JP6627656B2 - Focus detection device - Google Patents

Description

  The present invention relates to a focus detection device mounted on an imaging device, and particularly to an arrangement of a line sensor and a monitor sensor.

  In a single-lens reflex camera or the like, a phase difference type focus detection sensor is mounted as an automatic focus adjustment (AF) mechanism. In the focus detection sensor, a plurality of line sensors are arranged in accordance with a distance measuring point. Each line sensor has a configuration in which photodiodes are arranged in a staggered manner in pairs, and a monitor sensor is arranged along the side surface of the line sensor (for example, see Patent Document 1).

  The monitor sensor equipped with a photoelectric conversion element such as a photodiode detects the light intensity (light amount) of the photodiode to be monitored in order to prevent the photodiode of the line sensor from receiving light exceeding the dynamic range and overflowing. Is detected in real time and a monitor signal is output.

  When the monitor signal exceeds a predetermined threshold, the charge accumulation (integration) of the line sensor to be monitored ends, and the accumulated charge is temporarily stored in a memory or the like. When the charge accumulation of all the line sensors is completed, a series of pixel signals is output as an image signal of the subject image, and a calculation process for obtaining a defocus amount is performed.

JP 2011-22457 A

  The monitor sensor is arranged only on one side of the line sensor. Therefore, in the photodiodes arranged along a row apart from (not adjacent to) the monitor sensor, the amount of received light differs from the amount of received light of the monitor sensor, and the amount of light detection error of the monitor sensor increases. As a result, the pixel signal of the line cannot be used for focus detection due to signal saturation or the like, and the focus detection accuracy is reduced.

  Therefore, when focus detection is performed using a line sensor in which a plurality of photodiodes are arranged in pairs, it is necessary to arrange a monitor sensor so as to suppress signal saturation of the line sensor.

  The focus detection device of the present invention is applicable to an imaging device such as a camera, and includes a plurality of line sensors provided for focus detection, and a plurality of monitors arranged along a longitudinal side surface of each of the plurality of line sensors. And each of the line sensors has a plurality of photoelectric conversion elements arranged in a line in the longitudinal direction of the line sensor. For example, the plurality of photoelectric conversion elements can be arranged in a staggered arrangement. Further, a plurality of line sensors and a plurality of monitor sensors may be arranged on a distance measuring sensor constituted by a backside illumination type solid-state imaging device.

  According to the present invention, monitor sensors are arranged on both sides of the longitudinal direction of each line sensor, and each monitor sensor monitors an adjacent photoelectric conversion element row. Here, the monitor sensor and the line sensor may be arranged alternately and continuously adjacent to each other, or a space may be provided between the line sensors.

  A plurality of line sensors and a plurality of monitor sensors can be arranged alternately next to each other, and each monitor sensor is configured to monitor the photoelectric conversion element row of both adjacent line sensors. Can be. That is, the monitor sensor can be shared by different line sensors.

  When the photoelectric conversion elements are arranged in a staggered arrangement in each line sensor, the photoelectric conversion element rows facing each other across the monitor sensor can be arranged in a staggered arrangement between adjacent line sensors.

  For example, if one of the output signals of the monitor sensors on both sides of the line sensor exceeds a threshold value, a first exposure time control unit that terminates the exposure of the line sensor can be provided. Alternatively, when an output signal of a monitor sensor arranged between adjacent line sensors exceeds a threshold value, a second exposure time control for terminating exposure of photoelectric conversion element arrays facing each other across the monitor sensor between the adjacent line sensors. It is possible to provide a part.

  The user can switch between the exposure time control by the first exposure time control unit and the exposure time control by the second exposure time control unit. For example, during the AF process, the exposure time control by the first exposure time control unit is possible. The control and the exposure time control by the second exposure time control unit may be continuously executed to perform the distance measurement calculation.

  As described above, according to the present invention, the focus detection device can accurately detect the focus of the subject image.

FIG. 1 is a block diagram of a digital camera according to a first embodiment. It is the figure which showed partly the arrangement of the line sensor and the monitor sensor in the distance measuring sensor. FIG. 3 is an enlarged layout view showing a part of FIG. 2. FIG. 3 is a diagram illustrating a pixel structure of a line sensor. It is a pixel circuit diagram of a line sensor. FIG. 3 is a diagram illustrating a pixel structure of a monitor sensor. It is a pixel circuit diagram of a monitor sensor. FIG. 3 is a diagram schematically illustrating a circuit configuration of charge accumulation time control for a line sensor. 5 is a timing chart of charge accumulation time control. FIG. 10 is a diagram partially showing a circuit configuration of charge storage time control of a line sensor according to a second embodiment. 9 is a timing chart of charge accumulation time control according to the second embodiment. It is a flowchart of a ranging mode setting. It is a flowchart of a ranging calculation process.

  Hereinafter, the focus detection device according to the present embodiment will be described with reference to the drawings.

  FIG. 1 is a block diagram of a digital camera according to the first embodiment.

  Here, the digital camera 10 is configured as a single-lens reflex digital camera, and an interchangeable lens 20 is detachably attached to a camera body 30. A system control circuit 48 including a camera CPU includes a ROM, a RAM, a communication interface circuit, etc. (all not shown), and controls various circuits to control operations of the entire camera such as a photographing operation and an image recording process. . The operation control program is stored in the ROM in advance. The operation switch group 38 detects an input operation on a power button, a release button, a mode dial, a selection button (all not shown), and the like.

  The light that has passed through the photographing optical system 22 is guided by the movable mirror 15 in the direction of an optical finder (not shown), and the user visually recognizes a subject image through a finder window (not shown). On the other hand, part of the light that has passed through the photographing optical system 22 passes through the movable mirror 15 and is guided to an AF module 24 disposed below the movable mirror 15 by a sub-mirror 17 provided behind the movable mirror 15.

  The AF module 24 includes a condenser lens, a separator lens, and a field mask (all not shown), an infrared cut filter 24A, and a distance measurement sensor 40. The subject image divided by the field mask is separated by a distance sensor by a separator lens. The image is re-imaged on the light receiving surface 40.

  When the release button is half-pressed, the photometric sensor 19 arranged in the optical finder detects the brightness of the subject based on the light incident via the infrared cut filter 19A. At the same time, the AF module 24 outputs an image signal of the subject image projected on the light receiving surface of the distance measuring sensor 40.

  The system control circuit 48 performs defocus amount and focus adjustment based on the image signal sent from the AF module 24. The lens CPU 28 in the interchangeable lens 20 communicates with a lens control circuit 56 in the camera body 30 to control the lens driving mechanism 26 to shift the focusing lens in the photographing optical system 22.

  When the focus is adjusted in the release half-pressed state and the brightness of the subject is detected, the system control circuit 48 calculates and determines an exposure value (shutter speed, aperture value, sensitivity, etc.). When the release button is fully pressed, exposure control is performed. A subject image is formed on the image sensor 32 by the operation of the movable mirror 15, the aperture 23, and the shutter 31, and an image signal for one frame is output from the image sensor 32.

  The imaging sensor 32 here is configured by a CMOS image sensor and peripheral circuits such as an A / D conversion circuit, and M × N light receiving pixels are arranged on the light receiving surface. A color filter array is formed on-chip by a Bayer arrangement or the like. The image sensor driving circuit 36 drives the image sensor 32 to read out pixel signals, converts the signals into digital signals, and transmits them to the system control circuit 48.

  The image processing circuit 34 performs a color conversion process, a γ correction process, and the like on the read pixel signals for one frame to generate digital image data. The generated image data is stored in the image memory 35 after being subjected to a compression process or in an uncompressed state. When the reproduction mode is selected, a predetermined recorded image is reproduced and displayed on a display 37 constituted by an LCD or the like. The display 37 displays a preview image, a confirmation image after shooting, mode information, and the like.

  FIG. 2 is a diagram partially showing the arrangement of the line sensor and the monitor sensor in the distance measurement sensor 40. FIG. 3 is an enlarged layout view showing a part of FIG. The arrangement of the line sensor and the monitor sensor will be described with reference to FIGS.

  The distance measuring sensor 40 is configured by an integrated substrate on which a plurality of CMOS type line sensors are provided, and is configured as a backside illumination type imaging sensor. A plurality of line sensor groups are arranged on the light receiving surface 40S of the distance measurement sensor 40 in accordance with a plurality of distance measurement points set in advance (the arrangement of the line sensor groups is not shown in FIG. 2). Specifically, along the vertical direction of the substrate along the vertical direction of the subject image, a plurality of line sensor groups facing each other across the center of the substrate, along the horizontal direction of the substrate along the horizontal direction of the subject image, A plurality of line sensor groups facing each other across the center of the substrate are provided.

  One of the line sensors facing each other along the same line functions as a reference line sensor, and the other functions as a reference line sensor. The separator lens of the AF module 24 forms two pairs of subject images by pupil division, and forms a pair of subject images in each of the vertical and horizontal directions. Thereby, an image is formed on the reference line sensor and the reference line sensor facing each other with the substrate center interposed therebetween. FIG. 2 shows reference line sensors L1 to L3 facing the reference line sensor along the lateral direction of the substrate.

  The run sensor L1 has a two-row structure of a plurality of photodiodes PD, and has a configuration in which photodiodes PD that are elongated in the vertical direction of the substrate are paired and staggered in the horizontal direction of the substrate perpendicular to the longitudinal direction. Similarly, the line sensors L2 and L3 also have a staggered arrangement of the photodiodes PD (hereinafter, the photodiodes PD will be referred to as “AF pixels 40P” as necessary, and the photodiode rows of each line sensor will be described. "Al1, AL2").

  Monitor sensors LM1, LM2, LM3, LM4 are arranged on both sides of the longitudinal direction side surfaces of the line sensors L1, L2, L3, respectively, so that the line sensors L1, L2, L3 and the monitor sensors LM1, LM2. , LM3 and LM4 are densely arranged alternately without any gap. The monitor sensor LM1 has a configuration in which a plurality of elongated minute sensors LMA1 to LMA4 are arranged along the longitudinal direction of the line sensor, and are arranged to face the entire side surface of the line sensor. Other monitor sensors have the same configuration.

  The line sensor L1 includes a photodiode row AL1 and a photodiode row AL2, and the exposure time is adjusted by the adjacent monitor sensor LM1 in the photodiode row AL1 and by the adjacent monitor sensor LM2 in the photodiode row AL2. In the case of the monitor sensor LM1, the minute sensors LMA1 to LMA4 monitor the photodiode array AL1 facing the line sensor L1.

  FIG. 3 shows a photodiode belonging to the area EA of the line sensor L1 shown in FIG. 2 and the micro sensors LMA4 and LMB4 on both sides of the area EA. The micro sensor LMA4 monitors the photodiode belonging to the photodiode row AL1 in the area EA, and the micro sensor LMB4 monitors the photodiode belonging to the photodiode row AL2.

  On the other hand, the monitor sensor LM2 also functions as a monitor sensor for the photodiode array AL1 of the line sensor L2 opposite to the line sensor L1. That is, the photodiode arrays AL1 and AL2 of the line sensor L2 are monitored by the monitor sensors LM2 and LM3, respectively. Similarly, the photodiode arrays AL1 and AL2 of the line sensor L3 are monitored by monitor sensors LM3 and LM4, respectively.

  Further, in addition to the staggered arrangement of the photodiodes PD, the staggered arrangement is also used between adjacent line sensors. For example, the photodiode array AL2 of the line sensor L1 and the photodiode array AL1 of the line sensor L2 adjacent to each other with the monitor sensor LM2 interposed therebetween are arranged in a staggered arrangement. That is, they are offset from each other by half the longitudinal width.

  FIG. 4 is a diagram showing a pixel structure of the line sensor. FIG. 5 is a pixel circuit diagram of the line sensor. However, in FIG. 4, the arrangement of the camera body 10 is drawn with the front and back sides reversed.

  FIG. 4 shows a part viewed from the cross-sectional side and a part viewed from the front side with respect to the structure of some pixels of the line sensor. Each AF pixel 40P constituting the line sensor includes a photodiode PD and a pixel signal readout circuit 140. The pixel signal readout circuit 140 includes an anti-blooming gate ABG composed of transistors, a transfer gate TG, and a floating diffusion gate FDG.

  Further, the pixel signal readout circuit 140 includes a temporary charge storage capacitor MEM, a floating diffusion FD for performing charge-voltage conversion, a reset gate RG, a source follower amplifier SF, and a selection gate SEL (see FIG. 5). In addition, an element isolation region DTI is formed to reduce electrical and optical cross strokes. Although the p + region is formed wide to reduce dark current, such a configuration is not necessary.

  FIG. 6 is a diagram showing a pixel structure of the monitor sensor. FIG. 7 is a pixel circuit diagram of the monitor sensor.

  Like the line sensor, the microsensor LMA1 includes a photodiode MPD and a pixel signal readout circuit 240. The pixel signal readout circuit 240 includes an anti-blooming gate ABG including transistors, a transfer gate TG, a floating diffusion FD, and a reset gate. RG, a source follower amplifier SF, and a selection gate SEL.

  When light from the subject reaches the line sensor, signal charges (pixel signals) are generated by photoelectric conversion in the photodiode MPD, and charges are accumulated in accordance with the amount of light. On the other hand, the signal charge generated in the photodiode MPD is subjected to charge-voltage conversion by the floating diffusion FD, and a monitor signal is output as needed via the source follower amplifier SF and the selection transistor SE1.

  FIG. 8 is a diagram schematically showing a circuit configuration of the charge accumulation time control for the line sensor. FIG. 9 is a timing chart of the charge accumulation time control. Control of the charge accumulation time will be described with reference to FIGS. Here, the AF pixel 40P in the area EB to be monitored by the minute sensors LMB2 and LMC2 of the monitor sensors LM2 and LM3 arranged on both sides of the line sensor L2 will be described.

  When the execution of the AF process is started, the anti-blooming gates ABG of the AF pixels 40P of the line sensor L2 become low, and the anti-blooming gates ABG of the micro sensors LMB2 and LMC2 are switched to low. Be started. When the charge accumulation is started, the monitor signal, which is the output of the minute sensors LMB2 and LMC2, is compared with the reference voltage by the first exposure time control unit RC1.

  When one of the monitor signals reaches the reference voltage, a charge transfer pulse TGS is generated for the AF pixel 40P in the area EB. Thereby, the photocharge of the AF pixel to be monitored is transferred to the charge holding unit MEM at a time, and the integration is completed. In FIG. 9, the integration of the minute sensor LMB2 is completed at time t2 before the minute sensor LMC2.

  At this time, the transfer gate TG is turned ON, and a pulse signal is output to the AF pixels to be monitored in the pixel rows AL1 and AL2. As a result, the accumulated charge is transferred to the charge holding unit MEM. Then, the ABG signal is switched to High for the minute sensors LMB2 and LMC2 and the monitoring target AF pixel, and the integration is completed.

  When the integration is completed for all the line sensors, the accumulated charges are read. When reading out the accumulated charges, it is possible to alternately read out the charges of the photodiode rows AL1 and AL2 constituting the line sensor L2 in accordance with the staggered arrangement, or to read out the charges independently of the photodiode rows AL1 and AL2. It is possible.

  On the other hand, the monitor sensor LM2 also monitors the photodiode array AL2 of the line sensor L1. Each minute sensor of the monitor sensor LM2 is provided with a logic circuit shown in FIG. 8 between the minute sensor facing the monitor sensor LM1. Other monitor sensors such as the monitor sensor LM3 also monitor the photodiode rows on both sides.

  As described above, according to the first embodiment, in the digital camera 10 that executes the phase difference AF process by the distance measurement sensor 40 in which the monitor sensor is arranged beside the reference line sensor, the digital camera 10 includes the back-illuminated imaging device. Line sensors L1 to L3 and monitor sensors LM1 to LM4 are alternately arranged adjacent to the light receiving surface 40S of the distance measurement sensor 40. While the line sensors are composed of staggered photodiodes (AF pixels), each monitor sensor monitors an adjacent photodiode row (AF pixel row) in both adjacent line sensors.

  Monitor sensors are arranged on both sides of the line sensor in the longitudinal direction, and the monitor sensors monitor adjacent AF pixels, so that the difference between the monitor sensor received light amount and the line sensor received light amount is suppressed, and the line sensor integration is performed at appropriate timing. Termination can be performed, and signal saturation of the line sensor can be suppressed.

  In addition, by closely arranging the line sensors and arranging them closely, the monitor sensors can monitor the line sensors on both sides, that is, the line sensors can supply the monitor sensors. Thereby, it is possible to suppress a distance measurement error caused by the dead area. In particular, by configuring the distance measuring sensor 40 with the back-side illuminated image sensor, it is not necessary to arrange the readout circuit on the light receiving surface, and the line sensor and the monitor sensor can be more closely arranged.

  Next, a second embodiment will be described with reference to FIGS. In the second embodiment, the photodiode rows on both sides of the monitor sensor are to be monitored. Other configurations are substantially the same as those of the first embodiment.

  FIG. 10 is a diagram partially showing a circuit configuration of the charge accumulation time control of the line sensor according to the second embodiment. FIG. 11 is a timing chart of the charge accumulation time control in the second embodiment.

  Each monitor sensor monitors an adjacent photodiode row among the line sensors on both sides. For example, the minute sensor LMB2 of the monitor sensor LM2 targets the AF pixel 40P in the area EC extending over the line sensors L1 and L2. Accordingly, in the second embodiment, the ranging point is shifted from the ranging point of the first embodiment by the length of the photodiode along the substrate longitudinal direction, that is, the direction perpendicular to the photodiode row. A new ranging point different from the first embodiment is defined.

  When the execution of the AF process is started, the anti-blooming gate ABG of the monitor sensor and the line sensor is set to a low state, and charge accumulation (integration) is started for the monitor sensor and the line sensor. After the integration starts, when the output value of the micro sensor LMB2 reaches the reference voltage, the second exposure time control unit RC2 generates a charge transfer pulse signal for the AF pixels in the area EC.

  The timing generator pulse of the corresponding AF pixel is output, and the accumulated charge of the photodiode is transferred to the charge holding unit MEM. Then, the anti-blooming gate ABG of the microsensor LMB2, the anti-blooming gate ABG of the AF pixel on the photodiode row AL1 side, and the anti-blooming gate ABG of the AF pixel on the photodiode row AL2 are switched to High, and the charge accumulation ends.

  As described above, according to the second embodiment, between the line sensors adjacent to each other with the monitor sensor interposed therebetween, the monitor sensor monitors the photodiode array adjacent to the monitor sensor, and controls the charge accumulation time. By controlling the charge accumulation time between different line sensors, it is possible to perform distance measurement at a different distance measurement point from the first embodiment. Further, since the photodiode arrays are arranged in a staggered manner between different line sensors, accurate distance measurement can be performed as in the first embodiment.

  Next, a third embodiment will be described with reference to FIG. In the third embodiment, the line sensor charge accumulation control of the monitor sensor in the first embodiment (hereinafter, referred to as a normal distance measurement mode) and the line sensor charge accumulation control of the monitor sensor in the second embodiment (hereinafter, a line measurement mode). The distance measurement mode) can be selected by the user.

  FIG. 12 is a flowchart of the distance measurement mode setting.

  The user can select a distance measurement mode on a mode screen or the like. When the user selects the normal ranging mode, the normal ranging mode is set (S101, S102, S103). On the other hand, when the line-to-line distance measurement mode is selected, the line-to-line distance measurement mode is set (S101, S102, S104).

  As described above, according to the third embodiment, the user can select two ranging modes having different ranging points, and can perform various ranging.

  Next, a fourth embodiment will be described with reference to FIG. In the fourth embodiment, both the normal ranging mode and the line-to-line ranging mode are executed by the selection of the operator.

  FIG. 13 is a flowchart of the distance measurement calculation process according to the fourth embodiment.

  In step S201, when the line-to-line distance measurement mode has been set by an operator's input operation, execution of the line-to-line distance measurement mode is set. Otherwise, non-execution of the line-to-line distance measurement mode is set.

  First, the AF process based on the normal distance measurement mode is executed by the normal distance measurement mode (S202, S203). If the execution of the line-to-line distance measurement mode is set, the AF process is executed in accordance with the line-to-line distance measurement mode (S204 to S206). On the other hand, if the non-execution of the line-to-line distance measurement mode has been set (S204), the process ends.

  As described above, according to the fourth embodiment, when the line-to-line distance measurement mode is set, the distance measurement in the normal distance measurement mode and the distance measurement in the line-to-line distance measurement mode are performed together, so that a large number of distance measurements are performed. The focus position can be detected at the distance point.

  The line sensors may be arranged without staggering the photodiodes. Also, the monitor sensor may monitor the line sensor with one monitor sensor without using a plurality of minute sensors. Further, the line sensor and the monitor sensor may be arranged without using the back-side illuminated image sensor, or the monitor sensors may be arranged on both sides of one line sensor so that the interval between the line sensors is increased.

10 SLR digital camera 24 AF module (focus detection device)
40 distance measuring sensor 48 system control circuit (first exposure time control unit, second exposure time control unit)
RC1 First exposure time control unit RC2 Second exposure time control unit L1 to L4 Line sensor LM1 to LM4 Monitor sensor

Claims (9)

A plurality of line sensors provided for focus detection,
A plurality of monitor sensors arranged along a longitudinal side surface of each of the plurality of line sensors,
Each line sensor has a plurality of photoelectric conversion elements arranged in two rows in pairs in La-sensor longitudinal direction,
Monitor sensors are arranged on both sides of the longitudinal side of each line sensor,
A focus detection device, wherein each monitor sensor monitors an adjacent row of photoelectric conversion elements. The plurality of line sensors and the plurality of monitor sensors are arranged alternately side by side,
The focus detection device according to claim 1, wherein each monitor sensor monitors a photoelectric conversion element row on both sides. In each line sensor, the plurality of photoelectric conversion elements are arranged in a staggered arrangement,
3. The focus detection device according to claim 1, wherein photoelectric conversion element rows facing each other across the monitor sensor are arranged in a staggered manner between adjacent line sensors.   4. The apparatus according to claim 1, further comprising a first exposure time control unit for terminating exposure of the line sensor when one of output signals of the monitor sensors on both sides of the line sensor exceeds a threshold value. The focus detection device according to any one of the above.   When an output signal of a monitor sensor disposed between adjacent line sensors exceeds a threshold value, a second exposure time control unit that terminates exposure of the photoelectric conversion element rows facing each other across the monitor sensor between the adjacent line sensors is provided. The focus detection device according to claim 1, further comprising: When one of the output signals of the monitor sensors on both sides of the line sensor exceeds a threshold value, a first exposure time control unit for terminating the exposure of the line sensor and a monitor sensor disposed between adjacent line sensors. When the output signal exceeds the threshold, a second exposure time control unit that ends exposure of the photoelectric conversion element array facing each other across the monitor sensor between the adjacent line sensors,
4. The focus detection device according to claim 1, wherein exposure time control by the first exposure time control unit and exposure time control by the second exposure time control unit can be switched. 5.   7. The AF processing according to claim 6, wherein, during the AF process, the exposure time control by the first exposure time control unit and the exposure time control by the second exposure time control unit are continuously executed to perform the distance measurement calculation. Focus detection device.   The focus detection device according to claim 1, wherein the plurality of line sensors and the plurality of monitor sensors are arranged on a distance measurement sensor configured by a back-illuminated solid-state imaging device. .   An imaging apparatus comprising the focus detection device according to claim 1.

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