • This invention is generally related to solid state cameras and more Particularly to techniques for controlling the illumination of a scene being captured by the camera.
  • Solid state cameras are becoming increasingly popular as the price of imaging electronics including the solid state image sensor is being reduced through design and manufacturing improvements.
  • An essential part of taking good quality pictures under low light conditions using a solid state camera is to properly illuminate the scene being captured. Otherwise, the picture may become either too dark (not enough "flash”) or too bright, i.e. too much flash.
  • the flash or "strobe" is typically controlled using a dedicated photoelectric circuit. The illumination of the scene is detected by the photoelectric circuit and when a sufficient level has been reached, the strobe is quenched. While such a technique may achieve the proper illumination for taking good quality pictures, it can add significantly to the manufacturing cost of the camera.
  • the separate, dedicated photoelectric sensor circuit must be manufactured and incorporated into the camera together with its own optics, separate from the camera's image sensor and imaging optics.
  • the response of the dedicated circuit and associated optics needs to be calibrated in relation to the output from the image sensor and imaging optics, so that an accurate determination of the amount of strobe light required to illuminate the scene being captured by the image sensor can be made.
  • An embodiment of the invention is directed to an improved method for controlling illumination of a scene.
  • Light reflected from the scene is allowed to be incident upon an image sensor.
  • the image sensor has a bulk region.
  • a number of photosites of the image sensor are disposed on a surface of the bulk region.
  • a first signal representative of a bulk current from the bulk region is provided. Illumination of the scene is controlled responsive to the first signal.
  • Fig. 1 illustrates a block diagram of an image sensor that can be configured according to an embodiment of the invention.
  • Fig. 2 illustrates a side view of the image sensor, through a cross section, and a circuit for controlling illumination according to an embodiment of the invention.
  • Fig. 3 illustrates a side view of the image sensor and a circuit for controlling illumination according to another embodiment of the invention.
  • Fig. 4 shows a schematic of a circuit for controlling illumination.
  • Figs. 5 and 6 illustrate signal timing for controlling illumination and capturing a scene.
  • Fig. 7 shows a block diagram of an imaging system, such as a solid state camera, configured according to an embodiment of the invention.
  • the various embodiments of the invention provide improved techniques for controlling the illumination of a scene that is being captured by a solid state image sensor, such that the manufacturing cost of the imaging system that contains the solid state image sensor may be reduced without degrading the quality of pictures taken under low light conditions.
  • the conventional, dedicated photoelectric circuit and associated optics used for metering light to control the strobe are eliminated. Instead, the image sensor and imaging optics are used to measure the light reflected from the scene, through the same optical train that is responsible for producing pictures of the scene. This is accomplished by using a feedback system that controls the light source, e.g. the strobe, based on a signal that is representative of a bulk current.
  • This bulk current is due, for the most part, to photogenerated charge in the image sensor caused by the incident light reflected from the scene being captured. This photogenerated charge flows through a bulk terminal of the image sensor.
  • the embodiments of the invention provide an excellent opportunity for further reducing the cost of solid state cameras by eliminating the conventional, dedicated photoelectric circuit and its associated optics.
  • the image sensor 104 may be of a conventional type manufactured by a metal oxide semiconductor (MOS) process, or it may alternatively be of a charge coupled device (CCD) variety. In general, it will be apparent from the following description that the invention in its various embodiments is not limited to any particular type of image sensor.
  • the image sensor 104 includes an array of photosites 108, each to provide an electrical signal in proportion to the sensed, incident light such that together, the photosites can electrically capture the scene whose image is incident upon the array.
  • Each photosite 108 includes a photodetector (e.g.
  • the signals representing the incident light appear on bitlines, where each bitline is connected to a column of photosites for the example shown in Fig. 1. Each row of photosites is connected to a common reset line which is used to prepare each connected photosite at the start of an exposure interval to detect the incident light.
  • the signal representing the sensed incident light is placed on the bitlines by asserting the row select signals, allowing the signals on the bitlines to be sampled on a row by row basis.
  • the exemplary architecture for the image sensor 104 described above and shown in Fig. 1 is not the only architecture which can benefit from the invention's techniques for controlling illumination.
  • the image sensor 104 shown in Fig. 1 is merely a convenient example provided to more easily describe the various embodiments of the invention.
  • each photosite has a photodiode with a respective p-n junction formed between a first semiconductor region 206 and a bulk region 208, with a depletion region delineated by the dotted line.
  • the bulk region 208 may be a continuous substrate of an integrated circuit (IC) die in which all of the photosites of the array are formed, or it may be a number of wells (tubs) of the same conductivity type formed in a substrate of the opposite conductivity type in the IC die.
  • IC integrated circuit
  • the bulk region may alternatively be n- type, depending upon the type of photodetector used in the photosite. More generally, the bulk region 208 may be any semiconductor region on the surface of which the photosites of the sensor array responsible for capturing the scene are disposed, where a photosensitive portion of each photosite may be formed inside the bulk region.
  • the photons of the incident light create photogenerated electron-hole pairs in the photosensitive regions of the sensor array. These may be created either inside or outside the depletion region of a photodiode. Once created, the electrons (indicated by the "-" sign) are collected by the depletion region of the photosite, while some of the holes (indicated by a "+") contribute to a bulk current in a conducting terminal which may be shorted to the bulk region 208. Each photosite 108 and the region between photosites in the image sensor 104 may contribute such holes to form the bulk current. The bulk current has a primary contribution from photogenerated holes, but may also have an additional contribution due to leakage currents. The amplitude of this bulk current is proportional to the amount of light reflected from the scene and incident upon the image sensor 104 during the exposure interval in which the scene is being captured.
  • the bulk region is coupled to a common supply node 214 via a relatively low impedance path through a current measurement circuit 204.
  • the supply node 214 is ground (zero volts).
  • the current measurement circuit 204 is capable of sensing the bulk current as, for instance, a voltage referenced to ground, and produces a signal that represents the bulk current at its output.
  • the output of the current measurement circuit 204 is coupled to a threshold detection circuit 212 which provides an output signal for controlling the illumination of the scene in response to the output of the current measurement circuit 204 indicating that a particular threshold level of bulk current has been reached.
  • Fig. 3 illustrates an alternative to the circuit of Fig. 2, where the threshold detect circuit 212 is configured to compare a first signal being a bulk voltage, nonetheless representative of the bulk current, to a predetermined threshold level, and in response, generate a signal to control the illumination.
  • the bulk voltage is the voltage that is generated across a load (not shown) inside the threshold detect circuit 212 when the bulk current flows into the supply node 214.
  • Fig. 4 illustrates a schematic of a particular embodiment of the invention, including a particular version of the current measurement circuit 204 and the threshold detection circuit 212 that corresponds to the embodiment of Fig. 2.
  • the current measurement circuit 204 in this embodiment includes a resistor 420 connected between the bulk region 208 and the supply node 214.
  • a first switch 424 is provided to zero the output of the current measurement circuit 204, for the condition where no bulk current is to be sensed.
  • the current measurement circuit 204 also includes an integrator represented here by a capacitor 428 that is coupled to integrate the voltage across the resistor 420 which is buffered by an amplifier 432.
  • the output of the integrator takes the form of a ramp signal that has an amplitude proportional to the total energy incident on the image sensor from the scene under illumination.
  • a second switch 434 is provided to zero the output of the integrator. This will be done at the start of the exposure interval in which the photosites are allowed to detect the incident light.
  • the output of the integrator in this embodiment being the voltage across the capacitor 428, is compared to a threshold signal NREF1 using a comparator 440.
  • the output of the comparator 440 delivers the signal used to control illumination of the scene.
  • the output of the comparator 440 changes, thus acting as a trigger to quench, i.e. substantially lower the output of or shut off, the strobe which illuminates the scene being captured by the photosites 108a and 108b.
  • the circuit in Fig.4 may be modified to implement the alternative embodiment of Fig. 3 in which illumination is controlled in response to a bulk voltage having reached a predetermined threshold level, without integrating the bulk voltage.
  • the input of the comparator 440 in the threshold detection circuit 212 is shorted to the bulk region 208 which is referenced to ground through some load (not shown).
  • the various embodiments of the invention described above are used in a method for controlling the illumination of a scene while capturing the scene electronically.
  • the method is now described in view of the image sensor 104 illustrated in Fig. 1 and the particular embodiment of Fig. 4.
  • the references to RESET and SELECT signals below in Figs. 5 and 6 are to those in Fig. 1 that are applied to control the photosites 108.
  • Fig. 5 illustrates an exemplary timing diagram of the reset, select and other control signals that are used to capture the scene and control the strobe according to an embodiment of the invention.
  • RESET While RESET is asserted, the voltage across the capacitor 428 is zero.
  • the start of the exposure interval occurs when RESET is deasserted and the photosites are allowed to convert incident energy (reflected from the scene) into electrical signals.
  • the strobe may have already been turned on, such that the light reflected from the scene and incident upon the image sensor includes light from this strobe. This in turn causes a bulk current to flow from the bulk region 208 (see Fig. 4).
  • GROUND is deasserted which opens switch 424, such that the bulk current produced in the image sensor 104 can be detected by the current measurement circuit 204 as a voltage across the resistor 420.
  • An INTEGRATED signal that represents the bulk current begins to ramp upwards at the output of the buffer 432 as the incident energy is received by the image sensor 104.
  • the signal is compared to a predetermined threshold value VREF1 by the comparator 440.
  • the threshold value represents the predetermined point at which the scene being captured is deemed properly illuminated, such that at this point, the strobe is to be lowered or shut off. This latter event is accomplished in response to the ILLUM CONTROL signal being asserted.
  • the exposure interval continues, in other words the photosites are allowed to continue to convert incident energy into electrical signals, beyond the point at which ILLUM CONTROL is asserted. This may involve the situation where there may be sources of light other than the strobe that are also illuminating the scene.
  • the SELECT signal is asserted and the photosite signals may be sampled.
  • ILLUM CONTROL is deasserted to prepare the camera for the next exposure. Note that GROUND should be asserted at the same time as or before SELECT is asserted, so as to properly sample the photosite signals.
  • the lowering or shutting off of the strobe during the exposure interval is immediately followed by the end of the exposure interval, as shown in the alternative timing diagram of Fig. 6. This is in contrast to the timing of Fig. 5 in which the illumination is lowered or turned off at a much earlier time than the end of the exposure interval.
  • the illumination may be turned on or increased at some point later than the start of the exposure interval.
  • the period of time the illumination is turned on or is kept at a relatively high level may be shifted to anywhere in the exposure interval or slightly before it, to yield images having the desired quality. This may be done based upon factors such as the nature of the particular scene being captured, the length of the exposure interval, the sensitivity of the image sensor photosites, and other imaging system parameters.
  • the above described embodiments of the invention featuring techniques for controlling illumination using the bulk current of an image sensor may be applied to a wide range of image sensor technologies.
  • the sensor may be manufactured according to a metal oxide semiconductor (MOS) fabrication process in which each photosite has a photodiode coupled to reset circuitry and readout circuitry.
  • the photodiode has one end coupled to the bulk region (in Fig. 2, this end is also shared by the bulk region 208) through a low impedance path, and another end to provide a voltage representing a portion the sensed scene (in Fig. 2, this end is n-type).
  • the photosites of the image sensor may be charged coupled devices (CCDs).
  • CCDs charged coupled devices
  • the bulk current that is measured is primarily the result of an exposure of the photosites and the rest of the image sensor to an image of the scene under illumination which is being captured at the same time by the image sensor.
  • Fig. 7 illustrates a block diagram of an imaging system 700, such as a solid state camera, which features certain embodiments of the invention for controlling illumination of a scene being captured.
  • the system 700 has an image sensor 104 formed as a 2-dimensional array that provides photosite signals in analog form in response to light energy being incident upon the array.
  • the incident light is guided by imaging optics 730 having an aperture 732 and a focusing lens 736, after being reflected from a scene (represented by the arrow).
  • the incident light generates a bulk current (Ibulk) which flows into the current measurement circuit 204.
  • the current measurement circuit 204 and the threshold detect circuit 212 are part of control signal generation circuitry 704. This circuitry may also include column/row read control circuitry to generate the reset and select signals for the image sensor array.
  • the reset and select signals are provided with the appropriate timing, such that all of the photosites in the sensor array can be properly sampled upon completion of the exposure interval, to form a electronic image.
  • An exposure control circuit 706 is configured to instruct the threshold detect circuit 212 to quench the output of a strobe 740 prior to the end of an exposure interval in which the scene is captured by the sensor 104.
  • the photosite signals After the photosite signals have been sampled by bitline processing circuitry (not shown), they may be forwarded to an analog to digital converter 710 which digitizes the signals. These digitized signals are then processed according to known image and signal processing techniques, by digital processing block 714.
  • the digital processing may include, for instance, color correction functions, scaling, and perhaps compression, to yield a digital image file or a sequence of digital image "frames" that constitute a video stream.
  • the digital images may be communicated to an image processing and /or viewing system, such as a stand-alone personal computer (not shown) or a printer, via a communication interface 724.
  • the communication interface 724 may feature a computer peripheral bus interface, such as a high speed serial interface that is capable of transporting the digital images as a video stream.
  • the digital images, and in particular still shots may be placed in a removable storage device 728, such as a flash memory card, for subsequent transfer to the image processing and viewing equipment.
  • the overall operation of the components in the imaging system 700 may be orchestrated by a system controller 722 that may feature a microcontroller or a processor that is executing firmware.
  • the role of the system controller 722 may be expanded to include that of exposure control 706 and column/row read control 702, as well as the digital processing 714.
  • the system controller 722 may be a sophisticated, logic state machine rather than a programmed processor.
  • the system controller 722 may be configured to respond to configuration commands received from outside of the system 700 via the communication interface 724, where the timing of the exposure intervals and the processing and transport of the digitized photosite signals and /or digital images are controlled by these configuration commands.
  • the system 700 may be a digital camera that is tethered to a personal computer and is essentially controlled by software running on the personal computer.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Transforming Light Signals Into Electric Signals (AREA)
  • Studio Devices (AREA)

Abstract

Un des modes de réalisation de la présente invention concerne un procédé permettant de régler l'intensité de l'éclairage d'une scène saisie par un capteur d'image, répondant à un signal représentant un courant de masse. Le capteur d'image comporte une zone faisant masse sur laquelle sont disposés un certain nombre de photosites. La lumière réfléchie par la scène et incidente au capteur d'image contribue au courant de masse de la zone faisant masse.
PCT/US2000/041090 1999-11-29 2000-10-05 Retroaction de courant de masse de capteur d'image permettant de regler l'intensite de l'eclairage WO2001039491A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU21127/01A AU2112701A (en) 1999-11-29 2000-10-05 Image sensor bulk current feedback for controlling illumination

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US45047099A 1999-11-29 1999-11-29
US09/450,470 1999-11-29

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WO2001039491A1 true WO2001039491A1 (fr) 2001-05-31

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AU (1) AU2112701A (fr)
TW (1) TW490588B (fr)
WO (1) WO2001039491A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005096620A1 (fr) * 2004-03-25 2005-10-13 Eastman Kodak Company Capteur d'images de portee dynamique etendue

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4338514A (en) * 1980-04-07 1982-07-06 Spin Physics, Inc. Apparatus for controlling exposure of a solid state image sensor array
US4809076A (en) * 1986-04-16 1989-02-28 Hitachi, Ltd. Imaging apparatus using solid state image sensor
US4823199A (en) * 1986-03-11 1989-04-18 Minolta Camera Kabushiki Kaisha Still video adapter device detachable to a camera body
JPH0490688A (ja) * 1990-08-06 1992-03-24 Canon Inc 電子スチルカメラ

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4338514A (en) * 1980-04-07 1982-07-06 Spin Physics, Inc. Apparatus for controlling exposure of a solid state image sensor array
US4823199A (en) * 1986-03-11 1989-04-18 Minolta Camera Kabushiki Kaisha Still video adapter device detachable to a camera body
US4809076A (en) * 1986-04-16 1989-02-28 Hitachi, Ltd. Imaging apparatus using solid state image sensor
JPH0490688A (ja) * 1990-08-06 1992-03-24 Canon Inc 電子スチルカメラ

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 016, no. 318 (E - 1232) 13 July 1992 (1992-07-13) *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005096620A1 (fr) * 2004-03-25 2005-10-13 Eastman Kodak Company Capteur d'images de portee dynamique etendue

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TW490588B (en) 2002-06-11
AU2112701A (en) 2001-06-04

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