JP2010114654A - Imaging apparatus and charge transferring method of solid-state imaging element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve transfer efficiency without unnecessary lowering of frame rate. <P>SOLUTION: As the transfer mode for perpendicular transfer of signal charges in a CCD 19, an ordinary transfer mode and an image quality preferential transfer mode assuring an overlap period longer than that in the ordinary transfer mode are prepared. When the setting value of ISO sensitivity is less than the threshold value A, the CCD 19 is driven in the ordinary transfer mode for preferentially maintaining a frame rate, because influence on the quality of pickup image due to deterioration of the transfer efficiency is small. When the setting value of ISO sensitivity is equal to or higher than the threshold value A, transfer efficiency can be improved by driving the CCD 19 in the image quality preferential transfer mode. Accordingly, transfer efficiency can be improved without unnecessary lowering of the frame rate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an imaging device including a solid-state image sensor and a charge transfer method for the solid-state image sensor.

  2. Description of the Related Art CCD image sensors are known as solid-state imaging devices that are mounted on photographing devices such as digital cameras and camera-equipped mobile phones. The CCD image sensor includes a large number of photoelectric conversion elements arranged in a two-dimensional manner, a charge transfer path (vertical transfer path, horizontal transfer path) for transferring signal charges obtained by each photoelectric conversion element, A plurality of transfer electrodes (vertical transfer electrodes, horizontal transfer electrodes) arranged along the charge transfer direction on the transfer path.

  A driving pulse whose voltage level periodically changes is applied to each transfer electrode. As a result, a transfer packet (potential well) for accumulating signal charges is formed in the charge transfer path below the transfer electrode to which a voltage is applied. Then, the voltage applied to the transfer electrode in front of the transfer packet and the stop of the voltage application to the transfer electrode on the rear end of the transfer packet are alternately repeated by the drive pulse applied to each transfer electrode. Thus, the phase of each drive pulse is adjusted. Thereby, the transfer packet (signal charge) moves along the transfer direction.

At the time of the above-described charge transfer, if the signal charge transfer efficiency is low, the image quality is remarkably deteriorated due to noise generated in the captured image. Therefore, it is required to improve the signal charge transfer efficiency. Patent Document 1 discloses a technique for improving transfer efficiency by thinning out horizontal lines and vertical lines of a CCD image sensor.
JP 2004-328314 A

  By the way, if the thinning of the horizontal line and the vertical line is performed as in Patent Document 1, the transfer rate of the signal charge can be reduced, so that the transfer efficiency can be improved and noise can be reduced. Since the resolution is lowered, it is difficult to improve the image quality of the captured image. Also, if the transfer rate is lowered without thinning out, a drop in frame rate becomes a problem.

  The present invention has been made to solve the above-described problems, and is capable of improving transfer efficiency (preventing deterioration in image quality of a captured image) without unnecessarily reducing the frame rate, and charge transfer of a solid-state image sensor. It aims to provide a method.

  In order to achieve the above object, an imaging device of the present invention includes a photoelectric conversion element, a charge transfer path for transferring a signal charge obtained by the photoelectric change element, and a transfer direction of the signal charge on the charge transfer path. A solid-state imaging device having a plurality of transfer electrodes arranged along the transfer electrodes, and a transfer packet that applies a drive pulse to each of the transfer electrodes and accumulates the signal charge in the charge transfer path under the voltage-applied transfer electrode And alternately repeating the voltage application to the first transfer electrode in front of the transfer packet and the voltage application to the second transfer electrode on the rear end of the transfer packet after the voltage application, The transfer packet is divided into an extended state formed between the second transfer electrode and the first transfer electrode, and a third transfer current located in front of the second transfer electrode. Drive pulse application means for moving along the transfer direction while alternately switching from the bottom to the contracted state formed between the first transfer electrodes, and the time of the stretched state and the contracted state depending on the imaging conditions Control means for controlling the drive pulse applying means so as to be switched between a normal transfer mode in which the time is equal and a special transfer mode in which the time in the extended state is longer than the time in the contracted state, It is characterized by providing.

  The control means operates the drive pulse applying means in the normal transfer mode when the ISO sensitivity setting value is less than a predetermined sensitivity threshold value, and the ISO sensitivity setting value is greater than or equal to the sensitivity threshold value. In some cases, it is preferable to operate the drive pulse applying means in the special transfer mode.

  An exposure amount measuring means for measuring an exposure amount of the solid-state image sensor; and a temperature measuring means for measuring a temperature of the solid-state image sensor, wherein the control means is configured so that the exposure amount obtained by the exposure amount measurement means When the temperature is less than a predetermined exposure amount threshold and the temperature obtained by the temperature measuring unit is less than a predetermined temperature threshold, the drive pulse applying unit is operated in the special transfer mode, and the exposure amount is When the exposure amount threshold value or higher and / or the temperature is equal to or higher than the temperature threshold value, it is preferable to operate the drive pulse applying unit in the normal transfer mode.

  The solid-state imaging device has an effective pixel region that generates and accumulates signal charges, and an optical black region formed adjacent to the effective pixel region, and the temperature measuring unit outputs from the optical black region. It is preferable to obtain the temperature of the solid-state imaging device based on the dark current that is generated.

  The temperature measuring means is preferably a temperature sensor.

  Regardless of the imaging conditions, the control unit includes a selection operation unit for selecting whether to operate the drive pulse applying unit in the normal transfer mode, and the control unit is operated in the normal transfer mode by the selection operation unit. When this operation is selected, it is preferable that the drive pulse applying means is always operated in the normal transfer mode.

  In order to achieve the above object, a charge transfer method for a solid-state imaging device according to the present invention includes a photoelectric conversion element, a charge transfer path for transferring a signal charge obtained by the photoelectric change element, and a charge transfer path on the charge transfer path. And a plurality of transfer electrodes arranged in the transfer direction of the signal charge in a solid-state imaging device charge transfer method, a drive pulse is applied to each of the transfer electrodes, and a voltage is applied below the transfer electrode. Forming a transfer packet for accumulating the signal charge in the charge transfer path, applying a voltage to the first transfer electrode in front of the transfer packet, and a second transfer electrode on the rear end of the transfer packet after applying the voltage By alternately stopping the voltage application to each other, the transfer packet is stretched between the second transfer electrode and the first transfer electrode, And moving along the transfer direction while alternately switching from a third transfer electrode in front of the second transfer electrode to a contracted state formed between the first transfer electrode and a contraction state; Accordingly, the normal transfer mode in which the time in the stretched state and the time in the contracted state are equal to each other and the special transfer mode in which the time in the stretched state is longer than the time in the contracted state are performed. Controlling the drive pulse.

  According to the imaging apparatus and the solid-state imaging device charge transfer method of the present invention, the time (overlap period) of the transfer packet that moves while expanding and contracting the charge transfer path is changed from the time of the contraction state according to the imaging conditions. Therefore, it is possible to prevent a decrease in image quality due to a deterioration in transfer efficiency without performing thinning out as in Patent Document 1 described above. As a result, a high-quality captured image can be obtained. Furthermore, when shooting conditions in which noise or the like of captured images is not conspicuous, priority can be given to maintaining the frame rate over improving transfer efficiency. As a result, it is possible to improve transfer efficiency without unnecessarily reducing the frame rate.

  As shown in FIG. 1, the CPU 11 of the digital camera (shooting apparatus) 10 sequentially executes various programs and data read from the memory 14 based on control signals from the operation unit 13 including a shutter button 12 and various operation buttons. Thus, each part of the digital camera 10 is controlled in an integrated manner.

  The shutter button 12 is a two-step operation of half-pressing and full-pressing further pressed from the half-pressing. When the shutter button 12 is not pressed under the shooting mode, a subject image within the shooting range is continuously displayed on the display unit 16 so that a so-called through image is displayed.

  When the shutter button 12 is half-pressed, subject brightness is measured, and preparation processing includes AE processing for determining the shutter speed and aperture value according to the subject brightness, and AF processing for matching the focus of the photographing lens 18 to the subject. Is executed. Then, when the shutter button 12 is further pushed down and fully depressed, shooting is performed using the shutter speed and aperture value determined by the AE process.

  A CCD image sensor (hereinafter simply referred to as a CCD) 19 corresponding to the solid-state imaging device of the present invention is disposed behind the photographic lens 18, and subject light transmitted through the photographic lens 18 is incident on the light receiving surface of the CCD 19. Incident. The taking lens 18 incorporates a focus mechanism 20 for adjusting the focus and a diaphragm mechanism 21 for adjusting the amount of light incident on the CCD 19.

  The focus mechanism 20 includes a focus lens 20 a that forms an image of subject light on the light receiving surface of the CCD 19, and includes a motor and a motor driver that move the focus lens 20 a. The focus lens 20 a is an optical axis of the photographing lens 18. By moving in the direction, the subject within the shooting distance range between the shortest shooting distance and infinity is brought into focus. The aperture mechanism 21 includes an aperture blade 21a that forms an aperture opening on the optical axis of the photographic lens 18, an actuator that drives the aperture blade, and the like. By increasing or decreasing the aperture diameter of the aperture blade 21a, the amount of light incident on the CCD 19 is increased. Adjust.

  A large number of photoelectric conversion elements 23 (see FIG. 2) are two-dimensionally arranged on the light receiving surface of the CCD 19. The CCD 19 is driven by various driving signals from a timing generator (hereinafter referred to as TG: driving pulse applying unit) 24 controlled by the CPU 11, and each photoelectric conversion element 23 converts subject light into electric charges corresponding to the light quantity. The accumulated charge is converted into a pixel signal and output.

  The CCD 19 has an electronic shutter function for adjusting the charge accumulation time (exposure time). In this electronic shutter function, by inputting an electronic shutter pulse input from the TG 24, charges accumulated until then (unnecessary charges) are swept out and erased, so that the charge accumulation time (electronic shutter speed) during the frame period is erased. Adjust. The exposure value for the CCD 19 is determined by the combination of the shutter speed by the electronic shutter function and the aperture value by the aperture mechanism 21.

  In the TG 24, various parameters for performing various operations at predetermined timings are set by the CPU 11, and a driving signal (driving pulse) for driving the CCD 19, a synchronizing signal for synchronizing each part, and the like are generated. Depending on the parameters set in the TG 24, the shutter speed of the CCD 19 and the frame rate when the CCD 19 repeatedly performs charge accumulation and charge readout can be changed.

  The pixel signal from the CCD 19 is sent to the CDS / AGC circuit 26. The CDS / AGC circuit 26 performs correlated double sampling (CDS) on the pixel signal output from the CCD 19 to suppress noise, and thereafter, automatic gain correction (AGC) that changes the ISO sensitivity according to the signal amount. I do. When the ISO sensitivity is set by the ISO sensitivity setting switch 28 of the operation unit 13, the gain is changed to a value corresponding to the set value.

  The OB clamp circuit 27 performs OB clamp processing for each row of the photoelectric conversion elements 23 on the output signal output from the CDS / AGC circuit 26. The A / D converter 30 converts the pixel signal that has been subjected to the OB clamping process by the OB clamping circuit 27 into digital image data and outputs the image data.

  The DSP 31 performs various types of image processing such as gamma correction processing, white balance correction processing, and Y / C conversion processing on the digital signal input from the A / D converter 30 to generate image data.

  The AF detection unit 32 uses the image data from the DSP 31 to focus the photographic lens 18, extracts high frequency components from an AEAF detection area set in advance in the photographic screen, and integrates the high frequency components. The AF evaluation value is output to the CPU 11. The CPU 11 performs AF processing for matching the focus of the photographing lens 18 to the subject in the AEAF detection area based on the AF evaluation value.

  The AE detection unit 33 is a luminance detection unit that detects the luminance of the subject based on the image signal from the CCD 19. The AE detection unit 33 detects the luminance of the subject in the AEAF detection area based on the image data from the DSP 31. The detected subject brightness is sent to the CPU 11. The CPU 11 determines the shutter speed (TV value) of the CCD 19 and the aperture value (AV value) of the aperture mechanism 21 based on the subject brightness.

  The compression / decompression processing circuit 35 performs compression processing on the Y / C data obtained by the DSP 31 and also performs decompression processing on the compressed image data obtained from the recording medium 37 via the media interface 36. The display unit 16 includes a liquid crystal display, and displays an image based on Y / C data output from the DSP 31. The display unit 16 also displays an image based on image data obtained by decompressing the compressed image data recorded on the recording medium 37.

  As shown in FIG. 2, the imaging surface of the CCD 19 is arranged two-dimensionally, and is provided for each of a plurality of photoelectric conversion elements 23 that store light by converting light into signal charges, and vertical columns of the photoelectric conversion elements 23. A plurality of vertical CCDs 39 for transferring signal charges in the vertical direction, a horizontal CCD 40 connected in common to the output terminals of the vertical CCDs 39 and transferring signal charges in the horizontal direction, and provided at the output terminals of the horizontal CCDs 40. And an output unit 41 that converts the signal charge transferred from the signal into a voltage signal and outputs the voltage signal.

  The photoelectric conversion element 23 includes an effective pixel region 43 that photoelectrically converts subject light to generate an image signal, and an optical black region (hereinafter simply referred to as an OB region) provided adjacent to the side of the effective pixel region 43. And 44). The OB region 44 is shielded by a light shielding film 45 so that subject light does not enter. The OB area 44 is provided on the left and right sides of the effective pixel area 43, but only one of them is shown for simplicity.

  The signal charge received by each photoelectric conversion element 23 in the effective pixel region 43 and generated by photoelectric conversion is read out to the vertical CCD 39 via a read gate (not shown) of each photoelectric conversion element 23, It is transferred in the column direction and transferred to the horizontal CCD 40.

  The vertical CCD 39 extends in the column direction of the photoelectric conversion elements 23, and has a vertical transfer path 46 that transfers signal charges in the column direction, and a four-phase array that is repeatedly arranged in the transfer direction above the vertical transfer path 46. It is comprised from the vertical transfer electrodes 47a-47d (refer FIG.3 and FIG.4). The vertical transfer electrodes 47a to 47d are electrically connected in the row direction. In the vertical transfer path 46, signal charges are accumulated and divided by the vertical transfer electrodes 47a to 47d. By applying four-phase vertical drive pulses (φV1 to φV4) from the TG 24 to the vertical transfer electrodes 47a to 47d, signal charges are transferred in the column direction in the vertical transfer path 46.

  The first-phase vertical transfer electrode 47a and the third-phase vertical transfer electrode 47c also serve as the above-described read gate electrodes. The first-phase and third-phase vertical drive pulses (φV1, φV3) are low level (hereinafter referred to as “L” level), intermediate level (hereinafter referred to as “M” level), and high level (hereinafter referred to as “H” level). This is a drive voltage signal taking the three values. The H level vertical drive pulse becomes a drive pulse for the read gate corresponding to a signal read pulse (not shown) from the TG 24. The second-phase and fourth-phase vertical drive pulses (φV2, φV4) are drive voltage signals taking binary values of L level and M level. By appropriately adjusting the waveform and phase of each vertical drive pulse (φV1 to φV4), signal charges are transferred by well-known four-phase drive (see FIG. 3).

  The vertical CCD 39 is also provided in the OB area 44, and as described above, reading and vertical transfer of signal charges from the photoelectric conversion element 23 are performed.

  The horizontal CCD 40 includes a horizontal transfer path and horizontal transfer electrodes (both not shown). A two-phase horizontal drive pulse is applied from the TG 24 to the horizontal transfer electrode, and the signal charge for one row transferred from the vertical CCD 39 is transferred to the output unit 41.

  The output unit 41 is configured by a floating diffusion amplifier, converts the signal charge transferred from the horizontal CCD 40 into a voltage signal (pixel signal), and outputs the voltage signal (pixel signal). Of the signals output from the output unit 41, the signal corresponding to the OB area 44 is a dark current signal, and the OB clamp processing (black reference level calculation, signal from the effective pixel area 43) in the OB clamp circuit 27 described above. Correction).

  Returning to FIG. 1, the CPU 11 functions as a CCD drive control unit (control unit) 50 by executing various programs and data read from the memory 14. The CCD drive control unit 50 controls the operation of the CCD 19 via the TG 24. Further, the CCD drive control unit 50 switches the transfer mode of the vertical transfer of signal charges according to the photographing conditions, more specifically, the set value of the ISO sensitivity. As the transfer mode, the signal charge transfer efficiency was improved by extending the overlap period (see t2 and t4 in FIG. 3 and t2a and t4a in FIG. 4) compared to the normal transfer mode and the normal transfer mode. An image quality priority transfer mode (special transfer mode) is provided.

  When the ISO sensitivity setting value is high, the gain of the AGC circuit 26 is set high, so that noise generated due to signal charges left in the transfer source during vertical transfer is also amplified. As a result, the image quality of the captured image is significantly deteriorated. On the other hand, when the ISO sensitivity setting value is low, the gain is set low, so that noise in the captured image is not noticeable.

  Therefore, when the ISO sensitivity setting value is equal to or greater than a predetermined threshold A (for example, 1600: sensitivity threshold), the CCD drive control unit 50 drives the CCD 19 in the image quality priority transfer mode to lengthen the overlap period. This improves the transfer efficiency and improves the quality of the captured image.

  On the contrary, when the ISO sensitivity setting value is less than the predetermined threshold A, the CCD drive control unit 50 has little influence on the image quality of the captured image due to the deterioration of the transfer efficiency. Drive to give priority to maintaining the frame rate.

  Further, when the transfer mode fixing switch (selection operation means) 52 of the operation unit 13 is turned on, the CCD drive control unit 50 drives the CCD 19 in the normal operation mode regardless of the ISO sensitivity setting value. As a result, when it is necessary to perform shooting at a high frame rate, such as during moving image shooting or continuous shooting, the high frame rate can be maintained by turning on the transfer mode fixing switch 52. During single shooting, the transfer mode is switched according to the ISO sensitivity setting value by turning off the transfer mode fixing switch 52.

Next, with reference to FIG. 3 and FIG. 4, a signal charge transfer method (a method for driving the vertical transfer electrodes 47 a to 47 d) in the normal transfer mode and the image quality priority transfer mode will be described in detail. As shown in FIG. 3A, in the normal transfer mode, vertical drive pulses (φV1 to φV4) having waveforms and phases in which the following (1) to (3) are sequentially and repeatedly executed are respectively transferred to the vertical transfer electrodes. Applied to 47a-47d. Thereby, each of the vertical transfer electrodes 47a to 47d is driven in four phases. In order to prevent complication of the drawing, the signal readout pulse (H level) is not shown in the first-phase / third-phase vertical drive pulses (φV1, φV3).
(1): Application of voltage (M level) to two adjacent vertical transfer electrodes.
(2): Voltage application to three transfer electrodes obtained by adding one vertical transfer electrode in front of the transfer direction to the vertical transfer electrode of (1).
(3): Stop application of voltage to the vertical transfer electrode that is the rearmost in the transfer direction among the vertical transfer electrodes in (2).

  During the four-phase driving of each of the vertical transfer electrodes 47a to 47d, voltage application to the first-phase / second-phase vertical transfer electrodes 47a and 47b is executed in the period t1 in the continuous periods t1 to t4, and in the period t2. Are applied to the first-phase to third-phase vertical transfer electrodes 47a, 47b, 47c, and during the period t3, the voltage is applied to the second-phase / third-phase vertical transfer electrodes 47b, 47c. In the period t4, voltage application to the second to fourth phase vertical transfer electrodes 47b, 47c, 47d is executed. Although not shown, after the period t4, the third phase / fourth phase, the third phase to the first phase, the fourth phase / first phase, the fourth phase to the second phase,... A voltage is applied to the vertical transfer electrode.

  As shown in FIG. 3B, when a voltage (M level) is applied to each of the vertical transfer electrodes 47a to 47d, the signal charge existing in the lower electrode region is accumulated in the vertical transfer path 46 below the voltage (M level). A transfer packet (potential well) 54 is formed. When the vertical transfer electrodes 47a to 47d are driven in four phases as described above, the transfer packet 54 is formed between the vertical transfer electrode 47a and the vertical transfer electrode 47b in the period t1, and the vertical transfer in the period t2. It is formed between the bottom of the electrode 47a and the vertical transfer electrode 47c, and is formed between the bottom of the vertical transfer electrode 47b and the bottom of the vertical transfer electrode 47c in the period t3, and the bottom of the vertical transfer electrode 47b and the bottom of the vertical transfer electrode 47d in the period t4. Formed between.

  As described above, the transfer packet 54 is in a contracted state (periods t1 and t3) corresponding to two vertical transfer electrodes and an extended state (periods t2 and t4) corresponding to three vertical transfer electrodes. It moves along the charge transfer direction while switching between and alternately. As a result, the signal charge is transferred in the charge transfer direction. The transfer packet 54 in the stretched state overlaps the transfer packet 54 in the contracted state in the period before and after that. Therefore, the periods t2 and t4 are overlap periods.

  In the normal transfer mode, the waveforms and phases of the vertical drive pulses (φV1 to φV4) are adjusted so that the periods t1 and t3 are equal to the overlap periods t2 and t4.

  As shown in FIGS. 4A and 4B, in the image quality priority transfer mode, the vertical drive pulse (φV1) is set so that the overlap periods t2a and t4a are longer than the overlap periods t2 and t4 in the normal transfer mode. The waveform and phase of .about..phi.V4) are adjusted. Accordingly, in the image quality priority transfer mode, the transfer packet 54 is moved (signal charge transfer) in the same manner as in the normal transfer mode except that the overlap period is extended.

  Thus, by extending the overlap period, the frame rate is lower than that in the normal transfer mode, but the signal charge transfer efficiency can be improved. The overlap periods t2a and t4a are determined by experiments or simulations so that both improvement in transfer efficiency (improvement in the quality of captured images) and securing of a minimum frame rate that does not affect moving image shooting and the like are compatible. The

  In the image quality priority transfer mode, the overlap periods t2a and t4a are longer than those in the normal transfer mode, while the periods t1 and t3 other than the overlap periods t2a and t4a are equal to the periods in the normal transfer mode. In this way, since the image quality priority transfer mode does not extend the entire period uniformly but extends only the overlap period, a significant decrease in the frame rate is prevented.

  Next, the operation of the digital camera 10 having the above configuration will be described with reference to the flowchart shown in FIG. The user turns on the digital camera 10 and switches the camera operation mode to the shooting mode, and then turns on the transfer mode fixing switch 52 to perform single-shot shooting when shooting moving images or continuous shooting. In this case, the transfer mode fixing switch 52 is turned off. Next, when changing the ISO sensitivity setting value, the user operates the ISO sensitivity setting switch 28 to set the ISO sensitivity setting value to a desired value.

  The CCD drive control unit 50 selects the normal transfer mode as the transfer mode of the CCD 19 when the transfer mode fixing switch 52 is ON. Further, the CCD drive control unit 50 checks the set value of the ISO sensitivity when the transfer mode fixing switch 52 is OFF. The CCD drive control unit 50 selects the normal transfer mode when the ISO sensitivity setting value is less than the threshold value A, and selects the image quality priority transfer mode when the ISO sensitivity setting value is equal to or greater than the threshold value A. select.

  The CCD drive control unit 50 controls the TG 24 to drive the CCD 19 in the selected transfer mode. Thereby, vertical drive pulses (φV1 to φV4) having waveforms and phases corresponding to the transfer modes are applied from the TG 24 to the vertical transfer electrodes 47a to 47d, respectively. As a result, readout of signal charges from the photoelectric conversion element 23 and vertical transfer of signal charges in the vertical transfer path 46 (movement of the transfer packet 54) are executed.

  When the image quality priority transfer mode is executed, since the overlap period (see FIGS. 2 and 3) is longer than that in the normal transfer mode, the frame rate is reduced, but the transfer efficiency can be improved. Thereby, the noise of the captured image when the ISO sensitivity is set high can be reduced, and the image quality of the captured image can be improved. On the other hand, when the ISO sensitivity setting value is set to a low value, noise in the captured image is not noticeable. Therefore, maintaining the frame rate is prioritized over improving the transfer efficiency.

  In addition, the TG 24 applies a horizontal drive pulse to the horizontal transfer electrode of the horizontal CCD 40, and transfers the signal charge for one row transferred from the vertical CCD 39 to the output unit 41. The output unit 41 converts the signal charge transferred from the horizontal CCD 40 into a pixel signal and outputs it.

  The pixel signal from the CCD 19 is subjected to various processes by the CDS / AGC circuit 26 and the OB clamp circuit 27, further converted into digital image data by the A / D converter 30, and various image processes by the DSP 31. Is given. The display unit 16 displays a through image based on the Y / C data output from the DSP 31.

  When the user presses the shutter button 12 halfway, the AE / AF process is executed as described above, and when the shutter button 12 is fully pressed, shooting is performed using the shutter speed and aperture value determined by the AE process. Is done. The captured image is compressed by the compression / decompression processing circuit 35 and then recorded on the recording medium 37.

  As described above, in the present invention, by extending the overlap period, it is possible to prevent a decrease in image quality due to deterioration in transfer efficiency without performing thinning as in Patent Document 1. Furthermore, when shooting conditions in which noise of a shot image is not conspicuous, priority can be given to maintaining the frame rate over improvement of transfer efficiency. As a result, it is possible to achieve both prevention of image quality degradation of the captured image and increase of the frame rate as much as possible.

  Next, the digital camera 60 of the second embodiment will be described with reference to FIG. In the first embodiment, the case where the transfer mode is switched according to the ISO sensitivity setting value has been described, but in the second embodiment, the transfer mode is switched according to the exposure amount and temperature of the CCD 19. . Since the digital camera 60 has basically the same configuration as the digital camera 10 of the first embodiment, components that are the same in function and configuration as those of the first embodiment are denoted by the same reference numerals and description thereof is omitted. Omitted.

  The CPU 61 of the digital camera 60 executes various programs and data read from the memory 14, so that an exposure amount measurement unit (exposure amount measurement unit) 62, a temperature estimation unit (temperature measurement unit) 63, and a CCD drive control unit ( Control means) 64 functions.

  The exposure amount measuring unit 62 calculates the exposure amount of the CCD 19 based on, for example, the shutter speed of the CCD 19 determined during the AE process and the aperture value of the aperture mechanism 21. In this case, an LUT or the like that associates the shutter speed, the aperture value, and the exposure amount of the CCD 19 may be created in advance, and the exposure amount of the CCD 19 may be obtained from the shutter speed and the aperture value with reference to the LUT. .

  The temperature estimation unit 63 estimates the temperature of the CCD 19 based on the dark current from the OB area 44 of the CCD 19. Since the dark current tends to increase as the temperature of the CCD 19 increases, the temperature of the CCD 19 can be estimated based on the magnitude of the dark current. Therefore, the memory 14 stores a temperature estimation LUT 66 that associates the magnitude of the dark current with the temperature of the CCD 19. An arithmetic expression or the like may be stored instead of the LUT. Then, the temperature estimation unit 63 acquires the value of the dark current from the OB clamp circuit 27, for example, and estimates the temperature of the CCD 19 with reference to the temperature estimation LUT 66.

  The CCD drive control unit 64 switches the transfer mode of the CCD 19 according to the exposure amount of the CCD 19 obtained by the exposure amount measurement unit 62 and the temperature of the CCD 19 obtained by the temperature estimation unit 63. When the exposure amount of the CCD 19 is low, the transfer amount of the signal charge in the vertical CCD 39 is reduced (because the image becomes dark), so that noise generated due to the signal charge left behind at the transfer is easily noticeable. On the contrary, when the exposure amount of the CCD 19 is high, the transfer amount of signal charges increases (because the image becomes brighter), so that noise becomes inconspicuous.

  The mobility of signal charges in the vertical CCD 39 depends on the temperature of the CCD 19. For this reason, when the temperature of the CCD 19 is low, the mobility of the signal charge in the vertical CCD 39 decreases, so that the amount of signal charge left at the time of transfer increases, and the deterioration of the signal charge transfer efficiency is easily noticeable. On the other hand, when the temperature of the CCD 19 is high, the mobility of signal charges increases, so that the amount of signal charges left at the time of transfer decreases, and deterioration of signal charge transfer efficiency is easily noticeable.

  Therefore, the CCD drive control unit 64 is configured when the exposure amount of the CCD 19 is less than a predetermined threshold value E (exposure amount threshold value) and the temperature of the CCD 19 is less than a predetermined threshold value C (temperature threshold value: for example, 5 ° C.). The CCD 19 is driven in the image quality priority transfer mode to improve the transfer efficiency, thereby suppressing the occurrence of noise in the captured image. Conversely, when the exposure amount of the CCD 19 is equal to or greater than the threshold value E and / or the temperature is equal to or greater than the threshold value C, the CCD drive control unit 64 is difficult to notice deterioration of transfer efficiency (generation of noise), as described above. Is driven in the normal transfer mode to give priority to maintaining the frame rate.

  Next, the operation of the digital camera 60 will be described using the flowchart shown in FIG. When the user turns on the digital camera 10 and switches the operation mode of the camera to the shooting mode, a through image is displayed on the display unit 16 as described in the first embodiment. Next, when the user half-presses the shutter button 12, AE / AF processing is executed. The shutter speed of the CCD 19 and the aperture value of the aperture mechanism 21 are determined by AE processing.

  The exposure amount measuring unit 62 obtains the exposure amount of the CCD 19 based on the shutter speed / aperture value determined in the AE process. Further, the temperature estimation unit 63 acquires the dark current information of the OB region 44 from the OB clamp circuit 27 and then estimates the temperature of the CCD 19 with reference to the temperature estimation LUT 66.

  The CCD drive control unit 64 selects the normal transfer mode as the transfer mode of the CCD 19 when the transfer mode fixing switch 52 is ON. Further, the CCD drive control unit 64 checks the exposure amount / temperature of the CCD 19 obtained by the exposure amount measurement unit 62 and the temperature estimation unit 63 when the transfer mode fixing switch 52 is OFF. The CCD drive control unit 64 selects the normal transfer mode when the exposure amount of the CCD 19 is greater than or equal to the threshold value E and / or the temperature is greater than or equal to the threshold value C, and the exposure amount of the CCD 19 is less than the threshold value E and the temperature is higher. When it is less than the threshold C, the image quality priority transfer mode is selected.

  Hereinafter, as described in the first embodiment, the CCD drive control unit 64 controls the TG 24 to drive the CCD 19 in the selected transfer mode. Thereby, the noise of the captured image when the exposure amount and temperature of the CCD 19 are low can be reduced, and the image quality of the captured image can be improved. On the other hand, when the exposure amount and / or temperature of the CCD 19 is high, the noise of the captured image is not noticeable, and therefore the maintenance of the frame rate is given priority over the improvement of the transfer efficiency. When the user fully presses the shutter button 12, the captured image is recorded on the recording medium 37.

  As described above, also in the second embodiment of the present invention, the same effects as those described in the first embodiment can be obtained.

  Next, a digital camera 70 according to a third embodiment of the present invention will be described with reference to FIGS. In the second embodiment, the temperature estimation unit 63 estimates the temperature of the CCD 19 using the dark current information in the OB region 44 and the temperature estimation LUT 66. In the third embodiment, the temperature sensor 72 is used. The temperature of the CCD 19 is measured. The mounting position of the temperature sensor 72 is not particularly limited as long as the temperature of the CCD 19 can be measured. For example, the temperature sensor 72 may be mounted on the back surface of the CCD 19 (in the drawing, the two are separated from each other in order to prevent complication of the drawing). Is shown in the figure).

  The CCD drive control unit 64 determines whether the temperature of the CCD 19 is equal to or higher than the threshold C based on the temperature information obtained by the temperature sensor 72. Note that the measurement of the exposure amount of the CCD 19 and the switching of the transfer mode of the CCD 19 according to the exposure amount and temperature of the CCD 19 are the same as those in the second embodiment described above, and thus the description thereof is omitted. The operation of the digital camera 70 is the same as that of the second embodiment except that the temperature of the CCD 19 is acquired by the temperature sensor 72, and the same effect as that of the second embodiment can be obtained.

  In each of the above embodiments, the shutter speed of the CCD 19 is adjusted by an electronic shutter, but the present invention is not limited to this, and may be adjusted by a mechanical shutter.

  In each of the above embodiments, the case where so-called four-phase driving is performed by applying four-phase vertical driving pulses (φV1 to φV4) to the CCD 19 has been described as an example, but the present invention is limited to this. Instead, the present invention can be similarly applied to a case where the CCD is driven in three phases, six phases, eight phases, or the like. In each of the above embodiments, the case where the photoelectric conversion elements 23 of the CCD 19 are arranged in a square lattice pattern has been described as an example. However, the present invention is not limited to this, and the honeycomb arrangement is performed. The present invention can also be applied to cases where

  In the first embodiment, the case where the transfer mode of the CCD is switched according to the setting value of the ISO sensitivity and the transfer amount / temperature of the CCD in the second and third embodiments has been described as an example. However, the present invention is not limited to these, and the transfer mode may be switched to the image quality priority transfer mode under various shooting conditions in which transfer efficiency deteriorates or noise of a shot image is noticeable.

  In each of the above embodiments, a digital camera has been described as an example of a photographing device. However, the present invention is not limited to this, and is applicable to various photographing devices including a CCD such as a camera-equipped mobile phone. Can do.

It is a block diagram which shows the electric constitution of the digital camera of 1st Embodiment. It is a schematic plan view which shows the structure of CCD. FIG. 10 is an explanatory diagram for explaining a vertical transfer operation in a normal transfer mode. FIG. 10 is an explanatory diagram for explaining a vertical transfer operation in an image quality priority transfer mode. 4 is a flowchart for explaining a charge transfer method of the CCD in the digital camera of the first embodiment. It is a block diagram which shows the electrical constitution of the digital camera of 2nd Embodiment which switches the transfer mode of CCD according to the exposure amount and temperature of CCD. It is a flowchart for demonstrating the charge transfer method of CCD in the digital camera of 2nd Embodiment. It is a block diagram which shows the electric constitution of the digital camera of 3rd Embodiment in which the method of acquiring the temperature of CCD differs from 2nd Embodiment. It is a flowchart for demonstrating the charge transfer method of CCD in the digital camera of 3rd Embodiment.

Explanation of symbols

10, 60, 70 Digital camera 11, 61 CPU
19 CCD type image sensor 23 Photoelectric conversion element 28 ISO sensitivity setting switch 39 Vertical CCD
43 Effective pixel area 44 Optical black area 46 Vertical transfer path 47a-47b Vertical transfer electrode 50, 64 CCD drive control unit 52 Transfer mode fixed switch 54 Transfer packet 62 Exposure amount measurement unit 63 Temperature estimation unit 66 Temperature estimation LUT
φV1 to φV4 Vertical drive pulse

Claims (7)

A solid-state imaging device having a photoelectric conversion element, a charge transfer path for transferring a signal charge obtained by the photoelectric change element, and a plurality of transfer electrodes arranged along the transfer direction of the signal charge on the charge transfer path; ,
A drive pulse is applied to each of the transfer electrodes to form a transfer packet for accumulating the signal charges in the charge transfer path under the voltage-applied transfer electrode, and a first transfer in front of the transfer packet By alternately repeating the voltage application to the electrode and the voltage application to the second transfer electrode on the rear end of the transfer packet after the voltage application, the transfer packet is transmitted from under the second transfer electrode to the first transfer electrode. While switching alternately between the stretched state formed under the transfer electrode and the contracted state formed under the third transfer electrode in front of the second transfer electrode and under the first transfer electrode, Drive pulse applying means for moving along the transfer direction;
Switching between the normal transfer mode in which the time in the extended state and the time in the contracted state are equal and the special transfer mode in which the time in the extended state is longer than the time in the contracted state is performed according to the shooting conditions. Control means for controlling the drive pulse applying means;
An imaging apparatus comprising:   The control means operates the drive pulse applying means in the normal transfer mode when the ISO sensitivity setting value is less than a predetermined sensitivity threshold value, and the ISO sensitivity setting value is greater than or equal to the sensitivity threshold value. 2. The photographing apparatus according to claim 1, wherein the driving pulse applying unit is operated in the special transfer mode at a certain time. Exposure amount measuring means for measuring the exposure amount of the solid-state image sensor; and temperature measuring means for measuring the temperature of the solid-state image sensor;
When the exposure amount obtained by the exposure amount measurement unit is less than a predetermined exposure amount threshold value and the temperature obtained by the temperature measurement unit is less than a predetermined temperature threshold value, When the drive pulse applying means is operated in the special transfer mode, and the exposure amount is not less than the exposure amount threshold and / or the temperature is not less than the temperature threshold, the drive pulse applying means is operated in the normal transfer mode. The photographing apparatus according to claim 1, wherein the photographing apparatus is operated. The solid-state imaging device has an effective pixel region that generates and accumulates signal charges, and an optical black region that is formed adjacent to the effective pixel region, and
4. The photographing apparatus according to claim 3, wherein the temperature measuring unit obtains the temperature of the solid-state imaging device based on a dark current output from the optical black region.   The photographing apparatus according to claim 3, wherein the temperature measuring unit is a temperature sensor. Regardless of the photographing conditions, comprising a selection operation means for selecting whether to operate the drive pulse application means in the normal transfer mode,
6. The control unit according to claim 1, wherein when the operation in the normal transfer mode is selected by the selection operation unit, the drive pulse applying unit is always operated in the normal transfer mode. The photographing apparatus according to claim 1. Solid-state imaging having a photoelectric conversion element, a charge transfer path for transferring a signal charge obtained by the photoelectric change element, and a plurality of transfer electrodes arranged along the transfer direction of the signal charge on the charge transfer path In the device charge transfer method,
A drive pulse is applied to each of the transfer electrodes to form a transfer packet for accumulating the signal charges in the charge transfer path under the voltage-applied transfer electrode, and a first transfer in front of the transfer packet By alternately repeating the voltage application to the electrode and the voltage application to the second transfer electrode on the rear end of the transfer packet after the voltage application, the transfer packet is transmitted from under the second transfer electrode to the first transfer electrode. While switching alternately between the stretched state formed under the transfer electrode and the contracted state formed under the third transfer electrode in front of the second transfer electrode and under the first transfer electrode, Moving along the transfer direction;
Switching between the normal transfer mode in which the time in the extended state and the time in the contracted state are equal and the special transfer mode in which the time in the extended state is longer than the time in the contracted state is performed according to the shooting conditions. And controlling the drive pulse;
A charge transfer method for a solid-state imaging device, comprising:

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