JP2008191559A - Photoelectric converting device, focus detecting device and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct a difference of an output signal due to an output path difference between a pair of photoelectric conversion sensors. <P>SOLUTION: A photoelectric converting device includes: a plurality of photoelectric converting elements having light-shielding pixels A1 to A3 and B1 to B3, and non-light-shielding pixels O11 to O31 and O12 to O32; output circuits (F11 to F31, M1, A1, and T1) and (F12 to F32, M2, A2, and T2) which independently output signals from the plurality of photoelectric converting elements; and a correcting means for correcting the signals output independently from the output circuits based upon signals obtained by the light-shielding pixels O11 to O31 and O12 to O32 of the plurality of photoelectric converting elements among the signals output independently from the output circuits. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion device, a focus detection device, and an imaging device.

  The image sensor used in the phase difference detection type focus detection device is provided with a plurality of output terminals, and a signal sequence from a pair of photoelectric conversion element arrays for receiving a pair of subject images is taken out from a separate output terminal, and a pair of signals A focus detection device that shortens the column readout time is known (see, for example, Patent Document 1).

Prior art documents related to the invention of this application include the following.
Japanese Patent Application No. 2005-160059

  However, in the conventional focus detection apparatus described above, the readout time can be shortened by reading out the pair of signal strings from separate output terminals, but there is a variation in the amplification factor of the amplifier provided in the output circuit and the difference in the length of the output circuit. In addition, there is a problem that a difference occurs in the output level from the output terminal even if the output levels from the pair of photoelectric conversion element rows are equal due to dark noise caused by the location in the chip, resulting in a focus detection error.

(1) The invention of claim 1 includes a plurality of photoelectric conversion elements having light-shielding pixels and non-light-shielding pixels, output means for independently outputting signals from the plurality of photoelectric conversion elements, and independent of the output means. Correction means for correcting the signal output independently from the output means based on the signals obtained from the light-shielding pixels of each of the plurality of photoelectric conversion elements among the signals output as described above. Resolve.
(2) The invention of claim 2 includes the photoelectric conversion device according to claim 1 and a calculation means for calculating the focus adjustment state of the optical system based on the signal corrected by the correction means.
(3) The invention of claim 3 is composed of an optical black pixel and an effective pixel, and has a pair of photoelectric conversion pixel columns that receive a light beam from the optical system, and outputs an output signal of each of the pair of photoelectric conversion pixel columns. Correction means for correcting the output signal of the pair of photoelectric conversion pixel columns based on the output signal of the optical black pixel of the pair of photoelectric conversion pixel columns and the photoelectric conversion element that outputs via an independent output path, and the correction unit And a calculation means for calculating the focus adjustment state of the optical system based on the output signals of the pair of photoelectric conversion pixel columns after correction by.
(4) In the focus detection apparatus according to claim 4, the output of at least one of the pair of photoelectric conversion pixel columns is made so that the output signals of the optical black pixels of the pair of photoelectric conversion pixel columns become substantially equal by the correcting unit. The signal is corrected.
(5) The focus detection device according to claim 5 includes an amplifier included in at least one output path of the pair of photoelectric conversion pixel columns based on a ratio of the output signals of the optical black pixels of the pair of photoelectric conversion pixel columns by the correction unit. The amplification factor is changed.
(6) In the focus detection apparatus according to the sixth aspect, the correction unit determines the photoelectric conversion pixel column to be corrected based on the output signal level of the photoelectric conversion pixel column and the saturation output level of the photoelectric conversion pixel column. Is.
(7) A seventh aspect of the present invention is an image pickup apparatus including the focus detection apparatus according to any one of the second to sixth aspects.

  According to the present invention, it is possible to correct a difference in output signals caused by an output path difference between a pair of photoelectric conversion sensor arrays and improve focus detection accuracy.

  An embodiment in which a photoelectric conversion device of the present invention or a focus detection device having this photoelectric conversion device is applied to a single-lens reflex digital camera will be described. Note that the present invention is not limited to a single-lens reflex digital camera, and can be applied to any imaging device including a phase difference detection type focus detection device.

  FIG. 1 shows a configuration of a single-lens reflex digital camera according to an embodiment. Note that illustrations and descriptions of camera devices and apparatuses that are not directly related to the present invention are omitted. In a camera according to an embodiment, a photographic lens 2 is attached to a camera body 1. The camera body 1 is provided with a main mirror 3 and a sub mirror 4, an image sensor 5, a focus detection module 6, a controller 7, a finder optical system 8, and the like. On the other hand, the taking lens 2 is provided with a focusing lens 9, a lens driving mechanism 10 including a motor, and the like.

  Before shooting, the main mirror 3 and the sub mirror 4 are placed in the shooting optical path as shown in the figure, and part of the subject light that has passed through the shooting lens 2 passes through the main mirror 3 and is reflected by the sub mirror 4 to be reflected by the focus detection module 6. And the other part of the subject light is reflected by the main mirror 3 and guided to the finder optical system 8. On the other hand, at the time of photographing, the main mirror 3 and the sub mirror 4 are retracted from the photographing optical path, a subject image is formed on the image sensor 5 by the photographing lens 2, and an image is taken by the image sensor 5.

  The focus detection module 6 is disposed behind a predetermined imaging surface equivalent to the imaging surface of the image sensor 5, and includes a focus detection optical system 11 including a field mask, a condenser lens, a diaphragm mask, a re-imaging lens, and the like, and a photoelectric conversion element. 12. The pair of re-imaging lenses of the focus detection optical system 11 re-images the primary image of the photographing lens 2 formed on the predetermined imaging plane on the pair of photoelectric conversion sensor arrays on the photoelectric conversion element 12. The photoelectric conversion element 12 converts a light image on the pair of photoelectric conversion sensor columns into an electric signal, and outputs it as an A column signal and a B column signal via the output circuit 15.

  The controller 7 includes an A / D conversion circuit 13 and an arithmetic circuit 14 composed of a microcomputer. The controller 7 performs A / D conversion on the A column signal and the B column signal output from the photoelectric conversion element 12 to obtain a relative optical image. A deviation amount is detected, and a defocus amount representing a focus adjustment state of the photographic lens 2 is calculated based on the deviation amount.

  FIG. 2 is a front view showing a circuit configuration of the photoelectric conversion element 12. Four pairs of photoelectric conversion sensor arrays (A1, B1), (A2, B2), (A3, B3), and (A4, B4) are arranged on the photoelectric conversion element 12 of one embodiment. The signal accumulated in the photoelectric conversion sensor array A1 is output from the terminal T1 via the floating diffusion F11, the multiplexer M1, and the amplifier A1. The signals accumulated in the photoelectric conversion sensor arrays A2 and A3 are also output in the same manner. On the other hand, the signal accumulated in the photoelectric conversion sensor array B1 paired with the photoelectric conversion sensor array A1 is output from the terminal T2 via the floating diffusion F12, the multiplexer M2, and the amplifier A2. The signals accumulated in the photoelectric conversion sensor arrays B2 and B3 that are paired with the photoelectric conversion sensor arrays A2 and A3 are also output in the same manner.

  That is, the stored signals of these pairs of photoelectric conversion sensor arrays (A1, B1), (A2, B2), (A3, B3) are transmitted through different devices and different devices, that is, through floating diffusions, multiplexers, and amplifiers. Output from a separate terminal. On the other hand, the accumulated signals of the pair of photoelectric conversion sensor arrays A4 and B4 arranged at the center of the photoelectric conversion element 12 are output from the terminal T1 through the same floating diffusion F4, multiplexer M1 and amplifier A1.

  Next, each photoelectric conversion sensor array of the photoelectric conversion element 12 includes a dark current correction light-shielded pixel (hatched portion in the drawing) O11 called an optical black pixel (optical black; OPB) in addition to an effective pixel for imaging. , O12, O21, O22, O31, O32, and O4 are provided. In a charge storage type photoelectric conversion element, a CCD output voltage (noise) is generated thermally even when light is not incident, and dark current (dark output) flows. Therefore, an optical black pixel signal is converted from an effective pixel signal. The DC component of the dark current is removed by subtracting.

  In this embodiment, the output signals of the pair of photoelectric conversion sensor arrays (A1, B1), (A2, B2), (A3, B3) have different paths, that is, different circuit lengths and different devices (floating diffusion, multiples). The difference in the output signal level generated by being output via the power amplifier and the amplifier and the dark output difference for each location of the sensor array are expressed as a pair of optical black pixels (OPB) (O11, O12), (O21, O22). ), (O31, O32) is corrected by the difference in output signal level. In other words, the output signal levels of the optical black pixels (OPB) O11, O12, O21, O22, O31, and O32 have the same potential in any photoelectric conversion sensor array, and the optical characteristics of the pair of photoelectric conversion sensor arrays are obtained. The output signal level of one of the pair of photoelectric conversion sensor arrays is corrected based on the difference in the output signal level of the target black pixel (OPB).

  FIG. 3 shows an example of output signals from the pair of photoelectric conversion sensor arrays A1 and B1. FIG. 3A shows a signal string output from the photoelectric conversion sensor array A1 to the terminal T1 via the floating diffusion F11, the multiplexer M1, and the amplifier A1, and the horizontal axis represents each pixel (optical) in the photoelectric conversion sensor array A1. The black pixel (OPB) O11 and effective pixel), and the vertical axis represents the output signal level of each pixel. FIG. 3B shows a signal string output from the photoelectric conversion sensor array B1 to the terminal T2 via the floating diffusion F12, the multiplexer M2, and the amplifier A2, and the horizontal axis represents each pixel of the photoelectric conversion sensor array B1. (Optical black pixel (OPB) O12 and effective pixel), the vertical axis represents the output signal level of each pixel. In FIG. 3, MAX represents the saturation output level of each pixel.

  In FIG. 3, the output signal levels of the optical black pixels (OPB) O11 and O12 of the photoelectric conversion sensor arrays A1 and B1 are smaller in B1 than in A1 by a difference (O11-O12). This optical black pixel output difference (O11-O12) is caused by the circuit length in each output path of the photoelectric conversion sensor arrays A1 and B1 and the operation variation of the intervening device, and also in the output signal level of the effective pixel. This output difference (O11−O12) is included. Therefore, the output signal level of each effective pixel of the photoelectric conversion sensor array B1 is offset by the difference (O11−O12). That is, in this case, the difference (O11−O12) is added to the output signal level of each effective pixel of the photoelectric conversion sensor array B1, and the signal array is offset as indicated by a broken line in FIG.

  As a result, errors due to the circuit lengths in the output paths of the photoelectric conversion sensor arrays A1 and B1 and the operation variations of the intervening devices are removed, the matching of the paired signal strings is improved, and errors in image shift calculation are reduced. be able to. In the photoelectric conversion sensor arrays (A2, B2) and (A3, B3), errors caused by circuit lengths in each output path and operation variations of intervening devices are removed in the same manner.

  In the correction example described above, the output signal level difference (O11-O12) of the optical black pixel is added to the output signal level of the effective pixel of the photoelectric conversion sensor array having the lower output signal level of the optical black pixel. However, the correction method is not limited to the above embodiment, and the output of the optical black pixel is determined from the output signal level of the effective pixel of the photoelectric conversion sensor array having the higher output signal level of the optical black pixel. It may be corrected by reducing the signal level difference, or ½ of the output signal level difference of the optical black pixel is reduced from the higher output signal level of the effective pixel of the photoelectric conversion sensor array, and the optical signal is lowered to the lower side. You may correct | amend by adding 1/2 of the output signal level difference of a target black pixel.

  FIG. 4 is a flowchart showing the imaging operation of the embodiment. The operation of the embodiment will be described with reference to this flowchart. When the release half-press operation is detected by half-pressing the release button, the controller 7 starts this imaging operation. In step 1, the subject is measured by a photometry circuit (not shown), and the luminance of the subject is detected. In the subsequent step 2, the subroutine shown in FIG. 5 is executed to detect the focus.

  In step 11 of FIG. 5, charge accumulation of the photoelectric conversion element 12 of the focus detection module 6 is performed, and in the subsequent step 12, an image signal of the accumulation result is read from the photoelectric conversion element 12 for each photoelectric conversion sensor array. In step 13, a difference in output is detected between the optical black pixels (OPB) of the paired photoelectric conversion sensor arrays (A1, B1), (A2, B2), and (A3, B3). In step 14, the effective pixel output of the pair of photoelectric conversion sensor arrays is offset and corrected by the output difference of the optical black pixel. In step 15, focus detection calculation is performed based on the corrected output signal sequence of the pair of photoelectric conversion sensor columns, and the defocus amount of the photographing lens 2 is calculated. Thereafter, the process returns to step 3 in FIG.

  In step 3 after focus detection, the focusing lens 9 is driven by the lens driving mechanism 10 based on the defocus amount of the focus detection result, and the focus of the photographing lens 2 is adjusted. In the subsequent step 4, the release operation is detected when the release button is fully pressed. If the release operation has not been performed, the process proceeds to step 5 to check whether the release half-press operation has been continued. When the release half-press operation is not continued, the process returns to step 1 and the above-described processing is repeated. When the release operation is performed, the process proceeds to step 6 and imaging is performed with the aperture and shutter speed determined by the exposure calculation based on the photometric result. In step 7 after imaging, an imaging signal is read from the imaging element 5 and an image is recorded on a recording medium after image processing.

  Thus, according to the above-described embodiment, the output signals of the pair of photoelectric conversion sensor arrays are corrected based on the output signals of the optical black pixels of the pair of photoelectric conversion sensor arrays, and the corrected pair of photoelectric sensors is corrected. The focus adjustment state of the photographic lens is calculated based on the output signal of the conversion sensor array, that is, the output signals of the optical black pixels of the pair of photoelectric conversion sensor arrays are substantially equal. Since at least one of the output signals is corrected, even if there is a difference in the output path of the output signals of the pair of photoelectric conversion sensor arrays while reducing the readout time of the output signals of the pair of photoelectric conversion sensor arrays, The difference in the output signals of the photoelectric conversion sensor arrays can be corrected, and the focus detection accuracy can be improved.

  Note that the amplification factor of the amplifier included in at least one output path of the pair of photoelectric conversion sensor arrays may be changed according to the ratio of the output signals of the optical black pixels of the pair of photoelectric conversion sensor arrays. As a result, the difference between the output signals of the pair of photoelectric conversion sensor arrays can be corrected while shortening the readout time of the output signals of the pair of photoelectric conversion sensor arrays, and the focus detection accuracy can be improved.

  Further, the photoelectric conversion pixel column to be corrected may be determined based on the output signal level of the photoelectric conversion sensor column and the saturation output level of the photoelectric conversion sensor column. For example, if the output signal level of one of the pair of photoelectric conversion sensor columns is close to the saturation output level, the correction value is subtracted from the output signal of the photoelectric conversion sensor column for correction, or Alternatively, by correcting the output signal of the other photoelectric conversion sensor array by adding a correction value, the corrected output signals of the pair of photoelectric conversion sensor arrays become appropriate values below the saturation output level, and focus detection accuracy is improved. Can be improved.

The figure which shows the structure of the single-lens reflex digital camera of one embodiment Front view of focus detection photoelectric conversion element The figure explaining the correction method of a pair of photoelectric conversion sensor output The flowchart which shows the imaging operation of one embodiment The flowchart which shows the focus detection operation | movement of one Embodiment

Explanation of symbols

7 Controller 11 Focus detection optical system 12 Photoelectric conversion element 14 Arithmetic circuit 15 Output circuit O11, O12, O21, O22, O31, O32 Optical black pixel (OPB)
(A1, B1), (A2, B2), (A3, B3) A pair of photoelectric conversion sensor arrays A1, A2 Amplifier

Claims (7)

A plurality of photoelectric conversion elements having light-shielding pixels and non-light-shielding pixels;
An output means for independently outputting a signal from each of the plurality of photoelectric conversion elements;
Correction that corrects the signal output independently from the output unit based on the signal obtained by the light-shielding pixel of each of the plurality of photoelectric conversion elements among the signals output independently from the output unit. And a photoelectric conversion device. The photoelectric conversion device according to claim 1;
A focus detection apparatus comprising: a calculation unit that calculates a focus adjustment state of the optical system based on the signal corrected by the correction unit. An optical black pixel and an effective pixel are included, and a pair of photoelectric conversion pixel columns that receive a light beam from the optical system are provided, and output signals of the pair of photoelectric conversion pixel columns are output via independent output paths. A photoelectric conversion element;
Correction means for correcting the output signals of the pair of photoelectric conversion pixel columns based on the output signals of the optical black pixels of the pair of photoelectric conversion pixel columns;
A focus detection apparatus comprising: a calculation unit that calculates a focus adjustment state of the optical system based on the output signals of the pair of photoelectric conversion pixel columns corrected by the correction unit. The focus detection apparatus according to claim 3,
The correction means corrects at least one output signal of the pair of photoelectric conversion pixel columns so that output signals of the optical black pixels of the pair of photoelectric conversion pixel columns are substantially equal. Focus detection device. The focus detection apparatus according to claim 3,
The correction means changes an amplification factor of an amplifier included in at least one of the output paths of the pair of photoelectric conversion pixel columns based on a ratio of output signals of the optical black pixels of the pair of photoelectric conversion pixel columns. A focus detection device. In the focus detection apparatus of any one of Claims 3-5,
The focus detection apparatus, wherein the correction unit determines the photoelectric conversion pixel column to be corrected based on an output signal level of the photoelectric conversion pixel column and a saturation output level of the photoelectric conversion pixel column.   An imaging apparatus comprising the focus detection apparatus according to claim 2.

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