JP2016212301A - Focus detection device and its control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable an appropriate switch between a drive for charging monitor and drive for charging accumulation with influence on signals around subjects reduced.SOLUTION: A focus detection device comprises: a sensor unit which includes a sensor including a plurality of pixels and composed of the pixels, and in which a photoelectric conversion unit generating an electric charge in accordance with incident light, and a holding part holding the electric charge transferred from the photoelectric conversion unit are provided in each of the plurality of pixels; control means that switches a mode to any of a first mode of transferring the electric charge generated in the photoelectric conversion unit to the holding part to accumulate the transferred electric charge, and a second mode of accumulating the electric charge generated in the photoelectric conversion unit in the photoelectric conversion unit to control the electric charge accumulation in the sensor; and calculation means that uses an image signal based on the accumulated electric charge in any of the first mode and second mode to calculate an amount of defocus. The control means is configured to switch the first mode and the second mode in accordance with the amount of defocus.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a focus detection apparatus used for automatic focus detection.

  2. Description of the Related Art Conventionally, a configuration including the following two types of pixels is known as a phase difference detection type focus detection sensor (AF sensor). One is that the charge generated by the photoelectric conversion element (photodiode, PD) during the charge accumulation period is transferred to the memory means in the corresponding floating diffusion (FD) region via the transfer transistor, and the charge is transferred by the memory means. This is a charge monitor pixel having a configuration for integration. The other is that the charge generated by the PD is integrated by the pixel without being transferred to the memory means until the end of the charge accumulation period, and is transferred to the corresponding memory means via the transfer transistor when the charge accumulation period is over. This is a pixel for accumulation. Japanese Patent Application Laid-Open No. 2004-151561 describes that the same pixel is controlled by switching between driving for charge monitoring and driving for charge accumulation according to subject brightness.

JP 2013-54333 A

  However, in the control disclosed in Patent Document 1 described above, there is a risk of erroneous determination due to the influence of a signal around the subject when determining switching between drive for charge monitoring and drive for charge accumulation.

  SUMMARY OF THE INVENTION An object of the present invention is to reduce the influence of a signal around a subject and enable appropriate switching between driving for charge monitoring and driving for charge accumulation.

  In order to achieve the above object, a focus detection apparatus according to the present invention includes a sensor including a plurality of pixels, and generates a charge in response to incident light, and is transferred from the photoelectric conversion unit. A sensor unit that includes a holding unit that holds a charge to be stored in each of the plurality of pixels, a first mode that transfers and accumulates the charge generated in the photoelectric conversion unit to the holding unit, and the photoelectric conversion unit A control means for controlling charge accumulation in the sensor by switching the generated charge to any one of the second modes for accumulating in the photoelectric conversion unit, and accumulating in either the first mode or the second mode. Calculating means for calculating a defocus amount using an image signal based on the charged electric charge, and the control means switches between the first mode and the second mode according to the defocus amount. And wherein the frog.

  According to the present invention, it is possible to reduce the influence of signals around the subject and appropriately switch between driving for charge monitoring and driving for charge accumulation.

The block diagram which shows the electrical structural example of the AF sensor concerning this embodiment. 1 is a block diagram illustrating a schematic configuration of a camera body as an example of an imaging apparatus including a focus detection apparatus according to an embodiment. FIG. 3 is a diagram illustrating optical components included in the camera according to the present embodiment and an arrangement example thereof. FIG. 3 is a diagram illustrating a configuration of a focus detection optical system according to the present embodiment. The circuit diagram of the sensor pixel circuit part in the AF sensor concerning this embodiment. 3 is a flowchart showing a focus detection operation according to the first embodiment. The figure which shows the application range of mode setting. 5 is a flowchart showing mode setting determination processing according to the first embodiment; The figure which shows the relationship between the brightness | luminance in each storage mode, and S / N. The figure which shows the image signal from which a defocus amount differs. 6 is a flowchart showing AF sensor drive processing according to the present embodiment. The figure which shows accumulation time, Peak signal level, and accumulation | storage stop determination. 9 is a flowchart illustrating a focus detection operation according to the second embodiment. 9 is a flowchart illustrating mode setting determination processing according to the second embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Example 1>
FIG. 2 is a block diagram illustrating a schematic configuration of a camera body as an example of an imaging apparatus including the focus detection apparatus according to the present embodiment. In FIG. 2, the configuration other than the configuration related to automatic focus detection is omitted from the configuration of the camera.

  In the camera microcomputer (CPU) 100, there is a storage circuit 209 such as a ROM storing a program for controlling the timer and the camera operation, a RAM storing a variable, and an EEPROM storing various parameters. Built in. Connected to the CPU 100 are a signal input circuit 204 for detecting a switch group 214 for various operations of the camera, an image sensor (image sensor) 206 configured using a CMOS sensor, a CCD, or the like, and an AE sensor 207. . A shutter control circuit 208 for controlling the shutter magnets 218 a and 218 b and a focus detection sensor (AF sensor) 101 are also connected to the CPU 100. The CPU 100 transmits a signal 215 via a photographing lens 300 and a lens communication circuit 205 shown in FIG. 3 to be described later, and controls the position and aperture of the focus lens of the photographing lens 300. The operation of the camera is determined by the photographer operating the switch group 214. The switch group 214 includes a release button, a dial for selecting a focus detection area, and the like.

  The AF sensor 101 (sensor unit) includes a line sensor, and by controlling the AF sensor 101 by the CPU 100, a pair of image signals having parallax can be obtained from the line sensor. Then, the CPU 100 detects the focus state based on the phase difference between the pair of image signals obtained from the AF sensor 101, and controls the position of the focus lens, thereby controlling the focus position.

  Further, the CPU 100 controls the AE sensor 207 to detect the luminance of the subject, and determines the aperture value and shutter speed of the photographing lens 300. The CPU 100 controls the aperture value of the photographing lens 300 via the lens communication circuit 205 and controls the shutter speed by adjusting the energization time of the shutter magnets 218a and 218b via the shutter control circuit 208. Further, the CPU 100 exposes the imaging sensor 206 under the determined imaging conditions, reads the charges accumulated by the imaging sensor 206, and applies known image processing to generate captured image data. Then, the generated captured image data is recorded on a recording medium (not shown). In this way, the CPU 100 executes a series of shooting operations.

  FIG. 3 is a diagram illustrating optical components included in the camera according to the present embodiment and an arrangement example thereof. FIG. 3 shows an arrangement example of the optical components viewed from the side of the camera. Note that although the photographing lens 300 is illustrated in FIG. 3, the photographing lens 300 may be configured to be detachable from the camera.

  Most of the light beam from the subject incident through the photographing lens 300 is reflected upward by the quick return mirror 305 and formed on the finder screen 303 as a subject image. The photographer can observe the subject image via the pentaprism 301 and the eyepiece lens 302.

  Part of the light beam incident on the pentaprism 301 forms an image on the AE sensor 207 via the optical filter 312 and the imaging lens 313. The AE sensor 207 can measure the subject brightness based on an image signal obtained by photoelectrically converting this image.

  Part of the light beam from the subject passes through the quick return mirror 305 and is guided to the focus detection optical system below by the rear sub-mirror 306. The light beam incident on the focus detection optical system forms an image on the AF sensor 101 through the field mask 307, the field lens 311, the stop 308, and the secondary imaging lens 309. The focus state of the photographic lens 300 can be detected based on an image signal obtained by photoelectrically converting this image. Here, the focus state is detected based on the phase difference of the image signal by a known phase difference detection method. In this embodiment, it is possible to detect the focus state in a plurality of different focus detection areas. At the time of shooting, the quick return mirror 305 and the sub mirror 306 jump up and retract from the optical path, so that the incident light beam is imaged on the image sensor 206 and the subject image is exposed.

  FIG. 4 is a diagram schematically illustrating a configuration of a focus detection optical system included in the camera according to the present embodiment. The light beam that has passed through the photographic lens 300 (represented by a single lens for convenience) is reflected by the sub-mirror 306 as described with reference to FIG. 3, and in the vicinity of the field mask 307 on a plane conjugate with the imaging surface. Once imaged. In FIG. 4, the optical path reflected by the sub-mirror 306 and turned back is shown expanded. The field mask 307 is a member for blocking extra light to areas other than the focus detection area in the screen.

  The field lens 311 has an effect of forming each aperture of the diaphragm 308 in the vicinity of the exit pupil of the photographing lens 300. The secondary imaging lens 309 disposed behind the stop 308 is composed of a pair of lenses, and each lens corresponds to each opening of the stop 308. Each light beam that has passed through the field mask 307, the field lens 311, the stop 308, and the secondary imaging lens 309 forms an image on the line sensor on the AF sensor 101. In FIG. 4, only one pair of line sensors is shown on the AF sensor 101, but a plurality of line sensors may be arranged.

  Next, the circuit configuration of the AF sensor 101 will be described. FIG. 1 is a block diagram showing an electrical configuration example of an AF sensor according to an embodiment of the present invention. The control unit 103 is connected to the CPU 100 and controls each block of the AF sensor 101 based on a control command from the CPU 100. The control unit 103 includes a plurality of storage circuits 109 for storing accumulation time information, a flag register for various controls, a setting register, and a timer (not shown). In addition, the control unit 103 transmits accumulation stop information, accumulation time information, and the like of the AF sensor 101 to the CPU 100.

  The subject image formed by the secondary imaging lens 309 is photoelectrically converted by the line sensor group 102 including the line sensors 102-1 to 102-8 and accumulated as electric charges. The line sensors 102-1 to 102-8 here are each composed of a pair of line sensors. Each line sensor includes a transfer transistor control unit 210, a sensitivity control unit 211, a photodiode group, a transfer transistor group, an integration capacitor group, and a memory circuit group. The electric charge accumulated in the line sensor group 102 is integrated by an integration capacitor described later and output as a voltage. The sensitivity control unit 211 controls the sensitivity (gain) of the line sensor. The line sensor selection circuit 104 selects a pair of line sensors among a plurality of line sensors of the line sensor group 102. Then, the line sensor selection circuit 104 outputs the pixel signal of the selected line sensor to the peak detection circuit 105 and the output circuit 108 that monitor the feature amount accumulation state of the line sensor signal.

  Pixel signals accumulated in the line sensor group 102 are output to the output circuit 108 via the line sensor selection circuit 104. A control command for pixel readout is transmitted from the CPU 100, drives the shift register 107, and outputs it from the output circuit 108 to the A / D converter (not shown) of the CPU 100 as a pixel signal for each pixel.

  FIG. 5 shows a circuit diagram of a sensor pixel circuit unit constituting the line sensor. The line sensor includes a sensor pixel circuit unit, a transfer transistor control unit 210, a noise storage circuit unit, and a noise removal circuit unit. One sensor pixel circuit unit, one noise storage circuit unit, and one noise removal circuit unit are arranged in each of a plurality of photodiodes constituting the line sensor. One transfer transistor controller 210 is arranged for each line sensor.

  The sensor pixel circuit unit uses a photodiode PD (photoelectric conversion unit), an integration capacitor CFD, a memory capacitor CS, a current source 1, a current source 2, MOS transistors M1, M2, M3, M4, M5, and switches SWRES and SWCH. Composed. The integration capacitor CFD is a parasitic capacitance generated by a MOS transistor, a switch, a wiring, or the like. However, a capacitive element CL may be added.

  When the switch SWSENS controlled by φSENS is off, only the integration capacitor CFD is connected to the transistor M1, and the line sensor is set to high sensitivity. On the other hand, when the switch SWSENS is on, the integral capacitance CFD and the capacitive element CL are connected to the transistor M1, and the line sensor is set to low sensitivity.

  The voltage VRES is a reset voltage. The output VOUT is connected to the line sensor selection circuit 104. The switches SWRES, SWCH, and SWPHn are on / off controlled by signals PRES, PCH, and PPHn, respectively. A transistor MTX, which is a transfer transistor, is disposed between the photodiode PD and the MOS transistor M1.

  The AF sensor 101 has a first accumulation mode and a second accumulation mode as modes for accumulating charges. In the first accumulation mode, the transistor MTX is kept on during the charge accumulation period, and the generated charge is transferred to the integration capacitor (holding unit) and integrated while accumulating the charge. In the second accumulation mode, the transistor MTX is turned off during the charge accumulation period, and when the charge accumulation period ends, the generated charge is transferred to the integration capacitor and integrated. During the charge accumulation period in the second accumulation mode, the monitoring operation described later by the Peak detection circuit 105 cannot be performed. When the CPU 100 transmits a control command to the AF sensor 101 to control, the first accumulation mode and the second accumulation mode are switched.

  An example of the operation of the camera including the AF sensor 101 described above will be described with reference to the flowchart of FIG. FIG. 6 is a flowchart showing the focus detection operation of this embodiment. When a focus detection start signal is received by operating the switch group 214, the CPU 100 controls the AF sensor 101 to start the focus detection operation.

  In step S600, CPU 100 determines AF sensor drive mode setting. The mode setting of the AF sensor here includes setting of the accumulation mode determined by the sensor sensitivity switched by φSENS and the control method of the transistor MTX. Details of the process for determining the mode setting will be described later.

  In step S601, the CPU 100 transmits a control command to the AF sensor 101 based on the mode setting determined in step S600 to drive the AF sensor 101. The AF sensor 101 accumulates signals by a pair of line sensors according to a control command, and reads out the accumulated pair of image signals. Detailed description regarding drive control for each mode will be described later.

  In step S602, the CPU 100 uses the pair of image signals read from the AF sensor 101 in step S601 to perform a defocus calculation for detecting the focus state (defocus amount) of the photographic lens 300, and sets the defocus amount. calculate.

  In step S603, the CPU 100 determines whether or not the focus state of the photographic lens 300 is in focus based on the defocus amount calculated in step S602. If it is determined that the focus is achieved, the focus detection operation is terminated. If it is determined that the focus is not achieved, the process proceeds to step S604. Whether or not the lens is in focus is determined to be in focus if the defocus amount is within a desired range, for example, within 1/4 Fδ (F: lens aperture value, δ: constant (20 μm)). For example, when the lens aperture value F = 2.0, if the defocus amount is 10 μm or less, the CPU 100 determines that the subject is in focus and ends the focus detection operation. On the other hand, when the defocus amount is larger than 10 μm and it is determined that the in-focus state is out of focus, focus lens driving is performed to adjust the focus state of the photographing lens 300 to the in-focus position.

  In step S604, the CPU 100 instructs the photographing lens 300 to drive the focus lens via the lens communication circuit 205 based on the defocus amount. Then, the CPU 100 returns the process to step S600 and repeats the above-described operation until it is determined that it is in focus. The above is a series of flows in the focus detection operation.

  Next, the mode setting determination process in step S600 of FIG. 6 will be described with reference to FIGS. FIG. 7 is a diagram showing the application range of each mode setting. In FIG. 7, the horizontal axis indicates the contrast level of the image signal, and the vertical axis indicates the luminance.

  The mode setting determined in step S600 is one of MODE = 0, 1, and 2 shown in FIG. Hereinafter, each mode will be described.

  MODE = 0 is applied when the AF sensor 101 has low sensitivity, the first accumulation mode is set, and the luminance is BV ≧ K1. When the AF sensor 101 has low sensitivity, a large amount of signal charge can be accumulated because the integration capacitance described above is large. Since the optical shot noise is expressed by √S with respect to the accumulated signal charge number S, the SN ratio is expressed by S / √S≈√S in the region where the optical shot noise is dominant. For this reason, in a luminance range where light shot noise is dominant, such as a high-luminance subject, it is effective to increase the integration capacity and set it to a low sensitivity that can accumulate more signal charge.

  When MODE = 1, the AF sensor has high sensitivity and the first accumulation mode is set. MODE = 1 is applied when the brightness is BV <K1 and is outside the applicable range of MODE = 2 described later. When the AF sensor 101 has high sensitivity, the potential of the FD region during the same accumulation time is high because the integration capacitance described above is small compared to the case of low sensitivity. That is, since the pixel portion gain is high, it is possible to reduce the influence of random noise generated in circuits after the pixel portion. When the signal charge S is small as in the case where the subject has low luminance, the influence of circuit noise after the pixel portion is large. In this case, it is effective to set a high sensitivity.

  When MODE = 2, the AF sensor 101 has high sensitivity and the second accumulation mode is set. MODE = 2 is applied when the luminance is BV <K2 and the contrast is CNT ≧ CNT_th. In the second accumulation mode, the transistor MTX is turned off during the charge accumulation period and no charge transfer is performed, so that no noise is mixed into the pixel portion from the CFD and CL. For this reason, it is possible to output a low-noise signal. However, since the monitoring operation by the Peak detection circuit 105 cannot be performed during the charge accumulation period, the peak detection circuit 105 is applied only when the pixel signal has a low luminance that does not exceed the saturation voltage.

  Note that when the contrast is smaller than the threshold value CNT_th, the light shot noise becomes a dominant region, and the SN ratio is the same as that in the first accumulation mode, so the second accumulation mode is not applied. Therefore, even if the luminance is low, MODE = 1 is applied when the contrast is smaller than the threshold value CNT_th. The reason why the AF sensor 101 is low in sensitivity and does not have a MODE setting in which the second accumulation mode is set is also the same as the reason why the second accumulation mode is not applied when the contrast is smaller than the threshold value Cth.

  Next, the flow of determination for setting MODE = 0, 1, and 2 for the applicable range as described with reference to FIG. 7 will be described. FIG. 8 is a flowchart showing the mode setting determination process in step S600.

  In step S800, the CPU 100 determines whether or not the focus detection operation is the first time. When the focus detection operation is performed for the first time, the subject brightness and contrast are unknown. Therefore, in order to set MODE = 0 where the pixel signal is not easily saturated, the process proceeds to step S806. On the other hand, when the focus detection operation is performed for the second time or later, the process proceeds to step S801 in order to determine MODE based on the information of the image signal acquired by the previous AF sensor drive.

  In step S801, the CPU 100 determines the subject luminance. Although details will be described later, in this embodiment, the line selection is an arbitrary one-point mode, and only the pair of line sensors corresponding to the focus detection area selected by the user is driven by the AF sensor. Therefore, it is assumed that the subject luminance determined here uses image signal information obtained from a pair of line sensors corresponding to the focus detection region selected by the user. It should be noted that also in the determinations in steps S802 to S805 described later, information of image signals obtained from a pair of line sensors selected in the same manner is used.

  If the subject brightness is larger than the brightness threshold K1, the process proceeds to step S806 to set MODE = 0. On the other hand, if the subject brightness is equal to or lower than the brightness threshold value K1, the process proceeds to step S802 to determine whether MODE = 1 or MODE = 2.

  Here, the subject brightness BV obtained from the information of the image signal acquired by the previous AF sensor drive may be used for the determination. In this case, the subject brightness BV is calculated from the PEAK signal of the image signal acquired by driving the AF sensor, taking the accumulation time and sensor sensitivity into consideration. The subject brightness BV may be a photometric value detected by the AE sensor 207. The luminance threshold value K1 of the subject luminance that determines sensitivity is set to an optimum value from the viewpoint of S / N.

  In each of steps S802 to S805 described later, the reliability of the image signal is determined, and MODE = 1 and 2 are determined based on the determination result.

  In step S802, the CPU 100 determines whether or not the defocus amount calculated in step S602 in FIG. 6 is smaller than the defocus threshold DEF_th (predetermined value). If the defocus amount is greater than or equal to the defocus threshold DEF_th (more than a predetermined value), the process proceeds to step S807 to set MODE = 1. On the other hand, when the defocus amount is smaller than the defocus threshold DEF_th, the process proceeds to step S803 to determine the previous AF sensor drive mode. The defocus threshold DEF_th will be described later.

  In step S <b> 803, the CPU 100 determines the previous (previous) AF sensor drive mode setting. If the previous AF sensor drive is MODE = 0, the process proceeds to step S807 to set MODE = 1. On the other hand, if MODE = 1 or 2, the process proceeds to step S804 in order to determine the subject brightness.

  As described above, in the second accumulation mode with MODE = 2, the monitor operation by the Peak detection circuit 105 cannot be performed, and thus the image signal may be saturated. Therefore, when switching to the second accumulation mode in which MODE = 2, it is desirable to perform reliability determination from an image signal that has been driven by the AF sensor with MODE = 1, which is equivalent sensitivity. The image signal that can be acquired with MODE = 2 can obtain a signal with the same number of signal charges S and less noise components in each pixel than the image signal acquired with MODE = 1. Therefore, saturation of the image signal can be prevented by determining the reliability from the image signal acquired with MODE = 1. Note that switching from MODE = 0 to MODE = 2 may be performed by separately setting a threshold value for shifting from MODE = 0 to MODE2 based on the sensitivity ratio between low sensitivity and high sensitivity.

  In step S804, the CPU 100 determines the subject brightness. The luminance threshold value K2 used for the determination here has a relationship of K1> K2. If the subject brightness is equal to or greater than the brightness threshold K2, the process proceeds to step S807 to set MODE = 1. On the other hand, if the subject brightness is smaller than the brightness threshold K2, the process proceeds to step S805 to determine the contrast.

  The luminance threshold value K2 will be described with reference to FIG. FIG. 9 is a diagram illustrating the relationship between luminance and S / N in each accumulation mode, where the horizontal axis indicates subject luminance and the vertical axis indicates S / N.

  In FIG. 9, when the S / N of MODE = 1 indicated by the solid line and MODE = 2 indicated by the broken line is compared, the optical shot noise is dominant in the region where the luminance is higher than K3. It is equivalent. The reason why the S / N is constant in the region where the luminance is higher than K3 is that the pixel signal of the line sensor reaches the accumulation stop level and the accumulation is stopped, so that a constant signal charge number S is obtained. It is because it has been.

  On the other hand, the reason why the S / N deteriorates in the region where the luminance is lower than K3 is because the pixel signal of the line sensor does not reach the accumulation stop level, and the accumulation is forcibly stopped by the CPU 100. In this case, since the number S of signal charges decreases, S / N deteriorates.

  Here, as described above, MODE = 1 and MODE2 have the same sensitivity. Therefore, at the same luminance, the number of signal charges S is the same and only the noise is different. Therefore, as the luminance decreases, circuit noise or the like becomes dominant among the noise components, and the S / N difference increases. Here, as an example, the luminance at which the S / N between MODE = 1 and MODE = 2 is the difference of 0.5 steps is set as K2. Further, when MODE = 2, the luminance must be such that the image signal is not saturated, and therefore K3> K2.

  Returning to the description of FIG. 8, in step S805, the CPU 100 determines the contrast of the image signal. If the contrast is greater than or equal to the contrast threshold value CNT_th (greater than or equal to the threshold value), the process proceeds to step S808 to set MODE = 2. On the other hand, if the contrast is smaller than the contrast threshold value CNT_th, the process proceeds to step S807 to set MODE = 1.

  In step S806, the CPU 100 determines that MODE = 0, and sets the AF sensor driving in step S601 in FIG. In step S807, the CPU 100 determines that MODE = 1, and sets the AF sensor drive in step S601 of FIG. In step S808, the CPU 100 determines that MODE = 2, and sets the AF sensor driving in step S601 of FIG.

  Here, the contrast determined in step S805 and the defocus threshold used in the determination in step S802 will be described with reference to FIG. 10A and 10B are diagrams showing image signals having different defocus amounts, where the horizontal axis indicates the pixel position and the vertical axis indicates the signal level of the pixel signal. FIG. 10A shows a case where the phase of the pair of image signals is separated and the defocus amount is large, and FIG. 10B shows a case where the phase of the pair of image signals is close and the defocus amount is small. Yes.

In the calculation range for calculating the defocus amount, if the maximum value of the pair of image signals is PEAK and the minimum value is BOTTOM, the contrast CNT is expressed by the following equation (1).
CNT = PEAK-BOTTOM (1)

  In step S805, if the contrast obtained by equation (1) is CNT ≧ CNT_th, the mode is switched to MODE = 2. The method of obtaining the contrast is not limited to the equation (1), and may be obtained using another equation such as the sum of adjacent differences of image signals.

  Next, the defocus amount threshold value DEF_th used for the determination in step S802 will be described. When the defocus amount is large as shown in FIG. 10A, the focus lens is driven based on the defocus amount calculated from the image signal used for determining the mode setting. Therefore, the image signal when the mode setting is determined and the image signal when the next AF sensor drive is performed accumulate signals for different subject areas.

  For example, in FIG. 10B, the peak of the image signal at the left pixel position is the first subject area 1001, and the peak of the image signal at the right pixel position is the second subject area 1002. Of the pair of image signals, a solid line is an A image and a dotted line is a B image. In FIG. 10B where the defocus amount is small, only the range of the image signal corresponding to the first subject region 1001 is included in the calculation range, and the range of the image signal corresponding to the second subject region 1002 is included. I can't. Therefore, the accumulation mode can be determined without being affected by the second subject area 1002.

  On the other hand, in FIG. 10A where the defocus amount is large, the A image includes only the image signal range corresponding to the first subject region 1001 in the calculation range, while the B image includes the second subject region 1002. The range of the image signal corresponding to is included. Therefore, if the accumulation mode is determined in the state of FIG. 10A, it is affected by the second subject area 1002, and the step is performed in a state where the subject brightness and contrast are higher than those in FIG. 10B. The determination of S804 or S805 is performed. Thus, when the defocus amount is large, an erroneous determination may occur in the mode setting determination.

  Therefore, in the present embodiment, as in the second accumulation mode with MODE = 2, the monitor operation cannot be performed during the charge accumulation period, and the condition for shifting to the mode setting in which pixel saturation may occur is set. It is assumed that the defocus amount is within a predetermined range. As shown in FIG. 10B, the defocus threshold value DEF_th is set so that the mode can be switched to MODE = 2 only when the defocus amount is small and the subject to be focused is in the calculation range. Provided.

  Here, the set value of the defocus threshold DEF_th will be described. The defocus threshold DEF_th needs to be larger than the range set in the focus determination in step S603 of FIG. For example, if the defocus threshold DEF_th is 3Fδ (F: lens aperture value, δ: constant (20 μm)) and the defocus amount is within 3Fδ, it is determined that the subject whose focus is to be detected is within the calculation range. As described above, the AF sensor drive can be switched to MODE = 2 only when the defocus amount is within DEF_th and the subject brightness and contrast satisfy desired threshold values.

  Next, the AF sensor driving in step S601 in FIG. 6 will be described with reference to FIG. FIG. 11 is a flowchart showing the AF sensor driving process. As described above, in the present embodiment, the case of the arbitrary one-point mode will be described as an example, and here, driving of the selected pair of line sensors will be described.

  In step S1100, CPU 100 determines whether or not the mode setting determined in step S600 of FIG. 6 is MODE = 0. If MODE = 0, the process proceeds to step S1102 to perform initialization with MODE = 0. On the other hand, if MODE = 0, the process proceeds to step S1101 to determine whether MODE = 1.

  In step S1101, the CPU 100 determines whether or not the mode setting determined in step S600 of FIG. 6 is MODE = 1. If MODE = 1, the process proceeds to step S1102 to perform initialization with MODE = 1. On the other hand, if MODE = 1 is not satisfied, the process proceeds to step S1109 to perform initialization with MODE = 2.

  In step S1102, the CPU 100 performs various settings related to the focus detection operation. Here, the AF sensor 101 is assumed to be driven in the first accumulation mode, and the sensitivity is set according to the mode setting determined in step S600 of FIG.

  In step S <b> 1103, the CPU 100 transmits an accumulation start command to the AF sensor 101. When receiving the accumulation start command, the control unit 103 in the AF sensor 101 controls each circuit unit, performs a circuit reset operation and a noise storage operation, resets a built-in timer, starts counting, and starts charge accumulation. Measurement of elapsed time (accumulation time) from is started.

  In step S1104, the CPU 100 determines whether or not the accumulation time of the AF sensor 101 has reached the maximum accumulation time Tmax. If the accumulation time has reached Tmax, the process proceeds to step S1106. If the accumulation time has not reached Tmax, the process proceeds to step S1105.

  In step S1105, the AF sensor 101 performs an accumulation control operation. When the peak detection circuit 105 is operating in the first accumulation mode, the maximum value signal (Peak signal) which is the largest signal among the pixel signals of the line sensor being monitored selected by the line sensor selection circuit 104. Is output to the accumulation stop determination circuit 106. At this time, the control unit 103 turns on SWPHn, so that the line sensor outputs a signal to the peak detection circuit 105.

  FIG. 12 is a diagram showing the relationship between the signal amount and accumulation time of the Peak signal that is an output signal from the Peak detection circuit 105, and accumulation stop determination. The accumulation time 0 is the accumulation start timing, and the Peak signal increases as time elapses. The accumulation stop determination circuit 106 compares and determines the Peak signal and the accumulation stop level Vcomp.

  When the Peak signal becomes greater than the accumulation stop level Vcomp, the accumulation stop determination circuit 106 outputs an accumulation stop determination signal to the control unit 103. Then, in order to stop the accumulation of the line sensor being monitored selected by the line sensor selection circuit 104, the control unit 103 turns off the switch SWCH of the corresponding line sensor in the line sensor group 102 to accumulate the signal. Stop.

  In this embodiment, the case where the accumulation stop determination is performed by comparing the Peak signal and the accumulation stop level Vcomp has been described. However, the accumulation stop determination is performed by comparing the contrast CNT with a predetermined accumulation stop level. You may do it.

  In step S1107, the CPU 100 determines whether or not the accumulation of the line sensor is stopped. Since the AF sensor 101 transmits information of the line sensor that has completed accumulation to the CPU 100, the CPU 100 determines whether or not accumulation is stopped based on the received information. When the accumulation of the line sensor is stopped, the process proceeds to the pixel signal reading operation in step S1108, and when the line sensor is accumulating, the process returns to step S1104.

  On the other hand, in step S <b> 1106, the CPU 100 performs accumulation stop communication with the AF sensor 101. In this communication, an allowable maximum accumulation time Tmax is set in advance, and when the accumulation operation of the AF sensor 101 does not end by time Tmax due to shooting in the dark, the CPU 100 forcibly terminates the accumulation operation. It is.

  In step S <b> 1108, the CPU 100 reads an image signal (pixel signal) obtained from the charge accumulated in the AF sensor 101. The steps from S1102 to S1108 are the AF sensor driving process performed in the first accumulation mode.

  Next, the AF sensor driving process in the second accumulation mode will be described in steps S1109 to S1114. In step S1109, the CPU 100 performs various settings relating to the focus detection operation. Here, the AF sensor 101 is assumed to be driven in the second accumulation mode, and the sensitivity is set to the high sensitivity determined in step S600 of FIG.

  In step S1110, the CPU 100 transmits an accumulation start command to the AF sensor 101, as in step S1103. When receiving the accumulation start command, the control unit 103 in the AF sensor 101 controls each circuit unit, performs a circuit reset operation and a noise storage operation, resets a built-in timer, starts counting, and starts charge accumulation. Measurement of elapsed time (accumulation time) from is started.

  In step S <b> 1111, the CPU 100 determines whether or not the accumulation time of the AF sensor 101 has reached the maximum accumulation time Tmax. If the accumulation time has reached Tmax, the process proceeds to step S1112. If the accumulation time has not reached Tmax, the process of step S1111 is repeated.

  In step S <b> 1112, the CPU 100 performs accumulation stop communication with the AF sensor 101 as in step S <b> 1106. In the second accumulation mode, since the accumulation control operation in step S1105 cannot be performed, an allowable maximum accumulation time Tmax is set in advance and the accumulation operation is forcibly ended by the CPU 100. Note that the maximum accumulation time Tmax used for the determination in step S1112 may be different from the maximum accumulation time Tmax used for the determination in step S1104.

  In step S1113, the CPU 100 transmits a command to turn on the transfer transistor MTX in FIG. 5 to the AF sensor 101, and transfers the accumulated charge integrated by the photodiode PD to the integration capacitor CFD. Since charge transfer from the photodiode PD to the integration capacitor CFD is not performed during the charge accumulation period, noise generated in the integration capacitor CFD during the charge accumulation period is not accumulated in the photodiode PD.

  In step S1114, the CPU 100 reads out a pixel signal obtained from the electric charge accumulated in the AF sensor 101 as in step S1108. The flow from step S1109 to S1114 is the AF sensor driving process performed in the second accumulation mode.

  Thus, in the present embodiment, switching between the first accumulation mode and the second accumulation mode is performed according to the defocus amount. Thereby, the influence of the signal around the subject can be reduced, and focus detection can be performed in an accumulation mode suitable for the subject.

<Example 2>
In the first embodiment, on the premise of the arbitrary one-point mode, the AF driving of only a pair of line sensors corresponding to an arbitrary focus detection region selected by the user has been described. On the other hand, in the second embodiment, a case will be described in which a plurality of line sensors are driven to set a mode and perform focus detection. Since the configuration of the first embodiment can be applied to the configuration of the camera according to the present embodiment and the structure of the AF sensor, description thereof will be omitted.

  FIG. 13 is a flowchart showing a focus detection operation when driving a plurality (a plurality of pairs) of line sensors. In step S1300, CPU 100 determines AF sensor drive mode setting. Details of the process for determining the drive mode setting will be described later.

  In step S1301, the CPU 100 drives the AF sensor 101 for a plurality of line sensors based on the mode setting determined in step S1300. Details of the drive control will be described later.

  In step S1302, the CPU 100 performs defocus calculation using the image signals of the plurality of line sensors read from the AF sensor 101 in step S1301, and calculates defocus amounts for all line sensors.

  In step S1303, the CPU 100 stores the defocus amount information calculated in step S1302 in the storage circuit 209 of FIG.

  In step S1304, the CPU 100 determines whether or not the line sensor that has accumulated the signal in the main subject region out of the defocus amount stored in step S1303 is in focus. Here, as an example of a method of determining a line sensor that accumulates a signal in the main subject area, the line sensor indicating the closest distance among the defocus amounts calculated for all the line sensors is the main subject area. There is a method of using a line sensor that accumulates signals. Note that the main subject determination method is not limited to this.

  Step S1305 is the same as step S604 in FIG.

  Next, the process for determining the mode setting in step S1300 will be described using the flowchart of FIG. FIG. 8 is a flowchart showing the mode setting determination process in this embodiment.

  Step S1400 is the same as step S1100 in FIG.

  In step S1401, the CPU 100 determines a line sensor for determining mode setting. Here, the line sensor for determining the mode setting is referred to as a mode setting determination line.

  As a method for determining the mode setting determination line, for example, the line sensor indicating the closest side is set as the mode setting determination line using the defocus amount stored in step S1303 of FIG. Here, the mode setting determination line may be determined as any one (a pair) of line sensors, or may be determined as a plurality of line sensors if there are two or more line sensors indicating close distance information on the closest side. Good. If the mode setting determination line is a single line sensor, the processing from step S1402 to step S1409 is performed using information on the image signals of the determined pair of line sensors. In this case, the processes in steps S1402 to S1409 are the same as the processes in steps S801 to S808 in FIG.

  Further, when the mode setting determination line is a plurality of line sensors, the processes of steps S1402 to S1409 are performed for each line sensor. Here, when a plurality of line sensors are determined to have the same MODE, the MODEs of all the line sensors are set to the determined MODE.

  On the other hand, when different MODEs are determined among the plurality of line sensors, the MODE with the smallest number is set in the order of MODE = 0, MODE = 1, and MODE = 2. This is because if a MODE with a large number is selected, the line sensor determined to have a MODE with a small number may be saturated in the next driving of the AF sensor. The MODE is determined as described above, and all the line sensors are set to the MODE determined using the mode determination line.

  Next, AF sensor driving in step S1301 in FIG. 13 will be described with reference to FIG. Since the processing in steps S1100 to S1106 is the same as that in the first embodiment, description thereof is omitted.

  In step S1107, the CPU 100 determines whether or not the accumulation of all the line sensors (102-1 to 102-8) is stopped. Since the AF sensor 101 transmits information of the line sensor that has completed accumulation to the CPU 100, the CPU 100 determines whether or not accumulation is stopped based on the received information. When the accumulation of all the line sensors is stopped, the process proceeds to the pixel signal reading operation of step S1108, and when the accumulated line sensors remain, the process returns to step S1104. Since the subsequent steps S1109 to S1114 are the same as those in the first embodiment, description thereof will be omitted.

  As described above, in the second embodiment, a case where a plurality of pairs of line sensors are driven and MODE setting is performed to perform focus detection has been described. Also in the second embodiment, switching between the first accumulation mode and the second accumulation mode is performed in accordance with the defocus amount. Thereby, the influence of the signal around the subject can be reduced, and focus detection can be performed in an accumulation mode suitable for the subject. In the present embodiment, the same MODE is set for all the line sensors according to the determined MODE setting based on the mode determination line. However, the MODE may be set for each line sensor.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

100 CPU
101 AF sensor 102 Line sensor group 103 Control unit

Claims (16)

Each of the plurality of pixels includes a sensor configured to include a plurality of pixels, and a photoelectric conversion unit that generates charges according to incident light and a holding unit that holds charges transferred from the photoelectric conversion units. A sensor unit comprising:
Switch between the first mode in which the charge generated in the photoelectric conversion unit is transferred to the holding unit and stored, and the second mode in which the charge generated in the photoelectric conversion unit is stored in the photoelectric conversion unit Control means for controlling charge accumulation in the sensor;
Calculating means for calculating a defocus amount using an image signal based on the electric charge accumulated in either the first mode or the second mode;
The focus detection apparatus characterized in that the control means switches between the first mode and the second mode in accordance with the defocus amount.   2. The focus according to claim 1, wherein the control unit switches from the first mode to the second mode when a predetermined condition including that the defocus amount is smaller than a predetermined value is satisfied. Detection device.   The focus detection apparatus according to claim 2, wherein the control unit controls charge accumulation in the first mode when the defocus amount is equal to or greater than the predetermined value.   The focus detection apparatus according to claim 2, wherein the predetermined condition includes that the luminance is lower than the predetermined luminance, and that the contrast of the image signal is equal to or higher than a predetermined threshold.   5. The focus detection apparatus according to claim 2, wherein the control unit controls charge accumulation in the first mode when the predetermined condition is not satisfied. 6.   The said control means determines the reliability of the said image signal, and switches the said 1st mode and the said 2nd mode according to a determination result, The any one of Claim 1 thru | or 5 characterized by the above-mentioned. Focus detection device.   The focus detection apparatus according to claim 6, wherein the control unit determines the reliability of the image signal based on at least one of the defocus amount, luminance, and contrast of the image signal. Setting means for setting the sensitivity of the sensor;
When controlling charge accumulation in the first mode, the setting means sets a first sensitivity or a second sensitivity higher than the first sensitivity,
The focus detection apparatus according to claim 1, wherein when the charge accumulation is controlled in the second mode, the second sensitivity is set by the setting unit.   The focus detection apparatus according to claim 8, wherein the condition for switching from the first mode to the second mode includes that the second sensitivity is set in the previous charge accumulation.   10. The focus detection apparatus according to claim 8, wherein when the first sensitivity is set in the previous charge accumulation, the control unit controls charge accumulation in the first mode. 11. In the first mode, the detection unit detects a level of a signal based on the charge accumulated in the holding unit,
11. The control unit according to claim 1, wherein when the level of a signal detected by the detection unit reaches a predetermined level, the control unit performs control so as to stop charge accumulation in the sensor. The focus detection apparatus according to the item. The focus detection device has a plurality of focus detection areas,
The focus detection apparatus according to claim 1, wherein the sensor unit includes a plurality of the sensors corresponding to each of the plurality of focus detection areas.   13. The control unit according to claim 12, wherein the control unit switches between the first mode and the second mode in accordance with the defocus amount calculated by a sensor corresponding to the selected focus detection region. Focus detection device.   The control means determines one of the first mode and the second mode for each sensor based on the defocus amount calculated by each of the plurality of sensors. The focus detection apparatus according to 12 or 13.   The control unit controls charge accumulation of the plurality of sensors in the first mode when there is a sensor determined to be the first mode among the plurality of sensors. The focus detection apparatus described in 1. Each of the plurality of pixels includes a sensor configured to include a plurality of pixels, and a photoelectric conversion unit that generates charges according to incident light and a holding unit that holds charges transferred from the photoelectric conversion units. A method for controlling a focus detection apparatus including a sensor unit comprising:
Switch between the first mode in which the charge generated in the photoelectric conversion unit is transferred to the holding unit and stored, and the second mode in which the charge generated in the photoelectric conversion unit is stored in the photoelectric conversion unit A control step for controlling charge accumulation in the sensor;
A calculation step of calculating a defocus amount using an image signal based on the electric charge accumulated in either the first mode or the second mode;
In the control step, the control method of the focus detection apparatus, wherein the first mode and the second mode are switched according to the defocus amount.

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