WO2002032114A1 - Capteur optique - Google Patents

Capteur optique Download PDF

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Publication number
WO2002032114A1
WO2002032114A1 PCT/EP2001/011279 EP0111279W WO0232114A1 WO 2002032114 A1 WO2002032114 A1 WO 2002032114A1 EP 0111279 W EP0111279 W EP 0111279W WO 0232114 A1 WO0232114 A1 WO 0232114A1
Authority
WO
WIPO (PCT)
Prior art keywords
optical sensor
pixel
photocurrent
sensor according
measured value
Prior art date
Application number
PCT/EP2001/011279
Other languages
German (de)
English (en)
Inventor
Tarek LULÈ
Original Assignee
Silicon Vision Ag
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
Priority claimed from DE10125307A external-priority patent/DE10125307A1/de
Application filed by Silicon Vision Ag filed Critical Silicon Vision Ag
Priority to AU2002223570A priority Critical patent/AU2002223570A1/en
Publication of WO2002032114A1 publication Critical patent/WO2002032114A1/fr

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J1/44—Electric circuits
    • G01J1/46—Electric circuits using a capacitor
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/60—Noise processing, e.g. detecting, correcting, reducing or removing noise
    • H04N25/67—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response
    • H04N25/671—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response for non-uniformity detection or correction
    • H04N25/672—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response for non-uniformity detection or correction between adjacent sensors or output registers for reading a single image

Definitions

  • the invention relates to an optical sensor for detecting a useful light signal in an ambient light environment and a method directed therefor for the operation of an optical sensor, which operates in such a way that the light intensity incident on it is converted into an electrical photocurrent in each individual pixel of the sensor, this photocurrent (I ph ) is integrated into a measured value for a predetermined period of time and is stored as a measured value, and the measured values, which are stored pixel by pixel, are read out and combined to form the entire image.
  • Such an optical sensor is known from WO 98/14002. It is a pixel-by-pixel (pixel-by-pixel) organized sensor, which is typically designed as an area sensor or as a line sensor. The smallest unit of such a sensor is the individual pixel, which has evaluation electronics assigned to it.
  • the intensity-dependent or wave-dependent incident radiation is converted pixel by pixel via a photoelectric converter into a photocurrent which flows into a charge store, in particular a capacitor, for a certain time, the so-called integration period. After the integration period has elapsed, the current at the capacitor Voltage is a quantitative measure of the measured value. All the measured values assigned to different pixels are read out by central readout electronics of the optical sensor at the desired time in the desired order and, when put together, result in the image captured by the sensor.
  • the starting point of the present invention is the need to detect a useful light signal, for example the light of a light-emitting diode (LED) or the image of an object illuminated by an external light source, especially if it is arranged in an ambient light environment, the light intensity of which is that of the useful light signal far exceeds.
  • a useful light signal for example the light of a light-emitting diode (LED) or the image of an object illuminated by an external light source, especially if it is arranged in an ambient light environment, the light intensity of which is that of the useful light signal far exceeds.
  • a solution known from practice for the operation of an optical sensor consists in first capturing an image of the useful light signal in its ambient light environment, then a further image in the case of a non-activated useful light signal and then subtracting both images from one another.
  • the object of the invention is to create an optical sensor and a method for its operation which enable the resolution of useful light signals even if the stray light intensity is many times higher than the useful light intensity.
  • This object is achieved in the case of an optical sensor of the type mentioned at the outset in that a compensation current is superimposed on the measured photocurrent for each individual pixel in order to detect the useful light signal freed from the stray light component, the size of which is determined in this way, in particular on the basis of a calibration process preceding the measurement, that it corresponds to the photocurrent value which results solely from the stray light incident on the respective pixel, so that only the photocurrent component corresponding to the useful light signal incident on the respective pixel is stored as a measured value to be processed further.
  • each pixel _ the photocurrent is corrected by - a compensation current, the size of which is such that it corresponds to the proportion of the photocurrent caused exclusively by the stray light, so that only that of the stray light freed portion of the image caused photo current portion is stored as a measured value.
  • the invention is characterized in that the difference between the stray light signal component and the useful light signal component already takes place during the integration phase, specifically in the individual pixel.
  • the measure of subtracting pixel-based from the entire recorded photocurrent that part of the photocurrent which is solely due to the stray light and only feeding the difference signal to further processing also enables the resolution of useful light signals whose light intensity is less than that by a factor of up to 1000 Intensity of the ambient light.
  • Electronic compensation in the individual pixel effectively suppresses the physical effect of photon noise, which placed an upper limit on the previous resolution of known sensors.
  • the size of the respective compensation current in the individual pixel is preferably determined in each case by a calibration process preceding the measurement, in which the optical sensor only detects the stray light. During the calibration process, the stray light-related photo currents are detected and stored. In the subsequent step of measuring the useful light signal and the stray light signal, these stored values are available for the respective definition of the " . Kompensationsstro.ir.es in the individual pixel"
  • the compensation current is fed in at the connection point between the optoelectronic converter and the measured value detection device.
  • the compensation current is set by the previous calibration process in such a way that it corresponds to the pure interference signal and thus only the difference between the total measured photocurrent and the compensation current, which corresponds to the pure useful signal, is detected, stored and further processed in the measured value detection device.
  • a current source preferably integrated in the individual pixel, whose current value can be variably adjusted is used to feed the compensation current, in accordance with a further preferred embodiment in that it is associated with a further storage means in which a pixel-related manipulated variable for the compensation current that is determined in each case in the calibration process is stored, which is required to set the compensation current.
  • this value for the compensation current which is stored in the further storage means, results from the fact that a control loop is formed from the measured value detection device, the optoelectronic converter and the compensation current source, in which the compensation current is set during the calibration phase.
  • Embodiments for the optical sensor according to the invention emerge from the further subclaims 6 to 13 and 21 to 24.
  • the variant of the invention according to the method provides two operating phases for the sensor, namely first a calibration phase and then a measuring phase.
  • the calibration phase in which the active lighting, that is to say the useful signal, is switched off, the compensation current value is generated automatically pixel by pixel and stored in the further storage means.
  • the measurement phase in which the active lighting is switched on and in which the measured photocurrent is reduced locally at the location of the individual pixel by the previously specified compensation current, so that only the remains due to the useful light signal.
  • the switching process between the calibration phase and the measurement phase is modulated by the useful signal, for example by clocked switching on or off of the useful signal or by modulating the intensity of the useful signal.
  • a different time period or a different temporal relationship between the calibration phase and the measurement phase can be set. If the intensity ratio is very low, more frequent calibration of the sensor is required.
  • the duration of the integration of the photocurrent component I diff during the measurement phase also depends on the respective ratio of useful light and stray light.
  • the solution according to the invention is suitable for all types of sensors, that is to say area, line or sensors which consist of only a single pixel.
  • Fig. 1 is a circuit diagram for explaining the principle of the invention for compensating the stray light component
  • 2 shows a circuit design of an optical sensor according to the invention, based on a single pixel
  • Fig. 4 is a timing diagram for explaining the
  • Fig. 5 shows another timing diagram to explain the operation of the sensor according to the invention
  • FIG. 1 shows a circuit diagram to explain it, the functional principle on which the optical sensor according to the invention is based:
  • the circuit implemented for a single pixel consists of a photodetector 1, a storage capacitor 2 and a current source 3. All three elements are connected to one another via a common node.
  • the incident radiation that strikes the photodetector 1 is converted by the latter into a photocurrent I ph .
  • the photocurrent I h is composed of the proportions caused by the useful light and the disturbance light.
  • a current value I corap for the current source 3 is determined in a calibration process preceding the measurement, which is exclusively the Corresponding stray light signal component that falls in the individual pixel.
  • the compensation current I comp meets the photocurrent I ph in such a way that only the difference between the two currents reaches the storage capacitor 2.
  • This differential current thus corresponds to the proportion of useful light incident on the respective pixel.
  • the differential current is fed in during the duration of the integration time, which is determined by a switch (not shown).
  • the voltage U Int present at the storage capacitor 2 is thus a measure of the charge stored in the storage capacitor and caused by the differential current I diff .
  • the compensation current I comp By feeding the compensation current I comp into the node between the photodetector l_and the storage capacitor 2, the essential portion of the interfering light signal is subtracted during the integration. The compensation takes place locally for each pixel. In addition, the compensation current is determined in an automatic manner, as described below. This results in what is known as a locally auto-compensating sensor (LACS).
  • LACS locally auto-compensating sensor
  • the integration time in the individual pixel ie the time during which the integration of the photocurrent component I dlff in Storage capacitor 2 takes place, must be as large as possible in order to achieve the greatest possible resolution.
  • the lower limit for the integration time is defined by the time required to collect enough active charge carriers for the useful signal, not only to be above the photon noise ("shot noise"), but also above the "read noise” and reset noise "of the circuit arrangement.
  • FIG. 2 A practical exemplary embodiment for the optical sensor according to the invention is shown in FIG. 2.
  • this circuit arrangement is expanded in that the storage capacitor 2 works together with an amplifier A x and a first switch S- L is assigned to it.
  • the output of the first amplifier A t is coupled to a second amplifier stage A 2 , to which a further switch S 2 is connected, to which a further storage capacitor 4 (C CTRL ) is arranged.
  • This circuit point is connected to the input of the compensation current source 3.
  • the compensation flow I corap is determined in a first operating phase , the so-called calibration phase .
  • the optical sensor is only exposed to stray light.
  • both switches S 1 (“Reset”) and S 2 ("Store”) are closed.
  • a photocurrent flows from the optoelectronic converter 1 into the storage capacitor C Int , so that the integrated voltage U Int drops across the capacitor.
  • the measurement phase begins, in which both useful light and stray light are detected by the optoelectronic converter 1.
  • the current source 3 then feeds the compensation current value taken from the voltage U CTRL at the further storage capacitor C CTRL into the node, so that as a result the differential current I diff flows into the storage capacitor C Int during an integration period predetermined by the opening of the switch S x .
  • An improvement in the sensitivity of the aforementioned circuit can be achieved by repeating the two-stage operation described at certain intervals, the transition between the calibration and measurement phases correlated with the useful light, for example by appropriate pulsation, takes place (“synchronized exposure”).
  • a further improvement in sensitivity is achieved in that two alternative storage capacitors C int are used, into which the photocurrent component I diff flows in an alternating order.
  • FIG. 3 shows three sketches for the architecture of the readout control of the value stored by the storage capacity C Int .
  • the first variant, FIG. 3 (1) relates to the direct reading of the pixel memory value without the provision of a further buffer.
  • the READ switch is pressed, the. in. the measured value detection device 2 is read out via a read-out circuit 5 and passed on to the read-out control device for further processing.
  • This variant requires the smallest area on the sensor.
  • This variant is intended for continuous operation, in which the integration is running until the integration value has been read out.
  • the first amplifier stage A-. (Fig. 2) is reset when reading and the value in the reset state (reset value) is also read out. It is only possible to apply synchronized lighting to the sensor if the integration time of the readout time plus an additional time for the common exposure equivalent. Shorter integration times can be achieved, but without synchronized exposure. Preferably, one image should be taken with synchronized exposure and one without being able to subtract residual interference.
  • the time required to acquire the two images is 2 x (T readout + T sync ) + T comp , the integration time for each image is fixed to the value: T readout + T sync . Since the duration of the active lighting can therefore only be a fraction of the total integration time, the suppression of the interference light image is comparatively poor in this variant.
  • the variant shown in FIG. 3 (2) includes a “sample & hold” circuit 6 in order to record the previous integration result for the readout process while the next storage value is already being integrated. A synchronized exposure of any length is possible.
  • Fig. 4 shows a timing diagram for the variant according to Fig. 3 (2), ie the design with a single sample & hold circuit.
  • Fig. 4 (A) refers to the so-called "standard rolling shutter mode" without synchronized lighting.
  • FIG. 4 (B) shows an operation according to "Rolling Shutter Mode" with an additionally provided time T Sync in order to achieve a synchronized exposure.
  • Both images, with and without active illumination, are present within the pixel, one on the sample capacity and the other in the first amplifier group.
  • the image period is extended by the time for the synchronized exposure. Pixels of some rows initially integrate the remaining Störlichtbeleuchtung, while those of the other rows integrate first under the active illumination ⁇ . however, this procedure can lead to adverse secondary effects however, the advantage of this method is that both the measuring phases carried out the calibration as within one frame period, still sufficiently. can be kept short.
  • the readout process and integration are completely decoupled from one another.
  • the calibration and integration are fully synchronized between all pixels, with the results of the previous integration phase being read out line by line.
  • T Sync and T Int can now be made as long as the readout time. This results in maximum sensitivity and optimal suppression of stray light.
  • the disadvantage of this variant is, however, that the time between the calibration and the end of the integration, that with the Calibration should correlate, 2 x T Read is.
  • the circuit complexity per pixel is greater.
  • the improved sensitivity has already been mentioned above. The two images are read out one after the other, so that the first must be buffered in an additional memory during the readout of the second image.
  • Fig. 5 shows the associated time frame scheme.
  • the integration and readout phases appear completely separate so that the readout does not hinder the calibration process. However, the time frames add up to T Read + T I ⁇ t + T Komp .
  • the integration phase can be selected to be short, as a result of which the correlation of the compensation with the stray light lighting is improved, and likewise the suppression of the stray light. The effort per pixel is greatest here.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Photometry And Measurement Of Optical Pulse Characteristics (AREA)
  • Transforming Light Signals Into Electric Signals (AREA)

Abstract

L'invention concerne un capteur optique destiné à détecter un signal de lumière utile dans un environnement de lumière parasite. Ledit capteur comporte plusieurs unités de points d'image (pixels) respectivement constituées d'un convertisseur optoélectronique (1) destiné à transformer la lumière incidente en courant photoélectrique (Iph), et d'un système de détection de valeur de mesure (2) destiné à extraire et enregistrer une valeur de mesure correspondant au courant photoélectrique détecté. Ledit capteur comporte par ailleurs un dispositif de commande de lecture destiné à lire les valeurs de mesure enregistrées afin de créer l'image d'ensemble à partir de valeurs de mesure individuelles concernant les points d'image. La présente invention est caractérisée en ce qu'un courant de compensation (Icomp) est superposé au courant photoélectrique mesuré (Iph) pour chaque point d'image, pour la détection du signal de lumière utile essentiellement libre de lumière parasite, la grandeur du courant de compensation étant fixée notamment au moyen d'un processus de calibrage antérieur à la mesure, de manière que ledit courant de compensation corresponde au courant photoélectrique exclusivement produit par la lumière parasite incidente au niveau du point d'image correspondant, et qu'uniquement la partie du courant photoélectrique (Idiff) correspondant au signal de lumière utile incidente au niveau du point d'image correspondant est enregistrée en tant que valeur de mesure devant être traitée de façon ultérieure.
PCT/EP2001/011279 2000-10-07 2001-09-29 Capteur optique WO2002032114A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2002223570A AU2002223570A1 (en) 2000-10-07 2001-09-29 Optical sensor

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
DE10049691.1 2000-10-07
DE10049691 2000-10-07
DE10125307.9 2001-05-17
DE10125307A DE10125307A1 (de) 2000-10-07 2001-05-17 Optischer Sensor

Publications (1)

Publication Number Publication Date
WO2002032114A1 true WO2002032114A1 (fr) 2002-04-18

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PCT/EP2001/011279 WO2002032114A1 (fr) 2000-10-07 2001-09-29 Capteur optique

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WO (1) WO2002032114A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2004027985A2 (fr) * 2002-09-13 2004-04-01 Conti Temic Microelectronic Gmbh Ensemble photodetecteur et procede de compensation de lumiere parasite
WO2004027357A1 (fr) * 2002-09-13 2004-04-01 Conti Temic Microelectronic Gmbh Montage de photodetection et procede de compensation de la lumiere parasite
US6861637B2 (en) * 2002-08-12 2005-03-01 Micron Technology, Inc. Providing current to compensate for spurious current while receiving signals through a line
US8822901B2 (en) 2011-07-13 2014-09-02 Elmos Semiconductor Ag Device for ambient light compensation for optical sensors exposed to both useful light and ambient light

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0521255A2 (fr) * 1991-05-02 1993-01-07 Licentia Patent-Verwaltungs-GmbH Agencement de détecteur de photo
WO1999060777A1 (fr) * 1998-05-19 1999-11-25 Conexant Systems, Inc. Detecteur de pixels actifs a echantillonnage double correle sans condensateur

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0521255A2 (fr) * 1991-05-02 1993-01-07 Licentia Patent-Verwaltungs-GmbH Agencement de détecteur de photo
WO1999060777A1 (fr) * 1998-05-19 1999-11-25 Conexant Systems, Inc. Detecteur de pixels actifs a echantillonnage double correle sans condensateur

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
LULE T ET AL: "DESIGN AND FABRICATION OF A HIGH-DYNAMIC-RANGE IMAGE SENSOR IN TFA TECHNOLOGY", IEEE JOURNAL OF SOLID-STATE CIRCUITS, IEEE INC. NEW YORK, US, vol. 34, no. 5, May 1999 (1999-05-01), pages 704 - 711, XP000908584, ISSN: 0018-9200 *

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6861637B2 (en) * 2002-08-12 2005-03-01 Micron Technology, Inc. Providing current to compensate for spurious current while receiving signals through a line
US6927434B2 (en) 2002-08-12 2005-08-09 Micron Technology, Inc. Providing current to compensate for spurious current while receiving signals through a line
US7601999B2 (en) 2002-08-12 2009-10-13 Aptina Imaging Corporation Method and apparatus for reading signals through a line
US8159007B2 (en) 2002-08-12 2012-04-17 Aptina Imaging Corporation Providing current to compensate for spurious current while receiving signals through a line
WO2004027985A2 (fr) * 2002-09-13 2004-04-01 Conti Temic Microelectronic Gmbh Ensemble photodetecteur et procede de compensation de lumiere parasite
WO2004027357A1 (fr) * 2002-09-13 2004-04-01 Conti Temic Microelectronic Gmbh Montage de photodetection et procede de compensation de la lumiere parasite
WO2004027985A3 (fr) * 2002-09-13 2004-09-16 Conti Temic Microelectronic Ensemble photodetecteur et procede de compensation de lumiere parasite
US8822901B2 (en) 2011-07-13 2014-09-02 Elmos Semiconductor Ag Device for ambient light compensation for optical sensors exposed to both useful light and ambient light

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Publication number Publication date
AU2002223570A1 (en) 2002-04-22

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