JP2015231157A - Imaging apparatus and method of driving the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the power consumption of an imaging element, including a plurality of photodiodes for one pixel, in operation while maintaining focus detection precision.SOLUTION: An imaging apparatus comprises: an imaging element (1101) which has a plurality of unit pixels (100) each including a plurality of photoelectric conversion parts (101A, 101B), readout means, and control means (225, Vref) of controlling the amount of a current supplied to the readout means, and can be driven by a plurality of driving methods including a first driving method of reading signals out of some of the plurality of photoelectric conversion parts; and detection means (1104) of detecting whether a smear is generated on the basis of a signal output from the imaging element. Wile signals output from unit pixels in a row selected by the first driving method are read out, the control means supplies a less current when it is determined that no smear is generated than when it is determined that a smear is generated.

Description

  The present invention relates to an imaging apparatus and a driving method thereof.

  In recent years, multi-functionalization of solid-state imaging devices used in imaging devices such as digital still cameras and digital video cameras has been advanced.

  2. Description of the Related Art Conventionally, a technique capable of detecting a pupil-division focus in a solid-state image sensor has been disclosed. For example, in the imaging device disclosed in Patent Document 1, one pixel has two photodiodes, and each photodiode receives light passing through different pupil regions of the photographing lens by one microlens. It is configured. Then, by detecting the phase difference between the output signals of these two photodiodes, focus detection can be performed. Further, a signal of a captured image can be obtained by adding the output signals of the two photodiodes.

  When focus detection is performed using an imaging device in which two photodiodes are provided in one pixel as in Patent Document 1, in addition to outputting signals from each of the two photodiodes as described above, an addition signal for each pixel A signal may be acquired from one of the photodiodes. In this case, a signal from each of the two photodiodes can be obtained by subtracting a signal from one of the photodiodes from the added signal.

JP 2001-124984 A

  However, in any case, there is a problem that the amount of signals to be read increases and the average power during operation increases as compared with a conventional imaging device having one photodiode per pixel.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to reduce power consumption during operation while maintaining focus detection accuracy in an imaging device including a plurality of photodiodes in one pixel. .

  In order to achieve the above object, an imaging apparatus according to the present invention includes a plurality of photoelectric conversion units, each of which includes a plurality of pixels arranged in a matrix and a signal of a selected row among the plurality of pixels. An image sensor comprising: a reading unit that reads out from the pixel; an output unit that outputs a signal read out to the reading unit; and a current supply unit that supplies current to the output unit; and a plurality of photoelectric conversion units Based on the signal output from the image sensor and drive means for selecting one of a plurality of drive methods including a first drive method for reading out signals from some of the photoelectric conversion units, and driving the image sensor Detecting means for detecting whether smear has occurred, and when it is determined by the detecting means that smear has not occurred, the reading means reads by the first driving method. While outputting a signal to the outside by the output means, the current supply means supplies less current than when smear is determined to have occurred.

  According to the present invention, power consumption during operation can be reduced while maintaining focus detection accuracy in an image sensor including a plurality of photodiodes in one pixel.

FIG. 4 is a diagram illustrating a concept in which a light beam emitted from an exit pupil of a photographing lens of an imaging apparatus according to the first and second embodiments of the present invention enters a unit pixel. FIG. 3 is a block diagram illustrating a functional configuration of the imaging apparatus according to the first and second embodiments. FIG. 6 is a circuit diagram of a unit pixel of the imaging device according to the first and second embodiments. 3A and 3B are diagrams illustrating a readout circuit of an imaging device in the first and second embodiments. FIG. 3 is a circuit diagram of a reference current generation circuit of the imaging apparatus according to the first embodiment. 3 is a drive timing chart of the image sensor according to the first embodiment. 6 is a flowchart illustrating an imaging operation of the imaging apparatus according to the first embodiment. The figure for demonstrating the smear detection operation | movement in 1st Embodiment. The figure for demonstrating a smear phenomenon. The figure for demonstrating the subject at the time of smear phenomenon occurrence. The circuit diagram of the constant current load to the operational amplifier and vertical output line of the imaging device in 2nd Embodiment. 10 is a drive timing chart of the imaging apparatus according to the second embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. Here, the case where it applies to a digital single-lens reflex camera is demonstrated as an example of embodiment of this invention.

<First Embodiment>
First, the principle of focus detection by the pupil division method of the imaging apparatus according to the present invention will be described. FIG. 1 is a diagram illustrating a concept in which a light beam emitted from an exit pupil of a photographing lens enters a unit pixel 100. As shown in FIG. 1, the unit pixel 100 includes a first photodiode (PD) 101 </ b> A and a second photodiode (PD) 101 </ b> B, and is covered with a color filter 302 and a microlens 303.

  For the pixel having the micro lens 303, the center of the exit pupil 304 of the photographing lens is the optical axis 305. The light that has passed through the exit pupil 304 enters the unit pixel 100 with the optical axis 305 as the center. Further, as shown in FIG. 1, a light beam passing through a pupil region 306 that is a partial region of the exit pupil of the photographing lens is received by the first PD 101A through the micro lens 303. Similarly, a light beam passing through a pupil region 307 which is a partial region of the exit pupil 304 is received by the second PD 101B through the microlens 303. Therefore, each of the first PD 101A and the second PD 101B receives light that has passed through different areas of the exit pupil 304. Therefore, the phase difference can be detected by comparing the signals of the first PD 101A and the second PD 101B.

  Hereinafter, a signal obtained from the first PD 101A is referred to as an A image signal, and a signal obtained from the second PD 101B is referred to as a B image signal. Further, a signal read by adding the signal of the first PD 101A and the signal of the second PD 101B can be used as a captured image for the A + B image signal. For example, when the A image signal is read, signals from M photoelectric conversion elements are read out from a plurality of photoelectric conversion units corresponding to the microlens. Further, when reading out the A + B image signal, signals from N (N is larger than M) photoelectric conversion elements among a plurality of photoelectric conversion units corresponding to the microlens are read out.

  Next, the configuration of the imaging apparatus according to the first embodiment is shown in the block diagram of FIG. The photographic lens 1110 is subjected to zoom control, focus control, aperture control, and the like by a lens driving circuit 1109 to form an optical image of a subject on the image sensor 1101. A plurality of unit pixels 100 shown in FIG. 1 are arranged in a matrix in the image sensor 1101, and the subject imaged by the photographing lens 1110 is captured as an image signal. The signal processing circuit 1103 performs various corrections on the image signal output from the image sensor 1101 and compresses data. The signal processing circuit 1103 also generates a B image signal from the A image signal and the A + B image signal acquired from the image sensor 1101.

  The timing generation circuit 1102 outputs a drive timing signal to the image sensor 1101. The overall control / arithmetic circuit 1104 performs various calculations and overall control of the imaging apparatus, and also performs a focus detection operation and a smear detection operation of the present invention using the A image signal and the B image signal. The memory 1105 temporarily stores image data, and the display circuit 1106 displays various information and captured images. The recording circuit 1107 includes a removable recording circuit such as a semiconductor memory for recording or reading image data. The operation circuit 1108 electrically receives input from an operation member of the digital camera.

  Next, the configuration of the image sensor 1101 will be described with reference to FIGS. FIG. 3 is a circuit diagram of the unit pixel 100 of the image sensor 1101 according to the first embodiment. As shown in FIG. 3, the unit pixel 100 includes a first PD 101A, a second PD 101B, a first transfer switch 102A, and a second transfer switch 102B. Furthermore, a floating diffusion (FD) unit 103, an amplification unit 104, a reset switch 105, and a selection switch 106 are included.

  The first PD 101A and the second PD 101B function as a photoelectric conversion unit that receives light that has passed through the same microlens 303 and generates a signal charge corresponding to the amount of light received. The first transfer switch 102A and the second transfer switch 102B are controlled by transfer pulse signals PTXA and PTXB, respectively, and transfer the charges generated in the first PD 101A and the second PD 101B to the common FD unit 103, respectively.

  The FD unit 103 functions as a charge-voltage converter that temporarily holds the charges transferred from the first PD 101A and the second PD 101B and converts the held charges into a voltage signal. The amplifying unit 104 is a source follower MOS transistor, amplifies a voltage signal based on the charge held in the FD unit 103, and outputs it as a pixel signal. The reset switch 105 is controlled by the control signal PRES, and resets the potential of the FD unit 103 to the reference potential VDD. The selection switch 106 is controlled by the control signal PSEL and outputs the pixel signal amplified by the amplification unit 104 to the vertical output line 107.

  FIG. 4 is a diagram illustrating a readout circuit of the image sensor 1101 according to the present invention. Reference numeral 200 denotes a pixel region, and a plurality of unit pixels 100 are arranged in a matrix. In order to simplify the description, 8 × 4 pixels are shown, but the actual number of pixels is even larger. Each unit pixel 100 is provided with a color filter. A red color filter is provided, a pixel that receives red light is an R pixel, a green color filter is provided, a pixel that receives green light is a G pixel, a blue color filter is provided, and a pixel that receives blue light is a B pixel Call it. These three color filters are arranged on the unit pixel 100 according to the Bayer array.

  Reference numeral 201 denotes a vertical shift register, and a driving pulse is transmitted through the driving signal line 222 of each row. Note that the drive signal line 222 is shown one for each row for simplification, but actually, a plurality of drive signal lines are connected to each row.

  The unit pixels 100 in the same column are connected to a common vertical output line 107, and a signal from each unit pixel 100 is input to a common readout circuit 203 provided in each column via the vertical output line 107. Is done. The signals processed by the reading circuit 203 are sequentially output to the output amplifier 221 by the horizontal shift register 220. Reference numeral 202 denotes a constant current load (constant current source) connected to the vertical output line 107.

  The read circuit 203 includes a clamp capacitor C0, a feedback capacitor Cf, an operational amplifier 206, and a switch 223 for short-circuiting both ends of the feedback capacitor Cf. The switch 223 is controlled by a control signal PC0R. The reading circuit 203 further includes a capacitor CTSAB for holding a signal voltage, a capacitor CTN1, a capacitor CTSA, a capacitor CTN2, and switches 212, 213, 214, and 215 for controlling writing to these capacitors. The switch 212 is controlled by a control signal PTSAB, the switch 210 is controlled by a control signal PTSA, and the switches 213 and 215 are controlled by a PTN signal.

  In the readout circuit 203, the switches 216, 217, 218, and 219 are used for receiving signals from the horizontal shift register 220 and outputting signals to the output amplifier 221. The switches 216 and 217 are controlled by the drive pulse HABn of the horizontal shift register 220, and the switches 218 and 219 are controlled by the drive pulse HAn. Here, n represents the column number of the readout circuit 203 to which the control signal line is connected. Signals written to the capacitors CTSAB and CTSA are output to the output amplifier 221 via the common output line 224, and signals written to the capacitors CTN1 and CTN2 are output to the output amplifier 221 via the common output line 226.

  As described above, in an imaging apparatus having an imaging device including a plurality of photodiodes in one pixel, there is a problem that the number of signals to be read increases and average power during operation increases. For this problem, for example, it is conceivable to reduce the average power by driving as follows. That is, the addition signal of two photodiodes for a photographed image is read out in a normal mode, and the output of one photodiode used only for focus detection is read out while reducing the amount of current supplied to each part in the image sensor. This is based on the idea that the output of one of the photodiodes is not for a photographed image, so that a slight deterioration in image quality due to a reduction in the amount of current can be tolerated.

  However, when the characteristics of the added output of the two photodiodes and the output of one of the photodiodes change significantly, there arises a problem that the focus detection accuracy is deteriorated. This is because the output of each of the two photodiodes used for focus detection is read with one of the currents reduced, and the other is subtracted from the other output from the read output without reducing the current. It is for seeking. Therefore, if the characteristics of the output that is not added and the output that is not added are significantly different, the characteristics of the other output that is obtained by subtracting from the added output will also be different, and the accuracy of the comparison operation during focus detection will deteriorate. End up.

  As a phenomenon in which the characteristics of the output signal change greatly due to the change in the drive current amount in this way, there is noise called smear. Smear is a streak-like or band-like noise that occurs when a high-luminance subject enters the image sensor, and is widely known as a phenomenon that occurs in image sensors such as CCD and CMOS image sensors. FIG. 9 is a diagram for explaining smear. FIG. 9 is a view showing a photographed image when a high-brightness object is present at the center of a uniform luminance surface. Sinking has occurred. In this way, sinking and floating noises generated in the left and right and up and down directions of a high-luminance subject are smears.

  In a CMOS image sensor, smear occurs due to the wiring layout of the power supply and ground. Therefore, changing the drive current amount of each part in the sensor changes the smear characteristics. Therefore, when shooting is performed under conditions where smear occurs, the focus detection accuracy deteriorates if a method of reducing the amount of current is applied when reading out one of the photodiodes.

  FIG. 10 is a diagram for explaining a phenomenon in which focus detection accuracy deteriorates due to smear. The graph of FIG. 10 is a diagram showing images (A image and B image) corresponding to the output of each photodiode at the time of focus detection. In FIG. 10A, smear does not occur and the shapes of the A and B images are almost the same. Therefore, it is possible to accurately detect the positional deviation amount (phase difference) and to obtain the accurate defocus amount. On the other hand, FIG. 10B shows a case where smear is generated, and when a method of reducing the amount of current is applied at the time of reading one of the photodiodes, the shape of the A and B images is different due to the effect of smear. Will occur. Therefore, the detection accuracy of the phase difference is lowered, and the accuracy of the defocus amount obtained is also lowered.

  In view of the above-described problems, in the first embodiment, a reference current generation circuit 225 (current supply unit) that supplies a constant current to the output amplifier 221 is provided, and the amount of current to be supplied is switched as described below.

  First, a specific configuration example of the reference current generation circuit 225 will be described with reference to FIG. The reference current generating circuit 225 generates a reference current by converting the reference voltage Vref with the operational amplifier 502, the output MOS transistor 503, and the reference resistor R1. The generated reference current is duplicated by the current mirror circuit 504 and input to the output amplifier 221 that is a differential amplifier circuit. In the reference current generating circuit 225, the switch 505 and the reference resistor R2 are inserted in parallel with the reference resistor R1, and when the control signal PISEL becomes a high level (H), the switch 505 is turned on, and the reference resistors R1 and R2 are connected in parallel. It becomes a state. Therefore, the current amount of the reference current can be switched by switching the reference resistance value with the control signal PISEL. Since the amount of the reference current is inversely proportional to the reference resistance value, the amount of current is larger when R1 and R2 with PISEL = H are in a parallel state than when only R1 with PISEL = L.

  In addition, a switch 507 is inserted between the reference resistors R1, R2 and GND, and a switch 508 is inserted between the reference resistors R1, R2 and the reference voltage Vref. The switches 507 and 508 are adapted to conduct the signal PSAVE with the reverse logic. When the signal PSAVE becomes H, the conduction of the reference resistor to the GND is cut off and connected to the reference voltage Vref instead. At this time, since the voltage across the reference resistor R1 is 0, the amount of the reference current generated by the reference current generation circuit 225 is 0.

  Next, drive control of the image sensor 1101 will be described with reference to the timing chart of FIG. With the control signal PRES set to H, at time t1, the control signals PTXA and PTXB of the first transfer switch 102A and the second transfer switch 102B are set to H, and the first PD 101A and the second PD 101B are set to the reference potential VDD. Reset. At time t2, the control signals PTXA and PTXB are set to L, and accumulation of photoelectric charges obtained by exposing the first PD 101A and the second PD 101B is started. After accumulating the necessary time, the control signal PSEL of the selection switch 106 is set to H at time t3, and the amplifying unit 104 is turned on. By resetting the control signal PRES of the reset switch 105 to L at time t4, the reset of the FD unit 103 is released. The potential of the FD unit 103 at this time is read out as a reset signal level to the vertical output line 107 via the amplification unit 104 and input to the reading circuit 203.

  In the readout circuit 203, the reset signal level is input in a state where the operational amplifier 206 buffers the output of the reference voltage Vref (the control signal PC0R is H and the switch 223 is ON). Thereafter, the control signal PC0R is set to L at time t5, and the control signal PTN is set to H at time t6 and the switches 213 and 215 are turned on in order to write the output of the reference voltage Vref at that time to the capacitors CTN1 and CTN2. At time t7, the control signal PTN is set to L, the switches 213 and 215 are turned off, and writing is completed.

  Next, the control signal PTXA is set to H at time t8, the photocharge of the first PD 101A is transferred to the FD unit 103, and the control signal PTXA is set to L at time t9. By this operation, the electric charge accumulated in the first PD 101A is read to the FD unit 103. Then, an output corresponding to the change is supplied to the readout circuit 203 as an optical signal level via the amplifier 104 and the vertical output line 107.

  In the readout circuit 203, an inversion gain is applied to the voltage change at the ratio of the clamp capacitor C0 and the feedback capacitor Cf, and output. In order to write this voltage to the capacitor CTSA, the control signal PTSA is switched from L to H at time t10, the switch 214 is turned ON, the control signal PTSA is switched from H to L at time t11, and the switch 214 is turned OFF to perform writing. finish.

  Next, at time t12, the control signal PTXA is set to H again, and at the same time, the control signal PTXB is set to H. With this operation, the photocharges of both the first PD 101A and the second PD 101B can be simultaneously read out to the FD unit 103. After reading to the FD unit 103, the control signals PTXA and PTXB are switched from H to L at time t13. The read charge is supplied to the read circuit 203 as an optical signal level via the amplifying unit 104 and the vertical output line 107, as in the case of reading from only the first PD 101A.

  In order to write this voltage to the capacitor CTSAB, the control signal PTSAB is switched from L to H at time t14, the switch 212 is turned ON, the control signal PTSAB is switched from H to L at time t15, and the switch 212 is turned OFF to perform writing. finish. With this operation, an A + B image signal that is the sum of output signals from the first PD 101A and the second PD 101B is obtained by taking the differential voltage between the capacitors CTSAB and CTN1. This A + B image signal becomes a captured image.

  Further, by taking the voltage difference between the capacitors CTSA and CTN2, an A image signal which is an output signal from the first PD 101A is obtained. From this A image signal, information on the light beam that passes through a part of the pupil of the photographing lens 1110 is obtained, and further, by taking the difference between the A + B image signal and the A image signal, a B image signal that is an output signal from the second PD 101B. Is obtained. From this B image signal, information on the light beam passing through a pupil region different from the A image signal is obtained. Distance information can be obtained from the information of these two light beams.

  Next, at time t16, the control signal PRES is set to H, and the FD unit 103 is reset. Next, at time t17, the control signal PSAVE is changed from H to L, and the reference current generating circuit 225 is activated. That is, a constant current is supplied to the output amplifier 221 so that the output amplifier can be used. At time t17, the control signal PISEL is set. Here, the setting of the control signal PISEL is determined according to a smear determination result to be described later. That is, when it is determined that smear has occurred, the control signal PISEL remains at H so that the same amount of current is obtained when one photodiode signal is read and when two photodiodes are added. And On the other hand, when it is determined that smear has not occurred, the control signal PISEL is changed from H to L in order to reduce the average power during driving so that the constant current amount supplied to the output amplifier 221 has a low value. Set.

  Thereafter, the signals held in the capacitors CTSA and CTN2 are subjected to horizontal scanning of the A image signal between times t18 and t19. That is, the drive pulse HAn of the horizontal shift register 220 is sequentially changed from L → H → L for each readout circuit, and accordingly, the switches 218 and 219 are changed from OFF → ON → OFF. The signals held in the capacitors CTSA and CTN2 in the column where the switches 218 and 219 are switched from OFF to ON to OFF are read out to the common output lines 224 and 226, respectively, and the output amplifier 221 outputs the difference voltage to the outside of the image sensor 1101. Output. This difference voltage becomes an A image signal which is a signal from one of the first PDs 101A.

  Next, after the reading of the A image signal is completed, at time t19, if the control signal PISEL is L, it is changed to H, and the constant current amount supplied to the output amplifier 221 is set to a normal value. Next, during time t20 to t21, horizontal scanning of the A + B image signal for the captured image is performed. That is, the drive pulse HABn of the horizontal shift register 220 is sequentially changed from L to H to L for each readout circuit 203, and accordingly, the switches 216 and 217 are changed from OFF to ON to OFF. The signals held in the capacitors CTSAB and CTN1 in the column in which the switches 216 and 217 are switched from OFF to ON to OFF are read out to the common output lines 224 and 226, respectively, and the output amplifier 221 sends the difference voltage to the outside of the image sensor 1101. Output. This difference voltage becomes an A + B image signal. Next, at time t21, the control signal PSAVE is set from L to H, and a constant current is not supplied to the output amplifier 221.

  The above operation is sequentially performed for each row, and the reading of the A image signal and the A + B image signal is completed. The B image signal can be obtained by taking the difference between the output A image signal and the A + B image signal at the corresponding position, and a focus detection operation can be performed from the A image signal and the B image signal. .

  Next, the flow of the imaging operation in the first embodiment will be described using the flowchart of FIG. When shooting is started, first, it is determined whether or not the frame read in S101 is the first frame. If the first frame, the process proceeds to S110, and the normal drive mode in which the amount of current is not reduced during the horizontal scanning of the A image signal. Is set. That is, in the timing chart described with reference to FIG. 6, the drive is performed with the control signal PISEL = H during the period from time t17 to t19 during the horizontal scanning period of the A image signal.

  In step S104, the signal processing circuit 1103 generates a B image signal from the A image signal and the A + B image signal. In S105, the A + B image signal among the acquired images is displayed as a captured image on the display circuit. In S106, smear detection operation is performed in the overall control / arithmetic circuit 1104 using the A + B image signal.

  Here, the smear detection operation will be described with reference to FIG. The pixel area is divided into a plurality of blocks. FIG. 8 shows an example of 16 divisions in the horizontal direction and 8 divisions in the vertical direction. Then, an average value of pixel outputs is obtained for each block, and it is determined that smear has occurred when there is a block whose average value is equal to or greater than a threshold value. Further, the smear detection method is not limited to the above method, and may be detected by other detection methods. For example, it may be determined whether or not the output value of each pixel is equal to or greater than a threshold value, and it may be determined that smear has occurred when there are a predetermined number of pixels exceeding the threshold value. Further, smear may be detected using not the A + B image signal but the A image signal or both the A + B image signal and the A image signal.

  In S107, a known correlation operation is performed using the A image signal and the B image signal, the defocus amount of the photographing lens 1110 is calculated from the phase difference (image shift amount) of each image, and the calculated defocus amount is obtained. Based on this, the driving amount of the photographing lens 1110 is determined. In S108, the photographing lens 1110 is driven based on the determined driving amount. In S109, it is determined whether or not shooting is to be ended. If shooting is continued, the process returns to S102.

  If it is determined in S101 that the current frame is not the first frame, the process proceeds to S102, and it is determined whether smear has occurred based on the smear detection information in the previous frame detected in S106.

  If smear has not occurred, the process proceeds to S103, and an energy saving drive mode is set. That is, in the timing chart described with reference to FIG. 6, the control signal PISEL is changed from H to L during the period of time t17 to t19 during the horizontal scanning period of the A image signal, and the drive is performed by reducing the amount of current supplied to the output amplifier 221. Is called. Thereafter, the operations in S104 to S109 are as described above.

  As described above, by reducing the current amount of the output amplifier during the horizontal scanning period of the A image signal, it is possible to reduce the average power during photographing. In addition, it is determined whether smear has occurred, and if it is determined that smear has occurred, driving without reducing the amount of current suppresses deterioration in focus detection performance due to smear. It becomes possible to do.

  In the first embodiment, the configuration in which the smear determination operation is performed in each frame after the first frame has been described. However, the smear determination operation may be performed every several frames. In addition, the configuration for performing the smear determination operation regardless of the ISO sensitivity to be photographed has been described. However, the smear determination standard is changed according to the ISO sensitivity, or the smear determination is performed only at a predetermined ISO sensitivity or higher. It is good also as composition to do.

<Second Embodiment>
Next, a modification of the second embodiment of the present invention will be described with reference to FIG. In the above-described embodiment, the example in which the drive current amount of the output amplifier is changed in the horizontal scanning period of the A image signal based on the smear detection result has been described. In the modification, in the vertical transfer period in which the pixel signal is transferred to the readout circuit 203 via the vertical output line 107, the drive current amount and the vertical output line of the operational amplifier 206 arranged for each column based on the smear detection result. An example of changing the current amount of the current load 107 will be described. The configuration of the imaging device is the same as that described with reference to FIGS.

  FIG. 11A shows the constant current load supplied to the operational amplifier 206 arranged for each column, and FIG. 11B shows the constant current load 202 of the vertical output line 107. The constant current load circuit shown in FIG. 11 has basically the same configuration as the reference current generation circuit 225 described in FIG.

  The constant current load for the operational amplifier 206 shown in FIG. 11A generates a reference current by converting the reference voltage Vref with the operational amplifier 602, the output MOS transistor 603, and the reference resistor R3. The generated reference current is duplicated by the current mirror circuit 604 and input to the operational amplifier 206 arranged for each column. A switch 605 and a reference resistor R4 are inserted in parallel with the reference resistor R3. When the control signal PISEL2 becomes high level (H), the switch 605 is turned on, and the reference resistors R3 and R4 are in parallel. Therefore, the reference current can be switched by switching the reference resistance value by the control signal PISEL2.

  The constant current load 202 for the vertical output line 107 shown in FIG. 11B generates a reference current by converting the reference voltage Vref with an operational amplifier 702, an output MOS transistor 703, and a reference resistor R5. Then, the generated reference current is duplicated by the current mirror circuit 704 and used as a constant current load for each vertical output line 107. A switch 705 and a reference resistor R6 are inserted in parallel with the reference resistor R5. When the control signal PISEL3 is at a high level (H), the switch 705 is turned on and the reference resistors R5 and R6 are in parallel. Therefore, the reference current can be switched by switching the reference resistance value by the control signal PISEL3.

  The constant current load circuit shown in FIG. 11 does not include a switch for setting the current amount of the constant current load circuit to 0. However, as in the configuration of FIG. 5, the switch is inserted and controlled. Also good.

  Next, a driving method for reading out pixel signals in the second embodiment will be described with reference to FIG. With the control signal PRES set to H, at time t31, the control signals PTXA and PTXB of the first transfer switch 102A and the second transfer switch 102B are set to H, and the first PD 101A and the second PD 101B are set to the reference potential VDD. Reset. At time t32, the control signals PTXA and PTXB are set to L, and accumulation of photoelectric charges obtained by exposing the first PD 101A and the second PD 101B is started. After accumulating the necessary time, the control signal PSEL of the selection switch 106 is set to H at time t33, and the amplifying unit 104 is turned on. At time t34, the control signal PRES of the reset switch 105 is set to L to release the reset of the FD unit 103. The potential of the FD unit 103 at this time is read out as a reset signal level to the vertical output line 107 via the amplification unit 104 and input to the reading circuit 203.

  In the reading circuit 203, the reset signal level is input in a state where the operational amplifier 206 buffers the output of the reference voltage Vref (PC0R is H and the switch 223 is ON). Thereafter, the control signal PC0R is set to L at time t35, and the control signal PTN is set to H at time t36 in order to write the output of the reference voltage Vref at that time to the capacitors CTN1 and CTN2, and the switches 213 and 215 are turned on. At time t37, the control signal PTN is set to L, the switches 213 and 215 are turned off, and the writing is completed.

  Further, the control signals PISEL2 and 3 are controlled to determine the current amounts of the constant current loads of the operational amplifier 206 and the vertical output line 107 when the A image signal is vertically transferred. Here, the setting of the control signals PISEL2 and 3 is determined according to the smear determination result. That is, when it is determined that smear has occurred, the control signals PISEL2 and 3 remain H so that the same current condition is obtained during the vertical transfer of the A image as during the vertical transfer of the A + B image signal. . On the other hand, if it is determined that smear has not occurred, the control signals PISEL2 and 3 are set from H to L in order to reduce the average power during driving, and the constant current amount is set to a low value.

  Next, the control signal PTXA is set to H at time t38, the photocharge of the first PD 101A is transferred to the FD unit 103, and the control signal PTXA is set to L at time t39. By this operation, the electric charge accumulated in the first PD 101A is read to the FD unit 103. Then, an output corresponding to the change is supplied to the readout circuit 203 as an optical signal level via the amplifier 104 and the vertical output line 107.

  In the readout circuit 203, an inversion gain is applied to the voltage change at the ratio of the clamp capacitor C0 and the feedback capacitor Cf, and output. In order to write this voltage to the capacitor CTSA, the control signal PTSA is switched from L to H at time t40, the switch 214 is turned ON, the control signal PTSA is switched from H to L at time t41, and the switch 214 is turned OFF to complete the writing. To do. At time t41, PISEL2 and 3 are set to H and set to a constant current amount for vertical transfer of the A + B image signal.

  Next, at time t42, the control signal PTXA is set to H again, and at the same time, the control signal PTXB is set to H. With this operation, the photocharges of both the first PD 101A and the second PD 101B can be simultaneously read out to the FD unit 103. After reading to the FD unit 103, the control signals PTXA and PTXB are switched from H to L at time t43. The read charge is supplied to the reading circuit 203 as an optical signal level via the amplifying unit 104 and the vertical output line 107 as in the case of reading only the first PD 101A.

  In order to write this voltage to the capacitor CTSAB, the control signal PTSAB is switched from L to H at time t44, the switch 212 is turned on, the control signal PTSAB is switched from H to L at time t45, the switch 212 is turned off, and writing is performed. finish. By taking the voltage difference between the capacitors CTSAB and CTN1 by the above operation, an A + B image signal that is the sum of the output signals from the first PD 101A and the second PD 101B is obtained. This A + B image signal becomes a captured image.

  Further, by taking the voltage difference between the capacitors CTSA and CTN2, an A image signal which is an output signal from the first PD 101A is obtained. From this A image signal, information on the light beam that passes through a part of the pupil of the photographing lens 1110 is obtained, and further, by taking the difference between the A + B image signal and the A image signal, a B image signal that is an output signal from the second PD 101B. Is obtained. From this B image signal, information on the light beam passing through a pupil region different from the A image signal is obtained. Distance information can be obtained from the information of these two light beams.

  Next, at time t46, the control signal PRES is set to H, and the FD unit 103 is reset. Thereafter, the signals held in the capacitors CTSA and CTN1 are subjected to horizontal scanning of the A image signal between times t48 and t49. That is, the drive pulse HAn of the horizontal shift register 220 is sequentially changed from L → H → L for each readout circuit, and accordingly, the switches 218 and 219 are changed from OFF → ON → OFF. The signals held in the capacitors CTSA and CTN2 in the column where the switches 218 and 219 are switched from OFF to ON to OFF are read out to the common output lines 224 and 226, respectively, and output as a differential voltage by the output amplifier 221. This difference voltage becomes an A image signal which is a signal from one of the first PDs 101A.

  Next, during time t50 to t51, horizontal scanning of the A + B image signal for the captured image is performed. That is, the drive pulse HABn of the horizontal shift register 220 is sequentially changed from L to H to L for each readout circuit 203, and accordingly, the switches 216 and 217 are changed from OFF to ON to OFF. The signals held in the capacitors CTSAB and CTN1 in the column where the switches 216 and 217 are switched from OFF to ON to OFF are read out to the common output lines 224 and 226, respectively, and output as a differential voltage by the output amplifier 221. This difference voltage becomes an A + B image signal. The above operation is sequentially performed for each row, and reading of the A image signal and the A + B image signal is completed.

  With the above control, it is possible to reduce the average power at the time of photographing by reducing the current amount of the operational amplifier and the vertical output line arranged in each column during the vertical transfer period of the A image signal. In addition, it is determined whether or not smear occurs, and if it is determined that smear occurs, driving without reducing the amount of current suppresses deterioration of focus detection performance due to smear. It becomes possible.

  In the second embodiment, the example in which the constant current amounts of the operational amplifier 206 and the vertical output line 107 are changed together has been described. However, only one of them may be changed. Further, a configuration may be adopted in which the current control to the output amplifier 221 during the horizontal scanning period shown in the first embodiment is performed in combination.

  As mentioned above, although each embodiment of the present invention was described, the present invention is not limited to these embodiments.

  For example, in the first and second embodiments, the case where there is one readout system has been described. However, even when there are two or more systems, the present invention can be applied by configuring each system as described above. Can do.

  In the first and second embodiments, the case where each pixel has two photodiodes has been described. However, the pixel may include three or more photodiodes. In that case, in order to obtain a focus detection signal, a driving method for reading out from a part of the plurality of photodiodes for each pixel, and in order to obtain an imaging signal, the charges of the plurality of photodiodes are added and read for each pixel. Control may be performed according to the driving method. For example, when each pixel has four photodiodes divided into two in the horizontal and vertical directions, the charges of two photodiodes arranged in the horizontal or vertical direction are added for each pixel in order to obtain a focus detection signal. Read out. When it is determined that smear does not occur when reading out charges from a part of a plurality of photodiodes for each pixel, the amount of current supplied to the output amplifier 221, the operational amplifier 206 and / or the vertical output line 107 is determined. The invention of the present application can be applied by controlling so that it is reduced.

  100: unit pixel, 101A: first photodiode (PD), 101B: second photodiode (PD), 107: vertical output line, 201: vertical shift register, 202: constant current load, 203: readout circuit, 206: operational amplifier, 220: horizontal shift register, 221: output amplifier, 225: reference current generation circuit, 1101: imaging device, 1102: timing signal generation circuit, 1103: signal processing circuit, 1104: overall control / arithmetic circuit, Vref: Reference voltage source

Claims (22)

Each includes a plurality of photoelectric conversion units, a plurality of pixels arranged in a matrix, a reading unit that reads a signal output from a pixel in a selected row among the plurality of pixels, and a supply to the reading unit Control means for controlling the amount of current to be driven, and can be driven by a plurality of driving methods including a first driving method for reading a signal from some of the plurality of photoelectric conversion units. An image sensor;
Detection means for detecting whether smear has occurred based on the signal output from the image sensor;
When it is determined by the detection means that smear has not occurred, the control means has generated smear while reading the signal output from the pixel in the selected row by the first driving method. An image pickup apparatus that controls to supply a smaller current than the case where it is determined that. The readout unit includes a capacitor for holding a signal output from the pixel in the selected row, and an output unit for outputting the signal held in the capacitor to the outside of the imaging device,
When it is determined by the detection means that smear has not occurred, the control means has generated smear while reading the signal output from the pixel in the selected row by the first driving method. The imaging apparatus according to claim 1, wherein control is performed so that less current is supplied to the output unit than when the output is determined. The output means includes differential means for outputting a difference between an optical signal obtained by exposing each pixel and a reset signal of each pixel,
When it is determined by the detection means that smear has not occurred, the control means has generated smear while reading the signal output from the pixel in the selected row by the first driving method. The imaging apparatus according to claim 2, wherein control is performed so that less current is supplied to the differential unit than when it is determined that. The readout unit includes a capacitor for holding a signal output from the pixel in the selected row, and an amplifying unit disposed between the plurality of pixels and the capacitor.
When it is determined by the detection means that smear has not occurred, the control means generates smear while the signal output from the pixel in the selected row by the first driving method is read to the capacitor. 4. The image pickup apparatus according to claim 1, wherein control is performed such that less current is supplied to the amplifying unit than when it is determined that the current is being performed. 5. A vertical output line arranged for each column of the plurality of pixels and for reading out signals output from the pixels in the selected row to the reading unit;
A constant current source connected to the vertical output line;
When the control means further determines that smear has not occurred by the detection means, while the signal output from the pixels in the selected row by the first driving method is read to the reading means, 5. The imaging according to claim 1, wherein the control unit controls the constant current source so that a current is smaller than that in a case where it is determined that smear has occurred. apparatus. The plurality of driving methods include a second driving method of adding and reading out signals of the plurality of photoelectric conversion units for each pixel,
6. The imaging apparatus according to claim 1, further comprising a generation unit configured to process the signal read out by the second driving method to generate image data.   Each of the plurality of pixels includes two photoelectric conversion units, and is read by the first driving method from the signal read by the first driving method and the signal read by the second driving method. The imaging apparatus according to claim 6, further comprising a focus detection unit that performs focus detection based on a signal obtained by subtracting the obtained signal.   The imaging device according to claim 6 or 7, wherein the detection unit detects smear based on a signal read by the second driving method.   The image pickup apparatus according to claim 1, wherein the detection unit changes a level of a signal that determines that smear has occurred in accordance with an ISO sensitivity at the time of shooting. Each includes a plurality of photoelectric conversion units, a plurality of pixels arranged in a matrix, a reading unit that reads a signal output from a pixel in a selected row among the plurality of pixels, and a supply to the reading unit Control means for controlling the amount of current to be driven, and can be driven by a plurality of driving methods including a first driving method for reading a signal from some of the plurality of photoelectric conversion units. A driving method of an imaging apparatus having an imaging element,
A detecting step for detecting whether smear has occurred based on a signal output from the image sensor;
If it is determined in the detection step that smear has not occurred, the control means has generated smear while reading the signal output from the pixel in the selected row by the first driving method. A control process for controlling to supply less current than that determined to be,
A method for driving an imaging apparatus, comprising: Each includes a plurality of photoelectric conversion units, a plurality of pixels arranged in a matrix, a reading unit that reads a signal output from a pixel in a selected row among the plurality of pixels, and a supply to the reading unit Control means for controlling the amount of current to be driven, and can be driven by a plurality of driving methods including a first driving method for reading a signal from some of the plurality of photoelectric conversion units. An image sensor;
Detecting means for detecting whether a signal output from the image sensor includes a signal equal to or higher than a predetermined threshold;
When it is determined by the detection means that the signal does not include a signal equal to or greater than a predetermined threshold value, the control means is configured to read in advance the signal output from the pixel in the selected row by the first driving method. An imaging apparatus, characterized in that control is performed so as to supply less current than when it is determined that a signal equal to or greater than a predetermined threshold value is included. Each includes a plurality of photoelectric conversion units, a plurality of pixels arranged in a matrix, a reading unit that reads a signal output from a pixel in a selected row among the plurality of pixels, and a supply to the reading unit Control means for controlling the amount of current to be driven, and can be driven by a plurality of driving methods including a first driving method for reading a signal from some of the plurality of photoelectric conversion units. A driving method of an imaging apparatus having an imaging element,
A detecting step for detecting whether the signal output from the image sensor includes a signal equal to or higher than a predetermined threshold;
When it is determined in the detection step that the signal does not include a signal that is equal to or greater than a predetermined threshold, the control unit is configured to read in advance the signal output from the pixel in the selected row by the first driving method. A control step for controlling to supply less current than when it is determined to include a signal equal to or greater than a predetermined threshold;
A method for driving an imaging apparatus, comprising: An imaging apparatus including an imaging device having a plurality of photoelectric conversion units for one microlens,
A first drive for reading signals from M photoelectric conversion units among the plurality of photoelectric conversion units, and a first drive for reading signals from N (N is larger than M) photoelectric conversion units among the plurality of photoelectric conversion units. Reading means having two drives;
Control means for controlling a current supplied to the reading means at the time of reading the signal, and the amount of current supplied to the reading means when the signal is read by the first drive is determined by the second drive. There is a case where the first current amount is smaller than the case where the signal is read and a case where the second current amount is larger than the first current amount. Based on the signal read from the image sensor, An image pickup apparatus comprising: a control unit that switches between a first current amount and the second current amount.   The second current amount is a current amount controlled so as to be small or not change with respect to a current amount supplied to the reading means when a signal is read by the second drive. The imaging device according to claim 13. The reading unit includes a capacitor for holding the signal output from the photoelectric conversion unit, and an output unit for outputting the signal held in the capacitor to the outside of the imaging device,
14. The control unit according to claim 13, wherein when the first current amount is supplied, the control unit controls the output unit to supply a smaller current than when the second current amount is supplied. Imaging device. The output means includes differential means for outputting a difference between an optical signal obtained by exposing each pixel and a reset signal of each pixel,
16. The control means, when supplying the first current amount, controls to supply a smaller current to the differential means than when supplying the second current amount. The imaging device described in 1. The reading unit includes a capacitor for holding a signal output from the photoelectric conversion unit, and an amplifying unit disposed between the plurality of pixels and the capacitor,
14. The control unit according to claim 13, wherein when the first current amount is supplied, the control unit controls to supply a smaller current to the amplifying unit than when the second current amount is supplied. The imaging device according to any one of 16. The image sensor has a plurality of microlenses arranged in a matrix, is arranged for each column of a plurality of pixels, and a vertical output line for reading out a signal output from the photoelectric conversion unit to the reading unit; ,
A constant current source connected to the vertical output line,
14. The control unit according to claim 13, wherein when the first current amount is supplied, the control unit controls the constant current source so that a current is smaller than that when the second current amount is supplied. 18. The imaging device according to any one of items 17.     The imaging apparatus according to claim 13, further comprising a generation unit that processes a signal read by the second drive to generate image data.   A focus for focus detection based on the signal read by the first drive and the signal obtained by subtracting the signal read by the first drive from the signal read by the second drive The imaging apparatus according to claim 19, further comprising a detection unit.   The control means determines whether to supply the first current amount or the second current amount based on a signal read by the second drive. The imaging device according to any one of 13 to 20.   23. The control unit according to claim 13, wherein the control unit changes whether to supply the first current amount or the second current amount according to ISO sensitivity at the time of photographing. The imaging device according to any one of the above.